Death Roids: What's the minimum time to do anything?

[Cykeisme]

As I understand from previous posts here, ICBMs are designed to take relatively low suborbital ballistic trajectories to hit other surface targets. So, assuming an asteroid was coming, how high can we loft a present-day, ready-to-launch ICBM? Since we can predict the asteroid's path, speed shouldn't be a problem, but how far away (how high) can we put a nuclear detonation on it?

For that matter, would hitting it further away really help if we're looking at an impactor that we can fragment (but not totally deflect)? Would we simply be looking at a bigger "shotgun spread" striking Earth if we hit the asteroid further away? Or could we hope for some of the fragments to get enough lateral momentum to miss the planet entirely?

I recall an older thread that has stuff that might be relevant in this discussion too (although the timeframe involved changes things quite completely):
++bbs.stardestroyer.net/viewtopic.php?f=4&t=142937

[MKSheppard]

Anyway....

Link

Two asteroids will pass within the Moon's distance from Earth on Wednesday, Sept. 8. NASA scientists will be available for satellite interviews Tuesday, Sept. 7, and Wednesday morning to discuss these near- Earth objects.

The Catalina Sky Survey near Tucson, Ariz., discovered both objects on Sunday, Sept. 5. The Minor Planet Center in Cambridge, Mass., reviewed the observations and determined the preliminary orbits. The center's personnel concluded both objects would pass within the distance of the Moon to Earth, approximately 240,000 miles. The asteroids should be visible with moderate-sized amateur telescopes.

Neither asteroid will hit Earth. Asteroid 2010 RX30 is estimated to be approximately 32 to 65 feet in size and will pass within approximately 154,000 miles of Earth at 5:51 a.m. EDT Wednesday. The second object, 2010 RF12, estimated to be 20 to 46 feet in size, will pass within approximately 49,000 miles at 5:12 p.m. EDT.

Note the date; discovered on the 5th, flyby on the 8th. 6 to 20m in size; which is enough to at least explode with the force of 100 or more tons of TNT in midair.

[Skgoa]

As I understand from previous posts here, ICBMs are designed to take relatively low suborbital ballistic trajectories to hit other surface targets. So, assuming an asteroid was coming, how high can we loft a present-day, ready-to-launch ICBM?

I don't have the numbers, since my classes covered mostly civilian rockets(from a rocket science perspective BMs are "failures" ), but I can already tell you that its not going to be much higher than what they - or rather their nukes, to be precise - would reach on the way to the other side of the world. If you have mere hours without prior warning, you won't be able to do much more than reprogram the flight plan of the missile. Meaning your are bound by whatever the engineers found to be enough to get the reentry vehicles to how far they wanted the rocket to throw them.

Since we can predict the asteroid's path, speed shouldn't be a problem, but how far away (how high) can we put a nuclear detonation on it?

Actually, in orbital mechanics speed is heigth.

For that matter, would hitting it further away really help if we're looking at an impactor that we can fragment (but not totally deflect)? Would we simply be looking at a bigger "shotgun spread" striking Earth if we hit the asteroid further away? Or could we hope for some of the fragments to get enough lateral momentum to miss the planet entirely?

My answer to all of those is: maybe. It really depends on the make up and size of the asteroid and where its predicted to hit. It might be desirable to just let it hit the sahara or it might be VERY desirable to not let it hit the middle of the pacific ocean in one piece. Not letting it hit us at all is preferable in all cases, though.
And if we are talking about the ICBM plan, than anything else that hits further out will be tried first, since due to the low "service ceiling" of ICBMs they are by definition our last line of defense. (well ok, ABM will be effective against very small rocks, but with those we won't bother throwing nukes at them.)

[Sky Captain]

Anyway....

Link

Two asteroids will pass within the Moon's distance from Earth on Wednesday, Sept. 8. NASA scientists will be available for satellite interviews Tuesday, Sept. 7, and Wednesday morning to discuss these near- Earth objects.

