Shooting blocks of Uranium from planet to planet


by EthanNino
Tags: atomic, blocks, bomb, planet, shooting, spacegun, uranium
EthanNino
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#1
Feb3-14, 12:48 AM
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This idea stems from the Pascal B nuclear test, which placed a 900kg steel plate over a shaft in where a nuclear explosive was detonated: http://en.wikipedia.org/wiki/Operati...teel_plate_cap

The plate shot up at an estimated 66km/s, or 6x escape velocity. Say you could shoot blocks of weapons grade Uranium from planet to planet, moon to planet, or vice versa. If I understand correctly, the compression when the block lands on the planet's surface would be enough to cause a fission reaction right? These blocks would be small enough to be almost undetectable before it's too late, but big enough to cause serious damage on landing. Unlike the Pascal B test, the launch would be less of an abrupt blast, and more like a slow acceleration so the Uranium wouldn't blow up inside the shaft/gun barrel from compression. Instead of one block, you could shoot a shotgun blast of blocks to maximize the chances of hitting a target.

So this could be used as a weapon, or possibly a means of terraforming a planet. If you could shoot fission/fusion devices accurately to, say, the ice cap of Mars, you could cheaply sublimate enough CO2 to cause a positive feedback loop and heat up the planet. Also, a means of redirecting asteroids on a collision course with Earth. Would this work? I don't know much about nuclear physics beyond the wiki page.
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SteamKing
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Feb3-14, 01:37 AM
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Sure, you could do that if you don't mind making Mars glow in the dark from all the radioactive fallout.

http://en.wikipedia.org/wiki/Nuclear_fallout
DrDu
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#3
Feb3-14, 02:57 AM
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...if there were no atmospheric friction...

EthanNino
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#4
Feb3-14, 09:50 AM
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Shooting blocks of Uranium from planet to planet


Say the block was adequately heat shielded so that it could survive the launch and reentry. Would the force of impact be enough to trigger a fission reaction?

Also, I thought the fallout had a relatively short half life, right?
http://www.straightdope.com/columns/...ver-so-quickly

Second, most of the radionuclides had brief half-lives--some lasting just minutes. The bomb sites were intensely radioactive for the first few hours after the explosions, but thereafter the danger diminished rapidly. American scientists sweeping Hiroshima with Geiger counters a month after the explosion to see if the area was safe for occupation troops found a devastated city but little radioactivity. Water lilies blackened by the blast had already begun to grow again, suggesting that whatever radioactivity there had been immediately following the blast had quickly dissipated.

Which isn't good for terraforming, the more fallout at the poles, the more heat and the more ice melted/sublimated.
phyzguy
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#5
Feb3-14, 10:38 AM
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It helps to do some back-of-the-envelope calculations on these things in order to understand the magnitude of the challenge of changing a planetary atmosphere. Say you could generate a 1 megaton nuclear explosion this way. A megaton is 4E15 Joules. The total mass of the Martian atmosphere is 2E16 kg, mostly CO2. Say you wanted to increase the atmospheric pressure 10X, in order to make a significant change. So you need to add 2E17 kg of CO2 to the atmosphere. The heat of sublimation of CO2 is about 600 kJ/kg, so you need about 1E23 Joules of energy to do this. This would require between 10 million and 100 million 1 megaton explosions, assuming all of the energy goes into vaporizing CO2 (which of course it won't). Does this still sound like a good idea?
SteamKing
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#6
Feb3-14, 11:44 AM
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Quote Quote by EthanNino View Post
Also, I thought the fallout had a relatively short half life, right?
http://www.straightdope.com/columns/...ver-so-quickly
Hey, if you don't mind some radioactivity in your crops or water supply, go for it. Different types of fallout have different effects on living things. Your thyroid gland can retain radioactive iodine which will eventually give you thyroid cancer. The radiation which your body can tolerate when it is kept outside is one thing. When you ingest radioactive material, your body has almost no way to protect itself from the damaging effects of radiation on tissues.

