A spacecraft fired into a dangerous asteroid could change the rock's orbit just enough to prevent an impact with Earth (Image: ESA)
Posted on 04/26/2006 3:36:12 PM PDT by blam
Taking out a killer asteroid – with a tame one
17:38 26 April 2006
NewScientist.com news service
Maggie McKee
It sounds like a Hollywood blockbuster. A potentially deadly asteroid is heading for Earth, and scientists mount a mission to intercept it – using another asteroid. But that is exactly what two French researchers propose in a plan to capture and "park" a small asteroid near the Earth for just such emergencies.
But a second group of researchers says shooting a spacecraft into the asteroid would be simpler and more effective. Other experts warn that both plans risk having fragments of the initial asteroid strike the planet, but say they highlight the need for governments to devise strategies to ward off such impacts.
Relatively small asteroids, about 100 metres wide, are thought to hit the Earth every few hundred years. But their effects could be deadly. One such impact unleashed the force of 1000 atomic bombs when it struck an unpopulated area of Siberia in 1908.
"Asteroid impacts are very rare but they can potentially kill many, many people," says Dan Durda, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, US. "And they are 100% preventable."
Various plans have been put forward to deflect incoming asteroids. For example, lasers or giant space mirrors could evaporate ices on their surfaces, creating jets that propel them away from Earth. And half-painting an asteroid could make it radiate heat differently on each side, slowly nudging the object off course.
But many of these plans require several years of advance warning in order to push the asteroids into safe orbits. If an asteroid or comet is found barrelling towards the planet with a year or less to impact, "that's a case where perhaps our only option is to attempt a big kinetic kill", says Durda.
Parked space rock
Now, Didier Massonnet and Benoît Meyssignac of France's National Centre for Space Studies have come up with a new projectile to fire at the asteroid in such a "kill". They advocate capturing a small, 40 meter asteroid and "parking" it a stable Lagrange point 1.5 million kilometres from Earth, where the gravity of the Earth and the Sun balance.
If a larger asteroid were then found to be on a collision course with Earth, the small rock could be moved into its path within eight months, says the team. This "David's stone" would be too puny to cause any damage to Earth if things went awry, says the team. "Such an asteroid capture would be one of the most remarkable achievements of mankind," they write in Acta Astronautica.
But other experts say the plan is not realistic. It relies on using a small hopping robot to excavate tens of metres of rock per second from the little asteroid in order to provide the force to capture it and send it towards the larger rock. The capture would take a year of digging and would require the robot to remove 66% of the small rock's mass.
"To have a mechanical device work all on its own - without a person to kick it - in an essentially unknown surface environment full of dust and debris, is a very difficult thing to do technically," Durda told New Scientist.
Gerhard Hahn and Ekkehard Kührt of the German Aerospace Centre in Berlin agree. "It sounds rather like science-fiction," they told New Scientist in an email.
Hit and run
But Dario Izzo, an aerospace engineer at the European Space Agency's Advanced Concepts Team in The Netherlands, says the capture is technically feasible. "We can do it, but it would be really expensive," he told New Scientist.
Izzo worked with Massonnet and Meyssignac on earlier plans to capture an asteroid into Earth orbit. He is now working on a strategy based on ESA's plans for its Don Quijote mission. That mission is designed to put one spacecraft in orbit around an asteroid to watch as another is sent crashing into it. Don Quijote will be a technology demonstration mission, but Izzo's team has been working on ways to use just an impactor spacecraft to deflect a dangerous asteroid.
As a test case, the team used the orbital parameters of Apophis, a 400-metre-wide asteroid that will pass by Earth in 2029. During that pass, it may change course enough to hit Earth when it returns again in 2036 - a possibility that now has a one in 5000 chance of happening.
The team developed formulae to find out how much Apophis could be deflected by a 700 kilogram (1540 pound) spacecraft. "We found there are loads of trajectories, of launch windows, that would allow us to obtain a deflection," Izzo says. If a spacecraft were to launch by 2026, it could hit Apophis and change its speed by 0.01 millimetres per second – a tiny change, but enough to prevent it from colliding with Earth a decade later, he says.
