Earth Impact! How To Deflect A Doomsday Asteroid With An A-Bomb

The year is 2035 and a Near Earth Object (NEO) search team discovers an asteroid that appears to be on a collision course with Earth.

There is no panic at first because the uncertainty in the asteroid's position is large and the asteroid's impact ellipsis is also very large and only a small part of that ellipsis intersects with the Earth.

As the days and weeks go by the uncertainty in the asteroid's emphemeris parameters is steadily reduced and shockingly as the intersection ellipsis with the Earth gets smaller it also moves more on target with the Earth.

Eventually the entire intersection ellipsis covers the Earth. An impact from this object is 100% guaranteed.

The asteroid is 1600 metres in diameter (1 mile) and is estimated to be made of porous rock and so will have a density of about 1500 kg/m³. Calculations show that it will hit the Earth at about 30 km/s.

The impact will be in the ocean about 40 km off of the eastern seaboard of the United States and about 200 km from Washington DC. The resultant crater is calculated to be about 18 km in diameter (11 miles).

The energy of impact will be equivalent to 350,000 megatons of TNT which is far more power than the world's combined nuclear arsenal.

The impact will create an earthquake of magnitude 8.1 in Washington and exposed people will suffer 3^rd degree burns and their clothing will catch fire and the surrounding forests will all ignite.

The impact will hit a spot with a 500 metre water depth and the resultant tsunami is expected to be about 500 ft high.

No bueno.

So How Do We Deflect This Sucker?

The asteroid is made up of porous rock so simply hitting it with nuclear weapons will likely just cause it to break up and turn it from a bullet into a shotgun blast. The impact damage will not be averted, it will only be spread out over a much wider area.

So, the way to do this might be to explode the weapon just off to the side of the asteroid.

Imagine a ping pong ball in the palm of your hand. Purse your lips and hit it with a puff of air. The ping pong ball will go flying off in the opposite direction away from you.

This is the idea behind a stand-off nuclear explosion and it goes as follows.

You send a nuclear weapon strapped to some sacrificial mass and park it off the side of the asteroid some distance away. Detonate the weapon and both the weapon and the sacrificial mass are vapourized.

The rapidly expanding shell of gas will hit the asteroid and deflect it. If you tune your parameters right, and there are several, you can both deflect the asteroid and be gentle enough to not break it up.

The Tuneable Parameters

1. Weapon Yield

Weapon yield is the obvious first parameter you want to get right. Too little and the asteroid won't deflect much. Too much yield and you run the risk of splitting up the object.

2. Distance

The distance that you park your weapon from the asteroid is the second tuneable parameter. Too close and you risk breaking up the object, too far away you run the risk of not deflecting it very much at all.

3. Sacrificial Mass

The puff of gas that will deflect the asteroid will come mostly from the vapourized mass that the weapon is strapped to. Too much mass might mean that the gas will expand out too slowly, too little mass will mean that the gas will not have enough total momentum to deflect the asteroid.

If you tune your parameters right then you will get the result you want. A firm but gentle push against the entire surface of the asteroid that is facing the weapon as well as the much needed deflection.

Launch and Timing Issues

There might be issues with getting the weapon to the asteroid in time. Hopefully the asteroid will need to make a few orbits of the Sun before its path intersects with the Earth's and time will be plentiful.

However if it is not then a multi-rocket, multi-launch strategy might be needed. For the first launch you send the weapon and its guidance rocket into Low Earth Orbit. A second launch will send a large tank of fuel into Low Earth Orbit that will dock with the weapon and provide the fuel for all of the delta-v that you will ever need.

There is simply no time for a low-energy Hohmann transfer orbit for this job, we want to get there in the quickest straightest path possible. Since the fate of the Earth is at risk money is also no object so you would want to send a bunch of these weapons separated by a day or two from each other.

The earlier you can get to the asteroid the better. A small deflection very early on will generate a large deflection distance by the time it reaches the Earth in a few years.

If the time to impact is short (a few months) then the problem becomes exponentially more difficult.

Closing Words

The day may come when humanity is faced with the issue of deflecting an object in space. Nuclear weapons have been proposed and criticized because of the threat of just breaking the object up into a million pieces.

The idea of detonating a weapon just off to the side and hitting it with a more "gentle" expanding sphere of gas just might be the answer to this tricky problem.

Thank you for reading my post.

Post Sources

[1] Near Earth Object Search.
[2] Impact Earth! impact calculator.
[3] How destructive is the Earth's nuclear arsenal?
[4] Hohmann transfer orbit.