Spacecraft Could Save Earth from Asteroids

Sep 04, 2009 by Lin Edwards weblog
Asteroid (2867) Steins. Image: ESA

(PhysOrg.com) -- British space engineers working for a space company in Stevenage in England, have designed a "gravity tractor" spacecraft to deflect any asteroids threatening to collide with Earth. The announcement comes only weeks after an asteroid collision scar around the size of Earth was detected on Jupiter.

A collision with an is a rare event, but scientists believe it is inevitable that sooner or later an asteroid will come close enough to be a real threat. In fact in 2004 an asteroid called Apophis caused alarm when scientists predicted there was a 1:37 chance of it hitting Earth in 2029, which is the greatest threat in recorded history. They later revised their figures but it could still be on course to collide in 2036. The US space agency, estimates there are at least 1000 "potentially hazardous asteroids."

NASA is so concerned about the threat it has set up a monitoring program to track every space object that could be an asteroid on a collision course. They are so far tracking over 6,000 asteroids whose orbits bring them close to Earth, but there are an estimated 100,000 asteroids large enough to wipe out a city.

A collision could be catastrophic, depending on how large the asteroid is and where it hits. A direct hit to a city by even a relatively small asteroid the size of a football field, for example, could completely destroy the city and kill millions of people. Many more could be killed by tsunamis triggered by the impact, and by dust and burning material thrown up into the atmosphere after the collision.

The engineers, led by Dr Ralph Cordey, head of exploration and business at EADS Astrium, a British space company, have designed what they call a "gravity tractor", a ten-tonne spacecraft around 100 feet long that could provide a practical way of averting a collision with Earth.

The device would be launched as soon as an asteroid was found to be on course to crash into the planet, and would fly alongside it at a distance of about 160 feet away. The craft could divert an asteroid up to 430 yards in diameter, and an impact with an asteroid this size would release around 100,000 times the energy of the bomb dropped on Hiroshima in 1945.

The gravity tractor is designed to draw the asteroid towards itself by exerting a small gravitational force on it. The spacecraft would then steer the asteroid away into an orbit away from Earth.

The craft would use four ion thrusters, which are low energy and efficient, of the type commonly used on deep space probes. The ion thrusters enable the craft to adjust its position relative to the asteroid. The gravitational pull exerted by the asteroid would be enough to nudge the rock into a different, and less dangerous, trajectory.

The process of steering the asteroid away from a collision course would take several years, with the craft changing the angle of trajectory by only a fraction of an inch over 15 years, but that is enough change to divert an asteroid. The spacecraft would need to be launched at least 15 (preferably 20) years before the predicted collision to give it time to adjust the asteroid's trajectory away from Earth.

The design team say the gravity tractor could be built fairly quickly with existing technologies, although a prototype has not yet been built. They have planned the details of the mission, and expect the cost could be shared by a number of governments if an asteroid on track to hit Earth was discovered, and international agreements would need to be drawn up.

NASA published a paper earlier this year on the feasibility of using a gravity tractor for this purpose, and they concluded it could be extremely effective if there was enough warning. With scientists saying the asteroid Apophis could possibly be on a course to collide with in 2036, perhaps we do have enough warning.

© 2009 PhysOrg.com

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otto1923
2.8 / 5 (4) Sep 04, 2009
Too complicated, too politically correct- instead, spread albedo-changing powder over one side of the gravel pile or detonate a series of nukes in the vicinity. Both options have been possible (and most likely already performed) since Apollo.
MrFred
2.8 / 5 (4) Sep 04, 2009
OK, if you have enough warning...anything is possible! This thing would have to get shot out at the asteroid, then slow down, stop reverse directions back towards earth, match speeds with the asteroid and THEN it could start pushing...all this with ion engines? OK, it could work.
What doesn't work is our ability to predict an asteroid's exact path 15 years in advance. For all our technology we'd probably steer the thing right into a collision coarse!
jaggspb
3 / 5 (4) Sep 04, 2009
just design a spacecraft with phasers or photon torpedoes and be done with it already.
otto1923
3.7 / 5 (6) Sep 04, 2009
What doesn't work is our ability to predict an asteroid's exact path 15 years in advance. For all our technology we'd probably steer the thing right into a collision coarse
I know what I know and I'm not too sure I know what you know, but I'm certain I do not know the whole extent of what THEY know. It's a sure bet They wouldn't tell us they were launching an uncertain mission to maybe prevent a collision in a few years. Markets would crash, militias would take over Michigan. Hard to know what They know and what They are capable of. Inference and imagination help.  
Orly
3.5 / 5 (4) Sep 04, 2009
Shoemaker Levy was deteced ONLY 2 yrs. or so (give or take a few months)and soon after was predicted on course for impact on Jupiter. So they only had 1.5-2 yrs of prep for that one, but they were not observing Jupiter the way that Earth will is being monitored. But once these Comets/Ast. are found the clock starts ticking away !
RayCherry
4.3 / 5 (3) Sep 04, 2009
There is nothing new with this idea, other than the fact that some engineers have taken it from the concept to the design phase, with estimates of cost and potential effective use. An important step, but one that most people will ignore as irrelevant as any problem that is fifteen to twenty years away 'belongs to the people who will be here then'.

