Project Relay Digital Command System

The National Aeronautics and Space Agency (NASA) has developed a coded message sequence consisting of discrete, pulse-duration-modulated (PDM) tone bursts for commanding satellites. The message consists of a sync pulse followed by some combination of six pulses, three each of zeros and ones. This code allows for 20 commands (the combination of six things taken three at a time). This paper describes an equipment developed for the Relay satellite program which demodulates the tone bursts, converts the pulse-duration modulation into a binary code, and then decodes the message into twenty discrete commands. The demodulation and PDM-to-binary code conversion functions are accomplished by conventional transistorized circuitry which is described in a general manner. The circuitry for converting the code into command pulses is a novel utilization of magnetic circuitry and is described in detail. Magnetic cores are used to provide a shift register function and in addition perform the decoding, thus eliminating the conventional diode matrix usually employed for this function. A summary of the physical and electrical characteristics of the finished equipment is presented.