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Deflecting an Asteroid Will Be Harder Than Scientists Thought (upi.com)
schwit1 shares a report from UPI: According to new asteroid collision models designed by scientists at Johns Hopkins University, deflecting a large rock headed for Earth will be harder than previously thought. Using the most up-to-date findings on rock fracturing, researchers developed computer models to more accurately simulate asteroid collisions. For the newest study, scientists decided to divide the model into two phases. Phase one modeled the immediate fracturing that happens in the wake of a collision -- the processes that play in a matter of seconds. The second phase simulated the gravitational re-accumulation process that happens over the course of several hours or days.
The first phase of the updated model showed a large asteroid is not destroyed by a much smaller asteroid. Instead, millions of cracks form throughout, the core fractures and a crater is left behind. During phase two, the fractured core exerts a strong gravitational pull on the smaller pieces of debris and shrapnel broken during the impact. Because the asteroid did not crack completely during phase one, the space rock retained significant strength. If scientists are going to develop an asteroid deflection strategy that can actually work, they need to know how much force it really takes to destroy or deflect one. The latest study -- published in the newest issue of the journal Icarus -- showed it's more force than was originally thought.
The first phase of the updated model showed a large asteroid is not destroyed by a much smaller asteroid. Instead, millions of cracks form throughout, the core fractures and a crater is left behind. During phase two, the fractured core exerts a strong gravitational pull on the smaller pieces of debris and shrapnel broken during the impact. Because the asteroid did not crack completely during phase one, the space rock retained significant strength. If scientists are going to develop an asteroid deflection strategy that can actually work, they need to know how much force it really takes to destroy or deflect one. The latest study -- published in the newest issue of the journal Icarus -- showed it's more force than was originally thought.
A Stars and Stripes painted object will suffice
I always though the goal of the blast was not to destroy the asteroid but to change its trajectory...
Video of some good progressive thrash music
TFA seems to be about destroying or breaking up an asteroid. Yet they keep mentioning deflecting it, i.e. altering its trajectory so it’ll miss Earth.
If construction was anything like programming, an incorrectly fitted lock would bring down the entire building...
"Deflecting" and "destroying" are two different strategies to avoid collision with an asteroid - and "destroying" has long been seen as the worse one for that matter.
Of course news about a fake are Fake News.
The difference is that the birdshot has a better chance to burn up in the atmosphere without anything reaching the ground at all.
We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.
And I don't wanna miss a thing.
Wanna buy a shirt?
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It makes absolutely no difference, the kinetic energy will have to go somewhere anyways - whatever it is one large piece or many smaller ones. The result will be the same as the rocks will fall around the same time (so there wonâ(TM)t be enough time to disperse the energy between each collision).
You know nothing about physics. Kill yourself.
The uneducated only become educated through the sharing of knowledge, asshole. I'm certain there are things you know nothing about (it's called being human), and yet I'm not condemning you to death for it.
If a large asteroid on a collision course with Earth is fractured, that just turns it into a bunch of little asteroids that will hit Earth.
Not really. Space is big. Really big. If you break up an asteroid months, or even weeks, ahead of time, most of the fragments are going to miss earth by many thousands or even millions of kilometers.
A typical delta-v is 40,000 km/hr. So in a day, that is a million kilometers. In a month, it is 30 million km. The diameter of the earth is 12,000 km. That is about 0.02 degrees. That is not much of a deflection.
If an asteroid is not rotating, it makes sense that if fractured into pieces by a thermonuclear explosion, the pieces will tend to drift back together in one place.
So our strategy for an Earth-impacting asteroid should be: if it is rotating, blow it apart and watxch the pieces fly away; if it is not rotating, nudge its orbit with a series of small explosions.
I reckon $5 billion would be more than enough, and we'll get the Mexicans to pay for it.
Those who do not learn from commit history are doomed to regress it.
https://hub.jhu.edu/2019/03/04...
Looks like the editors did not even look at it and just "aggregated" the content from some random news site that also was no capable of summarizing the hart of the matter in a subject line.
In last resort we can always try to redirect all our active satellites to it's path and hope for the best :P
There have been many, very useful analyses of the trade-offs. I've seen many in fiction and science speculative scientific analyses: I remember reading J. E. Enever's analysis in a 1966 Analog magazine article. Given how little was known about the composition of asteroids that had never struck the Earth to be analyzed, and that the article predated the discovery of the dinosaur killer asteroid, it was quite good. Asteroids are high velocity projectiles, and whether they are solid rock, reasonably metallic, or icy makes enormous difference in the results of breaking them up.
