Again, as I mentioned earlier in the thread, they wouldn’t be just pebbles, they would be radioactive pebbles, which creates other issues.
It might work, especially on a smallish asteroid like a 100-meter one. One that size isn’t going to cook the atmosphere or kill species anyway.
BUT… what if the fragments are larger than sand? Your earlier post makes me think you overestimate the damage at Hiroshima. A building just 150 m from ground zero is still standing today. Brick and cement walls were knocked over, but not broken down into sand - you can see piles of bricks that are perfectly intact except where the mortar broke. Sidewalks and streets were sometimes cracked, but not smashed into gravel.
And let’s not forget that the military has hardened concrete structures designed to survive a direct hit from a nuke. Nukes are just not that good at blowing up solid objects. They’re much better at shaking and burning.
History will not remember you fondly if you take a 100-meter asteroid and fail to turn it into sand. What if you get 1,000 10-meter chunks and destroy dozens of cities across the globe instead of just one?
So, on a wider view, let’s do some realistic risk assessment.
Number of people in all of recorded history killed or injured by shit falling from space: 0
Number of people killed by military weapons: Well, we are somewhere near a million this century, which is only 10 years old.
Let’s not build the most powerfull weapons system in human historty to prevent something that hasn’t happened in a thousand times as long as all civilizations have existed.
Tris
‘Little Boy’ didn’t pulverize Hiroshima; it incinerated it. Because it was an air burst (~600 meters AGL) there was effectively no cratering, and the main damage occurred due to the thermal pulse and the shock wave, both of which were a result of the atmosphere absorbing the X-rays and converting them to heat. Buildings in Hiroshima were largely of stick-and-rice-paper construction (it was one of the few such cities spared from the firebombing campaigns of the 20th Air Force) and combusted readily, and could not withstand the >5 psi overpressure wave that extended for a 1.6 km radius from the epicenter. Many of the brick and mortar buildings in that radius were still partially or completely standing. Without an atmosphere, a nuclear weapon would emit mostly x-rays and neutrons; some ablation would occur due to induction, but the amount of damage, sans a way to convert this energy into thermal and shock impulse would be surprisingly little.
Remember, it takes just as much energy to “spread out” the debris cloud so most of it misses the Earth as it does to just shove it to the side, not including all the energy you’ve put into pulverizing it.
I think part of the problem here is understanding the scale of mass and energy we’re talking about in this situation. We’re used to thinking of a large thermonuclear device–say, a 1 MT nuclear device like the B28–as being a city killer, but by that we mean that (in a ~2000-5000 meter air burst) it will incinerate or flatten all aboveground unreinforced structures in a metropolitan region of ~10-15 km radius. Such a weapon detonated closer to the ground will suck up loose or broken ground in the uprush column of a mushroom cloud, but this is due to fluid dynamics in an atmosphere; the amount of pulverization done is small compared to the amount of work applied to lift the debris. An incoming meteor of threatening size, on the other hand, has kinetic energy that far exceeds the cumulative yield of a major nuclear arsenal, and disrupting its physical integrity or dispersing it widely “in time and space” requires enormous energies.
Imagine this; as part of your dastardly plot you plan to move all the gold in Fort Knox onto hijacked train cars and into you secret lair in a remote Caribbean island. Simple, you think; it just takes trucks and labor. Only, when you explain your plan in a fit of hubris to the bumbling secret agent you’ve just taken prisoner, he points out that “15 billion dollars in gold bullion weighs 10,500 tons; sixty men would take twelve days to load it onto 200 trucks,” and suddenly the scale of your endeavor becomes clear. it’s just not physically possible to exert that kind of effort on that scale. So, instead, you install an easily deactivated nuclear device and leave your steel-rimmed bowler sporting henchman to defend it.
The radioactivity is less worrying than you might think. For a period of about fifteen years both the United States and the USSR detonated hundreds of nuclear devices on the ground, in the water, and at altitudes from 500 feet to exoatmospheric; some of them extremely dirty, others of enormous yield (25 MT for the United States, 52 MT for the magnificent Tsar Bomba detonated by the Soviets). While estimates of mortality and morbidity due to the radioactivity released prior to the Partial Test Ban Treaty (which banned atmospheric and exoatmospheric testing, limiting tests to underground tests) vary, it clearly wasn’t cataclysmic and was a small fraction of the deaths directly attributable to tobacco smoking, alcohol consumption, and automobile accidents. With the right selection of device (emphasizing x-rays rather than neutron generation, which can “activate” radioactive isotopes of non-radioactive elements) the amount of residual ionizing radiation could be very small. Using a direct fusion device (none of which exist in the stockpile), it may even be negligible.
