How can I make an anti-matter "rod" warhead for interplanetary delivery?

Question

In the story I'm writing, a civil war is fought between Earth and Mars. Although there is a huge orbital and ground war campaign, conditions deteriorate to the point where Earth decides to unleash the most powerful weapon in its arsenal: The anti-kinetic rod. Using a delivery system similar to the "Rods from God" concept, the weapon can be deployed quickly in large numbers through satellite-deployed, kinetic bombardment rods. But unlike kinetic bombardment, the true power of the weapon is in its payload of 1 pound of anti-matter; making it a continent killing weapon.

But in order for it to work, the payload has make it to the ground. Because antimatter is ridiculously unstable, it needs to be contained in order to survive the trip by avoiding contact with normal matter. Is there a way to do this with a real or conceptually possible material, or without a ridiculous amount of energy (aka, a power supply that could actually fit on a rod)?

Answer 1

Any realistic antimatter weapon would resemble a traditional light bulb more than a kinetic energy impactor, and considering the mechanism of energy release, accelerating antimatter to high velocities really does not add anything in terms of damage (although for targeting solutions and to ensure the antimatter makes it through any defensive screen, a high velocity delivery system is a must).

The antimatter must be held in a vacuum to prevent it from interacting with matter before it is supposed to. It should also be cooled to as close to absolute zero as possible to make it relatively non reactive (no stray anti particles wandering from the surface of the antimatter bundle), and it would have to be suspended within a powerful magnetic or electrostatic field to keep it entered in the container.

Now since a microgram of antimatter reacting with a microgram of matter is the equivalent of 43kg of TNT (thanks to the atomic rockets boom table), a device carrying a pound of antimatter (@ 500 grams) should have the energy release of about 21.5 megatons. To give you an idea, modern strategic nuclear weapons are thought to have a yield of about 300 Kilotons. The only semi plausible suggestion that a 20 megaton weapon was ever deployed was speculation I read once that a regiment of SS-20 "Satan" ICBMs was held by the former USSR to carry one 20 megaton weapon each, with the sole purpose of turning Cheyenne Mountain into Cheyenne Lake.

So the question is what would EarthForce be targeting which requires such firepower? Have the Martians dug into Olympus Mons or the other Tharsis volcanos? Is Earthforce going to crack open the moons of Mars and neutralize them as potential orbital installations? Are the Martians hiding under the polar icecaps? Since the creation and use of antimatter is going to be very expensive and potentially quite dangerous for the user to handle, these targets must be extremely high value. Using antimatter for ground bursts provides some of the energy release will be converted into seismic activity, and the shockwaves travelling through the ground could collapse tunnels and bunkers, but airbursts could potentially sleet wide areas of Mars with highly energetic gamma radiation, as well as blasts of exotic particles moving at close to light speed, in addition to massive blast waves travelling through the atmosphere. Any surface installations would almost certainly be destroyed (like solar panels and communications antenna).

Of course there is a simpler way to get that sort of bang for the buck and more:

http://www.nextbigfuture.com./2009/02/unmanned-sprint-start-for-nuclear-orion.html

There was a three page paper: Nuclear explosive propelled Interceptor for deflecting objects on collision course with Earth. Johndale Solem, Los Alamos, proposed unmanned vehicle. No shock absorber or shielding. The pulse units were 25kg bombs of 2.5 kiloton yield.

Get to high velocities with only a few explosives and small shock absorbers or no shocks at all. Launch against a 100 meter chondritic asteroid coming at 25 km/sec. 1000 megatons if it hits. Launch when it is 15 million kilometers away and try to cause 10000km deflection. A minimal Orion weighing 3.3 tons with no warhead would do the job. 115 charges with a total of 288 kiloton yield. Launch to intercept in 5 hours. Ample time to launch a second if the first failed.

So this beastly device can be launched directly from Earth or the Moon, accelerate at 100g and strike with a gigaton of energy on impact. In terms of cost, I would suspect that since most of the parts would be churned out on an assembly line, and you have no exotic antimatter containment to deal with, it would be much cheaper to have these in squadrons based on the Moon or maybe even on NEO's, to provide the most dispersion and coverage for EarthForce's premier strike weapon.

And don't try to run away:

Mars Express Another aspect of the fast acceleration that is possible is that an unmanned Orion go from earth or earth orbit to Mars (decelerate at halfway) and get to Mars in under one day going at 100Gs if Mars and Earth are in the close approach. If the unmanned version was going at 1000Gs (which was a design that is possible), then Earth to Mars could be done in a few hours. At about 300Gs and you would be looking at a Mars Overnight package delivery.

Of course it is always possible the Martians have been thinking along these lines as well.....

Answer 2

The über-hard SF writer (and real physicist) Robert L. Forward describes a solution in his novel Camelot 30K.

As I recall, he summarized that the “trap chip” is the size of a AA battery and contains as much energy as a tanker truck of gasoline.

It is based on arrays of penning traps fabricated like RAM chips on a semiconductor wafer.

An explosive could be much denser, as it doesn’t need the mechanism around each trap to safely extract the antiproton and route it to a safe place to allow annihilation. So, I expect you would be able to store an antiproton in a semiconductor area maybe 10-20 nanometers square. This is 2 dimensional, and if stacked up the required thickness would be about the same size.

Answer 3

Sounds like throwing an egg off a tower without breaking it.
Put the antimatter in a box, in a vacuum (obviously), consisting of charged metal plates of the same charge as the particles. The plates are supported by shock absorbers attached to the body of the missile. Since both the plates and antimatter (let's say positrons) are in a vacuum, and are all the same charge, there will (ideally) be no charge leakage, and the plates will stay charged indefinitely, once raised to a sufficient level.

When the missile launched, the shock absorbers absorb much of the acceleration of the missile as it leaves the satellite. When it hits ground, or gets hit by anti-missile defences, the plates are separated, allowing the antimatter to be exposed. Contact triggered explosives at the tip to destroy the containment plates on impact will probably help to ensure it's not a dud.

Answer 4

Unless you just love to throw away money, forget the antimatter bomb.

Current cost estimates for anti-hydrogan are trillions of dollars per gram. Production rates are also insanely slow, billions of years to produce 1 kg of anti-hydrogen.

Old fashioned 1 MTon nukes are about 1 million USD each (when produced in volume), thus you could make millions of nukes for the cost of 1 gram of anti-matter. 1 million USD is just for the warhead, not the delivery system.

Maybe someday, we could make relatively cheap anti-matter, but production is so inefficient, it will be ludicrously expensive for a long time to come.

Easy enough to scale up thermonuclear bombs to the desired yield, so no real downside compared to anti-matter bombs.