Carrier alternatives?

BlondieBC

Banned
And how many tons of coolant do you have to carry, too?

Now, maybe when they finally get fusion working properly...

It is a lot less than a normal reactor. To make the nuclear aircraft engine work, you run the air from the outside directly over the nuclear fuel rods. There is not system of heat exchanges such as a nuclear power plant has installed. A nuclear powered aircraft throws out a huge radioactive plume out behind it.
 
It is a lot less than a normal reactor. To make the nuclear aircraft engine work, you run the air from the outside directly over the nuclear fuel rods. There is not system of heat exchanges such as a nuclear power plant has installed. A nuclear powered aircraft throws out a huge radioactive plume out behind it.
Wouldn't that system be a less effective when the plane was moving relatively slowly, to land or take off, and hardly workable at all -- unless there's a very strong wind, of course -- while it's stationary on the ground? I realise that you could shut-down the reactor when the plane is parked, of course, but then how quickly could it be re-activated again if you needed to get airborne in a hurry?
 
It is a lot less than a normal reactor. To make the nuclear aircraft engine work, you run the air from the outside directly over the nuclear fuel rods. There is not system of heat exchanges such as a nuclear power plant has installed. A nuclear powered aircraft throws out a huge radioactive plume out behind it.
Depends on the cycle type. As Asnys mentioned, there's two types. In a "direct-cycle" engine, the air is circulated as you describe and there is the potential for radioactive material to be exhausted if the fuel rods begins to fracture or shed material. However, the other option ("indirect cycle") uses a second material that serves as reactor coolant in a closed loop, passing between the reactor itself and a heat exchanger where the heat is transferred to the actual airflow of the engine. In this cycle, the air is not directly exposed to the reactor and the radioactivity of the exhaust is almost entirely eliminated.
 
Wouldn't that system be a less effective when the plane was moving relatively slowly, to land or take off, and hardly workable at all -- unless there's a very strong wind, of course -- while it's stationary on the ground? I realise that you could shut-down the reactor when the plane is parked, of course, but then how quickly could it be re-activated again if you needed to get airborne in a hurry?
No, you blow the air through with a compressor and use a turbine to take power off the exhaust to drive the compressor. Essentially it's a jet engine with the combustion energy of a jet fuel replaced by the thermal energy off a nuclear reactor. Like a jet engine, the airflow through the engine is thus divorced from the flight speed of the aircraft.
 
No, you blow the air through with a compressor and use a turbine to take power off the exhaust to drive the compressor. Essentially it's a jet engine with the combustion energy of a jet fuel replaced by the thermal energy off a nuclear reactor. Like a jet engine, the airflow through the engine is thus divorced from the flight speed of the aircraft.
Ah, okay.
But you still have to "warm-up" the reactor for a while before you can start a take-off, yes?
 
Ah, okay.
But you still have to "warm-up" the reactor for a while before you can start a take-off, yes?

Most programs planned to take off and land on chemical fuel. The reactor would be started up in flight, and shut down before landing. This also provided a backup propulsion method if the reactor conked out.
 
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And the conventional fuel counts as shielding too. The idea being, you use some jet fuel for takeoff, but most of it is in reserve for landing (which is after you've shut down the reactor) or emergency contingencies (again, you've scrammed the reactor). So when you've drained the fuel dry, the permanent shielding installation only has to deal with residual radiation from a shut-down reactor, not the full flux an operating one puts out. You can lighten it if you can count on the jet fuel being shielding. And with lots of hydrogen in it, jet fuel is a fairly good shielding material.

Of course then you have to face the fact that the neutron flux and other particles the fuel is blocking will transmute some of the jet fuel, or radioactive isotopes that are fission products that manage to escape the reactor core and lodge in the fuel will be contaminating it too, so your conventional jet will be putting out more radioactivity than normal. But I suppose that's a small factor.

A RAND study I read that one of y'all (I believe it was Asnys) found some on-line abstract of, written in the late '70s or early 80s, comparing many different fuel strategies for a really big airplane (1000 tonnes in the conventional jet fuel version, though this study's premise was that all the fuels would have to be some kind of synthetic since it was exploring post-oil crash options, so that was actually synthetic JP, but of course it would burn and mass and bulk just like conventional jet fuel)--anyway this study dwelt rather lovingly on the nuclear option. It featured a liquid-metal reactor that would pipe the hot metal (sodium I believe) into the spaces where a conventional jet engine has its burners, as explained above. The variation here was, the author believed these nuclear heat-exchanger jet turbines could also house conventional burners in the same space--in short they were to be dual kerosense/nuclear jet engines. It obviously saves the weight of having to have two different jet engine systems installed. I have to wonder if trying to shoehorn both types of heating into one engine would involve serious compromises of both modes. Also, if the purpose of the nuke engines is to maintain cruise, you probably don't need as much thrust as the conventional mode has to deliver for takeoff and landing and emergency maneuvers. Finally you might want the conventional jet engines far away from the reactor-heated ones in case the reason you have to shut them down is not a reactor failure but a breakdown or damage to the turbines themselves; clearly in that contingency the ability to run the engine conventionally does no one any good.

