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The first thing that comes to mind when someone asks: “How do we deflect a near Earth asteroid?” is “Fire some nuclear missiles at it.” However, this might not be the best course of action. Akin to opening a walnut with a sledgehammer, there might be a better, less messy option. This is what Apollo astronaut Rusty Schweickart thinks at least. Last year, NASA issued a report suggesting they were seriously considering a nuclear option should an asteroid threaten Earth. However, the ex-lunar module pilot believes this decision was manipulated by political pressure, possibly indicating the asteroid threat was being used to speed up nuclear proliferation in space…
When ex-Apollo astronauts express an opinion, people tend to sit up and listen. After all, the astronauts throughout the space race years in the latter half of the 20th Century (from the USA and Russia) were the ultimate explorers, going above and beyond the call of duty, putting their lives on the line for their countries. Several of the retired Apollo astronauts have come forward over the years with their opinions on modern NASA, concerns for the future of the US position in space exploration and their belief in extraterrestrial cover-ups (!). And last Wednesday, during a public lecture in San Francisco, legendary astronaut Rusty Schweickart voiced his opinion about NASA’s decision to use nuclear technology when faced with an asteroid threat.
Schweickart has expressed concern with the possibility of using nuclear weapons to destroy, or deflect Earth-bound asteroids, pointing out there are many other less harmful ways of dealing with the asteroid threat. At the moment he points out that we are completely unprepared to deal with asteroids, but by 2015, we should have developed a gentler means of deflection. Simply blowing asteroids up have many knock-on implications. First and foremost, Schweickart believes that NASA may be open to manipulation to put forward the proliferation of space-based nuclear weapons under the guise of international “safety.” Another problem I can see is blowing up a large piece of rock only to create many smaller (but just as deadly) pieces of rock, doesn’t really extinguish the destructive power of an asteroid on collision course, in fact, it might increase it.
Schweickart’s organization, the B612 Foundation examines other, more subtle ways of deflecting dangerous asteroids are examined (nuclear warheads not included). Decisions such as when to take action, how to better track asteroids and how to deflect them should be an international effort and not one nation’s decision to detonate a nuclear bomb in space.
Source: Wired
Hi Ethan!
Yes, I remember reading that article a while back. I don’t really have many personal issues with radioactivity in space, especially when trying to stop the mother of all boulders smashing into Earth. But my issue is with risking the break-up of the larger asteroid into smaller bits (although a lot depends on composition, density, material, size etc.). Regardless, for any plan to work, we’d need a lot more lead-time to do anything about it. I’d love to think that we’d have a decade or more to assemble a viable plan should an NEO look like it’s going to hit us… alas, I suspect, we might not have time on our side. But the main thing is, the coast is clear for now, so lets get planning for a worst-case scenario!
Cheers, Ian
PS. In your article, you mentioned that roughly half of the energy from a nuclear blast would be effective to move the mass of the asteroid. Is this a realistic figure? I would have thought it would be a lot more inefficient than that.
I agree with Ethan. Use nuclear weapons to detonate NEAR the asteroid instead of blowing it up.
It would be like using the Orion spaceship idea to slow the rock down and deflect into a harmless orbit.
We have the technology. GO NUKES!
(And by the way, develope less hard core, Marine Corps ways to deal with space rocks.)
Ian,
I don’t understand what the problem with nuclear explosions in space is, even in principle. I addressed these issues here.
But at the end of the day, if you want to deflect an asteroid, you need to impart energy to it. You do it all at once at the beginning, and you need less energy than you would at any other time; so a large impact/explosion as early as possible is the smallest amount of energy you could possibly need.
A nuclear fusion bomb has no radiation fallout, as it just leaves you with cleanly burned helium. There are debris and fragmentation issues, but that’s really it. Those could be controlled by the location of the explosion, assuming a spherically symmetric explosion of the nuclear bomb. Politicization accusations aside, nuclear bombs make sense from both an energy and environmental point of view. They are also the technology closest to being feasible for accomplishing this task.
Ethan
The trouble with Ethan’s argument is that he talks about conservation of energy and momentum, and then just assumes that half the energy of the bomb will go into moving the asteroid.
I think the calculation needs to be a lot more careful. What is the momentum of half the photons and debris from the bomb? That tells you how much the asteroid will move. From that you can work out the kinetic energy imparted to the asteroid. The difference between that and the (half-)energy of the bomb presumably goes into heating the asteroid up.
I think, ultimately, this is about the second law of thermodynamics: just because you’ve got a lot of energy stored somewhere, doesn’t mean you can automatically use it for anything you want. Efficiency, as Ian said, comes into it.
