NASA's plans for earth science research from the International Space Station

The International Space Station (ISS) should provide a valuable platform for earth science research for both externally-mounted (attached) payloads and for those using the Window Observational Research Facility (WORF). The mid-inclination (51.5 degrees) orbit provides excellent coverage of the tropics and mid-latitudes, and allows for viewing the earth under a range of lighting conditions. Further, ISS makes possible the retrieval of instruments for recalibration, repair, or modification, enhancing the possibility of its use both for long-term measurements and for testing of "first-generation" instruments, especially those requiring large mass, power, and volume. Possible complications for use of ISS, especially for Earth viewing payloads, are contamination, orbital variations, lack of pointing knowledge, platform stability, and interference with clear viewing of light sources. The only payload NASA's Office of Earth Science currently has definite plans for use on ISS is the Stratospheric Aerosol and Gas Experiment (SAGE III), with launch in 2002 being probable. SAGE III measures the vertical distribution of ozone, aerosols, and other trace constituents in the atmosphere using solar and lunar occultation. Addition of a series of infrared occultation instruments to ISS for the characterization of long-term variations in the concentrations of a larger number atmospheric trace constituents beginning several years alter the SAGE III launch has been identified as a desirable possibility, although no commitment has been made for this.