I am sure the albedo changing powder, (painting/covering one side of a threatening object), to make use of the solar wind is also being evaluated, but its effectiveness is limited due to the varied (multi axis) rotations of most of these objects.

As for the suggestion of nuking the object, or setting off of nukes in the vacinity of an approaching object, this runs the rick of simple not diverting the object from collision course while irradiating the object so that it is nuclear active when it arrives in our atmosphere, (even a bundle of rubble and powder would then leave a radiative cloud for us to deal with for hundreds of years thereafter).

As crazy as the Gravity Tractor sounds, perhaps it has the least possibility of making the situation worse, hence the cost/benefit analysis may prefer this method of deflection.

By the way, I doubt very much that the Tractor would be sent towards an approaching object so that it would have to stop and then reverse to stay along side an incoming object. Probably they are looking at scenarios where there will be one or more close approaches predicted before the impact approach, in which case the Tractor will launch, race to catch up with and then accompany the object in the orbit(s) prior to to the predicted impact.

As mentioned above, NEO 2004-MN4 "Apophis" is following a similar course ... perhaps a 2014 or 2021 launch of such a Tractor would help maintain the object away from Earth in 2029 and 2036.

Further, the Tractor could also communicate the accurate position of the object while the object passes 'out of view' - "Apophis" has not been seen since 2005, and may only be reacquired in 2014.
Mr_Man
3 / 5 (4) Sep 04, 2009
Let's just ignore the possibilities and focus on what the latest between Jon & Kate is.
Rdavid
3.7 / 5 (3) Sep 04, 2009
Employ bigger ion thruster and move Earth instead.
Tachyon8491
1.8 / 5 (5) Sep 04, 2009
Although the "gravity tractor" idea itself sounds technically feasible from a construction p.o.v., the amount of kinetic energy required in fuels, manouvring and positioning, appears more like sience-fiction at this juncture. Also the ratiometric difference between the masses of a real city-killer and a mere ten-ton dragbot would appear rather inefficient. Albedo-increasing substances may also well have their reflective efficiency partially destroyed by shadowing occlusion due to strong granular irregularity of the target surface.

