"Henry" == Henry Spencer writes:

Henry The dominant method is radio tracking -- radar, but with the
Henry assistance of the probe to repeat the signal back. (Normal
Henry radar is useless for such small objects at such distances.)
Henry Round-trip time gives range, and Doppler shift gives range rate
Henry (velocity along the probe-Earth line); these can both be
Henry measured extremely accurately. More subtly, the *change* in
Henry Doppler shift as the Earth rotates can be used to determine
Henry direction, although not as accurately. These measurements are
Henry combined using a sophisticated estimating process that looks at
Henry how the measurements *should* be changing for a given
Henry trajectory, and solves simultaneously for the most likely probe
Henry position/velocity and the most likely values of other
Henry parameters (masses of planets, errors in measurements, etc.).

This was a great help, but now that we have more and more deep space
probes, and with the DSN network starting to get overloaded, how would
you make it easier to send probes so that they can do more of their
own navigation work?

Would it help to put some sort of navigation beacon on the surface of
the target planet/moon? Something that the approaching probe could
use for it's own orbital insertion maneuvers?

It seems that MCO could have used some way of measuring it's distance
from Mars more accurately, not just the measurement of it's vector in
comparision to Earth.

Now that we have a bunch of orbiters, would it be cost effective to
have some sort of small beacon put onto them so that they can help
other approaches?

John