# A Orbit estimation

1. Mar 5, 2017

### AT36

Suppose I have to determine position and velocity of spacecraft from Range and Doppler measurements. Does range measurement only give position estimate and doppler only velocity estimate? Or range can give both position and velocity?How are they related?

2. Mar 6, 2017

### Staff: Mentor

There is no realistic measurement method that would give only distance ("range") or only velocity, but some measurements will have a much higher precision for one of those values.
If you emit a short signal and measure the time when it comes back, you mainly get a distance estimate. You know that the frequency is still in your detector range, so you also get some speed estimate.
If you emit a long signal with a well-defined frequency and measure the reflected frequency, you mainly get a speed estimate. You know when approximately the response came back, so you also get some distance estimate.

3. Mar 6, 2017

### snorkack

Obviously if you measure Doppler shift of something emitted at a known frequency, but unknown time and intensity, then what you get is just velocity, without distance.

4. Mar 27, 2017

### Jenab2

There are designer waveforms for radar that can give reasonably good estimates for both range and doppler. One of them is the spike-and-tail that comes from a laser pulse naturally. Then there's linear chirp and quadratic chirp, for which the waveform frequency changes with time across the pulse. And there's sequential pulse waveforms of various kinds (stutter). The potential for good estimations for range and radial speed are found from Fourier analysis.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted