KSP Quickie with Bob: Nuclear Lightbulb

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Robert Dodd

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Published on November 28, 2015 7:58:55 PM ● Video Link: https://www.youtube.com/watch?v=CRcUgx7KyWg

Duration: 17:04

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13

It is a perennial problem with rocket engines of all kinds. If you want to increase efficiency, you have to increase the temperature inside the combustion chamber. Increase the temperature however, and your engine may just melt.

This is a problem when trying to make nuclear engines more efficient: at a certain point you reach temperatures that no known material can withstand, and your reactor core melts.

One approach to this problem is, "let it melt." Hence the open-cycle gas core nuclear rocket engine was born. Just melt that shit, swish it around the combustion chamber and let it mix with the reaction mass ("fuel") and spit that shit out the end. The problem being that in addition to spitting out hot gas, an open-cycle GCNTR spits out fissionable materials as well. The problems with this are that 1. your engine has a case of radioactive diarrhea and 2. you lose nuclear material from the engine that you have to replace.

To overcome those limitations, the idea of the nuclear lightbulb was born. Essentially what you have is fissioning uranium hexafluoride gas contained within a quartz tube which is cooled while the engine is in operation. Outside these quartz tubes flows the reaction mass, which is liquid hydrogen seeded with tungsten particles. This quartz tube is transparent to radiation, and so while the hot nuclear gasses are swishing around they are spitting out lots of radiation which passes through the quartz wall but gets absorbed by the tungsten particles, causing them to vaporize, causing the reaction mass (the liquid hydrogen) to be heated up a lot, thus propelling your spacecraft.

Now, lightbulb is a bit of a misnomer in that the nuclear gas core is not giving off visible light. In fact the core is so hot and radioactive that all the light coming off it would be shifted to the ultraviolet wavelengths and above, so it would look quite dark to anyone so unfortunate as to be looking at it with the naked eye. ;)

This engine right now only exists in theory, no one has ever built one and the complexities involved in engineering and testing this bitch are mind-boggling so we may well never see one built. It may be that when the time comes, humanity finds a better way to go fast in space than shaking up a hot radioactive milkshake inside fragile quartz tubes. ;) It is nevertheless a proposed way to make the kind of leap forward in propulsion technology that would make places like Mars much more accessible.