Search | How to Catch an Asteroid |
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| Written by John Burch | |
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A proposal for grabbing an asteroid in order to change its orbit from Earth collision to near miss.
We are growing more aware of the consequences of asteroid impact on the Earth. They happen and they will continue to happen unless we do something to stop them. These collisions with the Earth have left their mark, and sometimes altered the evolution of all life. The pain and suffering was immense and we don't want to have to go through that again. It could mean the end of the human race or the death of millions. The fact that it is unlikely only means that it is more difficult to devote resources to the problem, but the danger is just as real. The goal of the B612 Foundation is "To significantly alter the orbit of an asteroid, in a controlled manner, by 2015". The Foundation is run by several scientists and two former astronauts. They described the project in their Asteroid Tugboat article in the November 2003 issue of Scientific American.  One outstanding issue is how do we attach to an asteroid in order to affect its rotation and direction of travel. Some of these rocks are metal, some stone, some dust and loose rock, or a combination. It would be hard to screw down a thrust pad to any arbitrary rock when you are in a life or death race to grab it and start thrust as soon as possible. . You really need to grab the entire thing and apply the force evenly over the body. The predictions in the Scientific American article indicate that an ion engine running for three months, ten years before a predicted impact could alter the orbit enough to miss the Earth. This present article attempts to describe a possible way to grab an asteroid in order to change its orbit. I have no idea if it will be effective. My own background includes 18 years as an electrical engineer , two years of student coop work at NASA back in the late 60's, but nothing else except considerable interest in this field of aerospace. Rusty Schweickart pointed me to their article and corrected several incorrect assumptions I had made. I hope this effort supports their work. First, the basic idea is to put a belt around an asteroid, pull it tight and use it to anchor a small spacecraft to the surface of the asteroid. The belt , only a few inches in width, would distribute the force of the rocket over a wide area. The target asteroid is 200 meters in diameter. With a belt 5 cm wide, you get 31.4 square meters in which to distribute the force around the rock. That is a very low force applied to the unknown surface and should not dig in or cut through the dirt for very far before finding something to hang onto. You can see the ion thrust craft in the image above. The ion engine is pointed along a tangent to the surface to stop rotation. Once the rock is not rotating, the single ion engine can change the orbit of the rock in a few months. The near end of the spacecraft is really the tug craft in docked position after delivering the end of the tape to the thrust craft. The large sphere is the ion engine fuel tank. The rectangular plates behind it are a microwave rectifying antenna that picks up energy from a nearby solar array. The heavy cable carries the power from the antenna to the ion craft where approximately 250 KWatts of energy is used by the single ion engine. If the asteroid is a rubble pile, then the problem is harder. If you can't lasso a large majority of the material in the asteroid then you are out of luck and will tear the pile apart if you can't grab most of it.. I get the impression that the small asteroids are solid with a dusty surface covered with small rocks that have been attracted to the larger object. The optimum situation would have two or three high thrust spacecraft in permanent orbit around the moon. This gets them up and out of the majority of the Earth's gravity well and ready to speed off in any direction to meet up with a newly discovered asteroid. The high thrust craft would carry two packages. Each package contains a small belt buckle craft and a fold up solar panel to power the ion rocket. The belt buckle craft is the ion rocket that will hold both ends of the tape tightly around the rock. A smaller tug craft wraps the tape around the rock during set up and performs other functions such as connecting the rectenna array to the ion rocket craft. I'm animating this idea and will add it to the animations we already host here at Scintillating Science. |
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