rosslink
C
TM
The Aerospace Corporation magazine of advances in aerospace technology
F lying in t o the
r o ck et plume
A er ospac e tak es
lidar t o new
heigh ts
IR e y es high
in the sk y
P hot o gr aph y and
launch-cloud
pr edic tion
Wea ther and
w ar far e
O bserving and measuring the atmosphere
The Aerospace Corporation celebrates 40 years
Summer 2000
Crosslink
Summer 2000 Vol. 1 No. 2
4
Departments
Rockets and the Ozone Layer
Martin N. Ross (left), Environmental Systems Directorate, leads research on the
stratospheric impact of Air Force launch vehicles. He holds a Ph.D. from the University
of California at Los Angeles in Earth and
planetary sciences and has been with Aerospace since 1989 ([email protected]).
Paul F. Zittel (right), Remote Sensing Department, leads research on the radiative
and chemical properties of rocket plumes
and has conducted basic research in the
areas of laser-induced chemistry, vibrational energy transfer, and cryogenic spectroscopy. He holds a Ph.D. in physical
chemistry from the University of California
at Berkeley and has been with Aerospace
since 1976 ([email protected]).
2 Headlines
38 Bookmarks
40 Links
11
18
26
Contents
4
From the Editor
S
Jon M. Neff
pace technology and atmospheric science are related in many ways. Space provides a unique vantage point for observing weather systems, and with the everincreasing frequency of satellite launches, the effect of rocket exhaust on the
environment has become a concern. In this issue, Crosslink explores the contributions made by Aerospace in the areas of weather forecasting and atmospheric analysis.
This year marks the 40th anniversary of The Aerospace Corporation. In its trusted role
as space systems engineer for the Air Force, the National Reconnaissance Office, and
other government agencies, the corporation has made lasting contributions to the
nation’s space programs. In celebration of the accomplishments of the last 40 years,
Crosslink introduces a series of historical articles on Aerospace’s involvement in various
military and civil programs during those years. The series begins with an article on the
Defense Support Program.
Crosslink presents this historical series to commemorate the contributions of all those
who have worked on these programs through the years. These past accomplishments are
noted as well for their significance as foundations for the important work ahead to meet
the space-technology needs of our government and commercial partners in the complex
environment of the future.
11
Water-Vapor Lidar Extends to the Tropopause
John Wessel (right), Photonics Technology Department, supports DMSP in the
areas of meteorological lidar and microwave remote sensing and has conducted research in molecular, atomic,
semiconductor, and surface spectroscopies. He holds a Ph.D. in chemical
physics from the University of Chicago
and has been with Aerospace since 1974
([email protected]). Robert W. Farley (left), Photonics Technology Department, is responsible for the development
and operation of a mobile lidar system
that supports satellite programs. He holds
a Ph.D. in chemical physics from the University of Colorado and has been with
Aerospace since August 1997 (u21670@
paros.aero.org).
34
18
The Defense Support Program
Fred Simmons (left), consultant to the
Space Based Infrared Systems program, has been the coordinator of various studies for SMC, BMDO, and
DARPA. He holds a Ph.D. in aerospace
science from the University of Michigan and has been with Aerospace
since 1971 (frederick.s.simmons@aero.
org). Jim Creswell (right), with 35
years of experience in space-based
warning satellite development and
operations, has been working as a
consultant on satellite-related tasks
since his retirement in 1994 from fulltime employment at Aerospace.
Among various appointments during
his Aerospace career, he was director
of the Mission Support Office of the
Defense Support Program. Creswell
holds an M.S. in systems engineering
from the University of California at Los
Angeles and has been with Aerospace
since 1965 ([email protected]).
34
Cloud Cover Over Kosovo
26
Aerospace Photos Capture Launch Clouds
Robert N. Abernathy, Surveillance Technology Department, has been responsible
for quantitative image processing in support of the Atmospheric Model Validation
and the Rocket Impact on Stratospheric
Ozone programs since 1995. He holds a
Ph.D. in analytical chemistry from Pennsylvania State University and has been with
Aerospace since 1980 (robert.n.abernathy
@aero.org).
John S. Bohlson (left), Systems Director, Sensors and Display Systems for
DMSP, supports both DMSP and the
National Polar Operational Environmental Satellite System in the areas of
remote sensing, data exploitation, and
user requirements. He holds an M.S. in
meteorology from the University of
Wisconsin and has been with Aerospace since 1988 (john.s.bohlson@
aero.org). Leslie O. Belsma (right),
Weather and Navigation Division,
manages unique quality-control tasks
for the Cloud Depiction and Forecast
System II. A retired Air Force Weather
officer with an M.S. in aeronomy from
the University of Michigan, she joined
Aerospace in September 1999 (leslie.
[email protected]). Bruce H.Thomas
(center) is senior project leader for the
DMSP Environmental Applications
Center, Aerospace Omaha field office,
at Offutt Air Force Base Nebraska.
Thomas established an additional location of the Aerospace field office at
the Air Force Weather Agency, extending the DMSP program office into the
user community. He holds an M.S. in
atmospheric science from Creighton
University and has been with Aerospace since 1990 (bruce.h.thomas@
aero.org).
Headlines For more news about Aerospace, visit www.aero.org/news/
First Launch of the
Century
T
he launch of an Atlas IIA from
Cape Canaveral on February 7,
2000, marked the first government launch of the century. It placed into
orbit a DSCS III (Defense Satellite
Communications System) B8 SLEP (Service Life Enhancement Program), an
improved military communications satellite, the seventh DSCS launched since
1992. The B8 SLEP is the first of four
improved satellites that will increase
tactical communication. The payload
included new electronics that add more
power per channel so that ground forces,
ships, aircraft, and submarines can use
smaller antennas when communicating.
The satellite replaces the A1, launched in
1982, in the primary DSCS Western
Pacific Theater constellation. Aerospace
provided a launch support team at the
Cape and supported the launch remotely
from locations in Colorado and California. The successful SLEP program has
been in operation for four years.
TIMED to Probe
Distant Regions
A
remote-sensing spacecraft carrying a payload developed with the
help of Aerospace will travel 40
to 110 miles above Earth this year to a
little-explored region of the atmosphere.
The two-year mission, TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics), will begin with a
launch from Vandenberg Air Force Base.
Its purpose is to study how humans and the
sun influence the mesosphere and lower
thermosphere and ionosphere. Those
regions absorb X-rays and extreme ultraviolet radiation. TIMED will carry the
Global Ultraviolet Imager (GUVI), a joint
effort between Aerospace and the Applied
Physics Laboratory at Johns Hopkins University. Aerospace handled the design, fabrication, and operation of the instrument
and was also involved in the software and
electronics for the GUVI payload. GUVI
will measure profiles of the region’s composition and temperature as well as highlatitude auroral energy input.
GPS for the Military and Civilians
T
he fourth in a series of
U.S. Global Positioning
System (GPS) replacement satellites, GPS IIR4, was
launched aboard a Delta II from
Cape Canaveral May 10, 2000.
Aerospace reviewed the hardware, software, and procedures,
and verified that the vehicle was
ready for launch. Aerospace
developed the fundamental concept of GPS for the Air Force in
1963. Today, GPS, a constellation of 28 navigational satellites
that orbit 11,000 miles above
Earth, is used increasingly by
civilians.
Civilian owners of GPS receivers
found their systems significantly more
accurate as of May 2, 2000. That day,
President Clinton ordered an end to the
intentional degradation of GPS satellite
signals by the military. The military will,
however, retain its right to selectively deny
the GPS signals over any given region.
Civilians use GPS for many purposes,
including search and rescue operations
and airplane and ground-vehicle navigation (GPS sensors placed in cars enable
drivers to use the Internet to navigate).
Unscrambling the signals should benefit
the GPS industry, which is expected to
grow from $8 billion to $16 billion in
the next three years.
Clothing That Computes
S
oon soldiers in the
battlefield may be
able to shed some of
their 70 pounds of gear and
don a lightweight wearable
computer that could send
and receive life-saving
information. For example,
a soldier whose vehicle has
broken down could be
wearing the repair manual.
Sound like science fiction?
It isn’t. Michael Gorlick (in
photo), project engineer in
the Computer Systems
Research Department, constructed suspenders that have electrical
conductors woven directly into the fabric.
Developed as part of a joint research project between Aerospace and The MITRE
Corporation, the suspenders act as a bus
and data network for wearable digital
devices. Civilian use of wearable computers is also on the horizon. Emergency
search and rescue and disaster response
teams could be equipped with them. The
computers may eventually be carried in
pockets, worn on belts, attached to wrists,
or worn as brooches and rings. Hardhats
and eyeglass frames could also house data
networks. Imagine those involved in the
meticulous work of satellite assembly
having essential information right before
their eyes.
Amazing MEMS
M
icroelectromechanical systems
(MEMS), machines so tiny they
cannot be seen with the naked
eye, are quickly gaining notoriety for their
capability and versatility in a variety of
areas. MEMS can be used to detect environmental pollutants, monitor the health of
a premature newborn, sense an impending
car crash and deploy the air bag, and be
“woven” into the clothes of soldiers on the
battlefield (where the sensors would warn
against an attack by chemical or biological
weapons). A more aggressive use of
MEMS is the potential for manufacturing
mass-producible, 1-kilogram-class nanosatellites with microelectronics-processing
technology.
More than 30 Aerospace scientists are
involved in MEMS research, including
Henry Helvajian of the Aerospace Center
for Microtechnology and the editor of
Microengineering Aerospace Systems (see
sidebar). Aerospace researchers sent aloft
a MEMS experimental testbed on the
space shuttle Columbia last year. Data
from 30 of the devices were analyzed to
see how the various MEMS performed
during launch, orbit, and reentry, compared with their performance in preflight
tests. One device, designed and built by
Aerospace, contains 15 microthrusters,
which act like 15 individual solid rocket
motors. The usefulness of MEMS in space
has yet to be fully realized, and the analysis by Aerospace was the first systematic
testing of MEMS in that capacity. Another
experimental MEMS test mission, planned
for 2001, will involve the International
Space Station.
Miniature Satellites Launched
T
he tiniest operational satellites ever
placed in orbit were launched
aboard a new Air Force booster for
light satellites January 26, 2000, from
Vandenberg Air Force Base. Each satellite
weighs less than one-half pound and is
slightly larger than a deck of cards. In a
project for the Defense Advanced
Research Projects Agency (DARPA),
Aerospace conceived the mission,
designed and built the “picosats,” tested
their components, and
handled flight operations.
The primary mission was
to demonstrate the use of
miniature satellites in
testing DARPA microelectromechanical systems
(MEMS). The two picosats were positioned in a
low Earth orbit after they
were released February 6,
2000, from the Orbiting
Picosatellite Automated
Launcher (OPAL), a satellite built by Stanford University students.
The satellites were joined by a tether,
which kept them in range of each other for
crosslink purposes as they simulated formation flying. Thin strands of gold wire in
the tether allowed the U.S. Space Command’s Space Surveillance Network to use
radar to locate and track the picosats. The
mission, concluded on February 10, 2000,
was the first of a series of missions
designed to validate MEMS technology.
Microengineering
Aerospace Systems
explains the use of
microengineering
principles to impart
“intelligence,” “volition,” and “motility”
to systems on the
miniature scale.
Henry Helvajian
Engineering “intelligent” functionality in microsystems
requires the ability to cofabricate microelectronics with sensors and actuators
using design rules that now approach
the submicron scale, but will soon reach
the nanometer scale.The concepts, presented in 17 chapters by some of the
pioneering experts in the field, provide
the foundation for enhancing existing
aerospace systems or developing new
significantly miniaturized systems, such
as the nanosatellite, picosatellite, and
femtosatellite probe.
The book covers the disciplines that
support microengineering: microelectronics,microelectromechanical systems
(MEMS), microsystems, nanoelectronics,
advanced packaging, material processing, micromachining, control systems,
information theory, and the basic disciplines (physics, chemistry, and mechanics). Third in a series of publications
covering this rapidly advancing technology,Microengineering Aerospace Systems
uses a textbook tutorial style to present
fundamental aspects of the technology
and specific aerospace systems applications through worked examples.
1999 • 707 pp • ISBN 1-884989-03-9
Published by The Aerospace Press and
American Institute of Aeronautics and Astronautics
Order from AIAA
800.682.2422
or
www.aiaa.org
Rockets and the
Ozone Layer
Martin N. Ross and Paul F. Zittel
Rocket engine exhaust contains chemical compounds that react
with ozone in the stratosphere. A new measurement program
suggests that current space transportation activities only
minimally affect Earth’s protective ozone layer.
P
Launch of the space shuttle Discovery
from Cape Canaveral
rotecting Earth’s ozone layer
remains an important environmental issue. Without this shielding layer, ultraviolet (UV)
radiation would harm life on Earth. We
hear alarming statistics on increasing incidences of skin cancer and other disorders
that may be linked to a thinning of Earth’s
ozone layer. We know that the presence of
chlorofluorocarbons (CFC)—chemicals
used as solvents and refrigerants—and
other industrial gases in the atmosphere is
the major cause of ozone depletion. But
what about exhaust from launch vehicles?
Can the cumulative effect of emissions
from rockets launched every three or four
days from various launch sites around the
globe significantly alter Earth’s delicately
balanced, natural sunscreen?
Space transportation, once dominated
by government, has become an important
part of our commercial economy, and the
business of launching payloads into orbit
is expected to nearly double in the next
decade. Each time a rocket is launched,
combustion products are emitted into the
stratosphere. CFCs and other chemicals
banned by international agreement are
thought to have reduced the total amount
of stratospheric ozone by about 4 percent.
In comparison, recent predictions about the
effect on the ozone layer of solid rocket
motor (SRM) emissions suggest that they
reduce the total amount of stratospheric
ozone by only about 0.04 percent.
Even though emissions from liquidfueled rocket engines were not included in
these predictions, it is likely that rockets
do not constitute a serious threat to global
stratospheric ozone at the present time.
Even so, further research and testing needs
to be done on emissions from rockets of
all sizes and fuel system combinations to
more completely understand how space
transportation activities are affecting the
ozone layer today and to predict how they
will affect it in the future.
The Ozone Umbrella
Ozone, composed of three oxygen atoms,
is the result of the action of UV radiation
on oxygen molecules, composed of two
oxygen atoms. In the upper regions of the
atmosphere, UV light breaks apart oxygen
molecules into two oxygen atoms, one of
which then combines with a second oxygen molecule to form ozone. Born of UV
light, ozone is also a powerful absorber of
UV light, accounting for its protective
role. Most of the ozone that protects
Earth’s surface is concentrated in the
atmospheric region called the stratosphere,
usually taken as the region between about
14 and 50 kilometers altitude. The term
“ozone layer” refers to the portion of the
stratosphere between about 15 and 30
kilometers altitude, where the bulk of the
ozone is concentrated.
Compared with the mass of all the gas
in the stratosphere, the mass of combustion emissions from even the largest rocket
is miniscule, so it’s easy to conclude that
the effect of all rocket launches on the
ozone layer must be inconsequential. The
ozone layer, however, is maintained by a
delicate balance of the production, transport, and destruction of ozone molecules.
Relatively small amounts of sufficiently
active chemical compounds can upset this
balance and cause important changes in
the amount and distribution of ozone.
Rocket engines produce small amounts of
such active compounds.
Early in the past decade, Aerospace
conducted research for the Air Force
Space and Missile Systems Center (SMC)
Environmental Management Branch on
how SRM exhaust affects stratospheric
ozone. These studies, which raised several
environmental concerns, were limited to
laboratory and modeling simulations of
rocket-plume chemistry. By the middle of
the decade, it had become obvious that a
complete understanding of rocket-exhaust
Ozone-Destroying Radicals
Complicated chemical and physical
processes, only partially understood by
atmospheric scientists, affect both the
amount and distribution of ozone in the
stratosphere. In general, ozone is formed
in the equatorial stratosphere at altitudes
above 30 kilometers. Large-scale winds
continuously transport the ozone to lower
altitudes and toward Earth’s poles to form
a layer about 10 kilometers thick, centered
at about 22 kilometers altitude. The concentration of ozone is determined by the
rate of ozone transport into the layer versus the rate of ozone loss by reaction with
ozone-destroying radicals such as the
chlorine atom (Cl), nitric oxide (NO), and
the hydroxyl radical (OH). Because each
radical is able to regenerate after destroying an ozone molecule (called a catalytic
cycle), radical molecules exert a major
influence on ozone even at the small quantities found in the stratosphere. This means
that small changes in stratospheric composition caused by industrial activity, including rocket exhaust, might cause relatively
large changes in the ozone layer.
The Composition of Rocket Emissions
Both solid and liquid rocket-propulsion
systems emit a variety of gases and particles directly into the stratosphere. A large
percentage of these emissions are inert
chemicals such as carbon dioxide that do
not directly affect ozone levels. Emissions
of other gases, such as hydrogen chloride
and water vapor, though not highly reac-
40
03
X
X0
02
30
Altitude (kilometers)
effects required moving beyond the
theoretical investigations to actual measurements. In 1995, responding to the concerns raised by the earlier studies, SMC
requested that Aerospace establish a practical, quick-to-implement program to collect actual data from SRM plumes in the
stratosphere. The program, named Rocket
Impacts on Stratospheric Ozone (RISO),
and led by the Aerospace Environmental
Systems Directorate, initially focused on
the stratospheric impacts of the heavy-lift
Titan IVA. RISO has subsequently been
expanded to include responsibility for
investigating the impact of all current U.S.
Air Force launch vehicles. The Air Force
Office of Scientific Research joined with
SMC during the RISO planning phase and
supported several investigators on the
RISO team. The initial pioneering RISO
plume measurement campaigns began in
1996.
Catalytic
reactions
20
re
osphe
Strat
re
osphe
Trop
10
Commercial airlines fly in the upper troposphere at an altitude of about 12 kilometers; the WB-57F aircraft typically
flies at an altitude of 19 kilometers, below the peak in ozone concentration but well enough into the stratosphere
that the chemical and mixing processes observed during RISO missions are representative of the ozone layer as a
whole. Reactive gases that constitute a small part of the rocket exhaust consume ozone, which deactivates them.
