Ideas to protect the Earth from possible asteroid impacts

  • #26
Then there is the question - Where is the best place to hit the asteroid? A lot of then are clunky, with an uncertain interior composition, and sore spot.
Seems like a lot of room for failure just right there - failure including leaving a large chunk still heading to earth after a successful hit.
Surface or near-surface blast may be preferable, it has a more predictable effect - part of asteroid is ablated away, pushing the entire remaining asteroid, still in one piece. Especially if you have even just an approximate control over the location of the blast and thus, the direction of the push, this is a nice, controllable deflection rather than "let's go with a big BOOM and hope for the best" approach.
 
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  • #27
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Surface or near-surface blast may be preferable
Absolutely! Deflection in one way or another is the only reasonable way of dealing with that threat. Hollywood's idea of nuking the asteroid into zillion pieces is fun and entertaining until you realize that the center of mass of resulting cloud of debris is still coming towards you. It may be unable to produce a huge crater, but it will affect much larger area in multiple impacts (reminder: you need only 20 m diameter asteroid to get Chelyabinsk-like fireworks), and don't forget that all that debris falling into the atmosphere over the continent(s) is now highly radioactive. Thank you Bruce Willis.
 
  • #28
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Surface or near-surface blast may be preferable, it has a more predictable effect - part of asteroid is ablated away, pushing the entire remaining asteroid, still in one piece. Especially if you have even just an approximate control over the location of the blast and thus, the direction of the push, this is a nice, controllable deflection rather than "let's go with a big BOOM and hope for the best" approach.
Any chance the shock wave, from a pretty much instantaneous heating zone of solid to liquid and gaseous, passes through the asteroid and blows out some material from the far side, negating the push from the vapourization on the near side. In fact, the main body of the asteroid could be "sucked" towards the blast from that effect, rather than away if that effect predominates. Has that been investigated at all?
 
  • #29
don't forget that all that debris falling into the atmosphere over the continent(s) is now highly radioactive. Thank you Bruce Willis.
Completely negligible, considering the magnitude of catastrophe humanity is trying to prevent in this scenario.
 
  • #30
Any chance the shock wave, from a pretty much instantaneous heating zone of solid to liquid and gaseous, passes through the asteroid and blows out some material from the far side, negating the push from the vapourization on the near side.
I imagine pretty much any type of asteroid has surface layer of dusty fractured regolith, similar to what Moon has. It does not transmit shocks well.
 
  • #31
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Completely negligible
I can agree if the asteroid in question is pulverized and it happens far enough from the Earth – it would be less harmful than fallout from nuclear tests. But would you say the same if Bennu-sized object was converted to several thousand Chelyabinsk-sized "dirty bombs"? We know very little about the material properties of the asteroids. Rubble pile reacts in a different way than rigid rock or chunk of metal, and there are probably more varieties out there. Deflection, nuclear or conventional, is way safer than blowing up. In a particularly bad scenario (too big asteroid, too small yield and/or unfortunate mechanic properties), the gravity can re-form the threatening object, making us wish we changed its trajectory.
 
  • #32
LURCH
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I’m pretty sure that, in any scenario, a bunker buster nuke, also known as a GPW (Ground Penetrating Weapon), is the best course of action. A surface or near-surface detonation wastes most of the device’s energy into the vacuum, while relying on heat to vaporize a small amount of material on the surface. A sub-surface blast excavates a large amount of material and turns it into reaction mass. These devices already exist and could be converted to this purpose with relative ease, and they can be programmed to detonate at a predetermined depth below the surface. Anywhere between the surface and the center of mass will result in a much greater deflection than a stand-off detonation.

The fear of turning one object headed for Earth into thousands of objects headed for Earth only applies to those scenarios that are so popular in the sci-fi thrillers, where the people in charge always wait to detonate until less than a minute before impact (for dramatic effect, I suppose). We are all in agreement that the key is to detect the threat and take action early, while it is many years away. In that case, such a concern does not exist.
 
