Then it’d be a 4-mile long rock, not a 4-mile wide rock. 
I think this should be nitpick-pick.
But as I mentioned above, if the object is sufficiently large and fast, letting the atmosphere absorb the billions of tiny fragments will just as easily result in our extinction.
For example, suppose we have a really enormous rock with a mass of about 10[sup]15[/sup] kilograms (much, much larger than 99942 Apophis, but much smaller than 1036 Ganymed; your 4-mile meteoroid would probably have a comparable mass) approaching Earth at a worst-case combined orbital speed of 60 km/sec. Relative to the Earth, it carries about 4 * 10[sup]24[/sup] joules of kinetic energy. Now let’s say you blast that into sand with a few well-placed nuclear arsenals.
If we make the gratuitous assumption that all the sand impacts Earth and burns up in the troposphere (which has a mass of around 7 * 10[sup]17[/sup] kilograms, and which I’ll gratuitously assume to have a specific heat capacity of about 2 J/(g*K) – more than dry air but less than liquid water), we can expect global average air temperature to rise by
(4 * 10[sup]24[/sup] kg) / (2 J/(g*K)) / (7 * 10[sup]17[/sup] kg) ~= 3000 Kelvin
Yup, we’re still doomed.
I Don’t Want to Miss a Thing is about as far from kick-ass as is possible without heading into outer space.
If you have enough energy to break apart a rock into sand sized particles, wouldn’t that reduce the kinetic energy by a significant amount? Hitting a baseball with a water balloon with slow it down a bit.
How much of that hear would radiate into outer space before it killed everybody?
Not that it matters. Those quotes are designed to show that breaking up the meteor is a significantly worse idea than anything else, but really we’re screwed no matter what we do so it’s a moot point.
A couple of examples of nuclear test shots in space:
Well, let’s say you used ten thousand 50-megaton thermonuclear warheads to blow apart the meteoroid. 500,000 megatons is equal to about 2 * 10[sup]21[/sup] joules. If we assume that somehow all of this energy went towards reducing the incoming kinetic energy of the fragments, the remaining energy is (4 * 10[sup]24[/sup] J) - (2 * 10[sup]21[/sup] J) = 3.998 * 10[sup]24[/sup] J. Considering that we were really only working with one significant figure, that’s still just 4 * 10[sup]24[/sup]. In other words, your ten thousand Tsar Bombas don’t even amount to a rounding error as regards the meteoroid’s total kinetic energy.
As for the second question, I’m not sure. I imagine a fair bit of the heat would be radiated away, but I’m sure it wouldn’t amount to much in the short term. We’d still see an enormous rise in global temperature that would pretty quickly kill us all. (Except for those hiding deep underground, maybe.)
I don’t know - The Earth actually is bombarded with about 10^6 to 10^8 kg of material every year - meteors and small particles from space - which have a negligible effect on the planet’s temperature. If 10^8 kg of mass in the form of an iron meteorite hit the earth, it would release hundreds to thousands of megatons of energy and could blow a crater in the ground several miles in diameter. The giant meteor crater in Arizona was created by the impact of a meteor about 3 X 10^8 kg.
The Earth receives about 1 X 10^22 joules of energy from the sun each day. That’s roughly equivalent in energy to a metallic meteor maybe a couple of miles in diameter hitting the earth. That’s on the order of the size of the meteor that wiped out the dinosaurs 70 million years ago, which is believed to have been about 10 km in diameter.
What would doubling the energy hitting the earth in one day do? I’m not sure, but I suspect we’d recover. Most of the heat would go into the upper atmosphere and it would radiate away at an accelerated pace. I’m not sure what it would due to ground temperatures, the ozone layer, and other things. Maybe someone else has a good guess.
True, but 10[sup]8[/sup] kilograms is small change – in my numbers above, I assumed a mass of 10[sup]15[/sup] kilograms, which is ten million times as much mass.
