So, this research is extremely cool. The way nuclear deflection works is not how you think. You probably don’t blast the rock to bits. Instead, Burkey’s model uses a bomb tunes to produce a crazy amount of x-ray radiation which heats up one side of the asteroid. You heat it up so much that the rock liquifies, then bubbles, and outgasses - and forms a propulsive engine, right on the surface, shooting out gaseous ultra-hot rock.
Newton’s third law kicks in: as the asteroid ejects mass in one direction, the asteroid reacts by going the opposite way. So you have altered the orbital trajectory of the asteroid, averting disaster.
The whole approach is very sensitive to the detonation height, asteroid composition and color, rotational characteristics, etc. So Burkey’s group has really made a simulation framework for modeling the right thing to do for a given asteroid.
> The whole approach is very sensitive to the detonation height, asteroid composition and color, rotational characteristics, etc. So Burkey’s group has really made a simulation framework for modeling the right thing to do for a given asteroid.
And don't forget that most asteroids are spinning over its own center-of-mass. The thrust generated by evaporating rocks on one of its sides will be changing direction as the asteroid spins around. Think of a rocket with thrust but no stabilization. Cool idea but very hard to make practical.
Given the dimensions involved, the billions of miles, any deflection would create a miss. If we are certain that an asteroid is actually going to hit earth many years/decades out, then even a microscopic nudge in any direction would shift the closest approach by an earth-width. So precise aim might not be as important as getting the bomb out there asap. The earlier it is done, the less push is necessary to generate a miss. Of course, this is premised on us having near-perfect knowledge of the initial trajectory.
As I understand it we are tracking certain asteroids that we predict have a chance of impacting on the following encounter with earth depending on what the outcome is of passing through a per-basis volume called a "keyhole". So it isn't that we detect them when they are a decade out on a direct trajectory.
Those are the ones we know about. If you think about the problem, it really is a very difficult one to solve. We're attempting to find and track tiny objects that could be anywhere in an absolutely massive volume of space using almost entirely ground based equipment that is hobbled by competing demands, atmospheric distortion and a very inconveniently nearby star that halves the observation time and makes it really hard to find objects on that side of our orbit. For all the fancy animated maps of the many asteroids we have located there are likely still a very large number of other asteroids we don't know about yet and may not find out about until after the fact.
A chilling tale, but step back and look at the odds: Not only does it rely on a significant original measurement/prediction error, but it also assumes the exact wrong nudge will occur that happens to compound that error.
In contrast, the vast majority of possible nudges will be neutral or beneficial, since the Earth is a very small target compared to the rest of space.
Presumably the same distance that gives the calculations uncertainty allows time to adopt a wait and see approach, refine the data and calculations and then make a decision based off of stronger inputs and still avert disaster if necessary?
No because the vector can also change in magnitude. Even if the spiral was perfectly aligned to impact the perfect center of the Earth we could change the magnitude of the object by nuking either pole to either slow it down or speed it up. Enough energy on any pole could make it miss regardless of the orientation.
Perfectly chaotic rotation might be worse. If it was a spiral then you could hit it at a pole. I think most things rotate about a semi-fixed axis (not totally fixed, often propagating over time)
The paper only simulated it up to 10 microseconds. But they also only used a simplified 2D toy model. They acknowledge that a realistic simulation will need to factor in a ton of other things, including rotation of the asteroid.
A balloon does that because it has very low mass and moment of inertia, compared to the thrust provided by the escaping air.
An asteroid is not like that, even when heating one side with a nuclear bomb. The goal is to create a tiny change in its velocity vector, which still adds up to a significant trajectory change over time.
We just need to build a spaced based array of microphones (comsaphones???) to listen for the high pitched squeal or the pfffft sounds as the air is rushing out the opening.
Really? C'mon. Walk this thread back up, and see if you can find where it went off the reality rails. Then, see if your comment fits with the seriousness of the thread.
You don't - but it doesn't apply. The size of the "engine" compared to the mass of the asteroid is enormous. A balloon has a relatively large engine compared to it's mass, and the engine is flexible - i.e. if you stiffened where the air comes out, the balloon would fly much more predictably.
hypothetically, even if this is how it worked, that would still be fine, because literally any direction other than the one directly targeting the earth is going to be a non issue. the probability of randomly nudging and hitting anything of consequence is basically zero.
I don't think a balloon would fly erratically if the air was released in space or a vacuum. As far as I can understand it, the air would rush to equilibrium in all directions - the balloon would deflate rapidly - but the air 'movement' would not move the balloon, as in a vacuum there is nothing to push against. Any erratic movement would be due to the elastic of the balloon returning to its resting state. I think you would also get movement in earth based vacuum chambers due to gravity.
> For a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. That is, the momentum lost by object 1 is equal to the momentum gained by object 2.
but this seems to support what I say - there is no collision occurring in a vacuum. What is the expelled air colliding with?
You can also see this by using newton's third law (equal and opposite reactions). The air is accelerating and the only other thing for it to act on is the balloon in equal and opposite fashion.
And just as an aside, IIRC conservation of momentum only applies to your standard physics objects, real objects make noises and sometimes permanently deform. This isn't usually a significant source of error but its neat to think about how if you were playing pool on a frictionless physics surface the difference between the models predictions of where the balls go and where they actually go (very very small difference) could be directly and perhaps entirely attributed to the noise they made on collision.
You might be confusing conservation of momentum and energy with respect in the context of elastic and inelastic collisions.
In a perfectly elastic collision, both momentum and kinetic energy are conserved.
As you say, many real collisions are inelastic to a significant degree. In these cases, momentum is still conserved, but the kinetic energy is converted to another form of energy.
Conservation of linear and angular momentum are fundamental and exact laws of nature resulting from translational and rotational invariance.
No, I don't think so. If you try to apply conservation of momentum as absolutely as conservation of energy (and that linked physics page states it in simple absolute terms) you can quickly encounter gaps because real objects tend to have less than their theoretically conserved momentum due to permanent deformations and interactions with the environment, or the situation involves friction in any way.
Conservation of energy always holds, whereas conservation of momentum has several important caveats and exceptions. Seemed worth pointing that out with an anecdote that amused me.
Hmmmm, actually can you explain a little more about 'momentum is still conserved'? In the cases that I'm pointing out momentum as a measurable property seems clearly not conserved, whereas the energy is (just transformed).
Same way a rocket does. That is, don't treat it as if there's a need for a second object.
The release of air is applying a force in whatever the balloon still has in the direction of travel, even though it's going on the other direction.
Imagine your sitting on a office chair with wheels. If you're holding a large weight and suddenly throw it forward, the chair will roll backwards. This would happen in a vacuum too.
This is a nice way to express it, imo. I also think it's possible to interpret what happens differently. A balloon or something in space doesn't have anything to move against, whereas the chair's wheels are on the floor. When you move the weight in an environment without anything to respond to, ie in suspension in a vacuum, there is no opposite to respond or work against. Both seem possible to me - that a chair+person-with-weight is capable of generating it's own momentum and that nothing happens in space, in a vacuum.
well, because an average asteroid in the solar system is nothing at all like a balloon. Or maybe you're confusing comets and asteroids, though it doesn't matter anyhow because your notion doesn't apply in either case and I can't at all see why it should.
I don't understand the whole 'we don't want to break up a loose conglomeration of rock'. I'd actually think breaking an asteroid up into multiple pieces that can be 'eaten' by the atmosphere would be easier/safer? The atmosphere does a good job of destroying smaller stuff. Breaking stuff up and letting it burn up seems much more feasible then trying to calculate the exact method to hit an asteroid without fragmenting it and still generate outgassing/thrust ?
> I don't understand the whole 'we don't want to break up a loose conglomeration of rock'. I'd actually think breaking an asteroid up into multiple pieces that can be 'eaten' by the atmosphere would be easier/safer?
Energy.
A large enough meteor impacting the Earth at speeds high enough to cause an extinction-level event has a lot of kinetic energy.
