British Company Takes Lead To Stop Asteroids

An anonymous reader writes to tell us that following the news of NASA's budget cuts impacting their ability to do things like watch the sky for asteroids, a British company has decided to create a "gravity tractor" ship that could divert asteroids away from Earth if the need should arise. Of course, a gravity tractor certainly isn't a new idea. "Dr. Cordey said the company had worked with a number of space authorities on other methods of protecting the Earth from asteroids, but this one would be able to target a wider range. He said: 'We have done quite a lot of design work on this with the European Space Agency and we believe this would work just as well on a big solid iron asteroid as well as other types.' But the high cost implications mean that before the device could be made, it would have to be commissioned by a government or a group of governments working together."

Re:Bad science

[Anonymous Coward]

!Bad Science.

Works perfectly fine if you have enough lead time. Plus much cheaper than pushing. Not a 'free lunch' but still cheaper

Not necessarily

[Sycraft-fu]

99942 Apophis will make a near pass to Earth in 2029. However, if it passes within a narrow window, called the keyhole, the Earth's (and Moon's) gravity will deflect it such as to place it on a direct Earth impact in 2036. Now this isn't all that likely to happen, but it is possible. Worth having some contingency plans for at least.

Re:Bad science

[SlashV]

Works perfectly fine if you have enough lead time

We should be happy enough when we see it coming at all.. How much "lead time" do you expect to have?

Re:Gotta find them first

[Anti_Climax]

IMHO, lets work on finding and tracking large asteroids first.

Already on it:

http://en.wikipedia.org/wiki/PAN-STARRS [wikipedia.org]

http://en.wikipedia.org/wiki/Large_Synoptic_Survey_Telescope [wikipedia.org]

Re:Not necessarily

[Exception Duck]

This should scare some people.
I actually don't recommend reading this if you obsess about things.
http://en.wikipedia.org/wiki/Risks_to_civilization,_humans_and_planet_Earth [wikipedia.org]

For the rest - have fun and sweet dreams.

Re:Bad science

[Nyeerrmm]

I'm curious what it being weaker than the weak and strong nuclear forces and the electromagnetic forces has to do with it. If the design works, it works. I'm curious to see your equations if you think it won't work. Also gravity is the only purely attractive force, and the one thats hardest to explain, which is why we really pay attention to it.

The advantage of a gravity tractor is that you don't have to land, because landing is a *VERY* hard problem on an asteroid. The biggest problem is that its very difficult to latch on, since you can't rely on gravity to hold you in place. Since you don't hae a good idea of the surface before you arrive, its rather difficult to design a solution thats going to work for all the different possibilities.

This leads one to consider how can you manage to deflect an asteroid without landing, and a gravity tractor is an obvious elegant solution. Note also that in this case you're still using the vaunted ion thrusters to impart the force on the asteroid. Considering the spacecraft and asteroid as two separate systems you have to use the thrust to maintain your standoff distance; considering them as one system (my preferred analysis), you have the thrusters moving the whole system, with internal gravity keeping the whole thing together. The only difference between it and landing, as far as thrust is concerned, is that you are limited to a maximum thrust by the gravity bond: the same sized ion thruster on a landed spacecraft and on a gravity tractor will have exactly the same effect.

The only time it would make sense to land is if you wanted to do a very high-thrust chemical burn (or maybe something like VASMIR, which would only be in the emergency case. Of course, in that case, the costs become irrelevant ($50B for a mission or wiping out Europe isn't a hard decision to make) and you're more likely to seek to impart a maximum impulse by doing a high-risk/high-reward method such as a kinetic impactor or nuke (and multiples as backup).

Re:Bad science

[SETIGuy]

Erm, actually, an asteroid big enough to knock out a city is about 10m in diameter. We'd probably have no notice whatsoever. Of course the likelihood that it would hit a city is pretty small.

Re:The only question is....

[Spy der Mann]

Don't worry, the time travelers will give us the technology JUST IN TIME.

Re:Not necessarily

[mhajicek]

Correction: through, not around.

Re:Bad science

[ppanon]

The problem is that a number of the objects of interest

1. may be particulate agglomerations that aren't solid enough to have something push at them,
2. are likely to be spinning, so that you would first need to stop their spin, otherwise see this [howstuffworks.com]
3. are likely to be of irregular shape and mass distribution that would make it difficult to push them efficiently in the direction you want without getting unwanted spin resulting.

Sure you could solve each of these problems individually, but a gravity tug bypasses them all at once, at the expense of needing either

1. more time to operate
2. a larger attractive mass requiring more energy to move both it and the target object

Probably the cheapest solution would be to refine a good sized nickel-iron asteroid into a compact solid metal mass and then attach a solar sail for thrust. Bonus points for compressing the metal mass into neutronium compressed by a diamond shell.