The Catalina Sky Survey near Tucson, Ariz., discovered both objects on Sunday, Sept. 5. The Minor Planet Center in Cambridge, Mass., reviewed the observations and determined the preliminary orbits. The center's personnel concluded both objects would pass within the distance of the Moon to Earth, approximately 240,000 miles. The asteroids should be visible with moderate-sized amateur telescopes.

Neither asteroid will hit Earth. Asteroid 2010 RX30 is estimated to be approximately 32 to 65 feet in size and will pass within approximately 154,000 miles of Earth at 5:51 a.m. EDT Wednesday. The second object, 2010 RF12, estimated to be 20 to 46 feet in size, will pass within approximately 49,000 miles at 5:12 p.m. EDT.

Note the date; discovered on the 5th, flyby on the 8th. 6 to 20m in size; which is enough to at least explode with the force of 100 or more tons of TNT in midair.

According to impact effects calculator a 20 m rock traveling at 17 km/s would produce 270 kt airburst. If a rock like this penetrated deeper into atmosphere and bursted close to ground at worst case scenarion even small asteorid has potential to destroy avarage sized town and cause casualities in few hundred thousand range.

[Zaune]

The US military is rumored to be working ways to destroy buried installations with ground penetrating nukes. Perhaps the technology can be adapted for use against small asteroids to efficiently destroy them from within rather than a wasteful surface detonation.

I was going to suggest something similar. Would it take long to retrofit an ICBM with a penetrator and impact fuse, even a fairly crude one?

[sciguy]

As I understand from previous posts here, ICBMs are designed to take relatively low suborbital ballistic trajectories to hit other surface targets. So, assuming an asteroid was coming, how high can we loft a present-day, ready-to-launch ICBM? Since we can predict the asteroid's path, speed shouldn't be a problem, but how far away (how high) can we put a nuclear detonation on it?

If you point an ICBM "straight up," it will probably reach an altitude of around 3000 km or so before it starts falling back down. Modern ICBMs use optical sensors to figure out exactly where they are in flight by looking at the stars, allowing them to make subtle course corrections as they fly to the target. You might be able to program them to look for the asteroid, which could provide an already-installed hardware solution for terminal guidance. The warheads will usually also have radar altimeters, which again give you an already-installed solution for letting the warheads know when they're actually approaching the surface of the asteroid and need to detonate. So it's possible that all the necessary hardware for such an asteroid-nuking is already available on the missile, and you wouldn't need to have engineers frantically making major modifications to the missile's hardware. As for how long it would take to reprogram the hardware to do all that, I have no idea. I guess to a large extent it comes down to how flexible the programming in the flight computer and warheads are. Perhaps a skilled programmer could just cobble up the necessary software changes and upload them to the missile/warheads by plugging in a data cable and pressing some buttons, but I certainly wouldn't count on it being that easy.

The scenario for the shortest possible reaction time might be to tell the missile to nuke some particular spot on the Earth, with the warheads set to detonate at a really high altitude. If you know exactly where the asteroid is going, you might be able to work it out so that this causes the warheads detonated near it when it's still pretty high up. I don't know whether or not you could quickly set a warhead to detonate at, say, 2000 km altitude. I suspect that the radar altimeters wouldn't work properly at that altitude, but perhaps it would be easy to put the inertial guidance system in charge of when they detonate.

As for how useful it would be to try to nuke an incoming asteroid like that, I have no idea. I suppose there has to be some size range for which it would be help.

[Sarevok]

^^

Thats a HUGE amounts of assumptions. Star trackers used in astro navigation are not same as a homing seeker. They are carefully built to point at specific stars. Similarly radar altimeters are not substitute for an actual radar. As for inertial navigation its drift error is bad enough for merely flying an airplane. Using it in place of a fuse to detonate a missile wont work at all. Furthermore making changes to guidance computer to accommodate intercepting an orbital target would also be tricky. Even US ICBMs use archaic and proprietary electronics. It would not be trivial to put together a team who can make radical changes in short time.

[sciguy]

Thats a HUGE amounts of assumptions.

