Neil deGrasse Tyson On How To Stop a Meteor Hitting the Earth 520
An anonymous reader writes "Astrophysicist Neil deGrasse Tyson talks stopping extinction-level meteor hits: '...Here in America, we're really good at blowing stuff up and less good at knowing where the pieces land, you know...So, people who have studied the problem generally – and I'm in this camp – see a deflection scenario is more sound and more controllable. So if this is the asteroid and it's sort of headed toward us, one way is you send up a space ship and they'll both feel each other. And the space ship hovers. And they'll both feel each other's gravity. And they want to sort of drift toward one another. But you don't let that happen. You set off little retro rockets that prevent it. And the act of doing so slowly tugs the asteroid into a new orbit.'"
Need some advance planning (Score:4, Insightful)
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The basic problem that I'm seeing is that if you're talking ELE it's a big rock, you're going to need a big mass to pull it off course. Coming to a position of relative rest quickly takes a lot of energy. The smaller the attractor ship, the earlier it has to get into position. But the larger the attractor ship, the more energy it will take to bring it to "rest". I'm still seeing impactors as the logical answer. You could collect rocks at stable points and then fire them at the mass.
If you could work out som
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A tiny nudge early enough just might be enough.
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A tiny nudge early enough just might be enough.
Better off, then, sending an impactor that goes splat. And either way, we don't tend to know that early whether it will hit or not. Right now we would have to send our hypothetical craft to rendezvous with every potential impactor, because otherwise we wouldn't even know if we needed to deflect them. So it's not really a workable idea without dramatically improving our detection network...
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Another method is to place a very powerful laser in orbit around Earth or another suitable orbit and then fire at the asteroid. If the laser is powerful enough it will cause the asteroid to shed some material and through that slightly change the orbit. This will work fine given enough time and precise enough calculations.
The problem by having a spaceship approaching an asteroid is that it requires a lot of fuel to get there. In addition to that there's no easy way to beforehand get enough information about
Great caution is Advised (Score:2)
If you change its orbit, the meteor may be set on a collision course in a later go-around. What you want to do is change its orbit so all future approaches are farther from impacting earth, not just this time. Another-words, pay attention to what you are doing. Do not just do something short term.
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All you have to do is generate a near miss once and the rock's orbit will be radically altered forever after, by the slingshot effect of Earth's own gravity as it passes by. Remember 2012 DA14? It will never pass so close to us again. When it went by that close, it got slung into a new orbit.
Why is "blow the thing up" a bad idea? (Score:5, Interesting)
"Knowing where the pieces land" seems like a red herring.
If we detect an asteroid a long way out on a collision course with Earth, then altering its velocity by just a bit will push it off of course and it'll miss us. If you set off an explosion near an asteroid, it will indeed likely fragment, but the only way we're still getting hit is if a large chunk somehow gets *no* delta-v from the explosion, and if that chunk is big enough to survive reentry.
OTOH, if we detect a big asteroid close to us, there may not be time for these things, and we need a large impulse quickly.
Either way, "nuke it" seems like the most sensible thing. Yes, this is a drastic thing, but if it's a true doomsday asteroid then it's called for.
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Honestly, nudging it off course with some ion drives or any source of contained thrust is a good idea. Nuking it is only better than an extinction level event. Such as last minute, too large, etc. Where humanity will still probably be largely hosed, but not completely. Even if you converted a large mass asteroid to sand, it'd still do not-great things.
Buddy of mine with a bunch of engineering degrees
Re:Why is "blow the thing up" a bad idea? (Score:4, Insightful)
You really want to avoid any pieces going even near orbit. We have a mess of expensive stuff up there.
It is not difficult to choose between "survival of the planet" and "doing without TV and GPS for a few years".
Conversation of energy (Score:3)
Wouldn't it just be better to smack into one side of the asteroid at full speed rather than use a bunch of energy to get to the asteroid, a bunch more to slow down and rendezvous, then use little puffs of energy to try and modify its orbit?
Seems to me that all that reaction mass would be much better served by hitting the rock traveling at 4X,000 MPH.
I think there is a better plan (Score:2)
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Setting the record straight) (Score:2)
The idea of using gravity (the proper name is Gravity Tractor) to deflect incoming rocks has been around for some years now - and it wasn't Neil's idea.
My 0.02 (Score:2)
Deflection is Rehashing Old Ideas (Score:4, Funny)
Remember, best block, no be there.
