Comet "Harpoon" Being Test Fired in NASA Lab
If launched, mission could return samples from deep inside icy bodies.
Since comets have very low gravity—maybe a millionth that of Earth's—landing a probe on one can be a challenge.
(Related pictures: "NASA Lands on Underwater Asteroid.'")
But getting close to a comet, even within 15 feet (5 meters) or so, is no problem, said project leader Joe Nuth, of NASA's Goddard Space Center in Maryland.
"Let's say you're 10 meters [33 feet] away from a comet [with all engines and control systems] turned off. It would still take you half an hour to fall to the surface of a large comet," Nuth said. "There's plenty of margin for error."
Hovering over the comet, "you can control [the craft] with just a small puff of gas—really just a sneeze."
(Related: "NASA Probe Has
