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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.'"
Do I get a nifty green hat to wear while I'm on it?
"It is a miracle that curiosity survives formal education." -Albert Einstein
I hope their simulations use doubles, not floats!
In a sense, you could apply the same approach, except try to modify earth's orbit, which might actually be easier...
Bruce Willis hovers over an asteroid for two action-packed hours!
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Will be done by holding monthly Gravity Tractor Pulls at the local fairgrounds, with free beer.
Just disrupt the deflector shield with a tachyon burst.
Could someone with the proper knowledge submit a Wikipedia article for keyhole? The word is used in the summary three times and seven times in tfa. I guess the term is here to stay.
Thank you.
Their they're doing there hair.
... and I thought it would be more like this.
How is gently pulling the asteroid with a weak gravity string more efficient than just landing the same "tractor" on the asteroid and pushing it gently but directly?
If all they're trying to do is move the orbit of the asteroid by a fraction or a millimeter per second, wouldn't it be easier to just, you know, harpoon the asteroid and use ion engines to gently pull on it rather than trying to keep a second spacecraft hovering over the non-smoking crater of the first spacecraft? Or, if harpooning isn't viable (cue 'Whalers on the Moon'), just have the spacecraft rest on the asteroid's surface and, using ion engines again, push on the thing.
Can someone more well versed in orbital mechanics and the motion of bodies in space please provide some information as to why these are not viable options.
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Wouldn't it be easier (and more effective) to have something land on it once, latch on, and fire rocket boosters to move it rather than to drive next to it for a long time?
The masses are the crack whores of religion.
TFA spells it out very nicely. Get there one orbit early (a year or a little longer) then gently tug. Of course that's for a small asteroid, for a dinosaur killer maybe five years. If you wait until the object is a few weeks away you are toast. Cindered toast. The entire "nuclear might" of the planet launched at the intruder will do diddley squat, Bruce Willis or no Bruce Willis. That's why NEAR should get lots more funding.
I choose to remain celibate, like my father and his father before him.
Its probably a good time to remind people that the distributed computing project to search for dangerous NEOs is soon to get under way. Test workunits have already been sent out and the news is that they ran very well.
After they've lined up, what then?
This article is sooo 2007. http://science.slashdot.org/article.pl?sid=07/03/17/0538220
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Barman: Do you really think the world's about to end?
Ford: Yes, in just over 3 minutes and 5 seconds.
Barman: Well, isn't there anything we can do?
Ford: No. Nothing.
Barman: I thought we were supposed to lie down, put a paper bag over our head or something...?
Ford: Yes, if you like.
Barman: Will that help?
Ford: No. Excuse me, I've got to go.
Barman: Ah, well. Last orders please!
We should be watching to see if the dolphins leave the Earth by their own means.
You are presuming that landing is possible. The object in question might be a loosly-conglomerated gravitationally bound pile of rocks and dust.
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If it can be guided away from the keyhole, could it not also be guided towards? I think this presents a wonderful opportunity for extortion. If I only had the resources I would shave my head, get a cool chair, and become adept at holding my pinky to the corner of my mouth in an evil fashion.
Even if the asteroid is solid, and there is some 'miracle' way of anchoring the rocket to the asteroid: Landing and pushing requires the assumption that the center of gravity and the shape of the asteroid is such that you can position the rocket push in a productive manner and not just cause the rock to pinwheel or split in two.
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.
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.
We will not send a robot to do it nor will we send some type of futuristic space ship driven by plasma/ion engines. It will be a manned ship with old style chemical rockets right out of the '60. Why? Because we have over 60 years experience with them and they will get the job done. We'll send men and not a robot because the mission is to important to have place in the hands on questionable technology. A robot breaks down and the mission is over. With men at least you have some hope they can fix it. Yes, it will probably be one way but the pilots will know that. They will go anyway.
Yes, we will break it up in to smaller pieces because that is best. Don't give me that shotgun crap about it scattering the damage over a wider area. We will think of that and cover it. If we let a huge honking rock ride in the atmosphere will not even slow it down. It will punch through it like it isn't even there. Worse is it will punch through the crust to the mantel causing shockwaves all around the planet.
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.
Supporting World Peace Through Nuclear Pacification
True, however in the case of a gravity tug, your maximum useful thrust is limited by the gravitational interaction, which is limited by how close you can get. Landing takes one of the variables away, and trades it for the ones you mentioned. If it's solid, your maximum effective thrust can be very high, even if you can only use it a shorter percent of the time.
In specific cases, landers probably would be more effective. But gravity tugs are a much better general solution, and mass-production favors general solutions.
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(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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Promote proofreading. Don't mod up sloppy posts.
Actually, there is no free meal there. If you exert a force F on the asteroid, you get -F exerted upon the tractor. (Imagine a cute little vector mark above the F, to be completely true.) There is no known way to escape that.
If you always stay X metres in front of the asteroid, then effectively you can treat the whole system as one body. You're not just accelerating the asteroid (with mass m1), you're also equally accelerating the tractor (let's call its mass m2) with the same acceleration, or they'll collide or drift apart. So effectively you're accelerating the sum of their masses, m=m1+m2.