Represented by X,these are thought to be mainly the chlorine atom,nitric oxide,and the hydroxyl radical,depending on the rocket propellant. A variety of chemical processes can reactivate ozone-destroying molecules, so that
each can destroy many ozone molecules before finally being removed from the stratosphere.
tive, indirectly affect ozone levels by
participating in chemical reactions that
determine the concentrations of the ozonedestroying radicals in the global strato-
Transient
Plume-Wake
Effects
11 12 1
2
10
9
3
8
4
7 6 5
sphere. A small percentage of rocketengine emissions, however, are highly
reactive radical compounds that immediately attack and deplete ozone in the
Mesoscale
Mixing
July
June
May
1
2 3 4 5 6 7 8
9 10 11 12 13 14 15
16 17 181 192 203 21 22
4 5 23 306 24 7
8 9 10
31 25 26 27 28 29
11 12 13 14 15 16 17
1 18
2 19
3 20
4 21
5 22
6 23 24
7 8 25
9 26
10 27
11 28
12 29
13 30
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31
Cumulative
Global Mixing
2002
2001
2000
1 – 10 km
Plume
Immediate
ozone loss
Deactivation of
reactive emissions
Long-term
reactions
The three main phases of propulsion system emissions. Instruments carried by high-altitude aircraft can only
measure the intense disturbances in the local phase.Stratospheric disturbances during the mesoscale and global
phases are too slight to be observed directly and must be predicted using computer models of atmospheric
chemistry and dynamics. These models, however, strictly depend upon key data from measurements obtained
during the local phase.
0.65
0.58
20
0.51
0.43
0.36
0
0.29
0.22
0.15
–20
Fraction of chlorine that is reactive
Distance from plume centerline (meters)
0.72
0.08
0.00
–40
0
200
400
600
Distance downstream (meters)
800
1000
Most chlorine emerges from solid-propellant rocket motors as hydrogen chloride (HCl). Some of the HCl is converted into reactive chlorine atom (Cl) and molecule (Cl2) by downstream chemical processes called “afterburning.” Computer models are used to predict how much of the chlorine is in the reactive form as a function of
distance away from the motor nozzle. Here, a model predicts that about one-third of the HCl leaving the nozzle
is converted into Cl and Cl2 in the plume of an Athena II rocket as it flies through the ozone layer.
plume wake following launch. Aerosol
emissions, such as alumina particles, carbon (soot) particles, and water droplets,
can also act as reactive compounds when
heterogeneous chemical reactions take
place on the surface of these particles.
Rocket emissions have two distinct
effects on ozone: short-term and longterm. Following launch, rapid chemical
reactions between plume gases and particles and ambient air that has been drawn
into the plume wake cause immediate
changes in the composition of the local
atmosphere. During this phase, which lasts
for several hours, the concentrations of
radicals in the plume can be thousands of
times greater than the concentrations
found in the undisturbed stratosphere, and
the ozone loss is dramatic (see figure on
page 10).
Long-term effects occur as gas and particulate emissions from individual launches
become dispersed throughout the global
stratosphere and accumulate over time.
The concentrations of emitted compounds
reach an approximate global steady state
as exhaust from recent launches replaces
exhaust removed from the stratosphere by
natural atmospheric circulation.
Before the RISO field campaigns, relatively little was known with certainty
about the highly reactive components of
rocket-engine emissions or the intensity of
ozone destruction in the plume wake. In
1995, managers and researchers from the
Air Force and the National Aeronautics
and Space Administration (NASA) met to
review rocket emissions and identify
critical knowledge needs. The meeting
participants concluded that airborne measurements inside actual stratospheric rocket
plumes should be a priority for further
research, and the RISO program was
designed with those conclusions in mind.
The Role of Chlorine Radicals
Researchers have long been aware that
hydrogen chloride (HCl) is a component
of SRM exhaust. It had been assumed that
HCl, which is relatively unreactive, would
contribute to ozone depletion globally
over the long term by slightly increasing
radical chlorine levels in the stratosphere
but would not alter ozone levels in the
plume-wake region immediately after
launch. Atmospheric scientists began to
wonder, however, if unreactive HCl could
be converted into highly reactive chlorine
radicals in plume combustion processes,
resulting in an immediate and possibly
deep ozone loss in and around SRM plume
wakes. Such a short-term loss could conceivably influence the intensity of the
sun’s harmful UV light on the ground near
launch sites.
To find an answer, Aerospace researchers
modified existing computer models of secondary combustion in SRM plumes by
incorporating a more complete representation of the chemistry of chlorine compounds. Secondary combustion, also
called “afterburning,” refers to the intense
chemical processing that takes place in
rocket plumes after the hot gases have left
the engine nozzle until they cool to the
temperature of the surrounding atmosphere. These new afterburning models predicted that a significant amount of HCl in
SRM exhaust would indeed be converted
into chlorine radical in the hot plume.
Given the inevitable, and important, implication of deep ozone loss, the reactive
chlorine emission index (EI) of SRMs
needed to be verified.
An EI provides a standardized way of
expressing how much of a particular
exhaust component is emitted into the
atmosphere by a rocket engine. The EI is
50
Chlorine molecule concentration
(1010 per cubic centimeter)
40
Titan IVA
April 24, 1996
25
0
0
15
30
Horizontal distance (kilometers)
The theory of reactive chlorine production in SRM
plumes was proved during a WB-57F mission
through the plume wake of a Titan IVA. The
concentration of chlorine molecule (Cl2) was measured as the aircraft flew through the eight-kilometerwide plume 40 minutes after launch. Because Cl2 is
not present in the undisturbed stratosphere, all of the
measured Cl2 could be attributed to the Titan IVA
SRMs. The data were obtained by J. Ballenthin and
associates of the Air Force Research Laboratory,
Hanscom Air Force Base.
calculated by dividing the total mass of a
particular component in the plume (in
grams) by the total mass of propellant
burned (in kilograms). For rocket engines,
the EI refers to the exhaust plume composition after the secondary combustion process has occurred
and the plume has expanded
Large mode
Medium mode
Small mode
Alumina particles emitted by SRMs come in three
distinct sizes, or modes. (A human hair is 20 times the
diameter of the large-mode particle.) Only particles
in the small mode remain in the stratosphere long
enough to mix throughout the atmosphere and possibly play a global role in stratospheric chemistry.
RISO studies of these modes in Titan IVA and space
shuttle plumes showed that less than 0.1% of the
total mass of SRM alumina particles appears in the
small mode, which is 10 to 100 times smaller than
previous estimates indicated.
to match the pressure and temperature of
the surrounding atmosphere. EIs serve as a
convenient way to analyze plume data,
provide input for computer models, and
quickly compare the potential stratospheric
impacts of different propulsion systems.
The true extent of the immediate
stratospheric response to the putative reactive chlorine emissions was not well
understood; the results of various models
were not in agreement. For example, predictions of the duration of the short-term
ozone loss in the wake of a Titan IV-class
vehicle varied from a few minutes to a few
hours from model to model. Without
actual plume data, it was impossible to
evaluate the accuracy of the various models, and the resulting uncertainty allowed
the possibility that the actual ozone loss
exceeded all predictions. The behavior of
ozone in SRM plume wakes needed to be
measured, and the plume-wake models
needed to be evaluated.
A third uncertainty concerned the alumina particles in SRM exhaust. These tiny
particles (most are less than one-thousandth of a millimeter in diameter) have
the same chemical makeup as sapphire
(Al2O3). Some laboratory measurements
had suggested that heterogeneous chemical reactions on the surface of alumina
particles might contribute to ozone loss by
converting chlorine from inactive to active
forms. The potential importance of this
effect is critically determined by the exact
sizes of the alumina grains in the exhaust.
The largest grains fall out of the stratosphere within several days, and so their
surfaces do not have time to promote significant chemistry in the global sense. The
smallest grains may remain aloft for several
years, however, possibly promoting
ozone-harmful reactions throughout the
stratosphere. To resolve this question,
alumina particles in SRM plume wakes
needed to be collected and the EI of the
smallest of them measured.
In-Situ Plume Experiments
At its inception, RISO conducted three
independent data-collection experiments.
Two of these, both completed in 1998,
used remote-sensing devices based at
Cape Canaveral Air Force Station. First, a
network of sensors measured the influence
of stratospheric plumes on the intensity of
harmful solar UV light on the ground near
the launch site. Second, a multiple-wavelength lidar (light detection and ranging)
system successfully illuminated plumes
with laser beams to measure the optical properties of plumes over Cape
Canaveral and provide insight into
how plume exhaust mixes into the
stratospheric background air. These
two efforts conclusively demonstrated that even though radicals in
rocket exhaust cause immediate loss
of UV-absorbing ozone in individual
plumes, rocket plumes disperse in a
way that makes it highly unlikely that
the intensity of UV light on the
ground near launch sites would
measurably increase following
launches of even the largest rockets.
RISO’s main focus, however, has
been to develop a detailed understanding of rocket emission chemistry by directly measuring the
composition of stratospheric air
inside plume wakes during the critical time from several minutes to several hours after launch. RISO chose
the NASA WB-57F aircraft to carry
instruments into lower-stratospheric
rocket plumes at an altitude of about
19 kilometers. During a typical mission, the WB-57F enters a plume
about five minutes after launch and
then executes figure-8 maneuvers around
the launch-vehicle trajectory, encountering
the plume wake about every 10 minutes
for up to two hours after launch. The aircraft travels at about 200 meters per second and spends between 2 and 60 seconds
in the plume during each encounter measuring composition.
Beginning in 1996, a variety of exhaust
plumes were sampled by the instrumented
WB-57F aircraft, including the space shuttle, Titan IVA, Delta II, Atlas IIAS, and
Athena II. Three instruments carried during the 1996 missions proved the scientific
value of the RISO concept. The instruments have steadily improved since the
first missions. Seventeen state-of-the-art
instruments carried during the 1999 missions collected a wide variety of gas and
particulate data that will allow a more
comprehensive characterization of plumewake chemistry.
Highlights from Early Missions
On April 14, 1996, the WB-57F carried
into a Titan IVA plume a Neutral Mass
Spectrometer developed by the Air Force
Research Laboratory at Hanscom Air
Force Base. Analysis of data from the
spectrometer unambiguously demonstrated that the plume contained significant
USAF
NASA
Exhaust plume of a Titan IVA launched from Vandenberg Air Force Base, as
seen from the WB-57F cockpit just before flying thorough the plume. Only
two minutes old in this view, the plume displays a pattern of breakup from
windshear and mixing characteristic of all stratospheric plumes. The California coast and San Miguel Island are visible.
The WB-57F high-altitude aircraft, operated by NASA’s Johnson Space Center, carries large scientific payloads well into the stratosphere. The WB-57F has served the RISO program since
1996, flying though 11 rocket-exhaust plumes.The two-person aircrew includes a dedicated
science officer who monitors instrument status and initiates plume data collections.
amounts of reactive chlorine molecule, a
gas not found in the natural stratosphere.
The RISO team concluded that the estimated chlorine molecule EI of the Titan
IVA SRMs was generally consistent with
predictions based on the Aerospace computer models of chlorine afterburning
chemistry.
RISO WB-57F missions have carried
up to four instruments to observe the
extent and duration of immediate ozone
loss in the plume wake. Data from each
plume encounter allow investigators to
quantify how much ozone is destroyed in
the plume over time. Measurements from
Titan IVA and space shuttle plumes show
that the amount of ozone destruction does
not increase without limit. RISO
researchers have shown that ozone loss
slows about one hour after launch, suggesting that the most ozone-destructive
emissions have been deactivated by reactions with various gases in the surrounding air. This important observation has
eased concerns that the short-term ozone
loss in rocket plumes might be much
greater than in the model predictions.
Surprisingly, data obtained from within
the plumes of several different rockets
show that launch vehicles with greatly differing SRM emission rates cause about the
same amount of ozone loss between 30
and 60 minutes after launch. Ozone loss in
the plumes of Delta II and Atlas IIAS
rockets was about the same as the loss in
the plumes of the much larger Titan IVA
and space shuttle. Existing plume-wake
models that include only SRM chlorine
gas emissions have not predicted this
result; why this discrepancy exists is not
yet known. It may be that SRM emissions
interact with the stratosphere in a fashion
not yet accounted for in plume models, or
perhaps the liquid-oxygen/kerosene core
engines of the Atlas IIAS and Delta II produce reactive gases that act alone or with
SRM emissions to cause some additional
ozone loss. Further data collection and
measurement of the actual radical EIs for
the various systems, and the development
of detailed models of plume-wake chemistry, are needed to solve this puzzle.
Interagency ACCENT Program
Thiokol Propulsion, the company that
manufactures the SRMs used on the space
shuttle and Atlas IIAS, and Alliant Techsystems, the company that produces the
Delta II SRM, joined RISO in 1998 as
contributing partners. In 1999, RISO
joined forces with NASA, the National
Oceanic and Atmospheric Administration,
and the National Center for Atmospheric
Research as part of the Atmospheric
Chemistry of Combustion Emissions Near
the Tropopause (ACCENT) mission, a
multiagency-sponsored effort to study the
effects of aircraft and rocket-engine
exhaust on the upper troposphere and lower
stratosphere.
ACCENT brings together RISO and
ongoing efforts of the NASA Atmospheric
Effects of Aviation Program (AEAP). The
Ozone concentration (1010 per cubic centimeter)
300
250
200
150
100
50
0
0
12
24 0
12
24 0
Plume wake (kilometers)
Ozone concentration measured across the plume wakes of four different launch
vehicles, all obtained about one hour after the different launches. Red represents
data obtained while the WB-57F aircraft was inside the exhaust plume. The total
amounts of chlorine emitted by the Titan IVA, Atlas IIAS, space shuttle, and Delta II
ACCENT partnership grew out of the realization that a common set of atmospheric
measurements from shared payloads on
the WB-57F aircraft could serve the interests of both the Air Force and NASA programs. The ACCENT payload included as
many as 17 instruments, significantly
enhancing the RISO/ACCENT science
team’s ability to understand plume-wake
chemistry and characterize rocket-engine
emissions. Three successful plume-wake
flights took place during the 1999
ACCENT deployments. The data collected
will allow several important unresolved
problems to be addressed, including estimating the nitric oxide radical EI of SRMs
and the soot EI of liquid-oxygen/kerosene
engines and measuring the intensity of
chemical reactions that take place on the
surface of alumina particles in the plume.
Looking Ahead
RISO represents but one component of
ongoing Aerospace activities to provide
the Air Force with cutting-edge research
and technical guidance on a wide range of
environmental issues—from solvent
chemistry to toxic ground clouds and
ozone depletion. For its part, the RISO
team allows SMC to claim world-class
scientific expertise with regard to the
12
24 0
12
24
SRMs at the altitude of these measurements are about 2, 0.2, 4, and 0.3 tons per kilometer of altitude. Despite such large differences in chlorine emission rates among
the four rocket types,the ozone losses in the plumes are comparable.The data were
obtained by J. Benbrook and W. Sheldon of the University of Houston.
influence that rocket emissions have on
Earth’s ozone layer. The advances coming
out of RISO are making the Air Force and
the entire space-launch community confident that ozone loss from both individual
and collective launches does not constitute
a significant environmental hazard. RISO
has proved that a low-cost program of
ongoing plume-wake intercepts using
appropriate instrumentation can help
resolve the scientific problems surrounding the issue. RISO has also shown how
joining forces with other agencies and
industry increases the scientific return on
investment for all interested parties.
The data and conclusions from the
RISO program reinforce a presumption
that rocket emissions do not seriously
threaten the ozone layer at the present
time. However, as the space transportation
industry grows, as new launch systems are
introduced, and as the ozone layer recovers from past damage caused by nowbanned substances, the effect of rocket
emissions on stratospheric ozone is likely
to become a more visible issue. The space
transportation community should continue
to support scientific research efforts to
fully understand the impact of rocketpropulsion systems on the composition of
Earth’s natural umbrella, the ozone layer.
Further Reading
B. B. Brady, L. R. Martin, and V. I. Lang.
“Effects of Launch Vehicle Emissions in the
Stratosphere,” Journal of Spacecraft and Rockets, Vol. 34, 774–779 (1997).
C. H. Jackman, D. B. Considine, and E. L.
Fleming, “A Global Modeling Study of Solid
Rocket Aluminum Oxide Emission Effects on
Stratospheric Ozone,” Geophysical Research
Letters, Vol. 25, 907–910 (1998).
M. N. Ross, et al., “Study Blazing New Trails
Into the Effects of Aviation and Rocket Exhaust
in the Atmosphere,” Transactions of the American Geophysical Union, Vol. 80, 442–444 (1999).
M. N. Ross, et al., “In-Situ Measurement of Cl2
and O3 in a Stratospheric Solid Rocket Motor
Exhaust Plume,” Geophysical Research Letters, Vol. 24, 1755–1758 (1997).
M. N. Ross, J. R. Benbrook, W. R. Sheldon,
P. F. Zittel, and D. L. McKenzie, “Observation
of Stratospheric Ozone Depletion in Rocket
Plumes,” Nature, Vol. 390, 62–65 (1997).
M. N. Ross, P. D. Whitefield, D. Hagen, and
A. R. Hopkins, “In-Situ Measurement of the
Aerosol Size Distribution in Stratospheric
Solid Rocket Motor Exhaust Plumes,” Geophysical Research Letters, Vol. 26, 819–822
(1999).
WMO, “World Meteorological Organization
Scientific Assessment of Ozone Depletion,”
Report No. 25, Chap. 10, World Meteorological Organization, Geneva, Switzerland (1991).
John Wessel and Robert W. Farley
In this NASA shuttle photo of a sunset over South
America, a pink layer, attributed to sulfuric acid
droplets and ammonium sulfate particles, begins
at the tropopause and extends upward into the
stratosphere to 19 kilometers.
NASA
Water-Vapor Lidar
Extends to the
Tropopause
Helium balloon
John Wessel and Robert W. Farley
Lidar’s role in obtaining accurate measurements of water vapor in
the upper troposphere is becoming increasingly important as the
issue of global warming heats up.
T
he question of whether Earth is
dangerously heating up has
become a subject of debate in
our time. But is global warming
fact or fiction? One thing is certain: The
surface temperature of Earth has increased
0.45 to 0.6 degrees Kelvin in the past century. A recent study supported by The
National Science Foundation predicts our
planet will warm by 2 degrees Kelvin in
the 21st century. Recent research conducted
by The Aerospace Corporation to validate
Defense Meteorological Satellite Program
(DMSP) measurements could shed some
light on global warming issues.
