Telstar 2, primarily a communications satellite, carried an experiment designed to measure the energetic proton and electron distribution in the Van Allen belts. The spacecraft spin axis shortly after launch was about 80 deg to the ecliptic plane. The initial spin rate was 180 rpm, and it varied slowly over the life of the spacecraft. Telstar 2 was essentially identical to the Telstar 1 satellite. It employed two transmitters, and data were telemetered via a PCM/FM/AM encoder. The telemetry sequence required about 1 min. Telstar 2 differed from Telstar 1 by employing provisions for scientific information to be transmitted in real time via the microwave telemetry system so that telemetry could be obtained after the 2-yr timer had turned off the VHF beacon. On May 16, 1965, at 1403 UT, during the satellite's 4736 orbit, the VHF transmitter was turned off. All systems operated normally until that time.