Intuitively it seems like the troublesome part is the meteor hitting the Earth and causing earthquakes, tsunamis, and clouds of ash and debris as a result. And those things are really bad. But they’re a consequence of that mountain of kinetic energy.
So you break the asteroid up into a cloud of dust. Fantastic! No more crater, no more big boom. But you still have a giant ball of kinetic energy headed right at you, and that energy is just going to dump into the atmosphere. And boil it.
Of course that’s even assuming we totally vaporize the thing. More likely is instead of one multi-mile asteroid we have a bunch of giant chunks that will spread death and destruction all across the side of the planet unlucky enough to be facing it… before boiling the atmosphere anyway.
That seems like it would require an absolutely huge amount of matter, given what's happened after old impacts or large volcanic eruptions. Would we realistically have enough nukes/energy on hand to divert something that massive? It just seems like an incredibly difficult way to do it?
P.S.
I you fragmented an asteriod - would at least _some_ of the pieces tend to change heading/speed enough so they miss earth?
The idea is that you catch them far enough away in time so that a small nudge pushes them enough to miss.
Far away in time doesn’t even need to mean far away in space, since many of the objects of concern are orbiting the Sun along with us. They may even have multiple close passes before being perturbed enough to become a threat.
Also, the masses involved don’t have to be huge. Two rocks intersecting in space are likely to be doing so with very different velocities. Kinetic energy is mass times velocity squared, so velocity rapidly overtakes mass as the dominant factor.
P.P.S.
Hmm - actually, if the object is that big...would we even have enough nukes/energy to break it up. Seems like either way (breakup/push) we're going to be limited by the amount of energy we can deliver compared to the mass of the asteroid? Oh! also, would a nuke actually keep stuff out gassing long enough before it cools back down? how long would you need to have that tiny lil push going on before it made any practical difference? thats a lot of mass to try and push ??
These aren't numbers, but a quick intuition reminder: nuclear-powered ablation drives are really good and we are really good at building them.
That's how you turn a fission bomb into a fusion bomb. If you just put LiD in a fission bomb, it doesn't squeeze hard enough. If you focus the x-rays from a fission bomb onto an ablation drive, it does squeeze hard enough and you 1000x+ the yield with fusion. Which is why fusion bombs look like metal peanuts.
Conveniently, this means we are also really good at designing x-ray reflectors and lenses that focus the primary output of a nuclear bomb for the purposes of building ablation drives. Depending on just how good, we could probably persuade an asteroid pusher to be far more unidirectional than one typically pictures from a "bomb," if we set it off some distance away and focused the x-rays in the direction of the asteroid.
Thanks! It actually appears it requires a lot LESS energy then I expected. According to [1] less then a tonne of TNT could accelerate 1 million tonnes to 0.1 m/s !! So it appears I was WAY off base (by at least 10^6 :-P). I swear I'm a better programmer then physicist!! :-D
I guess it depends on how big the pieces are. If you break a very large asteroid in 3, still large, pieces that might not be an improvement. A nuclear weapon exploding in a vaccum is likely to be a lot less destructive than one exploding in the atmosphere.
Enough energy is going to be dumped into the atmosphere either way it doesn’t make much difference. Further, even fist sized fragments are going to penetrate deep into the atmosphere so all options are effectively ground level detonations.
Suppose over one second you can be hit the earth with with either 1 30 gigaton weapon, 3 10 gigaton nuclear bombs. 3,000 100MT weapons, or 3 million 10 KT weapons etc. All of those suck in ways that are hard to comprehend.
Given multi-kilometer asteroids like mentioned above, I'm starting to think neither method (fragment/push) sounds viable. The amounts of energy required just seem off the scale? Maybe pushing (multiple?) smaller but still massive enough to have decent kinetic energy into its path would be more feasible. Sorta like pool balls bouncing off each other..I generally end up missing the pocket (earth) when that happens :-)
yeah - how do you keep it out gassing long enough to hit 0.1 m/s though? I would imagine you'd need to nuke it every couple of days or say every week to keep it out gassing long enough to generate that big a change speed?
