# How to clean-cut my space-borne enemies?

For my own amusement, I was reading through some of the XKCD What-If scenarios. This one in particular sparked an interesting idea: Could a particle accelerator be weaponized to slice an enemy spacecraft in half (or pieces, surgically, because, why not)?

Turns out, my idea isn't so feasible. Weaponizing a particle accelerator is basically a particle-beam weapon, but without all the death and destruction we're led to expect by fiction (nuts, but probably for the best). There was a Russian scientist who got his head caught in the beam of a particle accelerator; he didn't die, but he did get a large dose of radiation and have some unusual side effects. It's also been noted that a weaponized particle accelerator isn't particularly useful (or as lethal to the user as the target; those are equivalent, right?).

Still, my idea for my hyper-advanced aliens to use some novel technology to cleanly slice an enemy ship in half (or pieces, either works) urges me to find a way of making my vision a reality. (Kind of like a monomolecular wire weapon, but used against the (exotic) materials that comprise the hull of spacecraft.)

What method can I use to inflict clean cuts on an enemy spacecraft without damaging or destroying my own ship in the process, preferably only relying on aspects of science that we can currently at least theorize?$^{1}$

$\tiny \text{1 In other words, please refrain from handwavium devices and nanomachines; the latter is overused as an explanation, in my opinion.}$

The physical expression of this in a space scenario is called a "Matter Beam", and it is just what it sounds like.

This has been proposed for various uses, mostly as a method of spacecraft propulsion, but any device capable of transferring momentum on that scale can most certainly be used as a weapon as well. Taking your matter beam "emitter" up to "11" gives you the sort of concentrated beam of physical particles which can cause serious damage to the enemy spacecraft.

The mechanism is kinetic energy (Ke=1/2 MV^2), and each particle can carry a considerable amount of energy simply by virtue of moving at interplanetary speeds. An object moving at 3km/sec (fairly slow by interplanetary speed standards) will have an energy equal to its wight in TNT. Colloquially, this is known as "1 Rick" of energy. Since objects can be accelerated to 72 km/sec before they are no longer bounded by the Sun's gravity, you can pack a lot of "Ricks" into a stream of postage stamp or smaller sized particles. A full set of calculations is in the ever handy Atomic Rockets "Conventional Weapons" page.

Now the downside of all this is you need some pretty impressive hardware if you are going to saw through an enemy spacecraft. From Atomic Rockets:

As an example, suppose we have a synchronous coilgun, and that the coilgun can generate 1 tesla fields (a good number that will not saturate the ferromagnet). Our presumed ferromagnet is probably mostly iron, with about 8000 kg/m3. To reach 100 km/s, you will need 40 TJ per cubic meter of projectile. Since this is 100 million times the energy density of the field, you will need the projectile to sweep out 100 million times its volume in order to accelerate up to the desired speed. This means you need an accelerating track 100 million times the length of your projectile. If the projectile is the size of a dime, with 1mm thickness, you will need a 100 km long track. If 2.5% of the energy goes into the projectile as heat as a result of inefficiencies, you get 100 GJ of heat per cubic meter of projectile, or 12 MJ/kg. This is three times the specific energy liberated by detonating high explosives, so you can expect your projectile to explode like a bomb inside your coilgun barrel. Consequently, this appears to be an unworkable design.

So how do we get a compact, "workable" design?

Fortunately, the same page also discusses the use of nuclear weapons as compact, high energy power sources for projectile weapons. A nuclear "shotgun" can potentially accelerate pellets to 100 Km/sec. While this isn't going to saw through a ship, it will certainly cause a lot of damage.

A nuclear "Shaped Charge" can potentially accelerate a stream of liquid metal to @ 3% of c. You won't get a cut like a saw, but a hole drilled through armour, shielding, ships systems and anything else caught in the path of the stream.

A Casaba Howitzer accelerates a spindle shaped plasma to @ 10% of c, so evading becomes quite difficult. Once again, sawing through a ship might not be possible, but the damage could be similar to a high energy laser.

Finally, a large enough laser could do just what you want. On the Atomic Rockets page, Luke Campbell has done some rough calculations for a Free Electron Laser (FEL) capable of vaporizing metal and ceramic at a range of one light second, 300,000 kilometres, almost the distance from the Earth to the Moon. This Ravening Beam of Death (RBoD) will be capable of cutting through most ships (although there will be a time factor), and even when not slicing through ships, could have a "scorch" range of up to a light hour.

X-ray laser RBoD. The ultimate in firepower

To put that in perspective, the accelerator for the FEL will need to be a kilometre long, but when you absolutely and positively need that sort of firepower.....

• Couldn't you also spin the particles through a much smaller loop a lot of times to get the same result, or would that have negative consequences? – Frostfyre Nov 2 '16 at 18:02
• For physical particles (like a matter beam) a small accelerator would require far too much energy and release far too much wast heat (as the 100 km coilgun scenario showed). A kilometre diameter accelerator for an electron beam minimizes many losses (like Synchrotron Radiation), so the efficiency becomes reasonable for a massive device like the RBoD. – Thucydides Nov 2 '16 at 18:55

# Waterjet

Just without the water. A stream of abrasive particles could erode clean cut thorough anything, at least in theory.

# What would not work

Direct energy weapon would sublimate matter. Either you deliver a lot of energy in a short time, effectively causing explosion, or cloud of sublimated matter would son obscure your view and make cutting impossible.

Physical blades would bend target's hull, at least a bit. Try cutting soda can with a knife - no matter how sharp knife is, can will bend.

The simplest solution is use a really big sword! As long as the blade is sharp/strong enough, and is swung hard enough, it will cut through anything (or cut out the swung strength by making a kind of 'chain-saw' like sword).

A stream a Acid would probably work, but the acid would probably be too slow... so the ship would blow up from rapid depressurization before it was 'cut'.

You can also use a Water Jet Cutter! It should be moving fast enough to not freeze long enough to cut stuff. (Though, this is more just funny. it would be SUPER impractical).

You can tear apart with strong enough magnetic fields (depending on the target), but this wouldn't be a very 'clean' cut... (Same for using gravity fields somehow)

Of course, you could also just use a Machine Gun. (again, funny, but not too clean. And it would need to be REALLY good to cut in half before depressurization explosion)

Seems your only real issue here is 'cut faster than depressurization explosion can occur'