Estimates of the hazard probability of being killed by an asteroid collision are naturally full of assumptions that can easily vary by an order of magnitude, but one estimate (scroll down to the table entitled “Odds of Dying in the U.S. from Selected Causes”) offers the same odds as dying in an airplane accident; less likely than, say, being the victim of violent crime or an automobile accident, but not negligible. Of course, the odds aren’t spread out as evenly as other types of personal accidents; while the probability of incidence may be low in any giving year, or indeed, along your entire lifetime, the criticality of such an event–the amount of damage it will do not only in numerical terms but the disruption to the progress of human technological civilization–will be enormous. It is always a mistake to base the likelihood of a future occurrence upon the simple fact that it hasn’t happened yet; indeed, rather than offering comfort, it suggests that you are statistically closer to another occurrence for every year that passes without incident.
As for developing “the most powerfull weapons system in human history” we already have these weapons. While they may need to be altered or remanufactured to suit this purpose, the capability already exists, and if needed may save hundreds of millions if not billions of lives, and indeed, perhaps civilization as we know it. More powerful weapons–in terms of higher yields than those extant–aren’t really needed or desirable for this application; you’d rather have a large number of small bomblets for controlled impulse than a few ginormous ones.
Stranger
Does that actually matter when the damage is so localised and the chances of impacting a significant number of humans is so small?
The damage is localized only in the sense that it’d be restricted to a single planet.
And to nitpick Triskadekamus’s post, at least two people are known to have been injured by meteor impacts. Which isn’t really relevant, since those were small meteors, nothing like what we’re talking about here.
It might be instructive to look at underground nuclear testing. If you can bury a 1-megaton warhead inside a 350-meter-diameter asteroid, you might be able to shatter it to bits. Jack it up to 50 megatons, and you could maybe shatter a 1300-meter asteroid.
OTOH, Michael Bay will not be a part of this mission: it’s not technically feasible to gingerly install a warhead hundreds of meters below the surface of an extraterrestrial asteroid, so we’re back to having a near-surface detonation as our only option, and that won’t do much of anything to break it up.
Really? A million in the last ten years? I’d love to see a cite for that, Tris. That’s a big number.
What about using an asteroids kinetic energy against itself? I know that many armor piercing projectiles are merely depleted uranium fired at really high speeds, ala the kinetic energy penetrator. Could something along these lines take advantage of an asteroids high speed? I get that it probably wouldn’t change the path of an asteroid - but could it be effective at breaking one apart?
Look, smashing stuff is fun and all but it is much better to simply move these objects out of the way and not add excitingly new, fast moving objects we will have to track and deal with later on.
On what possible basis would you assert that the damage is “so localized” and the odds of affecting a significant population are “so small”?
It seems as if I’m failing to convey the scale of this. Let’s try another back-of-envelope calculation to get a rough sense of the scale of destruction of a large PHO that has been converted into rubble. Take a 100 m diameter iron-nickel object approaching Earth at 15 km/s (half of Earth’s orbital speed) and somehow fracture it into evenly portioned fragments of 1 m[SUP]3[/SUP]; this gives 4 million such fragments.Each fragment a kinetic energy of almost 900 GJ each, which is equivalent in energy to the yield of a >200 kT nuclear weapon (though, as discussed below, the energy release mechanisms may be very different). So the overall energy release would be (very) roughly the same as a nuclear exchange that is 200 times the number of weapons in all active arsenals at the height of the Cold War. I wouldn’t call this locallized or of small effect; I’d estimate this as literally apocalyptic, beyond any human comprehension on the scale of energy and resultant damage.
