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NASA's Martian dowsers

NASA's Martian dowsers

Call NASA's Mars exploration efforts "all wet," and you would be paying the agency's scientists a big compliment. More than any other single substance, water reveals fundamental details about the planet's climate, its ability to sustain life, and its potential resources for future manned missions, according to Dr. Dan McCleese, chief scientist for the Mars Program at NASA's Jet Propulsion Laboratory (JPL). "Water is critical in each category," he says. "It drives our entire understanding of the planet." That understanding crested last June when images from an orbital camera aboard the Mars Global Surveyor suggested the recent presence of liquid water on the planet's surface. Yet far from quenching NASA's thirst, these images provided just a taste of what's to come. "We're learning today from the Global Surveyor that we're still very much in the reconnaissance phase," McCleese says.

For its next Mars mission, slated for 2001, NASA will continue to search for signs of water remotely-using an updated Global Surveyor orbiter fitted with more sophisticated imaging systems. Ultimately, however, the agency's high-tech water witching will require a combination of remote sensing and technologies that will go after geological and chemical samples on the ground. "To date, we have good, sometimes very good, remote data," notes Scott Hubbard, director of NASA's Mars Program. "What we still need is the 'ground truth,' which requires us to get next to a rock and make measurements."


To push ahead with NASA's 'follow the water' strategy, future Mars rovers will gain a measure of autonomy as they find, collect, and help return scientific samples.

Last year's mission misadventures forced agency officials to reconsider their Mars strategy, which centered on technologies to collect and return scientific samples. Hubbard explains that the failure of the Polar Lander mission caused the agency to temporarily limit its "appetite" for all but orbital missions-which are less risky and less costly than landed missions. Indeed, the 2001 mission initially included plans for a lander, not just the orbiter in its current incarnation.

With the 2003 mission, however, NASA plans to go back to the surface with two new rovers that will land directly on the surface inside a Pathfinder-influenced landing system-which employs a parachute and airbags for a bounce-and-roll landing that's not so much gentle as manageable. Weighing in at nearly 150 kg, with a range of up to 100 meters per Martian day, these rovers or "mobile landers" will outweigh and outpace the small Sojourner rover that arrived on Mars as part of the 1997 Pathfinder mission. They will also play a larger scientific role than the Sojourner, thanks to an on-board suite of instruments for analyzing rock and soil samples (see sidebar). "This mission will give us the first ever robot field geologist on Mars," says Hubbard.

Looking beyond 2003, NASA's "follow the water" strategy still requires a massive technology development effort. Says Hubbard, "The technology landscape really opens up after '03."

The right samples. Of the technical challenges faced on Mars, one of the toughest relates to the seemingly workaday task of gathering and returning samples. "It's an extraordinary technical challenge," McCleese insists as he lists attributes that future rovers will need: To get to the sample, the next rover will need on-board navigation and hazard-avoidance systems. To pick the "right" samples, it will need some built-in science smarts-"something more than 'I know a fossil when I see it,'" he says.

Finding the "right stuff" represents only half the battle. Rovers must also possess the means to harvest samples on or below the Martian surface. And returning the samples won't be easy either. McCleese points to all the interconnected steps required to store the sample, launch it off the surface with a small lander-based rocket, rendezvous with a waiting spacecraft, and lastly return it to Earth safely. "Each of these steps is a mission in itself," he says.

Meeting all these goals will call for rovers to evolve substantially. They will have to become autonomous "science platforms," McCleese believes. These future rovers will gain a measure of autonomy via advances in computing power, decision-making software, and telecommunications. "The notion of an autonomous rover is really very new for us," he says.



The FIDO rover, designed to prove concepts for the next sample-return missions, bristles with robotic sample collection devices--like this miniature corer from Honeybee Robotics.

They will have to carry automatic sample-harvesting equipment, and NASA has in fact developed a keen interest in drilling technologies. Miniature drills from Honeybee Robotics (New York) have already been developed for coring rocks, but NASA also plans to go deep into the subsurface. In the short term, the agency's scientists want to drill in the 10-to-200 meter range-still shallow enough for some sort of robotic approach, McCleese reports. "We also believe liquid water may be five kilometers below the surface." Getting that deep may require human handiwork-space roughnecks-so it won't happen anytime soon. But NASA has gone so far as to consult the oil industry and has hired an oil-drilling expert from Chevron. "The oil industry is teaching us about measurements we need before we even attempt to drill," says McCleese.

As for payload, the descendants of today's rovers will likely sport Mars-ready scientific instruments to enable in-situ chemical or physical analysis. "We want to bring the capabilities of lab instruments to Mars," says McCleese. To take one example, NASA wants to develop instruments that can date samples on Mars. "We can do a good job at relative age, a poor job at absolute age," says McCleese. Looking further out, he envisions instruments that can detect bio-signatures through chemical or physical analyses of organic substances. "These instruments haven't been developed yet except in heavy and expensive lab versions."

While not all of the technologies McCleese envisions have been developed yet, a harbinger of what's to come does exist in FIDO. Short for Field Integrated Design and Operations, this robotic vehicle was initially developed to test concepts for the 2003 and 2005 sample return missions. Developed for multi-kilometer travel, this six-wheeled robotic vehicle weighs about 60 kg and measures 100x75x45 cm. It bristles with instruments-including a bore-sighted near-IR spectrometer, a microscope mounted to a robotic sampling arm, Raman and Moessbauer spectrometers, and a multi-spectral stereo mast camera. It also features an automated mini-corer and sample caching system. Late last spring, the FIDO rover took to the field-in the Nevada desert-for its first trials.

