The first Oscar Phase I amateur satellite was launched piggyback with Discover 36. A group of enthusiasts in California formed Project OSCAR and persuaded the United States Air Force to replace ballast on the Agena upper stage with the 4.5 kg OSCAR I package. The satellite was box shaped with a single monopole antenna and battery powered. The 140 mW transmitter onboard discharged its batteries after three weeks. 570 Amateurs in 28 countries reported receiving its simple 'HI-HI' morse code signals on the VHF 2 meter band (144.983 MHz) until January 1, 1962. The speed of the HI-HI message was controlled by a temperature sensor inside the spacecraft. OSCAR I re-entered the atmosphere January 31, 1962 after 312 revolutions.

The observations provided important information on radio propagation through the ionosphere, the spacecraft's orbit and thermal satellite design. The OSCAR I mission clearly demonstrated that amateurs are capable of (1) designing and constructing reliable spacecraft, (2) tracking satellites and (3) collecting and processing related scientific and engineering information. OSCAR I led to the creation of The Amateur Satellite Corporation (AMSAT) in 1969.