If Sam Kinison [wikiquote.org] were alive today, he'd apply his philosophy on world hunger and say:
You want to help end extinction-level meteors? Stop sending up shit to blow them up. Don't send them another one, send up huge orbit-altering rockets. Send the UN a guy that says, "You know, we've been coming up with a plan to blow up meteors for about 35 years now and we were blowing stuff up, and we realized there wouldn't BE extinction-level meteors if you people would live where the METEORS AREN'T! YOU LIVE INSIDE AN ASTEROID BELT!! UNDERSTAND THAT? YOU LIVE IN A FUCKING ASTEROID BELT!! Stop wasting rockets by launching them at each other. You too, North Korea... don't give me that look. We're going to do this together in one shot.
The most-effective solution is don't be where the meteor is going to be. This worked well for me the other week. Giant meteor fell in Siberia and I wasn't there.
After reading the comments at the CNN article... (Score:4, Insightful)
.... I'm confident that we have little to worry about. Asteroids will tend to avoid our planet out of sheer embarrassment.
Re:Sorry, little retro rockets won't work for that (Score:5, Funny)
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I would normally agree but the whole thing sounds preposterous. The gravitational pull of a spaceship is negligible. If you're going to send a spaceship up there and let it "hover" why not just have it actually contact the meteor and use its thrusters to push it out of the way?
Re:Sorry, little retro rockets won't work for that (Score:5, Informative)
The asteroidmay not be solid rock. It could be a rubble-pile type, and there might not be anything solid-enough to apply force to in a consistent way. It might be two closely orbiting bodies of rock, in which case you can't push on one in any type of consistent direction.
The benefit of the gravity-tug approach is that if you have a body of some concentrated mass moving at you, then if you have a spaceship sit away from it and maintain a constant position relative to a point other then the asteroid, then you can act on it's entire mass consistently.
Find it early enough, and you can do this with high-efficiency ion thrusters, rather then needing inefficient chemical rockets.
Re: reactive force from retrorockets - you fire them off-angle to the asteroid so exhaust doesn't hit them. You can easily mount orthogonal engines which would carefully cancel the attraction of the asteroid without directing any exhaust at it.
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Taking a 30,000 kg ship at 20 km from the asteroid and the gravitational constant to be 6.7x!0^-11 m^3 kg^-1 s^-2, you would have a gravitational acceleration of about 5x10^-14 m/s^2. To move it 6,400,000 m (one earth radius) would require 1.6x10^10 seconds (about fifty years).
Also, for two asteroids orbiting each other, if these are "small" asteroids, what gravity would obtain between them? Two asteroids of radius 20 kilometers each with 50 kilometers between their centers (and having earth's density for a
Re:Sorry, little retro rockets won't work for that (Score:4, Informative)
Taking a 30,000 kg ship at 20 km from the asteroid and the gravitational constant to be 6.7x!0^-11 m^3 kg^-1 s^-2, you would have a gravitational acceleration of about 5x10^-14 m/s^2. To move it 6,400,000 m (one earth radius) would require 1.6x10^10 seconds (about fifty years).
Also, for two asteroids orbiting each other, if these are "small" asteroids, what gravity would obtain between them? Two asteroids of radius 20 kilometers each with 50 kilometers between their centers (and having earth's density for a mass of 5x10^13 kg each) would have a mutual gravitational acceleration of 1.3x10^-5 m/s^2. Would it be that hard to separate them?
But you aren't talking about moving it X distance, you're talking about deflecting it X angle...
Even 1 degree is a decent change at a few AU
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I mention that the timing may get messed, but I'm stuck in 2D trig? Doesn't the 4-dimensiomality make it easier to solve?
Re:Sorry, little retro rockets won't work for that (Score:5, Insightful)
Because we are currently unable to judge the stability of the object, or it's internal mass distribution just by looking at it from long range.
Pushing it at any point might just lead to breaking off a small piece, or the spaceship slowly sinking into and through it.
If we miss the mass center, the push will mostly be transformed into rotation.
All these problems are a non issue with gravitiational pull.
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I would normally agree but the whole thing sounds preposterous. The gravitational pull of a spaceship is negligible. If you're going to send a spaceship up there and let it "hover" why not just have it actually contact the meteor and use its thrusters to push it out of the way?
The way the universe works doesn't really depend, in any way, upon you finding physics "acceptable".
And a great many people, who clearly are vastly more knowledgeable than you, have done the math and know what they're talking about
Re:Sorry, little retro rockets won't work for that (Score:4, Funny)
Don't know about six, but I can name 7 of 9.
