Radio Test Spacecraft American tracking network technology satellite. Mercury-Scout 1. Small satellite was to have verified the readiness of the worldwide Mercury tracking network
TTS American tracking network technology satellite. Tested Apollo tracking network. Experimental satellite built by TRW for NASA, USA. Launched 1967 - 1971.
TETR American tracking network technology satellite. Test satellite for NASA's Manned Space Flight Network.
Molniya-Yu Russian tracking network technology satellite. Study 1969. This was a modification of the Molniya-1 satellite to test deep space radio-based tracking methods for the Soviet Lunar program.