A Turns on traveling-wave tube filament voltage B Turns on traveling-wave tube helix and collector voltages; energizes all transistor circuits associated with communications experiments AA Turns off traveling-wave tube helix, collector, and filament voltages; de-energizes transistor circuits C Turns on traveling-wave tube by applying anode voltage CC Turns off traveling-wave tube anode voltage D Turns on telemetry and energizes radiation experiment circuits DD Turns off telemetry and de-energizes radiation experiment circuits E Turns on current in orientation torque coil EE Turns off current in orientation torque coil F Connects telemetry encoder No. 1 to circuit FF Connects telemetry encoder No. 2 to circuit SS Performs duties of AA, CC, DD, EE, and FF; de-energizes 136-mc beacon transmitter and removes all load from storage battery S Connects storage battery back into the circuit and energizes the 136-mc beacon transmitter T1 Turns off command receiver and decoder No. 2 for 15 seconds, so that command receiver and decoder No. 1 can be tested T2 Turns off command receiver and decoder No. 1 so that No. 2 can be tested [Illustration: _This block diagram of Telstar I’s command circuit shows the redundant receiver and decoder chains, No. 1 and No. 2, which are fed the command signals from the ground that are picked up by the VHF antenna. Decoded instructions go to the command switching control, which operates relays to turn equipment on or off. Reports on the operation of this control are sent back by telemetry to the ground station along with information from the satellite’s sensors._] VHF antenna diplexer command receiver No. 1 command decoder No. 1 T1 command command receiver No. 2 command decoder No. 2 T2 command command switching control (operates relays) S-SS relay D-DD relay other relays 136-mc beacon transmitter SS open S close telemetry DD open SS open D close sensors (radiation detectors, particle counters, solar aspect cells, thermistors, etc.) power supply solar cell power plant storage battery power plant SS open S close through other relays to communications circuits and orientation torque coil What Went Wrong With Telstar I