Re:Sorry, little retro rockets won't work for that (Score:4, Informative)
I would normally agree but the whole thing sounds preposterous. The gravitational pull of a spaceship is negligible.
The force of gravity between the asteroid and the ship is small, not necessarily negligible. Let's take some basic physics. The gravitational force between two objects is g (about 9.8 m/s/s) times the mass of the first object times the mass of the second object divided by the square of the distance between them.
F = g*m1*m2/d^2
The acceleration of an object imparted by a given force is the force divided by the mass of the object being accelerated.
F = m*a or a = F/m
So combining those two equations, the acceleration of the meteor being moved due to the gravity of the spaceship is g times the mass of the spaceship divided by the square of the distance between the meteor and the spaceship. The mass of the meteor cancels out.
a = g*m_{ship}/d^2
Now this is likely to be small, true. But just like interest in the financial world, the secret is time.If you can impart even a small acceleration over a long enough time frame, the thing you're accelerating ends up going at a pretty good velocity.
The approach you'd need to use to react to a meteor depends on the size and how long in advance of its impact you can detect it. If you detect it a year or two ahead of time? At _best_ you might have time to prepare an Armageddon-style mission; more likely you'd want to find some way to record information about humanity's progress so the survivors can recover or aliens can learn about the extinct human race. Ten years would be better for that type of "plant a bomb on it" mission or to prepare to launch a nuclear missile at it. Fifty to a hundred years? A low, slow method like gravitational towing may be good enough to ensure that Earth and the meteor don't pass through the same point in Earth's orbit at the same time.
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The value that you've given for g is the acceleration due to gravity ON EARTH. G in your first equation should be capitalised, and it's the Universal Gravitational constant. G ~= 6.67 x 10^-11 N(m / kg)^2
This doesn't make your logic less correct, but your numbers are going to be several orders of magnitude off.
http://en.wikipedia.org/wiki/Gravitational_constant [wikipedia.org]
http://en.wikipedia.org/wiki/Gravity_of_Earth [wikipedia.org]
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Where's "-1, appeal to authority" when you need it? Either "flyingfsck (986395)" makes a good point or he doesn't. There's no point in even having a comments section if nobody's going to actually discuss the subject, and flyingfsck (986395) is certainly makigna better contribution to that than you are.
Re:Sorry, little retro rockets won't work for that (Score:4, Insightful)
Appeal to authority is, in many, many cases, a perfectly valid argument. Appeal to authority is the entire reason our society can even function at all. We offload complicated decisions to people who are better at them than us.
And in this case, it is once again correct. Neil deGrasse Tyson does indeed know what he is talking about. The gravity tractor idea has been around for a long time, and in theory works just fine.
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I'm going to assume Astrophysicist Neil deGrasse Tyson is a much better source than you.
But the point is correct. The gravitational attraction of a spaceship to an asteroid is a weak force. It means you can only a apply a force equal to the weight of the ship on the asteroid. Also, the momentum of the propellant from the rocket pushes against the asteroid, countering the thrust of the rocket. (Unless you direct the rocket away from the asteroid, in which case the rocket escapes from the asteroid.) It's a bad idea.
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Re:Sorry, little retro rockets won't work for that (Score:4, Informative)
That gets you around the exhaust problem but worsens the problem of gravitational force limiting. The closer your tractor ship to the asteroid, the more propellant you must use pushing in useless directions. The farther you put it, the more efficient the use of fuel but the amount of time you must pull to get the same delta P increases as the square of the distance to avoid the tractor escaping.
The optima don't align at all. If you want to minimize the amount of time you must spend towing, you put the "tractor" very close, about 1.25 radii from the asteroid. (Actually maybe a little farther to ensure you don't hit the asteroid with any of the propellant.) That that reduces your efficiency to about 60% of what it would be in the limit and your force to about 38% of the weight of the tractor on the asteroid's (assumed spherical) surface. For non-spherical towed objects, it gets worse. But assuming efficiency isn't a consideration, you're still limited to less than the gravitational force between the asteroid and your tractor.
It must have a lot of mass when it gets there because if it doesn't it won't have enough gravity to pull anything anywhere. The smallest objects we'd probably need to move are 100-meter asteroids that mass something like 3E9 kg. So the force you can apply this way is limited to less than .074 Nt/ton of tractor. Over a year of such pulling, you get a delta-v of about .0008 meters per second. How much do you have to change the velocity to miss the Earth? About by the diameter of the Earth. It turns out to do that in a year takes about a 2 ton tractor. A rock twice that big has 8 times the mass and would take 4 times the tractor to move it in the same time.