Orbital mechanics and basic geography physical chemistry haven't changed much since that period. Guidance systems have improved tremendously, and humanity has learned a great deal about sending small probes to other worlds. But changing the orbital path, or shattering, something as large as a dinosaur killer asteroid is still an incredible engineering problem.
They should just ask APK for some ideas. He knows all about trying to deflect things even if it doesn't work. They might get some different ideas they could work with.
(like a comet would flying towards the sun does which eventually causes it to propel back out into space)
If I understand you correctly, you suggest that comets are flying directly towards sun, get decelerated by ablating gas, stop and then accelerate away like a rocket. I suppose that you imagine that at some point they stop spewing gases, but gravity still works, so they will finally come back. Just in case - this is completely wrong image. Comets are orbiting Sun and 'missing' it when they fly in, getting around Sun on tight gravity leash and flying back, still in very elongated orbit. Comet tail is way too weak to pull the 'stop and reverse' trick, plus, which is even worse, it points into wrong direction (away from sun, so if anything, it would accelerate comet towards Sun even more)
Assuming the asteroid isn't a lump of metal, you could harpoon it. Once harpooned, then you fired off an attached rocket to "push" it off course.
Life is not for the lazy.
Cant read TFA because of my ad-blocker - ads are more important than the future of the World.
Sounds like BS though, what have colliding asteroids got to do with deflecting one? Are we going to try to knock their silly heads together?
the fractured core exerts a strong gravitational pull on the smaller pieces of debris and shrapnel broken during the impact
More BS. Unless the asteroid is getting on for the size of a planet, in which case abandon all hope, the gravitational force will be very weak.
If scientists are going to develop an asteroid deflection strategy that can actually work, they need to know how much force it really takes to destroy or deflect one
WRT deflecting, I was taught at school that the force on a object multiplied by application time resulted in an increase in that object's momentum in that direction, momentum being velocity multiplied by mass. I think Newton said it first. But perhaps the laws of physics have changed lately, and I'm only an engineer not a scientist.
Nobody wants to deflect an asteroid with another one. That would be stupid. Instead of getting 10000 tons on our head in 1 piece it would just come down in several.
Landing a drive on the sucker is easier, if it far enough out there.
Indeed. If it takes more force than originally estimated to fracture an asteroid, that's a *good* think - it makes deflecting it easier. Fracturing is one of the things most asteroid-avoidance plans want to avoid.
You only want to shatter it (and only maybe) if it's already too late to deflect it - doing so turns a rifle slug who's impact point we can predict, into a shotgun blast that'll hit all over the place, but probably some of it will miss, and more of it will burn up in the atmosphere so that individual impacts are less damaging. The overall effect is likely to be more devastating though - unless the original impact point would have been something especially bad.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Go take a look at the long list of asteroids that have passed frighteningly close to Earth, that we didn't see until they were already past.
The problem is that we have a 50/50 chance that the asteroid will approach us from inside our orbit, in which case the side facing us will not be lit by the sun, rendering it nearly invisible (though the IR telescopes designed specifically for spotting asteroids by their heat signature will do better)
--- Most topics have many sides worth arguing, allow me to take one opposite you.
It depends on if he dies because he stays behind to make sure the bomb goes off.
Aah, change is good. -- Rafiki
Yeah, but it ain't easy. -- Simba
Capture in orbit around or impact it upon the Moon.
We that natural defense with significant mass and gravity.
Just look at all the craters on it, that stuff could have hit the Earth instead.
The asteroid is probably mostly rock, instead of the ice that comets typically have. But, having the bombs detonate at a distance in order to repeatedly blow (puff) at the comet will speed it up or slow it down eventually. Also, to escape two dimensional thinking, moving the orbit out of the solar plane would also make it much less likely to ever come near the Earth again.
Aah, change is good. -- Rafiki
Yeah, but it ain't easy. -- Simba
Most of the damage from thermonuclear weapons comes from a fast moving shock front of air. I still don't understand how exploding one in space where there is no air is supposed to alter the trajectory of a hugely massive object - which is the only kind you're going to be worried about in the first place.
Seven puppies were harmed during the making of this post.
