[meteorite-list] MIT Tether Could Aid Asteroid Missions

[Ron Baalke]

MIT tether could aid asteroid missions

For Immediate Release
TUESDAY, SEP. 25, 2007

Contact:
Elizabeth A. Thomson, MIT News Office
1-617-258-5402
thomson at mit.edu

CAMBRIDGE, Mass.-Using a tether system devised by MIT researchers, 
astronauts could one day stroll across the surface of small asteroids, 
collecting samples and otherwise exploring these rocks in space 
without floating away.

The ability to visit asteroids could also be invaluable for testing 
equipment for a mission to Mars by humans. Further, knowing how to 
tether an asteroid could be helpful if one needs to be towed away 
from a potential collision course with Earth, says Christopher Carr, 
a postdoctoral associate in MIT's Department of Earth, Atmospheric 
and Planetary Sciences.

Carr and Ian Garrick-Bethell, a graduate student in the department, 
describe their system in an upcoming issue of the journal Acta 
Astronautica.

Walking on an asteroid is much more difficult than walking on a planet 
because asteroids have so little gravity. An astronaut who tried to step 
onto one would likely fly off or hover above the surface.

Now Carr and Garrick-Bethell say that tying a lightweight rope completely 
around an asteroid could solve that problem. Once the rope was in place, 
astronauts could attach themselves to it and maneuver or possibly even 
walk along the surface.

That would allow an in-depth exploration of the composition and history of
asteroids, which could shed light on some of the big questions about our 
solar system, such as how the planets formed, said Carr.

"This is an innovative approach to a task nobody has spent much time 
thinking about," said former astronaut Jeffrey Hoffman, an MIT professor 
of aeronautics and astronautics who sponsored the paper. "NASA has taken a 
brief look at a human visit to a Near Earth Object, and it may be something 
we can do long before going to Mars. Clever ideas will be necessary
to allow people to do useful work near objects on which you cannot 'land,' 
but only 'dock.'"

An asteroid's gravity varies depending on its density and size, which can 
range from a speck of dust to hundreds of kilometers. On an asteroid that 
has a diameter larger than eight kilometers, an astronaut who jumps will 
probably come back to the surface, Carr said. But if the asteroid is smaller 
than that, the astronaut may float away.

Even if an asteroid has enough gravity to keep an astronaut on the surface, 
it would be difficult to move around or collect samples. "You couldn't touch
anything without sending yourself on a new trajectory or spinning yourself
around," said Garrick-Bethell, who is the first author of the Acta 
Astronautica paper.

Some people have suggested that astronauts could bolt themselves directly to 
the asteroid, but the granular material covering the asteroids could prevent 
this.

"It would be like trying to bolt yourself to a pile of gravel or sand,"
Garrick-Bethell said.

The MIT researchers envision deploying their system with an astronaut or a
remote-controlled rocket that unwinds a spool of rope while flying around 
the asteroid. When the craft reaches the starting point, a loop is formed 
and tightened. Astronauts could then be held to the asteroid using one or 
more ropes, permitting them to work on the surface.

One unknown is whether the rope would cut into the granular surface of an
asteroid, hindering the system's effectiveness. But even if the rope does 
not allow astronauts to walk on the surface, it could at least give them 
something to hold onto as they pull themselves along the asteroid without 
floating away, said Carr.