The MRO does not need replacement. The cameras aboard the MRO are equipped with CCD image sensors providing resolution of up to 1.5 m per pixel from about 300 km up. They are state of the art even today, with 800 megapixel and 160 megapixel cameras. They, in combination with the ESA Mars Express orbiter, have more than satisfied the need to map and examine the surface. What we do need to do is to rethink any future rover missions. All the rovers placed on Mars to date have in total traveled no more than just over 100 km. That seems like a huge expense when seen in that light. Now, we need to send a low altitude Helium-filled dirigible equipped with gigapixel cameras into the Martian atmosphere. We know where to send it.

All the rovers placed on Mars to date have in total traveled no more than just over 100 km. That seems like a huge expense when seen in that light.

If the science objective was to leave tracks over all the surface, I guess we've failed.

Now, we need to send a low altitude Helium-filled dirigible equipped with gigapixel cameras into the Martian atmosphere. We know where to send it.

WE don't know where to send it. Or rather we, as a whole, would not agree. Speaking only for myself (as should you), I'd rather leave that up to scientists who have the background, experience, and are recognized as experts in the field.

Ditto on the greater subject of remote sensing - what we should like to sense, to measure. It's not all about taking pictures. As you well know.

It's mostly about taking pictures. We need to get closer to [search Google Earth->View->Explore->Mars: 6°54'25.50"S 75°16'20.62"W] and we need to get closer to 31° 3'45.81"S 74°15'30.68"E, but we need to stay away from 79°54'8.61"N 166°52'24.37"W, because that may have been one of the deliverers of the Black Death from back in the 14th century.. lots of sightings of UFOs trailing the deadly mists behind them everywhere there was plague.