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Using Gravity To Tow Asteroids 508

cryptocom writes " 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."
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Using Gravity To Tow Asteroids

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  • by nizo ( 81281 ) * on Wednesday November 09, 2005 @05:24PM (#13992329) Homepage Journal
    2000 lbs in a ton
    20 ton spacecraft
    $10,000/pound to get to geosynchronous transfer orbit

    $400,000,000 just to launch this thing into a geosynchronous transfer orbit (not counting construction costs). I assume the fuel to move it isn't included in the 20 ton estimate either (since it will burn off on the way) so that would need to be lifted as well. I wonder if a huge nuke would be cheaper and easier to construct and launch? Then again, with the current U.S. national debt at over 8 trillion (with which we could pay for the launch costs of 20,000 of these things) maybe the launch costs aren't unreasonable.

    • by lightyear4 ( 852813 ) on Wednesday November 09, 2005 @05:28PM (#13992367)
      I don't think you should place a price upon the value of saving civilization.
    • by Gulthek ( 12570 ) on Wednesday November 09, 2005 @05:28PM (#13992370) Homepage Journal
      Maybe to stop a huge asteroid from impacting on the Earth's surface the cost would be quite reasonable.

      I.e. I don't think that world leaders would look at the figures and go "Hrmmmmm...when you say extinct?"
    • Hey, I have an idea. They could first launch a smaller satellite that would attract all kinds of space debris until it's big enough to take out an asteroid. It'd spin around the Earth until an asteroid came about, and then they could just fling it in the direction of the asteroid!

      Better yet, they could have several of these things circling up there, just in case.

      PS: yeah, I know it's not Tuesday, but I couldn't resist :7

    • Better to build the thing in orbit, using mass from the asteroid belt. Should cost a lot less to get the mass where you need it.

      Of course, that's going to require some infrastructure. Which reminds me, why was the ISS built in LEO again? ;-)
    • Lets say the asteroid hits New York and whipes out its population and buildings that is going to cost ALOT the country alot more than 8 trillion dollars. You cannot put a price on human life!
    • Nice illustration of the miniscule strength of gravity relevant to tonnage, and how over long periods of time, it's possible to use gravity assists for just about anything. It is important to understand how weak - but persistent - and wonderful - interactions with gravity can be. The Grand Tour that Voyager went on, for example, or the Interplanetary Superhighway [], or Lissajous orbits []....

      The spacecraft design with the angled rockets is wasteful, but if you are getting the fuel from the asteroid, the fuel i

      • by GryMor ( 88799 ) on Wednesday November 09, 2005 @06:14PM (#13992870)
        'Hoovering' isn't going to work, suction is just the difference between a high presure area and a low presure area. In order to 'hoover' in this environment you would need to have a zone inside the space craft with a presure lower than the presure outside the spacecraft. The presure outside the spacecraft is aproximately 0, so, good luck with creating an area of negative pressure (which would require a negative number of atoms, a negative absolute temperature or a negative volume...)
    • Well you probably want it to come back again too... if it was in two parts you could just eject one part the opposite direction with a giant cord attached to it. After the asteroid course was changed you could just reel the parts back together again. With some kind of 'cord' that could become rigid you could use solar power or nuclear power push/pull the pieces and so deflect any number of asteroids. And if there was some emergency you could also project one half into the path of the asteroid to break it
    • It would be more efficient to build it in space. Perhaps even on or orbiting the moon, using lunar material. This could then justify creating a permanent lunar base, which could have other uses besides saving the Earth.
    • Why not get the best of both worlds? Make it Orion []-powered.
    • I wonder if a huge nuke would be cheaper and easier to construct and launch?

      Most likley, but you might end up making the world's largest shotgun out of a asteriod made of iron.
    • Since most of it only needs to be mass, they could just start tacking moon rocks onto it or into it. Or defunct satellites, there are plenty of those around.
    • i don't think you want this in geosynchronous orbit. to change the trajectory of an asteroid with this small mass you would need to get close to it at a much larger distance from earth. if it's close enough to have something geosynchronous affect it then it's already too late.
    • by JesseL ( 107722 ) on Wednesday November 09, 2005 @05:55PM (#13992679) Homepage Journal
      Commonly quoted statistics with regard to price-per-pound are nearly meaningless. They are almost always based on simply dividing the cost of a launch by the mass of the payload.