As alternative I suggest raising a conspicuous sign on such a monster: "Free Hamburgers - This side only" - and translated into some of the more popular intergalactic languages - the repeated retro-thrust landings of alien spaceships should cause adequate deflection. The only problem then remaining is one of exopolitics, explaining to visiting complainants what happened to the "free burgers."
WhiteJim
4.7 / 5 (3) Sep 04, 2009
This is silly. A relatively small source energy of propulsion that is smaller than 10 tons will provide more change in tragectory that the small amount of gravity of a ten ton object. Sending a five ton size fire extinguisher to dock with the rock and release its contents would move the mass much more and do so relatively instantly compared to moving it inches after 15 to 20 years. Do they not teach Newton's Laws in engineering school? Maybe these engineers should consult a physicist before wasting their time.
otto1923
3.5 / 5 (2) Sep 04, 2009
Shoemaker Levy was
target practice. Shepherding planetesimals is an acquired skill. But an essential one for colonizing the inner system and surviving long-term on any planet.
otto1923
1 / 5 (2) Sep 04, 2009
Actually, little shepherd bots as described in the article would be better suited for resource recovery and delivery to orbital habitat construction sites for instance. Swarms could be sent to the asteroid belt or delivered via mothership for individual missions lasting decades. So we start practicing now with convenient potential threats. Humans will be none the wiser. Muahahahaaaa.
otto1923
1.5 / 5 (2) Sep 04, 2009
Interesting too that we have a very expensive asset of dubious real use in low earth orbit which may be decommissioned in 5 years because of the threat from debris, much caused recently by Chinese competitors blowing up a satellite and a propitious collision involving Russians. We must now consider ways of cleaning up this valuable area if we want to inhabit it for long periods. In the meantime this junk may keep less advanced militaries out of it (against the threat of plausable 'accidental' destruction)
NeilFarbstein
2.8 / 5 (4) Sep 04, 2009
space tractors are stupid and underpowered. Use brute force like nuclear bombs if there is real threat to our survival. Even a grenade a day can
beat space tractors. A grenade an hour might do the trick.
chiefWright
3.5 / 5 (2) Sep 04, 2009
I agree with RayCherry, seems like a gravity tractor has the least risk. If for no other reason it depends only on the object's mass & trajectory. An explosive device might fragment a weakly clustered object without changing it's trajectory (let alone the fallout threat if nukes were used). A thrust device might not be able to effectively attach to unknown surface with unknown rotation.
And as far as intercepting the object, consider that NASA has both hit an asteroid with an aluminum slug (and measured the spectra of the ejecta), and navigated into a comet's tail and returned the captured dust to Earth. Positioning a vehicle in space is not the tricky bit.
It may be slow, it may be weak, but I've yet to see a gravity failure.
Nukeheads, put it back in your pants, please.
x646d63
3 / 5 (1) Sep 04, 2009
I'm not a physicist, but I play one on physorg.

Explain to me how a "gravity tractor" would be more beneficial than just landing said ion jets on the 'roid and moving the 'roid with the jets. If we are moving the rocket, which is "pulling" the 'roid with its gravity then we're moving the 'roid and the rocket with the ion jets. Why try to move more than necessary?

... which is the greatest threat in recorded history.


I think Tunguska in 1908 demonstrated a slightly greater chance of impact.
NeilFarbstein
2.3 / 5 (3) Sep 04, 2009
I'm not a physicist, but I play one on physorg.



Explain to me how a "gravity tractor" would be more beneficial than just landing said ion jets on the 'roid and moving the 'roid with the jets. If we are moving the rocket, which is "pulling" the 'roid with its gravity then we're moving the 'roid and the rocket with the ion jets. Why try to move more than necessary?



... which is the greatest threat in recorded history.




I think Tunguska in 1908 demonstrated a slightly greater chance of impact.


gravity tractors are the least effective way of moving asteroids. the gravitational attraction is too weak
NeilFarbstein
1 / 5 (4) Sep 04, 2009
There is nothing new with this idea, other than the fact that some engineers have taken it from the concept to the design phase, with estimates of cost and potential effective use. An important step, but one that most people will ignore as irrelevant as any problem that is fifteen to twenty years away 'belongs to the people who will be here then'.



I am sure the albedo changing powder, (painting/covering one side of a threatening object), to make use of the solar wind is also being evaluated, but its effectiveness is limited due to the varied (multi axis) rotations of most of these objects.



As for the suggestion of nuking the object, or setting off of nukes in the vacinity of an approaching object, this runs the rick of simple not diverting the object from collision course while irradiating the object so that it is nuclear active when it arrives in our atmosphere, (even a bundle of rubble and powder would then leave a radiative cloud for us to deal with for hundreds of years thereafter).



As crazy as the Gravity Tractor sounds, perhaps it has the least possibility of making the situation worse, hence the cost/benefit analysis may prefer this method of deflection.



By the way, I doubt very much that the Tractor would be sent towards an approaching object so that it would have to stop and then reverse to stay along side an incoming object. Probably they are looking at scenarios where there will be one or more close approaches predicted before the impact approach, in which case the Tractor will launch, race to catch up with and then accompany the object in the orbit(s) prior to to the predicted impact.



As mentioned above, NEO 2004-MN4 "Apophis" is following a similar course ... perhaps a 2014 or 2021 launch of such a Tractor would help maintain the object away from Earth in 2029 and 2036.



