Recent comments in /f/space

cjameshuff t1_j6j0557 wrote

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

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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MisinformedGenius t1_j6ix7ch wrote

Reply to comment by bremidon in Number of manned orbital launches by year, 1961-2022 by firefly-metaverse

What? The fact is that they were the first nation to launch an object into orbit, the first nation to launch a man into orbit, the first nation to launch an object into orbit around the Moon, and many other firsts. They had put two satellites in orbit by the time our first attempt blew up on the pad.

Yes, of course they were behind the US by the time we got to the Moon, but when Kennedy announced the Apollo program, we were without a doubt behind them. Can you name anything at all we did before the Soviets before, say, 1965?

The idea that they were behind us yet somehow would figure out what we were already doing and beat us to the punch despite our head start is nonsensical to say the least.

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danielravennest t1_j6ivn9h wrote

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

> (nobody wants a dirty bomb going off in the sky)

Before you start up a reactor for the first time, the core is low radiation. Reactors produce short-life fission products, which is what makes nuclear waste dangerous.

Rocket mass is in kg, not moles. Exhaust velocity is ~9 km/s for hydrogen, vs ~4.5 km for H2-O2 engines.

I'm a space systems engineer, who has worked on nuclear rocket designs. My opinion is the time for nuclear-thermal propulsion is past. Solar-thermal can get the same performance - both heat H2 to the limits of the materials. But solar doesn't have all the nuclear baggage to deal with.

Nuclear-electric has much higher performance (3-20 times), though like all electric systems it has longer burn times. The reactor can be much smaller (1 MW rather than 1 GW), making radiators and such easier to do.

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