In one proposal (the "Mars Mobile Lander"), a duplicate of the Mars Pathfinder will bounce to an airbag-shielded landing -- but the lander itself will consist only of landing and control systems, with no science instruments or radio gear.

Instead, it will unfold its petals to release a copy of the 130-kg "Athena" Mars rover that had already been scheduled for a 2003 landing as part of the now-cancelled mission to launch samples of Mars' surface into orbit around the planet for later pickup and return to Earth by a French/American spacecraft.

That far more complex mission has now been put off for some time to come, since its expenses (even before the 1998 failures) had quickly soared past the billion-dollar mark.

Not only will it take some time to finance and design the sample-return flight properly, but -- given the high expense of Mars sample-return missions, and the fact that they will each return only about a kilogram of samples from one location -- NASA now wants to make as certain as possible that the few landing sites selected are the most promising that can be found for possible microbial or chemical fossil evidence of ancient Martian organisms.

Athena was originally supposed to pick up a collection of tiny soil samples and drilled-out cores from selected Martian rocks, and return it to its mother lander for blastoff back into Martian orbit.

It will no longer have that function, but even without it Athena can still be an extremely useful tool for studying Mars' surface in unprecedented detail.

Athena, 11 times heavier than the tiny "Sojourner" rover on the first Pathfinder, is capable of operating entirely on its own -- communicating directly to Earth rather than through its lander, prowling for a kilometer or more across the Martian surface over a period of at least a month, and analyzing soil samples and rocks in great detail with a set of six different instruments. They would include:

1. A high-quality multispectral stereo camera;
2. A thermal-infrared spectrometer to make panoramic maps of surface minerals (especially water-deposited ones);
3. An alpha-proton-X ray spectrometer like the one on Sojourner, to analyze all the important elements in rock and soil samples;
4. A black-and-white microscopic camera to photograph soil grains and rock crystals as small as 0.03 millimeter;
5. A "Mossbauer" spectrometer that would bombard samples with gamma rays to make a chemical analysis of all iron minerals -- providing data on ancient Mars' water supply, and perhaps even identifying some iron mineral crystals that are produced on earth only by bacteria; and
6. A "Raman" spectrometer that would take spectra of laser light reflected off samples, not only identifying many minerals but also providing a sensitive check for traces of organic compounds in Mars rocks.

Although it will no longer be returning samples to Earth, the drill might still be worthwhile, since the onboard instruments can look at and analyze the ends of extracted rock cores from below the layer of surface weathering that coats Mars rocks.

In addition to its panoramic science cameras, Athena would navigate using pairs of cameras on its front and rear, as well as a belly-mounted camera to provide closeup views of the sampled surface. It could, with luck, drive as much as 100 meters across the Martian surface each day.

On the previous night, its Earth controllers would study the previous day's photos, pick out the next day's desired destination (as well as one or more intermediate "waypoints"), and send the rover its marching orders.

On the next day, it would proceed automatically to each waypoint along a straight-line path, veering around detected obstacles automatically. (Instead of Sojourner's laser obstacle detection system, it would actually analyse the stereo photos from its cameras directly to detect dangerously large rocks or holes.

This technique sounds doubtful, but it has been developed -- and tested -- for several years on test rovers here on earth, with a very high success rate. (Only last month, Athena's earthly prototype "FIDO" underwent a long and very successful test in the Nevada desert.)

What is uncertain is whether this mission can be prepared in time. The Pathfinder landing system has of course been successfully tested on Mars itself -- and since Athena was already scheduled for a 2003 launch, its own development doesn't need to be speeded up. But there are still possible problems.

NASA is currently very closemouthed about the details of its 2003 Mars plans, but it's possible that there might be problems in making the total spacecraft light enough to be launched on a Delta 2 booster -- especially since the rover, which originally was supposed to communicate with Earth only through orbiting Mars relay spacecraft, will now have an X-band radio system with a pointable 30-cm dish antenna added to it to allow a backup communications link directly to Earth. (This system by itself could add about 20 kg to the rover's weight.)

There may also be problems in designing Athena to survive Pathfinder's high-speed bouncing landing, since it was originally designed to make a gentle touchdown aboard a full-fledged soft lander.

But if it is possible, this could be a mission of major scientific importance -- especially since the Pathfinder system, since it can make a safe landing in almost any kind of rough terrain, could plant Athena in a far greater number of scientifically interesting landing sites than the original soft-landing carrier spacecraft could.

In earlier articles, I confidently predicted that the next U.S. Mars lander would be a full-fledged soft lander -- which (like the Mars Polar Lander) would use a complex radar system and throttleable rocket engines to lower itself to a gentle touchdown -- rather than another Pathfinder.

I had two reasons. First, the Pathfinder system is a good deal heavier, due to its big and rather thick crash airbags -- so that it has to be launched on a full-scale Delta 2 booster, rather than the smaller and cheaper "Medlite" Delta used by the Polar Lander (and its cancelled 2001 twin).

But NASA has decided to absorb this cost increase, since its Mars program has now been stretched out over a much longer schedule. Both of the possible 2003 missions (and the 2001 Mars Surveyor Orbiter) are all scheduled for full-scale Delta 2s.

Second, when the U.S. finally does launch an unmanned Mars sample-return vehicle, it will certainly have to be a full-fledged soft lander, equipped with an automatic obstacle-avoidance system (using scanning laser radar and/or a descent TV camera) to minimize landing risks.

But such a system will probably have to be tested under Martian conditions first, using a smaller and cheaper soft lander, before we commit something as expensive as a Mars sample-return mission to it. I remain convinced that this will be done at some point.

In case the Mars Mobile Lander isn't possible, though, NASA is also studying an alternative 2003 mission -- another Mars Surveyor orbiter spacecraft with a new set of instruments.