      Does the cost of operating your car double when you add a passenger?
    • Not unprecidented (Score:4, Insightful)

      by pavon ( 30274 ) on Wednesday November 09, 2005 @06:19PM (#13992916)
      The Saturn V was capable of sending around 50 tons to the moon (over 120 tons to LEO), and the planned STS Heavy Lift Vehicle will be slightly more powerfull. Even with existing rockets, the Titan IVB/Centaur and the Delta IV are each capable of sending over 6 tons to geosyncronous orbit.

      For recent comparison, the shuttle orbiter is over 100 tons and capable of carrying about 30 tons of payload to LEO Cassini was about 6 tons, and we sent it all the way to Saturn.

      If we could afford to launch all these things, then we can afford to launch something to prevent a cataclysmic astroid strike.
  • 20 Ton Tractor (Score:3, Interesting)

    by geomon ( 78680 ) on Wednesday November 09, 2005 @05:24PM (#13992331) Homepage Journal
    That would make the rig smaller than an 18-weeler. Their gross weight capacity is 40 tons.

    That would place it safely in the realm of 'Cube Truck' capacity.

    Hell, they wouldn't even have to stop at the scales in some states.
  • by phpm0nkey ( 768038 ) * on Wednesday November 09, 2005 @05:25PM (#13992336) Homepage
    "The kind of spacecraft we've talked about could move an asteroid 650 feet (200 meters) across provided we have decades of advanced warning,"

    Neat... although, if this works, it will totally kill the Hollywood "asteroid catastrophe" genre. The concept of sitting a giant hunk of metal next to an asteroid for 20 years to gradually shift its path doesn't exactly make for fast-paced, high-tension action movie fare.
  • by Anonymous Coward
    Dealing with the impact of a 20-ton spacecraft on earth.
  • by Rei ( 128717 ) on Wednesday November 09, 2005 @05:27PM (#13992363) Homepage
    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.
  • "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."
    ... and blow it up!
  • by jkauzlar ( 596349 ) * on Wednesday November 09, 2005 @05:29PM (#13992381) Homepage
    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?

    • Well let's see... That would apply an acceleration of 1.11x10^-12 m/s^2 to the 'roid...

      On the other hand, the same gravitational force would be acting on the spacecraft, and F=ma gives us 5509 m/s^2 there...

      Am I calculating this wrong? Because it seems it would take a hell of a lot of fuel to keep that spacecraft from just crashing into the asteroid... And they plan to keep this spacecraft sitting next to the roid for years?

      Nuke it.
    • by twiddlingbits ( 707452 ) on Wednesday November 09, 2005 @05:59PM (#13992715)
      Wouldn't that would be 10^8 Newtons of force pulling the spacecraft toward the asteriod? The asteriod is much more massive and would have a gravity well of it's own. Wouldn't that attractice force have to be overcome for 20 yrs, plus a slight acceleration in the direction the asteroid needed to move? The 20 ton spacecraft would have a higher force of gravity on the 'roid than that of the Sun for 20 yrs (or however long the tractor lasts) so it could gradually change to orbit, How do we make things that can stay in space for 20 yrs w/o repair? How do you get that much fuel on-board? Solar Cells are not an option that far from the Sun. A nuclear reactor maybe but they would have all sorts of issues there, even if the "tractor" was not launched from Earth, the fission elements would have to be launched as I don't think you find Uranium just floating in space. And heaven forbid someone mis-calculates and they push it onto a collission course..they it takes another 20 yrs to fix that! This article sure makes a LOT of assumptions and figure on new ideas/technologies we don't have. It is a neat idea but IMHO it belongs under the topic of Science Fiction not in a journal like Nature.
    • by n0dalus ( 807994 ) on Wednesday November 09, 2005 @06:15PM (#13992880) Journal
      Actually the force is much less than that.

      F = GmM/r^2

      For a 20000kg object, and a 9e19kg object (Hygiea), with a distance of 205km between them (1 km away from the asteroid, but the distance between is the centre of masses is much greater, Hygiea has a radius of 204km), the force is 2870N. In comparison, the force of gravity from the Earth will be that much 3.53e12 km away (471 times the distance of Pluto from the Sun at it's farthest point in orbit). It's just more than the gravitational force of four 70kg people standing on the ground.
      In other words, if a big asteroid comes at us, we are royally boned.
  • How about using momentum from an astroid to provide power? Any Ideas?
  • by Spectre ( 1685 ) on Wednesday November 09, 2005 @05:30PM (#13992400)
    Great, the asteroids miss the earth, but damage from falling 20-ton spacecraft becomes an issue.
    • mir (Score:3, Informative)

      by elinden ( 155827 )
      mir weighed 135 tons and it burned up just fine on its way down. 20 tons, relatively speaking, isn't really all that much.
  • I for one welcome... (Score:2, Interesting)

    by xv4n ( 639231 )
    ... our new asteroid-deflector overlords.

