OV1-20 carried two experiments -- an energetic (above 70 MeV) proton analyzer and a particle energy and thermal flux detector for measuring the electron density and temperature in the upper ionosphere. In addition, the satellite served as the launching platform for the OAR 901 spacecraft (Cannon Ball 2). OV1-20 was cylindrical in shape, measuring 2.13 m in length and .6 m in diameter. A plasma probe was mounted on an approximately 1.5-m-long boom that protruded from the center of the vehicle. The spacecraft's electrical systems included a 136.740-mHz telemetry transmitter, a signal conditioner, a PCM multiplexer encoder, an s-band transmitter, and a c-bane transponder. Electrical power for the spacecraft and the experiments was provided by two silver-zinc batteries. To conserve power, the experiment operating sequence was controlled by an onboard timer. Only real-time data were transmitted, which limited the data acquisition to south-to-north passes between 65 deg S and 65 deg N latitude. The spacecraft performed normally after launch. All data acquisition activities were terminated on August 16, 1971, when the spacecraft's battery power pack became depleted. OV1-20 reentered the earth's atmosphere on August 28, 1971.

OV1-21 was one of two OV spacecraft simultaneously placed into orbit from a single launch vehicle. It carried two known experiments -- a velocity mass spectrometer that measured ion densities composition and temperature, and a VLF experiment that consisted of two 18.3-m-long ELF/VLF dipole antennas and a transceiver that operated in 14 narrow bands and one broad band. The satellite also served as a launching platform for eight spherical research satellites (71-067D through 71-067K). OV1-21 was cylindrical in shape measuring approximately 2 m in length and 0.6 m in diameter.