I’ve noticed that very few people seem to understand the concept of the Enhanced Gravity Tractor planetary defense technique that the ARM Option B approach plans on demonstrating. A friend recently forwarded me a great paper describing this concept that was presented last month in Italy at the IAA Planetary Defense Conference, that provides a good introduction to the concept:
IAA-PDC-15-04-11 Enhanced Gravity Tractor Technique for Planetary Defense
The high level version is that by collecting mass from the target asteroid, you can enhance the diversion speed of an asteroid by 10-50x or more compared to using a normal gravity tractor without local mass augmentation. This means that even for an Asteroid Redirect Vehicle with a capture mechanism about the size Altius analyzed in its ARM BAA study, you could redirect an earth-crossing 100m class asteroid with <1yr notice, and a 150m diameter (Tunguska-class) asteroid with <2yrs.
There were a bunch of points made in the paper, but a few of the more interesting ones are:
- Because an enhanced gravity tractor works via gravity, you could use it to divert debris from an unsuccessful nuclear diversion attempt.
- You can speed up the process by putting multiple EGT spacecraft into a halo orbit around the asteroid simultaneously.
- The EGT doesn’t necessarily require boulders on the target asteroid. If the redirect spacecraft has the ability to scoop regolith for instance, you could use regolith or smaller rocks instead of a boulder extractor system.
There’s a lot more to it than that, but I wanted to put this article up there because I think most people following ARM, especially critics, could benefit from access to the article.
Jonathan Goff
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When you say divert, do you mean a clean miss or will dropping the object in the remote reaches of the Pacific or the Southern Ocean do?
Pierce,
I think it meant applying a 1cm/s delta-V which would be enough to cleanly miss earth if applied with enough time in advance (I think they went into that in the paper). I think you’d prefer to have it miss entirely, since dropping it in the ocean could possibly cause tsunamis.
~Jon
Pierce,
Yeah, check out page two of the presentation and the figure there.
~Jon
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Pierce Nichols,
“or will dropping the object in the remote reaches of the Pacific or the Southern Ocean do?”
If you can’t achieve a miss, aim for land not sea. Thicker crust (up to 35km for cratons vs 2km for sea-floor plates) means less likelihood of a mantle breach. And no super-tsunamis. (Tsunamis are particularly bad because of the typical high population densities on all coasts surrounding the oceans, and alongside all rivers (which tsunamis can travel along much further inland.))
A nice desert somewhere. Ideally in a low population region. (My home, Australia, would seem to fit the bill. A year’s notice and sufficient international help and we could probably evacuate the whole continent.)