Global warming takes place when heat
becomes increasingly trapped in Earth’s
atmosphere. It is now widely believed that
“greenhouse gases” (so called because
these atmospheric constituents produce a
“greenhouse effect” over Earth) contribute
to this warming. Water is the most influential component of the greenhouse gas
mixture: Water vapor absorbs infrared
radiation emitted from Earth’s surface and
lower atmosphere more than any other
constituent, thereby trapping heat best.
Accurate knowledge of the amount of
atmospheric water must be obtained to
improve and test global-warming models.
Aerospace recently made significant
advances in the ability to measure the distribution of water vapor in the upper troposphere (upper portion of the lower
atmosphere). Using a ground-based lidar
(light detection and ranging) system,
Humidity
transducer
Temperature
transducer
Ground
plane
antenna
Ground
plane
antenna
Wire (flex)
antenna
A radiosonde is an instrument package carried by a
balloon that ascends to altitudes of 20 to 30 kilometers. It measures temperature, humidity, and pressure
in the atmosphere and broadcasts the information
back to a ground station. The Global Positioning System is used to record the trajectory during ascent to
determine wind speed and direction.
measure humidity, temperature, and air
pressure. First, radiosondes do not operate
correctly at the low temperatures typically
encountered above an altitude of 8 kilometers. Second, they are one-shot attempts at
measuring atmospheric conditions, and
they take one hour to reach their zenith.
The lidar system measures water vapor
continuously over the entire altitude range.
This is important because the lidar can
capture data from a satellite as the satellite
moves overhead, and satellites are only in
view for five minutes. During this brief
time, the “ground footprint” of the satellite must be in line with the lidar. The lidar
both global-climate and weather-forecast
modeling. One way to determine the causes
(and the only way to predict the future
extent) of global warming is to have accurate models, which presupposes having
accurate knowledge of the initial atmospheric conditions.
Global-climate-change studies rely
heavily on computer-generated models
that predict the future state of the atmosphere based on initial data retrieved from
ground- and satellite-based weather measurements. Although these models are
largely based on thoroughly tested principles of physics, a number of simplifica-
Pionee
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in
Space
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Meteo
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M
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The most reliable calibration occurs when the lidar
measures moisture in the satellite “ground footprint”
area as the satellite passes overhead. A lidar set up
over water works best during calibration of satellite
data because the water’s surface emits less interfering microwave energy than land. For this reason, setting up the lidar on a small island or on a shipboard
platform is ideal.
which operates much like radar, the
researchers discovered significantly more
water content in the upper reaches of the
troposphere than was previously thought
to exist. This capability was developed to
improve calibration of U.S. Air Force
meteorological satellites.
Lidar vs. Weather Balloons
The combined use of lidar and satellites
provides many advantages over conventional balloon-borne radiosondes, which
Setting up the Aerospace mobile lidar are Steven Beck,Yat Chan, and Jerry Gelbwachs. It was first used for satellite calibration at Kauai, Hawaii.The container was equipped with wheels and towed to the final site.The structure
on the left front of the container is the elevator that raises the beam director periscope (located on top of the
container).The beam director is stored below the roof line so the container can fit inside an aircraft.
then calibrates the data derived from the
satellite. Essentially, it verifies whether or
not a satellite is measuring water vapor
properly. (See sidebar “How Lidar Works,”
pages 14 and 15)
Finally, water-vapor data can now be
derived from multiple satellites that measure water vapor all over the world. Before
the advent of satellites, data were derived
from radiosondes routinely launched over
land by national weather services.
Improving Computer Models
Combining accurate ground-based lidar
measurements with high-quality imagery
obtained by satellites promises to improve
tions are used to improve calculation
speed and bypass scientific problem areas.
In addition, adequate computer power is
not yet available to process the volume of
data required for accurate prediction. The
result is that computer-generated weatherforecast and global-climate-change models yield oversimplified results. As more
computer power becomes available, more
complete data on initial conditions can be
processed, resulting in improved models.
Microwave Sounders vs. Radiosondes
DMSP recognized in 1979 the need for
accurate data to feed numerical (computer)
global-weather-prediction models and pio-
neered a microwave-sounding instrument,
the SSM/T-1 (Special Sensor Microwave/
Temperature), to measure temperature in
the atmosphere. Until then, radiosondes
alone were relied upon to gather data about
atmospheric temperatures.
Microwave sounders are passive
devices, radio receivers that listen for
emissions at various frequencies. Water
vapor emits microwaves, the intensity of
which is used to estimate water content in
the atmosphere, particularly over oceans,
where conventional methods of obtaining
measurements are in short supply.
(Radiosondes, which provide a more
because water provides the principal
means of energy transport in the troposphere and plays a critical role in global
warming. Additionally, water vapor
induces cloud formation and violent
weather events, determines atmospheric
visibility, causes icing, and influences aircraft contrail formation.
In processing water-vapor data derived
from SSM/T-2 measurements, serious
discrepancies were observed between
microwave and radiosonde water-vapor
data. The problem was traced to radiosonde humidity transducers. Errors show
up in the water-vapor data derived from
R. L. Jones, Sandia National Laboratories
The U.S. Navy Pacific Missile Range Facility on the island of Kauai. Because a minimum of land in view is desired
when a satellite aligns with the lidar, an island setting was ideal for The Aerospace Corporation’s test of its new
Raman lidar system. In addition, Kauai provided the necessary moist environment for the experiment.
direct means of measuring atmospheric
properties, are in widespread use over
land.)
In 1991, DMSP launched the SSM/T-2,
which measures water vapor. SSM/T-1 and
SSM/T-2 now serve as eyes on worldwide
weather, providing the data needed to initialize the computer models. Although the
SSM/T-1 temperature sounder has a long
history of success, the SSM/T-2 is newer
and has had limited development.
Because water vapor is highly variable
in the atmosphere, measurements of it are
generally neglected in computer-generated
forecast models. This is unfortunate
satellites because satellites are calibrated
against radiosondes.
Water-Vapor Lidar
Raman lidar is a specialized type of lidar
named after Sir Chandrasekhara Raman,
who won the Nobel Prize for physics in
1930 for his discovery of the shifts in the
wavelength of light that occur when a light
beam interacts with molecular vibrations
and rotations. Whereas lidar typically
measures light that remains at one
frequency, Raman lidar can measure
wavelength-shifted light. Because each
constituent of the atmosphere correlates to
a characteristic wavelength shift, Raman
lidar is useful in measuring the constituents of the atmosphere.
Raman lidar was initially developed at
NASA’s Goddard Space Flight Center.
Aerospace confirmed its feasibility for use
in DMSP applications in experiments performed during 1993 at the Air Force Malabar facility. Plans were then made to
develop a mobile lidar system capable of
calibrating satellites from a variety of
remote locations, and Aerospace designed
and constructed the system in-house. This
mobile lidar is housed in a surplus Air
Force transportable radar container.
Experimentation on Kauai
The new Raman lidar system was first put
to use during the calibration and validation
of the DMSP F-14 satellite. A sea-level
island location with an airport and controlled air space, clear dark sky, and, of
course, a moist atmosphere were required
for the demonstration. The Navy’s Pacific
Missile Range Facility on the Hawaiian
island of Kauai was chosen. The Hawaii Air
National Guard provided transportation.
Calibration was highly successful and
showed significant improvement over
radiosonde calibration. During a two-week
period, 10 lidar measurements were taken
that closely matched measurements
gathered by the SSM/T-2. However, the
radiosonde measurements suggested
considerable instrument error. Aerospace
concluded that radiosonde water-vapor
measurements taken above 8 kilometers
altitude are incorrect most of the time
because the water-vapor transducers carried by radiosondes become unresponsive
at the low temperatures encountered at high
altitudes.
High-Altitude Water Vapor
High-altitude water-vapor measurement is
a key element in modeling global warming because water has a much greater
influence on Earth’s tropospheric energy
balance than trace gases such as carbon
dioxide. However, water vapor is not accurately monitored, and little is known about
its influence on global climatic change.
Aerospace learned from the Kauai experiment that the lidar’s high-altitude accuracy
needed to be improved to accurately validate SSM/T-2 for upper-tropospheric
water-vapor measurement. A new highaltitude detector system was incorporated
into the lidar, which allowed measurements above 10 kilometers. When this new
system was used at the U.S. Navy’s Pacific
14
12
Radiosonde
Lidar
Altitude (kilometers)
10
8
6
4
2
0
0
20
40
60
80 100
Relative humidity (percent)
Steven Beck, Jerry Gelbwachs, and John Wessel preparing to launch a radiosonde near the Aerospace transportable lidar system at Kauai. The radiosonde, contained in a white plastic-foam package, is suspended below
the balloon.
Relative humidity measured at San Nicolas Island Oct.
7, 1998. Lidar measurements are appreciably higher
than corresponding radiosonde measurements.
Missile Range Facility at San Nicolas
Island, off the coast of California, SSM/T2 upper-atmosphere water-vapor measurements were validated.
The lidar measurements indicated that, on
average, four times more water vapor than
expected lies in thin layers near the
tropopause (top of the troposphere).
How Lidar Works
The picture of upper-tropospheric water
vapor observed from San Nicolas Island
was much different than expected based
on prior NASA satellite measurements.
Lidar has proved to be an improvement over ground-based
methods of measuring water vapor in the atmosphere.
Atmospheric
scattering
Laser transmitter
Laser
Frequency
shifters
Photodetectors
Collimator
(expands)
Telescope
Telescope primary mirror
Spectrum
analyzer
Shutter
A lidar consists of a laser transmitter, a
receiver telescope, photodetectors,
and range-resolving detection electronics (not shown). The Raman lidar
shifts the laser frequency from the
infrared range into the ultraviolet
range using harmonic generator crystals. The ultraviolet is expanded in a
collimator telescope to make the output eye-safe and to improve the divergence of the beam.
The operating principles of lidar are
similar to those of radar. The laser
transmits a short pulse of light in a
specific direction. The light interacts
with molecules in the air, and the molecules send a small fraction of the
light back to the receiver telescope.
0
Wind speed (meters per second)
10
20
30
40
Wind
speed
18
Wind
direction
Aerospace, Lidar
NASA, Sage II
Altitude (kilometers)
18
16
Mixing
ratio
14
12
Mastenbrook, frost
point hygrometer
Oltmans,
Mastenbrook, frost
point hygrometer
16
Kley, frost point
hygrometer
14
10
12
8
0
20
40
60
Mixing ratio
(parts per million/volume)
80
0
50
Mixing ratio
(parts per million/volume)
100
(Left) Mixing ratio of water vapor to air, measured by lidar on September 25, 1998.Wind direction in degrees from
north is 10 times the value shown on the wind speed scale. (Right) Average mixing ratios observed by Aerospace
lidar at San Nicolas and the Table Mountain Observatory June–October. NASA Sage II instrument midlatitude
measurements were lower than Aerospace averages, Oltmans-Mastenbrook measurements above Colorado
were much lower, and Mastenbrook’s, in summer over Washington, D.C., and Trinidad, V.I., were closest to Aerospace measurements. Most high-quality ground-based measurements for the upper tropopause were made in
equatorial regions; the Kley points are typical of these. (The mixing ratio is the ratio of water-vapor pressure to air
pressure in the atmosphere.)
Laser
r
eive
Rec
Lidar Atmospheric Profile
Raman Spectrum
Vibrational Raman
Logarithmic
intensity
Laser
wavelength
H2O signal
The returning light signal is measured
by photodetectors. The amount of time
it takes the light to return to the receiver
telescope indicates altitude, the wavelength shift of the light identifies the
type of air molecules that scattered the
light,and the intensity of the light represents the concentration of molecules.
In Raman lidar (the Raman process),
light interacts with vibrating and rotating molecules, and this causes the shift
in wavelength shown in the Raman
spectrum. Aerospace used separate
optical filters to isolate the wavelength
signals emitted by the water vapor and
nitrogen molecules.The ratio of the signals is proportional to the mixing ratio
of water vapor to air.
20
Altitude (kilometers)
A second set of data acquired in 1999
from the NASA Jet Propulsion Laboratory
Smithsonian Table Mountain Observatory
site, located at 2,300 meters in elevation at
Wrightwood, California, confirms this figure. The high location provided very clear
skies and reduced the range to the
tropopause, thereby improving measurements. Data from the two sites were similar, confirming that the data represent
weather in the vicinity of the local
tropopause.
If the results of these experiments are
broadly descriptive of the midlatitude
atmosphere, they may add to our understanding of global warming. Before now,
few high-altitude measurements had been
taken at those latitudes using precise
methods.
Atmospheric Circulation and
Hadley Cells
The combination of lidar data, wind data,
and SSM/T-2 upper-atmosphere watervapor imagery provided information that
supports the current scientific understanding of general atmospheric circulation.
Global atmospheric circulation is caused
by the uneven heating of Earth’s surface.
Lower latitudes receive more radiation
0
Time
N2
O2
Wavelength
H2O
June 30, 1998
Brightness temperature (kelvin)
275
San Nicolas Island
235
October 7, 1998
Brightness temperature (kelvin)
275
San Nicolas Island
235
Brightness-temperature mappings recorded in the SSM/T-2 upper tropospheric channel for satellite overpasses,
made during San Nicolas Island lidar measurements. Blue corresponds to low-brightness temperature, which
indicates the presence of moisture and signifies that emissions are primarily from the cold upper troposphere.
Red corresponds to high-brightness temperature. High-brightness temperatures occur when microwave emissions originate from low altitudes, which are normally warmer, and the middle and upper troposphere are dry.
Otherwise, the microwave emissions would be absorbed by high-altitude water vapor. In these images, San Nicolas Island, indicated by a small white triangle, lies near the boundary between moist and dry upper layers.
from the sun than do higher ones. To
understand atmospheric circulation, various models have been developed.
One such model is the Hadley circulation model. The sun shines approximately
overhead at the equator. This heats surface
regions, causing air to rise and cool. The
cool air loses moisture in the process.
Once cool, it moves north and south,
descending toward midlatitudes and then
returns at low levels back to the equator
where it gets reheated.
SSM/T-2 routinely identifies large midlatitude regions, including locations such
as San Nicolas Island, that have very dry
upper air. Dry regions are surrounded by
moist high-altitude regions. The dry air
presumably came from very high altitudes
near the equator and subsided to a lower
altitude upon reaching midlatitudes. The
lidar and radiosonde data can be used to
estimate how long ago this subsidence
occurred. Thin moist layers are usually
observed by lidar in regions that characteristically have dry air.
In the case of San Nicolas Island, we
hypothesized that wind shear carries moisture from moist regions into neighboring
dry areas. When we combined the windshear velocities with the distance between
the lidar location and the surrounding moist
region, we estimated that the air subsided
within 2 to 20 hours of our measurements.
The overall picture of dry high-altitude
equatorial air moving north and subsiding
at our midlatitude is consistent with the
Hadley circulation model, which predicts
that equatorial air moves toward the poles.
Applying Our Knowledge
Future research will extend water-vapor
measurements over regions representative
of the global atmosphere, and the capability of measuring temperature will be added
to the lidar. The new DMSP Special Sensor
Microwave Imager Sounder (SSMIS)
instrument will measure temperatures up to
80 kilometers altitude, which will require
a new validation method. This instrument
is being developed by Aerojet-Gencorp
and is scheduled for launch in November
2000. It combines the features of the current-generation SSM/T-1, SSM/T-2, and
SSM/I (SSM/Imager) instruments with
increased horizontal resolution and the
capability of measuring temperatures at
high altitudes.
Some researchers use Rayleigh lidar to
measure temperature up to 80 kilometers
altitude. We currently measure temperature
The Hadley Circulation Model
Cold and dry
Tropopause
Moist
layer
Dry
Ice, rain
Moist
Very warm
massive
convection
Equatorial Pacific
to an altitude of 40 kilometers using both
Rayleigh and rotational Raman lidar, and
expect to reach 80 kilometers in 2001. Lidar
will then provide the data needed to validate
all SSMIS atmospheric measurements.
Midlatitude
In general, lidar is an excellent method
for calibrating satellite microwave sensors. It accurately depicts the atmosphere
those sensors view. Enhancing lidar’s
capabilities will contribute to our increas-
In 1735, George Hadley, a British physicist (1685–1768), formulated a model to
explain the general pattern of global
atmospheric circulation. The Hadley
model describes, in the simplest form, a
large-scale circulation in Earth’s atmosphere, with a rising motion of air over
the equatorial regions and a descending motion northward and southward
toward the midlatitudes.
Massive convection in the equatorial
Pacific lofts air from the surface to altitudes above the tropopause. The tropopause is coldest in equatorial regions,
and water precipitates in the form of rain
and ice from the convected air masses.
This injects very dry air into the region of
the tropopause and above.The air moves
generally toward the poles and descends
in the process, accounting for our observations of exceedingly dry air layers at
midlatitudes. Frequently, moist layers
occur above the dry regions. Wind shear
causes this by transporting thin layers
from nearby moist regions.
ing understanding of the atmosphere,
which may one day in the near future lead
us to solving the puzzle of why Earth is
getting hotter.
Further Reading
M. A. Janssen, Atmospheric Remote Sensing by
Microwave Radiometry (Wiley-Interscience,
New York, 1993).
T. R. Karl and K. E. Trenberth, “The Human
Impact on Climate,” Scientific American,
December 1999, pp. 100–105.
R. M. Measures, Laser Remote Sensing
(Wiley-Interscience, New York, 1984).
S. H. Melfi and D. N. Whiteman, “Observation
of Lower Atmospheric Moisture Structure and
Its Evolution Using a Raman Lidar,” Bulletin
of the American Meteorological Society, Vol.
66, 1282–1292 (1985).
D. Rind, “Just Add Water Vapor,” Science, Vol.
281, 1152–1153 (1998).
F. W. Taylor, “The Greenhouse Effect and Climate Change,” Reports on Progress in Physics,
Vol. 54, 881–918 (1991).
Naval Air Warfare Center
The U. S. Navy Pacific Missile Range Facility, San Nicolas Island, off the California coast, where Aerospace used lidar
with a new high-altitude shutter system to validate SSM/T-2 upper-atmosphere water-vapor measurements.
J. Wessel, S. M. Beck, Y. C. Chan, R. W. Farley,
and J. A. Gelbwachs, “Raman Lidar Calibration for the DMSP SSM/T-2 Microwave Water
Vapor Sensor,” IEEE Transactions on Geosciences and Remote Sensing, Vol. 38, 141–154
(2000).