On the other hand, breaking one large lump into a lot of smaller ones might still be a good thing. The small pieces will have a greater surface area in aggregate, and so may be more effectively stopped or slowed by the atmosphere. You’d still end up with the same amount of energy delivered to the earth, but a series of huge airbursts may still be better than one really ginormous groundburst (or splash in the sea).
Either way the answer involves actual intellectual hard work and study, i.e. the opposite of what internet discussions are about.
I suggest that if you can access the mass, it might be better to make the nuclear explosion more effective by making a shaped charge out of it. This way you could use a smaller nuke and concentrate _more of_ its energy in a specific direction rather than having it radiate equally in all directions.
I like the idea of sending in a rag tag team of roughneck oil drillers to destroy the Asteroid, largely because I am more likely to become a roughneck oil driller than an astronaut.
If we identify and accurately monitor the Asteroids that have the potential to cause problems for us it would be nice to affix an engine to it and nudge it toward a Lagrangian point perhaps where it can essentially be corralled for future mining. Since they are covering a large distance over a long time period, a little energy might suffice, but I’m spitting into the wind.
Ian,
If you detonate the nuclear weapon right next to the asteroid, half of the emitted photons will collide with the asteroid. By sheer conservation of momentum and energy, half of the emitted energy will go into changing the kinetic energy (and hence momentum) of the asteroid.
I agree with you, though, that the biggest advancements need to be made in tracking so that we can have as much time as possible to figure it out!
Ethan
I think the concern with nukes in space lies with * using them on ourselves *. If you allow the foot in the door for weaponizing space, before you know it space colonies, space stations, other ships, and Earthbound targets can all be the victim of space-launched nukes.
And a space-launched nuke has the advantage of being undetectable until almost immediately before impact. There’s no ground launch site that spies can be observing, no radar will detect the launch… it will basically just appear above the target when it enters the atmosphere and a few minutes later the target is gone.
I have no objection to using nukes to deflect asteroids, but I think it should be a last resort, for instance if we’ve discovered an asteroid too late to deflect through gentler means.
For instance if you knew 20 years in advance that a nuke would likely hit Earth, you could send up a space probe with an ion engine and have it circle the asteroid continuously, drawing/adding momentum and slowly altering its course until it is no longer a threat.
Could also attach the engine directly to the rock itself and have it “push” the asteroid through acceleration, but it seems that would be overly complicated for a robot to do and unnecessarily dangerous for a human to do.
I think there is another problem with the “nuclear option”. Detonating a nuclear charge is a very quick event so you have to get all the mechanics right the first time which means you have to have a *really* good understanding of how the particular asteroid holds together, its gravitational characteristics, the geology etc. With a slow process of deflection you can observe where things are going and possibly modify some parameters. With a nuke you don’t have that luxury. If it doesn’t work the way you intended you’ll have to do it again but this time with even less understood object or collection of objects.
Kind regards,
/Adam
First of all, radioactivity in space? Come on, space is filled with radiation. Nuclear explosion wouldn’t make any difference.
You guys are watching too much movies if you believe that we could attach a engine to asteroid and it would skip hitting Earth.
1.) You should find the asteroid early enough to haul the massive engine and the massive load of fuel.
2.) You have to assemble that complex at the asteroid.
3.) You could try smaller option, but then you would have to find the asteroid even earlier.
Same applies on other SCIFI options. And yes, the composition of the asteroid plays huge role when you are planning to plant something on a asteroid.
Massive laser is much better option and imho mankind should develope massive lasers capable of heating and by that breaking or just changing the characterists of the asteroid. Three of those in the Earth orbit could cover up all directions towards Earth and they could be used together too.
But before that, we don’t have any other option than nuclear warhead. We don’t have even missiled to do that right now. And I don’t believe that we have big enough nukes.
I’m really interested in the efficiency of the nuclear missiles in the space. There is no air — nothing to burn (no fireball will blow up), no shock wave, and it won’t create vacuum. So what’s left? Radiation? In space? 🙂
A man cannot defeat a bear with his own strength. So use a gun to shoot it!
There are non-nuclear options. Rusty Schweickart himself apparently favours the gravitational tractor option, though that needs a lot of time. Prof. Colin McInnes of Strathclyde Uni has considered the kinetic option, a scaled-up version of NASA’s Deep Impact, and ESA is planning a similar mission. In the 1980s Gordon Ross of Glasgow School of Art came up with the idea of using a parabolic mirror to create a jet (first publication 1992, Analog October 1994). More recently he’s designed a multi-mirror system called Archimedes. That’s been evaluated by Glasgow Uni Aerospace Dept. in a study financed by ESA, and a detailed paper by Dr. Max Vasile endorsing it was published this month – not on web yet, but watch out for ‘mirrorbees’. His group considered other options but considered it was the best – superior to mass drivers, for instance.