The assumption here being your detection gear is good enough to let you determine years in advance which objects definitely need a nudge years in advance even after taking into account travel time to get there and set your solar sails up. Otherwise you end up chasing a whole lot of "might cause problems" rocks, which is the best we can do now, and then who is to say you won't be turning a near miss into a certain hit...
Seven puppies were harmed during the making of this post.
I wonder if long thin titanium rods could be used to hit the front of the asteroid and continue with digging a hole through the center. In doing that, i would think that it would produce a lot of cracking through out and after maybe 20-30 rods hitting it, a nuke in the center could cause splitting. Of course, this would need a bit of known time to get it together. IOW, if we have a week before it hits us, then this would likely not work. BUT, a month or more, it might.
Regardless, they will try different approaches on the models.
I prefer the "u" in honour as it seems to be missing these days.
There are those who say that this could actually be WORSE.
Seven puppies were harmed during the making of this post.
You'd obviously have to tamp the nuke, and detonate it inside the asteroid. I think there was a movie about that, something about a deep sea drilling team. This recent study actually goes directly to that: the energy required to break up a large asteroid enough to matter is just too high.
However, if the goal is to re-direct an asteroid, instead of break it into gravel, nukes are a good fuel source. "Project Orion: style propulsion is really easy if the ship deosn't need to survive. It still might not be enough, but nuclear propulsion is much more efficient than chemical rockets, and we do have a bunch of warheads pre-made.
The challenge for any asteroid redirect plan is detecting the danger early enough (we still suck at that) and getting out there to try to shift the asteroid's course far enough away where a small change matters (we're even more hopeless there).
Really, the only chance we'd have today is if an asteroid was identified as making near pass or two, then hitting, so that we could try to change the asteroid's course as it passed by very near to the Earth (well, passed in some way where it was low delta-v to intercept, which "near" doesn't guarantee), and we had lots of time to prepare for that intercept.
It's mostly a case of "doesn't even work in KSP".
Socialism: a lie told by totalitarians and believed by fools.
The difference is that the birdshot has a better chance to burn up in the atmosphere without anything reaching the ground at all.
For a large enough asteroid that doesn't actually help. The same total amount of energy is dumped into the atmosphere, and we all cook. It's hard to come up with a scenario where rolling the dice on breaking up an asteroid into an unknown number of pieces of unknown size and trajectory is a win. Perhaps if a mid-sized asteroid were going to hit the ocean (and we could somehow predict it that accurately), we might take the risk of random land hits to avoid the tsunami.
Socialism: a lie told by totalitarians and believed by fools.
We're not good at detecting dangerous asteroids while they're still at any distance.
We don't have the capability to deliver any meaningful mass (hundreds of tons) to an asteroid at a sizable distance, especially if it's moving very fast relative to the Earth.
Even if we did solve those problems, it's almost always going to be better to give the whole asteroid a predictable nudge than to risk breaking it into random-sized pieces still mostly going the original direction. And the farther out the asteroid is, the more that's true, as the asteroids own gravity is going tend to bring all the pieces back to the same overall course (blowing something up doesn't necessarily change the direction the center of mass is going).
It's almost always going to be better to give the asteroid a shove than to try to blow bits of it off.
Socialism: a lie told by totalitarians and believed by fools.
Read the crummy UPI story, and the original paper, and there is nothing in the paper or the scientist's quotes that is either about, or pertains to, deflection of asteroids, except for three sentences of the reporter bloviating about it. The reporter apparently believes, based on nothing, that asteroid deflection means "destroying the asteroid".
This paper is about how asteroids fracture and reassemble in collisions with other asteroids and thus the typical structure to be expected. It is an advance in the state of asteroid analysis, but we already expected most of them would be "rubble piles" from several lines of evidence.
Deflection is not "blowing up asteroids", and no one thinks the way to deal with an asteroid on a collision course with Earth is to "blow it up". Shattering an asteroid leaves it on the same collision course, but in many pieces which is worse since many large pieces can be expected to hit over a wide area -- turning it into an asteroid "cluster bomb:". It is the same reason that many small nuclear bombs do more damage than the same energy in one large bomb.
Deflection depends on changing the asteroid's trajectory, while leaving it in one piece. So as far as it goes, this paper says that should be easier (less chance of permanent fragmentation).
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
I think the point is that even if you shatter it, it pulls itself back together and brings in whatever hit it to add to the overall mass making the overall problem even worse.
Deflecting it would require a lot of sustained energy to push it in a new direction.
