— A basketball-size robot sits on the surface of an asteroid after unfolding its spherical shell, while its parent spacecraft hovers in the background (Illustration: Ball Aerospace)
A fleet of exploding probes could prepare the way for warding off hazardous asteroids. Several of the small spherical robots would land on a single asteroid, some exploding while others listen for vibrations that could reveal the object's inner structure.
NASA has a list of more than 800 asteroids considered to be potentially hazardous because their orbits carry them close to Earth's. If one of them is found to be on a collision course, knowing its physical properties will be crucial in devising a mission to divert it.
If the asteroid is a single chunk of rock, an engine could be attached to the surface to pull or push it off its catastrophic course. But that will not work if the asteroid is merely a collection of smaller rocks loosely bound together by gravity, like the one visited by Japan's Hayabusa spacecraft (see Rubbly Itokawa revealed as 'impossible' asteroid).
A "gravity tractor" would work better in that case, with a spacecraft simply hovering nearby and using its own gravity to nudge the asteroid off course (see 'Gravity tractor' to deflect Earth-bound asteroids).
Small and cheap
However, little is known for certain about the structure of asteroids because none has ever had its interior probed.
Now, a group of scientists and engineers have designed a robotic probe small and cheap enough that a fleet of them could be sent to investigate a near-Earth asteroid's composition and structure.
Dennis Ebbets of Ball Aerospace in Boulder, Colorado, US, presented the concept on 7 January at a meeting of the American Astronomical Society in Seattle, Washington, US.
As many as six of the 12-kilogram probes could be loaded on a single spacecraft, which could be launched at relatively low cost to rendezvous with the asteroid.
Out with a bang
The main spacecraft would stay a few dozen kilometres away, perhaps nudging the probes towards the asteroid using springs. Once on the surface, the protective spherical shell of each probe would open to allow the probe to scan the surface nearby.
To reduce complexity and costs, the probes lack solar panels and run on battery power, limiting their lifetime to a few days. But each probe could still cover a lot of ground in that time, as they could be fitted with small thrusters to let them hop across the surface.
Eventually the probes could detonate onboard explosives, sacrificing themselves for science one by one. Probes that had not yet detonated would listen for any seismic waves sent rippling out from the explosion, and the main spacecraft could observe the craters left behind. That would tell scientists about the asteroid's strength and internal structure.
Launch and learn
If funding can be secured for the probes, they and the host spacecraft could be built in two or three years. The team has identified several near-Earth asteroids that would make good targets, including an asteroid a few dozen metres across called 2003 WP25, which could be reached by 2011.
Asteroid expert Daniel Durda of the Southwest Research Institute in Boulder, Colorado, US, approves of the idea. "These small probes are the way to go," he told New Scientist. "They're cheaper, you can launch more of them, and the more you launch the more you learn."
But he says the failure of Japan's small Minerva probe to land on the asteroid Itokawa after being released from its parent spacecraft Hayabusa in 2005 shows that landing on an asteroid is tricky (see Robot asteroid-explorer is lost in space).
"It's not simple with a bumpy, quickly rotating object to drop something on the surface," Durda says. Ebbets says mission controllers would need to be very careful in getting the probes to land. "You have to have a pretty good mathematical model of the gravitational field of the object in order to release your probe at the right time and in the right direction," he notes.
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