Yes, it was an optimistic-as-possible assessment that's probably not very realistic. Closing velocities would probably also be a problem. I believe most warheads hit at around 4-5 km/sec, and an asteroid would probably be closing a lot faster than that. As I believe someone else already mentioned, you would probably have better luck with some sort of nuclear-armed ABM or surface-to-air missile.

[Chaotic Neutral]

A question about blowing up the asteroid:

Wouldn't having it blow into pieces mean that the vast majority of it will miss the Earth, and much of the rest will get destroyed by the atmosphere?

[JointStrikeFighter]

Depends on the distance of the strike and the Delta-Vee inflicted by the missile.

[Skgoa]

Realisticly: no, most probably none of the materiel will be propelled strongly enough to miss us. You have to remember that even with sciguy's claim of 3000 km (which I find dubious, but I put of doing the figures because the thread seemed to be winding down) you are really really near ground level already. Considering the high speed the asteroid would have at that point, I don't see how nukes would even spread it very far, even if they manage to break it up. Also, even if significant parts burn up in the atmosphere, the material would still enter the "earth" and put its energy into the system (i.e. expect heated up atmosphere leading to unpredictable weather patterns), I also don't want to speculate about poisionous substances being spread.

On the topic of terminal guidance: how exactly are the nukes supposed to steer? If you miscalculate the missile or target trajectory, there is absolutely no way you could get enough deltaV to hit anything at the speeds we are looking at. No, our best shot is nailing the flight of the rocket - coincidentaly (not really ) we have experience in that and have gotten fairly well at it.

On how the flight plan will be set up: yes, since the ICBM and its payload WILL invariably fall back to earth very soon after launch, it will essentially be the same as if we were trying to hit something. You would probably get an infinite number of points along the projected course of the asteroid were the flight path of the nuke would intercept it, you would the choose the best one by looking at what effects it would have on the projected impact sites. You could possibly get a number of nukes in the same spot at the same time, too.

[sciguy]

Realisticly: no, most probably none of the materiel will be propelled strongly enough to miss us. You have to remember that even with sciguy's claim of 3000 km (which I find dubious...)

Wikipedia claims 7 km/sec velocity right after the boost phase. That would get you in the neighborhood of 3000 km if pointed straight up. Trying to do really exact calculations is probably pointless, since there's probably a lot of variation from one specific type of missile to the next.

http://en.wikipedia.org/wiki/Icbm

[Skgoa]

And the problem with that number is that its not at all comparable to launching straight up, in fact I am certain it is much higher than what one could reasonably expect from such an idiotic way of launching a rocket. I don't want to insult you, but you don't seem to know what you are talking about - since there are severall (very basic) things wrong with your post.

[sciguy]

And the problem with that number is that its not at all comparable to launching straight up, in fact I am certain it is much higher than what one could reasonably expect from such an idiotic way of launching a rocket. I don't want to insult you, but you don't seem to know what you are talking about - since there are severall (very basic) things wrong with your post.

Perhaps you could explain the "several, very basic" things wrong with my post, and how you would go about calculating a maximum achievable altitude?

[Skgoa]

1. The speed you cite is reached under a very different launch trajectory, thus is absolutely meaningless to our discussion.
2. Even if we decide to use that number, it still has the problem of being a speed vector that is NOT going straight up. Only a portion of that is actually propelling the nuke higher... meaning you can't do the math with that number unless you know the height and angle at which the rocket was moving at cut-off and extract the pure "height gaining" part of the momentum.
3. Rockets aren't launched straight up for a reason. We nicknamed it GRAVITY. If the paylod+bus reach only 1100 km on a normal launch (i.e. one were much better performance is garanteed) I really really fucking doubt the same rocket could reach three times as high when having to fight gravity full on for the whole duration of the flight.
4. And as a minor point: launching straight up is... difficult. For starters you need to define straight, since the rocket will be in at least two frames of reference during its flight.

=> The actual speed you get from a rocket launched straight up will be much lower than what you expect and it can't be calculated with only knowing the speed at cut-off on a normal flight.


