Explorer 21
Explorer 21 satellite | |||||||||||||||||
| Names | IMP-B IMP-2 Interplanetary Monitoring Platform-2 | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 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 | ||||||||||||||||
| Rocket | Thor-Delta C (Thor 392 / Delta 026) | ||||||||||||||||
| Launch site | Cape Canaveral, LC-17A | ||||||||||||||||
| Contractor | Douglas Aircraft Company | ||||||||||||||||
| Entered service | 4 October 1964 | ||||||||||||||||
| End of mission | |||||||||||||||||
| Last contact | 13 October 1965 | ||||||||||||||||
| Decay date | 1 January 1966 | ||||||||||||||||
| Orbital parameters | |||||||||||||||||
| Reference system | Geocentric orbit | ||||||||||||||||
| 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 | |||||||||||||||||
| |||||||||||||||||
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), 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.