As shown on pages 32 and 33, the operation of the Telstar I satellite
was controlled by orders sent from the ground on a frequency of 123
megacycles. Fifteen different commands could be given to the satellite,
each a coded signal made up of a series of ones and zeros. The signals,
as you can see in the _table below_, turn on or off the radiation
experiments, the telemetry, the communications equipment, and the
orientation coil. These are important functions, and we wanted them to
be going on when they were needed. But we did not want them to be
operating continuously.
Command was the only Telstar I function that we felt had to be
“redundant,” so two duplicate chains of components were provided. As you
can see in _the block diagram on the next page_, the satellite has two
radio receivers in parallel, so that one can operate if the other fails.
There are also two command decoders, which take the pulse-coded signals
from the receivers and translate their zeros and ones into usable
instructions. In the command switching control, these instructions
operate nine relays that turn on or off the power to all the electronic
circuits except the command receiving chain, which operates
continuously.
Telstar I’s telemetry unit reported back 112 measurements every minute
over the 136-megacycle frequency. These told both what the satellite
encountered in space and the condition of the satellite’s own
components—as indicated by a variety of different sensors. The telemetry
also gave a check on whether the commands sent to the satellite were
actually obeyed.