DSP
E
arly in the morning on a day in
August 1972, all satellites in the
constellation that would alert the
United States of a missile attack
suddenly lost their warning capability. The
detectors and circuitry, according to the
status data, had been hit by a strong source
of ionizing radiation. This appeared to be
an ominous event to operators at the
ground stations, where the initial interpretation was that the Russians had detonated
a nuclear warhead in space, possibly as a
precursor to a ballistic missile attack.
Prompt analysis of the sensor outputs by
an Aerospace expert in nuclear and space
physics on duty at one of the sites provided
the actual cause: The satellites had been hit
with a massive proton flux from an extraordinarily intense solar flare. An unwise reaction by the government was averted. The
Aerospace Corporation subsequently
worked with the U.S. Air Force and the
system contractor to provide fixes to assure
uninterrupted operation through such
events. Aerospace has often provided
invaluable assistance to the Air Force, playing a key role in the development, operation, and success of this national asset—the
Defense Support Program (DSP).
Deployed 40,000 kilometers above
Earth in the equatorial plane, a constellation of satellites equipped with infrared
sensors (“IR eyes”) looks for ballistic missiles aimed at the United States or its
allies. The period of their orbits is 24
hours, so the satellites remain at constant
longitudes, that is, in geostationary orbits,
guarding against an attack on the United
States or its allies from anywhere in the
world. The system has been in operation
continuously since it went on line in 1971.
Fortunately, the United States has never
experienced a missile attack; of course, the
Launch of the Program 461 satellite by an Atlas Agena
from Vandenberg Air Force Base on August 19, 1966,
into a 3700-kilometer circular orbit.
IR Eyes High in the Sky
The Defense Support Program
Fred Simmons and Jim Creswell
Crosslink commemorates the 40th anniversary of The Aerospace Corporation by introducing
a series on the history of the corporation’s role in national space programs.
extent to which DSP has served as a deterrent to such an attack cannot be known.
In addition to performing their primary
mission, DSP sensors have produced a
wealth of information on a variety of
sources, military and otherwise, that has
served many other purposes. Certain civilian uses of these surveillance satellites are
described in the premier issue (January
2000) of Crosslink. Those particular appli-
cations of course are peripheral to the principal mission of DSP.
Early Development
The U.S. national early warning program
had its beginnings in the early 1960s,
when it became evident that the United
States was vulnerable to attack by the
intercontinental ballistic missiles (ICBM)
then under development in the Soviet
Union. By the mid-sixties, ICBMs
High altitude
(above 30 kilometers)
Sensor line of sight
Low altitude
(20–30 kilometers)
Sources of confusion for a space-based surveillance system. From low altitudes (0 to 10 kilometers), cultural
sources include industrial sites (such as heat exchangers, flare gas burners, smelters, and coke ovens), petroleum
and pipeline fires, explosions and dumps, and slash-and-burn regions; geophysical sources include forest fires,
volcanoes, and solar scatter from cloud edges, coastlines, water surfaces, high deserts, and snow-covered heights.
From high altitudes (above 30 kilometers), cultural sources include target-related clouds and tracks, objects in low
Earth orbits, and vehicle reentries; natural sources include meteors and bolides, volcanic clouds, air glow, and
aurora, as well as the sun, moon, planets, and stars.
108
107
Missile at
20 kilometers
Intensity
106
105
104
103
102
Terrain
Cloud at
10 kilometers
10
2.2 2.6 3.0 3.4 3.8 4.2 4.6 5.0
Wavelength
The blue and green curves show the spectra of typical terrain and a solar-illuminated cloud at 10 kilometers altitude; the red curve shows a hypothetical
missile at 20 kilometers altitude.
appeared in test flights, and the United
States adopted the MAD (mutual assured
destruction) strategy as its national
defense posture.
Early warning became critical to the
survival of U.S. retaliatory forces, and
launch detection by space-based sensors
was essential. Aerospace was called upon
at the start to perform trade studies and
prepare technical specifications for an
operational system. It provided the general
system engineering and technical direction
for the development of the program.
The ballistic missile defense studies as a
whole had been initiated earlier. As part of
its Project Defender, the Advanced
Research Projects Agency (ARPA) of the
Department of Defense in the late 1950s
explored concepts for early warning based
on the detection of the infrared emission
from rocket exhaust plumes by sensors
stationed in space. The ARPA program
consisted mainly of system studies and
various measurement programs to characterize the infrared properties of ballistic
missiles and the backgrounds against
which they would have to be observed.
Concurrent with much of that work, the
Air Force, aided by Aerospace, began
development of its own Missile Defense
Alarm System (MIDAS). That system, had
it been implemented, would have employed
a constellation of many satellites in low
Earth orbits.
A space experiment designated as Program 461, the final element of the MIDAS
program, provided the proof of principle
to support the development of a system
with far greater capabilities. Although the
exhaust plume from a rocket emits a great
deal of infrared radiation, so do many
other sources that might appear in the
background. To discriminate the rocket
from the background sources, the sensors
must operate in specific regions of the
spectrum. In their characteristic molecular
bands between two and three microns,
water vapor and carbon dioxide in the
atmosphere greatly suppress emissions
from fires and other hot terrestrial sources
and solar reflections from the ground and
low clouds.
Because water vapor and carbon dioxide are the principal products of rocketpropellant combustion, the hot exhaust
plume from the missile appears as a very
bright source moving against the background in those same spectral bands. Consequently, as a missile rises through the
atmosphere and absorption diminishes, the
apparent intensity of the plume rapidly
increases. Accordingly, the sensors are
The RTS-1 payload for Program 461 was built by Lockheed Missiles and Space Company (now Lockheed
Martin) for the Air Force Space Systems Division. The
sensor, built by the Aerojet-General Corporation,
included an 8-inch aperture concentric telescope and
a focal plane containing a linear array of 442 lead-sulfide detectors.A spectral filter defined a narrow bandpass within the band of water-vapor absorption in the
atmosphere.The sensor was mounted on a spin table
to rotate at 6 rpm, providing a scan of Earth every 10
seconds. A pair of star sensors provided information
for attitude determination.Three such payloads were
launched in 1966; two were successful. Each sensor
collected data for about a year.
Elevation
angle
Zenith
angle
rget
Target
Local
vertical
Ground
track
The Program 461 satellite was designed to operate
in a spinning mode to scan Earth below from a low
circular polar orbit (~3226 kilometers) with a period
of 10 seconds.
designed with detectors filtered to accept
radiation only in those molecular bands.
Furthermore, this spectral region favors
the use of lead-sulfide detectors, which
offer the advantage of high sensitivity with
passive cooling.
launched ballistic missile (SLBM), the
smallest missile of a direct threat to the
continental United States.
During 1966 and 1967, Program 461
collected data on many of the ballistic missiles and space launch vehicles in the
Soviet and U.S. arsenals, totaling dozens
of test launches. In the course of those
observations, Program 461 sensors produced a substantial database on the clutter
created by the scanning of the Earth-cloud
backgrounds, information also needed for
the optimization of the DSP sensors, the
development of which was commencing at
that time. Thus were provided the proof of
principle for space-based surveillance and
a valuable database for the design of the
sensors in the national early warning system to follow.
DSP Sensors
In the late-1960s, the design of the sensors
for the DSP system to some extent followed the concept for MIDAS. A linear
array of passively cooled infrared detectors, with spectral filters providing a bandpass in the center of an atmospheric
absorption band, was positioned in the
focal plane of a telescope mounted in a
satellite rotating at six revolutions per
Apparent radiant intensity
USAF
Sensor Design
In the design of a sensor for missile detection, a basic engineering decision involves
a choice between two approaches. A sensor can be designed to have relatively few
detectors that scan the field of view, or it
can be designed to have a very large number of detectors staring at the scene to
detect targets by their motion through the
field of view. The technology of the 1960s
enabled only the former approach, which
was incorporated in Program 461 and subsequently, DSP. In either case, a basic
design tradeoff is the optimization of the
spectral filter: The wider the bandpass, the
more target intensity is collected, but also
the greater the amount of highly variable
background. The early target and background measurement programs provided
sufficient information, mostly with airborne instruments, for the design of the
Program 461 sensors; the results of that
program provided the basis for further
optimization of the sensors in the DSP system that followed.
Program 461 satellites, built by Lockheed Missiles and Space Company,
observed many launches of missiles and
space launch vehicles from Cape Canaveral
and Vandenberg Air Force Base, as well as
from different sites in the Soviet Union.
After processing the signals received at the
ground stations, the target intensities were
reported as radiant intensities in the system
bandpass as functions of time for the particular viewing aspect and other parameters of
the observation. Extraction of such signatures from the raw data was a formidable
task in view of the relatively coarse pointing system of these satellites by today’s
standards; Aerospace provided much of the
analysis for that purpose.
Such data were obtained from observations of three SS-9 missiles in test flights
from the Tyuratam facility near the Aral
Sea to the Kamchatka peninsula in the Sea
of Japan. At the time, this liquid-propellant ICBM was the largest missile in the
USSR inventory and the principal threat to
the United States. Among other observations in the Eastern hemisphere, a
particular sighting of significance was that
of a single-stage missile launched in a test
flight from Kapustin Yar on February 3,
1967. The relatively short burn of that missile afforded observations in only three
scans between cloud break and thrust termination. That missile was later identified
as an SSN-6 medium-range submarine-
Oct 23, 1966
Mar 31, 1967
May 31, 1967
0
100
200
Time (seconds)
300
Program 461 observation. This plot, illustrative of the
product, shows the characteristic intensity profile of a
two-stage missile. The initial increase in intensity
occurs as the missile rises and the atmospheric
absorption decreases. After the maximum, the “afterburning” of hydrogen and carbon monoxide in the
exhaust diminishes as the vehicle and exhaust velocities become comparable and the density of oxygen
in the air decreases. After a minimum, the reported
intensity again increases as the missile velocity
exceeds the exhaust velocity, until the image of the
plume exceeds the detector field of view.
minute. The idea of a constellation of
many satellites in a low Earth orbit was
abandoned in favor of a few satellites in
geostationary orbits positioned at longitudes affording views of the launch sites of
concern. Accordingly, a sensor with a
USAF
DSP Flight 1 satellite prior to shipment to Cape Canaveral (1970). Note the offset of the telescope
from the vehicle axis. The two small telescopes pointing normal to the axis of rotation are the star
sensors that provide the data necessary to determine the precise pointing of the primary telescope.
The main body of the satellite contains a reaction wheel to control the spinning rate, propulsion
units for station keeping, and electronic components for data processing and transmittal. Solar cells
covering the body and four paddles provide power. The radiator, used for passive cooling of the
detectors, is located near the base of the telescope.
Azimuth
Elevation
Projection of
detector array
Equator
DSP mode of scanning.The detector arrays cover the
range from near nadir to slightly above the horizon.
The downlinked data include the responding detector identification and the universal time, which specify the target position in satellite coordinates of
azimuth and elevation.
much more powerful telescope and many
more detectors was designed by Aerojet
for installation in a satellite built by TRW
Inc. The DSP development effort was originally known as Program 266, then 949,
USAF
Launch of DSP Flight 1 from Cape Canaveral in November 1970.
and later 647. The system became DSP
when it achieved full functional capability.
DSP sensors incorporated many features representative of an advanced technology for that time. The design included
a larger array of detectors (2000 initially,
6000 eventually), spectral filters, electrical
circuitry for optimizing discrimination of
targets from a cluttered background, and
improvements in data processing onboard
and at the ground station. A key feature of
the DSP design (insisted upon by the
Aerospace advisors to the Air Force), was
the absence of moving elements in the sensor optics, elements that enormously simplified the bore sighting and precise
attitude determination. The optical axis of
the telescope was offset from the axis of
rotation of the satellite; the field of view of
the detector array extended from near the
nadir to slightly above the horizon. Thus,
the rotation of the satellite provided a scan
of most of a hemisphere every 10 seconds.
Two ground stations were initially built,
one located near Denver, Colorado, and
the other deep in the outback of Australia.
The initial satellite, Flight 1, was
launched in November 1970 by a Titan
IIIC launch vehicle with a Transtage third
stage. Unfortunately, it didn’t quite reach a
geosynchronous orbit, and the subpoint
circled Earth every five days. The orbit was
high enough, however, to allow checkout
of the ground data-processing sites and the
mission software and to provide nominal
Earth-pointing and sensor operation. Aerospace advisors at the ground sites and the
Air Force Satellite Control Facility provided the leadership for debugging and
modifying the software with “field-fixes”
and configuring the satellite for collecting
data. The anomalous orbit was fortuitous
because it provided the opportunity to
observe launches from both the United
States and the Soviet Union. The functioning of the system was proved, and data
from a considerable number of observations were collected.
In May 1971, Flight 2 was successfully
launched, and after on-orbit testing
(accomplished in a very short time), it was
turned over to the Air Force Systems Command. The satellite was stationed over the
Indian Ocean to view the major launch
sites of the Eurasian continent. For Flight 2
to effectively perform the warning mission, it had to recognize and report ICBM
launches and reject all infrared phenomena
USAF
NASA
Ground station in Australia.
Deployment of DSP Flight 16 from the shuttle in
November 1991.
restrict the spectral bandpass to suppress
terrestrial sources. That addition and other
changes in the detectors and electrical circuitry provided a substantial improvement
in sensitivity, which was needed to detect
and track upper stages. The average orbit
lifetime of a sensor has been five years,
with considerable variation. To date, 19
satellites have been built. All but one were
launched with Titan vehicles, those since
1989 with Inertial Upper Stages. The
exception was Flight 16, deployed from
the shuttle into a low Earth orbit for subsequent boost by an Inertial Upper Stage
motor to a geostationary altitude.
The research test series that preceded
the development of DSP provided no
effective means for establishing the precise pointing of the sensors. Aerospace
realized that a foolproof backup needed to
be added to DSP for determining the precise attitude of the infrared sensors. (In retrospect, the use of an Earth sensor for
pointing and star sensors for instantaneous, precise attitude determination
proved to be effective.) Aerospace concluded that a ground-based laser operating
in the infrared band of the sensor—analogous to a beacon or transponder in the field
of view of a radar—could serve that purpose. The idea was vigorously pursued,
and a DSP satellite was successfully illuminated within a year of the first satellite
launch. Aerospace developed and provided
hydrogen-fluoride chemical lasers for that
use.
Although the lasers were rarely needed
for precise attitude determination of DSP
satellites, they were used as a beacon for
functional checkout of the overall system.
0.160
0.153
0.145
3.75
Elevation (rad)
0.161
Elevation (rad)
from other sources. This required templates (intensities vs. time) for threat missiles to compare with the data as it was
transmitted to the ground. Analysis to that
end by other organizations would have
taken months.
Aerospace and the sensor contractor,
working closely with personnel at the site,
produced templates in a few weeks and
continually upgraded them as the data
from missile sightings were accumulated.
This analysis also facilitated some necessary modifications of the system software
by Aerospace and contractor personnel
assigned to the ground site. Transition of
Flight 2 to a fully operational status, consequently, was greatly accelerated.
The sensor met the requirements and
rapidly created a database of all the ballistic missiles and space launches of the time.
In later years, additional satellites were
deployed to maintain a constellation with
satellites in the East to report ICBM
launches and in the West to cover the
ocean areas from which SLBMs could be
launched. Later, a larger constellation of
satellites, stationed over a range of longitudes, provided multisensor viewing of
areas of particular concern.
The sensors have been upgraded and
improved in several respects throughout
the life of the program. One significant
improvement was the addition to Flight 6
and subsequent sensors of an array of sensors to view targets above the horizon. For
such fields of view, it was not necessary to
Horizon
3.79
Azimuth (rad)
3.83
0.155
Horizon
0.150
2.37
2.43
Azimuth (rad)
2.49
Apparent motion of target in the satellite field of view over the Atlantic Ocean (left), with time increasing upward
to the left, and over the western Pacific Ocean (right), where the launch site was beyond the horizon and the target appeared after rising above the Earth limb. Green indicates target positions of maximum intensity per scan in
the main array; blue indicates positions reported by the more sensitive cells in the above-the-horizon array. Note
the increasing spread as the vehicle accelerates.
Also, they were used for determining sensor resolution and bore sighting, new software validation and evaluation of stray
light properties, and assessing system
sensitivity to uncooperative laser illumination and developing means for its mitigation. Incidentally, after two star sensors on
Flight 8 failed, lasers were used in their
originally intended applications—beacons
in the sensor field of view as the primary
means of determining the precise attitude.
Target data downlinked from the satellites to the ground include the intensities
of the detected source above a prescribed
threshold, the identification of the
responding detectors, and the universal
time, the latter two providing the instantaneous target position in satellite
coordinates: elevation and azimuth. By
appropriate processing, including a comparison with stored templates of intensity
versus time based on prior sightings, the
target can be identified and its heading
established. The principal product of the
DSP system in near real time is a warning
message from the ground station relaying
that information to the national command
authority. DSP satellites have fulfilled
their primary mission by reporting thousands of missile launches over three
decades.
Data for Off-Line Analysis
The data from those DSP sightings have
also been provided to various centers for
off-line analysis, when appropriate, and
for archiving in a comprehensive database
maintained by Aerospace. The database
contains the reports on all ballistic missile
sightings, as well as on a vast number of
other events, military in nature and otherwise (for example, space launch vehicles).
The data listings include not only the maximum intensities in a given scan, but also
the lower intensities of the target distributed in the vicinity. For such analysis, data
from the satellites can be displayed in a
variety of forms.
DSP Support of Theater Operations
DSP took on a more direct and proactive
role in its missile-warning mission during
Desert Storm operations in 1991. In that
conflict, Iraq launched a large number of
Scud missiles at targets located in Saudi
Arabia and Israel. Specifically, the DSP
satellites stationed in the Eastern Hemisphere detected and tracked the missiles
during the boost period and reported their
headings to the appropriate Patriot missile
batteries fielded by the U.S. Army in those
areas. The information was provided by
telephone communication links, some of
which were staffed by Aerospace personnel, allowing the Patriots to intercept the
incoming Scuds. Although the effectiveness of the Patriots in destroying the warheads can be questioned, the interceptions
did take place, establishing the feasibility
of defense against theater missiles.
