[jryle70]

Stupid question in general. Given how long it takes for a spacecraft's signal to reach earth, I suppose we can use the time difference to calculate the distance from a spacecraft such as New Horizon to earth. But how do we know its exact location at any given moment? What are the equivalence of GPS and cell towers in space?

[travelton]

Don't have all the answers, but last night, on the webcast, they were explaining that the spacecraft uses the stars for navigation [1].

In addition, instead of wasting valuable power for radio transmission, they send a simple tone back to Earth [2]. With that, they can determine if various events were successful (tones are sent at specific event times), also calculate the changes in speed/rotation using doppler shifts from the "tones" [3] (validating the engine fired, current spin, etc)

[1] https://solarsystem.nasa.gov/basics/bsf13-1.php

[2] https://spaceflightnow.com/2016/06/30/juno-switched-to-autop...

[3] https://solarsystem.nasa.gov/basics/bsf6-4.php

[mturmon]

Because so many constraints are needed (position, pose, velocity) there is no simple single answer. Here is a summary -- https://solarsystem.nasa.gov/basics/bsf13-1.php

Skip down to "Navigation Data Aquisition"

[greeneggs]

This story partially addresses your question. It doesn't have enough details.

http://www.npr.org/2016/07/03/484259562/star-trackers-help-j...