Solar mirrors to save the planet

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On May 5, 2011, I wrote Asteroid Strike – The ultimate disaster!, describing the coming near Earth encounter of 2004 MN4 on April 13, 2029. I looked at what might happen, and what we could do about it. Since the discovery of 2004 MN4 on June 19, 2004, some good people have given the problem real thought.

Some of the ideas that have been floated are deflecting an asteroid with a nuclear blast, changing its orbit by crashing a large object into the asteroid, using a mass-driver to eject material mined from the asteroid, using a chemical rocket to nudge the asteroid from its orbit, using a low-thrust space craft over a longer time to do the same, using a spacecraft coupled to the asteroid by gravity to nudge it from its orbit, and using a fleet of mirrors in formation to focus solar energy (directly or as lasers) on the asteroid surface, ablating material to generate a thrust and nudge the asteroid from its orbit.

On March 6, 2007, at the Planetary Defense Conference at George Washington University, Drs. Massimilano Vasile and Gianmarco Radice of the Department of Aerospace Engineering at University of Glasgow presented a paper titled “Optimal NEO Deflection and a Comparative Assessment of Deviation Strategies,” comparing the various suggested deflection strategies, and making the case for using solar mirrors. These recommendations are now being presented in the popular press.

They made their case with thrust calculations and associated timelines, taking into consideration some of the potential side effects of the various techniques. For example, a nuclear blast, while very effective in terms of thrust, is unpredictable in how it can cause a potential break-up of the asteroid, and the subsequent consequences of the impact on Earth of the break-up fragments. Using any long-term technique that is fixed to a point on the asteroid surface can add extra complication because of the need to turn the thrust on and off to compensate for any rotational motion of the asteroid. The gravity tug concept bypasses this limitation, but has a typically longer timeline than the other techniques, requiring years earlier notification of the potential impact in order to counter it.


Gravity Tug – coupled to the Asteroid by gravity,
deflecting asteroid over a period of months to several years

Of all the proposed deflection techniques, Vasile likes a fleet of space mirrors in formation near the aberrant asteroid, focusing their reflected energy at a point on the asteroid surface at an angle that causes a continuous jet of gas to nudge the asteroid into a safer orbit. The concept apparently is independent of any asteroid rotation, it won’t break up the asteroid, and it produces significantly more thrust than the gravity tug. This, says Vasile, makes the solution ideal.


Mylar solar mirrors focusing energy to a point on the asteroid
heating the rock to 2,100C, causing a gas jet that deflects the asteroid

For example, an asteroid about 500 ft in diameter (the kind that would seriously damage a significant area of our planet, but not destroy all life) could be deflected in a few days by a swarm of a hundred light-weight Mylar mirrors. An asteroid the size of the one that wiped out the dinosaurs 65 million years ago would probably take a fleet of 5,000 mirrors two or three years to do the job. Fortunately, a larger asteroid like this one can be identified much earlier than a smaller, 500 foot rock, so we can have the necessary lead time to do the job.

The obvious key is that if we don’t know about future potential impacts, we cannot then prepare to deflect them. It seems pretty important, therefore, that we spend the money to create the necessary infrastructure, hardware, and methodologies, and that we test our ability to accomplish a deflection before our very existence depends on our actually accomplishing a deflection.

For more information on the subject, and to learn what you can do as an individual, visit the B612 Foundation.

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