Thursday, 22 December 2016

Star Wars: Rogue One review - they should have used railguns

I

Science fiction isn’t really my thing. Thankfully Star Wars isn’t science fiction. It’s really a Western.

However, Star Wars: Rogue One is actually a World War II commando movie with lasers. It even had a French partisan as a lead character. And the lasers weren’t lasers. They were colourful bullets.

In science fiction, it's acceptable to magically solve engineering problems (better materials, more precision, no budgetary constraints, faster computers, etc.) but it really gets annoying to ignore the laws of physics. They become fantasy set in space. People moving objects with their minds is just as plausible as jumping to hyperspace.

Rogue One’s robots weren’t terrifying either, and they should be. Pitting a robot against a human fighter would make firefights a turkey shoot. Not only will the robot never expose itself to human weapons, when the robot fires it will also shoot at the 40 places it predicts the human might jump to.

Star Wars is modelled after WWII dogfighting – relatively slow moving and highly manoeuvrable craft. That’s weird because planes operate on the basic principle of flying through the air to create lift. Spacecraft don't need lift because there's no air and they’re in orbit or interplanetary space under constant gravitational pressure.

Star Wars craft are also small, I suppose because WWII aircraft were small. But the age of whaling taught us that small manned craft are inefficient. The only reason we build them that size is because they have to get off the ground. The Saturn V rocket looked big but its job was only to carry fuel to get an orbiter and lander on a trajectory to the moon.

So it’s more efficient to build spacecraft huge. Super-tankers, cargo vessels, cruise ships and aircraft carriers are all enormous because it’s more economical – the only limit is the budget. Dogfights in space would probably mimic the tall ships of the 17th and 18th century.

II

It’s also really hard to hide in space. The reason submarines are difficult to detect is because of the environment.

The ocean is noisy, light doesn't penetrate, sonar doesn't work well, the water wicks off and disperses heat while the general planet earth puts out so much electromagnetic noise it makes instruments difficult to use.

The main concern in space is radiation (which can be filtered out by frequency) so finding things is simple if you know where to look. Radar works wonderfully. Even 35mm cameras work great in space. We can find planets hundreds of light years away. If a spacecraft is 450 degrees warmer inside than out along with electricity, motors and circuits, it’d be as easy to spot as a floating TV station on fire.

A nuclear detonation would be a pretty big problem though – electromagnetic pulse (EMP), gamma rays, x-rays, etc. The smaller the electronics, the more likely they are to be fried. EMP is why militaries don’t have atmospheric nuke tests anymore. A test in 1962 took out a number of satellites in orbit that weren’t directly affected by the blast.

Also, nuclear blasts release a ton of radiation straight through a craft’s hull into everyone's soft and squishy bodies. The metal then stays radioactive long after the blast is over. The craft could be formed out of lead, but lead melts at low temperatures and nuke blasts are pretty damn hot.

Humans are so fragile and space so hostile that a tiny robot with a power saw could probably kill everyone on board if it started cutting willy-nilly.

III

Every time you shoot a projectile weapon, it equals thrust in the opposite direction. So the bullet moves forward fast and the ship moves back slowly, but it keeps moving back because there's nothing to slow it down.

Magnetic rail guns would be a great answer. Railguns are the coolest thing ever and they are very real. The operating principle is that energy is energy whether it's kinetic or explosive.

A magnetic rail gun is basically a long rack of electromagnets (ideally on two equidistant sides or three sides spaced 120 degrees apart, like a Y) using a small conductive metal object as a projectile. The magnets turn on and off (or more precisely power up to one pole and switch to the other) in careful timing to accelerate the projectile.

The projectile could be as small as a baseball or a ball bearing and can be fired at insane speeds. It won’t fly at relativistic speeds, but it could easily move a few times the speed of sound, especially without air resistance. Kinetic energy is 1/2mv^2, so velocity is far more important than mass. Doubling the speed quadruples the energy. Whereas doubling the mass just doubles the energy.

Increasing the mass may be better because the projectile will move slower giving the gun more time to pump energy. But increasing mass means the craft has to carry it around all the time. That's more fuel needed to burn in every manoeuvre. What makes railguns appealing is they turn electricity into propulsion, so nothing is stored on board other than the projectile.

In space, an object in motion stays in motion. Turn a rocket engine on for two seconds, then turn it off and the object keeps going. To stop, a rocket has to face the other direction with enough power to cancel the forward momentum. So even today's cruise missiles, relying on vectored thrust rather than wings, would be deadly in space.

IV

Arthur C. Clarke wrote a story about very fast craft (60% of c) moving inside a giant cone of water ice to absorb the impact of small particles that would otherwise be deadly at those speeds.

For a craft getting shot with ball bearings, ice is a perfectly good shield. Also, ice is very light. But a spacecraft is basically screwed with or without the ice if explosives are used.

Which means if you expect explosions, it’s better to use steel or depleted uranium (the hard material coating of armour-piercing shells). Again, these are extremely heavy, requiring a ton of fuel. So if you don’t expect to get shot (as with the Apollo missions) a thin skin of aluminium is fine.

And not to get too picky, but most Star Wars craft have wings (although they hover as well, so wings are pointless). Yet the shape of a spacecraft doesn’t matter. What matters is the centre of mass, because that's the point around which a ship will rotate when it tries to turn.

On second thoughts, it’s probably a good thing that Star Wars’ lasers are actually colourful bullets.

Lasers are a useless space weapon. Laser beams diverge over distance. That’s a fundamental physical limit and cannot be defeated with improved technology. As the wavelength of the laser light is decreased, the angle of divergence decreases. Even with some exotic gamma ray laser beam will still spread out.

The further away the target is, the less energy per surface area will be delivered to it. By the time the craft gets close enough to use its laser, the other guy will probably have already launched a bowling ball at 10,000 kph. Bowling balls don't diverge. Bowling balls win.

In short, a dogfight in space is impossible. Hell, with modern fighter planes dogfights are 40 minutes of chase and two seconds of target and fire.

Ok, tongue has officially been retracted from cheek now…

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