Earth Moon Planet (2008) 102:293–298
DOI 10.1007/s11038-007-9184-0
The NASA Lunar Impact Monitoring Program
Robert M. Suggs Æ William J. Cooke Æ Ronnie J. Suggs Æ Wesley R. Swift Æ
Nicholas Hollon
Received: 12 September 2007 / Accepted: 25 October 2007 / Published online: 23 November 2007
Ó US Government 2007
Abstract NASA’s Meteoroid Environment Office has implemented a program to monitor
the Moon for meteoroid impacts from the Marshall Space Flight Center. Using off-theshelf telescopes and video equipment, the Moon is monitored for as many as 10 nights per
month, depending on weather. Custom software automatically detects flashes which are
confirmed by a second telescope, photometrically calibrated using background stars, and
published on a website for correlation with other observations. Hypervelocity impact tests
at the Ames Vertical Gun Range facility have begun to determine the luminous efficiency
and ejecta characteristics. The purpose of this research is to define the impact ejecta
environment for use by lunar spacecraft designers of the Constellation manned lunar
program. The observational techniques and preliminary results will be discussed.
Keywords Meteoroids Lunar impacts Space environments Hypervelocity impact testing
The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is
acknowledged.
R. M. Suggs (&)
NASA, Space Environments Team, EV13, Marshall Space Flight Center, Huntsville, AL 35812, USA
e-mail: [email protected]
W. J. Cooke R. J. Suggs
NASA, Space Environments Team and Meteoroid Environment Office, EV13, Marshall Space Flight
Center, Huntsville, AL 35812, USA
W. R. Swift
Raytheon/MSFC Group, Space Environments Team, EV13, Marshall Space Flight Center, Huntsville,
AL 35812, USA
N. Hollon
Jacobs Technology/MSFC Group, Space Environments Team, EV13, Marshall Space Flight Center,
Huntsville, AL 35812, USA
N. Hollon
Villanova University, Villanova, PA 19085, USA
123
294
R. M. Suggs et al.
1 Introduction
Video observations of the Moon during the Leonid storm in 1999 (Dunham et al. 2000;
Ortiz et al. 2000) confirmed that lunar meteoroid impacts are observable from the Earth.
One probable Geminid impact was observed from lunar orbit by Apollo 17 astronaut
Dr. Harrison Schmitt (NASA 1972). Since NASA’s Constellation Program, which will
place crews on the lunar surface for up to 6 months at a time, is currently in the preliminary
design stages a new lunar impact ejecta environment model is needed. This exposure time
is vastly increased over the Apollo Program and the risk from meteoroid impact ejecta
must be better understood so that shielding on lunar spacecraft, spacesuits, and surface
systems can be optimally designed. The existing model, NASA SP-8013 (NASA 1969),
shows ejecta at a given particle size to be 10,000 times as abundant as primary meteoroids.
This violates conservation of energy and is probably overly conservative which will result
in lunar spacecraft designs with too much meteoroid shielding and hence too much weight.
Since our organization, NASA Marshall Space Flight Center’s Natural Environments
Branch, houses the Meteoroid Environment Office and the Constellation Program Environments and Constraints co-lead, we have the responsibility for defining the ejecta
environment and have undertaken a program of observations, testing, and modeling to do
so. Our first results were reported by Cooke et al. (2006, 2007).
2 Observational Technique
The observations are carried out at the Automated Lunar and Meteor Observatory located
on-site at the Marshall Space Flight Center (latitude 34.66 N, longitude 86.66 W). The
instruments consist of two Meade RCX400 14 inch (355 mm) diameter telescopes with
Optec 0.339 focal reducers and StellaCam EX monochrome video cameras. The effective
focal length is approximately 923 mm giving a horizontal field of view of 20 arc minutes
covering approximately 4.5 9 106 km2 or 12% of the lunar surface (see Fig. 1). The
limiting stellar magnitude at the 1/30 s frame rate is approximately 12. The video from the
StellaCam EX is digitized using a Sony GV-D800 digital tape deck and sent by Firewire to
a personal computer where it is recorded on the hard drive for subsequent analysis.
Fig. 1 Camera field of view and
orientation
123
The NASA Lunar Impact Monitoring Program
295
The observations are made of the earthshine portion of the moon when the sunlit portion
is between 10% and 50% illuminated. This occurs on five nights and five mornings per
month. We do not observe during phases less than 10% since the time between twilight and
moon rise or set is too short. We do not observe during phases greater than 50% because
the scattered light from the sunlit portion of the moon is too great and masks the fainter
flashes. Large lunar features are easily visible in the earthshine and are used to determine
the location of the impacts on the lunar surface.
The recorded video is analyzed using two custom programs. LunarScan (available at
http://www.gvarros.com) was developed by Gural (2007) and modified to read the video files.