Further, the Tractor could also communicate the accurate position of the object while the object passes 'out of view' - "Apophis" has not been seen since 2005, and may only be reacquired in 2014.

There is nothing new with this idea, other than the fact that some engineers have taken it from the concept to the design phase, with estimates of cost and potential effective use. An important step, but one that most people will ignore as irrelevant as any problem that is fifteen to twenty years away 'belongs to the people who will be here then'.



I am sure the albedo changing powder, (painting/covering one side of a threatening object), to make use of the solar wind is also being evaluated, but its effectiveness is limited due to the varied (multi axis) rotations of most of these objects.



As for the suggestion of nuking the object, or setting off of nukes in the vacinity of an approaching object, this runs the rick of simple not diverting the object from collision course while irradiating the object so that it is nuclear active when it arrives in our atmosphere, (even a bundle of rubble and powder would then leave a radiative cloud for us to deal with for hundreds of years thereafter).



As crazy as the Gravity Tractor sounds, perhaps it has the least possibility of making the situation worse, hence the cost/benefit analysis may prefer this method of deflection.



By the way, I doubt very much that the Tractor would be sent towards an approaching object so that it would have to stop and then reverse to stay along side an incoming object. Probably they are looking at scenarios where there will be one or more close approaches predicted before the impact approach, in which case the Tractor will launch, race to catch up with and then accompany the object in the orbit(s) prior to to the predicted impact.



As mentioned above, NEO 2004-MN4 "Apophis" is following a similar course ... perhaps a 2014 or 2021 launch of such a Tractor would help maintain the object away from Earth in 2029 and 2036.



Further, the Tractor could also communicate the accurate position of the object while the object passes 'out of view' - "Apophis" has not been seen since 2005, and may only be reacquired in 2014.

I'm not a physicist, but I play one on physorg.



Explain to me how a "gravity tractor" would be more beneficial than just landing said ion jets on the 'roid and moving the 'roid with the jets. If we are moving the rocket, which is "pulling" the 'roid with its gravity then we're moving the 'roid and the rocket with the ion jets. Why try to move more than necessary?



... which is the greatest threat in recorded history.




I think Tunguska in 1908 demonstrated a slightly greater chance of impact.


gravity tractors are the least effective way of moving asteroids. the gravitational attraction is too weak.... the roid rage continues. Put bugs on it and track its position. If its a threat shoot it with recoiless rifles or shotguns.
Ashibayai
4.6 / 5 (5) Sep 05, 2009
To those of you wondering why we don't just put the ion thrusters on it:

It's rotation could be chaotic, and therefore ridiculously hard to land on, much less try and time thrusters to change it's trajectory.
Doug_Huffman
3.7 / 5 (3) Sep 05, 2009
Momentum is conserved. Asteroid has large momentum mass and velocity. When will we be able to send comparable momentum far enough to be effective?
Fazer
1 / 5 (1) Sep 05, 2009
Regardless of the technique used to move the asteroid, a 20 year lead time is politically imossible. We can't even agree on AGW, which, even if it was true, would present a more imminent danger. Add to that the fact that the danger would be based on a percentage. Without an immediate and definite threat looming, the only politicians who would vote for this would be the ones who want to cater to their special interest friends in the aerospace industry.

The idea of sending out a fleet of these things to shepherd every object that MIGHT hit the Earth one day is a bit silly.

Also, in the 20 years from first discovery to possible impact, our technical ability would have increased greatly and we would be able to tackle the job in a much shorter period of time with newer technologies.
x646d63
not rated yet Sep 05, 2009
... Its rotation could be chaotic ...


Thank you. I had not considered that.
Daryl
4 / 5 (1) Sep 05, 2009
ooohhhhh dupe from '06. http://www.newsci...ull=true
otto1923
not rated yet Sep 05, 2009
Regardless of the technique used to move the asteroid, a 20 year lead time is politically imossible
And yet it would absolutely have to be done. This is exactly why there would need to be an Agency which could do this sort of thing in secret.
Also, in the 20 years from first discovery to possible impact, our technical ability would have increased greatly
Maybe not. You couldn't count on it. Would you want to gamble the future of what may possibly be the only sentient species in the universe on that?