A soft landing. NASA's sample-analysis-and-return goals also trigger the need for new landing technologies. As rovers evolve into McCleese's "science platform," they will overflow with analytical instruments and heavy sample-return equipment. And getting rovers within striking distance of their targets will require smarter landing systems. "One of our major challenges is to develop robust, adaptive landing technology," Hubbard says.


NASA files show likely water locations on Mars.

To cushion the increasingly weighty payloads, NASA will likely have to come up with a replacement for the airbags it has used since the Pathfinder mission. "Airbags don't scale well with delivered mass," McCleese says, adding that they've nearly reached their practical limit with today's loads of 600 to 1000 kg. "We're already to the point where airbags become cumbersome and their effectiveness diminishes," he says. Likely airbag alternatives include revamping of the legged systems employed in lunar landings and also a "Frisbee-shaped" pallet landing system that can accommodate uneven or sloped terrain. Both of these landing concepts are currently under investigation at JPL, McCleese reports.

The next generation of landing craft will also require a better sense of aim. Hubbard notes that current landing technology can get within 10 to 100 km of a target, but NASA plans call for accuracy in the hundreds-of-meters scale. And he adds that this tighter landing accuracy "requires tools we don't have right now." NASA's list of possible solutions in this department includes adaptations of surface-mapping technology developed by the Department of Defense. Hubbard also predicts that faster on-board computer and neural net software will aid future landers as they avoid hazards and make real-time navigation decisions.

The human connection. While the data collected in robotic missions may be an end in itself, robotic missions also represent giant steps toward human voyages. "We have an integrated strategy," says Hubbard, explaining that today's early thoughts about human exploration already build on lessons learned from robotic missions. "Robotic missions could pave the way for human missions," agrees McCleese.

And when he says "pave the way," he means it-literally. He predicts that the future robotics will focus not just on science but on practical tasks such as building the habitat and other infrastructure components needed for human settlement. Thanks to robotics, he says, "the first humans on Mars can be explorers, not civil engineers."

Who says there are no RATs on Mars?
The large science rovers that will roam the Martian surface during the 2003 mission will bring along RATs. No, not the furry, disease-ridden kind you find in the subways. These RATs, or "rock abrasion tools," are high-tech grinders that will expose fresh rock surfaces for study. One promising RAT design, which was under review at press time, comes from the drawing boards of Honeybee Robotics (New York), a 15-person engineering firm that focuses on space hardware and has already built miniature drilling systems for NASA rovers.
Honeybee's RAT cuts through the Martian rind with a diamond-matrix wheel that grinds edge-wise to the surface, excavating one mm at a time until it get 5mm deep. Powered by four Maxon motors, it mounts on the same robotic arm as the rover's scientific instruments and steadies itself with a spike that extends into the surface. According to Stephen Gorevan, Honeybee's chairman, this shared arm approach saves development time, weight, and cost of coming up with a RAT that depends on its own robotic arm to provide the grinding head motion.
At the same time, a RAT that functions as an end-of-arm tool on the instrument arm also erected some engineering barriers. For one, this approach imposed some tight packaging limitations, with Gorevan noting that the entire device has to fit within an envelope of just 7 cm diam. and 10 cm long. For another, it had to be low mass-under 1000 grams-and grind gently so as not to overwhelm the instrument arm. "The arm wasn't designed for big loads," Gorevan explains. And finally, the RAT had to be engineered for uncertainty. "It operates 40 million miles from home, and no one on earth knows how strong the Mars rocks are," he says, describing a spectrum from "cotton candy to brown diamonds."
While the RAT's diamond matrix wheel may handle even the toughest rock, the unknown surface characteristics make it tough to estimate the RAT's power consumption. Honeybee has conducted "bread-board" tests on a RAT prototype that show that the grinder gets five mm into dense basalt with a power consumption of 30 watt-hr. "That's the worst case," says Gorevan, who adds that limestone consumes only about one watt-hr.
To meet these conditions, Honeybee engineers must come up with a grinding strategy that Gorevan sums up in just four words: "low force, high speed." By removing only a bit of rind at a time and grinding at speeds of up to 4,000 surface ft/min, the RAT keeps grinding forces down to 0.42 lb, Gorevan reports.
The past, present, and future of Mars exploration
Mission Launch Arrival Objective

Mariner VI

2/24/69

7/31/69 (fly-by)

Atmospheric and geologic studies.

Mariner VII

3/27/69

8/4/69 (fly-by)

Atmospheric and geologic studies.

Mariner IX

5/30/71

11/17/71

First spacecraft to orbit another planet.

Viking I

8/20/75

6/19/76 (orbiter)

6/20/76 (lander)

Global studies and surface exploration.

Viking II

9/9/75

8/7/76 (orbiter)

9/3/76 (lander)

Global studies and surface exploration.

Mars Pathfinder

12/4/96

7/4/97

Demonstrate lander and rover operations.

Mars Climate Orbiter

12/11/98

LOST 9/24/99

Climate studies.

Mars Polar Lander.

1/3/99

LOST 12/3/99

Study climate and geology near Martian

South Pole. Demonstrate micro-probe

technology.

Mars Global Surveyor

11/7/96

9/11/97 (still in orbit)

High-resolution surface imaging.

Mars Surveyor 2001

3/30/01

10/20/01 (expected)

Global studies.

(scheduled)

Mars Surveyor 2003

6/4/03

1/20/04

Search for evidence of ancient water

Mars Surveyor 2005

?

?

Mission objective under review
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