It also matters where the bombs are detonated. Air bursts high in the atmosphere generate the least amount of fallout, but winds high in the atmosphere disperse this material over a larger area. Ground bursts generate a great deal of fallout because of irradiation of the soil.

Surprisingly, the worst fallout problem is generated by underwater explosions, like those done at Bikini atoll. The contaminated water and other debris means that radiation quickly enters the food chain and persists over many years. The islanders were evacuated from Bikini before the tests commenced, and allowed to return briefly after the tests ended. However, when it became clear that the islanders were developing increased cancer due to the fallout, they were evacuated again and the atoll is considered uninhabitable today.
gmax137
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#7
Feb3-14, 01:14 PM
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Quote Quote by SteamKing View Post
... Your thyroid gland can retain radioactive iodine which will eventually give you thyroid cancer...
Iodine-131 has a half life of 8 days, whether it's in your thyroid or not. So a couple of months after the release it is essentially all gone. Not that that makes planetary uranium bombardment a great idea, but...
.Scott
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#8
Feb3-14, 02:34 PM
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Quote Quote by EthanNino View Post
If I understand correctly, the compression when the block lands on the planet's surface would be enough to cause a fission reaction right? These blocks would be small enough to be almost undetectable before it's too late, but big enough to cause serious damage on landing. Unlike the Pascal B test, the launch would be less of an abrupt blast, and more like a slow acceleration so the Uranium wouldn't blow up inside the shaft/gun barrel from compression.
Let's see how minimal we can make the acceleration during launch - making the most generous assumptions. We'll have no friction after launch so all we need is escape velocity (11,200 M/s). We'll use the deepest bore every accomplished (12,262 M). So the time spent during the acceleration is about 2.19 seconds (t=2*d/v). So the acceleration will be 5115M/sē (a=v/t) or about 522g's.
I'm wondering if a fission bomb device could be constructed that would remain functional after 522g's for 2.19 seconds?
SteamKing
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Feb3-14, 03:27 PM
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Quote Quote by gmax137 View Post
Iodine-131 has a half life of 8 days, whether it's in your thyroid or not. So a couple of months after the release it is essentially all gone. Not that that makes planetary uranium bombardment a great idea, but...
It doesn't matter that I-131 has a half-life of 8 days. This stuff is taken up by the body and stored in the thyroid gland unless you take a dose of KI (potassium iodide) to keep the body from accumulating the hot stuff. The damage to the thyroid gland is done while the I-131 is stored there.
.Scott
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#10
Feb3-14, 04:40 PM
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Quote Quote by SteamKing View Post
It doesn't matter that I-131 has a half-life of 8 days. This stuff is taken up by the body and stored in the thyroid gland unless you take a dose of KI (potassium iodide) to keep the body from accumulating the hot stuff. The damage to the thyroid gland is done while the I-131 is stored there.
If you start with 1 gram of I-131, wait 120 days, and then ingested it. You will be ingesting approximate 1 grams of Xenon gas and 32 micrograms of I-131. That's about 0.1% of the mean lethal dose. So coating Mars with I131 would not spoil the planet forever - or even for a year.
mfb
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#11
Feb4-14, 08:33 AM
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It is highly questionable if that steel plate ever escaped earth. Asteroids of that size disintegrate long before they reach the denser parts of the atmosphere.

Quote Quote by .Scott View Post
Let's see how minimal we can make the acceleration during launch - making the most generous assumptions. We'll have no friction after launch so all we need is escape velocity (11,200 M/s). We'll use the deepest bore every accomplished (12,262 M). So the time spent during the acceleration is about 2.19 seconds (t=2*d/v). So the acceleration will be 5115M/sē (a=v/t) or about 522g's.
I'm wondering if a fission bomb device could be constructed that would remain functional after 522g's for 2.19 seconds?
I would be surprised if that is not possible.
There is a big disadvantage, however: You need a nuclear explosion to launch the object. It is way more convenient to use a regular rocket to deploy a regular nuclear warhead. The object is slower, it will certainly (well, at least >95%) survive the way through the atmosphere.


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