Dr Stan Love, Johnson Space Centre, Houston, Texas
Part of the show Meteorites, Satellites and Avoiding Asteroids
Chris - Now you reckon you've come up with a way to solve the problem that may have wiped the dinosaurs out 65 million years ago. But what is it?
Stan - My co-author Ed Lu and I have come up with a way to make deflecting an asteroid that's coming at the Earth a lot easier than some of the schemes that have been proposed over the last few years.
Chris - What kind of schemes have been put forward? There are things like blowing it up, but that doesn't work too well does it?
Stan - Blowing them up has been proposed but it's hard to do. Asteroids are a lot tougher on impact than you might think. They're like big flying bags of rubble and bags of rubble do a great job of absorbing impact and explosion damage. It's hard to calculate exactly how much explosion energy you need to break up the asteroid, and if you got that calculation wrong, the rubble would break apart and come back together again under its own gravitational pull. It would then still be coming at us, which would be a problem.
Chris - So what's your solution?
Stan - Our solution is to use a spacecraft to gradually tug the asteroid out of the way. Ideas like this have been proposed before where you nuzzle up to the surface of the asteroid. It's got such weak surface gravity that it's hard to just plant a spacecraft on the surface the way we land on Mars or the moon. It's possible to nudge an asteroid out of the way like that. But once you've landed, you not only have to worry about attaching, but also that the asteroid is rotating. The thrust that you've gone to all the trouble to get out there and landed is now hosing around in circles like a lawn sprinkler. Our alternative is instead of touching the asteroid, you sidle up next to it and turn on a very low thrust engine that just manages to balance the weight of the space craft as it's being pulled along by the asteroid's gravity. You just hover there. As you hover for months or maybe a year, the very slight gravitational pull between the spacecraft and the asteroid will change the asteroid's orbit. If you then got there ahead of time, say twenty years in advance, the orbit will change enough to miss the Earth rather than hitting it.
Chris - Do we know of anything that's likely to actually be amenable to this kind of therapy? Are there things bound to Earth in your time frame for deploying this kind of measure?
Stan - Right now there's nothing that we know of that's going to hit us. But there is an asteroid that we're going to be paying attention to over the next couple of decades. It's going to come swinging by us in 2029 and if it passes at just the right distance from the Earth in that swing-by, it will get kinked onto a new orbit that will bring it back to hit us in maybe seven or eight more years. Now we don't know yet whether or not that's going to happen. The probability of it happening is very small, something like one in five or ten thousand, but we'll be keeping an eye on that asteroid. If it should turn out that it's heading on that collision course, then if we could get a spacecraft like the one we're describing called a 'gravitational tractor'. Once we get it out there, a tiny change in the asteroid's path before the approach will translate into a very big change in its orbit after that close approach. So you can multiply the effect of your deflection scheme by doing that.
Chris - Is technology up to doing that at the moment or is this just a speculative thing that could work if we have another set of technologies coming on line in the next couple of years?
Stan - Stuff of the kind we've been proposing hasn't been flown yet. The baseline gravitational tractor that we're talking about is a twenty tonne spacecraft, which is very big. It would be powered by a nuclear reactor, which has been done a few times but is not commonly done today. So these are not mature technologies, but NASA was proposing to put together just such a spacecraft to fly out to Jupiter and go into orbit successively around each of Jupiter's big moons. So the technology is not mature, but it's within reach.