    So, by the same means they can put an asteroid in a direct collision course.

  • I remember a NASA article about this, but it was in relation to using asteroids to engineer a change in earths orbit to compensate for global warming. Amusing!
    • A bit OT, but... Here's the article abstract to which I was referring: Astronomical Engineering: A Strategy For Modifying Planetary Orbits The Sun's gradual brightening will seriously compromise the Earth'sbiosphere within sim 109 years. If Earth's orbit migrates outward,however, the biosphere could remain intact over the entiremain-sequence lifetime of the Sun. In this paper, we explore thefeasibility of engineering such a migration over a long timeperiod. The basic mechanism uses gravitational assists t
  • Uhm... if we can send something so large that its gravity will affect an otherwise Life-on-Earth-as-we-know-it-ending asteroid's course, then how about an enormous tow cable in addition to that and slinging that puppy in another direction...say... the sun or something.
  • by shrewd ( 830067 ) on Wednesday November 09, 2005 @05:35PM (#13992461)
    this isn't a follow-up story to "asteroid on collision coarse with earth" IS IT!?!?
  • "...provided we have decades of advanced warning," Lu said. "That's not out of line with what you'd expect - we can predict the orbit of an asteroid decades in advance."

    This just in:

    Response from FEMA: "Not good enough. We need more time."

  • by novus ordo ( 843883 ) on Wednesday November 09, 2005 @05:36PM (#13992477) Journal
    ...with women, but I've had mixed success(wrong body part got gravitationally attracted to my face).
    • sheesh. It's simple physics, really. Action-Reaction. You have massively overestimated the size/mass of your 'attractor' and didn't calculate the vector of the reaction properly.
  • by Astin ( 177479 ) on Wednesday November 09, 2005 @05:37PM (#13992482)
    The big, huge meteor headed toward Earth. Could nothing stop it? Maybe Bob could. He was suddenly on top of the meteor--through some kind of a space warp or something. "Go, Bob, go " yelled one of the generals. "Give me that" said the big-guy general as he took the microphone away. "Listen, Bob," he said. "you've got to steer that meteor away from Earth." "Yes, but how?" thought Bob. Then he got an idea. Right next to him there was a steering wheel sticking out of the the meteor.

  • As suggested over at Intuitor [], why not send up a team of bowling experts to create a hole to the center, and then detonate a few nukes?


  • Terraforming? (Score:4, Interesting)

    by NelsonM ( 906317 ) on Wednesday November 09, 2005 @05:39PM (#13992507)
    If we're talking decades here, could this be used to send other asteroids [] into Mars to introduce the planet with some new water?
  • by popo ( 107611 ) on Wednesday November 09, 2005 @05:41PM (#13992541) Homepage

    Isn't the problem here the 20 ton spacecraft?


    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 article indicates that there is an issue of the asteroid/comet being broken apart by the shock of the thrust, but I have a hard time believing that this is the case if the amount of thrust is on the order of 1 lb. I would have to believe that a small thruster with a large plate to spread out the force of the thrust could be placed on the object.

    Of course, dragging the object by gravity would avoid the issue of having to despin the object or coming up with a thruster or multiple thrusters placed on the
  • Save Money (Score:2, Funny)

    by jatemack ( 870255 )
    Just send Kristie Alley up there. That should work.
  • "That's no moon!" (Score:3, Interesting)

    by skelly33 ( 891182 ) on Wednesday November 09, 2005 @05:47PM (#13992597)
    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.
  • 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."

    Sounds like the makings of a sequel. Armageddon 2: Nerds Save the World

  • by orichter ( 60340 ) on Wednesday November 09, 2005 @05:49PM (#13992622)
    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.
    • by adrianmonk ( 890071 ) on Wednesday November 09, 2005 @07:31PM (#13993571)
      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.