A couple miles? I dunno. Assuming a roughly spherical M-class asteroid with a mean density of about 6 g/cc, a diameter of two miles would yield a mass of 8 * 10[sup]14[/sup] kilograms. Even at a relatively slow 10 km/sec orbital speed, that’s 8 * 10[sup]22[/sup] joules, eight times the energy Earth receives from the sun in one day. That diameter probably would be about right for a rocky asteroid, though. However, it’s quite possible for near-earth objects to intersect us at much, much higher speeds, resulting in considerably more kinetic energy.
I guess it probably would get mostly dumped into the higher parts of the atmosphere, and a lot of it would radiate away, but I’d bet the results would still be pretty disastrous. Especially since, in my example, we’re not doubling the amount of energy received from the sun, but multiplying it by a factor of 400.
Many space launch vehicles (SLVs) are ICBMs or are developed directly from refurbished ICBMs, such as Titan II GLV/Titan 23 (now retired, developed from LGM-25C ‘Titan II’), Atlas E/F, -Vega, -Able, -Agena (retired, developed from the SM-65D ‘Atlas’), and the Orbital Sciences Minotaur IV/V (current production, developed from LGM-118A ‘Peacekeeper’), with the addition of new or modified guidance system, test range approved flight termination system (FTS) hardware, and apogee/insertion kick motors. Other systems utilize major propulsive elements from ICBM or MRBM systems, such as the Titan III/IV, Delta (developed from the PGM-17 ‘Thor’ MRBM), Juno II (developed from the PGM-19 ‘Jupiter’ MRBM), and OSC Minotaur I/II (using Minuteman II first and second stage motors) but add or mix-n-match additional booster systerms for main propulsion. And then there are commercial launch vehicles which are ‘derived’ from ICBMs, like the Atlas II/III/IV/V, Delta II & IV, et cetera, but are for all intents and purposes new SLV designs that share essentially no common hardware with predecessors. A few space launch class rocket systems, like the Saturn family used on Apollo (I, IB, INT20, V) and the Space Transportation System (American Space Shuttle) are distinctly non-ICBM designs that were never owned by the military and would be ill-suited for use as ICBMs or weapon delivery systems. The Ariane family of rockets are also developed from some missile technology but designed from the ground up as commerical launch systems.
The Soviet/Russian systems are something of a unique case, as all of their space launch systems were essentially developed by government-run bureaus for primarily military usage. While the R-7 ‘Semyorka’ was ostensibly the world’s first ICBM system, the fueling time and inability to remain at readiness made it a poor choice as a weapon system. However, it became the core design of the Soviet space launch effort and has performed remarkably well for that, propelling the Vostok, Voskhod, and Soyuz manned capsules into space reliably. However, the Russians have also used demilled ICBMs for purely orbital space launch systems, particuarly the R-36M//SS-18 ‘Satan’, while the N-1 rocket, developed as an Earth-escape SLV specifically for their Moon program, failed in four out of four launch attempts. The Soviet ‘Buran’ shuttle system (analogous in function and, to at least a visual extent, in form to the American STS) flew only once (unmanned).
To address the questions of the o.p., in order, to intercept an incoming meteor at presumably interplanetary distance (the more distance the better), at a minimum you would require a kick motor mounted atop the booster stack to achieve Earth escape, a guidance and telemetry system capable of flying beyond the normal ballistic return track, and any sensors, hardware, ordnance, antennae, et cetera, necessary to survive the space environment for an extended duration. It would probably be a good idea to repackage the physics package (the part that goes boom) into a different space vehicle system for terminal guidance, thus eliminating the needless mass of the reentry vehicle (RV). This might be possible on a really large ICBM like the Peacekeeper combined with a large apogee kick motor like the Interal Upper Stage (IUS), but you’d probably be better of launching on an Atlas V or Delta II/IV dedicated space launch vehicle with a Centaur transstage and a Mariner bus and propulsion system, which would give a sim-qualified spacecraft system which has withstood extended deep space and operational environments.
In terms of stopping a threatening meteor, as scr4 says, the best plan is to nudge it to the side rather than dry to demolish it into components too small to be a threat. This could be done by using one or more nuclear weapons equipped with a reflective cavity which focuses the x-ray output into a consumable pellet which converts the radiation to thermo-mechanical energy and expands into a cloud of expanding gas that generates a moderated impulse, pushing the meteor into a non-intercept orbit.
