Brian Wilcox, manager of space robotic technology at NASA’s Jet Propulsion Laboratory in Pasadena, California, is a little less sanguine about robotic hoppers’ long-term viability. There’s a reason only one planetary robot in history—NASA’s Surveyor 6, in 1967—has fired up its descent engine again for a relaunch and second landing. The idea, he says, has come up throughout the history of planetary landers, and for the most part been rejected—for instance, during the Viking Mars lander program, when some engineers at JPL proposed that one of the probes use fuel remaining after landing to power a hop. The relaunch isn’t the problem, says Wilcox; it’s making another safe landing. “It’s one thing if you do it once because you have to,” he says of landing a robot on another world, “but to do it more than once intentionally seems to many people to be too risky.” Too much risk, in other words, of cracking up an expensive robot for what Wilcox sees as a limited number of advantages. Exploring the bottom of a crater or lava tube, he says, could be accomplished with less risk by a rover deploying a power and communications station at the crater rim or tube entrance, reeling out a tether behind it, and rappelling down inside.
“Hopping is a very good idea for very-low-gravity places like asteroids,” says Wilcox. “The higher the gravity, the worse it is. The moon is a borderline case because at one-sixth gravity, if you fall out of the sky, you still hurt yourself real badly, even from a not-very-high altitude.” And, yes, the winning vehicle has to survive the hop—or at least stay intact enough, say the X Prize rules, to take a “panoramic photograph or photographs to yield a full 360 degree view of the CRAFT or secondary vehicle’s location at the end of the 500 meter journey.”
Wilcox has no doubt, however, that Draper Laboratory can develop the algorithms needed for a robot that will hop on the moon successfully. This is the organization that developed the guidance, navigation, and control systems for the Apollo moon landers, after all. And he allows that hopping actually does makes sense for this one X Prize-winning mission. The Next Giant Leap concept’s reduction in weight and complexity could make the risk that hopping incurs worth taking, especially since the mission won’t involve gratuitous hopping.
IT’S LATE IN THE DAY at the Draper lab. The TALARIS team has prepped their vehicle for one final test. Actually more of a demonstration. This one is for a visiting dignitary, the commanding general of the U.S. Army’s Research, Development and Engineering Command, who has come to evaluate technologies of potential use to the Army for soldier navigation, precision air-drop systems, and…lunar hopping.
By the time Major General Nick Justice sweeps in with an entourage of officers and business-suited officials, the Draper Lab team, now looking decidedly under-dressed in their polo shirts and jeans, is ready with a hopper freshly charged with nitrogen propellant. They pass out hearing protection and goggles to the general and the others, who now crowd the space behind the plywood and Plexiglas shielding. This time the TALARIS vehicle hangs suspended from its crane some four feet off the floor.
Again the ducted fans roar to life. Again the vehicle gently spins, but only for the briefest of moments before the cold-gas thrusters rapidly pulse. This time there is no lateral motion; the machine descends smoothly, just as a future vehicle will on the moon, perhaps following a 500-meter hop. When the machine reaches the end of its tether, Rossi shuts down the fans and the thrusters. The vehicle bounces briefly and comes to rest in the sudden silence.
The general nods his approval, asks a few questions, and moves on to his next appointment. One more time, the TALARIS team safes its vehicle, and this time calls it a day, mission accomplished.
Michael Belfiore is the author of Rocketeers: How a Visionary Band of Business Leaders, Engineers, and Pilots Is Boldly Privatizing Space (Harper Paperbacks, 2008). Find him online at michaelbelfiore.com.