SETI bioastro: The Future of Mars Exploration

From: Larry Klaes (lklaes@bbn.com)
Date: Mon Apr 17 2000 - 10:48:12 PDT


http://www.spaceviews.com/2000/04/17a.html

The Future of Mars Exploration

Published: 2000 April 17
5:40 am ET (0940 UT)

       by Bruce Moomaw
       Special to SpaceViews

       A revised Mars exploration plan may not
       be released by NASA until this fall as
       scientists and agency officials debate the
       best ways to return useful data about the
       Red Planet affordably, a key official said at
       an astrobiology conference last month.

          Dan McCleese, chief scientist of JPL's Mars Exploration
       Directorate, told attendees of the first Astrobiology Science
       Conference at NASA's Ames Research Center earlier this month
       that a revised Mars exploration plan, which NASA said last
       month would be released this summer, may not be ready until
       the fall as the space agency works to completely overhaul the
       program.

          McCleese indicated that a key aspect of the original Mars
       exploration program -- a sample-return mission -- might be
       pushed back well into the next decade, as NASA realizes it
       significantly underestimated the complexity and cost of such a
       mission.

       The Problems with Sample Return

          When it was initiated after the 1993 failure of Mars Observer,
       the Mars Surveyor program had three overall goals of equal
       importance: understanding Mars' potential for past or present
       life, its climate history, and the "natural resources" of the planet
       (which included both the resources that might support future
       manned expeditions, and -- rather awkwardly -- Mars' overall
       geological history). Indeed, both the 1998 spacecraft were
       designed to focus on the climate question.

          But in 1996, following the revelation of possible microfossils
       in Mars meteorite ALH84001, the program's central goal was
       changed by NASA Administrator Dan Goldin to focus on the
       hunt for present or (more likely) past life on Mars. Thus sample
       return, which had been a longer-range goal, was suddenly
       emphasized for the near future, without adequate consideration
       of just how expensive it might turn out to be.

          However, NASA's belief that a sample-return mission could
       be conducted for as little as $400 million was so overly
       optimistic that the Mars exploration program would have to
       have been overhauled even if Mars Climate Orbiter (MCO) and
       Mars Polar Lander (MPL) had not failed. In an earlier interview,
       McCleese said that the cost estimates for such a mission had
       soared to over $1 billion; at this conference he told another
       reporter that he now regards a sample return mission as a
       "Cassini-level program" -- and the Cassini Saturn probe cost
       over $3 billion and took a decade of planning.

          The current sample-return plan calls for a rover to collect
       samples up to a kilometer (0.6 miles) from a lander. The
       samples would then be launched into orbit with a small
       solid-propellant rocket, where they would be picked up by a
       French orbiter that would return the samples to Earth. However,
       McCleese said at the conference that the plan is now open to
       complete review, and other methods, such as directly launching
       the samples from the Martian surface to Earth, might be used
       instead.

          But in any case, such an effort will require a lot of time and
       money -- and that raises another question: given NASA's limited
       Mars funding, should it immediately focus on developing a
       sample-return mission, or should it instead devote the next
       several Mars launch opportunities to using smaller orbiters and
       landers to carefully survey Mars to locate the best possible
       landing sites for sample-return missions? After all, sample
       return flights will always be expensive and relatively few in
       number, and each one will return at most a few kilograms of
       samples, which means that we may have to put a great deal of
       thought into where to land them to maximize the chance that
       this small returned sample will contain evidence of ancient
       microfossils. According to McCleese, this question is currently
       bitterly dividing NASA's Mars science advisors -- and he rather
       plaintively asked the astrobiologists assembled at the
       conference for their input on the question.

       Shifting Scientific Priorities

          Now the question of whether life ever existed on Mars will
       still be the guiding question in designing the Mars program, but
       there has been a return to a multi-pronged investigative
       approach to answer that question. As McCleese says, answering
       that question one way or the other convincingly "will take
       decades, require also understanding the climatological history
       of Mars, and probably require deep drilling into its surface" --
       several meters deep in the short run, and maybe eventually
       kilometers deep, into or below the thick buried "cryospheric"
       layer of permafrost that most scientists believe underlies Mars'
       surface.

          In addition, data returned from the Mars Global Surveyor
       (MGS) spacecraft have left still dangling the central question of
       whether Mars had large amounts of liquid water flowing across
       its surface early in its history or whether it was always so cold
       as to be frozen at the surface, with its "valley networks" forged
       instead by slower trickles of liquid water (perhaps geothermally
       heated) a short distance underneath that frozen surface.

          MGS' thermal infrared spectrometer has also so far failed to
       discover the expected large deposits of carbonate minerals that
       should exist if (as believed) Mars' ancient dense carbon dioxide
       atmosphere disappeared because it reacted with that liquid
       water and the surface rocks to form carbonates.

