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Gravity Tractor Could Deflect Asteroids
Hugh Pickens writes "A new study at the Jet Propulsion Labs shows that weak gravitational pull of a "gravity tractor" could deflect an Earth-threatening asteroid if it was deployed when the asteroid was at least one orbit away from potential impact with Earth. First a spacecraft would be crashed directly into the asteroid, similar to the Deep Impact mission that impacted a comet in 2005. This would provide a big change of direction, but in a less controllable fashion that could push the path of the asteroid into a dangerous keyhole. But then a second spacecraft, the gravity tractor, would come into play, hovering about 150 meters away from the asteroid, to exert a gentle gravitational force, changing the asteroid's velocity by only 0.22 microns per second each day. Over a long enough time, that could steer it away from the keyhole. In the simulation, a simple control system kept the spacecraft in position, and a transponder on the asteroid helped monitor its position and thus determine its trajectory more precisely than would be possible otherwise. 'The gravity tractor is a wimp, but it's a precise wimp,' said astronaut Jack Schweickart. 'It can make very small, precise changes in orbit, and that's what you need to avoid a keyhole.'"
I hope their simulations use doubles, not floats!
I know you're joking but for just the speed values if they used time increments in the order of the second then the speed differences would be in the order of e-18, which is too small for a double's mantissa. I'd rather go with long doubles, or better (I think you can achieve something like that by using a number to store the closest representable value and another one to represent the tiny difference from what it should be).
You just got troll'd!
http://en.wikipedia.org/wiki/Gravitational_keyhole
This article is sooo 2007. http://science.slashdot.org/article.pl?sid=07/03/17/0538220
One of our competitors trademarked the term "hypothesis". From now on, we will call them "boneheaded ideas".
Who modded the parent "insightful". The answer is pretty simple, and is even illustrated in the article. The picture shows a craft with three thrusters all angled away from the asteroid. The resulting thrust is a vector normal to the target. Sure, it sacrifices efficiency, but it works.
You never really know how close to the edge you can go until you fall off.
(I think you can achieve something like that by using a number to store the closest representable value and another one to represent the tiny difference from what it should be).
Yup. It's the Kahan summation algorithm. It works as you describe it and it used to compensate the error that happens when doing very big sums of very small numbers (exactly the situation in the gravity tractor's problem)
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Gravity Tractor? You know I love these sky high fantasy ideas to deflect asteroids as much as anyone else but shouldn't we be concentrating on what is real? If an asteroid does threaten Earth in the next few years we will use nuclear demolitions on it. We will not use a gravity tractor, laser beams, or giant snow balls. Nor will we attach plasma engines or mass drivers to it. We will use nuclear demolitions because that is, simply, all we have.
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We wont' use one nuke. We will blowup the big one then we will blow up the smaller ones into smaller pieces. We will do this until the chunks are small enough that the atmosphere will handle. With smaller chunks there is more surface area for the atmosphere to work on. Most importantly the smaller chunks will not "crack the crust" as one fat ass one would.
Blowing up an asteroid isn't necessary, and with only a couple of years' notice, it isn't very effective, either. For details, see:
https://e-reports-ext.llnl.gov/pdf/343984.pdf
Nuclear explosives are a good tool for this job, just not in the way that you think they are.
A gravity tractor is not a sky-high fantasy idea. It's simply giving a name to the fact that all objects attract each other at least a little. They're hovering a little spacecraft near the asteroid and then moving it away under low-power. The asteroid follows slowly due to the laws of physics, not because the ship carries a star-trek tractor beam. Yes, in the future we will send men to explore non-threatening asteroids. But currently we don't even have manned ships built that can get beyond low earth orbit. So no, the odds are we won't be sending men to do it, except perhaps as a backup. A small robot "tug" like this one is the only option other than nuking it with ICBMs until we have longer-range craft built.