Work Safe Porn
SUBJECT: ASTEROID DEFLECTION - POTUS IMAGERY
CLASSIFY: NOFORN/REPEYESONLY
Analysts have determined that a cost effective method of asteroid deflection would be to simply paint Donald Trump's image on to an asteroid.
While counterintuitive to the casual observer, we believe this course of action will lead to an accelerated program by liberal factions within congress to approve expedited funding for an expedition to remove an incoming asteroid by any means necessary, including nuclear detonation.
While opposition to nuclear payloads have been exhibited by liberal opponents over fears of nuclear proliferation for space programs, we believe this will incite an immediate reaction that will override any prior objections and bring about a desired outcome for delivery of a nuclear device into space. Once launched, a hidden pod will be launched to deliver a 5 gallon container of white paint to a portion of the "face" that would correspond to acne, and a 5 gallon container of black paint in proximity to an "eye" that was previously painted on the asteroid, with a highly reflective metallic "Banksy" logo additionally placed therein.
The delivery of these two paint containers would result in multiple objectives:
- Photos of the resulting asteroid will increase Banksy's street cred, destabilizing art markets overseas as his work is driven to astronomical pricing levels (yes, pun intended)
- Liberal factions will direct their attention to a "greater good" message of intergalactic grafitti whereby the deflected asteroid will be advertising a more desireable message as it continues it's path throughout the solar system, with a recurring embarrassing message long after Trump's demise.
- Color and reflection disparities will cause a distortion in the planned trajectory and actually cause the asteroid to miss earth.
- A nuclear warhead is parked in space for optional use later.
- Trump will be assuaged in knowing he will be "immortalized" through the intergalactic, er trans solar-system art work.
The problem is that impact doesn't scale linearly with size - the size of the crater scales with the cube-root of the blast energy - in this case the mass, since we won't be appreciably modifying the impact speed. Break an asteroid into 8 chunks, and now you have 8 impacts, each still having half the blast radius of the original. 64 chunks would each have a blast radius 1/4 the size of the original.
And while we may not be able to accurately predict the impact point months or years in advance, it gets easier the closer the impact point becomes. It also becomes easier the larger the asteroid is, so that solar pressure, etc. have less effect on its path. Weeks away we'd know roughly where it will hit, so everybody can get ready in case they have to evacuate, and we'd have at least days to evacuate a particular city - which should be quite doable with the amount of warning possible.
Ironically enough, an ocean impact by a large meteor is probably the worst-case scenario - at orbital speeds water is only marginally less solid than rock. The tsunamis created by the blast of vaporized water would likely be more devastating than a direct land impact, and all that water in the atmosphere would wreak havoc with global weather patterns - flooding, dense cloud-cover, etc., which could devastate global food production.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
I'm trying to figure out what you might mean, given the fact that asteroids are typically invisible to radio telescopes, and the amount of radio power you'd need to broadcast to illuminate even a tiny sliver of the night sky brightly enough to spot an asteroid from half a billion km away would be mind-boggling.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
It seems to me you have people who have hammers, who love hammers, who want to use hammers for everything, even for buttering bread.
Who should be using a net.
Distributing lower amounts of force over a longer period of time, using a net to attach to an asteroid and ion drives to slowly alter the orbit, is a far more useful method of deflection than a short sharp shock. Getting that much energy at one point for a short duration is very very expensive in orbital mechanics, especially from earth surface, whereas doing intercepts with nets and ion boosters is something you can preposition in higher orbits and then deliver to a target.
-- Tigger warning: This post may contain tiggers! --
The best option is to develop better technology to detect asteroids farther away (a series of monitoring satellites covering all quadrants overlapping). Once detected other methods than brute force could be applied. I've seen ideas like using solar wind/particles to move it by making one side of the object a black body (to absorb energy - and thus apply a force), to applying force directly by 'docking' with it and using rockets to nudge it off course.
The real problem isn't how to move the asteroid, the real problem is early detection. The earlier we detect it, the less energy has to be applied to it.
Lodragan Draoidh
The more you explain it, the more I don't understand it. - Mark Twain
The net attraction in this case is toward the centre of mass of the cluster of broken up pieces.
In other words, it would tend to re-assemble, but in fairness, that would take a long time if they were actually substantially separated.
Where are we going and why are we in a handbasket?
on trajectory estimates.
Correct me if I'm wrong, but the true nature of the problem is that the further out we detect the object, the more uncertainty there would be about whether it will hit Earth or just be a close near miss.