The force to do that is still F=m*a, or F=(m1+m2)*a. There is no free lunch. You're still accelerating the same m1+m2, and if done at the same a, you must apply the same force F. I.e., if the same rocket engine is used, you get to burn the same amount of fuel, regardless of whether they're physically in contact or weakly pulled by gravity. Using gravity there just puts a (very low) upper bound on F.
But wait, that was assuming the ideal case, where you magically apply _exactly_ the amount of force to stay always at X metres drom the asteroid. Reality is much less ideal. Such a tractor would probably have to fire rocket engines back and forth, just to stay anywhere near the prescribed distance. I.e., it would use extra fuel for positioning and maneuvering, whereas a lander with a big jet pointed "upwards" would have no such worries.
Just about the only reason I see there, is if you have to essentially rotate the system, to execute some complex maneuver with the asteroids (over aeons, mind you.) Then it's probably less waste to just move the tractor around the asteroid, than to rotate the asteroid with your thruster embedded in it.
Still, I'm kind of at a loss as to when or why you'd need that, or have the luxury of enough time for such infinitesimal accelerations to do the job. More realistically, you'd just want the asteroid's orbit changed enough that it doesn't collide with Earth. And you'll likely not have that awfully much time. So you just want to push it out of the way, hard enough to make a difference, but not hard enough for it to shatter into a MIRV of death and destruction. Probably the safest bet being to push it upwards or downwards, in regard to Earth's orbit, so it becomes a lot more inclined than the orbit which threatened to collide. You have a lot more margin for error in the calculation there. You don't need to rotate and maneuver it accurately, you just want it out of the way.
So basically while I'll agree that their method could work, I'm kinda at a loss as to why would you want to do it that way.
A polar bear is a cartesian bear after a coordinate transform.
It seems that if you wanted to change it's course by a continuous amount, that simply increasing it's mass by pushing other material into it's field would make the sun do the work. Just a random thought.
I just got a patent on giant space traffic signs to divert and manage traffic flow. More effective and it does not get stuck in space mud. Plus I can't get sued if my product fails! hahaha I'll be rich.
lol: You see no door there!
If you place your massy spacecraft near an asteroid and let go, the two will mutually attract each other and eventually collide. The centre of gravity of the system won't change.
So, in order for this to work at all, you need a manouevering system on the spacecraft in order to maintain its separation from the asteroid.
The thing is, though, that from a pure orbital mechanics point of view, this is absolutely equivalent to simply mounting the spacecraft's thrusters on the asteroid itself. In fact, using the gravitational tractor is probably going to be rather less efficient, because the geometry of the system is such that you have to fire your thrusters towards the asteroid --- and a certain amount of your thruster exhaust is going to bounce off the asteroid's surface, imparting momentum in the wrong direction to the asteroid.
The only things I can think of that the gravity tractor does for you that direct acceleration doesn't is:
But, given the type of accelerations we're talking about --- which will be the same regardless what technique you're using --- I wouldn't imagine that either of these would be a problem in practice. So, what makes the gravity tractor so much better than just using rockets? Indeed, what makes it better than alternative approaches like spraying the asteroid with aluminium powder (which raises the albedo, causing increased photon pressure, which alters the orbit over time)?
How about we launch 'accelotrons" to generate wormholes around the threatening asteroids and cometary matter. Just send them off... POOF! GONE. (Well, until beings from Klixator Prime and other places come knocking on our door with cease and desist orders due to all OUR life-extinguishing heavenly bodies create junk yards in other worlds...)
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The 'Gravity Tractor' device was discussed somewhere on or off the net as it might relate to 'saving the earth'. As i recall, the topic was about the ultimate demise of our Sun .. in 5 billion years or so .. The process of the Sun's destruction will include its diameter expanding .. the Sun's surface approaching Earth's orbit.
LONG before that, of course, the heat would sterilize our world. The proposal was to navigate a large asteroid to 'lead the earth' in its orbit around the Sun.. accellerating Earth to a higher orbit, adding millions of years of biology to continue to exist.
I seem to recall that such an asteroid would need 64,000 years to accomplish its goal. At the time, i concluded that this would represent an engineering project of the largest possible scale ..
In the meantime, our highways and bridges would continue to fail, of course.
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I suggest you to check NASA's program for tracking asteroids: NEAR-EARTH ASTEROID TRACKING (NEAT). http://neo.jpl.nasa.gov/programs/neat.html
It will be much easier to colonize the moon if we move it a bit closer.
In one of his books Dyson warns against the idea of blowing up approaching asteroids and proposes mass drivers that push the asteroid into a new orbit over extended periods, possibly years. Factors I can think of from the top of my head:
- a mass driver needs mass, which it gets from the asteroid. So you don't have to sling huge masses towards the asteroids.
- anchoring the mass drivers can be a problem if the asteroid is brittle. Bigger asteroids may be stronger but you also have to push harder.
- you can have many mass drivers
- the more time you have the better.
So the special thing about a gravity tractor is that it's a reliable way to attach a mass driver to any type of asteroid. The tractor still needs mass drivers and it needs a lot of mass to build up the gravity. If you see the asteroid as a "soft waterball" that is hard to push, you could consider the tractor as an empty box with . It flies over, fills itself with parts of the asteroid and starts pulling.