I know star trackers are used in most cases for attitude determination of space craft traveling within the solar system.

But what methods are currently used for coordinate determination, i.e. the location of the craft within the solar system? If possible, please explain how they work.

  • $\begingroup$ Related: space.stackexchange.com/questions/6158/… $\endgroup$ Mar 2, 2015 at 17:49
  • $\begingroup$ Also: space.stackexchange.com/questions/2358/… $\endgroup$ Mar 2, 2015 at 17:51
  • $\begingroup$ From reading these posts and looking at a few others under navigation tag, I gather that the craft essentially beam back at Earth and measure time it takes for the signal to arrive. Is that correct? Is this is the only way currently? $\endgroup$ Mar 2, 2015 at 23:46
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    $\begingroup$ Tracking via DSN or similar is the primary method. Optical relative navigation is often used when operating in the vicinity of a target body such as an asteroid, which itself may have an imperfectly-known orbit. $\endgroup$ Mar 3, 2015 at 1:28

1 Answer 1


There is really only one method to obtain the location of the spacecraft, and this is via carefully tracking the spacecraft from the ground. Usually they determine the range by a process called, well, ranging, basically they send a ping to the spacecraft, which responds as soon as it can. The time it takes for the probe to respond determines it's exact range. If you have its range for a few time samples, and you know the gravitational constants of everything, you can determine what trajectory the spacecraft is on. This method is very good, and works well.

Other methods are usually only used if the location of the target body isn't very well known. These can include images, radar, and similar systems from the spacecraft to determine where the object is. This is because knowing the exact position of some objects can be difficult, and more accurate measurements can be made from close. However, this will only tell you where the object of interest is relative to the spacecraft. The spacecraft is determined by the ranging operation.

Very close objects can also be found via a ground based radar system.


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