Explorer 21

Explorer 21
	Image of Explorer 21.
Mission type	Earth science
Operator	NASA
COSPAR ID	1964-060A[1]
SATCAT no.	889
Spacecraft properties
Manufacturer	GSFC
Launch mass	138 kg (304 lb)
Start of mission
Launch date	4 October 1964, 03:45 UTC[2][3]
Rocket	Delta C
Launch site	Cape Canaveral LC-17A[4]
End of mission
Last contact	October 13, 1965
Decay date	January 1, 1966
Orbital parameters
Reference system	Geocentric
Regime	Highly Elliptical
Eccentricity	0.86478[1]
Perigee altitude	917 km (570 mi)[1]
Apogee altitude	94,288 km (58,588 mi)[1]
Inclination	33.7°[1]
Period	2,080 minutes[1]
Epoch	3 October 1964[1]
Instruments
Instruments
	Retarding Potential Analyzer
	Fluxgate Magnetometer
	Cosmic-Ray Range vs Energy Loss
	Cosmic Rays
	Ion Chamber and GM Counters
	Solar Wind Protons
	Faraday Cup
	Explorers

Explorer 21, also called IMP-B and Interplanetary Monitoring Platform IMP-B, was an American satellite launched as part of Explorers program. Explorer 21 was launched on 4 October 1964 from Cape Canaveral,[5] Florida, United States, with a Delta rocket. Explorer 21 was the second satellite of the Interplanetary Monitoring Platform.

Mission

Explorer 21 was a solar cell and chemical-battery powered spacecraft instrumented for interplanetary and distant magnetospheric studies of energetic particles, cosmic rays, magnetic fields, and plasmas. Each normal telemetry sequence of 81.9 s in duration consisted of 795 data bits. After every third normal sequence there was an 81.9-s interval of rubidium vapor magnetometer analog data transmission. Initial spacecraft parameters included a local time of apogee at noon, a spin rate of 14.6 rpm, and a spin direction of 41.4-deg right ascension and 47.4-deg declination. The significant deviation of the spin rate and direction from the planned values and the achievement of an apogee of less than half the planned value adversely affected data usefulness.

Otherwise, spacecraft systems performed well, with nearly complete data transmission for the first 4 months and for the sixth month after launch. Data transmission was intermittent for other times, and the final transmission occurred on October 13, 1965.[1]

References

"IMP-B". NSSDC Master Catalog. NASA Goddard Space Flight Center. This article incorporates text from this source, which is in the public domain.
"Jonathan's Space Page".
"Letter dated 22 December 1964 from the Permanent Representative of the United States of America addressed to the Secretary-General". COMMITTEE ON THE PEACEFUL USES OF OUTER SPACE (64-28156). Retrieved June 9, 2018.
"NASA'S YEAR". FLIGHT International. Retrieved June 9, 2018.
"Explorer-21 Satellite Falls Far Short Of Orbital Goal". The Palm Beach Post. October 5, 1964. Retrieved June 9, 2018.

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[nssdc-1] "IMP-B". NSSDC Master Catalog. NASA Goddard Space Flight Center. This article incorporates text from this source, which is in the public domain.

[jonathan-2] "Jonathan's Space Page".

[3] "Letter dated 22 December 1964 from the Permanent Representative of the United States of America addressed to the Secretary-General". COMMITTEE ON THE PEACEFUL USES OF OUTER SPACE (64-28156). Retrieved June 9, 2018.

[4] "NASA'S YEAR". FLIGHT International. Retrieved June 9, 2018.

[5] "Explorer-21 Satellite Falls Far Short Of Orbital Goal". The Palm Beach Post. October 5, 1964. Retrieved June 9, 2018.