A supersonic airliner that flies at three times the speed of sound – and runs on nuclear fusion. Stephen Dowling investigates the challenges of making airliners run on atomic power.

It could whisk you from London Heathrow and have you stepping onto the air bridge at New York’s John F Kennedy airport just three hours later. It would take you in no small comfort – luxuriously so, if you’re in first class – at speeds approaching 2,300mph (3,680km/h), the Atlantic Ocean racing below your feet.

The Flash Falcon, looking like a spacecraft from the video game franchise Halo, is a futuristic peg to fill the hole left by the retirement of the Supersonic Concorde in 2003. No prototypes have been built though – the design so far lives only in the imagination of Spanish designer Oscar Vinals, who also designed a ‘whale-shaped’ giant airliner BBC Future profiled back in 2014.

The Flash Falcon, Vinals’ concept imagines, would carry 250 passengers at Mach 3, in an airframe more than 130ft (39 metres) longer than a Concorde and with a wingspan twice as wide. Its engines would even be able to tilt up to 20 degrees to help the aircraft take-off and land like a helicopter.

I think nuclear fusion could be the best future source to obtain great amounts of electric energy – Oscar Vinals

At the heart of the Flash Falcon is something even more revolutionary; Vinals' aircraft is designed to fly on nuclear power, with a fusion reactor pumping energy to its six electric engines.

“I think nuclear fusion could be the best future source to obtain great amounts of electric energy,” Vinals tells BBC Future. “At the same time, it’s ‘green’ without creating dangerous waste.

“Today, we have a very clear idea about how nuclear fusion works; there are many projects working on it, such as Tokamak, Iter, and Stellarator. I'm very optimistic that in the next five-to-seven years we will have the first stable and productive fusion reactor,” says Vinals.

Whether the long-awaited key to cheap and plentiful power arrives quite so quickly, Vinals’ concept revives a dream that has preoccupied aircraft designers since the 1950s – how to fit a nuclear reactor into an aircraft.

The invention of nuclear fission reactors brought the promise of cheap energy not just to the home, but to ships; in the 1950s the first reactors small enough to be used on a vessel entered service. Within only a few years, they’d shrunk enough that they could be used to power a submarine.

The 1950s was one of the golden ages of aircraft design, with giant leaps of technology, fuelled both the airline market emerging across a post-war world, and the Cold War. As tensions between the US and Soviet Union grew, the US looked for a way to keep their long-range nuclear bombers in the air for as long as possible, making them far less vulnerable to an attack on their airfields.

Nuclear fission produces a lot of neutrons, and they can be very harmful – Simon Weeks, Aerospace Technology Institute

Nuclear reactors could theoretically stay in the air for months at a time – as long as you had an aircraft big enough to have crew that could fly and sleep in shifts.

But, says Simon Weeks of the Aerospace Technology Institute, there are some major issues that come with putting a fission reactor on an aircraft. Not only would you need a “closed loop system” – a reactor that reuses the waste fuel – but it would also need large amounts of heavy shielding. “Nuclear fission produces a lot of neutrons, and they can be very harmful,” says Weeks.

The only nuclear-powered aircraft that flew in the West was a heavily modified Convair B-36 bomber in the early 1950s. The already gargantuan aircraft was further weighed down with 11 tonnes of shielding to keep radiation at bay. Though the NB-36H flew 47 times, the onboard reactor was only tested in the air, and never actually used to power the aircraft.

The potentially catastrophic effects of a nuclear fission-powered aircraft crashing curtailed further development. And while military crews might have followed orders and manned a nuclear-powered aircraft, the idea of passengers willingly stepping aboard a plane with a nuclear reactor only a few metres away seems unlikely. The nuclear-powered airliner remained in the artists’ impressions of what air travel may look like in 50 or 100 years’ time.

It’s not nuclear fission that will power Vinals’ concept, however. “It’s common for people to hear the words ‘nuclear power’ and think that it is dangerous, but in the case of nuclear fusion it’s not true.” Rather than creating a chain reaction like nuclear fission, fusion – the fusing of two or more atoms into a larger one – creates more energy but does not create polluting waste products.

Vinals is not dissuaded by the fact that nuclear fusion remains technologically out of reach. Concepts like the Flash Falcon don’t have to be weighed down with the limitations of the tech we have today; part of their role is to imagine what designs might look like using technologies we haven’t yet mastered.

Fusion is still some way off, however. “Nuclear fusion is always 50 years away,” says Weeks.

Reactors are still at the experimental stage; for instance, the Iter project currently being built in France is still some 10 years away from being activated.

We’ve been working on fusion since the 1950s, and we’ve not yet built a practical, working reactor – Simon Weeks

Even if such reactors prove to be practical, and can generate the cheap, clean energy promised, that is only the beginning of the puzzle.

“The challenge then is making it very small and very lightweight,” says Weeks.

“Between the 1940s and the 1980s, we saw considerable development in nuclear fission technology, and that was relatively quickly. We’ve been working on fusion since the 1950s, and we’ve not yet built a practical, working reactor. That’s still 20 or 30 years away.”

Making a portable nuclear fusion reactor that generates enough energy to power an aircraft – a supersonic aircraft, in the case of Vinals’ design – is a far greater challenge than building an airliner that could travel at three times the speed of sound, says Weeks.

Any alternative fuel has big shoes to fill – kerosene, the fuel used in jet engines, is an incredibly versatile propellent. “It’s an incredibly good medium for creating energy. It’s energy-dense, it’s easy to handle, and it performs well across a whole range of temperatures,” says Weeks.

“And it can also be used for other things, not just fuel. It can be used as a coolant, as a lubricant, and even as a hydraulic fluid.” Climate change may be a pressing reason to find alternative fuels for aircraft, but the incredible amount of energy needed to fly an aircraft at such high speeds. The kind of batteries used on aircraft like the Solar Impulse can only generate 1/20th of the energy from an equivalent weight of kerosene.

Nuclear fusion-powered aircraft might be just too difficult to pull off in the next century. Much more likely, says Weeks, will be forms of hybrid power; for instance, propeller that help generate energy to be stored on board and used to help the aircraft take off.

The Flash Falcon is too ambitious a design to fly with today’s technology. But aviation history is littered with achievements once thought impossible. Nuclear fusion might, one day, join them.

More of Oscar Vinales' images of the Flash Falcon can be seen here.

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