Names | IMP-B IMP-2 Interplanetary Monitoring Platform-2 | ||||||||||||||||
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Mission type | Space physics | ||||||||||||||||
Operator | NASA | ||||||||||||||||
COSPAR ID | 1964-060A | ||||||||||||||||
SATCAT no. | 00889 | ||||||||||||||||
Spacecraft properties | |||||||||||||||||
Bus | IMP | ||||||||||||||||
Manufacturer | Goddard Space Flight Center | ||||||||||||||||
Launch mass | 138 kg (304 lb) | ||||||||||||||||
Power | 4 deployable solar arrays and batteries | ||||||||||||||||
Start of mission | |||||||||||||||||
Launch date | 4 October 1964, 03:45:00 GMT[1][2] | ||||||||||||||||
Rocket | Thor-Delta C (Thor 392 / Delta 026) | ||||||||||||||||
Launch site | Cape Canaveral, LC-17A[3] | ||||||||||||||||
Contractor | Douglas Aircraft Company | ||||||||||||||||
Entered service | 4 October 1964 | ||||||||||||||||
End of mission | |||||||||||||||||
Last contact | 13 October 1965 | ||||||||||||||||
Decay date | 1 January 1966[4] | ||||||||||||||||
Orbital parameters | |||||||||||||||||
Reference system | Geocentric orbit[4] | ||||||||||||||||
Regime | Highly elliptical orbit | ||||||||||||||||
Perigee altitude | 917 km (570 mi) | ||||||||||||||||
Apogee altitude | 94,288 km (58,588 mi) | ||||||||||||||||
Inclination | 33.70° | ||||||||||||||||
Period | 2080.00 minutes | ||||||||||||||||
Instruments | |||||||||||||||||
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Explorer 21, also called IMP-B, IMP-2 and Interplanetary Monitoring Platform-2, was a NASA satellite launched as part of Explorer program. Explorer 21 was launched on 4 October 1964, at 03:45:00 GMT from Cape Canaveral (CCAFS),[5] Florida, with a Thor-Delta C launch vehicle. Explorer 21 was the second satellite of the Interplanetary Monitoring Platform, and used the same general design as its predecessor, Explorer 18 (IMP-A), launched the previous year, in November 1963. The following Explorer 28 (IMP-C), launched in May 1965, also used a similar design.[6]
Trajectory
was invoked but never defined (see the help page).