OSCAR IV was the fourth amateur radio satellite launched by Project OSCAR and the first targeted for Geostationary orbit on 12 December 1965. The satellite was launched piggyback with three United States Air Force satellites on a Titan IIIC launch vehicle. Due to a booster failure, OSCAR 4 was placed in an unplanned and largely unusable Geostationary transfer orbit.

OSCAR 3 is the third amateur radio satellite launched by Project OSCAR into Low Earth Orbit. OSCAR 3 was launched March 9, 1965 by a Thor-DM21 Agena D launcher from Vandenberg Air Force Base, Lompoc, California. The satellite, massing 15 kg (33 lb), was launched piggyback with seven United States Air Force satellites. Though the satellite's active life was limited to sixteen days due to battery failure, OSCAR 3 relayed 176 messages from 98 stations in North America and Europe during its 274 orbit life-time -- the first amateur satellite to relay signals from Earth. As of 2023, it is still in orbit.