  • #33
Surface or near-surface blast may be preferable, it has a more predictable effect - part of asteroid is ablated away, pushing the entire remaining asteroid, still in one piece. Especially if you have even just an approximate control over the location of the blast and thus, the direction of the push, this is a nice, controllable deflection rather than "let's go with a big BOOM and hope for the best" approach.
If it's a large asteroid, it could take hundreds of nukes (maybe even more) just to nudge it enough. I haven't seen anyone bring up the possibility of using lasers. I imagine that it would probably take a lot of time to do that though.
 
  • #34
I haven't seen anyone bring up the possibility of using lasers
If I remember correctly, laser technology is not that powerful yet. I don't think it can cause any sort of damage to an asteroid. I have to mention that last time when I checked it was like a year ago. Some stuff may have changed.
 
  • #35
The City of Berkeley, for example, requires that nothing radioactive - even a single disintegration - enters the city limits.
So what do Berkeley hospitals do about the medical radioisotopes they need for medical treatments? Are they exempt?
 
  • #36
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I believe all objects made of physical matter would have to be exempt. It’s possible that this was the intent; that the entire city should only be made of metaphysical constructs. I mean, this is Berkeley we’re talking about.
 
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  • #37
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Build an orbital soleta/solar sail for climate cooling from lunar aluminum. Change its shape to a parabolic reflector and use focused sunlight to vaporize the side of the asteroid, blowing it slowly off course.

With nukes, careful mapping and reevaluation after each strike would yield the best results by making sure each detonation acts most effectively. Vaporizing ice is probably more effective than blowing up rock. Detonations in craters more effective than on convex areas.
 
  • #38
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First, you must detect the object with enough lead-time to plan.
http://spaceweather.com/ has interesting lists. Note some objects may only be detected upon impact or outbound..

Then, you must remember the 'Deep Impact' mission { NOT the movie } which whanged a 100 kg copper ingot into comet Tempel 1 (9P/Tempel) at a crossing speed of ~10 km/sec, made but a ~150 metre crater. It certainly did not affect the orbit to any measurable degree. Would ten such make a difference ? Twenty ? Fifty ??

I'm reluctant to venture into 'finger breaking' territory, but mitigating fallout from the 'whack it' approach would seem to need possibly-mythical shaped-charge nukes...

That still puts you into 'Hydra Killing' country. Even if your first, second or third thermo-nuke shatters the monster, you now have multiple city-killers inbound. Behind a protective cloud of debris that may thwart subsequent attacks...

With sufficient time to work, more elegant solutions such as an ion-engined orbiter playing 'gravity tug' may serve...
 
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  • #39
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With sufficient time to work, more elegant solutions such as an ion-engined orbiter playing 'gravity tug' may serve...
You have to get the ion drive there with enough fuel to actually accomplish something.

Using nukes like an Orion drive instead of for demolition might be faster and more efficient. You could always send out a pusher plate to protect the asteroid.
 
  • #40
LURCH
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Then, you must remember the 'Deep Impact' mission { NOT the movie } which whanged a 100 kg copper ingot into comet Tempel 1 (9P/Tempel) at a crossing speed of ~10 km/sec, made but a ~150 metre crater. It certainly did not affect the orbit to any measurable degree. Would ten such make a difference ? Twenty ? Fifty ??

I'm reluctant to venture into 'finger breaking' territory, but mitigating fallout from the 'whack it' approach would seem to need possibly-mythical shaped-charge nukes...

That still puts you into 'Hydra Killing' country. Even if your first, second or third thermo-nuke shatters the monster, you now have multiple city-killers inbound. Behind a protective cloud of debris that may thwart subsequent attacks...
I hear this statement a lot, and I strongly believe it to be false. The statement is usually phrased along the lines of; "A nuke will turn one object headed for Earth into many objects headed for Earth", but that is not cosistant with reality. One key to understanding this is to realize that the phrase, "many objects headed for Earth" claims two conditions; that the object has been broken into many pieces, and that those pieces are headed for Earth. I do not believe that these two conditions can both be realised.

