Spacecraft Could Save Earth from Asteroids
September 4, 2009 by Lin Edwards
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 asteroid 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, NASA 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 Earth in 2036, perhaps we do have enough warning.
© 2009 PhysOrg.com
Apr 17, 2008 |
not rated yet |
0
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 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.
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."
beat space tractors. A grenade an hour might do the trick.
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.
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?
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
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.
It's rotation could be chaotic, and therefore ridiculously hard to land on, much less try and time thrusters to change it's trajectory.
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.
Thank you. I had not considered 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.
Wake up guys! It's a joke! :))
http://www.physor...554.html
Employ bigger ion thruster and move Earth instead.
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?
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?
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?
Interesting ideas, but increasing the complexity of the solution increases the probability of a failure occuring during the mission.
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.
http://www.physor...388.html
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).
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.