Discoverer 28, also known as Corona 9021, was an American optical reconnaissance satellite which was lost in a launch failure in 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.

The satellite had a mass of 1,150 kilograms (2,540 lb),[5] 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).

[4] Images were to have been recorded onto 70-millimeter (2.8 in) film, and returned in a Satellite Recovery Vehicle.