Fraunhofer studies probe impacts to deflect asteroids


September 6, 2013

An asteroid impact has the potential to produce a mass extinction event (Image: NASA/Don Davis)

An asteroid impact has the potential to produce a mass extinction event (Image: NASA/Don Davis)

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There are hundreds of near-Earth asteroids hurtling through space that are a potential danger to our planet. One way of dealing with the problem is to deflect them with a space probe deliberately set on a collision course. To see how effective such a collision would be, Frank Schäfer of the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI in Freiburg, Germany is looking at what asteroids are made of and how this affects a deflection impact.

It may seem odd to use a space probe the size of a washing machine to fend off an asteroid that weighs in at a couple of hundred tons, but then, a few ounces of lead are enough to bring down an elephant. It’s a matter of putting enough energy behind the bullet. In this case, the bullet is a spacecraft, but even moving at orbital velocity the effect wouldn’t do much to an asteroid large enough to pose a danger to Earth. However, it doesn’t have to, if the impact is properly timed.

“In actual fact, the impact of a space probe would change the speed of the asteroid by just a few centimeters per second. But that’s enough to deflect its course to a significant degree over a longer period. So if we want to stop an asteroid on collision course with the Earth from hitting us, we’ll need to fire at it many years ahead of time,” says Schäfer.

Artist's concept of a space probe impact on an asteroid, with another probe observing (Image: ESA)

The study originally wanted to look at how to deflect asteroids between 100 and 300 m (330 and 990 ft) in diameter by striking them with massive space probes in a manner that was described as similar to two balls colliding in billiards. However, Schafer noticed that something else was going on, other than simple recoil. The substance that the asteroid was made of was also a factor, especially if the impact threw off a plume of debris. In this case, the momentum transfer is up to four times greater than a simple impact.

“During impact, not only does the probe transfer its own momentum to the asteroid, there is also the recoil of detached material from the crater, which is ejected against the direction of the impact,” Schäfer says. “This recoil effect acts like a turbocharger on the deviation of the asteroid.”

Schäfer’s experiments involved taking pendulums and attaching materials similar in consistency to those that make up asteroids, such as dense quartzite, porous sandstone or airy concrete. He fired aluminum projectiles at them at up to 10 km/s (6.2 miles per second) while recording the results with high-speed cameras, interferometers and lasers.

The results of the experiments demonstrated that the asteroid’s substance affects the outcome of a probe impact. A porous substance will absorb the strike, similar to how the crumple zone of a car soaks up the energy of a crash. Conversely, a denser, more elastic substance will enhance the deflection.

Part of the NEOShield program, Schäfer’s work will be used by the project in its plans to try deflecting an asteroid by mid-2015.

Source: Fraunhofer

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past. All articles by David Szondy

The problem with toying too much with this system is that we might cause a chain reaction. These bodies have been moving around our sun for billions of years, so they are fairly set in their ways. We displace something out of it's usual orbit, and other bits and bobs may degrade and/or collide, sending something else off into interstellar space or even something bigger/faster into Earth's orbit. Before we start blasting away, we ought to run comprehensive simulation programs first. Only with a full understanding of the solar system's planetary topography and past interactions can such a comprehensive simulation program be run. We should be able to run it backwards to discover simultaneous impacts, too, with such information. Sure, we would need to mount expeditions to all the pieces of our solar system to parse it all out, but significant discovery might thereby be obtained.


I second this. Nevermind the climate change we leave behind for our kids to deal with. Should our grandkids also have to face asteroids. :b

Nah, not concerned. you can't downplay just how much firepower 100 years will bring to humanity's hand. Planet killer class weapons will be available for the odd occasion where an asteroid is detected that is in the path of colonies or trade routes.


if the 'recoil' of the impact turbocharges the deflection momentum with an ordinary impactor, shouldn't this be even more so the case with a nuclear weapon impactor? shouldn't the energy in the impact be even greater and the recoiled mass would contain even more momentum if a nuclear explosion was detonated precisely AFTER the impact is made? ( especially if the heat of the nuclear explosion gassifies more of that mass because gas can carry even more momentum than solid matter as it can be more readily accelerated


@TogetherinParis. Nicely put! Good point.


@ zevulon

Yes nuclear explosives would enhance the deflection but then they would have to confront their views on nuclear energy.

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