NASA’s SMALL SATELLITE MISSIONS FOR EARTH
OBSERVATION
Steven P. Neeck, Thomas J. Magner, Granville E. Paules
NASA Headquarters, Office of Earth Science
Washington, DC 20546, USA
Phone: +1 202-358-0832, Fax: +1 202-358-2769, [email protected]
ABSTRACT
The mission of NASA's Earth Science Enterprise (ESE) is to develop a scientific understanding of the Earth system and its response to natural and human-induced changes to
enable improved prediction of climate, weather, and natural hazards for present and future generations. The ESE has an end-to-end strategy to assure that information,
understanding, and capabilities derived from its research program achieve maximum
usefulness to the scientific and decision-making communities. Small satellites (<500
kg) have been crucial contributors to satisfying the research strategy since the inception
of NASA’s Earth observation program in the 1960’s. In the last decade, NASA’s ESE
has placed a renewed emphasis on small satellites. This reemphasis reflects advancements in compact sensor, small satellite bus, and launch vehicle technologies in addition
to management innovations. Near term and advanced planning suggest that this trend
will continue. A number of related small satellite missions have been recently launched,
are in development, or are planned. Multi-satellite constellations under study include
small satellites as key architectural elements. Studies indicate that low cost, capable
microspacecraft along with compact sensors and increased autonomy are technology
enablers to the sensorwebs and associated distributed spacecraft infrastructure required
to realize the long term NASA Earth Science Vision (ESV).
1. NASA’S EARTH SCIENCE ENTERPRISE
Improving life here on planet Earth is foremost in NASA’s vision, and the larger purpose of NASA’s Earth Science Enterprise (ESE). Using the vantage point of space, the
ESE gains an understanding of our home planet that could not be achieved otherwise.
Increasing our knowledge of the Earth system is the goal of the ESE's research program,
which is complemented by applications, technology, and education programs. Figure 1
shows the integrated process of conducting research that results in useful information
products and demonstration of practical applications. The ESE has defined its research
strategy around a hierarchy of scientific questions:
·
·
·
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How is the global system changing?
What are the primary forcings of the Earth system?
How does the Earth system respond to natural and human-induced changes?
What are the consequences of change in the Earth system for human civilization?
·
How well can we predict future changes in the Earth system?
Education
Earth Science &
Technology
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Inputs
21st Century
Workforce
Outputs
Outcomes
Models
Earth
Science
Questions
Measurements
& Monitoring
Scientific
Discovery
New
Understanding
Assessments
Policy
Decisions
Decision
Support
Tools
- Satellites
- Sub-orbital
- Surface-based
Science
Community
Input
New
Instruments
& Platforms
Information
Products &
Services
Data
Computational
Management Modeling
Capability
Capability
Impacts
Management
Decisions
Education
Tools
Visualization
Future Scientists
& Engineers
Adaptation to
Users’ Systems
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Technology
Figure 1. Earth Science for Society
The research strategy is supported by information obtained from a variety of space vantage points and complemented by airborne and in situ observational data. The ESE's
spaceborne missions fall into four classifications: Systematic, Exploratory, Operational
Precursor, and Technology Demonstration. New measurements from space are considered exploratory. Many exploratory measurements prove sufficiently valuable to
science that they become systematic, i.e., data continuity spanning multiple mission lifetimes is required. Where practical, mature systematic measurements that also become
an element of the operational community are transitioned to operational satellites and
operated by other agencies.
2. HISTORY OF ESE SMALL SATELLITES
Small satellites (<500 kg) have been crucial contributors to satisfying the research strategy since the inception of NASA’s Earth observation program in the 1960’s. Notable
pioneering examples include the TIROS, NIMBUS, and ATS series of spacecraft.
The TIROS Program (Television Infrared Observation Satellite) was NASA's first
experimental step to determine if satellites could be useful in the study of the Earth.
TIROS-1, launched in 1960, provided the first demonstration of the use of low Earth
orbit (LEO) for meteorological purposes. The 122 kg spin stabilized spacecraft carried
high and low resolution television cameras. Later TIROS spacecraft had improved sensors, exhibited lifetimes of over three years, and were used for routine and severe
weather forecasting.