But it needs to be detected far out to have time to plan, build, execute the intervention.
What if we spend the 100s of billions of dollars needed to do an intervention like ion engine course correction, or painting, and then find out as it gets closer that, well, it looks like it most likely was going to miss "to the left" by a small margin, but we seem to be correcting it to the right just enough to actually hit Earth. Oops!
Or we realize that it's going to miss, three quarters of the way through the 100s of billions project, and cancel it. Predictable result in human affairs: You never get the funding again, ever, even if it happens to be actually needed next time.
This is what is technically known as a conundrum.
And yes, blowing it up is beyond stupid in almost all cases. Just get more chunks hitting Earth. Even more destructive probably. That's only suitable for movie plots written, sorry to say, by artsies.
Where are we going and why are we in a handbasket?
1) That we don't mind spending a lot of money on possibly unnecessary intervention missions.
AND
2) The intervention (e.g. rotation-timed ion engine push) needs to be enough of a correction to alter the trajectory by a lot more than the error bars on the trajectory estimate. So a lot of energy will need to be delivered. The math, anyone?
Where are we going and why are we in a handbasket?
The answer is ablation.. You're going to flash-boil some rock, which is going to expand against the main body, and create thrust as it leaves in the other direction at a very good clip.
As for wasting energy from the blast into space, there are approaches to mitigating that, which go all the way back to Project Orion.
Someone better tell Bruce Willis.
Break an asteroid into 8 chunks, and now you have 8 impacts, each still having half the blast radius of the original
You are assuming that the 8 chunks all hit Earth. That is extremely unlikely unless you let the asteroid get very close first : within the moon's orbit say.
If you know that the asteroid is going to hit Earth, then breaking it up at eg the radius of Mars orbit will send the fragments into a cone of debris which, by the time it reaches us, will be spread over an area vastly more than the target area of Earth - even if that cone angle is quite small. Earth is a tiny target from the distance of Mars (just look at Mars from here, even allowing that Earth is twice its diameter). We would be unlucky to be hit even by one large piece, although there would be lots of smaller fireworks to see.
And if we are not sure if the asteroid would hit Earth, and the further away the more unsure we would be, it is nevertheless better to act sooner. The cone spread would be so wide by the time it reached us that we would be very unlucky to get a big hit.
I still don't understand how exploding one in space where there is no air is supposed to alter the trajectory of a hugely massive object
You explode it in a reasonable depth below the surface, so that the largest possible amount of the asteroid's mass is ejected at a speed somewhat higher than local escape speed (which is usually meters per second or so), to maximize the terminal momentum of the ejected mass. Bunker buster technology like the B61 Mod 11 bomb should be suitable; the cohesion of the asteroid's surface is unlikely going to be higher than Earth's regular soil.
Ezekiel 23:20
We have the tech, quite often Mars can recognize asteroids in our blind spot of the Sun. thoughts... ?
[($)]
Finally somebody with some sense of physics! No, we never want to try to fracture an asteroid.
Straight ablation across one hemisphere seems like the best idea and change the orbit. Use something like the huge Spartan warhead encased in gold (for maximum x-ray creation). This was already created to heat and fracture the high Z atoms in enemy warheads and should work OK on a nickel-iron asteroid.
Best scenario would be to have years of warning, and land powered ion engines which could be controlled and changes accurately measured so no risky shots with unclear geological effect need to be taken.
If it was "many smaller ones", depending on the time of fracturing, the vast majority of them might never hit Earth at all, with some hitting it initially and some of the rest potentially becoming a regular smaller meteor shower.
Ezekiel 23:20
Of course then you bring in one of the articles' findings - if the cone is too small, the asteroid will re-coallesce. And one of the big problems with shattering as a goal is that you don't significantly change the path of the center of mass - so Earth will still be right in the bullseye.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Go take a look at the long list of asteroids that have passed frighteningly close to Earth, that we didn't see until they were already past.
In other words, asteroids that were too small to notice earlier...
Ezekiel 23:20
If size was the issue, you'd see them for just as long coming as going. The problem is light. An unlit object in space is completely black in the visible spectrum. And black also happens to be the exact shade of empty space. The result being that anything coming at you from the general direction of the sun, and thus only being lit on its far side, is completely invisible.
