| Mission type | Optical reconnaissance |
|---|---|
| Operator | US Air Force/NRO |
| Mission duration | Failed to orbit |
| Spacecraft properties | |
| Spacecraft type | KH-5 Argon |
| Bus | Agena-B |
| Manufacturer | Lockheed |
| Launch mass | 1,150 kilograms (2,540 lb) |
| Start of mission | |
| Launch date | 21 July 1961, 22:35 UTC |
| Rocket | Thor DM-21 Agena-B 322 |
| Launch site | Vandenberg LC-75-3-4 |
| Orbital parameters | |
| Reference system | Geocentric |
| Regime | Low Earth |
| Epoch | Planned |
Discoverer 27, also known as Corona 9020A, was an American area survey optical reconnaissance satellite launched in 1961, but which failed to achieve orbit. It was a KH-5 Argon satellite, based on an Agena-B. [1] It was the fourth KH-5 to be launched, the second consecutive KH-5 launch failure, and the fourth consecutive KH-5 mission failure.
A reconnaissance satellite or intelligence satellite is an Earth observation satellite or communications satellite deployed for military or intelligence applications.
KH-5 ARGON was a series of reconnaissance satellites produced by the United States from February 1961 to August 1964. The KH-5 operated similarly to the Corona series of satellites, as it ejected a canister of photographic film. At least 12 missions were attempted, but at least 7 resulted in failure. The satellite was manufactured by Lockheed. Launches used Thor-Agena rockets flying from Vandenberg Air Force Base, with the payload being integrated into the Agena.
The RM-81 Agena was an American rocket upper stage and satellite bus which was developed by Lockheed initially for the canceled WS-117L reconnaissance satellite program. Following the split-up of WS-117L into SAMOS and Corona for image intelligence, and MIDAS for early warning, the Agena was later used as an upper stage, and an integrated component, for several programs, including Corona reconnaissance satellites and the Agena Target Vehicle used to demonstrate rendezvous and docking during Project Gemini. It was used as an upper stage on the Atlas, Thor, Thorad and Titan IIIB rockets, and considered for others including the Space Shuttle and Atlas V. A total of 365 Agena rockets were launched between February 28, 1959 and February 1987. Only 33 Agenas carried NASA payloads and the vast majority were for DoD programs.
The launch of Discoverer 27 occurred at 22:35 UTC on 21 July 1961. A Thor DM-21 Agena-B rocket was used, flying from Launch Complex 75-3-4 at the Vandenberg Air Force Base. [2] The booster began exhibiting abnormal pitch gyrations within seconds of liftoff, which worsened during flight and eventually exceeded its design limits. At T+59 seconds, the Agena disintegrated due to either structural loads or inadvertent activation of the range safety destruct charges. The Thor's engine shut down due to loss of electrical power caused by damage to the forward section of the vehicle. Twenty seconds later, the Thor exploded and all telemetry data ceased, although the telemetry transmitter continued operating until 300 seconds after launch, likely at the point where water impact occurred. Range Safety issued the destruct command at T+94 seconds, but only as a formality and there was no indication that it did anything.
Thor-Agena was a series of orbital launch vehicles. The rockets used Thor first stages and Agena second stages. They are thus cousins of the more-famous Thor-Deltas, which founded the Delta rocket family. The first attempted launch of a Thor-Agena was in January 1959. The first successful launch was on February 28, 1959, launching Discoverer 1.
Vandenberg Air Force Base is a United States Air Force Base 9.2 miles (14.8 km) northwest of Lompoc, California. It is under the jurisdiction of the 30th Space Wing, Air Force Space Command (AFSPC).
The failure was traced to an open circuit in the guidance programmer.
Discoverer 27 was designed to operate in a low Earth orbit, and had a mass of 1,150 kilograms (2,540 lb). [3] It was equipped with a frame camera with a focal length of 76 millimetres (3.0 in), which had a maximum resolution of 140 metres (460 ft). [4] The camera would have recorded images onto 127-millimeter (5.0 in) film, which would have been returned in a Satellite Recovery Vehicle, before the satellite ceased operations. The Satellite Recovery Vehicle carried by Discoverer 27 was SRV-524. [3]
A Low Earth Orbit (LEO) is an Earth-centered orbit with an altitude of 2,000 km (1,200 mi) or less, or with at least 11.25 periods per day and an eccentricity less than 0.25. Most of the manmade objects in space are in LEO. A histogram of the mean motion of the cataloged objects shows that the number of objects drops significantly beyond 11.25.
The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated (parallel) rays are brought to a focus. A system with a shorter focal length has greater optical power than one with a long focal length; that is, it bends the rays more sharply, bringing them to a focus in a shorter distance.
