I believe with Nick, I'm preaching to the choir (correct me if I'm wrong). We really need more MER type general surveys of the Martian surface. After we have found the ultimate cherry spot, then we should send down a big expensive lander like MSL preferably using an EDL (Entry Descent and Landing) not based on Sky Crane. Our data points now are Viking I, II, Mars Pathfinder (MPF), MER-A and MER-B. The data from the floor of Gusev Crater as observed by MER-A was almost the same as observed from the Viking landers and MPF (basaltic rock with lots of olivine). The observations of MER-B was wildly different from everything else and provided evidence of an aqueous environment. Also the observations of MER-A became more interesting as it got into the hills above the floor of Gusev. In essence we have 1 1/2 in-situ data points for selecting a landing site for comprehensive study. I think we can do a lot more science with MER "as is" by stacking several landers under one aeroshell of a big booster (Atlas V). MER's EDL was ballistic entry (non-lifting, zero angle-of-attack). The MER aeroshell could be redesigned with a center-of-mass offset and RCS system like Viking's to enable a lifting entry. This would increase MER's cross range capability and make it easier to soft land with airbags at higher latitudes and higher altitudes. MER could also be redesigned with more efficient photovoltaics with a larger surface area (have extra fold out panels). The resultant vehicle would be heavier but that could be swept under the carpet by stacking three or four clones under one fairing of a single large booster. The resultant vehicles would still be cheaper than MSL and a lot easier to design and build. Maybe after we've landed 10 more MER clones on Mars, we might find that perfect spot that could justify the expense and program risk of an MSL.

Gary