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Solwind / P78-1
P78-1-Solarwind sat.gif
The P78-1
Mission type Solar physics
Operator USAF Space Test Program[1]
COSPAR ID 1979-017A[2]
SATCAT № 11278[2]
Mission duration 6 years, 6 months, 20 days
Spacecraft properties
Manufacturer Ball Aerospace
Launch mass 1,331 kilograms (2,934 lb)[3]
Dry mass 850 kilograms (1,870 lb)
Start of mission
Launch date February 24, 1979, 08:24:00 (1979-02-24UTC08:24Z) UTC[3]
Rocket Atlas F
Launch site Vandenberg SLC-3W[3]
End of mission
Disposal Destroyed by ASAT
Destroyed September 13, 1985 (1985-09-14)
Orbital parameters
Reference system Sun-synchronous[4]
Regime Low Earth
Epoch April 14, 1979[2]

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 destroyed in orbit on September 13, 1985 to test the ASM-135 ASAT anti-satellite missile.

Construction and payload[edit]

The satellite's 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.[5] 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 uses of a CCD in space.


By 1985, the satellite's batteries were degrading. This caused more and more frequent "under-voltage cutoffs", a condition where the satellite detected a 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, so data collection could only occur while the spacecraft was in contact with a ground station.[1] A normal contact lasted only about 15 minutes, so this was a serious impediment. 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), discussions were already underway to terminate the mission.[citation needed]

This led to the satellite being chosen as a test target for the ASM-135 ASAT anti-satellite missile. The mission was extended for several weeks solely to support the test. During this final phase, the satellite was often allowed to remain in the under-voltage condition for several days at a time.[citation needed]

F-15 plane launching the missile that destroyed the P78-1

On September 13, 1985, the satellite was destroyed in orbit by the ASM-135 ASAT launched from a US Air Force F-15 Eagle fighter aircraft.

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".[6]

See also[edit]


  1. ^ a b Krebs, Gunter. "Solwind (P78-1)". Gunter's Space Page. Retrieved March 20, 2014. 
  2. ^ a b c McDowell, Jonathan. "SATCAT". Jonathan's Space Pages. Retrieved March 20, 2014. 
  3. ^ a b c "Solwind". Encyclopedia Astronautica. Retrieved March 20, 2014. 
  4. ^ "The P78-1 Satellite". NASA Goddard Space Flight Center. June 26, 2003. Retrieved March 20, 2014. 
  5. ^ Space Test Program P78-1 at Ball Aerospace
  6. ^ Eberhart, Jonathan (Sep 28, 1985). "ASAT target was working research satellite". Science News. 

External links[edit]