P78-1 or Solwind was a United States satellite launched aboard an Atlas F rocket from Vandenberg Air Force Base in California on February 24, 1979. The satellite operated until it was shot down in orbit to test the ASM-135 ASAT anti-satellite missile.
Construction and payload
The Orbiting Solar Observatory (OSO) platform included a solar-oriented sail and a rotating wheel section. Ball Aerospace was the primary contractor for design and construction, and provided the attitude control and determination computer programs. The P78-1 carried a gamma-ray spectrometer, a white-light coronagraph, an extreme-ultraviolet imager, an X-ray spectrometer, a high-latitude particle spectrometer, an aerosol monitor, and an X-ray monitor. The X-ray monitor, designated NRL-608 or XMON, was a collaboration between the Naval Research Laboratory and Los Alamos National Laboratory. The white-light coronagraph and the ultraviolet imager were combined in a single package, designated NRL-401 or SOLWIND, which was built by the Naval Research Laboratory. The coronagraph was the flight spare of the white-light coronagraph on the OSO-7 satellite. The ultraviolet imager used a CCD imager, one of the first instances of a CCD in space.
In 1985, the satellite batteries were degrading. This caused more and more frequent "under-voltage cutoffs", a condition where the satellite detected low main bus voltage and automatically shut down all non-vital systems. In addition, the last of the three tape recorders failed in the spring of 1985, which resulted in the data collection to be only during contact of the spacecraft with the ground. The normal contact with the ground lasted only about 15 minutes, which was a serious degradation. Special arrangements could be made to string several contacts together. As a result of these failures, an ever-increasing amount of time and network resources were spent reconfiguring the satellite for normal operation. Data collection from the few remaining payloads was severely limited. Because of the additional burden on the Air Force Satellite Control Network (e.g., extra support and antenna time at the tracking stations), serious discussions were already underway to terminate the mission.
This led to the satellite being chosen as a test target for the ASM-135 ASAT anti-satellite missile. It was extended for several weeks solely to support the test. During this final phase, it was often allowed to remain in the under-voltage condition for several days at a time.
The test outraged some scientists because although five of P78-1's instruments had failed at the time of the test, two instruments remained in operation, and the satellite was what one solar physicist called "the backbone of coronal research through the last seven years".
- NASA page about the satellite
- List of research papers based on P78-1 observations
- Air Force Link, Milestones Thursday, January 01, 1970 - Sunday, December 31, 1989
- Encyclopedia Astronautica Solwind Page
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