Gravity tractor
But NASA astronaut and physicist Ed Lu says any plan that involves striking an asteroid risks breaking it into fragments. Some fragments would have their orbital periods unchanged, and "any such debris will strike the Earth," he told New Scientist.
"For any realistic scenario where the Earth is threatened by an asteroid, would we really choose a method that cannot guarantee that it will not make the problem worse?" he says. Lu has previously proposed a "gravity tractor" plan to fly a spacecraft near an asteroid and use its own gravity to pull it off course.
But Durda, who is also president of the B612 Foundation, which aims to build a spacecraft to test the gravity tractor idea, says it is important to consider many different plans for protecting the Earth from impacts. "We want to have a lot of options at our beck and call," he says. "Depending on the lead time and properties of an asteroid, a technique that might work very well in one circumstance might not work at all in another."
Currently, the US government has not assigned any agency responsibility for dealing with any impact threat that may be identified. But NASA is trying to identify what those threats are.
It is expected to finish a survey of potentially dangerous asteroids larger than 1 km across by 2008. But Durda says it has not yet been funded to begin a congressionally mandated programme to find all such space rocks larger than 140 m across.
Journal reference: Acta Astronautica (DOI: 10.1016/j.actaastro.2006.02.030, DOI: 10.1016/j.actaastro.2006.02.002)
A spacecraft fired into a dangerous asteroid could change the rock's orbit just enough to prevent an impact with Earth (Image: ESA)
If it stays for five years, it'll be a naturalized citizen.
I think I'll stay with Bruce and the boys, they know
how to kick Assteroid.
Placing a 50 megaton thermonuclear warhead on the spacecraft should change the speed of the asteroid by a little more than 0.01 millimetres per second.
ping
I'm not sure of the exact physics, But I believe you would have to design a device similar to a bunker buster bomb that would penetrate seventy to one hundred feet into the surface before detonating to cause even a tiny effect on a large body moving at orbital velocities.
Think of deflecting a runaway Mack Truck moving at 200mph by hitting it with long range bottle rockets from ten thousand miles away. It would probably take multiple hits to achieve a miss. Of course, the farther away the intercept the less devices required.
The other problem is arranging the intercept at the right time and the right angle in time. You can't just point and shoot. Also, if you miscalculate the structure of the mass and merely break it up into several sub-masses, you run the risk of one or more slightly less devastating impacts that could still wipe out life on Earth. Only now you don't have the time to calculate a new intercept path for each fragment and make a second, far more complex attempt.
Put a dust cloud in front of it.
They probably read my paper, but didn't understand a word.
I think you may be talking with a little tong in cheek but I also think that we had better be well prepared for such an event. It's not a matter of if, but when. It may not happen for another thousand years. Then again, it could happen in two. Any really large Earth killer type body would probably give us at least decade or two to get prepared. However, a far smaller body that could still trigger a dark age could conceivably sneak up on us with much less warning. An Earth Killer might even be actually easier to deal with because it's physical properties and trajectory would probably be much more solid and predictable.
This guy sounds as though he's speaking to an elementary school audience, and that he jsut found out about this problem last year.
"100% preventable" Oops, that kinda ranks up there with "An Unsinkable Ship."
Clearly, in addition to proper scanning, we need a plan to put a mass driver on the targeted asteroid, using its own mass as reaction material. Even a simple spring operated trebuchet could redirect the asteroid's trajectory. Maybe I should patent this "better mousetrap."
You could do that but you'd still have to hit it a very long time before impact and would still require a very large mass of dust. If you had twenty or thirty years of lead time and an comet or two worth of mass to grind up...
This might actually be the perfect solution. Say you had a large iron nickle asteroid bearing down on the Earth and twenty five years of lead time. You could put a mining operation on it and fire chunks of it's mass off calculated to go into orbit around the Moon. It would pay for itself with little risk of bombarding the earth with large chunks of iron ore. You could continue to mine it long after it had passed the Earth.
FReeper RightWhale has talked about mining these suckers all the years I've known him on FR.
That's right. Probably my first post was on asteroid mining.
Right. Patent it! I am a patent agent, but retired. Don't imagine I would come out of retirement for this. Won't matter anyway since there are no property rights to celestial bodies. Get the US out of the 1967 UN Outer Space Treaty, then we'll talk.
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