| Discoverer 28 | |
| Mission Type: | Optical reconnaissance |
| Operator: | US Air Force/NRO |
| Mission Duration: | Failed to orbit |
| Spacecraft Type: | Corona KH-2 |
| Spacecraft Bus: | Agena-B |
| Manufacturer: | Lockheed |
| Launch Date: | UTC |
| Launch Rocket: | Thor DM-21 Agena-B 309 |
| Launch Site: | Vandenberg LC-75-1-1 |
| Orbit Epoch: | Planned |
| Orbit Reference: | Geocentric |
| Orbit Regime: | Low Earth |
| Apsis: | gee |
| Programme: | Discoverer |
| Previous Mission: | Discoverer 27 |
| Next Mission: | Discoverer 29 |
| Programme2: | Corona KH-2 |
| Previous Mission2: | Corona 9019 |
| Next Mission2: | Corona 9026 |
Discoverer 28, also known as Corona 9021, was an American optical reconnaissance satellite which was lost in a launch failure in 1961. It was the seventh of ten Corona KH-2 satellites, based on the Agena-B.[1]
The launch of Discoverer 28 occurred at 00:01 UTC on 4 August 1961. A Thor DM-21 Agena-B rocket was used, flying from Launch Complex 75-1-1 at the Vandenberg Air Force Base.[2] It failed to achieve orbit after the Agena's guidance and control system malfunctioned.[3]
Discoverer 28 was to have operated in a low Earth orbit. The satellite had a mass of,[4] and was equipped with a panoramic camera with a focal length of, which had a maximum resolution of .[5] Images were to have been recorded onto 70mm film, and returned in a Satellite Recovery Vehicle. The Satellite Recovery Vehicle carried by Discoverer 28 was SRV-512.[4]