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Nukes Not the Best Way To Stop Asteroids, Says Apollo Astronaut
MajorTom writes "Right now, we are not tracking many of the asteroids that could destroy earth. But within the next decade, new telescopes will make that possible, and leave us with the tough decision of what to do about objects with an alarming chance of hitting our planet. Last year, NASA said that the best option is to nuke them. This week, Apollo astronaut Rusty Schweickart, explained that there are far better options, and he has started an organization to prove that they can work."
To save you all the horror and pain of reading TFA (since TFS doesn't state), Schweickart is suggesting we either push or pull them away with unmanned spacecraft.
Nukes have been a popular options because:
1. We have them.
2. They have a high ISP (a measure of efficiency) when used as propulsion against a large object. Paradoxically, the ISP for Orion-style nuke propulsion increases with the size/mass of the object.
3. They're much more portable compared to most other types of methods.
Schweikart has identified the REALLY valuable truth, that we need to improve our detection method. We also need to develop deep space capability because the further out we can intercept them, the less energy is needed to perform the deflection. Lower energy can also mean less danger of fracturing the mass.
A nuclear warhead intended to deflect an asteroid could be designed to penetrate the asteroid prior to detonation. Blasting away debris from the surface of the asteroid would allow you to "push" it effictively.
And blasting it into little pieces would most certainly have an effect, since smaller pieces have more drag, they would be more likely to burn up harmlessly in the atmosphere (same total energy, much wider dispersion). Also none of the resulting pieces are likely to have exactly the same trajectory as the original asteroid. Depending on the angle of impact, they will be moving at a different speed or in a different direction than the original.
Oh man, oh man. I'm literally facepalming right now. Facepalming SO HARD.
Nuclear explosions follow the inverse square law. The further you are from the source, the less radiation is hitting you. Nuclear weapons on Earth derive most of their destructive power from the shockwave they create in our atmosphere. However, they are still incredibly powerful reactions, and if you're close to one in space, it will still fry you.
Project Orion would not 'take years to accelerate.' Unless you meant to add 'to a tenth the speed of light' at the end of that sentence. As it stands, Project Orion is the fastest, most practical spaceship would could design and build today. Chemical rockets don't even come close to what Project Orion is capable of.
And the Orion doesn't have a 'reflector', it has a pusher plate. It's a heavy metal plate, on the end of a gigantic shock absorber, coated in oil or similar [To reduce ablation.] that absorbs the energy from the nuclear explosion so that everyone on board the ship doesn't get splattered by the intense acceleration. The ship is ultimately pushed by a plasma wave created by the explosion.
An asteroid would be no different. Except that the surface might vaporize and act as additional reaction mass. The biggest problem I can envision with using a nuke to propel an asteroid is the difficulty you might have in predicting its new course.
Making it miss is a matter of nudging its orbit just enough that it doesn't intersect Earth any more. Capturing it requires slowing it down all the way to Earth-orbit speed. In space, just because something goes nearby doesn't mean it's easy to catch.
An Orion style propulsion system is capable of getting a craft from earth to Pluto and back inside a year. If we're talking about speeding up, slowing down and then repeating after turning around, we're only talking about a few months to accelerate 100+ tons of spacecraft to it's cruising speed. Now I'm sure the math is different when dealing with a planet-killer sized asteroid, but the normal orion system is not accelerating for years.
It bears mentioning that we don't need to stop or reverse a planet-killer sized mass, just push it off course for direct impact. Depending on how far out you're able to intercept it, you can get away with a very small push.
And there is something to be said for blowing one into small pieces. Even if it's hitting us with the same total energy, having it dissipate in the atmosphere as those small pieces vaporize seems preferable to having several hundred or thousand tons of mass vaporize seawater or throw up a nuclear winter style plume of dust on impact with the surface.
Even people that believe in pre-destiny look both ways before crossing the street.
Wiki, Asteroid Deflection
NYT Study suggests mirrors best
NASA has non-nuke plans
Using a 300Kg impactor
Seems the consensus is that nukes would only be used if we discovered the asteroid too late for other methods to be effective.
Anarchists never rule
I saw a presentation by the group behind this report. Using a nuke to divert an asteroid is not a crazy idea. They basically explode the nuke and cause a debris cloud of dust and gravel from the surface of the asteroid that provides the thrust to divert it.
They did very detailed simulations and it is very doubtful that the asteroid would break up like in the sci-fi shows... The parts that see the explosion break up into itty-bitty pieces and flow around the asteroid like a liquid... the interior of the asteroid remains intact. This is true for many different models of asteroid composition.
Schweickart makes the over-the-top claim that the study report is trying to push some secret nukes in space agenda. This is pure conjecture on his part. If he would have put his giant astronaut ego aside and spoke to the people who did the report he would have found out that it was done by people who had a strong aversion to nukes, and that the panel had initially tried to leave out the nuclear option or marginalize it for political reasons. But they were persuaded by the strength of the science in the nuclear advocates' arguments.
I was convinced... and I am a Pugwasher pacifist... and the people I know on the committee who were persuaded are also of the same ilk. But when you look at the analysis, you see that nukes do work. And in terms of energy imparted to the asteroid compared to launch mass, nothing else comes remotely close to the efficiency of nukes (E=mc^2 and all that.)
Yeah nukes are awful things. But so are ICBMs... and ICBMs are the basis for most of the launch vehicles used for peaceful space exploration. Why not beat swords into plowshares and start developing some asteroid-stopping nukes?
There are 10 types of people in this world, those who can count in binary and those who can't.
I'm having one of those days where I can't find a reference book (dammit!) ... sorry ...
What you want is "The Curve of Binding Energy" by John McPhee, (ISBN 0374515980) which is the story of Ted Taylor. In it Taylor describes digging tunnels with directed nuclear explosives. I recall him muttering that this isn't done because of incredible conservatism in civil engineering. Taylor also says that such explosives can be tuned up and down the electromagnetic band.
Ted Taylor has been described as the best designer of nuclear weapons that the U.S. ever had, so he probably would know.
"Project Orion" by George Dyson (ISBN 0805072845) has a nice diagram on pp. 113 of a sample "pulse unit" that's setup to direct its energy mostly at the pusher plate. Taylor did that design. It's a 1 kiloton design for outer space, but it's not hard to imagine it set up for nuclear digging.
One problem you're going to run into with "channeled radiation" and so forth is that classification people get touchy in this area. It's known that channeled soft X-rays from the primary fission device help set off a series of steps that trigger the secondary fusion device in modern hydrogen bombs (see, for example, 'The Making of the Atomic Bomb', 'The Making of the Hydrogen Bomb', both by Richard Rhodes, and Wikipedia). The precise details are not talked about. Freeman Dyson and Ted Taylor have to not discuss certain areas of "Project Orion" and they say so. Stuff like opacities of materials which are critical to Orion have other applications and they stay classified.
And George Dyson carefully notes that the Atomic Energy Act of 1946 (as amended in 1954)forces his Appendix to be incomplete. If you haven't looked at the "Born Classified" aspects of the AEC act, you should. It's quite amazing.
I hope these sources help.
-- thanks,
Dave Small