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 |  | Sailing with Sunlight: Non-nuclear Asteroid Deflection
By Michael Paine
Special to SPACE.com
posted: 08:32 pm ET
08 February 2000
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Asteroid expert Jay Melosh from the University of Arizona has looked at a range of ideas for deflecting asteroids without resorting to nuclear weapons.
| Defending the Earth | | FACT VS.FICTION An asteroid or comet impact with Earth is the only type of natural disaster that could instantly wipe out human civilization, and yet -- unlike earthquakes, floods and volcanoes -- it is within our grasp to prevent the collision. [more] | 
CHASING ASTEROIDS: Previous spacecraft missions to asteroids and comets have involved quick flybys with no attempt to match speed with the object. In the future, vehicles will try to land on their surfaces. [more] |
TO NUKE OR TO NUDGE? Blowing up asteroids may work in the movies, but in reality it could lead to bigger problems. However, nuclear warheads could be used to alter the course of an errant asteroid or comet. [more] |
They include:
- Deploying a giant parabolic mirror to concentrate the sun's rays and vaporize rock on the surface of the asteroid. The vaporized material flies off at high speed and generates a re-coil action that pushes the asteroid, slowly but surely, in the opposite direction.
- Landing cannon-like devices on the surface to fire asteroid material into space. This also depends on re-coil action. An ion drive, as used on the Deep Space 1 spacecraft, might also do the trick.
- Attaching a giant solar sail to the asteroid
The solar sail (pictured below) uses the small, but constant pressure of sunlight acting over a large area to steadily move the asteroid.
Melosh points out that the sail needs to be steerable, like those on a modern yacht, to tug the asteroid in the right direction:
"An along-orbit push (at right angles to the sun) is by far the most effective in changing a collision into a miss," Melosh says.
There are two other ideas related to the solar sail concept: a giant silvery balloon, which in theory would be easier to deploy than a sail and wrapping the asteroid in foil (or painting it) to increase its reflectivity. Melosh explains, "with such a reflector it is hard to steer -- it can only apply a force directly away from the sun, which is the least helpful direction".
(Credit: NASA/JPL)
Melosh is cautious about techniques that depend on being attached to the asteroid.
"The asteroid is rotating and perhaps tumbling -- a hard object to tie anything up to," he says. "It would probably have to be enclosed by a system of gimbals anchored to the asteroid surface: a mechanical nightmare begging for a catastrophe."
The solar mirror scheme, preferred by Melosh, has the advantage that it could avoid the need for physical attachment to the asteroid. During the 1960s NASA did some work on solar mirrors for use in space, but little has been done since then.
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