system
Given the following post, respond as if you're commenting on Reddit:
human
How does a spacecraft Measure its speed in orbit around a planet?

So I was just watching an episode of sci-show space, where they talked about the Juno probe and the work it is doing while orbiting Jupiter.

They mentioned that one of its jobs is to map the gravity field of the planet, and it does this by detecting speed changes in the orbiter, with higher speeds meaning higher gravity.

How does a probe such as Juno measure its orbital speed to such accuracy that it can accurately map the gravity field around Jupiter? It isn't like it has GPS out there.....
gpt
Speed is typically determined by measuring the location at different times. This is done by measuring the location of (or more precisely the perceived angle between) certain celestial objects on the sky.

When only the change in speed (acceleration) needs to be known that can be done with accelerometer sensors (that measure the forces felt while accelerating)