Fleets of asteroid recovery vehicles will eventually be a part of commercial mining and resource utilization, as well as making this system safer to live in. Obviously. 
zbarlici
5 / 5 (1) Sep 05, 2009
i think Peter Griffon would be a lot more efective as a gravity tractor. Now you just gotta get him to agree.
otto1923
3 / 5 (2) Sep 06, 2009
Peter Griffon- assume that's a large Brit. He would do it for Queen and Empire would he not?
Mechanic
not rated yet Sep 06, 2009
Not so silly, I believe the reason that a "propulsion source" might not work is because the device would have to "land" on the asteroid and it might be spinning at a rate that would be difficult to administer propulsion bursts at the correct time and vector. Also I believe that given the ability to bring a certain mass to a certain location, the ion propulsion is recognized as being able to provide the greatest energy over a long period of time. An ion propulsion tractor would not be on a rotating surface therefore can administer a predictable pull over an extended period of time. I am sure these folks talked to or are the (astro) physicists that you refer to.

This is silly. A relatively small source energy of propulsion that is smaller than 10 tons will provide more change in tragectory that the small amount of gravity of a ten ton object. Sending a five ton size fire extinguisher to dock with the rock and release its contents would move the mass much more and do so relatively instantly compared to moving it inches after 15 to 20 years. Do they not teach Newton's Laws in engineering school? Maybe these engineers should consult a physicist before wasting their time.

toyo
1 / 5 (4) Sep 06, 2009
It's clearly a sham. The whole idea is utterly unworkble and obviously is a set-up to suck in those weak-minded enough to fall for such drivel.
Wake up guys! It's a joke! :))
otto1923
5 / 5 (1) Sep 06, 2009
Here's another physorg article on same subject, with 'gravel pile' nature of some asteroids and the difficulty of pushing them:
http://www.physor...554.html
otto1923
3 / 5 (1) Sep 06, 2009
I would think a fairly intelligent probe equipped with the proper sensors could analyse the composition of the 'roid, decide just where and when to apply proper thrust, and monitor the results. A slight push for a long enough period of time should be able to move gravity-bound rockpiles.
probes
1 / 5 (2) Sep 07, 2009
I agree with Rdavid -

Employ bigger ion thruster and move Earth instead.
RayCherry
3 / 5 (2) Sep 07, 2009
Perhaps one of the contributors above could design the appropriate equipment to put a landing craft into a dual axis orbit above a pile of rubble and dust, and slowly descend the craft to the surface and then attach itself securely, where it would deploy a thruster that must produce enough force to change the course of the entire asteroid without disturbing the rocks and dust it has landed on ... plus the firing must occur when the asteroid's dual axis spin has the thruster pointing in the correct direction, which may be once every two complete rotations, or once every few thousand asteroid rotations, and after each firing of the thruster, the craft would need to recalculate the new rotation behaviour to anticipate the next thruster firing opportunity.

Pretty complicated so far?

Now imagine the disappointment when the thruster dislodges the piece of rock that the craft landed on from the collection that makes up your asteroid.

Well, at least that rock could be directed away from Earth - not a complete failure, eh?
RayCherry
not rated yet Sep 07, 2009
Back to the non-explosive, non-invasive, non-destructive, non-contact weak course disturbance of the 'gravity tractor' ... does gravity have to be the only force of attraction?

Asteroid ... meteor ... meteorites ... iron content

Most arrivals at the surface of Earth have been found to contain iron and other metals ... could an electro-magnet producing a weak attractive field between the tractor and an asteroid help pull the asteroid a little further from its original course?

We have the technology to remotely detect the geology/chemistry of objects in space. If we find a Near Earth Object has a useful metal content, surely the tractor could make use of it?
RayCherry
2.5 / 5 (2) Sep 07, 2009
Perhaps, if the metal content is more concentrated in one area of the asteroid (like our own North Pole) the magnet could eventually stabilise the rotation, reducing the spin to a single axis which might permit a probe to achieve a viable orbit for landing.

Maybe the contributors above could also consider an Earth bound Sun grazing comet composed of loosely bound ice crystals (powder) with possible liquid water content, as was discovered when we hit that comet with a metal slug a few years back.