This has to be compared in practicality to other methods. While it solves the problem of not having to physically land on the object, you still must match velocities exactly and must send a bunch of dead weight to pull your object with.
Re:Sorry, little retro rockets won't work for that (Score:4, Interesting)
Actually maybe a little farther to ensure you don't hit the asteroid with any of the propellant.
In a vacuum, the gas from the propellant won't dissipate quite as much...
An additional force to think about - if you're using gas propellant, or perhaps an electrostatically accelerated ion engine, you're going to build up quite a charge throwing those ions around, aren't you? You'd have to consider that in your calcs. Might change the shape of the attraction curve between the two bodies.
Re:Sorry, little retro rockets won't work for that (Score:5, Informative)
Only if you let it. The Gravity Tractor idea usually uses two ion engines aimed so the exhaust goes either side of the body being towed. The tractor stays in place and there's no unwanted momentum transfer.
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Mod parent up !! This point is missed in most discussions on this topic
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I'm going to assume Astrophysicist Neil deGrasse Tyson is a much better source than you.
But the point is correct. The gravitational attraction of a spaceship to an asteroid is a weak force. It means you can only a apply a force equal to the weight of the ship on the asteroid. Also, the momentum of the propellant from the rocket pushes against the asteroid, countering the thrust of the rocket. (Unless you direct the rocket away from the asteroid, in which case the rocket escapes from the asteroid.) It's a bad idea.
Do they not teach basic science in the US anymore? The fact that it would work should be something can be easily proven by anyone who has taken highschool physics. You do realize that rockets don't take off because they're pushing against the ground, right? You just need to move the center of gravity the tiniest amount. When you're traveling a billion or two miles, and you're trying to miss something that is only 13,000km across, you don't need to put a lot of pressure on it, you just need to put a little pressure for a very long time.
Do they not teach Newton's third law in your country, or has it been repealed for your convenience?
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Do they not teach Newton's third law in your country, or has it been repealed for your convenience?
Yes, and even Newton could've figured out how a rocket works.
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The blast from the little retro rockets hitting the much larger asteroid, will cancel the whole thing out - every action having an equal and opposite reaction and all that pesky old Newtonian conservation of momentum stuff...
Just use a tractor beam instead.
Use the EM drive (Score:2)
the EM drive has no emissions:
http://en.wikipedia.org/wiki/EmDrive [wikipedia.org]
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Re:Sorry, little retro rockets won't work for that (Score:5, Informative)
They don't need to be thrusting directly at the asteroid. Think 3 or more at angles, so they cancel each others' sideways thrust and the overall thrust misses the asteroid, whilst providing net 'away' thrust. Yes, this reduces efficiency.
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The blast from the little retro rockets hitting the much larger asteroid
Have you notices how quickly gases expand in vacuum? There won't be any such thing as "hitting the much larger asteroid".
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It may not be much, but those little tiny bits of acceleration add up [ucla.edu].
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What range from the asteroid are you expecting this tiny little space probe to be at while its gravitational pull is deflecting the asteroid away from the Earth?
That can be easily calculated from the mass of the asteroid, mass of the probe, and the thrust of the engine. Give me the numbers and I will tell you.
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The blast from the little retro rockets hitting the much larger asteroid, will cancel the whole thing out - every action having an equal and opposite reaction and all that pesky old Newtonian conservation of momentum stuff...
Just aim the rockets at an angle from the anchor ship so the mass from the retrorocket exhaust avoids the asteroid.
It's not clear how close the ship needs to be, if it's hundreds or thousands of miles from the asteroid, the gas plume from the rockets may have expanded to many times the diameter of the asteroid, so only a tiny fraction of the energy is transferred to the asteroid.
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You can compute the force on the asteroid as a function of distance: if it's 1000km away from the asteroid, the acceleration of the asteroid is 7*10^-19 m/s^2 for a 10-ton spaceship. That r^2 in Newton's law of gravity is a bitch. If this is going to work at all you've got to get closer.
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Stop dragging facts into Slashdot!
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Why would the blast of the rockets hit the asteroid?
And if it would why would it cancel the movement of the satellite out? did you do the math? Do you even know how to do it?
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it would be a hellva lot more efficient to use the rockets to just push the damn asteroid, rather than rely on gravity.
