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."

Comments

Interesting, but slow

[Rei]

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.

It's been awhile since I've taken physics...

[jkauzlar]

but since it seemed strange to me that a 20 ton object could possess any considerable gravitational force I did a quick calculation, with a lot of rounding, to determine the force between the 20-ton object (~18150 kg) and the fourth largest asteroid Hygiea which has a mass of about 9x10^19 kg. My result, for a distance of 1 kilometer between the spacecraft and the asteriod, was 10^8 Newtons of force.

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?

Terraforming?

[NelsonM]

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...

[popo]

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.

Why can't we simply use an Ion engine.

[orichter]

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.

Re:Why can't we simply use an Ion engine.

[adrianmonk]

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.

I thought of this exact idea, but then realized there is bit of a wrinkle: the ion stream will be pushing the asteriod away from the craft (and vice versa) but at the same time, gravity will be pulling them towards each other. So, you will be working against gravity.

And then the problem becomes that ion thrusters don't tend to have a very high amount of thrust. Their strength is that they can produce thrust without wasting very much matter because of the high velocity with which the ions move away from craft. So, I wonder if the ion drive will even produce as much force as the gravitational attraction between the asteroid and the craft. It might not. Even if it does, you still are fighting against gravity.