Rand Simberg: "Should NASA Be Doing More Asteroids?"
In fact, it’s not at all clear that NASA is the right place for this to happen, particularly given all its organization dysfunction. I would submit that there is currently no government agency chartered to protect the planet. I think I’m going to write up an op-ed or two declaring that it’s time to fundamentally reorganize the federal space establishment, including the formation of the Space Guard.
When I hear "Space Guard", I imagine NASA as implemented by the staff of Homeland Security.
Seems to me the fastest way to get effective planetary defense is large-scale asteroid micromining. I was skeptical about the practicality of the asteroid micromanufacturing idea I mentioned here last month ("Autonomous asteroid manufacturing"). But suppose we had a company with the technical ability to ship an indefinite number of 70 kg payloads from the asteroid belt to Earth. That company has everything needed to fling an indefinite number of 70 kg impactors from the asteroid belt at another asteroid in a lower, Earth-intersecting orbit.
This is essentially the same idea as the "kinetic bombardment" concept for space weapons -- inert masses that strike targets at orbital velocity, nicknamed "rods from God". Instead of having to launch all that mass from Earth up to escape velocity, the scheme can use a huge amount of mass already at higher orbital energy, using autonomous manufacturing to package the mass with devices that can decelerate into an intercept orbit. Assuming a lead time of a few years, this ought to be a lot cheaper and more flexible than any Earth-based solution, and it has the side effect of providing material and goods for wider space colonization.
The best reason to manufacture things in space is so that you can use them in space, after all.