Asteroids usually rotate. So the rocket (or more likely an ion thruster) would need to cycle on and off if it was on the surface of the asteroid. But it would still be far simpler and cheaper to just detonate a small fission bomb. Then instead of tons, it would just need to be a few dozen kg.
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Asteroids usually rotate. So the rocket (or more likely an ion thruster) would need to cycle on and off if it was on the surface of the asteroid. But it would still be far simpler and cheaper to just detonate a small fission bomb. Then instead of tons, it would just need to be a few dozen kg.
To what effect? [nasa.gov]
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This has always struck me as the most direct, reliable solution.
If you're going to use rockets with small thrust, you'd be better off just sticking two rockets on your probe, using one to push on the asteroid (with the exhaust gases or ions or whatever) and the other pointed in the other direction for station-keeping. Gravity is pretty damn weak.
Re:Sorry, little retro rockets won't work for that (Score:5, Insightful)
Even if it wasn't the case, it seems to be it would be a hellva lot more efficient to use the rockets to just push the damn asteroid, rather than rely on gravity. A couple of tonnes of probe isn't going to exert much influence on a couple of hundred (thosand?) tonnes of space rock.
You don't need much deflection if you have enough time.
Re:Sorry, little retro rockets won't work for that (Score:5, Informative)
No, because you use ion engines on the tug which are tremendously more efficient per launch weight than chemical thrusters.
This isn't a strategy for an "OMG - it's going to wipe us out next week!" asteroid - it's for ones where the orbit shows a near hit of Earth fairly far into the future. Small gravitational tugs over a long period of time are all that's required.
Now, ideally those asteroids can be brought into a useful orbit where they can be mined for more mass to deflect more and more asteroids. In the mid-term perhaps only the ion engines need to be sent up from Earth.
Tyson isn't inventing this - it's a well-accepted strategy in the community that he's trying to explain to a larger audience.
Re:Neil deGrasse Tyson (Score:5, Insightful)
Why do you say that? He's an established scientist and has a Bachelors in Physics and a Graduate/PH-D in Astrophysics. He's held positions at several universities and is the director of the Hayden Planetarium. Sure he goes on television more than your average physicist, but so did Carl Sagan. He's charismatic, and it works well for him. Nothing wrong with that.
Dr. Phil is a pool of waste that puts people on television and exposes their issues to millions of viewers, for the ratings and a fat pay check. He doesn't add anything to his profession, and his discussions on television don't enlighten anyone.
There's a huge difference.
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He doesn't add anything to his profession
I disagree. I think he's a great example for other circus performers.
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Re:Neil deGrasse Tyson (Score:5, Insightful)
I agree, he's great for explaining stupid shit to proles, but as far as a professional scientist goes he has very little credibility in my book.
Great. You'd be comfortable with this future:
Scientists: By the way, there is a huge hunk of rock that is going to hit the earth tomorrow and wipe us all out.
Public: Wait - what? Why didn't you warn us?
Scientists: We discussed it at length at our obscure meetings. Why should we have to take time out of our important work to explain complicated shit in your terms? Stupid proles.
Re:Neil deGrasse Tyson (Score:5, Insightful)
Actually according to Doug Adams definitive history:
On a planet called Golgafrincham there was an an nouncement that the planet would soon be destroyed in a great catastrophe They planned an evacuation using a group of arcs:.
The passengers of the “A” ark were to be all the brilliant leaders, scientists, great musicians, data analysts, engineers and architects. The passengers of the “B” ark were to be all the “middle men” , marketing executives, telephone sanitizers , sales assistants and telemarketers etc. The passengers of the “C” ark were to be the real workers, construction, manufacturing and other craftsman.
As I remember it, everyone fought for a place on the B Arc which blasted off into space programmed to land on the third planet of an obscure star at the edge of the galaxy. Shortly after its departure, they discovered it was all a mistake and the planet was not going to be destroyed.
Golgafrincham entered into a period of exceptional peace and prosperity.
The planet that was the destination of the B Arc had a different kind of history.
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Writing...
Ever
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Actually, they died by a mysterious virus spread through their filthy phones unless I'm mistaken.
Re:Neil deGrasse Tyson (Score:4, Informative)
Golgafrincham entered into a period of exceptional peace and prosperity.
Um, no. They all died from a virulent disease contracted from a dirty telephone.
Re:Neil deGrasse Tyson (Score:5, Insightful)
I agree, he's great for explaining stupid shit to proles, but as far as a professional scientist goes he has very little credibility in my book.