How about using the metal content, (implanting some where it does not exist - iron ballistic pins, or adhesive iron dust spray), and use the magnet on the tractor to reduce/eliminate the rotation, permitting one side of the object to face the sun continuously providing the small additional thrust from the solar wind (the Yarkovsky Effect); then continue to use weak magnetic and gravity fields of the tractor to pull the object further off course?
Fazer
4 / 5 (1) Sep 07, 2009
How about using the metal content, (implanting some where it does not exist - iron ballistic pins, or adhesive iron dust spray), and use the magnet on the tractor to reduce/eliminate the rotation, permitting one side of the object to face the sun continuously providing the small additional thrust from the solar wind (the Yarkovsky Effect); then continue to use weak magnetic and gravity fields of the tractor to pull the object further off course?

Interesting ideas, but increasing the complexity of the solution increases the probability of a failure occuring during the mission.
I am sure the albedo changing powder, (painting/covering one side of a threatening object), to make use of the solar wind is also being evaluated, but its effectiveness is limited due to the varied (multi axis) rotations of most of these objects.

Albedo changing materials don't need to be on one side only, the accumulated change in velocity along the direction of travel would build up over time, regardless of how much of the asteroid was covered, where it was covered, or how it was spinning. There would still be a change in orbital dynamics, however small.

The only problem would arise if it was tidally locked with one side facing the sun and you only painted the back side, or if the painting itself ended up causing one side to be perpetually turned away from the sun, due to solar wind pressure aligning it away from the force of the wind.
RayCherry
2.5 / 5 (2) Sep 07, 2009
The Yarkovsky O'Keefe Radzievskii Paddack (YORP) effect is believed to alter the way small bodies in the solar system rotate. YORP is a torque due to sunlight shining on the surfaces of asteroids and meteoroids and warming their surfaces, leading to a gentle recoil effect as the heat is emitted. By analogy, if one were to shine light on a propeller over a long enough period, it would start spinning.

http://www.physor...388.html

Derek Richardson, of the University of Maryland, his former student Kevin Walsh, now Poincare Fellow in the Planetology Group in the Cassiopee Laboratory of CNRS at the Cote d'Azur Observatory, France, and that group's leader, co-author Patrick Michel outline a model showing that when solar energy "spins up" a "rubble pile" asteroid to a sufficiently fast rate, material is slung off from around the asteroid's equator. This process also exposes fresh material at the poles of the asteroid.

If the spun off bits of asteroid rubble shed sufficient excess motion through collisions with each other, then the material coalesces into a satellite that continues to orbit its parent.

http://www.physor...202.html

It appears that the reduction of rotation rate is a necessary precaution to avoid the breakup of a single NEO into multiple objects. Painting the entire object to increase the Yarkovsky (or YORP) Effect would in fact increase the rotation rate and the potential for the object to break apart, which would appear to be highly undesirable in most NEO scenarios.

Correct identification of the 'YORP emission areas' (hot spots) on the surface of a NEO may indicate which small areas need to be painted brighter or darker to reduce the object's 'natural thrusters' effects of increasing rotation velocity.

The Yarkovsky Effect is very small and requires a long time period to produce enough heat radiation to produce the 'thrust' that effects the rotation of such an object.

Local magnetic field effects would be far greater and more effective in changing the rotation and course of an object that contains magnetic material (such as naturally occuring iron deposits).
Fazer
1 / 5 (2) Sep 07, 2009
Hmmm, I wonder if that rotation could be put to work? If it was fast enough, perhaps many of the pieces would spread out enough over time? If we did end up crossing paths with the constellation of smaller pieces, we'd only get clobbered by a few smaller pieces, instead of one big clump.

On the down side, the cloud of rocks would now present a larger target, increasing the chances of a strike with one of the pieces.

So, how about we put all of our efforts together here on Earth and build a big laser facility next to a nuclear reactor and periodically hit the rock(s) with intense pulses of energy. Perhaps more energy than it would ever recieve from the sun (can someone do the math?) Keep hitting it over the years and either slow it down or spin it apart. Once it has spun apart, keep hitting the pieces with energy to both encourage them to spin apart into smaller and smaller clumps, and also slow them down, until we end up with a bunch of debris spread over such a large area that it no longer presents a threat.
Thadieus
5 / 5 (2) Sep 07, 2009
May I suggest the use of sheeps' bladder to alter the course. Wait a second, sheeps bladder prevents earthquakes. So sorry.

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