The way the RAND study had it, probably the best and perhaps only way with a conventional airplane layout, the reactor(s) (I forget if there was one or two) were situated in the center of the plane, right at the wing roots in the fuselage, dividing the cargo space fore and aft. And the jet engines were laid out in a row of eight right on top of the fuselage there, a layout I've only ever seen elsewhere on an early approach by Boeing to their first jet bomber back in the 1940s. That's to minimize the distance the hot metal coolant has to travel of course!

So if you wanted to skip the option of making those engines bi-propellant and just make them cruise maintainers running only on nuclear heat, you could put the conventional engines in a conventional location on the wings or at the tail, and they'd be far away from anything that might take out the nuke turbines all at once.

I believe Asnys has shared elsewhere designs with a radically different airframe layout that puts the nuke reactor and associated engines in a less awkward place, near the tail, so shielding can be forward only. I think this is a canard layout that again has the reactor near the center of mass, but that's far back.

Personally if we are going to put nuclear reactors aloft I like the idea of putting them on a really big airship. For the mass of aircraft you are moving, they would be a lot smaller, and sheer distance can accomplish a lot of the shielding. Also airships benefit more than an airplane would from a constant-weight powerplant and can make some good uses of waste heat too. And yes I do believe a really huge airship can serve as an aircraft carrier, recovering airplanes with stall speeds much faster than it can fly with some sort of reverse catapult--I favor relatively simple pendulum-trapeze based systems using both airbraking and gravity as the arresting mechanisms.

But I've come to understand how gargantuan and how vulnerable such a system would be. A seaborne carrier is vulnerable to certain modes of attack too of course.

In the RAND study my actual favorite was not the nuke plane versions but the hydrogen-fueled ones; the fuselage was bloody huge but the wings were small, due to hydrogen's much lower weight for a given heat value. But I have to admit, the nuclear planes would have a unique ability to loiter around in the air for days, weeks, indeed for times limited mainly by the human limits of the embarked crew rather than the endurance of the aircraft itself. If you can have shuttle airplanes transferring crew on and off the airborne nuclear airplane, you only have to come down when the reactor is getting worn out or for maintenance.

The nuclear engines envisioned in the RAND study would need to be replaced once a year, given the duty cycle anticipated for them--continuous flight might demand more frequent replacements yet!

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I am afraid I see little utility in the air-tug model of nuclear airplane for manned aircraft for manned warplanes. Basically a carrier allows the flight crew to share reasonably spacious and adequate living conditions with the ship crew until they go on duty, on routine patrols or in a defensive scramble or offensive strike. You could probably tow a squadron of F-18s all right, but you can't crew them on the fly! And it isn't clear how well they could moor again to the tow lines when the mission's done.

I guess it might be OK for the purpose Asnys mentioned it was designed for--towing civil airliners or freighters. Presumably it flies along heavily traveled routes and various planes fly up and join it (presuming the in-flight tethering issues get solved, which I guess are much the same as airborne refueling linkups) then fly off when they approach their particular destination, thus needing only fuel for takeoff, landing and emergency contingencies.

Or as Asnys suggests, a flock of cruise missiles, or even air-launched ballistic missiles. And RPVs.

This certainly doesn't strike me as a cheaper option than a surface carrier though! The giant airships--I figure to match the capabilities of a modern big US nuclear surface carrier, it has to mass similarly and so would be literally a mile long:eek:--somewhere between 1500 and 1800 meters long and 250-300 meters in diameter, so the smaller version would be broader than Hindenburg was long and the big one, wider than the beam of a surface carrier!:eek:--would also cost a pretty penny too, not only to construct but to maintain--we'd need hangars that dwarf the VAB at Cape Canaveral! To be sure I figure it would use no more power than a surface Nimitz-class carrier to proceed at twice the speed, 60-80 knots airspeed, and it can take shortcuts over land, and at a kilometer to a mile cruising altitude would be able to see an awfully long way. And be seen, more's the pity.

That is, it's sad in a scenario where a powerful enemy is determined to bring down the fleet--in real life our seaborne carriers are about that vulnerable anyway in case of all-out Armageddon; we get use of them in situations far short of full-scale global war however and for purpose of intimidation or other forms of force projection against much weaker foes, visibility has its benefits as well as risks!

I've pretty much purged dwelling on the sheer majestic spectacle of such a ship from my mind, or musings about how such a gigantic airship might survive something like a nearby nuclear strike.

But these are the sorts of thoughts threads like this dredge up in my twisted mind!

I didn't mention them earlier because these giants would be a kind of carrier, not a "carrier-alternative." So would giant nuclear-powered airplanes tend to be.

The hydrofoil or if you like aircushion/ground effect landing seaplanes I mentioned would be closer to the idea of a "carrier alternative." I have to agree with the criticism they'd need some kind of tender(s) too. But the fuel, living spaces, munitions magazines, maintenance shops and command centers would not all have to be in the same hull, which the requirement of a big ship for a big landing strip tends to strongly favor. And some or all of those hulls might be submarines. (Or nuke-powered ekranoplans!:eek::p) Or various land bases used ad hoc.
 
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