In 2001, NASA invited five major aerospace firms (Ball Aerospace, Boeing, Lockheed Martin and TRW), along with JPL's "Team X" advanced mission design group, to develop their own designs for a sample return mission and estimate its cost.
The various designs of course varied widely, but all of them cost in the range of 1.5 to 2 billion dollars -- a cost that the Bush Administration indicated it finds unacceptable. Moreover, it became clear that the sheer technical difficulty of this mission, and the huge number of completely new and as-yet untested technologies it requires, would force it to be delayed to 2016 at the earliest.
A central problem is the danger of trying to plan exploration of Mars too far in advance. Since the Viking missions of the 1970s it has become increasingly clear that Mars is an extremely complex and geologically varied world. And then in the late 90s, Mars Global Surveyor began returning a flood of startling, downright revolutionary new findings about the planet that have grown to include:
Complicating matters still more, other evidence from MGS directly flies in the face of all these promising indications of significant amounts of liquid water on Mars' surface throughout its history.
Closeup photos of the famous "valley networks" show no real evidence that they were carved by surface rivers of liquid water billions of years ago, and indicate that they may be collapsed tunnels carved instead by much more limited flows of liquid water hundreds of meters below Mars' desolate surface.
And MGS' thermal IR spectrometer, intended to map Mars' surface minerals, stubbornly refuses to show any evidence of the carbonate minerals or evaporated salts one would expect from a world that ever had substantial amounts of surface liquid water, indicating that they exist at most in small amounts -- although, to complicate things still further, it HAS found strong evidence of several patches of hematite, one of them several hundred km wide, that were probably water-deposited.
In short, not only has MGS provided a revolutionary flood of new observations, but it's an embarrassing fact that we have no real understanding at all of what its often contradictory observations really mean, and whether or not Mars actually did have substantial amounts of surface liquid water capable of developing and supporting life during its ancient days (and perhaps even small local eruptions of it since then).
We simply do not yet have even a good basic understanding of the planet's geological and climate history.
This has extremely serious implications for planning the first sample return mission.
The main purpose of Mars exploration today, and the central reason as much money is spent on Mars -- as on all the rest of the Solar System put together -- is the search for evidence either that life evolved on early Mars, or that the evolution of nonliving organic compounds into living cells did proceed partway - in which case such preserved "prebiotic" remnants would provide crucial information on how life first appeared on THIS world.
But any such ancient life, if it did appear, very likely died out as much as 3 billion years ago -- and it's extremely hard to find and firmly identify any such ancient evidence of life even in the rocks of Earth. Most of the evidence that has thus far been found is still subject to serious dispute.
Such ancient biological fossil evidence may actually be preserved much better on Mars, since it lacks a whole set of factors that have destroyed almost all of it on Earth - where massive amounts of liquid water, the remelting of ancient rocks by crustal tectonic recycling, and the simple fact that the huge amounts of life that have appeared on Earth since have eaten almost all the organic remains of past life.
But each sample return mission to Mars will cost over a billion dollars -- meaning that, even at best, we'll be able to fly only one mission every four to six years -- and each such mission will return, at most, only a few kilograms of material.
This obviously means that we will still have to be extremely careful -- and extremely lucky to boot -- in our selection of the best conceivable sampling locations on its surface to have any chance whatsoever of finding any meaningful biological evidence within the ancient rock and mineral deposits that have most provably been associated with, and deposited by, large amounts of liquid water over long periods of time.
We cannot pick that tiny scattering of best possible sampling locations until we have a fairly detailed understanding of Mars' geological history. And, as I've said, as yet we do not understand even the most basic features of Mars' history -- and if the Mars missions of the next few years are anything like MGS, they will throw one astonishing surprise at us after another, forcing us to radically revise our models of the planet and its history.
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