The NIMBUS series of spacecraft, initiated in 1964, continued the development of
space-based meteorological observations from LEO. Later satellites in the series extended observations of the Earth to include sea-ice
coverage, atmospheric temperature, atmospheric
chemistry, the Earth's radiation budget, and seasurface temperature. Beginning with 377 kg for
NIMBUS-1, the series grew in mass by NIMBUS-7,
reflecting increased payload sophistication and launch
vehicle lift capabilities.
The Applications Technology Satellite (ATS) series
pioneered the use of geostationary Earth orbit (GEO)
Figure 2. TIROS-1
for observation and communications. Initiated in
1966 with the 414 kg ATS-1, the ATS series by its
conclusion in 1969 demonstrated the engineering basis for the meteorological and
communications satellites of today.
Despite a trend towards larger multisensor spacecraft, small satellites remained a feature
of NASA’s Earth observation programs throughout the 1970’s and 1980’s. A brief list
includes the Synchronous Meteorological Satellite (SMS) series and the Earth Radiation
Budget Satellite (ERBS).
3. RECENT AND NEAR-TERM ESE SMALL SATELLITES
In the last decade, NASA’s ESE has placed a renewed emphasis on small satellites.
Figure 3 shows the distribution of spacecraft masses for 25 ESE missions launched or in
development between 1990 and 2005. Some recent examples include TOMS-EP,
SeaWiFS, and ACRIMSAT. This reemphasis reflects advancements in compact sensor,
small satellite bus, and launch vehicle technologies, in addition to management innovations (e.g. Principal Investigator mission management and streamlined “catalog”
acquisition approaches). Near term and advanced planning
suggest that this trend will continue. Related small satellite
>1000 kg
missions recently launched, in development, or planned
<500 kg
33%
include SORCE, OCO, AQUARIUS, HYDROS, and
42%
OSTM.
500-1000
kg
25%
The Orbiting Carbon Observatory (OCO), AQUARIUS, and
HYDROS are exploratory missions that will make new
measurements from space. OCO will provide space-based
observations of atmospheric carbon dioxide (CO2), the prinFigure 3. ESE Satellite
cipal anthropogenic driver of climate change and the highest
Mass (1990-2005)
priority
carbon
cycle
measurement
requirement.
AQUARIUS is a focused satellite mission being developed
with Argentina to measure global sea surface salinity. It will resolve missing physical
processes that link the water cycle, climate, and the ocean. HYDROS will provide the
first global views of Earth's changing soil moisture and land surface freeze/thaw conditions, aiding weather and climate prediction and understanding of processes linking the
water, energy, and carbon cycles. Small satellite architectures coupled with missions
lead by a Principal Investigator permit streamlined management processes and costeffective implementation with rapid turn around.
The SOlar Radiation and Climate Experiment (SORCE) and Ocean Surface Topography
Mission (OSTM) provide data continuity with previous ESE missions to ensure longterm systematic measurement of important climate variables. SORCE measures total
and spectral (1–2000 nm) solar irradiance, the dominant energy source in the Earth's
atmosphere and one of its primary climate system variables. OSTM, being developed
with France, will continue the measurement of precise ocean height provided by previous ESE missions. This long-term information about the world's oceans and currents is
important to understanding climate and weather patterns. Small satellite architectures
provide cost effective implementation.
4. ESE SMALL SATELLITES AND THE FUTURE
Permanent
Future Earth science measurement needs dictate an evolution to multi-satellite formations from single satellite missions. Initial steps in that evolution include coordinated
formations of LEO satellites in orbits with close temporal proximity. Current examples
are the Morning Train that includes the Landsat 7, Terra, EO-1, and SAC-C satellites
and the Afternoon Train, that will include the Aqua, CALIPSO, CloudSat, Aura, and
PARASOL satellites. Small satellites are featured in both formations. Multi-satellite
constellations under study, like the Global Precipitation Measurement (GPM) initiative,
include small satellites as key architectural elements. Studies indicate that low cost, capable micro-spacecraft along with compact sensors and increased autonomy are
technology enablers to the sensorwebs and associated distributed spacecraft infrastructure required to realize the long term NASA Earth Science Vision (ESV). Figure 4
represents such an integrated Earth observing network of the future.
Vantage Points
Capabilities
FarSpace
L1/HEO/GEO
TDRSS &
Commercial
Satellites
LEO/MEO
Commercial
Satellites
and Manned
Spacecraft
NearSpace
Deployable
Airborne
Aircraft/Balloon
Event Tracking
and Campaigns
Terrestrial
Forecasts & Predictions
Figure 4. Integrated Observing Network
User
Community