A proposed spacecraft-to-earth communications link: The unified carrier approach

This paper documents the design and performance of a proposed unified carrier, range-tracking, and communications system for cislunar ranges in which phase-locked loop techniques are used in the spacecraft to relate received and transmitted carriers coherently. The design of the composite angle-modulated carrier waveform for the spacecraft-to-ground link has been accomplished by using a statistical method of waveform design. The pseudonoise ranging code is biphase; telemetry is pulse-code modulated (PCM); and voice is frequency modulated (FM). The “best” selection of modulation parameters and frequency locations for the various functions has been determined by a method of successive iteration. The unified carrier system has been tested for a simulated lunar mission for spacecraft velocities of 36,000 ft/sec (feet per second), and the results indicate that the statistical method of waveform design used is practical for this case.