"Such results [from analysis of a Mars sample returned to Earth] are most meaningful when understood in the context of global data sets that can only be provided by extensive orbital and in-situ landed missions... By the end of approximately 2011, we will have a wealth of high-resolution photographic and global chemical and mineralogical data for the surface of Mars, but we still will not really understand the temporal geologic, atmospheric, or hydrologic evolution of Mars. We will be ready to bring back samples of Mars' rocks, regolith, and atmosphere for analyses in order to formulate informed hypotheses about Martian processes and evolution."

And so super-detailed study of Martian material from one spot on Mars -- as compared to observations of the same region by in-situ instruments on landers and orbiters -- will provide a "ground truth" benchmark, giving us much more confidence that we are coming up with correct scientific interpretations of the data obtained by such cameras and instruments at the other parts of Mars where they indicate that the surface makeup and geological structures are different from those at the returned-sample site.

"Global exploration of Mars will necessarily be done by remote sensing means, especially from orbit. Experience from exploration of Earth's moon has demonstrated that proper interpretation of remote sensing data must be accompanied by the kind of detailed knowledge of lunar rocks and fines that was obtained by laboratory analysis of the Apollo and [Soviet] Luna materials. Conversely, the remote sensing data sets provided by the Clementine and Lunar Prospector missions put the Apollo and Luna mission samples in a global context...

"Whereas the Apollo experience [in returning lunar samples for study] demonstrated that regolith from almost anywhere on an ancient planetary surface will contain interesting lithologies that bear on a wide range of planetary evolution questions, the search for possible ancient microbial life demands more carefully targeted samples...

"A key step in deciding where to go for the more targeted [later] astrobiology [Mars sample-return] missions is to obtain basic representative samples of Martian lithologies, in order to begin to understand Martian rock/hydrosphere and rock/atmosphere interactions -- essential to understand Martian climate and habitability.

"These first samples will almost certainly not contain information about past or present life, but they will tell us a great deal about the Martian environment and its habitability... In short, the first MSR [Mars Sample Return] mission will enable later, more targeted missions aimed at astrobiology.

"Because the existing body of knowledge of Martian materials is so small, all samples collected by the groundbreaking first sample return mission will have a clear and disproportionate influence on planning for the targeting and instrumentation of subsequent MSR and in situ landed missions."

Very well; if we don't necessarily need to hunt specifically for biological trace evidence on the very first Mars sample return mission, is it necessary -- or cost-effective -- for that mission to include that kilometer-range sample-collecting rover? The MEPAG subgroup concluded that, all in all, it is not.

The same four aerospace firms, and JPL's Team X, were ordered early this year to do comparative studies of the cost of a simplified "Groundbreaking MSR" mission, in which the sample-collecting rover was not carried, and the sampling lander simply collected half a kilogram of pebbles, soil and atmosphere from its own immediate vicinity using a 2-meter-long arm equipped with a soil scoop and a sieving rake to collect small pebbles. (Most of these would actually be bits of gravel as small as a millimeter, but a few would be as much as 2 or 3 cm across, in case the smaller fragments had been completely weathered.)

The Groundbreaker would be flown on another copy of the Smart Lander, with the same ability to land precisely at a scientifically good spot as chosen by data from the earlier missions. But, this time, there would be more emphasis on trying to find a spot -- such as an outflow plain -- where still-distinguishable materials from several different types of Martian geological terrain are mixed together, since this mission's purpose is to do detailed study of the planet as a whole.

The only crucial point is that it must land in an area where there's strong evidence of some water-modified rocks. Groundbreaker -- unlike the MGE rover -- may well be solar-powered, limiting its landing site to lower latitudes.

The subgroup considered having Groundbreaker land near the earlier MGE rover and have that rover deliver its own carefully pre-collected cache of samples to the Groundbreaker lander itself, but finally concluded that the total cost and complexity of such a combined mission would be too high this time -- although this team-up of long-range rover and separate sample-return lander may well be a promising technique for later Mars exploration.

Groundbreaker's arm would dig no more than 20 centimeters below the surface, and its only on-board analytical instruments would be a multi-spectral camera to inspect the digging operations and locate interesting-looking pebbles, and a similar camera located on the end of the arm for detailed closeups of possible samples. All the samples would be dumped together into a single container. The lander might be optionally enlarged with a meter-long drill for a separate subsurface soil sample, and a separate sealed container for a sample of Mars air (since the Martian air in the main sample container would get mixed with volatiles evaporating from the rest of that sample).

After the lander had been on the surface for only a few weeks (as opposed to several months for the more complex sample-return mission), it would launch the sample into Mars orbit, and the rest of the mission would go just as with the more complex mission -- but the comparative cost studies by the five groups indicated that this stripped-down, roverless sample return mission would probably cost only under $1.5 billion, - up to $500 million less than the version with a rover and a larger set of in-situ analytical instruments.

