Nukes Not the Best Way To Stop Asteroids, Says Apollo Astronaut 367
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."
TFS (Score:5, Informative)
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.
The reason for nukes (Score:5, Informative)
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.
Simple answers become complex... (Score:3, Informative)
The simply answer is that the physics are already known, and it all depends on how far in the future the impact is before we detect it. Given a century just about anything would work. Given less than a year, almost nothing would.
Given a couple decades, yes, there are a number of non-nuclear options. A nice high impulse drive, perhaps a number of them, set into the surface of the asteroid. They thrust in the proper direction over a long period of time, and we end up being able to put the asteroid pretty much where ever we want it.
In a shorter time frame or larger asteroid, nukes might end up being the best choice. Of course, for best propulsion, like in the horrible movie, burying it might be the best option - that allows part of the mass of the asteroid to be used to propel the asteroid in the opposite direction. The ejecta, even though some is almost guaranteed to hit the earth, is okay because it'll overwhelmingly burn up in the atmosphere.
Re:TFS (Score:4, Informative)
Re:I always wondered (Score:5, Informative)
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.
Re:TFS (Score:5, Informative)
I hope you realize that Pournelle and Niven didn't just make that up? Project Orion [wikipedia.org] was a very real attempt to develop nuclear pulse propulsion. It is still a viable option for space travel, as long we're not talking about a ground-launch using nuclear pulses. To get the sucker into orbit, we might have to resort to something a bit more mundane. Like a dozen SRBs or somesuch.
Re:I always wondered (Score:5, Informative)
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.
Re:The reason for nukes (Score:4, Informative)
Redirecting an asteroid on an Earth impacting trajectory was discussed in depth quite a few years ago in Scientific American magazine. There are a variety of ways to deal with such an asteroid, depending on size, composition, and how advanced the warning is.
There are two main responses: redirection and pulverization. If the asteroid is structurally week and small it can be pulverized so that the pieces will burn up on atmospheric entry. This has the advantage that it can be done with little advance warning. One novel proposal involved a 3 dimensional mesh built around tungsten nodes. It would be compact for launch yet still spread out and stay grouped together for a long distance strike.
Redirection is necessary for large or durable asteroids. Spin would make it difficult to have a vehicle in contact with it redirect it over time. Reliable redirection would require delivery of multiple kinetic payloads over time. Each payload strike would have the danger of fracturing the asteroid; widening the potential Earth-impact damage.
Focused, reflected, solar energy has been proposed to redirect ice based asteroids with much advanced warning. Even X-ray cannons have be proposed, along with other laser based solutions. A thermonuclear device ignited adjacent to an asteroid would vaporize a layer off its exposed surface, redirecting the asteroid. This would even be effective against iron-ore asteroids. There is also less likelihood of fracture than kinetic impact. Close asteroids can be acted upon multiple times for faster redirection.
A nuclear solution has the advantages of being effective at long range and at ranges to close for the other listed methods to be effective. It is less likely to cause fracturing and would work against any material composition.
Reliable long range detection would allow other methods to be effective, but thermonuclear warheads are a mature technology, would be effective at short range and we do not have to station them in space ahead of use.
That would take a lot of delta-V (Score:5, Informative)
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.
Re:It depends on the timing... (Score:3, Informative)
Of course. I left the calculations for longer lead-times as an exercise for the reader. I figured that having shown how much of a change you could get in only six months was enough to demonstrate the principle.
Actually, now that I think about it, under some circumstances 2000 miles or so might well be ample. If the impact is expected along what might be called the Earth's trailing edge, or near one of the poles that would be enough to make it miss completely, without even skimming the atmosphere. Not all impacts are going to be dead center, you know.
Re:TFS (Score:4, Informative)
Re:I always wondered (Score:4, Informative)
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.
Mod this junk down (Score:2, Informative)
You honestly believe that the flight time for an icbm allows the opportunity for the target to evacuate an area? fuel up lots of bombers? launch a counter strike?
With icbms there is no need for nukes in orbit to attack land targets. It is a totally pointless exercise *and* it leaves your nukes sitting around in orbit subject to damage from debris, jamming, capture, or attack from anti-sats or land based energy weapons.
Ridiculous.
Re:I always wondered (Score:1, Informative)
Compute the kinetic energy of the asteroid. If there is a collision this energy will go somewhere. Part of it will go into Earth own kinetic energy but not much (I did the computation once but I'm too lazy at the moment
to redo it), another part may go into "momentum" energy depending on wheter the collision is frontal or not.
Anyway a huge part of it will not be accounted and will be released one way or another.
Whether you blow it up or not will not change the amount of energy Earth will receive! Only how it will receive it. So the alternative is
-let the asteroid in one piece and let it hit a continent or the ocean, meaning most of the energy will be absorbed by the 6000km radius ball of molten rock ( I would guess as earthquakes)
-blow it up and let all the debris blow up on Earth atmosphere punching the exact same amount of energy into Earth's atmosphere.
Now, I don't think it is even necessary to compute what is more robust and more likely to wistand a massive input of energy: the small layer of gases known as atmosphere or the big rock known as Earth.
If this were to happen... (Score:2, Informative)
nukes only if not enough time for safe method (Score:4, Informative)
Wiki, Asteroid Deflection [wikipedia.org]
NYT Study suggests mirrors best [nytimes.com]
NASA has non-nuke plans [theregister.co.uk]
Using a 300Kg impactor [arstechnica.com]
Seems the consensus is that nukes would only be used if we discovered the asteroid too late for other methods to be effective.
Re:Test Trial (Score:3, Informative)
> and in the end any direct action would be vetoed by China.
And likely Russia too. :-)
(Flying there later today... Russia, that is, not China or an asteroid, although I'm sure are those who would prefer I travel to the latter :-)
Next century, not decade (Score:1, Informative)
Hopefully people are not mislead by the post -- it says "next decade", while the article writes "next century" is when the powerful new telescopes will be operational.
Nukes are the way to go (Score:4, Informative)
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?
Re:TFS (Score:3, Informative)
Re:Hit asteroid with "slap" very repeatedly. (Score:3, Informative)
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