It's scientists like him that are personable and able to "explain stupid shit to proles" that help keep people interested in science and help make sure the scientists in your "credibility book" get enough funding from the proles to do their work.
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I think you may need to consider feasibility when coming up with your plans. It's a lot easier to just fly somewhere and hover than to land, or to make and deploy a gigantic asteroid net.
And its a lot easier to fly somewhere close and send in a rocket powered Bunker Buster [wikipedia.org] bomb.
Most of the rocky bodies we've investigated and photographed are loose creations of material which would most likely burn up in the atmosphere if you simply spread them out a bit. Even a solid rock of extinction size would do less damage if you break it up into more than one piece, and in doing so deflect significant chunks of it such that they would not even hit the earth. 2/3rds of the remaining pieces would land
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Where do you get your ideas that blowing up a giant rock is a good idea. I'm talking giant, because the smaller ones, while being a problem for whoever's head they land on, don't pose an Extinction Level Event.
Maybe because the full rock DOES pose an extinction event?
And you might also want to look up the definition of "burn up in the atmosphere". And also you might want to supply some actual backup about your claim that they will have the same basic trajectory after a nuclear warhead scatters the big rock into much smaller pieces. Placed close to center, at least half the rock would get a significant retro acceleration. Another significant portion gets a forward acceleration. When you do this early enough there
Re:Neil deGrasse Tyson (Score:5, Insightful)
I usually welcome hearing Tyson's latest addition to lay science understanding.
I sort of like character-celebrity-scientists. Mister Wizard, Bill Nye, and local college instructor / news-show scientist "Chemical Kim" are just a few of the scientists I applaud for their work in bringing science to the masses as a fun and interesting subject.
I don't like the stand-in experts like Michiu Kaku or Tyson, who take a different tack of bringing science to just a large audience, not really packaged for the masses at all, often with their own opinions added, and typically very pompously presented.
Tyson manages to keep my respect by being relatively sane and mainstream, basing his conclusions and projections on "establishment" science.
I can't say the same for Kaku, who I haven't heard from in awhile because I purposefully stop visiting web sites and stop listening to radio shows that give him a podium (no, this is not a viable way to get me to stop visiting /.)
But Tyson also manages to capture my interest by doing the same thing Bill Nye does: making comments about human affairs and human nature. They both humanize science.
But Tyson's pomposity sort of makes it hard for me to "like" him. And I just read something about him recently, so now it's like a second serving of buttered scallops when I clearly had trouble finishing the first serving.
Re:Neil deGrasse Tyson (Score:5, Insightful)
But Tyson's pomposity sort of makes it hard for me to "like" him..
They're fine as long as they don't get uppity, eh?
Re:Neil deGrasse Tyson (Score:5, Funny)
But, he just stomped on the idea for the Open Crowd Source Asteroids Initiative.
A giant bank of lasers spread over the Earth activated by an online MMG of people playing a "free" version of " Asteroids" fed by satellite for positioning and trajectory.
Some people just have no imagination...
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There have been a lot of discussions about these asteroid scenarios. The real trick, is to identify the threat early. The doctor is right, we're good at blowing things up, then wondering where shit's going to land. That's why it's so important to identify the threat early. If you can send out an impactor rocket months before the projected impact, then you can use a small amount of power to move the asteroid into a new orbit. We like making things go "boom", with or without the audible "boom". So, giv
Re:Neil deGrasse Tyson (Score:4, Insightful)
Not Mike Tyson, it's Neil De Grasse Tyson, Miss Latella.
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Yep. Surely it's far better to fire a cable at it and give it a good pull at 100% engine thrust than wait for a microscopic amount of gravity to have an effect.
Use magnetism it's 10^34 times stronger (Score:5, Interesting)
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Re:Use magnetism it's 10^34 times stronger (Score:5, Insightful)
As mentioned elsewhere, spin. Pretty much every rock in the solar system spins, to a greater or lesser degree. Old sci fi from the masters always took this into consideration. Heinlein and Niven both wrote about eliminating spin before moving an asteroid via rockets. Their reason was because they wanted precise control of the rock, with the intention of putting it into a specific orbit. If all you want to do is miss Earth, and you don't care what the new orbit is, that's less important.
In theory, it's possible to use direct thrust to revector an inbound rock without eliminating spin first. You just have to mate the engine and its (very large) fuel and oxidizer tanks to a spinning rock, precisely centered on its spin axis. Which means, if your engine and its fuel tanks are of any significant size, you're going to have to spin them to match precisely first. Needless to say, this isn't exactly easy.