Consider the scenario in which the original object is indeed shattered into a thousand pieces. If we examine the resulting debris field, we can see that it is expanding over time. For specificity, let us look at this from the perspective of one of the pieces of debris. If we observe the spatial relationship between that piece and its nearest neighbors at one second after the blast, and then again at two seconds, and again at thirty, we see that with each successive observation, the distance between any two of these objects has steadily increased. If they are all moving away from one another, getting farther apart over time, then they cannot all be headed for the same target. In fact, no two of them can arrive at the same destination (unless they are large enough to pull themselves back together gravitationally). This puts a very specific upper limit on the maximum number of fragments that might still be on a collision course with Earth. That maximum limit is one.

Even this maximum may not be possible. The only reason the object would break into many pieces would be because each of those pieces has undergone an acceleration. If each of them was originally on a collision course with Earth before being subjected to an acceleration, then it would seem that this course (the collision course) is the one path in all the universe along which none of them can now be progressing.
 
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  • #41
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So what do Berkeley hospitals do about the medical radioisotopes they need for medical treatments? Are they exempt?
No idea. I try not to get sick inside Berkeley city limits. I'm afraid instead of real medicine they may want to align my chakras.
 
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  • #42
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perhaps the most feasible way is "preventative medicine" -- detect collisions far far far in advance, and supply the future would be dangers with a slight nudge in the outer solar system... long long before they get up to speed and take full aim at earth ?

Otherwise, sitting back on our heels, waiting for asteroids to show up on our solar doorstep at relative speeds of 11+ kps is probably impossible
 
  • #43
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An object that takes us by surprise is not going to give us much of a response time, and "nuking" it and hoping for the best is the only option that seems likely to me.

For an object that we're already tracking, we're going to have a much wider window of opportunity. We already know how to land on these things, so one reasonable approach is to land a thruster on it - maybe an ion engine - and slowly nudge it into a harmless orbit. A tiny change in direction really adds up over millions of miles, so it won't take much of a nudge; the trick is to get to it early enough.
 
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  • #44
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We already know how to land on these things, so one reasonable approach is to land a thruster on it - maybe an ion engine - and slowly nudge it into a harmless orbit
The primary problem with this notion is that the ion engine AND all of its fuel have to get out to the incoming asteroid, change direction 180° to match its incoming velocity, land somewhere stable enough to thrust against and still have enough time/fuel to push it far enough off course to matter.

Ion engines are practical for spacecraft because spacecraft are relatively light compared to the fuel they carry. But an asteroid is hugely massive and none of that is ion engine fuel.
 
  • #45
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What are you talking about?? Moving either the Earth or the Moon by even a microscopic amount is totally beyond our capabilities in the next few thousands of years. Moving an asteroid is way more practical.
Well, yes with sufficient lead time, but what if you're in a hurry?
Two questions arise:

- can you displace the earth?
- how quickly can you do this without "breaking it"?

power available (half revolution): 5x10^24W
half revolution period: 4.3x10^4s
earth mass: 6x10^24kg
displacement: earth radius 6.4x10^6m
power=mass x acceleration x displacement / time so a=pt/md
I get a rough maximum acceleration of about 5mm/s^2

Actual result might be much less, but I don't know how little the earth could tolerate (oceans, plates, etc...)
 
  • #46
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Something like a big ball of spongy stuff it must get through before hitting Earth.
This idea not copyright protected.
 
