OT?: Goodbye to an era

Think about a baseball bat or a golf club hitting a ball. You can transfer a lot of momentum in a few milliseconds.

The xray and gamma radiation from an h-bomb would soak into and vaporize enormous amounts of rock or ice or iron or anything nearby. No contact or velocity matching would be needed... it would be a drive-by shooting. Launch a dozen of them, at different times, all designed by different countries, and a few will succeed.

If you vaporize 1% of the mass of a rock, and the plasma leaves at, conservatively, 1000 meters/second, what's left heads off at 10 m/s in the opposite direction. Do that a year, or even a month, before it intersects earth, and it misses.

John

Surface blasts are not that powerful, especially against hard targets. The energy is ~V^2 whereas the transferred impulse is only ~V. If a charge could be buried at 1m under the surface, that would improve the efficiency by orders.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Yes, except that it is more like using a toothpick to jab at a bowling ball.

You speak of an instance where the force applying object is more massive than the object it is pushing.

The case would not be such with an asteroid that needed to be pushed into a different path. The nuke would be far less energy.

Hell, there is a 4 foot marble ball at Fry's out here. It is more like trying to push that with a toothpick one short duration at a time. Or say a 'Ladyfinger' type firecracker. Hell, a million of 'em wouldn't net you anything like what you want.

You guys need to get your ratios and proportions right.

I doubt that much more than a quarter inch thickness would result, and that only directly perpendicular to the blast center.

Well, a 15Mt explosion left a crater 200 ft deep and a mile across in one H bomb test.

...and use the Shuttle to get them up there, right, AlwaysWrong?

You never cease to amaze, AlwaysWrong.

There are two major differences between a lightning strike and a nuclear explosion at a suitably close distance from an asteroid:

1. In a lightning strike, nearly all of the energy is dissipated between the source and the target. Only an extremely small fraction of the energy is dissipated in what the lightning strikes.

In comparison, a close nuclear explosion in vacuum would have nearly half of its energy reaching the target. Not that all 49% or whatever is actually absorbed by the target, but I see a couple orders of magnitude higher percentage than with a lightning strike.

To add on to this, a typical lightning strike has energy merely in the hundreds of megajoules, equivalent to .1-.2 ton of TNT. The extremely small percentage of that dissipated into solid material also tends to have little of even that resulting in vaporization, let alone (as mentioned below) presence of an atmosphere being a major impairment to converting heat energy to mechanical energy. (However, lightning does occaisionally blow up a tree.)

1. Nuking an asteroid to deflect it has 2 advantages of environment of a vacuum instead of an atmosphere: One is that targeted heated material vaporizes a lot more easily in a vacuum than in an atmosphere. The second is that vaporized and dislodged target material has a tendency to be catured by an atmosphere, resulting in the momentum of the ejected material is returned to the atmosphere-bearing body.

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I do agree that adding tubes to improve directionality of a mass ejection and to increase pressure developed where the ejection starts would be an improvement. However, I see a problem with "gun barrels" large and massive enough to survive a nuclear explosion long enough to do their job being payloads anywhere as practical as enough nuclear warheads to do the job without these "gun barrels".

Deflecting an asteroid a year in advance is about like that. But people like Issac Newton have showed us how to do the math.

OK, a bullet hitting a frying pan. If you transfer X N-s of momentum into an object, it acquires the same net velocity no matter whether the momentum is applied slowly or quickly. Physics.

A megaton nuke delivers a lot more energy than a hundred rocket engines. And it's much easier to apply: fly by, boom, repeat as necessary.

How many firecrackers does it take to equal a megaton of TNT equivalent?

Seriously: try doing the calculation. Order of magnitude is close enough. Do it.

There are battleship shells that out-weigh the Fry's thing. They are blasted out of a cannon barrel in milliseconds. With a couple of silk sacks of gunpowder. Imagine what a million tons of TNT can do.

You need to learn some physics. Except that you're math phobic.

John

The idea is that, in vacuum, a lot of the bomb's energy is in xrays and gamma rays; momentum transfer will be trivial by comparison. The exposed surface of an object will absorb the radiation and turn to vapor and plasma, and blow off. That will deliver a massive momentum kick to what's left.

There are no hard targets for gamma rays.

