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Solar smarts: A robot designed to recharge by following the sun will be put through its paces in Canada

Monday, June 25, 2001

By Byron Spice, Science Editor, Post-Gazette

Explorers through history have often been forced to live off the land, hunting game and scavenging roots, fruits and berries once they exhausted their own provisions.

Ben Shamah, a senior research engineer on the CMU Robotics Institute project, checks a chain that broke during a test of the solar robot. (Andy Starnes, Post-Gazette)

The robotic explorers that NASA plans to send to Mars and other planets similarly will need to find ways to re-energize themselves if their missions are to last more than a few weeks or months. Rather than food and water, however, these mechanized Lewis and Clarks often will look to the sun to replenish depleted batteries.

It's not an easy task, requiring not just solar cells to convert sunlight to electricity, but also sufficient smarts to know where the sun will be and how to avoid staying in shadow for long. So researchers from Carnegie Mellon University's Robotics Institute will set out next week for the upper reaches of Canada, taking with them a robot named Hyperion that they hope will prove that a robot can learn to be self-sufficient.

Hyperion bears the majestic name of a Titan and the father of the Greek sun god Helios. But it is an ungainly looking contraption, resembling nothing so much as an oversized drafting table on wheels. The "table" consists of eight, poster-size solar cells, set at a fixed angle above the robot to catch the rays of a sun hovering above the horizon.

The trick will be for Hyperion to keep the sun in view of its left-facing solar panels at all times so it can capture as many rays as possible.

On desolate Devon Island, above the Arctic Circle, that's a 24-hour chore in midsummer, when the sun never sets. The summer sun constantly circles the island, varying from 10 degrees to 35 degrees above the horizon.

During the demonstration, scheduled for July 10-20, Hyperion also will move in steadily expanding circles, walking opposite to the Earth's rotation so that it can keep pace with the sun. That should keep its solar cells constantly bathed in sunlight, or "insolated," as solar power experts say.

At the robot's top speed of one kilometer per hour, Hyperion will be able to negotiate a circular traverse of up to 24 kilometers, or almost 15 miles, in a day.

For several summers now, NASA has used Devon Island as a stand-in, or "analog," for Mars. The world's largest uninhabited island, it has a rocky, gravel-strewn surface and, in summer, an arid climate with temperatures near freezing. The cold desert of Mars is far harsher, but conditions are similar enough that researchers can use the island, and particularly its 12-mile-diameter Haughton impact crater, for field-testing technologies and techniques that might be used to explore other planets.

A sun-synchronous robot, such as Hyperion, might be useful in exploring the polar regions of Mars and the moon, said Pascal Lee, a planetary scientist at NASA Ames Research Center and principal investigator for the experiments on Devon Island.

"The sun's energy is really an incredible powerhouse," Lee said, and the ability to tap into it continually could open the door to polar explorations.

On the moon, for instance, researchers speculate that ice -- a potential source of water, oxygen and fuel -- might be found inside craters near the poles. Robots sent to explore for ice must be adept at planning their forays into the dark craters, timing them so they emerge into the light in time to recharge their batteries.

"Similarly, by accessing the polar regions on Mars, you're entering a very interesting area where water ice may be very near the surface," Lee said.

Robots that are unable to recharge their batteries will have limited lifetimes, unless nuclear power sources are used. Sojourner, the robot that explored Mars in 1997, ran out of power after 78 days, noted David Wettergreen, a research scientist at the Robotics Institute who is leading the Hyperion project. Dust that accumulated on the solar cells on Sojourner's flat deck contributed to its inability to recharge itself.

But proving that sun-synchronous robots can work is going to be difficult.

"The Earth is one of the worst places to do it," said Ben Shamah, a senior research engineer on the project. The Earth's gravity is greater than either that of Mars or the moon, which means terrestrial robots must expend more energy to move. And Earth's atmosphere reduces the amount of solar energy that reaches the surface.

So Hyperion is designed to be as light and energy-efficient as possible, weighing a little less than 350 pounds and rolling on bicycle wheels. Its frame is 6 feet long and 6 feet wide, supporting a virtual sail of solar panels measuring 3 square meters.

The solar cells can capture up to 200 watts of power. The robot requires 80 watts to run its computers, sensors and other electronic equipment. That leaves up to 120 watts available for locomotion.

But the technical advance that will make the mission possible isn't the hardware, but the software, Wettergreen emphasized.

"The robot really has to be able to reason," he said. It has to keep track of where the sun is, how much power the robot is using, how much power is being generated and what terrain lies ahead. In addition to dodging boulders, cliffs and streams that its video cameras reveal in its direct path, it will analyze large-scale maps to help it avoid hills, valleys and other features that might block its view of the sun.

Wettergreen and six other staff members and graduate students will leave with Hyperion for Devon Island July 3. The NASA-sponsored Hyperion project will cost about $1 million.

In addition to proving that sun-synchronous operation is possible, Hyperion may also be used in conjunction with other researchers on the island to see how well robots and humans can work together, Lee said.

Scientists hope to use video relayed by Hyperion to plan excursions by human explorers. "That's an interesting concept because on Mars ... EVA [extravehicular activity] time will be precious," Lee said. Information from robots could help humans select the most interesting spots for visits and plan what sorts of tools and other equipment to take with them.

People sometimes tend to think of planetary exploration either in terms of robotic exploration or human exploration. "In my view," Lee said, "it's not an either/or situation. I think it will be robots first, but then it will be robots and humans together."


For more information:

Hyperion Web site: www.frc.ri.cmu.edu/projects/sunsync

Haughton-Mars Project Web site: www.arctic-mars.org



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