You start getting a slight visible crescent as the angle between the asteroid and the sun expands, but we know the Earth probably has companion asteroid fields around its L4 and L5 points, we've spotted at least one when it wandered very close to us, but at 60 degrees from the sun the main field remains invisible from Earth.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
You know, you're right! I apparently replied to the wrong comment, and then completely failed to notice.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Of course then you bring in one of the articles' findings - if the cone is too small, the asteroid will re-coallesce.
Only if nothing reaches escape velocity, which is reasonably easy to prevent. In fact, it's very difficult to arrange for anything else to happen.
Ezekiel 23:20
Perhaps, but I think you're underestimating how much energy is needed to move mountains. I'll run some numbers to confirm:
Lets take a modestly large asteroid, say 10km across, the lower extreme of the 10-80km size estimate for the dinosaur killer. There's an estimate 10,000 asteroids that size or larger. Maybe make it a bit bigger to make it an even 1000cubic kilometers, and we'll say it's a nice low-density icy asteroid, at around 1kg/L. So the whole thing masses about 10^15 kg
Then we'll hit it with a Tsar Bomba, the largest nuke ever developed,at 60 megatons, or 2.5x10^17J. Assuming we're able to convert 100% of that energy into accelerating asteroid fragments, we're talking 250J/kg = 250(m/s)^2 = 16m/s.
So I guess you're right - plenty of energy to accelerate the entire asteroid *way* past self-escape velocity. We could blow it into a million smithereens, never to re-coallesce. Well, except that all the smithereens are still in basically the same orbit, 16m/s isn't enough to make more than a tiny difference to that. And eventually their repeated close passes, collisions, and mututal gravitation will cause at least some of them to re-coallesce again. But that could take a very long time.
That's if we're lucky. The real question is could we make it break up in a way that we could be sure doesn't leave any major fragments on a collision course with Earth? And that could be a trick, as demolition of completely unknown rock formations can be more than a little chaotic. And the debris cloud could make a second attempt all but impossible. Becasue the real problem is that it's impossible to distribute the acceleration uniformly if it breaks up, and you'll have lots of debris that got barely any kick at all, and will float in lazy chaotic orbits around the remaining center of mass.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
>Fortunately, there's also this 1360 W/m^2 light flux near 1 AU making things significantly easier for us.
Which is only useful if we are between the asteroid and the sun. That's my point. My shining a flashlight towards you doesn't help you see anything between us, except in silhouette. And there's no background in space for a silhouette to be visible against.
Worse, we're not actually looking. Current astronomy amounts to a few hundred people looking through drinking straws at the sky - the vast majority of the sky never gets looked at for long enough to spot any particular asteroid, even if it's perfectly visible in theory.
Plus, near-Earth asteroids are the most persistent threat - and they spend their entire orbital path quite near Earth's orbit, mostly locked into a 1:1 orbital resonance with Earth. Which means they're basically invisible from Earth, except when we happen to be inside their orbit near their closest approach. Any other time, they're lit from the wrong direction to be visible. And Lagrangian orbits tend to be chaotic strange-attractor type paths when viewed from the non-reference point of the planet they're locked in resonance with - there's no guarantee that they'd get anywhere close to Earth, and thus become visible, before they're on a path for collision. And a relatively minor collision or gravitational deflection at the wrong time could deflect an asteroid from a previously stable orbit onto an Earth-colliding path.
It's not that they're hard to see - they're just hard to see *from here*. One of the proposals (several, probably), is to put asteroid spotting space-telescope(s) in a solar orbit inside our own, looking outward, so that they'll circle the sun independently from us, and every time they lap us around the sun, they will have had a chance to photograph the entire near-Earth asteroid belt in full sunlight. That, and some good software to spot the asteroids amongst the camera noise, and we could actually be fairly confident we spotted everything big (at least that's not extremely dark-colored). That strategy also has the benefit that the telescope stays very close (relatively) to what it's photographing, making it much easier to spot smaller still-dangerous asteroids.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Then don't blow it up isotropically. That's an obviously bad idea. An anisotropic detonation could ensure that an appreciable portion of the mass will leave the asteroid in a cone with velocities spread in a spectrum in such a way that they won't meet the main mass again for centuries (in such a way that after a single orbit, they're already hundreds of kilometers apart, with the distance increasing every period). The remaining mass will have been nudged by the negative of the total momentum of all the fragments that left the main mass, divided by the remaining main mass. If you only manage to blow off 1% of the mass, and the conversion to kinetic energy is only 1% efficient, you will have impacted a delta v of 0.2 m/s onto the remaining mass. That is 200000000 MNs of impulse transferred onto the main mass, which is massively higher than the "nudging" capability of any other propulsion system we've ever had (gravity tractors with existing electric thrusters could hope for perhaps 100-500 MNs or so, limited by the total design thrust of their thrusters). I don't see a 10 km asteroid threatening us any time soon, though. The larger these objects are, the fewer of them exist, and also the lesser the chance we don't know about them yet in the first place.