Largely because of their success in
Desert Storm, DSP satellites currently
play the key role in the Air Force’s Attack
and Early Reporting to Theater (ALERT)
system, an operational function of the 11th
Space Warning Squadron of the 21st
Space Wing. Aerospace provided invaluable assistance to the Air Force in the procurement of that system by generating
specifications and providing support with
the contractor selection process. For the
ALERT system, data from the entire DSP
constellation and other sources are
integrated and processed at one facility
located at Schriever Air Force Base in Colorado. The detection reports, considerably
improved in accuracy, are transmitted rapidly to commanders in the theaters through
U.S. Army
Launch of a Scud missile for engagement by an
improved Patriot in the Willow Dune experiment at
the Kwajalein Missile Range in 1997.
space-based communication links. DSP
satellites provide worldwide coverage so
that the ALERT system can monitor all
major regional conflicts and areas of concern simultaneously, and provide threatmissile descriptors, such as launch point,
heading, position, velocity, and predicted
impact location.
Observations of Other Sources
The database contains hundreds of sightings of other sources that appear in the
fields of view of the sensors; many are
assigned descriptors that characterize the
nature and time variation of their movement across the monitor screen. In no
instance has analysis failed to identify the
sources of those sightings. (Contrary to
some assertions in the popular press, there
have been no sightings of alien spacecraft.)
29100
29200 29300 29400 29500
GMT (seconds)
Time variation of maximum single-detector intensities over a range of two orders of magnitude. (GMT:
Greenwich mean time).
300
250
200
GMT = 29348
150
300
Altitude (kilometers)
Intensity
Altitude (kilometers)
300
250
200
GMT = 29348
150
400
500
Range (kilometers)
600
Intensity
(Left) Spatial distribution of signals reported in a single scan. The signals from the extended plume merge into
those of a persistent trail. (Right) Distributions intensities reported in a single scan with altitude. The solid symbol on both graphs indicates the position of the vehicle.
DSP
DSP
DSP
ALERT
control center
CONUS
ground station
Communications
networks
National
command authority
Theater
commanders
Overseas
ground station
(Australia)
European
ground station
The ALERT architecture. (CONUS: Continental United States)
Among the objects of current interest are
the occasional meteors of significant size.
Earth is constantly bombarded by small
meteors, most the size of a grain of sand.
Their numbers, and intensities due to
atmospheric drag, appear to vary inversely
with mass. Large meteors of potentially
catastrophic size are rare. Nevertheless,
during the last 30 years, DSP has observed
some very sizable meteors. For example,
in 1972 an exceptionally large meteor was
observed in a grazing trajectory that came
within an astronomical whisker of hitting
Salt Lake City. Analysis by Aerospace led
to the conclusion that the object was of
sufficient mass that a slightly deeper penetration of the atmosphere would have
resulted in an impact equal to the explosive force of the atomic bombs that
destroyed Hiroshima and Nagasaki in
World War II.
In addition to such moving objects, very
intense stationary thermal sources on the
ground can be seen in spite of the background suppression afforded by the spectral filters and electronic circuitry. Such
sources include fires, gas flare-offs from
oil refineries, volcanic eruptions, nuclear
explosions, and solar scatter and reflections. The observation of such events is of
course facilitated by very low humidity,
which minimizes absorption in the path to
space.
Some particularly mysterious sightings
occurred in the early 1970s. Extremely
bright stationary sources suddenly appeared
in the area adjacent to the Caspian Sea, with
apparent intensities of nearly a megawatt
per steradian lasting for several minutes.
Certain analysts elsewhere attached a sinister interpretation to those events. However, analysis at Aerospace solved the
mystery simply by noting that these
sources all appeared precisely along a
pipeline to Moscow from the natural gas
fields in the area. Clearly, the sources were
burning gas, presumably flared off for
maintenance of the pipeline, a conclusion
later confirmed by other information. Gas
flares from oil refineries are also routinely
observed, particularly in dry regions such
as Southern California and the Near East.
Likewise, volcanoes are frequently
observed at various locations throughout
the world, sometimes by the emission
from the lava flow, but more often by
reflected sunlight from the ash plume rising high in the atmosphere.
Observations of many other infrared
sources, both stationary and moving, have
been routinely observed, reported, and
processed at Aerospace for inclusion in the
database, archived at the Ballistic Missile
Defense Organization Advanced Missile
Signature Center, Air Force Arnold Engineering and Development Center, Tullahoma, Tennessee, which is accessible to
qualified users. Over the years, there have
been innumerable reports analyzing the
data to fulfill the needs of various Space
and Missile Systems Center program
offices and other government agencies.
The results of most of those analyses are in
the classified literature.
The database contains an extensive collection of events, the observations of
which were not even thought of when the
system was originally conceived. Among
other uses, that collection provides the
fundamental basis for evaluating the effect
of such events on the performance of the
Space Based Infrared Systems (SBIRS)
that will replace DSP in a few years. It is
axiomatic in the field of infrared phenomenology that when more sensitive sensors
are deployed in space, unexpected obser130°
125°
55°
Edmonton
120°
115°
Calgary
110°
50°
Missoula
Perigee
Meteor
ground track
45°
Boise
Salt Lake
City
40°
Path of a meteor moving north at 18 kilometers per
second over several western states, at closest
approach a mere 94 kilometers above Earth.
vations and other surprises are invariably
produced. This is true of the DSP sensors,
not only in their original configuration, but
especially in the improved versions. The
new system will feature many improvements in the sensors and advances in overall capability, and will be assigned
additional missions. SBIRS will quite likely
bring many surprises when it is deployed.
Fred
Simmons
Large meteor seen in broad daylight in August 1972. The fireball is the bright spot just to the right of the cloud,
in the left center, followed by a faint trail to the right. Later, at a closer approach, the fiery source was much
brighter, with a teardrop shape and a more visible trail. (Photo extracted from video conversion of a film recording submitted to the government some years ago by an amateur photographer.)
References
W. Kellogg and S. Passman, “Infrared Techniques Applied to the Detection and Interception of Intercontinental Ballistic Missiles,”
Rand Corporation Report No. RM-1572 (October 1955).
R. Zirkind, “Review of Project Tabstone,”
Journal of Missile Defense Research, Vol. 4,
No. 1 (Summer 1966).
R. G. Hall, “Missile Defense Alarm: the Genesis of Space-Based Infrared Early Warning,”
Space and Missile Systems Center Conference
Honoring IR Pioneers (The Aerospace Corporation, June 3, 1999).
Missile Defense Data Center, Bits-n-Bytes, Vol.
5, No. 2 (Spring 1997).
R. D. Rawcliffe, et al., “Meteor of August 10,
1972,” Nature, Vol. 247, 449 (1974).
D. W. Pack, et al., “Civilian Uses of Surveillance Satellites,” Crosslink, Vol. 1, No. 1 (January 2000).
R. S. J. Sparks, et al., “The Giant Umbrella
Cloud of the May 18th Explosive Eruption of
Mount St. Helens,” Journal of Volcanology and
Geothermal Research, Vol. 28, 257–274
(1986).
E. E. Lapin, “Surveillance by Satellite,” Journal of Defense Research, Vol. 8, No. 2 (Summer 1976).
E. Tagliaferri, et al., “Detection of Meteoroid
Impacts by Optical Sensors in Earth Orbit,”
Hazards Due to Comets and Asteroids, edited
by T. Gehrels (University of Arizona Press,
1994).
Col. J. Kidd, and 1st Lt. H. Caldwell, USAF,
“Defense Support Program: Support to a
Changing World,” AIAA Space Programs and
Technologies Conference (Huntsville, AL,
March 24, 1992).
Col. D. L. Burkett II, USAF, “Space Based
Infrared Systems SBIRS,” Space and Missile
Systems Center Conference Honoring IR Pioneers (The Aerospace Corporation, June 3,
1999).
Maj. J. Rosolanka, USAF, “Defense Support
Program—A Pictorial Chronology 1970–
1998,” Space and Missile Systems Center Conference Honoring IR Pioneers (The Aerospace
Corporation, 3 June 1999).
F. S. Simmons, Rocket Exhaust Plume Phenomenology (The Aerospace Press and American Institute of Aeronautics and Astronautics,
El Segundo, CA, 2000).
Rocket Exhaust Plume Phenomenology
is an introductory treatment of the
multidisciplinary subject of plume
phenomenology as it relates
to the development of spacebased defense systems. The text
covers the elementary principles of
rocketry, basics of rocket-propellant
combustion, gas dynamics of supersonic exhaust plumes, infrared radiation processes, theoretical plume
models, physical properties of
exhaust constituents, diagnostic
measurement techniques, and
other related topics. More specifically, this work is primarily concerned with the phenomenology of
rocket exhaust plumes as the targets of space-based surveillance
systems; however, the spectral, temporal, and spatial distributions of
the infrared emission from rocketpowered vehicles are also required
for the design and optimization of
sensors for various other defenserelated missions. It is written at a
level intended to bridge the gap
between space systems engineers
and scientists involved in detailed
studies of plume observables.
2000 • 286 pp • ISBN 1-884989-08-X
Published by The Aerospace Press and
American Institute of Aeronautics and Astronautics
Order from AIAA
800.682.2422
or
www.aiaa.org
Aerospace Photos
Capture Launch Clouds
Robert Abernathy
A new and improved method of measuring
launch-vehicle ground clouds leads to fewer
launch delays and reduces costs.
T
he spectacular display of billowing smoke that envelops
the launchpad during a rocket
launch has become synonymous with the launch itself. Rockets
release immense amounts of exhaust.
Titan IVB solid-rocket motors emit
118,000 pounds of exhaust during the
first 10 seconds of firing. The hot
exhaust accumulates at the launchpad
to form what is called the “ground
cloud.” As the rocket ascends, it also
leaves behind a continuous stream of
exhaust, known as the launch column.
During countdown to the launch, the
U.S. Air Force Range Safety uses an onsite
computer model known as the Rocket
Exhaust Effluent Dispersion Model
(REEDM) to predict the rise and dispersion of the expected ground cloud.
REEDM relies on meteorological data
such as wind, cloud cover, solar angle, and
weather-front conditions to predict the
extent of the toxic hazard corridor, the
downwind area where ground concentrations of chemicals may exceed allowable
public exposure limits. When REEDM
predicts the launch may cause exposure to
unsafe levels of toxic gases, the launch is
delayed until meteorological conditions
improve.
When REEDM was being developed
during the 1960s and 1970s, several cloudtransport parameters were not well known,
so the model was deliberately designed to
be conservative. Over the years, the level
of toxic compounds considered acceptable
for public exposure has been lowered,
increasing the likelihood of a launch delay.
By 1994, toxic hazard corridor predictions
were beginning to reduce launch availability at both Air Force launch ranges, the
Eastern Range at Cape Canaveral Air
Force Station and the Western Range at
Vandenberg Air Force Base.
The high cost of launch delays, up to
$1 million a day, and the continued concern for public welfare prompted development of the Air Force Atmospheric
Dispersion Model Validation Program
(MVP) to test and improve REEDM’s
accuracy. The Aerospace Corporation
developed this validation program and
provides technical management.
An Aerospace method of monitoring
exhaust clouds using photographic
imagery showed that REEDM consistently
underestimated the ground-cloud stabilization height and overestimated the
extent of the toxic hazard corridor. With
subsequent Aerospace modifications,
REEDM predictions have improved
launch-range availability, preventing
Launch of a Titan IVB rocket from Cape Canaveral
Air Force Station.
unnecessary launch holds and saving the
government millions of dollars while protecting the public safety.
Monitoring Ground Clouds
Ground clouds are difficult to monitor.
Within the first few minutes after a launch,
they grow to dimensions of 1–2 kilometers
and rise to similar heights. Also, although
the optimal wind for a launch carries the
ground cloud out to sea, such a wind direction does not allow for the use of groundbased launch-cloud sampling systems.
Aircraft instrumented to sample and
measure ground-cloud concentrations of
toxic compounds have been used during
launches of the space shuttle, but aircraft
sampling is expensive and doesn’t provide
an instantaneous three-dimensional extent
for the cloud. Additionally, this method of
measurement typically relies on the pilot’s
ability to fly into the center of the visible
cloud, which precludes accurate nighttime
sampling. Without visible feedback, the
pilot doesn’t know the aircraft’s location
relative to the center of the cloud, so concentration measurements are extracted
from unknown regions.
Aerospace proposed an alternative
approach to monitoring the rise and expansion of exhaust clouds, and in 1994 it developed the technology to track ground clouds
using multiple cameras that capture images
simultaneously from various locations surrounding the launch pad. Because a ground
cloud rises and stabilizes quickly, the cloud
needs to be tracked for only a few minutes
following launch. The images captured
during the tracking complement measurements garnered from aircraft sampling.
Day and night images of the launch
cloud were needed to test REEDM under
all launch conditions. Visible and infrared
imagery would be captured, using visible
charge-coupled-device cameras and thermal infrared scanners. In daytime, the visible cameras “see” the scattering of
sunlight caused by aerosols from the solidrocket motors. Throughout the day and
night, the infrared scanners observe the
temperature difference between the warm
launch cloud (vapors) and the cooler background sky.
Cameras provide better-resolution
images than infrared scanners, but the
quality of camera imagery is subject to
adequate lighting, which depends upon the
relative positions of the sun, cloud, and
camera. The camera can also provide
clearer cloud-edge-detection imagery of a
low-elevation cloud on a hot sticky day
because atmospheric humidity and cloud
elevation affect the quality of the infrared
imagery.
Because the two imaging systems complement each other, Aerospace designed
and built four visible and infrared imaging
systems (VIRIS) in which the visible camera and the infrared scanner are mounted
on a single tripod. The camera and infrared
scanner are “coaligned,” meaning the center pixel of each camera simultaneously
views the same distant object. The four
systems were shipped alternately to Cape
Canaveral and Vandenberg for use during
Titan IV launches from both launch ranges.
Calibrating VIRIS
Aerospace designed custom tripod heads
that accurately encode, or digitize, the
viewing direction (azimuth and elevation)
as VIRIS tracks a cloud. Optimal camera
locations depend upon wind direction, so
they cannot be selected until a few hours
before launch. The challenge is to quickly
calibrate the systems, aligning a known
pixel with true north for zero azimuth and
level for zero elevation.
Calibrating the angle encoders of the
tripods requires the camera crew to identify large landmarks that can be observed by
both the cameras and the infrared scanners.
Before the imagery systems are deployed,
a survey provides accurate position information on the observable landmarks, using
either a differentially corrected Global
Positioning System (GPS) receiver or
accurate maps of the launch range. Once
the camera is set up, the GPS receiver provides the camera-site location.
The camera crew calculates the azimuth
and elevation from the camera to the landmark. Once the center pixel is aligned with
the landmark, it is a simple matter to set
the correct azimuth and elevation readout
from the tripod. The field of view is calibrated by scanning the landmark horizontally and vertically while recording the
change in encoded azimuth and elevation.
Typically, camera crews can set up and
calibrate to 0.1 degree of accuracy within
45 minutes. Each calibrated imagery system provides a real-time display of the
The Aerospace Corporation’s imagery crew tracking a Titan IV ground cloud at the Eastern Range at Cape Canaveral Air Force Station. The vehicle assembly building on the left and the mobile service tower next to the ground
cloud served as useful calibration landmarks.The rocket’s launch column extends above the ground cloud.
azimuth and elevation to the ground cloud
from each camera’s perspective. Hence,
the ground cloud’s approximate position
can be triangulated in real time using the
pointing angles to the cloud from all sites.
Triangulating Cloud Position
Aerospace developed PLMTRACK software to triangulate the position and extent
of a ground cloud with imagery captured
simultaneously from any two sites. Once
an image is calibrated, each pixel represents a ray into space from the camera’s
position. PLMTRACK converts a selected
pixel in one image (the top of the cloud,
for example) into an azimuth and elevation
from that image’s camera location. It then
projects that ray across the simultaneous
image from the other site. The analyst
identifies the same feature (top of the
cloud) in the sister image using the projected ray for perspective, and the same
feature is thereby seen from two perspectives. PLMTRACK converts this information into a ray from each site that passes
through the same feature and calculates
the closest approach of the two rays,
which represents the position of the
selected feature in three-dimensional
space. This approach works well when an
object or feature can be observed from
two perspectives.
Triangulating the top and bottom of a
cloud at low elevations is easy because
both top and bottom are observable from
multiple perspectives. But how is the horizontal extent of the cloud determined when
the same sides cannot be seen from both
perspectives? Where is the “middle” of the
cloud? PLMTRACK allows the analyst to
use a rectangle to define the top, bottom,
left, and right extremes of the cloud from
each camera’s perspective, and the projection of these rays provides an estimate of
the extent for the cloud. The middle of the
rectangle provides the ray through the middle of the cloud from each site, and the
nearest approach of these middle rays represents the position of the cloud.
Validating Multicamera Imagery
Neither the camera nor the infrared scanner directly detects the toxic hydrochloric
acid in rocket exhaust. For this reason, it is
important to document not only that the
cameras and infrared scanners see the
same extent (angular size) of the ground
cloud, but also that the observable (seen by
VIRIS) extent contains the toxic acid that
might pose a hazard.
Aerospace images obtained from the
coaligned camera and infrared scanner
have consistently shown the same angular
extent for the Titan IV ground clouds, verifying that both image-capturing methods
are similarly useful when applied to tracking ground clouds. However, these observations do not prove that hazardous levels
of toxic chemicals do not extend beyond
the observable extent of the cloud.
Aircraft sampling of hydrochloric acid
within four Titan IV exhaust clouds provided the complementary data needed to
validate the coaligned multicamera
imagery. An aircraft was fitted with a
Geomet hydrochloric-acid monitor to
obtain concentration profiles during four
launches between May 1995 and December 1996—two each from Cape Canaveral
and Vandenberg. Comparison of the aircraft data and imagery showed that the
observable extent contained the measurable acid (in the form of both vapor and
aerosol). These observations are consistent
with the mechanism of atmospheric dispersion: Atmospheric eddies mix vapors
(seen in the infrared) and aerosols (seen in
the visible) equally well. These results
show that VIRIS provided the cloud’s
extent for Titan IV day and night launches,
and that the extent includes the hazardous
levels of hydrochloric acid.
Predicting Ground-Cloud
Stabilization Height
Because it is initially warmer than the surrounding air, the ground cloud rises. As it
does, it entrains the ambient air, which
causes it to cool and lose buoyancy. Within
three to four minutes, the cloud reaches its
“stabilization height,” where it attains thermal equilibrium with the surrounding air
and stops rising. The 1995 version of
REEDM was used to predict the height of
the ground cloud prior to the May 14, 1995,
launch of a Titan IV. The REEDM prediction underestimated the stabilization height
of the cloud by half, which corresponds to
overestimating the ground-level concentration by a factor of eight. During the next
three years, the Aerospace Titan IV groundcloud imagery consistently showed a difference between the observed and predicted
stabilization heights for 13 launches from
both launch ranges.