Stranger
Make that 64 radioactive pieces. :smack:
Admittedly, the radioactive fallout will pale in comparison to the actual impact of a 4 mile wide rock, but it would be an issue for a smaller rock where a nuclear blast has more chance of influencing the trajectory significantly or breaking the rock into smaller fragments.
And I seem to recall that Meteor (the 70’s disaster movie) relied on secret Russian and American orbiting missile platforms to get the bombs to the meteor.
Si
It may not take much more energy to go from an intercontinental ballistic “lob” (an elliptical orbit whose path passes through the earth) to a circular orbit. Depends how high the original ICBM was designed to lob its warhead, and (as you noted) the weight of the warhead.
I’ll note that low earth orbit requires about 17,500 MPH, whereas escape velocity is on the order of 25,000 MPH, just over TWICE the kinetic energy. That’s a pretty big difference. The weight multipliers mean that if you want the final payload to have that much more energy, you need a LOT more fuel, which means a bigger rocket to push all that extra fuel, and more fuel to power that bigger rocket, and so on. IIRC, on the Apollo missions, 1 pound of final-stage payload required something like 25 pounds of overall Saturn launch vehicle weight. Look at the difference between the space shuttle (an orbiting vehicle) and the Saturn (meant to achieve escape velocity), and you’ll see how much more it takes to get away from earth:
Space shuttle:
184 feet tall
6.8 million pounds thrust
4.47 million pounds overall weight
~240,000 pounds (orbiter + payload) to low earth orbit
Saturn:
363 feet tall
7.6 million pounds first-stage thrust
6.7 million pounds overall weight
100,000 pound payload to lunar vicinity (the Apollo missions), OR 262,000 pounds to low earth orbit (the Skylab missions)
Bottom line? The earth sucks pretty hard, and a simple ICBM just ain’t gonna come close to achieving escape velocity unless you strap on some serious booster rockets.
No, because what you want to do is push the asteroid off course. An explosion from a nuclear weapon is powerful, but in the vacuum of space it has very little to push. The asteroid would be hit with atomized nuclear materials and little else. The push will be so weak that it will not affect the trajectory. Unless the asteroid was very, very small and the bomb landed on a fault point, then you cant expect much. Even in that scenario you may only be able to crack it into a few pieces, thus multiplying your problems.
I read one proposal to launch a lot of mass, like millions of gallons of water and setting them off with a nuke so the steam pushes the meteor, but I dont know how plausible that is. The lifting capacity to move that much water doesnt exist.
Some proposals to fight meteors is to install a mass driver that will drill and push out material, thus forcing it to change course. You only need to push it a little bit to avoid hitting the earth.
The missile guidance systems are based on GPS satellites, aren’t they? (That was the original reason that we put GPS satellites into orbit.) So once these missiles exit earth’s orbit and go out into space to hit the meteor, what is left to guide them? Do they just depend on Newton’s laws?
Nope, most nuke missile systems were designed, built, and deployed before the GPS was up and running. Many of those were probably before the GPS system was even seriously considered.
I suspect the inertial navigation and mechanical? computer systems of the ICBM systems are some of mankinds most amazing technological achievments.
The GPS system was built to help virtually everything else besides ICBMS that the military uses that moves or could move. Guys and gal and bombs and planes and cruise missiles and tanks and robots and ninja squirrels (didnt know about those did ya?).
To go even further, you really would NOT want a nuclear missle to rely on any system outside of itself to work, because if someone can bugger that up in a time of war your missiles are going to be useless.
Missiles/rockets use a variety of guidance systems and space probes do just fine getting from here to all sorts of places in the solar system. It doesnt even need to be automated, as that asteroid isnt making evasive maneuvers. It’ll be no different than landing a probe on a moon or comet. Guidance is a non-issue.
Wiki on deep impact mission here:
If we can hit a comet we can sure as heck hit a giant slow moving asteroid.
How are MIRV warheads terminally guided? Because if they they use aerodynamics, then in space they will not hit anything.
Si
Of course, we had 6 years from approval/funding to accomplishment of the mission using a specially built probe. The movie scenario gives only 24 hours using existing hardware not intended for that purpose.