How to Explore the Surface of a Comet or Asteroid
Comets and asteroids are very fascinating places. They may contain building blocks or remnants of the building blocks of the solar system.
However to explore, they present a unique set of challenges.
There's the low gravity environment, or microgravity, as we'll call it.
For example, a person here on Earth would weigh as much as a paperclip on the surface of a comet.
So a rover, like Curiosity, which is currently exploring Mars would actually only weigh a couple of kilograms. It wouldn't be able to generate much traction. And in fact, as it turns its wheels it would probably just push itself away from the surface. It's actually quite likely to end up rotating and landing upside down, at which point it's end of the mission for the rover.
So instead, together JPL and Stanford University have been working on a totally different rover concept that is well suited to these environments called Hedgehog.
Instead of rolling around on wheels, the Hedgehog design actually puts three flywheels on the inside of a cube. By spinning these flywheels up very slowly and then very quickly applying the brake, which transfers all the momentum from the fly wheels, we're able to cause Hedgehog to either hop, or tumble, or perform small adjustments.
We've done many tests here on Earth in gravity off-loading test beds.
Recently we have flown two hedgehog prototypes on a zero-G aircraft.
In these tests we demonstrated that we would be able to perform on a comet or an asteroid.
Hedgehog doesn't have a right way up. Instead it can tumble over the surface and come to rest on any one of its faces and still work perfectly.
The Rosetta mission has sent back lots of fascinating images from the surface of comet 67P and these images show us some incredibly rugged terrain, including large sinkholes where a traditional rover would get terribly stuck.
So we've even tested Hedgehog performing a type of escape maneuver where it spins itself up and does this tornado-like maneuver, where it can actually launch itself vertically out of a sandpit.
In our future work we're looking at increasing the level of autonomy, giving the Hedgehog rover the ability to think for himself and navigate from one point to another.
The Hedgehog rovers' ability to move around on the surface of comets and asteroids can enable a wide range of applications in science in the future