Because the stabilization heights
derived from the images consistently
remained much higher than REEDM’s
predictions, the REEDM code was
reviewed, revealing several errors. Yet
even after these errors were corrected, predictions of stabilization height remained
too low. Speculating that the values of two
volumetric parameters in the cloud-rise
algorithm might be wrong, Aerospace
focused its image-analysis efforts on the
accurate measurement of the cloud’s volume immediately after launch and during
the cloud’s rise. The desired volumetric
parameters, which are simply the initial
+
+
PLMTRACK’s analysis of blimp imagery from two sites.The red pixel (+) is projected as a blue ray,and the blue pixel (+)
as a red ray,in the sister images.The Good Year blimp was used to test the accuracy of both PLMTRACK and PLMVOL.
X
M2
PLMTRACK Calculations
X
Top of plume = T1 × T2
Bottom of plume = B1 × B2
Middle of plume = M1 × M2
Other points = nearest point
of approach for defined lines
X
L1
M1
X
X
X
X X X
R1
Site 1
L2
R2
Site 2
T1
L1
M1
T2
R1
L2
M2
R2
B1
B2
Image 1 Site 1
Image 1 Site 2
PLMTRACK-derived Cartesian extent and position from analysis of multiperspective imagery.
radius of the ground cloud and the rate of
increase in radius with altitude (the air
entrainment coefficient), would come
directly from these measurements.
Reconstructing the Cloud
Aerospace developed PLMVOL, a software application based on a second analy-
sis algorithm, which reconstructs the
three-dimensional cloud from the twodimensional imagery collected simultaneously at multiple locations. First, the
simultaneous imagery from all available
locations is digitized and imported with
the calibration information into PLMVOL.
How Meteorological
Conditions Affect
Launches
The local meteorological conditions
control the transport and spread of
potentially toxic rocket exhaust in
the atmospheric boundary layer,
the layer that is directly influenced
by Earth’s surface—where we live
and breathe. During the day, the
boundary layer roughly corresponds to the height to which pollutants are mixed (the mixing
height).
The atmospheric boundary layer
is classified as stable, neutral, or
unstable based on altitudinal temperature (the temperature profile).
Mixing is most vigorous in the
boundary layer when there is free
convection (unstable). The boundary layer stability and height are
affected by many variables, including latitude, time of year, time of
day, synoptic conditions, surface
roughness, terrain, cloud cover, and
wind variation with altitude. These
variables are necessary for dispersion-model predictions because
they determine the thermal and
mechanical generation of turbulence and the buoyant forces on the
ground cloud.
Wind shear, a very strong variation in wind direction or speed with
altitude, can also threaten the physical integrity of the launch vehicle
or prevent its accurate insertion
into orbit. Lightning, either natural
or vehicle-induced, can damage the
vehicle. A variety of meteorological
conditions can cause large electric
fields aloft and pose a lightning hazard to ascending vehicles and
determine the propagation of blast
waves in the case of a vehicle failure. The meteorological conditions
over a launch range can cause a
launch delay for many reasons and
are critical in determining whether
a range is available for launching a
rocket.
Then the analyst traces the
outline of the exhaust
cloud within each image.
Next, PLMVOL converts the pixels within
these outlines into rays
projected into space from
each camera’s location.
The exhaust cloud is located at the intersection of
these rays. To derive the
points where the rays intercept, PLMVOL divides
space into small cubes and
marks them as occupied by
the ground cloud only
when intercepted by rays
from all available perspectives. It maps the threedimensional extent of the
ground cloud as the Cartesian locations (x,y,z) of all
the occupied volume elements. Since the volume
elements are adjacent
(stacked cubes), summing
all occupied volume elements yields the imageryderived volume of the
ground cloud.
Finally, the sphereequivalent radius, used by
REEDM, is calculated
from the imagery-derived
cloud volume by determin- USAF
ing the radius of a sphere The ground cloud and the abort cloud are produced by a failed launch. If
the abort occurs several hundred feet above ground, REEDM may predict
with an equivalent volume.
a larger toxic hazard corridor for the unburned oxidizer than for the
Typically, the Titan IV ground cloud.
ground cloud is not spheridid not always provide the complementary
cal in shape, but the sphere-equivalent
perspectives needed to accurately map the
radius is a convenient unit for comparison.
cloud volume.
The accuracy of PLMVOL estimates
depends upon the relative position of the
Analyzing Amateur Imagery
camera sites to the ground cloud’s
REEDM also predicts toxic exposure
position. PLMVOL can’t provide an accufrom a low-altitude launch-vehicle abort.
rate cloud volume if cameras do not see
In the event of an abort, the launch vehicle
the ground cloud from complementary
would be destroyed in an explosion that
perspectives, for example along-wind and
releases a hypergolic mixture of liquid
crosswind perspectives, simultaneously.
fuel and oxidizer. If the abort occurs sevAerospace used PLMVOL to extract
eral hundred feet above the ground,
cloud-volume data for only 6 of 13 imaged
REEDM may predict a larger toxic hazTitan IV ground clouds. Several factors led
ard corridor for the unburned oxidizer
to this low yield of volumetric data. For
than for the ground cloud.
example, the cloud didn’t always travel in
Aerospace proved that normal launchthe predicted direction, Vandenberg
cloud data could be applied to the abortrestricted access to camera sites to the east
cloud scenario. It measured the behavior
and south of the launch pad, and low
(rise, growth, and stabilization) of normal
atmospheric clouds blocked visibility
launch clouds during launches from 1994
from one or more of the sites. In sum, the
and 1997. Abort clouds weren’t measured
available camera locations and visibility
Camera site 1
Camera site 2
PLMVOL’s cloud volume (purple shape) is mapped by projection of pixels (rays) into volume elements.The rays are
identified as outside (dotted) or inside (solid) the ground cloud’s outline (red line) from each perspective.Volume
elements are occupied by the ground cloud only when intercepted by “inside”rays from all available perspectives.
Height in meters (mean sea level)
because no Titan IVs failed during
deployment. Without abort-cloud data, the
accuracy of REEDM predictions for an
abort situation could not be validated nor
could the ground cloud’s entrainment data
be shown to apply to the abort cloud.
The few options for obtaining the necessary data were considered in 1997. One
possibility was to use an explosive release
of oxidizer to simulate the abort cloud
because the most toxic component of the
abort cloud is unburned oxidizer. Safety
concerns, however, limited test sites to
desert locations that did not match the terrain or the meteorological conditions of
the launch ranges. Two other options were
to continue imaging Titan IV launches on
the chance of a failure or search for
imagery of earlier aborts hoping to interpret that imagery quantitatively. We chose
the latter.
A worst-case abort scenario was inadvertently tested on April 18, 1986, when a
defect in a Titan 34D-9 solid rocket motor
caused the rocket to explode at an elevation of 830 feet at Vandenberg. Aerospace
reviewed the videotapes from the three
range-tracking cameras. Unfortunately,
the camera operators at two locations did
not keep the abort cloud completely within
the field of view. To obtain a cloud’s volume, which involves analyzing the abortcloud imagery from the third range
camera, a second, complementary perspective of the abort cloud had to be available. Without abort-cloud imagery from a
second camera, the abort-cloud imagery
from the third range camera could not be
interpreted quantitatively (as cloud position and volume).
Luckily, an amateur photographer
videotaped the launch and its abort cloud
with a handheld camcorder. This photography provided the necessary second,
nearly perpendicular, perspective. Interpretation of the abort-cloud imagery was
complicated because both cameras were
panned and zoomed several times during
the three minutes the images were captured. Neither camera was mounted on an
1800
1600
Imagery-derived
1400
1200
1000
0.64 was REEDM’s default
800
REEDM version 7.05 prediction
(3 hours before launch)
600
400
200
0
0.00
4.00
8.00
12.00
16.00
Time after launch (minutes)
20.00
The REEDM-predicted and Aerospace-imagery-derived cloud-height curves for a
May 14, 1995, Titan IV launch. The imagery-derived rise curve for the ground cloud
revealed a factor-of-two discrepancy between measured and predicted stabilization
height. Subsequent MVP deployments documented that REEDM systematically
underestimated the stabilization heights for all 13 Titan IV ground clouds at both
ranges under a variety of launch conditions.
Aerospace imagery-derived air-entrainment rates for normal Titan IV ground clouds
and for the Titan 34D-9 abort cloud. The values are substantially lower than the
default value used in REEDM calculations during the past 30 years. Legend: A—solid
rocket motor; B—upgraded solid rocket motor; C—Cape Canaveral Air Force Station;V—Vandenberg Air Force Base.
Calibrating Amateur
Abort-Cloud Imagery
Top left of SLC-4W Umbilical Tower (574,232)
An amateur video of the 1986 Titan 34D-9
aborted launch provided the second perspective necessary to measure the volume of the abort cloud. In 1998 an analyst
used the launch facilities shown in a frame
of the video to provide the known landmarks needed to calibrate the field of view
and the pointing angle of the camera for
the image. The analyst also chose various
unknown landmarks (such as patches of
sand on the hillside) and measured their
pixel locations in x, y coordinates (shown
in parentheses). Once the image was calibrated, each pixel could be converted to a
specific azimuth and elevation from the
camera site. As the camera was panned
and zoomed, these landmarks provided
the calibration for subsequent unknown
features (tertiary calibration points) as
they moved into the field of view. This
method of transferring the calibration to
subsequent imagery was used by Aerospace to interpret quantitatively the amateur photography of the abort cloud.
The simultaneous images collected at
surf (amateur video) and program sites
reveal the shape and size of the red abort
cloud from almost right-angle perspec-
tives. The map shows the position of the
launch pad and the abort-cloud images
taken at each identified camera site. The
colored lines on the map show that the
right and left edges of the images correspond to the angular field of view of the
cameras and that the cameras are pointing at the abort cloud above the launch
pad. A pixel (+ sign at the top of the abort
cloud) in the image from the surf site’s
perspective (north of the abort cloud) is
projected by PLMTRACK as a ray (red line)
into the simultaneous image from the
program site’s perspective (southeast of
the abort cloud). The fact that the projected ray touches the top of the abort
angle-encoding tripod, nobody intentionally calibrated the field of view of the cameras, and the camera operators did not
realize that abort clouds would later be of
more interest than burning ground debris.
Fortunately, Aerospace was able to calibrate much of the abort-cloud imagery and
used PLMVOL to quantify the position and
volume of the abort cloud during its rise.
Improving Model Predictions
Aerospace imagery-derived air entrainment rates for the Titan 34D-9 abort cloud
measured at Vandenberg and for normal
Titan IV ground clouds measured at both
Cape Canaveral and Vandenberg were substantially lower than the default value used
in REEDM calculations during the past 30
years. These values indicate that REEDMbased predictions of ground-cloud stabilization height have been consistently too
low and toxic-hazard predictions too high.
The imagery-derived results also show
that the air entrainment coefficient and the
initial cloud size are constants for the Titan
IV normal launch cloud and have the same
value for both launch ranges and for both
sets of solid rocket motors. The coefficient
is the same for the 34D-9 abort cloud,
which indicates similar behavior for both
normal and abort clouds.
The current version of REEDM (7.09)
provides improved stabilization height
predictions through the use of Aerospace
imagery-derived values for both the air
entrainment coefficient and the initial
radius. The new REEDM predictions,
which are in closer agreement with the
observed launch-cloud stabilization
heights, have improved launch-range
availability by preventing unnecessary
launch holds.
In addition, a Titan IV database now
establishes the margin of safety for current
and future dispersion models. The MVP
database includes quantitative analysis of
imagery from nine Titan IV launches at
Cape Canaveral and four at Vandenberg
between 1994 and 1997. MVP deployments involved collecting meteorological
data, necessary for running REEDM or
improved future dispersion models.
Aircraft samples were taken from two
Cape Canaveral and two Vandenberg Titan
IV launches during MVP. Aerospace
analysis of these aircraft data revealed that
both the visible and the infrared imagery
“see” the full extent of the cloud containing hydrochloric acid during the first few
minutes after launch. This means that the
observable aerosol and vapor disperse at
the same rate as the unobservable acid,
which is consistent with the behavior of
aerosols and the mechanism of turbulent
dispersion in the atmosphere.
Tracking Tracer Gas
The Aerospace imagery of the Titan IV
launches provided useful cloud rise and
stabilization data under favorable meteorological conditions, that is, when winds
SLC-4E Mobile Service Tower
Top of Titan 34D-9 (100,268)
Top of SLC-4E Umbilical Tower (100,262)
SLC-4W Mobile Service Tower
Patch 2 (72,143)
Patch 3 (484,93)
Patch 1 (231,103)
Patch 4 (601,110)
FOV = 6.62 deg by 4.96 deg
Surf site
+
N
W
560 ft
Surf’s Image
640 ft
720 ft
SLC-4E
launch pad
for Titan 34D-9
cloud in the sister image illustrates the
usefulness of the PLMTRACK software and
the accuracy of our calibration for both
sites. If the analyst identifies the top of the
cloud in both images, PLMTRACK reports
the point of nearest approach of the rays
projected from both sites and, therefore,
the position of the top of the cloud.
Program
site
Program’s Image
carried the ground cloud out to sea or over
unpopulated areas. Aerospace imagery
crews at Cape Canaveral and Vandenberg
supported four two-week-long elevatedtracer-gas releases that provided complementary dispersion data, including winds
that carried the innocuous tracer toward
populated areas. During these MVP
efforts, Aerospace established the usefulness of quantitative imagery for measuring
the near-field (2–5 kilometers) dispersion
of tracer gases.
A blimp released an invisible inert tracer
gas at various heights when the wind was
blowing inland. This allowed for dispersion measurements over the complex
inland terrain of both ranges. Analysis of
the infrared imagery provided the crosswind and along-wind expansion rates in
the near field at the release altitude. During
these elevated-tracer-release experiments,
aircraft and van sampling provided trajectory and dispersion information further
afield. These tracer data complement the
Titan IV launch-cloud data.
Predicting Ground Clouds in the Future
The ability of Aerospace to capture and
process quantitative imagery of Titan
ground clouds has provided, at a low cost to
the consumer, the rise and dispersion data
necessary to tune REEDM for more accurate prediction of ground-cloud toxic hazard corridors. Such accurate prediction also
reduces the launch costs because it leads to
fewer launch holds. A similar measurement
program could be used to tune current and
future dispersion models for the other
heavy launch vehicles, such as the space
shuttle today and the Evolved Expendable
Launch Vehicle in the future. In addition,
routine imagery of launch clouds could
provide real-time range-safety information,
not only for normal launch clouds but also
for the more toxic abort cloud.
Further Reading
R. N. Abernathy, B. Lundblad, and B. Kempf,
“Tracer Puff Dispersion at Launch Sites,” Proceedings of the JANNAF Propellant Development and Characterization and the Safety and
Environmental Protection Joint Meeting. CPIA
Publication 687 (Naval Submarine Base at San
Diego, CA, April 26–30, 1999).
The Aerospace surveillance technology crew in front of a mobile laboratory.These mobile laboratories, equipped
with visible and infrared imagery systems, support remote detection and tracking of chemicals, such as those in
launch abort clouds, bomb detonations, and tracer release experiments. They are deployed at launch and test
ranges throughout the continental United States. Shown in the photo from left to right, beginning with the back
row (in doorway): Bruce A. Rockie, Luis J. Ortega, Michael A. Rocha; left center row: Gary N. Harper, Brian P. Kasper,
Karl R. Westberg, Jess T. Valero; right center row: Robert N. Abernathy, Kenneth C. Herr, Jeffrey L. Hall, Donald K.
Stone; front row: Mark L. Polak, Andrew D. Shearon, J.Thomas Knudtson, Naomi J. Rose, George J. Scherer, Roberta
S. Precious, Karen L. Foster.
B. L. Lundblad, R. N. Abernathy, and Capt. B.
J. Laine, “Atmospheric Dispersion Model Validation Program,” Proceedings of the JANNAF
Propellant Development and Characterization
and the Safety and Environmental Protection
Joint Meeting, CPIA Publication 674 (NASA
Johnson Space Center, April 21–24, 1998).
Cloud
Cover
Over
Kosovo
In response to an Air Force
request for better weather
forecasting in the Balkans,
Aerospace developed a
higher-resolution cloudanalysis prototype that
provided more accurate
cloud-cover information in
support of operations in
Kosovo.
John S. Bohlson
Leslie O. Belsma
Bruce H. Thomas
Clouds over Yugoslavia and the Adriatic Sea.
NASA
E
arth’s cloud cover frequently
affects the outcome of modern
combat because sophisticated
aircraft (and weaponry such as
laser-guided missiles and night vision
sights) do not operate reliably in the presence of clouds. Knowing the state of the
cloud cover can determine the success of
reconnaissance missions, and it is the most
critical factor in the accuracy of humanitarian airdrops. To be of value, cloud data
must be current and accurate, but such
data can be difficult to obtain, especially
in areas where access is limited by military or political restrictions.
Brig. Gen. Fred Lewis, director of Air
Force Weather, recognized in 1998 a need
for improved cloud data to support military operations in the Balkans. Gen. Lewis
wanted a cloud-analysis model that could
do a better job at analyzing and forecasting
clouds than either the Air Force Weather
Agency (AFWA) model then in use or
even the extensive upgrade under development at the time.
The Aerospace Corporation stepped in
to develop a prototype system that
leapfrogged over the planned AFWA
cloud model upgrade to deliver automated
cloud-analysis products (such as amount
of cloud cover or cloud classification) at a
much higher resolution. This prototype
became the basis for a cloud-analysis system that was then put into operation in less
than 60 days in the spring of 1999 to
improve weather support for the war in
Kosovo. The improved resolution allowed
forecasters to provide more accurate
cloud-cover predictions to the battlespace
planners and pilots.
Cloud-Analysis Model
The Air Force Weather Agency, at Offutt
Air Force Base, Omaha, Nebraska, has
used automated cloud-analysis models to
generate quantitative information on
clouds since 1970. The earliest AFWA
three-dimensional cloud-analysis model,
the 3-D Neph, used space-based cloudcover imagery from Defense Meteorologi-
cal Satellite Program (DMSP) satellites.