Hmm - I guess not! According to [1] it would take less then a ton of TNT to accelerate 1 million tonnes (eg like asteroid 12932-zephyr) to 0.1 m/s...So its probably a good thing I'm not responsible for these things!
Let’s go to the extreme and think 10 km wide ball of sand.
Normally when a single bit of sand hits the atmosphere it dissipates energy in every direction. So you a tiny fast moving glowing dot radiating energy in every direction. However you can’t dissipate energy when you’re right next to another particle at the same temperature. Thus energy from each bit of sad can basically only go in 2 directions down or up and you’re not transferring energy through the entire thing before a crust of plasma followed by ~10km wide ball of sand hits the surface.
Hell it could be a ball of water that size and the same basic effect kicks in.
Spread a 10km wide ball of material into a 1,000 km wide diffuse cloud and you are basically slapping the earth with 1,000 km wide disk with an average width of ~17 cm (maximum width ~1m) going 10’s of thousands of km/h. Again things don’t go well, you may be shifting how many minutes various people survive but it’s not actually addressing the issue.
Would it then also work to fly a small rocket engine to the asteroid, attach to the asteroid, and turn on the engine to divert the asteroid?
It sounds a bit more precise to execute than the nuclear detonation, but it also sounds like you would have much better control over it this way than with nuclear detonation?
To have enough of an effect, you have to do your thing while it's quite a ways away.
That means you have to go pretty fast to get out to it before it gets too close to you.
You can blow up a bomb while the ship has a large difference in velocity with the asteroid.
You cannot attach a rocket engine when you're traveling 1000m/s past what you're trying to attach it to.
So if you take Earth to be your stationary velocity, you need to slow down, stop, and accelerate backwards to catch up to the asteroid's velocity.
Acceleration/deceleration requires fuel, or specifically mass.
More mass at the same acceleration requires even more fuel.
So either you send up a bomb to hit the asteroid with a glancing blow, or you launch a very complicated bit of machinery atop a very very large ship, have it do its delta-V stuff, delicately land on the surface, not so delicately drill in and and anchor to an unpredictable surface, and then start burning the even more fuel that you carried along (at a cost of yet more fuel). All while hoping desperately that no bit of sand or gravel gets into something and sticks it in place while setting things up.
I'm liking the bomb approach. I imagine you'd even make use of the speed of impact rather than paying for it. You're essentially installing a rocket engine on the asteroid this way anyway, using its mass as propulsion mass, and you can even send up multiple redundant attempts because you've supposedly calculated the trajectory so precisely that it's enough to add some force in pretty much any direction. (Or the rest of the swarm could disarm themselves when they detect the first successful hit.)
This is definitely one of the possible approaches, which is being studied too. As other commenters mentioned, this would be much harder technically and much more expensive than "nuking", but in some particular scenarios (I think when an asteroid is very loose and easy to break into large parts) this approach has some advantages.
Of all the approaches I've read about the coolest in my mind is to paint a large part of the asteroid surface with high-albedo paint, thus using Yarkovsky effect to alter the orbit. This however requires a lot of paint!
Could a similar effect be had by painting half asteroid surface with a lower-than-surface-albedo material like vanta-black? Not certain which would be harder....
I guess if an asteroid is has high albedo already, a dark paint would be better for this purpose then dark. What you want is to make sure that some parts reflect much more light than other parts.
However, I don't think you need vanta-black for this. You hit diminishing returns on a thing like this; so something like common soot would do just fine.
- Then the huge amounts of fuel required for all of those
Meanwhile with the nuke you can get away with much lower mass and "just" have to worry about making the bombs and detonating them at the right distance.
We invented nukes before we went to the moon, after all.
I don't know, if maybe not that much thrust is required in some scenarios, perhaps a tiny alteration of course can already be enough to avoid hitting Earth
Of course as you say, if the nukes do it even cheaper, makes sense. Perhaps a bit risky to be launching them though! (sensible risk for a sure-hit asteroid, not for deflecting low-probability ones)
An asteroid could weigh millions of tons. For even a tiny deflection I think you would need quite a few tons of propellant. It would be quite a challenge getting that onto the surface of the asteroid.
