How do the increasing number of LEO satellites keep track of their position? I know they use ground stations, but do they employ private companies to keep track for them? It seems like there are way too many satellites for the ground stations. Or are there lots of ground stations too?
Initially, when a new satellite is launched in space orbital dynamics models using launch and deployment parameters to provide an estimation of the orbit of the target satellite.
As @pearsonartphoto said on another comment, many LEO satellites do have GPS (or other GNSS systems) on-board to retrieve information on the exact position of the spacecraf,t which could then be transmitted back to Earth via a ground-station or via a ground-station network like SatNOGS.
Most satellite operations teams get their info on the position of their satellite from Space Situational Awareness Services such us SpaceTrack; I recommend checking out this overview of Space Situational Awareness Services to get some understanding of the techniques used and the information they provide to satellite operator teams.
Since nowadays many LEO satellites are routinely deployed in batches, identifying which orbital object tracked by Space Situational Awareness services corresponds to which satellite can be challenging. Satellite ground-station networks can assist identification by using doppler shift measurements across several of their ground-stations to facilitate timely identification.
There are a lot of different way the positions are tracked. Typically, some combination of the following 3 things is done to track satellites (And then using orbital dynamics to propagate things forward)
- GPS signals- Can be received, especially in LEO. A bit harder to do above the constellation (MEO or HEO).
- Space Track- Mostly US, but also other governments that are allied track the satellites and provide periodic updates to the public. This is using radars primarily, and possibly other sensors, to detect the satellites.
- Ranging- Sending a "ping" to a satellite and seeing how long it takes to respond to the signal will give you a pretty exact position. Also related is detecting the first moment a satellite can be heard, Doppler shift, and several other similar things.