Why a persistently airborne nuclear-powered fortress isn’t feasible.



Similar to the Ausmerzer in Wolfenstein II: New Colossus or the Helicarrier in the Avengers universe.

In: Engineering

Is there a utility to be provided by such a thing that isn’t already fulfilled by something more simple?

We also do not have the technology to generate the lift needed for something of that size.

Flying takes a large amount of energy, per unit weight. Nuclear reactors are very heavy, requiring more power, requiring more reactors, … It’s been tried several times and it’s not a viable engineering solution.

You can go small, NASA is sending a nuclear powered drone named Dragonfly to fly around on Titan. It uses nuclear electricity to charge batteries and then makes flights on battery power; oh yes, and the gravity on Titan is 14% of Earth gravity.

But Avengers large – we can’t even make things like that powered by fossil fuels. Nuclear is much more massive per unit power output.

Nuclear reactors are really heavy. Getting over the drag from that weight is a real challenge.

Also while a nuclear sub melting down in the ocean would be an environmental catastrophe it’s nothjng like one blowing up in the air.

And with the range of modern weaponry today any of the missiles or planes from ships in the ocean can reach nearly any target on earth.

You can do the math to see that your power requirements are just ludicrous.

Unless you’re planning on nuclear powered rockets then you’re really looking at something with fans electric like a helicarrier powered by a nuclear reactor.

The Sikorsky CH-53E can take off when weighing 33,300 kg with 3 3,270 kW engines for a kw/kg ratio of 0.2945 kW/kg, this is about the best you’ll get among heavy lift helicopters so we’ll assume you just sprinkle CH-53E rotors around to keep you airborne.

If you want to lift even a little aircraft carrier like a Wasp-class Amphibious Assault Ship used by the USMC then you need to lift 41,150,000 kg which will require 12.2 GW of power. The new Gerald R Ford Class Carriers have two reactors rated for 700 MW_thermal so you’d need at least 18 nuclear reactors to stay airborne, but you just made your ship even heavier so now you need more fans and more reactors, and more fans and more reactors

Turns out drones are really cheap, versatile, and easy to move around to where ever you need them. Even staging planes at a ground base will cost you less than trying to engineer a flying carrier, it’d cost trillions easily.

It takes a lot of energy to keep planes in the air. You could have a satellite that orbits Earth and shoots nukes down at it though. It doesn’t exist because of international treaties.

There have been experimental nuclear powered planes. But the weight of the reactor and the necessary shielding have meant any payload was minimal. https://en.wikipedia.org/wiki/Nuclear-powered_aircraft
Having something hover requires far more power than having it flying with convectional wings.

A caveat to the excellent answers here (shoutout to /u/WRSaunders): nuclear reactor powered aircraft are way too heavy to fly, *if* you care to bring enough shielding to protect the crew and the people on the ground. If you don’t care about safety and you just want to create an uncrewed nuclear cruise missile that spews deadly radiation out the back like a firehose, it’s probably possible, though research efforts in the 1960s were brought to a halt due to a mix of technical difficulties and “Why bother? We’ve already got better ways to horribly kill everyone on Earth.” And so nobody ever got one off the ground…

… Except. Last year, the Russians announced the development of a new nuclear-powered cruise missile with unlimited range, that sounds like it might be this same awful idea come back to life. And a few months ago, there was a nuclear accident on the north coast of Russia involving an “isotope power source for a liquid-fuelled rocket engine” that killed several workers. Many have suggested this might have been a failed test of a new nuclear-powered missile, though it’s hard to say.




… but that’s all uncrewed missiles. Crewed helicarriers? No way.

It’s possible, just highly impractical.

The US and Soviet air forces actually did experiment with nuclear aircraft during the early Cold War. The simplest way is to build a conventional jet engine and remove the combustion chamber. Instead, compressed air is funneled through a pipe to the reactor, which heats it. It’s then directed through a turbine, then out the back where it expands and generates thrust. The turbine powers the compressor, like a normal jet engine.

The problem with nuclear reactors though is they need to be shielded. If you were to install this in an airplane, you wouldn’t want it belching out radioactive gases out the back, nor would you want radiation leaking into the cabin. Those shields are typically made out of lead, thick steel, or concrete, which are very heavy. The heavier a plane is, the more powerful the engine needs to be to get it airborne. Which means even bigger engines, which means even more weight, which means more power is needed. This quickly eliminates any advantage nuclear power would have in an aircraft.

Speaking of size, most larger planes have their power plants separate from the fuselage. Usually attached to the wings on pylons. While they have internal fuel tanks, a lot of it is also stored inside the wings. Freeing up more room inside the fuselage for passengers, cargo, or ordinance. A nuclear reactor would have to be built inside the fuselage just due to its sheer size. Which means less room for other things. Again limiting practicality.

Same reason modern cars are much heavier than their 1960s-1970s counterparts: safety.

Modern cars routinely weigh 3500-4500 lbs, whereas previous generations could be 2000-2500 lbs. I drive a 2016 Dodge Charger that weighs about 4500 lbs, while its 1969 version weighed about 3285 lbs.

The difference is that we as a society became conscious of the lack of protection afforded, and technology caught up to the needs, and the net result is that you’re much more likely to survive or “walk away from” a car crash in 2019 than you were in 1969 because all that extra weight is the airbags, crumple zones, anti-lock brakes, and on and on.

If you’re unconcerned about safety of the environment (land, air, and sea in the vicinity that you want to keep non-radioactive) or the logic inside (silicon-based or meat-based also needs to survive), you can make a light powerful nuclear vehicle that can operate airborne indefinitely. This is why space-based interplanetary nuclear ships can work. However, the reality is that safety has to be taken into account, and with current nuclear technology, there’s no way to safely operate that kind of vehicle.

Note that we currently have nuclear-powered vehicles, namely aircraft carriers and submarines, that can operate for decades without refueling. The rub is that they are extremely heavy because of the multiple layers of safety surrounding a combat vehicle, and therefore only operate in the ocean, where weight is less of a problem.

Well, it’d be theoretically possible, it’d just be hard. Helicopters need a pretty high power to weight ratio – a Chinook, with a mass of 22.7 tonnes and ~7000 kW of maximum power, has a power to weight ratio of ~310 kW/tonne. To compare, a nuclear-powered Los Angeles-class submarine has 52000 kW of power, and weighs ~7000 tonnes, for a power to weight ratio of about 7.5 kW/tonne.

So, to make a nuclear-powered flying fortress, you’d need to make something nuclear-powered that has about forty times the power to mass ratio of a nuclear submarine, and unless you want the whole thing to be just a reactor with a tiny bit of actual aircraft stuck on, that means an at least ten times more power dense reactor as well. This is probably going to end up with the reactor being less safe, and you might need to skimp out on the shielding, too. Such power levels from a nuclear reactor aren’t totally unachievable though – the nuclear rocket engines tested during the NERVA program achieved specific powers in excess of 50000 kW/tonne, and even though you’d want to scale that down a bit for use in a long-endurance vehicle, it shows that this sort of thing is at least theoretically possible.

* The [square-cubed law works](https://tvtropes.org/pmwiki/pmwiki.php/main/squarecubelaw) against a giant flyer ” For example, if you double the size (measured by edge length) of a cube, its surface area is quadrupled, and its volume is increased to *eight times* its original volume. ”
* The USAF and the Soviet Air Force tired to make a nuclear powered bomber – trouble is that the shielding for the reactor made the aircraft too heavy to be a good bomber.
* this means that a large craft needs more energy just to move, factor in the shielding to prevent the crew from dying of radiation and a helicarrier doesn’t work