          McCleese said that this could mean either that
       wind-deposited materials, which have turned out to dominate
       virtually all parts of Mars, are covering up the clues of its
       ancient surface, or that our current theories about Mars' history
       are significantly wrong. He suspects the latter. In either case, he
       says that we're left with a major question: if surveys by Mars
       orbiters continue to fail to reveal convincing evidence of
       water-deposited minerals or sedimentary rocks on Mars'
       surface, do we assume that they really don't exist -- or do we
       send some landers down for a more thorough search?

       The Shape of Mars Missions to Come

          So now what? The 2001 Orbiter will definitely go up on
       schedule in April 2001; it's a near-twin of Mars Climate Orbiter,
       but all indications are that MCO would have worked well if its
       controllers hadn't flown it into the planet due to an undersized
       navigational staff. In addition, the 2001 Orbiter carries two
       instruments which are very important in selecting promising
       future landing sites to look for evidence of life.

          The 2001 Lander, though, is a different matter. A whole series
       of serious flaws was found in its design that could have ruined
       it, besides the touchdown-contact switch problem that was the
       most likely cause for MPL's failure. Proposed changes to the
       lander, including an enlarged communications system to allow
       engineering telemetry during the landing itself, and also a
       direct backup communications link to Earth after the landing,
       will add about 30 kg (66 lbs.) to the spacecraft's mass and push
       back its launch until at least 2003.

          Moreover, changes to its landing engine and a desire to add
       both a computerized landing-obstacle avoidance system and
       stronger (and heavier) landing gear to better deal with the
       rugged Martian terrain may also be in the works. The lander is
       already largely built; its avionics and scientific instruments will
       probably be used at some point -- but it is by no means certain
       that it will ever fly. That decision must be made within a month
       or so.

          Whether it flies or not, what happens to the future Mars
       program? At his talk, McCleese briefly presented a whole table
       of proposals for future Mars spacecraft in 2003 and beyond. He
       also quoted the Polar Lander failure review board as taking one
       look at this list and telling JPL, "No wonder you're having
       failures -- you're spreading your design efforts much too thin.
       You must focus firmly on one specific goal of Mars exploration
       -- presumably the search for life -- and on designing a limited
       variety of spacecraft to achieve it." If NASA does decide to
       reconnoiter a whole set of possible landing sites before
       dispatching sample-return spacecraft to a few of them, what's
       the best way to do it?

          McCleese described one idea that has been mentioned at
       several recent conferences: the "Mars Scout". This proposal,
       currently under study at JPL, would involve launching 5 to 10
       small, cheap landers to various potential sample-return sites
       (and maybe other interesting areas) over several Mars launch
       opportunities, perhaps starting as early as 2003. They would be
       similar to the Mars Pathfinder -- hard landers that would come
       down fast, use inflatable airbag cocoons to cushion the landing
       shock, and then prop themselves upright by unfolding side
       petals with solar cells -- but they would be much smaller,
       weighing perhaps only 30 kg or so, like the "Beagle 2" lander
       that Europe plans to launch in 2003.

          The Scouts would carry limited science payloads: two
       cameras to photograph the area close-up both during descent
       and after landing to check its safety and scientific interest for
       more expensive landers, infrared spectrometers to map the local
       minerals and check for signs that they were water-deposited,
       and perhaps (like Beagle 2) a few other instruments to further
       check the area's suitability for the return of samples containing
       possible fossils -- and they would work for only a few weeks.
       These might be small enough that they could be carried on the
       100-kg (220-lb.) "Mars Micromission" spacecraft that the U.S.
       plans to launch to Mars starting in 2003, as piggyback payloads
       on Europe's Ariane 5 launches of large satellites.

          There are already numerous proposals to have micromission
       spacecraft carry various science payloads both into Mars orbit
       and on tiny surface landers. One idea drawing great interest is
       the "Mars Micromission Aerobot", in which a little helium
       balloon would drift for weeks or months at about 4 km altitude,
       transmitting thousands of pictures and carrying other
       instruments such as IR mineral spectrometers, soil-water
       detectors and magnetometers.

          If NASA decides to start focusing immediately on
       developing a sample return spacecraft, though, there will
       probably not be enough money to fly many (if any) of these
       little reconnaissance craft as well -- and if they are flown, we
       probably won't see a sample-return mission launched until
       early in the next decade. The agency's Mars funds, after all, are
       sharply limited -- and the feeling now is that the remaining
       money had better be very wisely spent.

          At any rate, sometime later this year NASA should decide
       how to proceed -- and with luck, we'll get some information on
       this earlier, starting with the fate of the 2001 Lander.



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