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> I think it’s a reasonable supposition in the absence of further information that they had something go very wrong with a static fire of a nuclear ramjet - pro

> I think it’s a reasonable supposition in the absence of further information that they had something go very wrong with a static fire of a nuclear ramjet - probably not a nuclear detonation Can you explain this a bit more for those of us who know almost nothing about missiles/nuclear weapons. If I'm understanding the Project Pluto wikipedia correctly a ramjet isn't able to fire from a standstill and a nuclear ramjet would require both initial forward motion and then a nuclear detonation (not sure if that's the right word, perhaps just "reaction"). So I guess my question is, how would they safely static fire these types of missiles for testing purposes? Assuming Russia's project uses a similar setup to Project Pluto and has conventional rocket boosters to get the missile to ramjet speed is that what they'd be static firing - the boosters? And if they're testing the boosters attached to the nuclear ramjet without allowing the ramjet's reactor to go critical what would have to go wrong with the static fire that would result in radiation?

trevyn 7y ago
Just force air in with a big fan or jet engine to simulate forward motion?
- madaxe_again 7y ago
  Jet engine with a huge bypass factor for the compression stage, when testing on a static rig, yes.
LorenPechtel 7y ago
If the ramjet didn't go critical it wouldn't be of much use. The key number when you are talking about an operating reactor is called the multiplication factor--when an atom fissions on average how many other atoms will be split by the neutrons released from that fission. When this number is less than one things just peacefully sit there. If an atom fissions the chain soon dies out. If this number is more than one things get hotter and hotter until it comes apart. If this were the whole story there would be no nuclear power, but there's one very useful detail--a small number of those neutrons are not emitted at once. This gives you a margin to control things. When the immediate neutrons are enough to cause more than one fission you have the state known as prompt critical, you have lost control, the reactor will run wild and destroy itself. (An atom bomb is the same idea, except rather than just edging past 1 a bombmaker pushes the ratio as high as possible so it takes a city with it in destroying itself.) I am aware of two cases where reactors had issues with control rods and crossed the prompt critical line, both were immediately destroyed. SL-1 and Chernobyl. The zone between critical and prompt critical gives you a way to control things. You have time to turn the heat up or down as needed. A nuclear ramjet is going to be designed to operate at a very high power density, it's going to be a lot closer to the line than a reactor is normally run. Stick one toe over the line and you get what SpaceX calls a RUD. Alternately, it might have run too hot, something softened or melted and the core shape changed to cross the prompt critical line, same outcome.
- elliekelly 7y ago
  Interesting, so because a nuclear ramjet runs closer to the line there’s less time to make adjustments and control things to prevent RUD. I guess that makes testing all the more difficult/dangerous. Thanks for such a thorough explanation that I could actually follow! Much appreciated.

trevyn 7y ago

Just force air in with a big fan or jet engine to simulate forward motion?

madaxe_again 7y ago
Jet engine with a huge bypass factor for the compression stage, when testing on a static rig, yes.

LorenPechtel 7y ago

If the ramjet didn't go critical it wouldn't be of much use. The key number when you are talking about an operating reactor is called the multiplication factor--when an atom fissions on average how many other atoms will be split by the neutrons released from that fission. When this number is less than one things just peacefully sit there. If an atom fissions the chain soon dies out. If this number is more than one things get hotter and hotter until it comes apart. If this were the whole story there would be no nuclear power, but there's one very useful detail--a small number of those neutrons are not emitted at once. This gives you a margin to control things. When the immediate neutrons are enough to cause more than one fission you have the state known as prompt critical, you have lost control, the reactor will run wild and destroy itself. (An atom bomb is the same idea, except rather than just edging past 1 a bombmaker pushes the ratio as high as possible so it takes a city with it in destroying itself.) I am aware of two cases where reactors had issues with control rods and crossed the prompt critical line, both were immediately destroyed. SL-1 and Chernobyl. The zone between critical and prompt critical gives you a way to control things. You have time to turn the heat up or down as needed. A nuclear ramjet is going to be designed to operate at a very high power density, it's going to be a lot closer to the line than a reactor is normally run. Stick one toe over the line and you get what SpaceX calls a RUD. Alternately, it might have run too hot, something softened or melted and the core shape changed to cross the prompt critical line, same outcome.

elliekelly 7y ago
Interesting, so because a nuclear ramjet runs closer to the line there’s less time to make adjustments and control things to prevent RUD. I guess that makes testing all the more difficult/dangerous. Thanks for such a thorough explanation that I could actually follow! Much appreciated.