Thanks everone for the reactions.
To begin with the last one from Ark. Don't despair, the problem is not so much in making the mesh once you know the drill, but in finding the right images to make the textures. The one's I use come from Mars Express as it makes color pictures of large objects (50 km or more). Downside is that the opinion of Mars scientists of what is a useful picture is not the same as mine. (only half a crater, small details, too oblique, no colour, false color is ok, I can change that, different lighting conditions on composite pictures). Different needs I suppose. The positive side is there are still coming in new ones. For Gale crater the general view came in 6-11-2012 on
http://mars.jpl.nasa.gov/multimedia/images/
One can allways use ones imagination, Jtiberius for instance did a great job on Vallis Dao with a small mesh inside.
Making the mesh is simple. The data comes from Mars Global Surveor MOLA Laser altimeter (1999-2006) mapping the whole surface of Mars with 128px/degree with height info. Look for 3Dem as tool to convert to .dem or .ter file. Convert .dem with FW-tools, Gdal_translate to grayscale height map and import in Blender as heightmap. Export with io-orbiter-mesh plugin (
http://orbiter-forum.com/showthread.php?p=373330#post373330)
For .ter import in Terragen and export as .lwo lightwave or use For-export-only plugin to export as .3ds. Import in Blender or Gmax (non commercial free version of 3D Max, as they can handle large 1000 km meshes, which Blender can't do very well, but you can allways downscale and upscale).
This appproach gives the mesh immediately with the right size.
Reduce the vertices by 90 percent if you do not want half a million faces, do some uv-mapping with the texture of your choice and export as .msh (see the link above)
As for the rover, I hope someone else will step in. For now I would suggest taking the Spirit or Opportunity rover, blow them up to the right size, remove those little nice wings and replace it with a thermonuclear battery for power. All the animations are there, the robotic arms, the camera, and race into unknown territory, don't stop too often for rocks who seem to appear interesting, go straight to the top of the mountain and admire the view. (
http://www.orbithangar.com/searchid.php?ID=3955http://, for further info).
Note. It's a pity meshland does not work in Orbiter 2010, but it does so in the 2006 version. Dumbo2007 is working on a new collision detection model for Orbiter though.(
http://www.orbiter-forum.com/showthread.php?p=371775&postcount=7). I hope this will be an answer to the wish of Mattyv (and many others).
About the rocks. I think I've seen somewhere (AMSO) on the moon some display of random rocks on one of the Appollo missions, the first landing. Not sure though. But if you supply the generator I will supply some rocks. Could be fun, some of them will sink in the Martian sand.