Just to set the expectations: the size of the asteroids they considered was around 100 to 200 meters. The nuke they envisioned was a 1 megaton one, which is basically the yield of the largest active nuke in the US inventory (B83 = 1.2 megatons).
For comparison the asteroid that killed the dinosaurs was 10 to 15 kilometers wide. Since volume goes with the cube of the diameter, it follows that that asteroid was about one million times larger than the asteroids being studied here. The largest nuke ever tested was 50 MT, and the Soviets intentionally dialed it down from its designed 100 MT yield. Even that one would have been just a pinprick for the dinosaur-killer asteroid.
I suppose that making an impact may still make sense for larger and softer asteroids (not solid metal): a blast a few meters deep would evaporate and eject more matter than a surface blast.
> Instead, Burkey’s model uses a bomb tunes to produce a crazy amount of x-ray radiation which heats up one side of the asteroid. You heat it up so much that the rock liquifies, then bubbles, and outgasses - and forms a propulsive engine, right on the surface, shooting out gaseous ultra-hot rock.
Sounds similar to the ablation ("outwards firing rocket engine") theory for how the secondary gets compressed in a thermonuclear bomb. Pretty cool.
Given the speed of the rock, it's difficult to conceive of how this theoretical action would even marginally change the course of an asteroid large enough to be worried about. It'd be like blowing on a hypersonic missile that is larger than a building.
I'd strongly suggest playing some KSP to get intuition about orbital mechanics. A warning though: you'll never be able to enjoy space movies and shows, since they almost never present orbital mechanics correctly.
But in any case, the comparison with a hypersonic missile here can't be made:
1. hypersonic missiles have a guidance system, while asteroids do not. If an asteroid is moving in a certain direction, it will continue to do so until acted upon by an external force.
2. hypersonic missiles operate in the atmosphere, while asteroids do not. The speed of sound is entirely irrelevant to asteroids.
3. because of these two things, it is not hard to intercept an asteroid.
Given the difference in velocity (and F=mv^2), it may even be possible to deflect an asteroid by impacting it with an inert lump. This was actually tested in the DART mission[1], where a 610kg object impacted an asteroid at 6km/s and significantly changed its orbit.
Yeah the expanse gets plenty of the newtonian orbital mechanics physics right but totally gloss over other important parts of space travel such as: how do you deal with the thermal buildup-space is a nearly perfect insulator. Wheres the radiators? They are regularly moving at speeds that would have a small but additive relativistic effect. Wheres the belters/other spacers who live several hundreds of earth years but not nearly as many from their perspective. Not to mention the pure impossibility of the Epstein drive. The Epstein drive is probably the most glaring example of human clarketech in the whole story.
Anyways I love the Expanse but the books were better anyway
In the same way that when you point a laserpen at the night sky, and then twist your wrist ever so slightly to the right, it's now pointing at another point 1000s of lightyears from the first. As long as you attempt the procedure early enough you have a chance.
I get space. What I'm saying is that, assuming we can even hit it, any such rock is moving with too much momentum to be able to change its course. Given any tech that we have. It's easy to underestimate the energy represented by a large asteroid.
How can you be so confidently wrong? Clearly researchers at Lawrence Livermore think it’s a viable approach, or they wouldn’t bother with developing detailed simulations. Why do you think you know more than those researchers?
Stating that I'm "confidently wrong" is rank nonsense, when predicated on an appeal to authority of government-funded low level employees.
"Clearly" their "bother" to develop simulations and conclusions is 100% downstream from government funding to make interesting noise. That doesn't mean that they are wrong. What it does mean is that its nonsense to couch a counter-argument to criticsim in an appeal to authority.
Ok Mr. Expert, what relevant expertise do you have? And what kind of research have you done in the field?
Because surely you have some kind of knowledge to draw on other than a gut feeling if you are going to say professional researches working in the field are wrong, no?
It's not the Yarkovsky effect. The Yarkovsky effect is where a body emits photons (which have momentum, and therefore change the momentum of the emitting body).
