Review – Rogue One: A Star Wars Story needs more railguns and nukes

Rogue One: A Star Wars Story is a World War II commando movie with lasers, or should I say – colourful bullets. It even has a French partisan as a lead character. And who could miss the Nazi-like empire costumes and mannerisms?

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 when it ignores the laws of physics. The movie becomes fantasy set in space. So with that in mind, and tongue firmly in cheek, I want to play around with some of the ideas presented in the film.

First, Rogue One’s robots weren’t terrifying, and they should be. Pitting a robot against a human would make firefights impossible. Not only do robots never miss, they will also shoot at the 40 places it predicts the human might jump to. So there’s no running from robots with guns.

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

Star Wars battles are certainly modelled after WWII dogfighting – relatively slow moving and highly manoeuvrable craft. That’s why they look weird because aircraft 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.

It also not clear why all the spacecraft are small. The age of whaling taught us that small, manned craft are inefficient in open seas. And the only reason we build small spacecraft is because they have to get off the ground. The Saturn V rocket was big, sure, but its job was only to carry fuel to get the orbiter and lander on a trajectory to the moon.

It’s actually 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. So dogfights in space would probably mimic the tall ships of the 17th and 18th centuries.

What about radiation?
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 giveaway 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 using these. If a spacecraft is warmer inside than out, along with electricity, motors and circuits, it’d be as easy to spot as a floating TV station on fire.

Speaking of radiation, a nuclear detonation would be a pretty big problem – 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 conduct 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 will release a tonne of radiation straight through a craft’s hull into everyone's soft and squishy bodies. The metal then stays radioactive long after the explosion is over. To counter this, the craft could be formed out of lead but lead melts at low temperatures and nuke blasts are pretty damn hot.

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

Magnetic railguns would be a great alternative. 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 railgun 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 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 for railguns. 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 rails more time to pump energy. But increasing projectile mass means the craft has to carry that mass around all the time. That's more fuel needed to burn in every manoeuvre. Railguns are appealing because 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. The Jedi could guide missiles with their minds, I guess.

A few other concerns
The shields in Rogue One are either non-existent or pointlessly weak. 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 would be a great shield. Also, ice is very light. Then again, 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 tonne 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 (even though they hover…). But in space, everyone knows the shape of a craft 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 just colourful bullets.

Lasers are a useless weapon in general. Laser beams diverge over distance. That’s a fundamental physical constraint 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, the laser beam will still spread out unmanageably.

The further away the target is, the less energy per surface area will be delivered to it. And by the time the craft gets close enough to use its laser effectively, 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 space dogfight 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…