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bizdog1
2005-Feb-10, 11:51 PM
Most movies these days deal with the concept of deflecting an asteroid already on its path to Earth. But what would it take to attempt to change the path of an asteroid to cause it to hit the earth? For those astronomy-minded folks, I'm just curious what sized nuclear bomb would be necessary if all the variables were considered "average".

N C More
2005-Feb-11, 12:26 AM
How large is the asteroid? BTW, why the 'death wish' scenario?

Here (http://www.space.com/businesstechnology/technology/nudging_not_nuking_000211.html) this might help.

edited to add link

Inferno
2005-Feb-11, 12:42 AM
What's interesting is all those recent movies seemed to deal with the event of a comet hitting an asteriod and sending it towards Earth. This to me seems like a much more unlikely event than just simply discovering an asteriod on an Earth intercept path.

joema
2005-Feb-11, 01:04 AM
Given years of warning, a mass driver vehicle could be devised to land on the asteroid, and gently nudge the asteroid off course.

Given several months of warning, existing boosters (e.g. Delta IV Heavy) could lift 60 megaton-range warheads to intercept. A terminal guidance package would also be needed. A very small asteroid, say 50-80 meters, could probably be vaporized totally. Note the Arizona meteor crater is thought caused by an 80 meter asteroid.

Larger asteroids cannot be vaporized by any warhead current boosters can lift. Even a Saturn V could only lift an approx. 200 megaton warhead to earth escape velocity.

Given weeks of warning, the existing ICBM force could be modified to intercept it. On the 10-warhead Peacekeeper and 8-warhead Trident II D-5 missiles this would consist of removing around all but one warhead to give sufficient delta V to reach escape velocity, plus adding ground control to the steerable "bus" for refined targeting. That's especially needed for a precise stand off detonation. You don't want to detonate on the surface.

The problem is the warhead is only 300-400 kilotons. However there are currently 50 Peacekeepers and 264 Trident II D-5 missiles available, so multiple shots would be possible.

Given just days warning, the only option would be stripping all but one warhead off, and reprogramming the inertial guidance, and hoping for the best. After several hundred thousand miles it could probably get within a mile or two, but the results would be unpredictable.

In general you want a precise stand off detonation to avoid fragmenting the asteroid. At 500-1000 meters, the heat and radiation from a large warhead would vaporize a thin layer of rock, the resultant impulse pushing the asteroid the opposite direction. It wouldn't fragment it, as there's no blast pressure in space.

While fragments intuitively may seem less dangerous, in general it's worse. The reason is similar to why a cluster bomb or multi-warhead MIRV ICBM is more destructive than a single warhead of the same total weight. Due to the inverse square law, one big asteroid (or warhead) only does so much damage. Damage drops off as the SQUARE of the distance. Three times the distance from ground zero, only 1/9th the damage. However using multiple small warheads (or fragments) a much larger area is affected.

The only exception would a pulverized asteroid where all fragments were smaller than, say, 10 meters, where they burned up in the atmosphere. Based on our current knowledge, achieving that is unlikely.

Brady Yoon
2005-Feb-12, 03:25 AM
^^ Wouldn't the total mass of the asteroid still enter the atmosphere?

The BA said something like that on his deep impact review if i recall correctly

darkhunter
2005-Feb-12, 09:32 AM
Most (if not all) of the mass would enter the Earth atmosphere--and being the same mass, would add just as much energy to the Earth--it'll just be more spread out and leave many smaller craters instead of one really big crater. Life on Earth would be just as dead :(