by Martin Archer
Queen Mary University of London
December 15, 2016

from TheConversation Website

That's no moon.

KillamarshianUK/Flickr, CC BY-SA

So you want to build a Death Star? Here's how to get started

I'm very excited about seeing Rogue One - A Star Wars Story, which tells the tale summarized in the original Star Wars' opening crawl.

This is the story of how the rebels stole the plans to the original "Death Star" - a space station the size of a small moon with a weapon powerful enough to destroy a planet.

If we could get our hands on those plans, could we build a similar fortress?

I decided to try and work out some aspects of how a Death Star might actually work. In Star Wars lore, the 120km (75-mile) diameter space station was made from quadanium steel (a fictional metal alloy) and crewed by 2m Imperial personnel, including officers, Stormtroopers and TIE pilots.

So, would it possible in the real world? Let's not worry about the vast quantities of raw materials required.

For example, at current production rates of steel it would take 182 times the current age of the universe to accrue enough. I'm more concerned conceptually with how to power such a colossal battle station and how to generate gravity for everyone on board. It turns out our conventional technologies might not cut it.

The International Space Station requires about 0.75W of power for every m³ of the space station. These are provided by eight solar arrays, 112 feet (34m) long by 39 feet (12m) wide.

Even if we had 100% efficient solar panels covering the much larger Death Star, we'd still be a factor of 45 times short of the ISS's power requirements per unit volume. Not to mention that power would severely diminish if we took the space station further away from the sun.

You might think we could learn lessons from the sci-fi classic 2001 - A Space Odyssey in terms of the gravity and just spin the Death Star to create artificial gravity via centrifugal forces.

To replicate the gravity on Earth (9.81 meters per second squared or 1 g), the station would only need to revolve once every 3.5 minutes, which doesn't sound too absurd.

But there was a reason the station was ring-shaped in 2001. The centrifugal force is proportional to the radius of your circular path. As you travel either towards the centre of the station or towards the poles, this radius decreases meaning the artificial gravity would start to vanish.

If indeed gravity was created this way, it calls into question the Death Star's spherical design.

## Dyson sphere

Perhaps the clue was in the name the whole time.

What if at the heart of the Death Star is an artificial star? Surely that would solve the gravity problem?

This makes the station something of a Dyson sphere, the sort of technological mega-structure physicist Freeman Dyson imagined advanced civilizations might be able to build to harness all the energy from their stars.

However, Dyson spheres of the rigid shell variety usually run into problems from being under immense stresses due to the gravitational forces.

Even if the sphere isn't ripped apart by this, just a small push certainly would be enough to send the structure crashing into its star.

But Dyson spheres are usually imagined to be the size of the Earth's orbit around the sun.

For a much smaller Death Star, most of the problems with the Dyson sphere go away. The 13.2km diameter reactor core would only require a mass 370 times less than our moon's.

It turns out while steel and titanium would just about fail under these conditions, the wonder material graphene, for example, could easily withstand the gravitational forces involved.

And we wouldn't actually need a real star at the centre of the station - the future technology of nuclear fusion could easily provide enough power.

While at the moment we tend to put more energy in than we get out in our fusion experiments, many plasma physicists think the key is going bigger and hope that the ITER experiment, which will be one-third of the volume of an Olympic swimming pool, will turn the tide in this regard.

If successful, we could expect power from our Death Star up to two million times that consumed by the entire human race.

But there are still problems. The pressures involved inside our Death Star reactor would be immense. The artificial star's own gravity would not be enough to contain the fusion plasma, so we would need something extra.

As we've learned from thinking about lightsabers, magnetic fields could provide the solution.

The only snag is that we'd need some of the strongest magnetic fields in the universe - a million times greater than we've ever created on Earth and comparable to those of magnetars - a type of neutron star with an extremely powerful magnetic field.

Back to the drawing board it seems, unless I can get my hands on those plans…