To calculate the maximum height, I would combine Tsiolkovsky's equation (no Idea what its called in english, but we call it Raketengrundgleichung) with an equation for gravity at certian distances (Newton comes to mind) to get the acceleration during boost phase. We will probably have to integrate over the whole time the engine is runing, since weight and height of the rocket change. Then we would have the speed we are looking for. The rest is just finding at which heigt the velocity reaches zero. We would have to take the changing acceleration through gravity into it, but thats the only hard thing I can see. Then we have the height we are looking for.
And after that I would calculate the actual potential of the rocket and show you that launching it at an angle will be much much better.

Note however, that its the summer holiday over here and I have much work to do before the next term starts. So I have no intention of actually doing the math.

[sciguy]

Skgoa, earlier in the thread you talked like you've had physics classes that cover rocket flight and orbital mechanics, but you sound like the one who doesn't know what you're talking about. If you know that it's going 7 km/sec after the boost phase, you don't need to work the Tsiolkovsky equation, since you already know that the rocket is capable of 7 km/sec delta-V. Unless you think some of that delta-V came from somewhere other than the rocket engine? It's not like the Earth's gravity will pull harder if your velocity has more of an upward component. The rocket has already climbed upward against Earth's gravity to a height of 100+ km, while also achieving a velocity of 7 km/sec, at which point it goes ballistic. The only question, then, is how high could it get if you pointed all 7 km/sec straight up rather than at a 45 degree angle (or whatever non-perpendicular path ICBMs take).

Your claim about getting better altitude out of a rocket by launching it in any direction other than perpendicular to the surface seems absurd on its face. Your rocket has a fixed potential delta-V. If you expend it on anything other than going straight up, you won't get as high as you might have gotten.

[Skgoa]

And as long as you claim that instead of asking a rocket scientist, I am not going to talk to you about it any further.

[Sea Skimmer]

^^

Thats a HUGE amounts of assumptions. Star trackers used in astro navigation are not same as a homing seeker. They are carefully built to point at specific stars. Similarly radar altimeters are not substitute for an actual radar. As for inertial navigation its drift error is bad enough for merely flying an airplane.

Airplanes have you know, wind to fuck with them, big difference. Ballistic missiles can drop a warhead within a few hundred meters of a target at six thousand miles. What do you think happens to a say 100 meter diameter rock if a 475kt warhead goes off a few hundred meters away? All you are doing to engage a rock, which has a quite predictable course once it enters radar tracking range, is firing a ballistic missile on a ballistic trajectory which ends at a very high point of burst. Super accuracy is not required because a moderately high yield nuke will blast the shit out of usefully big rock at a range of a kilometer. Fire a pattern of warheads and a kill is assured.

The fast the incoming rock BTW, the more predictable its course will become.

Using it in place of a fuse to detonate a missile wont work at all.

In all reality a timer will work fine. If the radar fusing would work or not is a question you cannot possibly know the answer too.

Furthermore making changes to guidance computer to accommodate intercepting an orbital target would also be tricky. Even US ICBMs use archaic and proprietary electronics. It would not be trivial to put together a team who can make radical changes in short time.

Nope you fail to keep up to date. All Minuteman III guidance systems were completely replaced by 2008 under a contract with Northrop Grumman. So its not only modern, people who worked on it in very recent history exist. Other programs have modernized the flight control systems, rocket motors and replaced a fair number of warheads and warhead buses with W87's leftover from Peacekeeper.

[Marko Dash]

is there enough volume in the warhead bay of a MIRV ICBM to house a second stage rocket with a single warhead?

[Sea Skimmer]

The bus that carries the MIRVs already is rocket powered, this is how it’s able to maneuver and aim the MIRVs which then fall on separate ballistic trajectories onto the target. The fewer warheads, the more agile the bus will be because it has less mass. However it’s not a second stage, it’d be the forth stage on a Minuteman III. You’ve certainly got the volume that you could design a better bus with bigger fuel tanks and a more powerful rocket motor, leaving space for only one integral warhead, but that would take years and many flight tests to develop.

