The IBSS-SPAS (Infrared Background Signature Survey - Shuttle Palette Satellite)
experiment carried on the SPAS-2 satellite supported scientific research that
assisted the United States in the development of ballistic missile defense sensor
systems.
The IBSS experiment, sponsored by the Strategic Defense Initiative Organization,
consists of an infrared radiation sensor, a multispectral sensor that measures light in
several wavelengths, two low-light-level television cameras, and various support
equipment. IBSS's instruments observed Discovery and measure
the plumes created as Discovery fired its reaction control and
orbital maneuvering system engines. By comparing the geometry and spectral characteristics
of the plumes, as seen by IBSS, with the known firing directions, burn durations, and
chemical composition of the exhaust gases, the experiment provided valuable data for
the development of ballistic missile sensors.
Part of the IBSS experiment will involve chemical releases of xenon, neon, carbon
dioxide, and nitrous oxide gases from canisters in the orbiter's payload bay. The IBSS
examined the interaction of the gases, as they spew from the payload bay, with Earth's
magnetic field force lines. Still another aspect of the experiment began with ejecting
several chemical release observation subsatellites (CRO).
Subsatellites are small satellites released from the Shuttle's payload bay as a part of
the experiments the Shuttle is conducting. When the CRO
subsatellites had drifted to distances of 50 to 200 kilometers from the SPAS/IBSS
satellite, they were commanded to release their chemical loads of rocket propellants to
vaporize in space. Simultaneous observations by the IBSS and ground-based sensors
permitted researchers to characterize similar releases that occur when ballistic missiles
make midcourse maneuvers.
On day three of the mission, Discovery maneuvered to
within grasping distance of the SPAS/IBSS satellite. It was captured with the RMS and
held above the bay so that the IBSS payload could be used for additional experiments.
At the end of the mission IBSS/SPAS was placed back into the payload bay and was returned to earth with the orbiter.