On Titan, the inflatable robotic explorer could float through the satellites thick atmosphere, giving it a global perspective on a surface otherwise obscured by a stubborn layer of organic haze. The rover could then drop from the air to the ground to rumble across even its rockiest terrain. Nor would Titans mammoth
hydrocarbon lakes give it pause: the lightweight rover would simply skim their surface on its buoyant wheels."This is the one body in the solar system that allows this kind of all-purpose vehicle that can fly, drive and float," said Jack Jones, the JPL engineer behind the
Titan Amphibious Aerover, originally conceived for the exploration of Mars.A working prototype of the rover relies on its three mammoth inflatable wheels to tackle land, sea and sky.
Each 5-foot (1.5-meter) diameter white-pumpkin-of-a-wheel comes clad in Vectran, the material used for Mars Pathfinders cushioning
airbags. A skeletal frame connects the wheels, supporting a steering mechanism, battery and camera.~
Although the size of a real SUV, the entire rover -- as recently tested in the Mojave Desert -- weighs more like a bicycle than a truck. At 55 pounds (25 kilograms), the rover requires a scant 20 watts of power to drive it along at 1.25 miles (2 kilometers) per hour. On Titan, even less juice -- perhaps just 8 watts -- would suffice.
"Thats zippo," Jones said.
On land, the rover can tackle rocks one-third the size of its wheels, making quick work of terrain that would halt either of the twin roving probes going to Mars in 2003 dead in its tracks. On water, treads glued to the rear wheels allow the aerover to paddle its way around, albeit somewhat more slowly.
The trick, Jones said, is getting the rover to fly, although Titan itself is the least of his worries.
On Titan, gravity is one-seventh that of Earth, but its atmosphere is four times as dense. Flap your arms hard enough on Titan, and you would have a fair shot at taking flight.
Float or fly?
"Titan is probably the easiest place in the solar system to fly in any way, whether its lighter- or heavier-than-air flight," said Ralph Lorenz, a planetary scientist at the Lunar and Planetary Laboratory at the University of Arizona and consultant to the project.
But how to get the rover airborne -- and keep it there -- is hard.
The easiest scenario would be to fill the rovers wheels with buoyant helium. As it circled the globe, perhaps once every two weeks, the rover could pick promising spots where to land at its leisure. To descend, the rover would vent a wheel until it began to drop. To regain altitude, Jones said, the rover could then drop off a small scientific payload, such as a meteorological station.
"Basically, youd be dropping ballast," Jones said. Once on the ground for good, the rover could vent all its helium and re-inflate its tires with good old Titan nitrogen-rich air before roaming about.
Another plan calls for the rover to be suspended from a separate helium balloon packaged with a smaller hot-air balloon, forming a hybrid called a Rozier balloon. The Breitling Orbiter 3, which made the first nonstop balloon flight around the world in March 1999, was such a hybrid.
To fill the hot air balloon, the rover would rely on the waste heat generated by the rovers electrical power source -- radioisotope thermal generators (RTG). (Since Titan receives just one one-thousandth the sunlight we bask in here on Earth, solar power is out of the question, making RTGs the only likely power source.)
The advantage of that arrangement is the rover could make repeated ascents and descents to better reconnoiter the moons surface.
Sticky problem
While tricky, its whats sticky that might doom the concept.
The seas of ethane or methane that slosh on Titans surface might well be as gooey as petroleum is here on Earth, easily bogging down the rovers fabric wheels.
"Its easy to think of things that could go wrong, and stickiness is one," Lorenz said.
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