  • by 8127972 ( 73495 ) on Wednesday November 09, 2005 @05:51PM (#13992639)
    ....Bruce Willis happy.
  • ...this 20 ton vehicle wouldn't you be better off simply sending the engine up without the 20 tons and have it push the asteroid directly? Even if the asteroid rotated, you could fire the engine in bursts, once per revolution. This is hardly 'complicated', it's elementary physics. You (1) wouldn't have to launch 20 tons and (2) you could get the job done much quicker. If you can spot an asteroid 20 years in advance you wouldn't need to use the thrusters for long to push it out of harm's way.
  • Fuel? (Score:3, Interesting)

    by ThePyro ( 645161 ) on Wednesday November 09, 2005 @06:00PM (#13992723)
    From the article:
    "But pushing it would require too much fuel..."

    Correct me if I'm wrong, but wouldn't pulling it with gravity use even MORE fuel, since you're basically expending the same amount of fuel to move the target, plus additional fuel to move the 20-ton gravity "tug"?
    • Re:Fuel? (Score:5, Insightful)

      by phritz ( 623753 ) on Wednesday November 09, 2005 @06:24PM (#13992962)
      Actually, it would take precisely the same amount of fuel - either way, you're moving the tug plus the asteroid. The whole idea with this method is simply that gravity is a very gentle force. Pushing the asteroid by attaching a rocket to it or exploding something next to it are both very sharp, uneven forces that could very well break it up in to little pieces. Some of those pieces would probably hit the earth, even if the main bulk didn't.
  • by nmos ( 25822 ) on Wednesday November 09, 2005 @06:23PM (#13992947)
    What makes them think we're going to have that much warning? A few years ago we had a fairly near miss and only had a few days warning. There wasn't a whole lot of warning about the comet that hit Jupiter either. Remember asteroids don't emit any light of their own, they are small compared to a planet or even our moon, and they are are coming in from quite far away from the Sun so they aren't exactly the easiest things to see.
  • Absurd (Score:3, Interesting)

    by gseidman ( 97 ) <`gss+sdot' `at' `'> on Wednesday November 09, 2005 @06:55PM (#13993239)
    If you are willing to accept the small size and long lead time, there are better solutions. How about a solar sail? How about giving it a static charge (perhaps spraying from an ion drive, but cathode rays would do the job, too) and using big-ass magnets? If it's icy you can just focus lots of heat (big-ass mirrors) on one side and make its eruptions change its course. Hell, if it's that small, just fire lots of small, fast projectiles (magnetic acceleration of moon-mined iron, perhaps). There are innumerable ways of providing the energy for the dV needed to alter the asteroid's course that do not involve that much mass, that much expense, that much Earth-provided energy, that much fine control, or even that lack of reusability. What a godawful idea.
  • by Physics Dude ( 549061 ) on Wednesday November 09, 2005 @09:10PM (#13994266) Homepage
    They do the force calculations, but don't think this through far enough.

    Assuming a spherical iron asteroid with a 100m radius (the article mentions two football fields across) and a 20 ton ship you can provide a maximum gravitational force of about 1 pound. This is find and dandy and could provide a deflection of nearly the diameter of the earth over a decade period.


    The problem is how to produce that required force on your ship without impacting the asteroid. Conventional rockets or ion thrusters would necessarily be directed in the direction of the asteroid which would nullify any net force on the system (ship+asteroid). If you get enough distance between the asteroid and the ship so yout thrust can miss the asteroid and provide a net force, the force you can provide on the asteroid due to gravity drops as the square of the distance and becomes unusably low. You'd need litterally centuries or millenia of advance warning!

    If anyone has ideas how to avoid this problem, I'm all ears. :)

    • by bigsteve@dstc ( 140392 ) on Wednesday November 09, 2005 @10:10PM (#13994632)
      The article addresses this. They say that the thrusters would be angled to miss the asteroid. They also mention that this results in less efficient use of fuel.

      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" :-)

  • by darklordyoda ( 899383 ) on Wednesday November 09, 2005 @09:26PM (#13994372)
    An asteroid called Apophis has a chance of hitting Earth, and I don't see one Stargate SG-1, or by extension, MacGuyver joke.

    I'm disappointed in you, Slashdot nerds. For shame!

  • by griffjon ( 14945 ) <> on Wednesday November 09, 2005 @09:30PM (#13994395) Homepage Journal
    Next: Nasa patents "A Method and Process for Using Gravity To Tow Asteroids"

    God loses his appeal based on prior art, ends civilization in retaliation.
  • by wisebabo ( 638845 ) on Wednesday November 09, 2005 @10:12PM (#13994649) Journal
    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?).


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