Given this lesser cost -- plus the now-recognized need to return an initial non-biological sample as quickly as possible, to provide a big chunk of the reconnaissance data needed to pick good landing sites for later biologically oriented sample-return missions -- MEPAG has now firmly decided that this "Groundbreaker" mission should be the first Mars sample return mission. With luck, it might get off the ground as early as 2013, and return the first sample of Mars to Earth labs in 2016.

The MEPAG subgroup assigned to study the worth of such a minimal sample-return mission also located one other possible though still uncertain way in which the very first sampling mission could be considerably cut in both cost and launch delay: the question of how to minimize the very slim, but not totally nonexistent, danger of returning harmful living Martian microbes to Earth.

The plan for Groundbreaker is still to limit the chances that it would "forward-contaminate" its local landing site with any Earth germs or organic compounds to less than one in a hundred, and the chance that it would accidentally "back-contaminate" Earth with Martian germs (harmless or otherwise) to less than one in a million even if such germs do exist.

But even the simplified version of the initial Mars Quarantine Facility recommended by the National Academy of Sciences in a report last year -- which would simply check out the returned samples for any evidence of current or fossil Martian life, without itself doing any more detailed scientific studies of the samples -- would be complex and expensive.

For one thing, it would have to be two-layered, combining a "biohazard facility" (whose internal air pressure is less than that outside, preventing any harmful germs from being wafted outside) with a "clean room" (whose internal pressure is higher than outside, keeping Earth dust from drifting into the building and contaminating the samples). The Academy concluded that such a facility might cost $170 million, and that its design must be begun fully seven years in advance for it to be ready in time.

For this reason, the sample-return subgroup of MEPAG states that careful consideration should be given to ways to cut the Facility's cost without actually increasing the danger of contamination at all -- such as using it to simply seal up the returned Mars samples without doing any studies of them, and then very carefully shipping some portions of the returned sample off to the country's existing Centers for Disease Control for the search for evidence of life, while recognizing that those parts of the sample would be contaminated by the CDC's studies and so would be useless for any other research.

But MEPAG says another possibility should be considered for this first, "non-biological" Mars sample mission: having the spacecraft itself sterilize the samples on the way home. Doing so by roasting them at high temperatures would disastrously alter them. But some initial studies have indicated that having the spacecraft slide the sample container into a sleeve made of radioisotopes that would bombard it with high-intensity gamma rays throughout the long journey home might very effectively destroy even the toughest conceivable living germs, while being almost completely harmless to all studies of non-organic minerals in the samples (including radioactive age-dating), and even leaving any organic material in the sample intact enough that it could still be reliably studied to see whether it was actually the remains of past or present living organisms.

Further study is needed, though, to see if in-flight sterilization by gamma rays would be scientifically acceptable for Groundbreaker. But if it is, one appraisal concludes that it could allow the Mars Quarantine Facility to be cancelled completely, and cut as much as a quarter-million dollars off the Mars program's total cost.

This might even be acceptable for later sample-return missions to biologically interesting sites -- for, if a radiation-sterilized sample from such a site did reveal evidence of fossil or present-day life, the proposed more costly and complex second sealed-off lab facility could then (and only then) be built to carefully study later non-sterilized samples from the same place on Mars. In-flight sterilization might also be immensely reassuring to the general public, since there is a real danger that public apprehension about the long-shot danger of back-contamination may turn into a serious political roadblock, fair or not, to returning any Mars samples at all.

Two of the five firms assigned to design a version of this mission came up with variations on the classic design, instead of having the Mars orbiter part of the mission (assuming that France does finally back out of the project and the U.S. has to build the orbiter itself) brake itself into Mars orbit and blast back out with a chemical rocket engine. TRW's orbiter would use 10 solar-powered ion engines to gradually spiral into orbit around Mars and then later spiral back out to send itself back to Earth. However, this would cost about an extra $200 million.

Lockheed Martin, on the other hand, didn't have the sample-retrieval spacecraft brake itself into orbit around Mars at all! Instead, this spacecraft (patterned after the Stardust comet probe) would trail the lander to Mars by several weeks and simply fly past the planet without stopping at the same time that the Groundbreaker lander launched the sample container off Mars' surface into space.

The two-stage solid-fueled Mars Ascent Vehicle, instead of just accelerating the sample container to about 14,500 km/hour to put it into low Mars orbit, would ram it to fully 22,000 km/hour so that it escaped from Mars completely -- after which the retrieval spacecraft would rendezvous and dock with it in solar orbit, and return to Earth with it one and a half solar orbits and two years later.

This would, of course, mean that the Mars Ascent Vehicle would have to be bigger and more powerful, but not greatly so (given the tiny size of the sample container that it launches) -- and it would mean that the retrieval spacecraft could completely skip the need to carry a huge supply of fuel to brake itself into and later leave orbit around Mars, vastly lowering its size, cost, and launch-vehicle cost.

It might even make the rendezvous easier, since the retrieval craft wouldn't ever have its view of the sample container blocked by the planet's horizon during its rendezvous. In fact, both the company itself and two independent review groups concluded that this mission design was about $100 million cheaper than the others.