lites in Earth observation, particularly in the context of complementing (not replacing) larger missions.29 Especially when configured with single sensors, small satellite missions can add significantly to architectural and programmatic flexibility. An emphasis on smaller platforms also potentially reduces cost through the use of smaller and cheaper launch vehicles, including opportunities for launching multiple payloads on a single launch vehicle, and “piggyback” launches, using excess capacity on larger launch vehicles.
In 2007, the Hyperspectral Imager for the Coastal Ocean (HICO) was manifested for the Japanese Experiment Module-Exposed Facility (JEM-EF) on the International Space Station (ISS), and installed on orbit on September 24, 2009. HICO was sponsored by the Office of Naval Research (ONR) to “develop and operate the first Maritime Hyperspectral Imaging from space.”30 HICO was integrated and flown under the direction of DOD’s Space Test Program. One of the HICO mission requirements was to “demonstrate new and innovative ways to develop and build the imaging payload (reduce cost, reduce schedule).”31 The sensor was delivered 16 months after project start and was installed within a total time of 3 years of its proposal. HICO has since met its demonstration requirement. HICO’s implementation demonstrated that the ISS is a viable platform for demonstrations of Earth observing technologies and Earth observations.32 (See Figure 4.2.) Another instrument scheduled for manifestation on the ISS is NASA’s Stratospheric Aerosol and Gas Experiment III-ISS (SAGE III-ISS) to measure atmospheric ozone, water vapor, and aerosols. SAGE III is scheduled for launch in 2014 on a SpaceX rocket from NASA Kennedy Space Center.33
Formation flying can deliver multiple benefits, not the least of which is the ability to flexibly combine (and maintain over time) multiple, synergistic, and multisensor measurement types.34 Advances in both station-keeping ability and coordination protocols now make it possible to achieve formation flight with a diverse set of spacecraft, whether launched simultaneously or years apart, including the large EOS observatories, small satellites, and co-manifested satellites. Constellations may remain in place beyond the lifetime of individual satellites if appropriate planning and funding remain in place. The Afternoon Constellation (A-Train) continues to exemplify the best of international scientific cooperation and coordination35 and can provide valuable experience, best practices, and lessons learned for future constellation efforts (e.g., potential establishment of a constellation based on the Joint Polar Satellite System, JPSS). Coordinated formation flight efficiencies can include the synergies of complementary measurements, where the assigned degree
29 National Research Council, The Role of Small Satellites in NASA and NOAA Earth Observation Programs, National Academy Press, Washington, D.C., 2000.
30 M.R. Corson (Naval Research Laboratory) and C.O. Davis, (Oregon State University), “HICO Science Mission Overview,” available at http://hico.coas.oregonstate.edu/publications/Davis_HICO_for%20IGARSS.pdf, p. 22.
31 Corson and Davis, “HICO Science Mission Overview,” p. 7.
34 Formation flight can provide a much clearer way of quantifying errors in parameter estimation and identifying major biases/flaws in past data derived from single sensors. For example, the combined cloud information from CALIPSO and CloudSat has exposed significant biases in interpretation of ISCCP (International Satellite Cloud Climatology Project) global cloudiness, the combination of CALIPSO and CloudSat has led to a new and more accurate way of retrieving aerosol optical depth, and CALIPSO has yielded powerful new information about polar stratospheric clouds, and so on.