The threshold for pixel exceedance is set to 3.5 times the standard deviation over the mean
image. The mean and standard deviation are tracked on a frame by frame basis using a first
order response filter for each pixel channel independently. The threshold exceedances are then
examined using a spatial correlation filter that looks for a row containing an adjacent triplet of
exceedances bordered two rows above or below by a pair of exceedances. The software finds
flashes in the video which meet these criteria and presents them to a user who determines if
they are cosmic ray impacts in the detector, sun glints from satellites between the Earth and the
Moon, or actual meteoroid impacts. By requiring that a flash be simultaneously detected in
both telescopes, cosmic rays and electronic noise can be ruled out. Some of the detected
impacts were observed with only one telescope early in the program but only flashes which
spanned more than two video frames and showed a proper light curve (abrupt brightness
increase followed by gradual decay) were counted. There have also been two impacts independently observed by amateur astronomers using 8 inch (200 mm) telescopes (G. Varros,
D. Clark private communication). For short flashes where satellite motion might not have been
detectable, custom software was used to check for conjunctions with Earth orbiting satellites
whose orbital elements are available in the unclassified satellite catalog (http://www.spacetrack.org). Since there is some probability that orbital debris or a classified satellite not listed in
this catalog could cause such a short flash, another observing station has been constructed in
northern Georgia about 100 km from MSFC. This will allow parallax discrimination between
impact flashes and sun glints from manmade objects, even at geosynchronous altitude.
After detection and confirmation, another computer program, LunaCon, is used to
perform photometric analysis (Swift et al. 2007). Background stars are used as photometric
standards to determine the observed luminous energy of the flashes. Modifications to
LunaCon to improve photometric calibration, determine observed lunar surface area
(collecting area), and detection threshold are described in Swift et al. (2007).
3 Observational Results
A total of 54 impact flashes were observed between November 2005 and May 2007
(Fig. 2). These were observed in a total of approximately 190 h of observation. We
assumed that impacts detected during the 3 days around the peaks of major meteor showers
which were located on the portion of the Moon visible from the shower radiant (determined
using LunarScan) were due to shower meteoroids. It is possible that sporadics caused some
of these impacts but the rates increased so dramatically for the showers that it is likely they
were actually shower meteoroids. Since the velocities and impact angles of shower
meteoroids are well determined, we are currently following the technique of Rubio et al.
(2000) to determine luminous efficiency using our Lyrid and Geminid impacts (11 impacts
each). There were approximately 16 h of observation time during these shower periods and
27 possible shower impacts were seen giving approximately 1.6 flashes per hour.
123
296
R. M. Suggs et al.
Fig. 2 Impact flashes observed between November 2005 and May 2007. Continuous monitoring was from
April 2006 to May 2007. The yellow numbers are probably sporadics, the white is likely a Taurid, blue are
Leonids, green are Geminids, and red are Lyrids. A complete list of candidate impacts is given at
http://www.nasa.gov/centers/marshall/news/lunar/index.html
There were coincidentally a total of 27 likely sporadics; 21 were observed on the western
hemisphere of the Moon (waxing phase) and six on the eastern (waning phase). Figure 3
shows the observation and impact geometry. The observed impact rate during waxing
phases is approximately 0.19/h and during waning phases is 0.07/h. During waxing phases
the observed portion of the Moon is exposed to the antihelion, north and south toroidal, and
apex sporadic sources while during the waning phases the observed portion is exposed only
to the antihelion and toroidal sources. The apex meteoroids are impacting the lunar far side
which we cannot observe. Clearly, the higher speed apex meteoroids at 55 km/s deposit
much more kinetic energy than a similar sized antihelion or toroidal meteoroid at 25 km/s
making their observed rate much higher than their flux would indicate. Thus, a clear
signature of the apex source is present even in this relatively small data sample.
The field of view of the camera encompasses approximately 10–12% of the total surface
of the Moon. Assuming that helion meteoroids have the same flux as antihelion, this
observed rate means that somewhere on the Moon, there are approximately 2–3 sporadic
impacts per hour of sufficient energy to be observed from the Earth. These impacting
meteoroids have masses of order 1 kg with a kinetic energy roughly equivalent to 200 kg
of TNT. During meteor showers the rate increases dramatically, partially due to the flatter
population index and hence larger percentage of larger particles.
