B612 and Asteroids

by Chris McMahon

Still recovering from the dreaded flu virus at the moment – worse one I’ve had since I had the Swine Flu a few years ago.

I caught a great video on the ted.com site last week – How to Defend the Earth from Asteroids. I’ve read about this topic and thought about it at various times over the years.

Everyone would agree it would be better if we did not host any city-sized asteroids on homeworld if we can help it. The bus to football ground-sized ones are survivable and have hit us recently – as demonstrated by that crater in Arizona mentioned in the presentation, and of course the famous Tunguska impact of 1908. Interestingly, the Arizona impact was from an iron asteroid that stayed together prior to impact. The Tunguska explosion was thought to result from a rocky asteroid that actually exploded prior to impact, creating a massive shockwave that levelled the forest for square kilometres from the impact site.

One of the key things required to avoid catastrophic asteroid impact is to first know the damn things is on its way. This is one of the core missions of the B612 Foundation (named after the asteroid the Little Prince lived on in the famous novella), to launch its own privately funded mission to map the asteroids in the inner solar system that might present a threat to Earth.

The earlier you can start changing the orbit of the approaching asteroid the better, as slight adjustments to its position will do the job of getting it out of Earth’s way.

Prior approaches to avoiding impact have relied on putting thrust on the asteroid itself to adjust its orbit. Typically this involved doing a survey of the asteroid first to determine its nature and structural stability and how well the applied thrust would be distributed over the body. Nuclear Thermal Rockets were suggested for supplying this thrust because of their versatile fuel requirements – they can take ice, water or just about any chemicals from the surface of the asteroid and use it for thrust.

The latest approach is to ‘couple’ the asteroid with a probe that has mass of about a tonne or more via a ‘gravity tether’. Here the probe is placed close enough to the asteroid so that there is a gravitational attraction between it and the asteroid, but no actually touching it. Then a very slight thrust is applied, such as might be delivered by an ion drive, which can sustain that thrust for long periods. This toes the asteroid into a safe orbit. The beauty of this approach is that it will work regardless of the nature/structure of the asteroid, there was always the risk with direct applied thrust that it would break the asteroid apart, creating many dangerous fragments in new unpredictable orbits.

Knowledge of the orbital dynamics has also improved. Astronomers are now aware of ‘keyholes’, small windows nearby Earth that represent a ‘sweet spot’ of disaster. If an asteroid that will narrowly miss Earth passes through one of these keyholes, it will change its orbit into one that will intercept Earth on its next approach – perhaps months or years down the track. The idea is to keep asteroids passing by Earth out of these keyholes. They can also be used in a positive way. There is also the possibility of nudging an asteroid through the right keyhole so that it will hit Earth say in three years instead of six months – giving more time to deal with the problem of shifting it into a safer orbit.

Anybody come across any interesting things is asteroid defence lately? No not the hidden base on the dark side of the Moon – everybody knows about that one.

Of course the real problem is we need new Earths!


  1. Aside from one almost so-bad-its-good movie, no, no other ideas. The energy requirements for a repulsor field of some sort always negate that plan, and if we had that much energy to squander we wouldn’t still be here pointing up going “ooooh, that looks bad.”

      1. Precisely. If you could project a targeted shield from a stable platform and deflect the object somehow, it might take less energy, but again, if we have that level of technology, we should be off of Earth and partying hard. And you still might have the dangerous object in somewhat close proximity to the planet, depending on whether you could steer the deflection.

  2. What we need to do is deflect the asteroids just enough to get them into Earth orbit. Say, two to three times as far as the Moon, just waiting to be dissected for goodies.

    Now, I’m begining to think that Mars just isn’t going to be a useful colony, but I could be wrong. I hope we satisfy ourselves about life in the premafrost or deepest canyons, or edges of the ice caps before we contaminate it with Earth bacteria ands so forth. But once it’s definitely dead, perhaps we ought to consider it as a useful target for any troublesome asteroids or comets. If we could just pump up the atmosphere, it would change the economics of colonization immensely.

    But near term mitigation methods for dangerous asteroids? Haven’t heard anything new.

    1. Hi, Pam. I really like the idea of putting this approaching asteroids into useful near-space holding areas for cutting up. Maybe you could come up with a scheme for a few neat adjustments to orbit, then lob them into the Lagrange fields. Nice idea.

      In terms of colonisation, I suspect we may need to think small scale before we go to planet-sized terraforming. I wonder what the critical mass size of a self-sustaining, asteroid based colony would be? I guess you’d need to spin it for gravity and live in tunnels. Love the idea of space-miners in some gnarly old asteroid:)

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