“A man cannot defeat a bear with his own strength.”
UP here near the Arctic Circle, we found it much more efficient to defeat all the Bears at once by using a Favre instead.
🙂
I have absolutely no reservations about using nukes in space to deflect an asteroid, but I have to admit that since the first big budget movie came out of Hollywood suggesting we blow an asteroid to smithereens with nukes, a little imp in the back of my mind has whispered softly, “but what about all the detritus left from the explosion. Isn’t it just as dangerous?” I suppose it would depend upon the asteroid.
In his famous book “High Frontier” Gerard O’Neill has suggested a method for maneuvering moderately sized asteroids (the size that nukes would have a prayer of moving) and it may be worth considering for something like this. He was a great fan of the mass driver and suggests that mass drivers could be installed on a hunk of rock and it could be turned into a controlled object; the rock itself providing the reaction mass and energy from the sun powering the driver. If it works for changing a random space nugget into a spaceship, why not change an asteroid with its eye on earth into something similar. I presume that we would have to find it in time to get to it and apply the small but continuous thrust that would be needed to change its trajectory enough to matter, but other than that one admittedly large difficulty, everything else is known technology and simple physics.
Even if the nuke broke the threat into smaller pieces, it will at least improve the situation. What’s better, being hit by a bullet or shotgun pellets? Niether is pleasant, but you have a much better chance of surviving the shotgun blast.
Ethan: your calculation assumes a 100 Megaton bomb which is the correct order of magnitude since the Russians tested a 57 MT bomb. But you can’t put half the energy into kinetic energy of moving the asteroid by exploding it next to the surface. You need to provide momentum p = mv, and you have energy E = 0.5mv^2.
So p = sqrt(2mE). Your article assumes m is the mass of the asteroid, but it really will only be the mass of half the bomb, and the deflection will be a million times smaller.
We need to use the energy to lift a large mass off the surface of the asteroid at a low velocity to get the most momentum for a given energy. The key is to use part of the asteroid as the reaction mass. The only way to achieve Ethan Siegel’s limit is to use the bomb to split the asteroid into two halves. This would require landing and drilling as in the worst sci-fi movie ever, Armageddon.
With lots of lead time, one could just drop lime on the asteroid to paint it white, which would change the Yarkovsky force and deflect it.
A 20 tonne spacecraft with an ion drive could be used as a gravity tractor with enough lead time.
With less lead time one could land a solar powered “gravel pit” on the asteroid and use a conveyer belt as a low speed mass driver to send gravel off the asteroid in the direction opposite to the desired deflection.
With minimal lead time one could try standoff nuclear explosions designed to lift a layer of rock about a meter thick off the surface of one side of the asteroid with a speed of 100 m/sec or so. Fragmenting the asteroid has to be avoided, so this would be a pretty dangerous operation. But one could try a large standoff distance first and then gradually increase the energy density delivered to the surface by moving the explosion points inward. So many bombs would have to be delivered toward the incoming asteroid with enough time in between to judge the effects of the previous shots. An exciting time for all concerned.
So we need a long lead time! Find all the dangerous objects. Then we only have to worry about comets which can’t be predicted so far in advance even if found early.
Fragments are not necessarily as dangerous. If the fragments are large enough to survive reentry and enough of them hit the Earth, the total damage could be increased. However, if the fragments are small enough that they burn up before hitting ground, lose most of their energy in the upper atmosphere, or if they are dispersed enough to miss the Earth entirely, damage could be greatly reduced. Fragmenting the asteroid could only make things worse, but it could also turn a catastrophic impact into a light show and a few cool summers. In addition, there are things that could be done to minimize the probability of fragmenting the asteroid.
Avoiding use of nukes in space is foolishness. We have nukes now, hitting a habitat with one would be no enormous challenge. In addition, a spacecraft with a rocket motor and moderate sized fuel tank is at least as dangerous a weapon as a nuke. Nukes have many peaceful uses in space, and refusing to use them in those ways simply means that they’ll only be used for violent means…except that the availability of rocket engines makes kinetic weapons far more likely.
In my opinion, worry about nukes in space being part of a weaponization in space is silly. If a nation the size of China or Russia or the US wanted to launch a quick strike, they’d be better off pulling some submarines to their enemies coast and blasting them. That would be much easier than trying to launch from a space platform which would have a predictable orbit, easily observed and a good target. Since the US has a good fleet of such subs still around, why bother with the expense? It seems to me that many of the opponents of using nukes don’t ever want to admit that they could ever have any use.