4 Hypervelocity Impact Testing
In order to experimentally determine the luminous efficiency, a series of hypervelocity
impact tests have been undertaken at NASA’s Ames Vertical Gun Range. Pyrex spheres of
123
The NASA Lunar Impact Monitoring Program
297
Fig. 3 Observation and major sporadic source geometry. The observed impact rate is higher near first
quarter because the earthshine portion of the moon (dark part) is exposed to the apex, toroidal and antihelion
sources. At last quarter the rate is lower since only the antihelion and toroidal source meteoroids impact the
observed portion of the Moon. Note that the north and south toroidal sources are out of the plane of the page
¼ inch (6.3 mm) diameter were fired into ground pumice in a vacuum at speeds from 2.5
to 5.5 km/s and the impact flashes were recorded with the same StellaCam EX video
cameras used for our lunar observations. Figure 4 shows the luminous efficiencies determined by the first series of shots in September 2006. The point in the upper right is the
luminous efficiency g = 2 9 10-3 for Leonids determined by Rubio et al. (2000). All of
the determinations of g have been plotted even though the impact angle was varied from
90° to 30° and the camera viewing angles varied between approximately 90° and 0°.
Subsequent to these shots it was determined that the neutral density filters used to reduce
the intensity of the impact flashes were not really neutral and had a factor of 10 higher
transmissivity in the near infrared (where our cameras are sensitive and much of the
thermal radiation from the impact is emitted) than in the visible. Thus the results in Fig. 4
are biased toward cooler impacts and should be treated as very preliminary. A second
series of shots using truly neutral filters and lunar stimulant as the target material was
Fig. 4 Preliminary luminous efficiencies determined from Ames Vertical Gun Range tests (left hand side of
figure) and from Leonids observations by Rubio et al. (2000) (point at upper right of figure)
123
298
R. M. Suggs et al.
completed in August 2007 and the analysis is underway. Future impact testing will be used
to determine the mass flux, particle sizes, and particle velocities so that new cratering
models can be validated and calibrated.
5 Conclusions
NASA Marshall Space Flight Center has begun a campaign to observe sporadic and shower
meteoroid impacts on the Moon. The fluxes of large impactors will be determined using
luminous efficiencies from hypervelocity impact testing and shower meteoroid impact
statistics. Further impact testing coupled with cratering models to be developed during this
research will be used to calculate ejecta characteristics from impacts of various energies.
The observed impact flux, sporadic source directionality from the Meteoroid Engineering
Model (McNamara et al. 2004), and a Monte Carlo and orbit generation model will be used
to propagate the ejecta around the Moon. This engineering model of the ejecta environment
will be used by space hardware designers to build the systems needed to explore and
establish permanent bases on the Moon.
Acknowledgments The authors wish to acknowledge the meticulous and dedicated support of the following observers who recorded much of our video: Danielle Moser, Heather McNamara, Leigh Smith,
Victoria Coffey, and Richard Altstatt. We also wish to thank Peter Schultz and Carolyn Ernst of Brown
University, the staff of the Ames Vertical Gun Range, and Danielle Moser for their assistance during the
hypervelocity impact testing.
References
L.R. Bellot Rubio, J.L. Ortiz, P.V. Sada, Luminous efficiency in hypervelocity impacts from the 1999 lunar
Leonids. Astrophys. J. 542, L65–L68 (2000)
W.J. Cooke, R.M. Suggs, R.J. Suggs, W.R. Swift, N.P. Hollon, Rate and distribution of kilogram lunar
impactors Lunar and planetary science XXXVIII, Houston, Texas, LPI, Paper 1986 (2007)
W.J. Cooke, R.M. Suggs, W.R. Swift, A probable taurid impact on the moon. Lunar and planetary science
XXXVII, Houston, Texas, LPI, paper 1731 (2006)
D. W. Dunham, B. Cudnik, D.M. Palmer, P.V. Sada, J. Melosh, M. Frankenberger, R. Beech, L. Pelerin, R.
Venable, D. Asher, R. Sterner, B. Gotwols, B. Wun, D. Stockbauer, The first confirmed videorecordings of lunar meteor impacts. Lunar and planetary science conference XXXI, Houston, Texas, LPI,
Paper 1547 (2000)
P. Gural, Automated detection of lunar impact flashes. Meteoroid environments workshop, NASA MSFC,
Huntsville, Alabama (2007)
H. McNamara, R. Suggs, B. Kauffman, J. Jones, W. Cooke, S. Smith, Meteoroid Engineering Model
(MEM): A meteoroid model for the inner solar system. Earth, Moon, Planets 95, 123–139 (2004)
NASA, December 1972. ‘‘Apollo 17 air-to-ground communications transcript’’, http://www.jsc.nasa.gov/
history/mission_trans/AS17_TEC.PDF p. 455
NASA SP-8013: 1969, Meteoroid environment—1969, near earth to lunar surface
J.L. Ortiz, P.V. Sada, L.R. Bellot Rubio, F.V. Aceituno, J. Aceituno, P.J. Gutierrez, U. Thiele, Optical
detection of meteoroidal impacts on the Moon. Nature 405, 921–923 (2000)
W.R. Swift, R.M. Suggs, W.J. Cooke, Algorithms for lunar flash video search, measurement, and archiving,
this issue (2007)
123