Once you mate an engine to a spinning asteroid, the rest is easy. The spin will even work to stabilize the thrust vector via gyroscopic effects. Regardless of the axis of spin, you never have to do more than move the rock one Earth diameter. Even if the axis of spin means your thrust is aimed directly along the asteroid's orbit, thrust will still work. You just make the rock cross Earth's orbit earlier than it would have, before Earth has shown up, thereby generating a miss. Any other axis of spin, you're pushing it aside, one direction or another.
The only question that remains is which method is most fuel efficient and least risky. Say the rock is in a near-hit orbit, but its spin axis means you have to push it the entire diameter of Earth to generate a miss. It might then be more fuel efficient to stop the spin first, then choose your thrust axis yourself, so you only have to move the rock's orbit a small fraction of Earth's diameter in the other direction to generate a miss. So is it more fuel efficient to eliminate the spin and push any direction you want, or to leave it spinning and push along the spin axis? You'd have to do some math to find out, and the answer varies depending on the rock. You also have to factor in the risk of failure. Are you more likely to fail if you have to mate two engines to the rock (one for spin reduction, the other for adjusting direction) or just one?
The gravity trick is intended to avoid all that. No mating required, so all you have to do right is navigate a spacecraft. Something we're getting fairly good at. Magnetic coupling is less appealing for the same reason: more systems with more parts doing something we've never done before. And we REALLY don't want to screw this up. We're talking about the end of civilization, remember, not to mention an extinction event for many species.
And that, ultimately, is the reason for Neil deGrasse Tyson's answer: it's the most pragmatic method. All we have to do is something we already know how to do. Nothing new, anywhere, thereby minimizing the risk of failure.
If that asteroid mining company actually gets to the stage of mating a rocket to a rock and moving it for mining purposes, then everything is different. With proven expertise in rock-rocketry, that becomes the new best answer.
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Re:Neil deGrasse Tyson (Score:5, Interesting)
The whole idea is conceptually idiotic. You spend a strong force of reaction mass ejection to maintain a weak force of gravity at a constant distance from the target mass producing a microscopic tug on the object. This guy must have received his degree in a box of crackerjack.
Place the reaction mass generator (be it ion jet, or rocket) directly on the mass and divert it.
Amazing that they didn't think of that!!! You must be a genius...
Or... maybe they did consider that, then realised that many, many small asteroids are apparently heaps of weakly bound rubble, just as bad as a solid object when hitting the surface of earth, but impossible to attach a rocket to.
The "gravity tug" concept works the same regardless of the structural integrity of the asteroid, *that* is why this is the proposed mechanism, not because Tyson is stupid...
Bet you feel a lot less like a genius now, smarty-pants?
Re:Neil deGrasse Tyson - Heavyweight (Score:2)
If we worry about a 2 km dia asteroid (rough sphere) it weighs 15 BILLION TONS.
Putting enough energy on over a year or two to pull the asteroid say 10,000 miles is going to be one hell of an amount of energy every second of the year. We don't have that sort of energy source we can deploy that I'm aware of.
Re:Neil deGrasse Tyson (Score:5, Informative)
The whole idea is conceptually idiotic. You spend a strong force of reaction mass ejection to maintain a weak force of gravity at a constant distance from the target mass producing a microscopic tug on the object.
I pity the cranially impoverished people who modded this up as "Insightful". Go back to high school, would you? The two forces you're referring to are exactly equal in size, as per Newton's third law. The probe gets positioned at a distance at which the thrust of the engine is equalized by the asteroid's gravity, and the probe consequently pulls the asteroid with identical force (modulo its sign) while keeping a stationary position above its surface.
What you get here is exactly what you'd get by putting the probe onto the asteroid and pushing it, but you're avoiding the potentially dangerous contact with the asteroid. Moreover, the probe is likely to be powered using solar arrays, and asteroids sort of tend to rotate, which would severely complicate your attempts at creating a sustained thrust, not to mention the fact that your thrust vector would also rotate. Separating the probe from the asteroid and acting gravitationally upon it gives you constant insolation of the panels and the ability to exert constant thrust in a single direction.
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Re:Gravity is a poor tractor beam (Score:5, Informative)
The "pull" between a spaceship and an asteroid would be equal to the apparent weight of the spaceship on its surface, decreased by the square of the distance between the two objects. This would reduce the traction to a very limited amount.
