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Using Gravity To Tow Asteroids
cryptocom writes "Space.com is reporting that two scientists at NASA are proposing using a 20-ton spacecraft to pull asteroids off a possible collision course with Earth, using the spacecraft's own gravity as an attractor. This idea would not only be cheaper, but have a much higher chance of success, due to not having to actually land on the asteroid's surface."
Interesting proposal, although the rate of towing still seems a concern if it takes a year to tow a 200 meter asteroid the small amount needed to make it miss Earth, with 20 years prep time required. Hopefully there aren't too many asteroids much larger than that which aren't currently tracked, but you never know.
If they're concerned about the amount of impulse delivered by a direct nuclear weapon impact, why not a series of projectile impacts (or at-a-distance, low impulse nuclear detonations)? While you'd have to launch more payload into space, the prep time would certainly seem to be far lower.
He's just being nice so my real father won't freeze him in carbonite and sell him for spice.
So comes the hard part of determining how far out the spacecraft would have to meet the asteriod and glide along beside it so as to veer the asteroid to a safe range of R kilometers from Earth. Any ideas?
If we're talking decades here, could this be used to send other asteroids into Mars to introduce the planet with some new water?
Isn't the problem here the 20 ton spacecraft?
Which
a) is difficult to move all by itself.
b) doesn't do much to a 6800 ton asteroid travelling at 1600 miles per hour.
------ The best brain training is now totally free : )
Here's a thought: how about launching a far smaller, more capable space craft which is able to gain mass on its way out of Earth orbit by collecting up whatever tonnage of free-floating space junk it needs from Earth's orbit?
If it employed some sort of lightwight truss-style, perhaps geodesic framework with cable "netting", it could form a lightwieght, but voluminous enclosure that could be used to capture orbiting space junk before heading off for its mission.
Overall, the idea of gravity-towing sounds pretty neat to me.
I know that people have already discussed the possibility of mounting a rocket on an asteroid, and it has many problems (namely that the asteroid rotates, and it would be difficult to mount the rocket) But if we are talking about parking a spacecraft next to an asteroid, why couldn't you simply mount an ion engine on opposite sides of a space craft, and point one beam at the asteroid, and one beam in the opposite direction. Wouldn't this beam impact the asteroid, and thus impart a thrust. I realize this would theoretically cost twice the energy of mounting the same ion beam on the asteriod, but it could fire continuously. Does the ion beam spread out too fast, because if it could stay collumated, I would think it could be quite effective.
And there is another way to do it. If you put two thrusters at the end of a boom that is that is the same length as the asteroid's diameter (assuming it is spherical), you could aim them so that they are nearly tangential to the asteroid's surface, resulting in more efficient use of fuel. The downsides are 1) extra mass for the boom & dual thrusters, and 2) balancing the thrust so that the "tug" doesn't spin.
But this entire approach strikes me as overly complex. Given that the whole setup is only going to exert less than 1lb of force on the asteroid, I'd have thought it was easier to mount a gymballed 5lb thruster on the surface and fire it in synchrony with the asteroid's rotation. You'd need to spread the force across a wide surface area, and take steps to minimize vibration stresses, but that's just engineering ... not "rocket science" :-)
I'm posting this here for attribution, just in case in 20 (or 50 or 200) years from now someone rediscovers this idea. Then they'll use the archives to discover that the idea used to save the world was originally conceived by me! (and boost my Karma score into the ionosphere!).
Basically one of the big problems of moving an asteroid is its rotation. Trying to move a big spinning object, is really hard. There is a tremendous amount of energy contained in the spin so fighting it will be very expensive.
So don't fight it, USE it. Lower a long rope to the surface of the asteroid letting the spin of the asteroid keep it taught. (same idea as a space elevator). Now ferry rocks way beyond the "Geosync" point, if the rotation is anything substantial it shouldn't be too far from the surface (a few tens of kilometers, no need for carbon nanotubes). Release the rocks into space, timing the release so that they shoot off in the same general direction.
What you're doing is converting the enormous rotational energy of the asteroid into kinetic energy of the rocks. Depending on how long your rope is (and thus how fast your rocks are released) you are going to get a substantial thrust in the opposite direction. (for every action there is a reaction). You are also making the asteroid smaller. As for the released rocks, while they may someday in the distant future hit the earth they'll be small and won't make it past the upper atmosphere.
Of course in addition to the long time frame (given) that this will take; this assumes that the asteroid is rotating (probably won't have to be too fast) and that you can attach the cable to some point on the asteroid. I believe most asteroids we've discovered have a substantial rotation, this is probably due to the violent manner in which they were formed and subsequently battered. As for the cable attachment, some nets and cables stretching around the asteroid should handle this just fine.
So there you have it. Instead of launching a huge expensive power hungry spacecraft that'll provide an absolutely tiny acceleration, you could send a relatively tiny spacecraft consisting of a few solar powered low mass robots (to move the rocks to the cable) and some sort of conveyor mechanism. While this'll take some engineering, it certainly is less than trying to have a 20 ton spacecraft do precision (because gravity is inverse squared you need to be close) station keeping off a tumbling (maybe chaotically!) asteroid for decades. If the rotation rate is high enough, you could even use the asteroid to generate energy (microwave beaming?).
wisebabo