Asteroid Billiards: Space Mining and Earth Defense

Engineers have recently proposed steering asteroids around in order to exploit their potential. One plan is to carefully nudge them in to orbit, so that atmospheric pressure can slow them down enough for us to mine ice water. That procedure is called “aerobraking”. Another proposal delineates how to respond in case of emergency – we steer one asteroid in to a potentially fatal meteor, re-directing it away from a collision course with Earth.

Aerobraking is not as dangerous as it sounds. First of all, the proposal only focuses on asteroids smaller than 30 meters in diameter – those of which disintegrate upon contact with the lower atmosphere. There are over 1000 of such near-Earth asteroids fitting this size requirement. However we may need the second contingency plan for larger rogue asteroids that we do not see coming.

It is true that large meteors have struck in the past, sometimes with devastating consequences – so it’s pretty much guaranteed that a potentially dangerous asteroid will approach Earth on a collision course some time in the future. Whether or not we’re here to see the day is another story entirely.

Asteroid mining is the next big thing. By expanding our industry up instead of over each other entire nations could potentially stave off recession, prevent war and gather plenty of much needed resources from outer space without further endangering the eco-system.

Furthermore, it lays the groundwork for space colonization by creating a re-fueling infrastructure around the Earth. Which is of course vital if we cannot reverse the course of climate change quickly enough. The problem? Asteroid mining can be equally dangerous if engineers and physicists don’t plan ahead with a surgical degree of accuracy.

The first proposals for asteroid mining involve barges embarking on a bit of a quest to near-earth asteroids, and upon arrival – dispatching a cluster of microsats to survey the rock or attaching a drill for extraction of samples.

Another proposal is more ambitious – we travel to an asteroid with mining gear at the ready, land, completely hollow out the interior, attach thrusters to the rear, and fly the rest back to the Earth. This plan would  apparently make heavy use of 3D printers to transform the entire asteroid in to a temporary space ship.

However, recent discoveries have revealed the possibility of “mini-moons” in geocentric orbit. Small asteroids that end up orbiting Earth for a few revolutions before departing once more. We’ve seen them before, but only a couple, and one of them actually became a meteor.

A new telescope is being constructed for completion in 2020 that will detect all of these mini-moons, if they were to indeed exist. One of the potential applications could be to use mini moons as a test bed for the more risky/ambitious proposals listed above.

However, now scientists are asking whether or not we should create our own mini moons? Asteroids millions of miles away only need a small bump to anchor themselves safely in Earths orbit so why not park them close enough to mine without endangering the surface? That would be like playing billiards or golf in a 3 dimensional gravity well except time-tested mathematics guarantee an accurate “shot” with multiple contingency plans.

We have lots of experience with aerobraking. In fact every incoming spacecraft aerobrakes to slow themselves down before landing on Earth. Even in alien atmospheres for example the Venus Express and ExoMars mission utilize the same aerobraking procedures to land on the surface.

However, before attempting such a feat it is important we understand the asteroids underlying compositon. Elements react differently in a gravitational well, metals for example are heavier and so take more kinetic energy to re-direct from the downward pulling force of gravity characteristic of orbital planes.

“If it’s made out of solid iron, you won’t be able to slow that sucker down,” sai Fieber-Beyer sayspath

Another potential complication lies in oblong, awkwardly shaped asteroids. An asymmetric asteroid with irregular density would begin to spin out of control due to an uneven distribution of atmospheric pressure impinging upon the object.

“The risk would lie in the asteroid having an irregular shape and hence experiencing torque, beginning to spin and hence go out of control,” Mueller-Wodarg says. “When we do aerobraking with satellites, we carefully fire small rockets to keep [them] on course and compensate for any such wobble.”

As long as scientists take great care in surveying, selecting and directing the asteroids in to orbit at different stages, there is very little risk if any to the surface of Earth. Furthermore, allowing the asteroid mining industry to extract ice water from implanted asteroids could allow us to develop a native fuel source for hydrogen elecrolysis which would reduce the cost of space colonization and give humanity hope for the future.

 

Photo Credit: Don Davis, South West Research Institute

http://www.sciencemag.org/news/2018/08/asteroid-miners-could-use-earth-s-atmosphere-catch-space-rocks

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