You'd get better results with a cable from the ship attached to the surface, but the problem would be the rotation of both objects.
To do a decent job, the spaceship would need to collect a large quantity of mass before attempting to drag the asteroid.
I think the point is that you don't know how fragile the asteroid is (it could just be a big pile of rubble held together by its own gravity), so anything you do to it through physically touching it, like attaching a cable, landing on it, etc, may break it up into smaller pieces with the result that instead of one large asteroid, you now have a dozen or maybe hundreds of smaller asteroids that you have to deflect. And the set of smaller asteroids will have the same effect on earth as the one large asteroid.
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No, it won't. The surface/mass ratio will be different (smaller pieces can burn up more readily), and if they're spread out enough, instead of all that mass hitting at once, we just get a few nights of falling stars of little consequence.
We seem to survive the Leonids OK, and we've been surviving them for a long time.
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You're right, of course - if a large portion of the mass comes into contact with the atmosphere.
Newton's First Law [wikipedia.org] (aka law of inertia) says that things will keep going in a straight line, unless acted upon by an outside force. We apply such an outside force when we break the asteroid apart; the pieces start dispersing on new courses.
Doing this at a far enough distance from Earth (not unlike nudging the asteroid's course slightly when it's quite far away) means that the parts will be dispersed enough to n
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And the set of smaller asteroids will have the same effect on earth as the one large asteroid.
That would be the case if the earth lacked an atmosphere, but 1,000 1-km asteroids are preferable to one 10-km asteroid. Assuming that all those asteroids actually hit the earth.
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Maybe I'm having a hard time understanding what he's talking about, but this sounds like a violation of Newtons III at a glance. Suppose you have an asteroid in space, and a rocket beside it. The asteroid attracts the rocket, and likewise the rocket the asteroid. For the rocket to "tug" the asteroid away, it will have to use some sort of propulsion, and all we really have are momentum-exchange drives - rockets, ion-thrusters, ect. To move, it must thrust with a larger force than the force of gravity, in exactly the opposite direction of the gravitiational force vector. The problem is, those particles used for thrusting the rocket, will impact the asteroid as well, assuming the asteroid is large enough to worry about moving. Even worse, some of them may even recoil! Wouldn't this absorbtion of momentum of the ions, gas, ect, undo the "tug" of the rocket in the first place?
Don't aim your rockets at the asteroid, or stay far enough away that the gas plume from the rockets expands to a diameter much larger than the asteroid.
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Imagine 3-orthogonally mounted rocket engines. The sum force of the asteroid has to ultimately be a vector combination of force in those 3 directions. You apply thrust off angle such that you counter the asteroid's attraction without thrusting at it.
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Trivial?
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Well, we can work that out.
As was pointed out earlier, the spaceship needs to be far enough out that its exhaust gases (from the retrorockets used for station-keeping) don't mostly strike the asteroid and cancel the force of gravity. (Perhaps we can use multiple retrorockets at angles pointed away from each other to ensure all the gases miss the asteroid, but this is inefficient -- you can do the trig.) If the asteroid is 500m across, let's say that we'll need to be at least 500m away. But in computing the
Unknown unknowns (Score:2)
All asteroids large enough to make this work are known and known not to collide with earth.
All presently known asteroids large enough...
Fixed that for you. We find things in space all the time that we weren't aware of before. You are claiming we know of every body that could possibly threaten us when we cannot possibly be certain of that.
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We know all km-sized asteroids including their trajectories for centuries - that's because they are few and stick out like a sore thumb in comparison with a 28m (equivalent) asteroid like 2012-DA14.
The danger are those asteroids we don't know about - and those are the small ones.
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...what evidence does he have that we act that way when dealing with real civilization threats or difficult engineering challenges?
The problem will arise when the solution is frightening expensive and although the general problem is understood, the specifics will have uncertainties. Politicians *will* evade problems where they are sincerely (or opportunistically) uncertain that immediate sacrifice is needed.
This is exactly what we have now with climate change.
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I don't buy the climate change analogy. There's a big difference between a one-off $50 billion dollar expense (spread out among a half-dozen years) that has no big policy implications and could potentially be done by a single country and a multi-trillion dollar, decades long campaign that many claim requires a fundamental change in a wide range of policies (energy, economic, social) by nearly every country in the world. (For the record, I believe that AGW is real and requires action - I just think the analo
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How we would now if it's really our hour if we don't try it? ;-)