Close your eyes for a moment and imagine you're the head of North Korea's space program. It's Friday afternoon, you've had a tough week, and you're just sending a last few emails before you go home when a message drops into your inbox from Kim Jong-Un. Uh-oh, better answer this. The subject line is just two words. "Death Star".
Turns out he's been watching some of his dad's old movies, and one of them featured a huge planet-sized space station – he wants to know if it's possible to build it. A giant megastructure floating in space that's also capable of firing planet-destroying lasers – what could be simpler? You look at the plans. You look at the email reply window. You can't say "no." You know what a "no" would mean for you and your family.
That's sort of how I felt when my editor emailed to tell me he wanted to know how to build a Death Star. "Could we actually build a real working death star in space?" he asked. I looked at the email reply window. I couldn't say "no." I knew what a "no" would mean.
So I rang the European Space Agency, and asked for their foremost expert on Death Stars. They gave me Kim Nergaard, the head of their Advanced Mission Concepts Office, who was on holiday in Britain when I called him up and informed him of my mission.
I asked if the European Space Agency happened to have a death star secretly in development that I could crib from. "At the moment, there are no plans for building a Death Star," he told me. "However, we are doing the first steps. We've started preparing for a human base on the Moon. So before building a full-on Moon-sized Death Star, maybe the first step should be to use the Moon that we have and start transforming that into something like a Death Star."
He's talking about recently-announced plans for a collaboration with Russia's space agency ROSCOSMOS to explore an area of the Moon's south pole that might be suitable for a manned moonbase. But I needed to know about a Death Star, not its precursors. "A real-life, full-sized Death Star you mean?" he said. "Yes", I said. "OK. If everyone wanted to do it, and the world became ruled by a dictator who also wanted this, then I guess you could do a smaller version of it in the next 30-50 years."
That smaller version, Nergaard says, would be around the same size as the International Space Station (about 110 metres across) but spherical. Anything larger – approaching the size of either of the Death Stars seen in Star Wars – would take hundreds of years with conventional shooting-it-up-in-a-rocket technology.
Instead, a better solution might be to capture a metallic asteroid, put it into Earth's orbit, and use that for materials instead. We've got the technology to do that today, but it would take a long time to find the right asteroid and alter its orbit to get it around Earth.
In terms of materials, Nergaard says the best options for building a Death Star would be strong and lightweight, meaning mostly aluminium and modern composites. But there are two problems with that approach, he said. Firstly, it'd be too weak to withstand any kind of attack. Secondly, and perhaps more importantly, when it left the Earth's orbit everyone inside would slowly die of radiation poisoning.
"What?" I said. Turns out that the Earth has a magnetic field that protects us from the space radiation that does significant long-term damage to anyone leaving the planet. "This will, by the way, also be a problem when going to Mars," said Nergaard. "A more serious problem than I think many people consider." To fix that, you'd need heavier, denser materials like lead – and getting those into orbit would dramatically expand the timescales involved.