Ezekiel 23:20
You are right - I should have said the sun needs to be on the same side of the object as us, not necessarily behind us. Venus and Mercury orbit separately from Earth, so they're often at the opposite side of the sun from us, and with the sun between us, they're illuminated.
Most near -Earth asteroids never get far enough from Earth for that to work though. They wander within about +/- 60 degrees of Earth in roughly the same orbit, and while they get better lit in terms of percentage of surface area the further they are from us, the inverse-square law means they don't really get much brighter as seen from Earth.
As for my "relative close up view", picture this: If we're trying to, from Earth, see something at the L5 point, 60 degrees away in our orbit, we're trying to see something from 1 AU away, with only a sliver of visible crescent
If instead we put that orbital telescope in a slightly smaller orbit around the sun than us, say at 0.9AU, and then have it look directly outward at our orbit, it will never be more than 0.1AU away from whatever it's photographing. And, in the time it takes it's faster orbit to lap us, going all the way around the sun from our perspective, it will get that 0.1AU close-up of the entire orbit of Earth. Including the L3 point that's forever invisible from Earth, on the exact opposite side of the sun, 2 AU away.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
As for my "relative close up view", picture this: If we're trying to, from Earth, see something at the L5 point, 60 degrees away in our orbit, we're trying to see something from 1 AU away, with only a sliver of visible crescent
If you want to see whatever has somehow accumulated in Earth-Sun L4/L5, or even L3, why not simply send a small probe to those specific places?
Ezekiel 23:20
Except projectile orbital motion always brings you back to where you began. Every single one of those fragments will return to the detonation point at the end of every orbit. And the orbital period will not have been appreciably altered by a few m/s change, so they'll all be doing so at roughly the same time.
It's similar to the problem of trying to launch something into orbit using some sort of "cannon" on the planet's surface - it can't be done, because after one orbit the object will pass back through the point where the cannon was located, and impact with the surface. You can launch to escape velocity, or you can fire some secondary rockets to circularize your orbit, raising your perigee to avoid intersecting the planet. But on a purely ballistic orbital trajectory, it's a guaranteed impact within one orbit. Same thing trying to use air-breathing engines to reach orbit - so long as you can only apply thrust while inside the atmosphere, your orbit will always bring you back into the atmosphere.
Besides, once you're committing to not blowing it up symmetrically, why try to blow it up at all? The thing about a detonation, is that the center of mass always continues on the exact same trajectory it was on, so you're trying very hard to avoid leaving any major fragments traveling along along the original orbital path.
If instead you detonate off to the side, the jet of vaporized surface material (and reflected blast energy) act as a rocket engine, pushing the asteroid off course. And without fragments, you don't have to worry about how they get distributed.
As for there being fewer objects as they get larger - absolutely. But there's still an estimated 10,000 such objects larger than 10km in the asteroid belt alone, and we haven't spotted most of them.
And then there's the outer system objects. The real dark horse of the problem. Something trans-Neptunian, or from the Oort cloud, would be going screamingly fast by the time it got close in enough to have any chance of seeing it. Even with a broadly distributed asteroid-spotting system, we might only have months between it first becoming visible, and impact.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
1) because you don't want to see what's at *one* specific place - you want to see what's at *all* the specific places something might be
2) because if you're sitting at the L5 point, asteroids "orbiting" around that point could be passing you in any direction in 3D space - you'd want an omni-directional camera to avoid missing anything, and you'd still end up having a lot of things passing you closer closer to the sun so you couldn't see them. Much easier to sit with the sun at your back, and be relatively certain that everything of interest is going to pass in front of your uni-directional camera.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Are there any conceivable halo orbits at an L4/L5 point that wouldn't pass in front of an outward-oriented camera? Or in the worst case, one outward-oriented and one prograde-oriented?