John

But it did not liquefy nor 'turn to plasma' any of it to speak of.

Back on track now?

That is a fairly big button press though. It did use the atmosphere, however.

Which is why the SRBs would be the choice.

Since there is no need for recovery of anything, make a big hole and then use a nuclear device or string of them to make a nuclear rocket motor.

There is a nuclear rocket motor that relies on small bursts already in the research channels.

Scaling something like that up would not be easy, and would have to have the payloads fed in individually after each blast gets executed.

If anything, the atmosphere limited the amount of material ejected. On a comet or asteroid the low gravity would have meant that most of the displaced material would have been permanently lost. The biggest problem with nukes is shattering the asteroid or comet and multiplying the danger.

Do you mean vaporizing a 50 meter radius hemisphere? Probably being ejected at largely around speed of sound of 2000 C silicon dioxide or something like that? (I figure by square root of temperature ratio nad inverse of molecular weight ratio to room temperature air, to be 750 meters/second at least for some sort of rough ballpark. I would divide that by pi/2 for average velocity component perpendicular to the asteroid surface in a hemispherical eruption, for 477 meters/second.)

I would like to figure a mere 10 meter radius hemisphere getting such a fate! Make that 2,512 cubic meters out of 4.71 E9!

At this rate, I work out the asteroid to have its velocity changed by

Suppose we do this to such an asteroid 2 years before impact. I get changing the earth-approaching path of the asteroid by 16 kilometers.

That does not sound like a lot yet...

Even however, I think it would take quite a few megatons to turn a 10 meter hemisphere of rock into vapor... With density of 2.7 metric tons per cubic meter, accelerating 2,512 cubic meters of "typical rock" to 750 meters/sec requires kinetic energy of 1.91E12 joules... a mere .455 megaton! I think that would only require several to a few dozen megatons of nuclear warheads!

At this rate, I see an easily-doable amount of nuclear firepower hardly budging a 2 km diameter asteroid with 2 year warning. But what about a

Nuclear firepower of a few hundred megatons to get an order of magnitude greater deflection of a 2/3 km diameter one or same deflection of a 1.45 km diameter one (or more) (10 years in advance) sounds easy enough to do.

I think this is not that far off base!

I have a lot of agreement there!

- Don Klipstein ( snipped-for-privacy@misty.com)

Shame that you haven't seen more of them.

Wait... that likely accounts for your behavior!

Bwuahahahahahaha!

You would probably do a type of 'shaped charge' sort of thing, where the nuke is designed to impart much of its radiation in a specific direction. Maybe an x-ray laser type of arrangement, where the nuke is just to charge the lasers...

Charlie

The Castle Bravo nuclear bomb had yield of 15 megatons (weighed 10.7 tons), and left a crater 2 km in diameter and 75 meters deep. If the crater was paraboloidal in profile, then the volume ejected from it was .08 cubic kilometer (if I figured correctly). That is 80,000 cubic meters.

IIRC, that bomb was detonated a couple meters or something like that above the surface. Think what would have happened if it was detonated a meter or a few below the surface.

We're talking about pushing it in a vacuum, and only need to change its velocity by a fraction of a mm/sec to maybe a few mm/sec.

How can you know that? It sure disappeared, and a lot of it became very radioactive. The top few feet was probably heated to millions of degrees.

John

If a nuke detonated, say, a couple of radii away from an asteriod, the solid angle intercepted might be a few per cent of the bomb's radiation; most of it would miss and be wasted. The rock or iron or whatever that did get lluminated would get awfully hot. The top few meters would probably become plasma, deeper stuff would merely vaporize. Those depths depend on the wavelengths and penetrating power of the bomb's radiation, and on what they hit, iron vs ice for example. A lot of stuff will get vaporized anyhow.

Probably being

That's conservative. The top layers might be 100K C. Nukes are ferocious up close. The gammas from a small fission primary heats the secondary of an hbomb enough to ignite nuclear fusion a meter or so away. That's pretty hot.

(I figure by square root of temperature ratio nad

I seem to recall that one hbomb vaporized an entire Pacific atoll. Look at the water columns and clouds from ocean blasts; more like kilometer sized spheres vaporized than 10 meter ones.

A magaton blast can theoretically vaporize 1.7e9 kg of water, if I did the math right.

John