SAC-B, an Argentine / US mission, is designed to study of solar physics and astrophysics through the examination of solar flares, gamma-ray burst sources and the diffuse soft X-ray cosmic background. The mission is organized as a cooperative effort between the National Aeronautics and Space Administration (NASA) and Argentina's National Commission of Space Activities (CONAE). NASA provides two scientific instruments and launch services on a Pegasus XL vehicle. CONAE is responsible for the design and construction of the SAC-B satellite.
The Hard X-Ray Spectrometer (HXRS) provided by the Argentine Institute of Astronomy and Space Physics (IAFE) searches the hard X-ray spectrum between 20 and 320 keV of rapidly varying events on time scales as short as tens of milliseconds.
The Goddard X-Ray Experiment (GXRE) provided by NASA/Goddard Space Flight Center (GSFC) has two sets of detectors. One of them, the Soft X-Ray Spectro-meter (SOXS), performs coordinated observations with the HXRS by observing soft X-ray emissions from solar flares. The other, the Gamma Ray Burst Spectrometer (GRaBS) provides time profiles of the X-ray emission from non-solar gamma-ray bursts in the energy range from ~20 keV to > 300 keV.
The Cosmic Unresolved X-Ray Background Instrument using CCDs (CUBIC) is provided by the Pennsylvania State University. CUBIC measures the spectrum of the diffuse X-Ray background with unprecedented sensitivity and spectral resolution between 0.1 and 10.0 keV in selected areas of the sky.
The Imaging Particle Spectrometer for Energetic Neutral Atoms (ISENA), provided by the Italian Istituto di Fisica dello Spazio Interplanetario (IFSI), measures neutral atoms at spacecraft altitudes.
Status as of 11/5/96
SAC-B deployed its solar panels successfully and operated for about 10 hours. On-board software was modified to permit operation without a separation indication and the ACS system was placed in safe-hold mode in an attempt to gain control and point the solar panels at the sun. However, the ACS system was not designed to control such a massive tumbling object. With the Pegasus 3rd stage shadowing part or all of the solar array, there is not enough power to charge the batteries, even during the daylight part of the orbit. At the last contact, battery power continued to decrease, and four subsequent passes over Wallops did not produce any signal from the satellite.
Because the SAC-B/HETE/Pegasus object is so long, it will eventually stabilize in a gravity-gradient capture mode, although it will probably take a long time for it to lose its existing angular momentum. It could be captured in either orientation: SAC-B up or SAC-B down. In any event, it is unlikely that spacecraft control will be regained.
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