The current model, RealTime Nephanalysis, known as RTNeph, combines groundbased observations with data from DMSP
and the Television and Infrared Observation Satellite (TIROS) of the National
Oceanic and Atmospheric Administration
to produce worldwide cloud analyses at a
48-kilometer resolution. It computes the
number of cloud layers, the percentage of
cloud coverage, and the height of the base
and top of each layer on a 48-kilometer
grid. A cloud-forecast model uses the
analyses to produce cloud forecasts at this
same grid resolution.
The grid is an array of points superimposed on a map of Earth’s surface. Observations of clouds are not taken at grid
points, but at irregularly spaced points.
Nephanalysis is the process that interpolates cloud data observations to the points
on the grid. The distance between adjacent
grid points on the AFWA polar stereographic whole-mesh reference grid is 381
kilometers at 60 degrees latitude. All finer-
Weather and Warfare
The war in Kosovo demonstrated dramatically that weather affects every
aspect of battle. The impact of
weather on war has long been recognized. In The Art of War, circa 500 B.C.,
Sun Tzu advised, “Know the ground,
know the weather; your victory will
then be total.” Vice Adm. Scott A. Fry
echoed these words 2,500 years later
when he told reporters during a briefing on Operation Allied Force that the
Serbs had two main allies—geography and weather.
In 480 B.C., storms at sea broke up
the “bridge of boats” across the
Hellespont, turning back the army
of Xerxes, the emperor of Persia,
from its march to invade Greece.
In 1588 storms off the coasts of
Scotland and Ireland wrecked
many ships of the Spanish Armada
as they retreated after Spain’s
failed invasion of the British Isles.
In June 1812, Napoleon invaded
Russia with 500,000 men, only to
withdraw five months later in snow
and bitter cold with fewer than
10,000 surviving troops.
During World War II, storms forced
Gen. Dwight D. Eisenhower to delay
the Normandy invasion one day.
•
•
•
U.S. Air Force drawing of a DMSP Block 5D-2 spacecraft.
resolution grids are defined relative to this
whole-mesh reference grid. For example,
the distance between points on an 8thmesh grid is 48 kilometers; on a 16thmesh grid, 24 kilometers; and on a
64th-mesh grid, only 6 kilometers.
Because cloud cover data at 64th mesh
presents much finer detail than data at 8th
mesh, data at 64th-mesh is called fine-grid
data. Data from a lower-resolution grid,
such as that based on an 8th mesh, is
called coarse-grid data.
Image of cloud cover over the Balkans, April 15, 1999,
generated by the current AFWA low-resolution
cloud-cover-analysis model with grid points 48 kilometers apart.
Clouds over the Balkans on the same date in a
higher-resolution image generated by the new
CDFSII cloud-cover analysis model. Grid points are
24 kilometers apart.
•
The highest-resolution image of the same area on
the same date generated by the Aerospace prototype model, with grid points 6 kilometers apart.
The AFWA polar stereographic whole-mesh reference grid. The distance between the grid points is
381 kilometers at 60 degrees north or south latitude.
Aerospace cloud-cover analysis prototype image of the Mediterranean area, April 6, 1999. A visual representation
of the gridded cloud data (cloud mask) can be used by the weather officer to quickly assess cloud conditions.
Tools added to the prototype system enable color-coding of the data to highlight aspects of the cloud mask.
Improved Resolution Enhances
Forecasting
The Air Force Space and Missile Systems
Center is developing the upgrade to
AFWA’s current cloud-detection and forecast system. The new system, known as
CDFSII, will increase the resolution of the
AFWA cloud analyses and forecasts from
an 8th mesh (48-kilometer) grid to a 16th
mesh (24-kilometer) grid. Also, by combining data from multiple weather satellites, it will improve cloud detection in
stressing conditions such as low clouds
and fog, thin cirrus clouds, and tropical
clouds.
When completed in December of this
year, the new CDFSII system will
• provide a multiple-satellite data-acquisition system that combines the high
spatial resolution of DMSP imagery
with multispectral data from TIROS
• merge the global coverage of these
polar-orbiting systems with the frequent refresh available from an international constellation of geostationary
weather satellites
• perform multiple-satellite-specific cloud
detection using science algorithms
from SERCAA (Support of Environmental Requirements for Cloud Analysis and Archives)
• use clustering techniques to accomplish
cloud layering and typing and then
combine these independent satellite
cloud data records using an optimal
interpolation scheme
•
feed the cloud analyses into a singlecloud forecast model to deliver shortterm (12-hour) and long-term (48-hour)
forecasts
Battlespace Weather Forecasting
Although CDFSII will improve forecasting beyond that provided by the current
system at AFWA, Gen. Lewis decided that
an even finer-scale automated cloudanalysis and forecasting system was
needed to support operations, specifically
the “weather function,” in the Balkans.
Under a new centralized support concept, an Operational Weather Squadron
was activated in Germany. The Weather
Squadron performs the weather function
continuously during the intelligence
preparation of battlespace in a series of
steps that converts weather data into intelligence and communicates it to users. The
weather officer collates weather information collected throughout the battlespace,
combines it with weather data received
from weather flight observers and forecasters and from higher headquarters, and
then generates the weather forecasts.
The Aerospace Prototype
In response to Gen. Lewis’s call for highresolution cloud analyses to better support
the Weather Squadron, Aerospace developed a prototype cloud-analysis model at a
fine-scale grid, increasing the resolution to
6 kilometers (64th mesh) from the 24 kilometers planned for the CDFSII system.
Aerospace developed the prototype by
modifying the CDFSII SERCAA algo-
rithms to improve computing speed. Faster
processing enabled use of DMSP “fine
mode” data, which is higher resolution
than the DMSP “smooth mode” data used
in CDFSII.
The Aerospace cloud-analysis prototype represents the first quantitative use of
DMSP fine-mode data in a meteorological
model. Fine data is not available worldwide, so the prototype model produces the
64th-mesh fine grid regionally using the
fine data and then combines it with a
worldwide analysis at the coarser CDFSII
grid using DMSP smooth-mode data.
The new model began generating cloud
analyses as a prototype in January 1999 at
the Aerospace Environmental Application
Center facility at AFWA. The Kosovo conflict prompted the Air Force to issue a
request to put this prototype system, along
with high-resolution forecasting capability,
into operation within 60 days. Within two
weeks of the Air Force request, Aerospace
wrote code to post fine-grid cloud data
over Kosovo from the prototype system as
images on the Air Force Weather Information network, which provides data to
weather forecasters in Europe. Color-coding was added to highlight aspects of the
cloud mask.
From Laboratory to Battlespace
Aerospace, AFWA, Atmospheric Environmental Research, and Sterling Software
(the CDFSII contractor) worked together
to develop an operational system based on
the Aerospace prototype. The prototype
DMSP Cloud Data
Cloud forecast image of the Balkans on April 6, 1999,
derived from the CDFSII 24-kilometer analysis.
Cloud forecast image of the Balkans on April 6, 1999,
derived from the Aerospace prototype 6-kilometer
analysis.
had to be ported from the laboratory environment to a 24-hour-a-day operational
capability, expanded to include multispectral TIROS algorithms, and combined with
the forecast model. A capability to “tune”
the algorithms on a regional basis to produce a better cloud analysis was added.
Tuning is not as critical for the TIROS
algorithms because additional channels
allow for more cloud-discrimination tests,
but because DMSP has one visible and
one infrared channel, a single-test clouddetection algorithm that is very sensitive
to threshold settings is used. Aerospace
found that using the same thresholds in the
DMSP algorithms for each satellite was
inadequate because of differences in
DMSP smooth- and fine-mode calibration.
Fine data typically exhibits a 5-degree
Kelvin cold bias, so a bias term was added
to the fine-mode infrared threshold values
that greatly improved the fine-grid (64thmesh) results.
A major task in the transition of the prototype to an operational forecast system
involved modifying the CDFSII coarse-grid
cloud-forecast model to run at the higher
resolution (6 kilometers). Code was written
to overwrite the coarse-grid values with fine
grid for all grid points touched by one satellite swath of DMSP fine data, which is typically an eighth or less of an orbit. The
forecast model then advected the resulting
fine-grid cloud analysis with highresolution winds from an operational
mesoscale model to produce the cloud
forecast.
The team completed the system in less
than 60 days, and Gen. Lewis specifically
commended Aerospace for this support to
the nation’s warfighters. The operational
implementation of the Aerospace prototype cloud model improved weather forecasting for operations across the Balkans
by providing more accurate cloud-cover
data to the air tasking, order-planning, and
execution processes. This system is still in
use to support regional high-resolution
cloud forecasting.
Further Reading
R. S. Dudney, “McPeak on the War,” Air Force
Magazine, May 1991, p. 21.
D. A. Fulghum, “Pentagon Criticizes Air Strike
on Iraq,” Aviation Week, January 25, 1993,
p. 47.
L. D. Kozaryn, “More Planes, Better Weather
Mean More Strikes,” American Forces Press
Service, http://www.defenselink.mil/news/
May1999/n05261999_9905261.html, March
2000.
L. D. Kozaryn, “No Silver Bullet to Stop Serb
Aggression,” American Forces Press Service,
http://www.defenselink.mil/news/Mar1999/n0
3311999_9903311.html, March 2000.
M. P. Plonski, G. Gustafson, B. Shaw, B.
Thomas, and M. Wonsick, “High Resolution
Cloud Analysis and Forecast System,” AMS
Satellite Meteorology Conference (Long Beach,
CA, Jan. 2000).
J. Pulley, “Some War Heroes Have Their Heads
in the Clouds,” Air Force Times, April 26, 1999,
p. 12.
Defense Meteorological Satellite Program (DMSP) satellites have been providing worldwide cloud imagery for
national programs since 1966. The Air
Force Weather Agency uses data from
three-dimensional cloud analyses in
developing computer cloud-forecast
models for the military. Data from
DMSP satellites formed the cornerstone of the Aerospace protoype
cloud model.
The U.S. Air Force has launched
more than 30 DMSP satellites.The constellation includes at least two sunsynchronous polar-orbiting satellites
flying at about 800 kilometers above
Earth, with one satellite orbiting in
early, and the other in late, morning.
Unlike other meteorological satellites, DMSP provides imagery at the
edge of its 3000-kilometer swath that
nearly matches the quality of imagery
directly below the satellite. The primary sensor, the operational line scan,
collects cloud imagery in a visible and
a long-wave-infrared band. The operational line scan calibrates, indexes, and
stores the data for transmission. During daylight, the fine-mode resolution
of the visible-band data is 0.62 kilometers, and the resolution of the infraredwavelength data is 2.8 kilometers. Fine
data is collected on a regional basis up
to a quarter obit. On-board smoothing
is used to decrease the data rate (and
therefore resolution) to provide data
for the entire orbit. The operational
line scan also has a unique capability
that allows it to gather visible-light
data at night at a 3.5-kilometer resolution with as little as one-quarter-moon
illumination. Additional satellite sensors measure atmospheric vertical
profiles of moisture and temperature
and a variety of space environmental
parameters.
DMSP has proved to be a valuable
tool in scheduling and protecting military operations. The last of the Block
5D-2 series of satellites was launched
April 4, 1997.The Block 5D-3 series, the
first of which was launched in December 1999, accommodate larger sensor
payloads and feature a larger power
supply, more on-board memory, and
increased battery power that will extend the life of the satellites from the
current four years to five.
Bookmarks Recent Publications and Patents by the Technical Staff
Publications
(August 1999–March 2000)
W. H. Ailor, “Space Traffic: Do We Need
Control?” Aerospace America (Nov.
1999), pp. 34–38.
E. J. Beiting, “Measurements of Stratospheric Plume Dispersion by Imagery of Solid
Rocket Motor Exhaust,” Journal of Geophysical Research, Vol. 105, No. D5,
6891–6901 (Mar. 16, 2000).
K. D. Bell and D. C. Marvin, “Power Generation and Storage Technology Selection for
an Optimal Spacecraft System Design,”
Proceedings of Intersociety Energy Conversion Engineering Conference (Vancouver, BC, Aug. 2, 1999).
I. D. Boyd, M. W. Crofton, and T. A. Moore,
“Near-Field Measurement and Modeling
Results for a Flight-Type Arcjet: Hydrogen Atom,” Proceedings of the 26th International Electric Propulsion Conference
(Kitakyushu, Japan, Oct. 17–21, 1999),
pp. 1–8.
C. C. Chao, “MEO Disposal Orbit Stability
and Direct Reentry Strategy,” AAS/AIAA
Space Flight Mechanics Meeting (Clearwater, FL, Jan. 23–26, 2000).
D. W. Chen and K. M. Masters, “CW 4.3 µm
Intracavity Difference Frequency Generation in an Optical Parametric Oscillator,”
Proceedings of the OSA Advanced SolidState Laser Topical Meeting (Davos,
Switzerland, Feb. 25, 2000).
M. W. Chen, L. R. Lyons, and M. Schulz,
“Stormtime Ring-Current Formation: A
Comparison Between Single-Dip and
Double-Dip,” Journal of Geophysical
Research, Vol. 105, No. 2 (Feb. 2000).
M. W. Chen, J. L. Rodder, and J. F. Fennell,
“Proton Ring Current Pitch-Angle Distributions: Comparison of Simulations and
CRRES Observations,” Journal of Geophysical Research, Vol. 104, No. A8,
17,379–17,389 (Aug. 1, 1999).
V. A. Chobotov and A. B. Jenkin, “Analysis
of the Micrometeoroid and Debris Hazard
Posed to an Orbiting Parabolic Mirror,”
Proceedings of the 50th International
Astronautical Congress (Amsterdam, The
Netherlands, Oct. 4–8, 1999).
J. H. Clemmons, “Birkeland Currents Associated With Optical Aurora,” Advances in
Space Research, Vol. 23, No. 10, 1653–
1656 (1999).
J. H. Clemmons, “Driving Dayside Convection Northward IMF: Observations of a
Sounding Rocket Launched from Svalbard,” Journal of Geophysical Research,
Vol. 105, No. A3, 5245–5263 (Mar. 2000).
J. H. Clemmons, “Evolution of Mesoscale
Auroral Cavities Before Substorm Onset,”
Journal of Geophysical Research, Vol. 104,
No. A8, 17,201–17,215 (Aug. 1, 1999).
M. W. Crofton, “Preliminary Mass Spectrometry of a Xenon Hollow Cathode,” Journal
of Propulsion and Power, Vol. 16, No. 1,
157–159 (1999).
S. V. Didziulis and P. P. Frantz, “SubstrateDependent Reactiveness of Water on
Metal Carbide Surfaces,” Journal of Physical Chemistry B, Vol. 103, No. 50,
11,129–11,140 (Dec. 16, 1999).
R. P. Frueholz, “Rabi Resonance-Enhanced
Gain in a Simple V-Type System,” Physical Review A, Vol. 61, No. 2 (2000).
R. G. Gist and D. L. Oltrogge, “Collision
Vision: Covariance Modeling and Intersection Detection for Spacecraft Situational Awareness,” Proceedings of
AAS/AIAA Astrodynamics Specialist Conference (Girdwood, AL, Aug. 16–19,
1999), pp. 1–14.
R. G. Gist and D. L. Oltrogge, “Collision
Vision: Situational Awareness for Safe
and Reliable Space Operations,” Proceedings of the 50th International Astronautical Congress (Oct. 4–8, 1999, Amsterdam,
The Netherlands).
D. L. Glackin and G. R. Peltzer, Civil, Commercial, and International Remote Sensing Systems and Geoprocessing (The
Aerospace Press and AIAA, El Segundo,
CA, and Reston, VA, 1999).
M. M. Gorlick, “Electric Suspenders: A Fabric
Power Bus and Data Network for Wearable
Digital Devices,” Proceedings of International Symposium on Wearable Computers
(San Francisco, CA, Oct. 1999).
E. K. Hall and M. Papadopoulos, “GPS
Structural Modifications for On-Orbit Servicing,” Proceedings of AIAA Space Technology Conference and Exposition
(Albuquerque, NM, Sept. 28, 1999), pp.
1–10.
S. W. Janson, “Mass-Producible Silicon
Spacecraft for 21st Century Missions,”
Proceedings of AIAA Space Technology
Conference and Expo (Albuquerque, NM,
Sept. 28–30, 1999), pp. 1–10.
R. F. Johnson and P. L. Smith, “Projection of
Future Launch Capacity and Demand,”
Proceedings of 50th International Astronautical Congress (Amsterdam, The
Netherlands, Oct. 4–8, 1999), pp. 1–11.
J. A. Kechichian, “Low-Thrust Trajectory
Optimization Based on Epoch Eccentric
Longitude Formulation,” Journal of
Spacecraft and Rockets, Vol. 36, No. 4,
543–553 (July–Aug. 1999).
J. A. Kechichian, “The Optimization of Continuous Constant Acceleration Transfer
Trajectories in the Presence of the J2 Perturbation,” Proceedings of AAS/AIAA
Astrodynamics Conference (Girdwood,
AL, Aug. 16–19, 1999), pp. 15–21.
D. E. Keenan, “High-Altitude Balloon Experiment,” AIAA Space Technology Conference (Albuquerque, NM, Sept. 28–30,
1999).
R. Koga, S. Crain, and K. Crawford, “Single
Event Burnout Sensitivity of Embedded
Field Effect Transistors,” IEEE Transactions on Nuclear Science, Vol. 46, No. 6,
1395–1402 (Dec. 1999)
H. Koons, “The Impact of the Space Environment on Space Systems,” Proceedings of
Spacecraft Charging Technology Conference ’98 (Hanscom AFB, MA, Nov. 2–6,
1998).
H. C. Koons and J. Roeder, “A Comparison of
ULF/ELF Measurements Associated With
Earthquake Regions,” Seismo Electromagnetics Monographs, 171–181 (Aug.
1999).
T. J. Lang, “Characteristics of Crosslinks
Between Satellites in Large Symmetric
Constellations,” Proceedings of AAS/
AIAA Astrodynamics Specialist Conference (Girdwood, AL, Aug. 16–19, 1999).
M. Lauriente and R. Koga, et al., “Spacecraft
Anomalies Due to the Radiation Environment,” Journal of Spacecraft and Rockets,
Vol. 36, No. 6, 902–906 (Nov.–Dec.
1999).
S. Lazar and J. E. Clark, “Signal Design
Guideline for Navigation Satellite System
Design,” ION GPS ’99 Proceedings
(Nashville, TN, Sept. 17, 1999), pp. 1–8.
C. A. Lee and J. P. Stepanek, “A Network Performance Tool for Grid Environments,”
Proceedings of Supercomputing ’99 (Portland, OR, Nov. 13, 1999), pp. 1–16.