Ezekiel 23:20
because you don't want to see what's at *one* specific place - you want to see what's at *all* the specific places something might be
Objects changing their relative position to Earth (i.e., objects not at L4/L5) should be already covered by telescopes on or near Earth, since they'd have to pass fairly nearby from time to time.
Ezekiel 23:20
Except projectile orbital motion always brings you back to where you began. Every single one of those fragments will return to the detonation point at the end of every orbit. And the orbital period will not have been appreciably altered by a few m/s change
It will if it's at least few tens of meters per second (near 1 AU). So it's a matter of getting the ejection velocity statistically right (in the sense of imparting just enough velocity to as large mass fraction as possible). If that happens, why care about when another encounter between the fragments happens if it happens after hundreds of orbital periods or more? By that time, we'll have completely different means to solve the situation, I'm sure.
It's similar to the problem of trying to launch something into orbit using some sort of "cannon" on the planet's surface - it can't be done, because after one orbit the object will pass back through the point where the cannon was located, and impact with the surface.
It's not really similar because the movement of Earth around the barycenter of the two bodies (Earth and the launched object) is negligible, whereas here we're talking about two elliptical orbits, which you're trying to make just enough different by changing one of them to prevent future problems of re-coalescence. In the latter case, a sufficient velocity for that exists that prevents such and event for a period long enough that by the time the problem could repeatedly arise, you won't have to worry about it anymore.
Besides, once you're committing to not blowing it up symmetrically, why try to blow it up at all? The thing about a detonation, is that the center of mass always continues on the exact same trajectory it was on, so you're trying very hard to avoid leaving any major fragments traveling along along the original orbital path. If instead you detonate off to the side, the jet of vaporized surface material (and reflected blast energy) act as a rocket engine, pushing the asteroid off course. And without fragments, you don't have to worry about how they get distributed.
Why? So as to maximize the momentum change of the remaining mass. If you have a fixed energy budget (dictated by the size of your nuclear explosive), ejecting a larger mass at a lower speed imparts higher impulse to the large body than ejecting a small amount of mass at a very low speed.
As for there being fewer objects as they get larger - absolutely. But there's still an estimated 10,000 such objects larger than 10km in the asteroid belt alone, and we haven't spotted most of them.
I'm sure we'll spot them soon enough. And given sheer variety of orbital parameters these objects can have, 10,000 seems like a *very* small number to pose a danger with any higher probability.
And then there's the outer system objects. The real dark horse of the problem. Something trans-Neptunian, or from the Oort cloud, would be going screamingly fast by the time it got close in enough to have any chance of seeing it. Even with a broadly distributed asteroid-spotting system, we might only have months between it first becoming visible, and impact.
Of course, you can always make up a scenario in which you can't win, if you ignore its sheer improbability. We *could* also get invaded by aliens tomorrow. I wouldn't worry about it, though.
Ezekiel 23:20
Except, you're not going to find things *at* L4/L5, you're going to find things "orbitting" them on all sorts of strange paths, and not necessarily just neatly planar ones.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
A 1% speed change... yeah, I guess after a year thing will have spread out enough it wouldn't be an issue. I'm sure it might re-coallesce eventually, but as you said, we should hopefully have better solutions at hand - if we haven't already mined the fragments to nothingness.
>So as to maximize the momentum change of the remaining mass.
Fair enough. Except - maximizing the momentum change isn't actually your goal. Minimizing the risk to Earth is. Unless it's a *very* last-minute operation, you've got momentum to spare to deflect the asteroid onto a safe path. The risk, is that you fail to deflect a dangerously large fragment, which is then shielded from further efforts by a cloud of debris.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
I don't believe we've even begun to exhaustively characterize all possible Lagrangian orbits, though I could be wrong about that.
But for starters, every single orbit that passed near you (as seen from "above"), substantially out-of-plane. You'd need a camera with a near 180* field of view along at least 1 axis, perpendicular to the ecliptic, to be able to spot all possible orbits, while still being able to spot an asteroid from hundreds of thousands of miles away, since those halos can be large. And you'd be haunted by those high angles suffering from the same poor illumination crescent that you get from Earth. You'd be much closer, so it's a reduced issue, but it still increases the maximum size of an unspottable object significantly.
You could no doubt make something work, it just seems much simpler to take a more typical telescope and put it a little closer to the sun, so that at least the vast majority of orbits would lie entirely within the viewing volume it sweeps out, and you'd have maximally-effective lighting conditions.
--- Most topics have many sides worth arguing, allow me to take one opposite you.