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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

Eric Urban
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  • 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. – user19742 Jun 18 '17 at 22:53
  • Relevant link https://sbir.gsfc.nasa.gov/sites/default/files/450-SNUG_V10.pdf – Tristan Jun 19 '17 at 00:12
  • This excellent answer discusses moving directional antennas in LEO that talk to TDRS. They are on the ISS. It also links to this video: https://youtu.be/PJzjs4EI22k – uhoh Jun 19 '17 at 04:04
  • You should look at the pictures of the Wikipedia article, especially this https://en.wikipedia.org/wiki/File:TDRS_gen2.jpg
    Three directional antennas in two different directions, probable even three directions possible.     – Uwe Jun 19 '17 at 08:33

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