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danielravennest t1_j6ilp8k wrote

Reply to comment by GeorgeOlduvai in NASA tested new propulsion tech that could unlock new deep space travel possibilities by Creepy_Toe2680

Nuclear rockets use pure hydrogen as propellant. Lighter molecules move faster, and H2 is much lighter than H2O.

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cjameshuff t1_j6j0557 wrote

And you can use heavier things as propellant, like ammonia (water and methane are both bad choices for various reasons), but anything but LH2 gives you only slightly more performance than chemical engines.

Meanwhile, instead of a pile of steel, copper, and nickel alloys carefully arranged to burn stuff really well, you need enriched uranium arranged to sustain a nuclear fission chain reaction. That's a huge step up in cost and regulatory complications, and nobody's going to do it for something barely better than a chemical engine, so LH2 it is.

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stanspaceman t1_j6jhkvt wrote

They don't use high enriched Uranium FYI, it's HALEU, mandated for all space systems currently being designed.

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cjameshuff t1_j6jk6m5 wrote

I didn't say HEU, I said enriched uranium. HALEU is enriched to a U-235 content of 5-20%, natural uranium is only 0.72% U-235.

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