In terms of effectiveness, if you could use a rocket motor and some other technology to move an asteroid to a new orbit or divert it more efficiently, then I’d be for that. BUT, since I don’t know that we actually have any alternatives ready, I’d keep a bunch of nukes ready just in case. Like war or anything else, the nukes are the last chance card. You play it when there is not other choice.
Didn’t the American Indians have a big laser that could deflect asteroids? Oh. Wait. That was a Star Trek episode…never mind.
Oh and…
Geokstr: Good one!
Just imagine the average asteroid rolling and spinning in space before trying to land the hope of our species on it.
Dave – gravity tractors don’t rely on landing on anything. A space probe simply circles the asteroid continuously, the motion slowly nudging it into a new course over many years.
As for this:
“BUT, since I don’t know that we actually have any alternatives ready, I’d keep a bunch of nukes ready just in case. Like war or anything else, the nukes are the last chance card. You play it when there is not other choice.”
Umm, alternatives? We don’t have asteroid-killing nukes ready yet either. It’s ALL theoretical at this point, because we’ve never moved an asteroid. So the nuclear option is just as experimental as the gravity nudge.
any non nuclear method of asteroid deflection is either impractical from the engineering point of view, or simply impossible. This is because of newton’s first, and second laws. Far left wing political ideaology may not be substituted for sound
science and sound engineering.
tim mayes
asreoids are too massive to be moved by anything except nuclear explosions.
it is simply a matter of newtons second law.
tim
Asteroids can be moved by mind control if everyone on Earth concentrates on it.
We could also move the Earth out of its way !
When it comes to survival no options should be left off the table. You have to know what is coming at you though..
Low density carbon style asteroid? 70% or so of the asteroids out there… What would a nuclear blast do to it? Fuse it into a solid lump or somehow impart enough energy to overcome the gravity that formed it? Gravity tractor sounds more feasable to me
Medium density silica/iron style asteroid? 10% or so population wise. 50/50shot grav tractor vs hydrogen device nuclear weapon?
2 mile wide chunk of nearly pure iron/nickel? 5ish % population, would probably be the best candidate for deflection goal nuclear detonation
Ice/Comet who knows what effect a nuke would have…
Ethan mentioned a no-fallout fusion device but the problem there is getting one of those monsters out of earth orbit. Any other would be a plutonium – deturium / tritium weapon.
As far as space detonations go, both US and Soviets did experiments as far out as 300 or so miles, most of the american tests resulted in pretty lights in the sky and knocking out the power grid of Hawaii
“Far left wing political ideaology may not be substituted for sound science and sound engineering.”
And explosions! Don’t forget the explosions.
I like explosions.
Ned,
I double checked. m should indeed be the mass of the asteroid, as I originally contended, not the mass of the bomb (the E term comes from the energy emitted by the bomb). Sending a nuclear device this powerful on an accurately aimed rocket could reach an asteroid and detonate, changing course, in a matter of months.
Other solutions, like the ion drive + painting one side (assuming stabilization against the rotation which would result) would take decades for a comparable effect. I’m not saying that your solution isn’t safer or just as effective given sufficient lead time, I’m saying that it’s a long way down the pipeline.
Ethan
This seems to be a pretty straightforward engineering issue; just use the tools that are appropriate for the job. If you have plenty of time, the non-nuclear options seem appropriate.
If time is short, use nukes. If the asteroid breaks up into chunks, use more nukes. Eventually you’ll end up with a really epic meteor shower and a little radioactivity. Better than a giant smoking hole in the ground.
One question: If we see a comet coming at us from the great void, as in Lucifer’s Hammer, will we have time to deflect it with nukes?
Well I guess no one understands how one uses a nuclear bomb to deflect a threat:
You dont blow it up. People who think you do blow it up got that information from others who are wrong, or from a film.
It is called mass ejection redirection. You detonate close to the surface so that you blow off just enough material to move the impactor slightly. The key here is you have enough warning time.
It would take a huge amount of power to destroy a serious impactor, or deflect it once close. At that point, you might as well focus on digging tunnels.
Tim your wrong, there are hundreds of other ways to move an astroid especially with lots of time. You can’t just say “newton’s second law” and hope u make sense. However i do agree with the use of nukes
This sounds crazy, but can Earth be moved at all? Far enough that gravity would not attract an asteroid if it were to hit? And building tunnels? I don’t think that would work if an atroid did hit. Wouldn’t the asteroid cause tsunami if it did hit Earth, wether it hit sea or land and people would dround in tunnels. Not too sure about any of this because I really don’t know too much.