Extracting Power from Nuclear in Space

This argument is a clear case of "a vanablackened cat calling a kettle black". I am not against NTR, I am not an admirer of the current NTR because frankly they suck. Here is why they suck. Except for the fact that no current fissile NTR design is in use and Solar electric propulsion is one of the most popular forms of propulsion. Proof of the pudding is in the eating, and no-one want to eat NTR, it leaves a bad taste in the mouth.

NERVA 825 ISP = 8093 m/s. If we assume the nozzle is say 6.7 meters. a = 7,700,000 j = 30,732,000 J/kg

177 MeV is the amount of fission energy in a of 235U. This is 0.0000000000283585 J/235U. One 235U weighs 3.902E-25 kgs. Thats 72,000,000,000,000 J/kg. Lets assume that an NTR rocket has at ION drive efficiency converts 1 kg of Uranium-235 into dead fission products. How much fuel would you need to carry to make the reaction efficient you would need to carry 2364 tons of hydrogen. The big STS orange tank carried 106 t of H2.

The peewee project had 36.8 kg of uranium. 9200 m/s Ve. Lets be generous and say 40,000,000 J/Kg. The burn length was 80 sec at 12.5 kg/sec = 10t of fuel.

Available power = 36.8 kg (assuming pure U235) * 72TJ/kg = 2.6PJ of Energy available. Of this 400 GJ was used for an efficiency of .015%. If we compare this with solar electric power, the SA power utilization is 0.2 to 0.3, the power efficiency of the drive is .7 to .8 the total Power inefficiency is 14%. In terms of power utilization SEP is almost 1000 times more efficient than NTR. Even if we granted the Uranium235 mass ratio was unenriched at .0072:1 the energy efficiency of Peewee would have been 2.08%. So don't give this BS about ION drives being power inefficient. The NTR rockets are the least power efficient system right now, and it does not really give a spectacular product for the numerous risks and shortcomings. If you could come up with a closed loop fission system (such as a fast breed reactor) at 10% power efficient with a coupled ION drive system would produce a better and safer result than the NTR. At least the Soviets repeatedly placed such reactors in space, NTRs have no space track record at all. . . . .and I don't even like fission electric.

The advantage of fission electric over NTR.

No need to carry liqH2. Xenon and argon pack quite nicely. Magnesium maybe a future fuel. You could provide a fuel that both blocks radiation and can be used in the ION drive.

Fission electric can be shut down if 235U is used as a fuel because its much easier with little weight to reach to approach prompt critical.

Its much easier to shield because you are not spewing products into the space your ship is flying through.

Solar power can both provide power for ship system and manuevering and low power operations through ION drives when reactor is shut down.

The ISPs are much, much better.

Remember that the inside skin of the nozzle both slows the gas and cools it down, eventually you will have accumulation.Extracting Power from Nuclear in Space

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