Some additional points to consider and summarize:
[ul]
[li]We’re all familiar with the effects of nuclear weapons in an opaque (to x-rays) atmosphere, i.e. shock, blast, and thermal effects. However, the initial yield from a nuclear supercriticality is mostly ionizing and neutron radiation; x-rays, gamma rays, and neutrons, which is converted to shock and thermal by the atmosphere. The ionizing radiation may do some damage by induction resulting in thermal shock, but electromagnetic radiation, even x-rays and gamma rays, aren’t going to penetrate very far into solid dense material. In short, the idea that a nuclear weapon in space will “blast” an object to small fragments, much less pulverize it into sand-sized grains, just isn’t accurate.[/li][li]The gross energy comparison to nuclear weapons above doesn’t account for the fact that while a nuke delivers energy primarily to the surface (and only a fraction of the total energy release effects that damage), an incoming object with a large amount of momentum will deliver its energy directly to the ground or water, creating substantially larger seismic effects than you’d get from an air burst or even ground-contact nuclear explosion. Such effects aren’t limited to the immediate impact area; seismic shocks of this scale can destroy building foundations and civil constructions for tens of miles, doing far more damage than a comparable nuclear weapon. A strike near a port or inland sea may do incredible damage from a tsunami and flooding. [/li][li]Pulverizing an object (if you could even do so) won’t significantly divert or disperse such a mass; in order to spread it out enough that most of the field doesn’t impact the Earth, you’re going to have to expend the same energy as pushing the whole mass off to one side. Also, a large field of debris would put existing and future satellites and spacecraft at extreme hazard for years or decades, costing tens of billions of dollars in property damage and untold cost in overall limitations of vital telecommunications and climate observation capabilities. This alone could justify the costs of such a program, even if an object or field doesn’t pose a severe hazard to the surface.[/li][li]A 1 km diameter object would have a total kinetic energy of over 450 million teraJoules; this is about 20% of the solar energy absorbed by the Earth over a day, but delivered in a span of seconds. Whether you leave it in one big chunk, or parcel it out in fragments, whether it is burned up (absorbed) by the atmosphere, or delivers a shock impulse into the ground or ocean, that’s is what scientists call “a big f**king bag of energy”. However it is distributed, it will have a major impact on the climate and biosphere of Earth.[/li][li]The technology to identify, intercept, and divert such objects is not far out science fiction, but is a reasonable (if costly) extrapolation of conventional and tested technology. It doesn’t require the development of radical new propulsion systems or fantastically destructive new weapons.[/li][/ul]
Indeed. Remember, that anything you blow up now will eventually come back across your path again, sooner or later. Better to divert it in such a way that it is as intact as possible, in a predictable orbit that isn’t likely to come back around near Earth for a long period. “Blowing it up” sounds gratifying, but it’s really just creating more hazardous debris.
Stranger
[quote=“Stranger_On_A_Train, post:71, topic:549435”]
My comments rely upon an explosive device that, due to placement, shaped charge, extreme power or whatever, can pulverize the offending object.
Let’s say that the bomb is embedded in the object before explosion. Where will the debris go? Remember, this is space, where any particle is not slowed down by atmosphere. Particles will fly off in all directions and continue to move in the same direction at the same velocity as the original force imparted to them.
Some particles will eject “sideways” to the object’s path, or even “backwards”, and continue along that direction unless acted upon by other forces. They will put a considerable distance between them and the original trajectory, and that distance will continue to widen. The debris field will not hold together unless it was a large enough object to cause it to collapse due to its own gravity. Pretty soon all parts of the original object are on widely diverging orbits relative to the Earth. Some may leave the Solar System entirely, some may head for the Sun. Only a very few will remain on the same path as before the explosion. So no, everything you blow up will not come back to haunt you.
Wow. Put into slightly different perspective: Little Boy, the bomb that destroyed Hiroshima, is estimated to have yielded between 13 and 18 kT. That means each of these fragments is packing more energy than 12 Hiroshima bombs, and there’s four million of them.
AND they hit harder, kT for kT:
[quote=“Stranger_On_A_Train, post:71, topic:549435”]
[li]The gross energy comparison to nuclear weapons above doesn’t account for the fact that while a nuke delivers energy primarily to the surface (and only a fraction of the total energy release effects that damage), an incoming object with a large amount of momentum will deliver its energy directly to the ground or water, creating substantially larger seismic effects than you’d get from an air burst or even ground-contact nuclear explosion. Such effects aren’t limited to the immediate impact area; seismic shocks of this scale can destroy building foundations and civil constructions for tens of miles, doing far more damage than a comparable nuclear weapon. A strike near a port or inland sea may do incredible damage from a tsunami and flooding. [/li][/QUOTE]
I came to say the same thing (well, not leave the solar system part, but different enough trajectories to not be an immediate issue). And, even if they ARE a threat, they are threat you can track and most likely they will be a threat (and a much lower one) a long ass time from now.
Busy getting ready for an Alaska vacation very soon so I don’t have time to make my points. Given there have been two bush plane crashes in the last few weeks…well, hey, if you guys don’t hear from me again…its been…well…something at least 
Explosives, conventional or nuclear, don’t pulverize. They apply a mechanical or thermal shock, which causes objects to break along fracture lines, usually into large chunks. The only objects that get pulverized by such shocks are structures that are already pulverized and are cemented together like concrete or dirt. Small grains of rock are formed by crushing or gradual abrasive action (like water waves on sand), not imparted shock.
