|Mission type||Optical reconnaissance|
|Operator||US Air Force/NRO|
|Harvard designation||1961 Alpha Beta 1|
|Mission duration||2 days|
|Spacecraft type||KH-3 Corona'''|
|Launch mass||1,150 kilograms (2,540 lb)|
|Start of mission|
|Launch date||17 September 1961, 21:00UTC|
|Rocket||Thor DM-21 Agena-B 324|
|Launch site||Vandenberg LC-75-1-1|
|End of mission|
|Decay date||26 October 1961|
|Perigee altitude||233 kilometers (145 mi)|
|Apogee altitude||380 kilometers (240 mi)|
The launch of Discoverer 31 occurred at 21:00 UTC on 17 September 1961. A Thor DM-21 Agena-B rocket was used, flying from Launch Complex 75-1-1 at the Vandenberg Air Force Base. Upon successfully reaching orbit, it was assigned the Harvard designation 1961 Alpha Beta 1.
Discoverer 31 was operated in a low Earth orbit, with a perigee of 233 kilometres (145 mi), an apogee of 380 kilometres (240 mi), 82.7 degrees of inclination, and a period of 90.7 minutes. The satellite had a mass of 1,150 kilograms (2,540 lb), and was equipped with a panoramic camera with a focal length of 61 centimetres (24 in), which had a maximum resolution of 7.6 metres (25 ft). Images were recorded onto 70-millimeter (2.8 in) film, and were to have been returned in a Satellite Recovery Vehicle. The Satellite Recovery Vehicle carried aboard Discoverer 31 was SRV-552. During the spacecraft's thirty-third orbit, the attitude control and power systems malfunctioned, and as a result Discoverer 31 was unable to complete its mission or return images. It decayed from orbit on 26 October 1961.