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Discoverer 21
Mission typeTechnology
OperatorUS Air Force/ARPA
Harvard designation1961 Zeta 1
COSPAR ID1961-006A
SATCAT no.00084Edit this on Wikidata
Spacecraft properties
Launch mass1,110 kilograms (2,450 lb)
Start of mission
Launch date18 February 1961, 22:58 (1961-02-18UTC22:58Z) UTC
RocketThor DM-21 Agena-B 261
Launch siteVandenberg LC-1 launch pad 75-3-5
End of mission
Decay date20 April 1962 (1962-04-21)
Orbital parameters
Reference systemGeocentric
RegimeLow Earth
Perigee altitude243 kilometers (151 mi)
Apogee altitude1,026 kilometers (638 mi)
Inclination80.7 degrees
Period97.4 minutes
← RM-1
The launch of Discoverer 21
The launch of Discoverer 21

Discoverer 21, also known as RM-2, was an American satellite which was launched in 1961. It was a technology demonstration spacecraft, based on an Agena-B.[1]

The launch of Discoverer 21 occurred at 22:58 UTC on 18 February 1961. A Thor DM-21 Agena-B rocket was used, flying from launch pad 75-3-5 at the Vandenberg Air Force Base.[2] Upon successfully reaching orbit, it was assigned the Harvard designation 1961 Zeta 1.

Discoverer 21 was operated in a low Earth orbit, with a perigee of 243 kilometres (151 mi), an apogee of 1,026 kilometres (638 mi), 80.7 degrees of inclination, and a period of 97.4 minutes.[3] The satellite had a mass of 1,110 kilograms (2,450 lb),[4] and was used to demonstrate an engine restart,[5] and to test infrared sensors for the Midas programme.[4] It remained in orbit until 20 April 1962,[3] when it decayed and reentered the atmosphere.


  1. ^ Krebs, Gunter. "RM 1, 2 (Discoverer 19, 21)". Gunter's Space Page. Retrieved 30 June 2010.
  2. ^ McDowell, Jonathan. "Launch Log". Jonathan's Space Page. Retrieved 30 June 2010.
  3. ^ a b McDowell, Jonathan. "Satellite Catalog". Jonathan's Space Page. Retrieved 30 June 2010.
  4. ^ a b Wade, Mark. "Midas". Encyclopedia Astronautica. Archived from the original on 20 November 2010. Retrieved 30 June 2010.
  5. ^ "Discoverer 21". NSSDC Master Catalog. NASA. Retrieved 30 June 2010.

This page was last edited on 24 October 2020, at 14:26
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