Discoverer 21

 1961-006

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The Flight 21 MIDAS-support radiometric mission, RM-2, was the first to demonstrate in-orbit restart of the Agena engine. At the end of the first orbit on 1961 Feb 18, the Agena B restarted for a 1 s burn to raise the orbit from 204 x 727 km to 256 x 1062 km. This capability was needed to allow retargeting of the ground track on multi-day missions; the more powerful engine was also needed for the higher orbit ARGON missions. Planned parameters had been lower: initial orbit 209 x 537 km x 81.8 deg, final orbit 227 x 791 km.

RM-2 carried a Midas radiometer payload to obtain background data in CO2 and H20 bands. It returned data for 6 stable orbits.

CORONA 21 (RM-2)
Date	Time	Event	Orbit
1961 Feb 18	2258	Launch by Thor Agena B	V 75-3-5
	2300	Thor MECO (T+2:42)
	2300	Thor VECO (T+2:52)
	2301	Thor sep (T+3:05)
	2302	Agena burn (T+4:00)
	2306	Agena cutoff (T+8:01)	204 x 727 x 80.7 (VCR)
1961 Feb 18	2358		97.78 239 x 1068 x 80.7
1961 Feb 19	0035?	Agena B restart	256 x 1062 x 80.7 (VCR)
1961 Feb 19			97.8 240 x 1069 x 80.7 (RAE)
1961 Feb 20		End of ops?
1961 Feb 22	0752		97.75 243 x 1059 x 80.7
1961 Mar 5	0428		97.59 243 x 1043 x 80.7
1961 Jun 7	1333		96.52 248 x 935 x 80.7
1961 Dec 17	1200		93.49 239 x 649 x 80.7 (RAE)
1962 Jan 4	0015		93.09 234 x 617 x 80.7
1962 Feb?			91.3 212 x 458 x 80.6 (SATCAT)
1962 Mar 22	2239		90.99 214 x 432 x 80.6
1962 Apr 9	1900		90.19 212 x 344 x 80.6 (RAE)
1962 Apr 18	1147		89.30 204 x 275 x 80.63
1962 Apr 20	2130??	Reentered