This spacecraft would probably be designed along the lines of the Mars Global Surveyor that is currently mapping Mars' surface with great success, although it might also be made lighter weight by incorporating some elements of the smaller Mars Climate Orbiter spacecraft (which would have worked very well if its ground controllers hadn't flown it into the planet, and which will have a near-duplicate launched to Mars in 2001).

The instruments it would carry (although there's some uncertainty) might include the following:

1. Another flight of the heavy "PMIRR" multichannel IR sounder carried on the Climate Orbiter (or a lighter instrument with the same capabilities), to map Mars' weather patterns -- air temperatures, dust clouds and ice clouds -- with unprecedented detail.
2. Another very high-resolution telescopic camera which, like the one on the current MGS, could photograph small patches of the Martian surface with a resolution of only about 2 meters.
3. A copy of the pair of tiny wider-angle cameras (only 0.6 kg apiece) on the Climate Orbiter.
4. A "VIMS" spectrometer to make very detailed maps of Mars' surface, using high-frequency infrared sunlight near the border of visible red light and reflected off the surface (thus mapping a different set of minerals than the longer-wavelength IR radiation emitted by Mars' surface because of its warmth and currently being mapped by MGS).
5. A UV spectrometer to analyze gases in the atmosphere and ionosphere.
6. Perhaps -- if weight allows -- another laser altimeter and magnetometer like those on MGS.

Most of its instruments are near-duplicates of those on the European Space Agency's "Mars Express" orbiter, already firmly scheduled for 2003. Still, more coverage of greater areas on Mars' surface would be scientifically valuable in itself, and Mars Express doesn't really carry any good analog of the PMIRR instrument.

(This makes me wonder whether NASA may perhaps end up going with a third and cheaper alternative: simply reflying the Mars Climate Orbiter in 2003, along with whatever additional instruments can be safely crammed onto it.)

On NASA may end up simply flying nothing to Mars in 2003, and waiting till 2005 to resume its program. One inside source tells "SpaceDaily" that NASA has decided to delay the tiny Mars communications satellite -- weighing only 220 kg -- that it had planned to launch separately in 2003 as a piggyback "Micromission" on board a European Ariane 5 rocket. If so, this puzzles me.

If the Mobile Lander is flown in 2003, this would leave it with only two possible Mars orbiting relay comsats -- the (old) 2001 Orbiter, and the Mars Express -- and if they both failed, it would have to fall back entirely on direct-to-Earth communications that would very greatly reduce its scientific return. I'm awaiting further word on this subject.

Even if Mobile Lander does fly, I also wonder what will happen to the four additional instrument packages that had been scheduled for the 2001 Lander (along with a duplicate of the Sojourner rover and five of Athena's six instruments, mostly on the stationary lander itself).

I think it very likely that one of them -- the tiny descent camera first carried on the Polar Lander, which would have photographed the surface from altitudes of 7 km down to only 7 meters -- will be added to the Mobile Lander, perhaps hung from its parachute harness with its photos recorded on the rover for later playback.

Scientists are agreed that aerial photos of the landscape around a landing site are extremely important in order to understand its geology -- and that they are absolutely indispensable to plan out in advance the scientifically best possible route for a rover to follow after landing.

But the other three are more doubtful.. Two of them, the "MARIE" radiation detector and the "MECA" package of chemical and microscopic soil analysis instruments, were part of NASA's "HEDS" (Human Exploration and Development of Space) program; they were designed to detect possible environmental hazards for later manned expeditions to Mars -- which, as NASA freely admits, are now even farther off than they were before.

I think it possible that some of the smaller and lighter sensors in the MECA package might be added to Athena, such as a sensor on the rover's instrument arm to detect static electrical charge buildups from Martian dust that could be dangerous to electronic equipment on both manned and unmanned vehicles. But except for that, I think it's safe to say that these two experiments are now very much on the back burner.

The final experiment set for the 2001 Lander was "MIP", a set of devices to test the possibility that later ships blasting off from Mars' surface could very greatly lighten their launch weight by manufacturing the propellant they need to get back into space from Mars' native atmosphere, instead of having to carry it all the way from Earth.

If this technique works out, it would very greatly reduce the cost not only of manned Mars ships, but of unmanned Mars sample-return vehicles in the near future -- and so MIP seems to me a much higher-priority item than MARIE and MECA. But the first package of MIP sensors weighs 8.5 kg, which I think is too heavy to be carried on Athena.

I wonder, though, about a longer-shot possibility. According to the April 14 "Space.com", the Jet Propulsion Laboratory is still seriously considering developing a "black box" for later Mars soft landers -- a very lightweight and shockproof recorder and transmitter package that could survive a crash on Mars and later radio back the engineering data recorded during the landing attempt, allowing the detailed post-mortem that couldn't be done on the Polar Lander.

I wonder whether such a lightweight transmitter could be added to the 2003 Pathfinder Lander along with the package of MIP experiments, so that they could transmit back data to Earth separately after the Athena rover had left the lander.

This first set of MIP experiments -- which would do such things as test the ability to manufacture small amounts of liquid oxygen out of Mars' carbon-dioxide air, and test techniques to keep solar cells clean from airblown Mars dust -- mostly has a very low data transmission rate, and could make use of such a system. This, however, is very speculative on my part.

Indeed -- as I said -- outsiders currently know very little about NASA's plans. Separate teams at JPL and Lockheed Martin are currently doing feasibility studies of both the Mobile Lander and the 2003 Orbiter, and NASA will make the decision as to whether to fly one of them -- or neither -- in July.

In the meantime, SpaceDaily will continue to report on Mars developments will hopefully more advance information about the details of these two missions and the course that the U.S. Mars program will take after that.

Mars at JPL

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