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Although the exact usage of the system is classified, NASA has a system called TDRS which is used by other government agencies for relaying data to ground stations.

To maintain communications with a ground station, a satellite would be stabilized in some manner and use a directional antenna. If the satellite is in a low earth orbit, the antenna essentially just has gain in the direction towards the earth. A tracking station acquires the satellite and communicates with it while it is in view.

How do two satellites in low earth orbit establish communications. Do they use directional antennas? For a satellite in typical low earth orbit, what is the radio horizon? How do they avoid interference amongst one another?

Wikipedia link:https://en.wikipedia.org/wiki/Tracking_and_data_relay_satellite

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  • $\begingroup$ In LEO, omnidirectional antennae are usually enough unless you need very high datarates. I'd assume that satellites with directional antennae would use omnidirectional antennae to find each other's position. $\endgroup$ – Deimophobia Jun 18 '17 at 22:53
  • $\begingroup$ Relevant link sbir.gsfc.nasa.gov/sites/default/files/450-SNUG_V10.pdf $\endgroup$ – Tristan Jun 19 '17 at 0:12
  • $\begingroup$ This excellent answer discusses moving directional antennas in LEO that talk to TDRS. They are on the ISS. It also links to this video: youtu.be/PJzjs4EI22k $\endgroup$ – uhoh Jun 19 '17 at 4:04
  • $\begingroup$ You should look at the pictures of the Wikipedia article, especially this en.wikipedia.org/wiki/File:TDRS_gen2.jpg Three directional antennas in two different directions, probable even three directions possible. $\endgroup$ – Uwe Jun 19 '17 at 8:33

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