This is uninformed fantasy. First of all, all of the objects of whatever size resulting from said explosion are going to remain in the same general orbit. Presuming that they are in a stable solar orbit, there is no way that they’ll get enough impulse from this blast to achieve solar escape velocity (~42 km/s at Earth’s orbit). Most of the field will just enter a slightly more or less elliptical orbit, and will pass back through the same point. If it was a hazard before, it’ll continue to be a hazard that is just slightly more spread out; in other words, a bigger and more persistent hazard.
Again, it takes at least as much energy to redirect the debris field enough that it doesn’t impact the Earth in one aggregate mass as it does to shove it off into another orbit, notwithstanding all the energy applied to fragment it. “Blowing up a hazardous object”, even if could be done in the manner you imagine, does not fix the fundamental problem that the Earth stands to be impacted by a large amount of mass with a lot of kinetic energy.
Stranger
I think you’re missing two key points that have been made already.
- Your first paragraph about your postulated explosive device is like saying “My comments are based on the flying spaghetti monster entangling the asteroid and throwing it into the sun.” What people have been trying to explain is that there aren’t any such devices. Hiroshima did not suffer the level of damage you think it did. Nukes are not that effective at shattering anything, let alone asteroids in space.
Even if you did shatter it, relatively small fragments (and there would be thousands or millions of them) are still sufficient to destroy a city. So instead of destroying one city from the original impact, you are now destroying hundreds (or more) of cities.
- The idea of bits of the asteroid flying around takes energy. If you could throw bits of it in every direction, then you also had enough energy to push it aside without breaking it up - the amount of energy is equivalent.
Even if you did make it fly apart in all directions, they won’t head directly into the sun or out of the solar system. You are again overestimating the amount of energy needed. In this case, the energy needed to change an orbit. Let’s say your nuke expels fragments of asteroid at the speed of a bullet - that’s 350 m/s. Impressive, right?
But that’s not impressive. Let’s use Apophis as a real near-Earth object for example. It’s average orbital speed is almost 31 km/s. So what’s the final orbital speed of the fragment? Just 31,000 +/- 350. You’ve only changed the velocity of the fragments by, at most, 1%. So they’ll settle into new orbits… but those new orbits (at least some) will intersect the Earth again in the future.
Magiver said:
Depends. From 50 feet away, the bird shot spreads out and you get a smaller fragment of the total mass hitting you, for less penetration per hit. But at 6 inches from the barrel, there isn’t much difference.
One open question is how you go about deflecting the varieties of types of asteroids out there. It may be relatively easy to deflect a solid nickel/iron chunk, but some asteroids are rubble piles - clumps of rocks hanging together only by gravity (as opposed to chemical bonds). Try pushing on that, you may just get the energy absorbed into the clump, stir the clump up, and still have essentially the same mass on essentially the same orbital path.
We don’t know what will and won’t work. We have some good ideas, but need to try them out to see how they work in practice.
Let’s say the intact object is traveling with a certain velocity, which includes both speed and direction. Absent influence from some other mass, it will continue that way indefinitely.
After being pushed, the object or parts of the object in the case of shattering, now have a different velocity. Their new path is a composite of the old plus the vector imparted by the explosion or shove, and it is affected by nearby mass.
The new vector isn’t the same as the old one. Parts of the object, if split separate, and continue to separate. They won’t return to the original path and they will increasingly diverge. They will not be a cloud of debris held together by anything as it would work on the surface of Earth. The cloud will expand forever. If the initial impetus is great enough, parts might reach escape velocity for the solar system.
If I explode something over an Earth body of water, the debris stays close together after the initial impact is passed because of atmospheric influences. This makes recovery from an airline disaster over water possible. In space, this debris field continues to spread out forever.
I can’t speak as an expert on explosives as to whether pulverization is possible or even likely. I do know that demolition experts have considerable control over how and where a charge acts depending on the desired outcome. I suspect there is some control available in space, too.
People speak of an “orbit” of a threatening object, but it’s possible the object is just passing through the Solar System and is orbiting nothing unless captured. It’s also possible the orbit is extremely eccentric and extends past Pluto. While we might not eliminate it from future consideration, we might be able to remove it from the present.
Look these things travel about 30,000 m/s. Shoving it sideways 300 m/s isn’t going to throw it out of the solar system.
Well, since 2001 wars in Iraq, Afganistan, counting all deaths on the various side are variously estimated to be quite near a million on the lower end. Given that the entire rest of the world was not at peace during the decade since then, it is not an unreasonable estimate. But, even if it’s wrong by a factor of ten, that puts the two assessments at 100,000 to zero for one decade. Mathematically, I think the proportions are indestinguishable.
But, this is not great debates, so I will leave my contention as a simple suggestion, and not debate it.
Tris