Further if you're not looking for realtime direction finding and you're willing to wait a few minutes for a fix, you can get away with far fewer satellites.

Putting 6 small satellites in orbit and getting position fixes every hour would still be way better than nothing.

How would the satellites themselves maintain their proper positions relative to Mars, without ground stations to orient against?

We already stipulated that we're landing something on the surface. That could include a stationary transmitter, which satellites could use to periodically update their location and velocity.

Yeah, agreed, my comment was meant to politely point out the necessity to the people thinking we could get away with "dropping a few satellites" ;)

All of these things can be done remotely without any wetware on Mars.

"How?"

Like we do everything on and around Mars now.

Neutron stars -- http://www.nasa.gov/topics/universe/features/zombie-stars-si...