From 8-1/3 bits/s to 100,000 bits/s in ten years

During the first 11 years of its planetary program, the United States sent seven spacecraft to explore the inner planets: Venus, Mars, and Mercury. At the beginning of this period, the telemetry data rate was 8-1/3 bits/s; by the end of the period it was 120 kbits/s, a more than ten-thousand-fold increase. To identify the major factors involved, the form of a deep space telemetry system is described and the values of the major factors for each of the seven spacecraft are given. The amount of the improvement in each is computed and the way in which the improvement was achieved is discussed. Finally, some possible directions for possible future improvements are suggested.