Has NASA given any thought to sending a geosynchronous orbiting telecommunications spacecraft to Mars?
With Mars' rotation period just slightly over 24 hours, geosynchronous altitude would be only slightly
higher than the 22,000 miles it is for Earth. If you position it directly over, say, an MSL-type rover ten or
so years from now, you could have near-continuous high data rate transmission to Earth. Probably not
continuous because Mars would block transmission to Earth some of the time, but more than 12 hours
a day because of the altitude.

Admittedly, you couldn't do high-resolution orbital science with such a spacecraft, but you could
probably do some useful particles and fields measurtements. Yeah, you would need three or four such
spacecraft to cover all of Mars, but to start with, one spacecraft dedicated to one high data producing
rover would do.

There has certainly been thought given to such a satellite (whose orbit would be close to that of Deimos, but not so close as to risk a collision) The general feeling has been that we simply don't need that many Mars comsats yet -- thus the initial plan to have only one Mars Telecom Orbiter in a high-altitude but non-synchronous orbit allowing it to cover as much of the total surface of Mars as possible. Now it's been deided that we won't even need that for a couple of decades.

...but if you have 2 rovers on both sides of the planet, 1 stationary telecom satellite is not enough. Probably best to have one that comes over a few times each sol.

You're also subject to the dear ol' inverse square law with a higher altitude ComSat - a more moderate altitude means far smaller antennae on the spacecraft at both ends of the link and or/higher signal strength. Perhaps some variation on a Molniya orbit would be worth considering, with a series of satellites gathering data at different times - or a polar-orbiter, with orbital parameters timed to pass over the terminator. Presumably NetLander-class spacecraft will, in any case, have relatively slight amounts of data to return anyway...

Bob Shaw

The correct term is Areosynchronous but what you really want is an Areostationary orbit (an equatorial, prograde areosynchronous orbit). On Mars that is at an altitude of ~17000km, vs ~37.000km for Earth. It's lower on Mars even though the Martian day is longer because Martian gravity is lower. Deimos orbits only 3000km higher up so even though a collision is not a risk it is still close enough to be a potential problem due to its proximity. Tony Dunn, the author of Gravity Simulator, has tested this and it seems that it's unlikely to be a problem.

NASA has had plans for this in the past with the MARSats concept but that seems to be no longer under active consideration. The current plans for the Mars Science and Telecommunications Orbiter (MSTO) have a 2011\2013 launch timeframe however that will not be areostationary - I don't have any information on what orbit is being planned for it but I think it will be similar to that used by existing orbiters since that provides a thorough global surface mapping capability (elliptical sun synchronous polar orbits).

For global coverage, three satellites in Molniya orbits might be fine. As an example, here is a plot of the orbits of Molniya-2, 3 and 4. There orbits optimized for coverage over the Soviet Union of course.

Click to view attachment

Only two should be required

The process by which a 4450-km altitude Sun-synchronous orbit (which requires a retrograde inclination of 130 degrees) was picked as the optimal orbit for the Mars Telecom Orbiter is described in http://trs-new.jpl.nasa.gov/dspace/bitstre...2/1/02-1120.pdf (at a time when Italy was still supposed to be involved in the project and it was therefore called the Marconi Orbiter).