Space Communications

Here I am balancing one seriously high gain antenna on my head - the 70m steerable dish at Goldstone, California, used by JPL's Deep Space Network for communications with deep space probes like Galileo, Voyager and Pioneer.

This antenna was originally 64m in diameter. In the 1980s, it was upgraded at considerable expense to 70m to support Voyager at the outer planets. The increase in gain at X-band (8 Ghz) was about 2 dB. This was worth it to JPL because they had already milked as much as they could out of low noise preamps, efficient modulation and coding schemes, etc.

If you're into deep space communications, be sure to check out the JPL Deep Space Network pages.

I've written a software demodulator for the low-rate telemetry signal from the Advanced Composition Explorer spacecraft.

The NASA Technical Reports Server has a remarkable amount of information on a wide range of topics, including communications. Here are two very comprehensive handbooks on microwave propagation:

Here is a page with two figures scanned from NASA SP-419 that show the freespace and terrestrial microwave windows.

Here is an informal Mars Pathfinder X-band downlink budget I worked up.

Robotic planetary exploration is one government project that I don't mind supporting with my tax money. Not only is it fully worth it for the basic science alone, but the technological spinoffs in robotics, imaging, computing and especially in communications have been profound. For example, the need to communicate reliably across the vast distances between Earth and the outer planets prompted JPL to devise the concatenated Reed-Solomon/Viterbi coding technique first used by Voyager 2 at Uranus in 1986. Now the same technique is used, with only minor parameter changes, in millions of small direct broadcast digital satellite receivers for Direct TV, Primestar and EchoStar.

The "bang for the buck" of the robotic space program, both in scientific results and in technological spinoffs, vastly exceeds that of the manned space program. Keep that in mind the next time Congress cancels yet another planetary mission and shovels the money into the growing black hole of the Space Station.