At that point we wouldn’t use an ICBM as the launcher, we’d more likely place it on a dedicated space booster more suited to this task.

[Sky Captain]

What do you think happens to a say 100 meter diameter rock if a 475kt warhead goes off a few hundred meters away? All you are doing to engage a rock, which has a quite predictable course once it enters radar tracking range, is firing a ballistic missile on a ballistic trajectory which ends at a very high point of burst. Super accuracy is not required because a moderately high yield nuke will blast the shit out of usefully big rock at a range of a kilometer. Fire a pattern of warheads and a kill is assured.

Would a standoff blast of few hundred kt actually be able shatter the the solid rock into small pieces. There would be no direct shock wave if a nuke detonates few hundred m away. Could a sudden heating and evaporation of surface layer from radiation cause enough shock to break asteorid apart? If asteorid is just a piece of dirt and ice then it would work but what if it is made of solid rock or iron. Ideally you would want to have individual fragments smaller than 10 m since those are likely to burn up/explode harmlesly at high altitude.

[Skgoa]

Sea Skimmer: Adding a fourth stage is not going to get much more deltaV, even if we ignore the added weight it would most likely result in. Rockets are designed for very precise weight/speed capabilities and most importantly the weight ratios are tuned for maximum effectiveness.

[Skgoa]

ghetto edit: I meant Marko Dash. :/

[Sea Skimmer]

Would a standoff blast of few hundred kt actually be able shatter the the solid rock into small pieces. There would be no direct shock wave if a nuke detonates few hundred m away. Could a sudden heating and evaporation of surface layer from radiation cause enough shock to break asteorid apart? If asteorid is just a piece of dirt and ice then it would work but what if it is made of solid rock or iron. Ideally you would want to have individual fragments smaller than 10 m since those are likely to burn up/explode harmlesly at high altitude.

Nickel or iron would be much harder to deal with. But most asteroids are thankfully rock and rock will shatter from the thermal pulse to a considerable depth. While we have no blast wave, all the energy that would be blast still exists, it just stays as being radiation. So the result is a far more intensive thermal pulse and a lot more hard radiation which will turn into heat as it passes through rock, adding depth to the heating effect. Note also that the process of dumping this heat into the rock actually does create a shockwave through the rock, all that mass being vaporized and blown off has to have an opposing reaction. I couldn't tell you just how big a rock this will break up, but it should surely be into the hundreds of meters.

This is also the reason why I keep saying we'd use salvo. If a nuke went off on each side of the asteroid then we get a crushing effect, and cracks from each side are more likely to connect and lead to a mass breakup. Anyway we have fair reason to believe that we could score a direct hit on a rock that was at least 200-300 meters across (free falling ICBM warheads should actually be more accurate bursting at very high altitude because the low level wind does cause inaccuracy), and its doubtful we'd decide to nuke something much smaller then that.

Fragments still impacting will always be trouble, but ABM systems and even some higher end SAM systems ought to be able to engage them if they turn off whatever radar filters they have to ignore normal meteorites. These modifications might actually take longer to accomplish then mods to the nuclear systems but one might dream that someone at Lockheed or what have you already thought of it.

[someone_else]

Adding a fourth stage is not going to get much more deltaV, even if we ignore the added weight it would most likely result in. Rockets are designed for very precise weight/speed capabilities and most importantly the weight ratios are tuned for maximum effectiveness.

I think he was talking about dumping some of the multiple warheads an ICBM is supposed to carry and place a fourth stage (or maybe a fuel tank for the aiming thingy to make it become the fourth stage with little effort)


And here a seemingly stupid question: What about fallout?
If you hit an asteroid and manage to blast it to pieces that then reenter, you still get fallout.
If you just redirect it, the fallout shouldn't be so severe (or shouldn't exist).

Would such fallout be a problem? Even if it isn't, any eyeballed estimate of it?

Yes, I know that someone so desperate to throw ICBMs on a 'roid is highly unlikely to give a damn, but I'm curious nontheless.