Y. Phillip Li, “dClips: A distributed Clips
Implementation,” Computing in Aerospace 9 Conference (San Diego, CA, Oct.
19–21, 1993).
M. D. Looper and J. B. Blake, “Continuing
SAMPEX Observations of Shock-Injected
Ultrarelativistic Electrons,” Proceedings
of XXVI International Cosmic Ray Conference (Salt Lake City, UT, Aug. 17–25,
1999).
J. Ly and C. Truong, “Stability Analysis of
the International Space Station Electrical
Power System,” Proceedings of IEEE
Conference on Control Applications
(Kohala Coast, HI, Aug. 22–27, 1999), pp.
628-633.
D. K. Lynch, ed., Cirrus (Oxford University
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D. K. Lynch, “Some Paradoxes, Errors and
Resolutions Concerning the Spectral Optimization of Human Vision,” American
Journal of Physics, Vol. 67, No. 11, (Nov.
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D. K. Lynch and S. Mazuk, “On the Size
Parameter for Thermally Emitting Parti-
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5229-5231 (Aug. 20, 1999).
D. H. Martin, Communication Satellites,
fourth edition (The Aerospace Press and
AIAA, El Segundo, CA, and Reston, VA,
2000).
H. Mirels, “Effect of Wall on Impulse of Solid
Propellant Driven Millimeter-Scale
Thrusters,” AIAA Journal, Vol. 37, No. 12,
1617–1624 (Dec. 1999).
J. A. Morgan, “Neutrino Propulsion for Interstellar Spacecraft,” Journal of the British
Interplanetary Society, Vol. 52 No. 11/12,
424–428 (Nov./Dec. 1999).
T. Mosher, “Evaluating Small Satellites: Is the
Risk Worth It?” Proceedings of AIAA/USU
Conference on Small Satellites (Logan, UT,
Aug. 23, 1999), pp. 1–13.
T. M. Nguyen, J. Yoh, and G. Goo, “Performance Evaluation of the DVB Waveform
Using LSI Logic L64724 Satellite Receiver
Model with Imperfect Components,” MILCOM ’99 Proceedings (Atlantic City, NJ,
Oct. 31–Nov. 3, 1999), pp. 1–6.
D. P. Olsen, “A Hybrid Interleaving that
Enables Packet Switching on Multi-access
Channels,” IEEE Transactions on Communication, Vol. 47, No. 12, 1777–1780 (Dec.
1999).
W. Park and M. R. Hilton, “Characterization
of Cryogenic Mechanical Properties of
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Materialia, Vol. 41, No. 11, 1185–1190
(Nov. 1999).
G. E. Peterson, Dynamics of Meteor Outbursts
and Satellite Mitigation Strategies (The
Aerospace Press and AIAA, El Segundo,
CA, and Reston, VA, 1999).
T. D. Powell, “Automated Tuning of an
Extended Kalman Filter Using the Downhill Simplex Algorithm,” Proceedings of
AAS/AIAA Astrodynamics Specialist Conference (Girdwood, AL, Aug. 16–19,
1999), pp. 1-11.
A. Prater, E. Simburger, D. A. Smith, P. J. Carian, and J. H. Matsumoto, “Power Management and Distribution Concept for
Microsatellites and Nanosatellites,” Proceedings of the 34th Energy Conversion
Engineering Conference (Vancouver, BC,
Aug. 2–5, 1999), pp. 1–5.
S. Raghavan, S. Lazar, and R. Kumar, “The
CDMA Limits of C/A Codes in GPS
Applications-Analysis and Laboratory Test
Results,” Proceedings of the Satellite Division of the Institute of Navigation 12th
International Technical Meeting (Sept.
14–17, 1999), pp. 1–12.
M. N. Ross, “Study Blazing New Trails Into
Effects of Aviation and Rocket Exhaust in
the Atmosphere,” EOS Transactions, American Geophysical Union, Vol. 80, No. 38,
437, 442–443 (Sept. 21, 1999).
P. R. Rousseau, “An Algorithm to Reduce Bias
in Planar Near-Field Measurement Data,”
Proceedings of Antenna Measurement
Techniques Association 1999 Symposium
(Monterey Bay, CA, Oct. 4–8, 1999).
R. Rudy, R. Puetter, and S. Mazuk, “Paschen
Lines and the Reddening of the Radio
Galaxy 3C109,” Astronomical Journal, Vol.
118, 666–669 (Aug. 1999).
R. S. Selesnick and J. B. Blake, “On the
Source Location of Radiation Belt Relativistic Electrons,” Journal of Geophysical
Research, Vol. 105, No. A2, 2607–2624
(Feb. 1, 2000).
M. R. Shane, H. G. Yeh, G. L. Lui, and A. H.
Yamada,“Uplink Timing Detection for Frequency Hopping Communication,” MILCOM ’99 Proceedings (Atlantic City, NJ.
Oct. 31–Nov. 3, 1999), pp. 1–5.
E. J. Simburger, D. Smith, D. Gilmore, and M.
Meshishnek, “Development of a Thin Film
Amorphous Silicon Space Solar Cell for
the PowerSphere Concept,” Proceedings of
16th Space Photovoltaic Research and
Technology Conference (Cleveland, OH,
Aug. 31, 1999).
F. S. Simmons, Rocket Exhaust Plume Phenomenology (The Aerospace Press and
AIAA, El Segundo, CA, and Reston, VA,
2000).
K. Tsai and G. L. Lui, “Binary GMSK: Characteristics and Performance,” ITC ’99 Proceedings (Las Vegas, NV, Oct. 27, 1999).
K. Tsai and G. L. Lui, “Coherent Viterbi and
Threshold Demodulators for Pulse-Driven
GMSK Signals,” ITC ’99 Proceedings (Las
Vegas, NV, Oct. 27, 1999).
C. S. Tsang and T. M. Nguyen, “Long Loop
Time Tracking Performance for Satellite
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Proceedings (Atlantic City, NJ, Oct. 31–
Nov. 3, 1999), pp. 1–5.
C. C. Wang and T. M. Nguyen, “Using ShortBlock Turbo Code for Telemetry and Command,” 1999 International Telemetering
Conference (Las Vegas, NV, 25–28 Oct.
1999).
C. C. Wang, “Improving Faded Turbo Code
Performances Using A Biased Channel
Side Information,” MILCOM ’99 Proceedings (Atlantic City, NJ, Oct. 31–Nov. 3,
1999).
R. L. Walterschied, G. Schubert, and D. G.
Brinkman, “Wave Disturbances in a Model
of the Comet SL-9 Impacts into Jupiter’s
Atmosphere,” Icarus, Vol. 145, 140–146
(May 2000).
J. Wessel, S. M. Beck, Y. C. Chan, R. W. Farley, and J. A. Gelbwachs, “Raman Lidar
Calibration for the DMSP SSM/T-2
Microwave Water Vapor Sensor,” IEEE
Transactions on Geoscience and Remote
Sensing, Vol. 38, No. 1, 141–154 (Jan.
2000)
Patents
(November 1999–April 2000)
J. C. Camparo, “Method of Stabilizing Electromagnetic Field Strength in an Atomic System,” U.S. Patent No. 6,025,755, Feb. 2000.
C. J. Clark, A. A. Moulthrop, M. S. Muha, C. P.
Silva, “Frequency Translating Device
Transmission Response Method,” U.S.
Patent No. 6,041,077, Mar. 2000.
R. W. Dezelan, “Satellite Communications
Facilitated by Synchronized Nodal Regressions of Low Earth Orbits,” U.S. Patent No.
5,999,127, Dec. 1999.
R. B. Dybdal, “Adaptive Control of Multiple
Beam Communication Transponders,” U.S.
Patent No. 6,055,431, Apr. 2000.
R. W. Postma, R. B. Pan, B. T. Hamada, L. K.
Herman, “Flexure Washer Bearing and
Method,” U.S. Patent No. 6,022,178, Feb.
2000.
R. W. Postma, R. B. Pan, B. T. Hamada, L. K.
Herman, “Roller Washer Bearing and
Method,” U.S. Patent No. 6,036,422, Mar.
2000.
G. Radhakrishnan, “Apparatus for Magnetic
Field Pulsed Laser Deposition of Thin
Films,” U.S. Patent No. 6,024,851, Feb. 2000.
K. Siri, “Shared-Bus Current Sharing Parallel
Connected Current-Mode DC to DC Converters,” U.S. Patent No. 6,009,000, Dec. 1999.
D. M. Speckman, “Method of Making Indium
Oxide Microspheres for Antistatic Coatings,” U.S. Patent No. 6,027,673, Feb. 2000.
C. C. Wang, “Error-Floor Mitigating Turbo
Code Communication Method,” U.S. Patent
No. 6,028,897, Feb. 2000.
C. C. Wang, “Repetitive Turbo Coding Communication Method,” U.S. Patent No.
6,014,411, January 2000.
R. P. Welle, “Mechanical Valve Having N-Type
and P-Type Thermoelectric Elements for
Heating and Cooling a Fluid Between an
Inlet and an Outlet in a Fluid Pump,” U.S.
Patent No. 6,007,302, Dec. 1999.
R. P. Welle, “Method of Pumping a Fluid
Through a Micromechanical Valve Having
N-Type and P-Type Thermoelectric Elements for Heating and Cooling a Fluid
Between an Inlet and an Outlet,” U.S.
Patent No. 5,975,856, Nov. 1999.
R. P. Welle, “Ultrasonic Data Communication
System,” U.S. Patent No. 5,982,297, Nov.
1999.
R. P. Welle, “Ultrasonic Power Communication
System,” U.S. Patent No. 6,037,704, Mar.
2000.
A. D. Yarbrough, S. S. Osofsky, R. E. Robertson, R. C. Cole, “Micromachined Monolithic Reflector Antenna System,” U.S.
Patent No. 6,008,776, Dec. 1999.
A. D. Yarbrough, S. S. Osofsky, R. E. Robertson, R. C. Cole, “Micromachined Reflector
Antenna Method,” U.S. Patent No.
6,045,712, Apr. 2000.
Links Conferences,Workshops, and Symposia Sponsored or Hosted by The Aerospace Corporation
October 3–5, 2000
19th Aerospace Testing Seminar: Balancing the Forces of “Faster,
Better, Cheaper in Aerospace Testing”
Sponsored by The Aerospace Corporation and the
Preseminar tutorials (October 2) are
Institute of Environmental Sciences and Technology
• Handbook for Dynamic Environmental Criteria
The forum will include presentations from industry leaders in
• Integration and Test Systems Engineering
testing, instrumentation, and program planning. Also offered
• Data Validity Requirements for Your Test Data
will be tutorials and a special panel discussion featuring
• Vacuum Physics and Vacuum Techniques
members of the ongoing Broad Area Review commissioned
• Signal Processing
by the U.S. Air Force.
• Satellite Structural Testing
Topics include
• Thermal Balance and Thermal Vacuum Testing
• Lessons Learned
• Introduction to Modal Analysis and Testing
• Industry Test Practices, Standards, and Processes
The seminar will be held at the Manhattan Beach Marriott,
• Testing Methodologies, Innovations, and Challenges
1400 Parkview Ave., Manhattan Beach, CA 90266.
• Risk Management
For more information visit www.aero.org/conferences/ats/.
• Integration for “Best Practices”
October 22–25, 2000
MILCOM 2000: 21st-Century Military Communications—Architectures and
Technologies for Information Superiority
Hosted by The Aerospace Corporation and TRW, Inc.
• Advanced Communications Standards and Protocols
Sponsored by Institute of Electrical and Electronics Engineers,
• Advanced Communications Technologies
Inc., IEEE Communications Society, and Armed Forces ComTopics of the classified sessions are
munications and Electronics Association
• Milsatcom to Support Joint Vision 2010
The Military Communications International Symposium offers
• Strategic and Tactical Communications Architectures
a diverse program of both classified and unclassified sessions,
• Advanced Techniques and Technologies for Information
guest speakers, panels, and tutorials.
• Information Warfare, Security, Superiority
Topics of the unclassified sessions include
Unclassified sessions will be held at the Los Angeles Airport
• 21st-Century Communications Architectures
Marriott, 5855 W. Century Blvd., Los Angeles, CA 90045.
• Advanced Commercial Systems for Military Application
Classified sessions will be held at The Aerospace Corporation
• Advanced Communications Networks
in El Segundo.
• Advanced Communications Techniques
For more information visit www.milcom2000.org.
November 28–December 1, 2000
Risk Management 2000: Lessons for the Millennium
Sponsored by The Aerospace Corporation and the Air Force
Space and Missile Systems Center
The goal of this third annual symposium is to stimulate broader
interest in risk management at the national level. A tutorial,
Earned Value Risk Management, will be offered the first day.
Discussion topics include
• Effective Risk Management Practices
• Application of Tools and Methodologies
• Lessons Learned
• Comprehensive Areas of Interest (launch vehicles, spacecraft, ground systems)
The Conference will be held at the Hilton McLean Tysons Corner, 7920 Jones Branch Dr., McLean, VA 22102.
For more information visit www.aero.org/conferences/risk/.
The Aerospace Press
Four Decades of Communication Satellites
Donald H. Martin
Communication Satellites, fourth edition, was published in May by The Aerospace Press and the American Institute of
Aeronautics and Astronautics. Since the
book was first published in 1986, it has
become a standard in the chronicles of
communication satellites. The fourth edition has more than doubled in size from
that first publication, reflecting the phenomenal growth in communication satellites. The author, Donald H. Martin, here
presents an analysis of two of the many
changes in the industry.
Communication satellites represent one of
the most significant applications of space
technology. Almost every year since the
early 1960s, a new communication system
has launched its first satellite. Today,
applications reach more than 100 countries, providing a variety of communication services to both large and small
terminals on land, ships, and aircraft.
During these four decades, advances in
electronics and satellite technology and an
expanding market for communication
satellite services have generated changes
in communication satellite design.
Two aspects of this broad scope of
change—increase in weight and in design
life—are shown in the graphs, which are
based on data from Communication Satellites, fourth edition. Points on the graphs
represent all satellite programs described
in the book—whether experimental or
operational, civil or military, commercial
or noncommercial—from all manufacturers except those in Russia and China. The
points are positioned on the graphs to
show the date of the program’s first
launch. Blue triangles represent satellites
in geostationary orbits; magenta squares,
satellites in lower orbits.
Satellite weight is usually stated as dry
weight without fuel or weight with fuel at
the beginning of the satellite’s life in orbit.
The latter weight is shown on the first
graph. The growth in satellite weight
accommodates more communications
equipment, thereby increasing satellite
capacity to respond to the growing market
for satellite services. Also, the mission
effectiveness of any given weight has been
increased by technological improvements.
These improvements, occurring in small
increments over the decades, include
lighter materials and higher-efficiency
solar cells and propulsion.
The weight of most nongeostationary
satellites has been restrained by very limited
budgets. Only since 1997 have larger nongeostationary satellites been launched for
programs that provide voice communications to handheld user terminals.
Satellite life is limited by three factors:
random failures, exhaustion of consumables, and component wear-out. Design
life is a requirement related to consumables, such as propellant, and to components subject to wear-out, such as rotating
mechanical devices.
For those programs that have
announced a design or mission life, the
increase in satellite life, shown on the second graph, is a result of improved technology; lessons learned in the manufacturing,
testing, and operation of satellites; and the
ability to build and launch larger satellites. Horizontal lines of triangles show
the increase in common communication
satellite design lives from 5 to 7 to 10 to
12 to 15 years.
16
8000
Life (years)
Weight (pounds)
10000
6000
4000
2000
0
1962
1972 1982 1992
Launch date
2002
12
8
4
0
1962
1972 1982 1992
Launch date
2002
Horizontal lines of triangles in the figure show the increase in common communication satellite design lives
from 5 to 7 to 10 to 12 to 15 years. (Left) beginning of life of satellite weight. (Right) satellite design life.
Communication Satellites,fourth edition,
describes communication satellites
beginning with the
U.S. Army’s Project
SCORE launched in
1958 through satellites now being manufactured. The
book focuses on the satellite and its
communication subsystem, but also
describes some broader aspects of the
larger communication system that
includes the satellite.
Satellite drawings, communication
subsystem block diagrams, coverage
maps, and lists of references augment
the text. An extensive bibliography of
more than 3,500 entries cites literature
on communication satellite systems
and their applications, ground terminals, transmission methods, spectrum
use, network engineering, satellite
hardware, and social, economic, and
legal issues.
Appendixes present information
about the International Telecommunications Union and the World Trade
Organization in relation to communication satellite systems.A glossary defines
abbreviations and acronyms and provides a table showing frequency bands
used by each satellite system.
Information is derived from sources
available to the public by October 30,
1999; launch dates are current through
February 2000.
2000 • 286 pp • ISBN 1-884989-08-X
Order from AIAA
800.682.2422 or www.aiaa.org
Crosslink
Summer 2000 Vol. 1 No. 2
Editor in Chief
Donna J. Born
Editor
Jon M. Neff
Managing Editor
Peggy L. Haynes
Copyright  2000 The Aerospace Corporation. All rights reserved. Permission to copy or
reprint is not required, but appropriate credit must be given to The Aerospace Corporation.
Art Director
Thomas C. Hamilton
Illustrator
John A. Hoyem
Photographer
Eric Hamburg
Editorial Board
William C. Krenz, Chairman
David A. Bearden
Harlan F. Bittner
Donna J. Born
Linda F. Brill
David J. Evans
Isaac Ghozeil
David J. Gorney
Linda F. Halle
Michael R. Hilton
John P. Hurrell
Mark W. Maier
John W. Murdock
Jon M. Neff
Mabel R. Oshiro
Frederic M. Pollack
Alfred N. Sorenson
The Aerospace Corporation
P.O. Box 92957
Los Angeles CA 90009-2957
Crosslink (ISSN 1527-5264) is published by The Aerospace Corporation, an independent,
nonprofit corporation dedicated to providing objective technical analyses and assessments
for military, civil, and commercial space programs. Founded in 1960, the corporation operates a federally funded research and development center specializing in space systems
architecture, engineering, planning, analysis, and research, predominantly for programs
managed by the Air Force and the National Reconnaissance Office.
For more information about Aerospace, visit www.aero.org or write to Corporate Communications, P.O. Box 92957, M1-447, Los Angeles, CA 90009-2957.
For questions about Crosslink, send e-mail to [email protected] or write to The Aerospace Press, P.O. Box 92957, Los Angeles, CA 90009-2957.
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