This idea is using incoming photons to heat the body to the point where it vaporizes part of the surface. The emitted atoms have momentum.
very tangential similarity that photons have momentum, and so impart a force on massive object. But it's also confusing compared to this, because photons are heating the substance (which actually would impart an opposing momentum), to "boil" it, to use kinetic forces to push in the desired direction. I appreciate the link but I don't think the effects are that similar.
So if an orbit brought an asteroid close enough to a star to have this effect on the surface of an asteroid, you would consider it an entirely different phenomenon?
Burning up in the atmosphere is still a concern. In the Cretaceous–Paleogene, aka the day the dinosaurs died, most of the damage was done by matter ejected on suborbital trajectories by the impact falling back into and superheating the atmosphere.
I wonder if Stevenson was thinking about that event when writing Seveneves:
In the near future, an unknown agent causes the Moon to shatter. As the pieces begin to collide with one another, astronomer and science popularizer "Doc" Dubois Harris calculates that Moon fragments will begin entering Earth's atmosphere, forming a white sky and blanketing the Earth within two years with what he calls a "Hard Rain" of bolides, causing the atmosphere to heat to incandescence and the oceans to boil away, rendering Earth uninhabitable for thousands of years.
Well, but the basic assumption is, the more surface of the asteroid is exposed, the more will burn up in the sky. And that is pretty solid physic and should be valid.
Also most of the surface on earth is water. And one big impact would create a mega tsunami. And that is magnitudes worse, than many small impacts, where the waves will then even partly cancel each other out.
So obviously deflecting is the prefered solution - but breaking up as much as possible will always result in way less damage overall to the planet - but the more impacts you have, the more likely it is, that they will also hit densly populated areas. So this decision will be highly political, as if something goes wrong and for example china gets mainly hit - the final outcome might be worse.
Ordinary waves travelling through the ocean, mostly yes. But when 2 Tsunamis crash into each other, you can bet, that there is lots of turbulence and energy lost and they wont have the same height afterwards.
I think you're imagining two towering waves crashing into each other. But in fact tsunamis only pile up like that when they enter shallow water. In the open ocean a tsunami is a wide area (~100km) of slightly raised (~1m) water. If two overlapped it would just be raised twice as high, which wouldn't cause much turbulence.
If the asteroid is far enough away, blowing it apart, even partially, would change all trajectories to almost certainly miss the absurdly tiny target that is the earth from a distance of tens or hundreds of millions of miles away.
On the other hand, if it happened close enough to Earth that all the little pieces, even if very tiny individually, still fall into the atmosphere, their evaporation friction would roast our world's surface for minutes to hours, terribly, causing global extinctions despite there never having been a single major impact at all.
The movie Deep Impact badly fucks that last scenario up near its end when humanity is saved by the main asteroid being completely blown apart just hours away from impact with the Earth. In reality, there'd have been no literal deep impact, but the'yd have all died anyhow, literally baked to death along with every other flammable thing on the earth's surface.
Depends when you do it, I'd think. If it's on final approach, yeah most of the bits still hit the earth, so maybe not great.
If you blow up something that you're pretty sure is going to hit the earth a few orbits in the future, the bits are going to have diverse paths and hopefully many will miss or at least arrive farther in time.
You'd need a very, very big explosive for any but the smallest grains to have divergent paths. They would form a cloud of debris that would travel on the same orbital path but spread out a bit. Breaking an asteroid up only works if it's fairly small to begin with since anything over about 50 meters that is solid is still going to be dangerous. If you broke a 2km asteroid into a mixture of 50m to 100m chunks of solid rock or metal then you're still going to have a very bad time when all that debris obliterates a state or small country.
Newton’s third law kicks in: as the asteroid ejects mass in one direction, the asteroid reacts by going the opposite way. So you have altered the orbital trajectory of the asteroid, averting disaster.
The whole approach is very sensitive to the detonation height, asteroid composition and color, rotational characteristics, etc. So Burkey’s group has really made a simulation framework for modeling the right thing to do for a given asteroid.