  • #47
When asked this question, Neil DeGrasse Tyson offered two possible solutions, neither one practically viable: First, a "gravity tractor" and second, painting half the asteroid white so that the difference in solar reflectance would slowly push it off course...The problem with the second one is obvious - any deflection of the asteroid would be too minute to make enough of a difference by the time it arrives. While the problem with a gravity tractor is that you need a spacecraft with enough mass to pull the asteroid off course, but that mass is going to have to be launched from the surface of the Earth and that requires enough fuel to get the job done, but that would probably be prohibitive both in cost and supply. Then there's the dilemma of, if it's massive enough to be detected early it would be too massive to deflect, but if it's smaller it won't be detected until it's too late to effectively deflect it. There was a third solution proposed by the T.V. show "Salvation" which is to use a solar sail to deflect it, but solar radiation and even the solar wind wouldn't be able to provide enough thrust to alter the orbit of an asteroid. Wikipedia provides a few more possibilities: Attaching solid rocket boosters to gradually deflect it and alter it's orbit enough that it misses the Earth. Using mass drivers to expel material that would provide a thrust to alter the orbit. Jay Melosh, a planetary astrophysicist who is known for discovering lava tubes on the Moon, is the one who originally pointed out the shortcomings of using nuclear weapons to "destroy" the asteroid, came up with the most elegant solution, which Tiran also mentioned in post #37, and that is to use a parabolic solar reflector to ablate a portion of the asteroid to provide enough thrust to blow it off course. A refinement to this solution would be to use the reflector to pump an industrial size laser to more efficiently ablate the material...
 
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  • #48
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The best approach to preventing a collision with an incoming asteroid relies heavily on its trajectory. Deflecting it to one side or another might not always be the best use of your resources. In some cases, speeding up the asteroid in its orbit might be best. A collision between asteroid and the Earth depends on both the Earth and asteroid arriving at the same point of Earth's orbit at the same time. Speeding up the asteroid will change its orbit; in the best case, both causing it to cross further along in Earth's orbit and crossing Earth orbit earlier, and thus crossing Earth orbit before the Earth has quite arrived there.
There is another reason why accelerating the asteroid could be the best answer. This involves the impact parameter. As the asteroid gets closer to the Earth,the Earth's own gravity will begin to act on it deflecting its trajectory. So even if the initial trajectory would have had the asteroid missing the Earth, Earth's gravity could draw it into a collision. The lower the relative velocity between asteroid and Earth, the more time Earth's gravity has to act on the asteroid and the larger the "target" the Earth makes. Accelerating the asteroid (under the right conditions) can increase the relative velocity between Earth and asteroid at orbital intersection, effectively making the Earth a smaller target to hit.
 
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  • #49
Janus said:
The best approach to preventing a collision...speeding up the asteroid in it's orbit might be best.
I agree! This would also make it easier to orient a reflector to be facing the sun while ablating it from behind. There's also an alternative option of deflecting it to a lower energy orbit so that the Earth passes first and the asteroid crosses Earth's orbit later...whichever method is used, we have to be careful that another collision is not realized at a later orbit.
 
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  • #50
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This involves the impact parameter. As the asteroid gets closer to the Earth,the Earth's own gravity will begin to act on it deflecting its trajectory. So even if the initial trajectory would have had the asteroid missing the Earth, Earth's gravity could draw it into a collision.
I see what you're saying, but how much of a velocity change is required vs. how much that is going to decrease the attraction of Earth's gravity on drawing the asteroid in?

I ask because speeding up an incoming object is essentially the most difficult way to do it because you can't do it with electromagnetic or ballistic means, which means getting some sort of drive system out to the object. If the object is tumbling, you won't be able to dock a drive and will have to settle for something like a ersatz Orion. If it isn't tumbling, that means we'll have no data on the "dark side" where whatever device is going to have to act. That could be a disaster if the dark side has a composition incompatible with the drive mechanism. So speeding up really seems like the most difficult method that resists secondary methods, because you wouldn't want to speed it up and then only have slow-down back up techniques if the drive fails.

Which brings up another concern - redundancy. It would be best if whatever primary method was largely compatible with any secondary methods that could be built in parallel. They could act on the same vector, or complimentary vectors.

You can change the object's trajectory by pushing it in, out, up, down, right or left in the plane of the ecliptic, including combinations. What are problematic combinations are speeding it up while steering it down orbit, or slowing it down while steering it up orbit. In those cases you're cancelling out the action of either vector.

I don't know for sure, but my instinct is that the most efficient steering vector is going to be perpendicular to a line running from the center of the earth through the potential impact zone.
 

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