How do you power a missile by nuclear energy? There’s speculation that’s what the Russians were trying to do and it went wrong. But how would that work? Wouldn’t the shielding around the nuclear source be too heavy to allow flight? And what would the propellant be?
You only need shielding if you’re interested in protecting what’s around it. Which isn’t generally the case with a missile.
The propellant can be pretty much anything: Generate enough heat to vaporize it, and shoot it out the back.
The US had similar development efforts in the Cold War under Project Pluto. Not having a crew they didn’t worry about the level of shielding you might expect. The propellant is air. The nuclear reaction heated the air forcing it to expand and push out the nozzle in the back.
What about the soldiers who use them? Don’t they need to be protected?
That doesn’t require building the shielding into the missile itself. Options for loading the reactor remotely and servicing the missile are even greater with current tech than they were when the US was experimenting with nuclear ramjets in the 50s.
This? Nuclear thermal rocket - Wikipedia
I recall there are analogs in KSP. They had better specific impulse than other engines, but less thrust per mass. It took me a while to see how they were useful since for a long time thrust/mass was more important, but I eventually realized on the last stage that specific impulse was more important. But that was years and years ago, and was a video game.
This is not my area of expertise, but from what I have read, there are a couple of advantages of nuclear missiles based around their lack of propellant.
Missiles that have a propellant either need the propellant to be always loaded into the missile, which has risks associated with it, or they need to have the propellant loaded prior to launch, which adds a significant delay between the decision to launch and actually sending the missile away. In either case, the propellants have a limited shelf life and need to be replaced periodically. A nuclear missile uses air for its propellant, so it would not need any of this propellant maintenance.
Since a nuclear missile does not carry its own propellant, this also means that you can put a heavier payload onto the missile.
The problem with most of the nuclear thermal rockets I’m aware of, like the infamous Pluto mentioned upthread, is that they also need a conventionally powered stage to accelerate them to the point where the nuclear ramjet will work. Which is what I believe happened with the Russian Burevestnik accident in Severodvinsk. The liquid fueled booster went tits up, which breached reactor shielding on the rest of the missile.
There are designs for a nuclear ramjet that don’t require a booster to get up to speed, like a nuclear saltwater rocket or a pulsed detonation propulsion concept, but they’re even tougher on the environment…
The Russians must not be confident about their ICBM deterrent at all, if they’re screwing around with things like Burevestnik, and Poseidon/Status-6, IMHO.
Can a nuclear ramjet be used to take a spaceplane into orbit? I’m guessing not, because it is designed for long cruising flights, not quick, energetic acceleration.
I’m try not to hijack too much, but considering the trouble they have keeping up maintenance on all of their other military equipment, what are the odds of an ICBM launched from Russia making it all the way to the continental US and striking its target? Seems like there’s a possibility some won’t launch, some will blow up after they launch, some will lose their guidance during flight, some will fail to detonate, some will try to blow but fizzle in to a dirty bomb…
Not sure if it was here or Reddit, but someone commented that the Russians wanted a credible card to trade in an eventual arms treaty. But i would agree that the Russian crystal ball is pretty bleak on their sluggers getting through a first generation BMD shield.
All very interesting - thanks everyone.
(Please keep on talking; I’m not trying to close down the discussion, just expressing my appreciation.)
One thing about a nuclear missile is that it is, in principle, no different to any other sort of ramjet. Air is jammed in the front, compressed, and some sort of energy source heats it up (a lot) and then it is ejected out the back to create thrust. The extra energy translates to higher velocity out the back, and so you have thrust. Normal ramjets burn stuff in the air to get the heat, a nuclear powered one uses the air to cool the reactor. The reactor can be quiescent in storage, and pretty safe to handle. Once the thing is in flight (as noted earlier, something needs to get it up to ramjet speed - probably a solid fuel motor) it can pull the control rods and get going. The entire thing probably becomes quite radioactively hot, but given it is a long way from anyone it may be considered to be less of a problem. Just how you get the energy from the reactor into the airstream inside the ramjet - given the near supersonic flow - is probably part of the deep magic. At least when you pump fuel into the air the gas is implicitly heated as it burns. The problem is just making it burn fast enough. I sort of doubt fast neutrons will thermalise the flow fast enough, but maybe they can. No doubt it is pretty toasty in there.
The big advantage of nuclear cruise missile is that they can stay aloft indefinitely, or at least for a much longer time than a conventional cruise missile. This allows them to do things like mimic flight plans of other aircraft, take long circuitous routes through air defences, or, if you had enough of them you could always have some flying near enemy territory, ready to swoop in on a moment’s notice.
Eh, you don’t want them loitering in friendly airspace, because of the fallout, and if you loiter them in unfriendly airspace, they’ll be shot down.
If they wanted to mimic the flight plan for a conventional aircraft, couldn’t they just put a bomb on an airliner and program the autopilot appropriately?
It seems more likely that they intend to fly the missile at very low altitude to evade radar and surface-to-air missiles. Flying at low altitude takes a lot more energy than flying at typical aircraft cruising altitude, so nuclear power would be useful.
Another huge problem with these missiles as a weapon is they aren’t stealthy.
As they fly, they will glow like a small sun in the gamma ray spectrum. The U.S. air force could counter by developing satellites or jet fighter armed with gamma cameras. Fly high enough that you can cover the possible flight paths that a missile like this will likely take, and detect it in the gamma camera as a bright white dot.
Not stealthy at all.
Though I recall that the strategy was to fly ridiculously fast and low, such that fuel burning interceptors cannot really catch the missile.
Seems like a lot of trouble when ICBMs still work just fine and are usually not going to be intercepted.
Can gamma ray sources be pinpointed with accuracy? Isn’t that why determining the origin of gamma ray bursters is quite a challenge?
Well, bursts are a very short duration and jillions of miles away and anywhere in the sky. A nuclear missile is contained to the earth, only thousands of miles away at most, and running indefinitely.
Edit: unless I’m misunderstanding what you are calling “gamma ray bursters”. I was thinking of the cosmological event.
Gamma rays are challenging, to say the least, to image, because they’ll just go straight through most sorts of optics. But there are methods that can be used, and having multiple vantage points would help a lot.