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The One-Pound Problem

All the Mars Ascent Vehicle has to do is deliver 16 ounces of rocks in a container the size of a grapefruit to Martian orbit. If only it were as easy as it sounds.

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(Continued from page 4)

Still, there were some good, experienced Mars mission designers in industry, and by mid-summer Caldwell had hired two study teams--one to look at propulsion and the other to evaluate the overall system architecture with a fresh perspective. Almost immediately the teams found ways to improve the MAV. Based on some of the contractor presentations, it started to look like two stages would be better than three. It was a lot simpler and it saved weight: one less interface between stages, no third propulsion system. Even without guidance on the second and third stages, the trade studies showed that the old version was still heavier and more expensive. It was actually pretty obvious, says Caldwell. But "you get mentally tied to a concept," and the JPL engineers had been trying their damnedest to make the MAV work with the spinning upper stages stabilized NOTSNIK-style. Now none of that would be necessary.

What had Brian Wilcox's novel idea, so celebrated just a few months earlier, really contributed then? "What it really did was force the thinking in a different direction," says Caldwell--away from big, heavy liquid engines and a design gridlock that had all but paralyzed the project.

Frank Jordan, a senior JPL manager in charge of Mars mission planning and an old hand at planetary spacecraft design, thinks that Mini-MAV deserved its accolades. "Most of the rah-rah was justified, in my view," he says. "I mean, it's not a 20-kilogram little-bitty rocket anymore, but it's 170 kilograms, and that's better than 300 kilograms." Jordan has seen a lot of engineering concepts come and go. He worked on the first mission to orbit Mars, Mariner 9, which entered Martian orbit in 1971. "So much of engineering, I think, works this way," he says. "You have some really innovative something, and by the time you bring it to fruition it's compromised--but still better."

The Mars rocket is still evolving, and it's still hard work. Caldwell and his team hope to have the design pretty well nailed down by December. Meanwhile, Wilcox has moved on to other projects and, like most people at JPL, has several things on his plate. He doesn't especially mind that in the end, his Mini-MAV didn't prove practical for the Mars sample return. Logic prevailed just as it did in the 1950s, when his father was trying to orbit another small object around another planet. Back then, scrapping the guidance system made sense because it weighed a lot more than NOTSNIK's payload. Once the payload grows beyond a certain size, the advantage is always with active guidance, and the MAV sample canister turned out to be much heavier than Mini-MAV's 200-gram payload.

Wilcox spends most of his time these days building a tiny "nano-rover" to roam the surface of an asteroid, which will be included on a Japanese mission called MUSES-C, scheduled for launch in 2002. He has ideas for true Mini-MAVs, rockets so small they could be ferried around the Martian surface on the backs of rovers--that is, if the payload delivered to orbit were small enough. Then there's the Venus Sample Return concept he and others at JPL have been cooking up. They'd use a balloon to float a golf-ball-size sample up through the thick Venusian atmosphere to an altitude of 40 miles, where they would then fire a rocket from the balloon (just like NOTSNIK did from an airplane) to continue the journey to orbit. Now that, Brian's father might have agreed, is pretty clever--if it works.

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