How do real-life spacecraft get their orbital velocity?

[Silicon014]

What processes do real-life spacecraft (Orbiters, satellites, etc.) use to get an accurate reading of their orbital velocity and/or surface velocity. A technical explanation would be helpful! Thanks!

[lajoswinkler]

For surface velocity, I think they use radar and the Doppler effect.

[TheShadow1138]

I'm not 100% certain, but I believe that various accelerometers and radar gather what information they can to determine position and velocity relative to Earth and any acceleration the spacecraft is experiencing and then uses an algorithm known as the Kalman Filter to process the information continuously predicting the next state (position, velocity, and acceleration) of the craft and then updating the prediction each second. Through this method the guidance system can determine the orbital parameters of the spacecraft.

[Teirusu]

A number of ways, in fact:

1) On-board accelerometers/gyroscopes can semi-accurately track a spacecrafts movement through space.

2) Many deep space probes will have separate star-tracking cameras on board that they can use to further refine their velocity/orbit/direction.

3) As Lajoswinkler said, satellites closer to home we can track with radar.. to some extent. Not perfectly, but fairly accurately. Obviously, that drops off the further the satellite is from us.

4) Doppler effect can be used quite accurately, using the radio signals, to plot the orbit and velocity of a satellite. This particular one is employed when creating gravity maps of planetary bodies. This requires having an on-board clock that is fairly accurate.

[FellipeC]

Apollo had 3 systems: The primary was radar from Earth, that measured position and trajectory, then send the info to the Guidance Computer. Also there was a inertial navigation system, that used mechanical gyroscopes. And they also have a sextant connected to the guidance computer, so they can measure their position and input it again in case they lost the radio signal and the inertial system resets someway.

As far as I know, Shuttle does not have a sextant, but two star tracker cameras, that keep track of starts (and position of shuttle) automatically, in addition to inertial system and radar from Earth.

[K^2]

It amuses me greatly, whenever the subject of space navigation comes up, that we are still using, effectively, 13th century methods of navigation. The tools are more advanced, but ultimately, we are still just looking at the stars and measuring angles.

[Mr Shifty]

Well current spacecraft also use GPS for positional data, which is a step up from 13th century technology:)

[lajoswinkler]

Lots of basic info can be found here.

[magnemoe]

It amuses me greatly, whenever the subject of space navigation comes up, that we are still using, effectively, 13th century methods of navigation. The tools are more advanced, but ultimately, we are still just looking at the stars and measuring angles.

Well if you was a probe deep in space the way you would orient yourself would be to first locate the sun then rotate around the sun axis to find one and then another distinct stars.

Now you are oriented so you can locate earth by using an table to find where it is at this time and restore communications.

Getting the direction to an target like mars while knowing direction and speed from earth gives you even more accuracy.

[Technical Ben]

It amuses me greatly, whenever the subject of space navigation comes up, that we are still using, effectively, 13th century methods of navigation. The tools are more advanced, but ultimately, we are still just looking at the stars and measuring angles.

Theories come and go. Observations and mathematical truths last forever.

[K^2]

Well current spacecraft also use GPS for positional data, which is a step up from 13th century technology:)

LEO sats hardly count. You can track them from Earth, which is what they've been doing before GPS network became so much easier to use. It's like sailing along the shore and boasting that you have advanced means of navigation.

But once you leave Earth, the only way to navigate is by watching stars. That has not changed, and probably won't change for a while still.

[Mr Shifty]

LEO sats hardly count. You can track them from Earth, which is what they've been doing before GPS network became so much easier to use. It's like sailing along the shore and boasting that you have advanced means of navigation.

But once you leave Earth, the only way to navigate is by watching stars. That has not changed, and probably won't change for a while still.

Deep space probes use the Deep Space Network, in addition to celestial navigation.

http://www.scientificamerican.com/article.cfm?id=how-do-space-probes-navig

[Brotoro]

When Voyager was flying by Jupiter they were checking its position based on exactly where the edges of some Jovian moons were showing up in photos vs. where they were predicted to be. This is why one of the scientists happened to be closely examining the limb of Io in some photos and first noticed a volcanic plume jetting out of that moon.