RM 2 (Discoverer 21)

RM 1 and 2, part of the Corona program, served as test platforms for instruments related to the MIDAS early warning satellite program, unlike typical reconnaissance satellites. They lacked return capsules and transmitted data via radio telemetry. Integrated with the Agena-B upper stage, they carried radiometers to characterize background infrared radiation for MIDAS calibration, with RM 2 also testing Agena engine reignition.