End of an Era for an IMP
After 28 years of service, NASA pulled the plug in 2001 on the Interplanetary Monitoring Platform (IMP-8) spacecraft that had radioed solar wind conditions to Earth since 1973.
Interplanetary Monitoring Platform (IMP-8)
monitoring solar wind 1973-2001
Last of NASA's Interplanetary Monitoring Platforms, the seemingly forgotten IMP-8 was drum-shaped and weighed 818 lbs. It was sent to orbit above Earth on October 25, 1973. Only Pioneer-6, launched in 1965, and Pioneer-10, launched in 1972, were in service longer in space.
In fact, IMP-8 was so old that its telemetry link frequency was in the VHF radio band. Long ago, NASA had abandoned that band of frequencies for routine spacecraft use.
IMP-8 had no tape recorder. Instead, its data was beamed straight to the ground continuously at 6,000 bits per second.
The satellite's unusual orbit -- approximately circular, nearly halfway to the Moon -- allowed its instruments to monitor electromagnetic conditions both inside and outside Earth's magnetosphere.
Scientists became re-interested in IMP-8 data during the 1990s when no other spacecraft was watching the solar wind. In fact, a new receiving station was built at the South Pole.
But the launch of new satellites in the late 1990s, such as the Advanced Composition Explorer in 1997, redcued the value of IMP-8 as a solar sentinel. When IMP-8's magnetometer failed in 2000, its solar wind data became less useful. However, at the time it was shut down, seven of IMP-8's eleven experiments were working.
The scientists who had managed IMP-8 would have liked to have seen the satellite continue in use as a cosmic ray monitor. In that role, its observations could have complemented data sent back from the outer edge of the heliosphere by Voyager 1 and Voyager 2. Unfortunately, NASA said it couldn't afford it. Flight controllers sent their last commands to IMP-8 on October 26, 2001, and data collection ceased.
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