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by Karellen 886 days ago
> Kilmartin said one of the questions he asked when he first got into the business was “who came up with this idea? He had to be a madman.”

Kilmartin should spend more time around rocket scientists. After hearing a few tales of some of the stuff they've come up with in the name of performance - like a Hydrogen/Lithium/Fluorine(!) tripropellant engine (but you get an Isp of 542s!!!) - using Hydrogen for cooling will sound positively tame, and easily controlled.
1 comments
Tuna-Fish 886 days ago
Rocket science as a field moved out of exotic energetic fuels by the end of the 90's, because the juice wasn't worth the squeeze, and there is currently an ongoing industry-wide exodus from hydrogen to methane for the same reason.

Getting the peak of performance sounds cool when you ignore costs, but in the real world with limited budgets, building a rocket twice as large is easily worth it if it means you never have to touch liquid hydrogen.

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le-mark 886 days ago
> there is currently an ongoing industry-wide exodus from hydrogen to methane for the same reason.

Exodus seems a bit of an overstatement. Other than spacex who else has or is planning to develop a methane engine? And other than SSME and Vulcain which other widely used engines used H2?

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Tuna-Fish 885 days ago
What Karellen said, but also ArianeSpace (Prometheus) and Landspace (TQ-12).

It is very hard for a hydrogen-fueled rocket to be cost-competitive against a methane-fueled one. Not strictly because of the cost of the fuel, but because of the cost of everything else that LH requires that LCH4 doesn't.

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Karellen 886 days ago
> who else has or is planning to develop a methane engine?

BO's New Glenn first stage, RocketLab's Neutron, and Relativity Space's Terran 1/Terran R, are all/will all be methane.

> which other widely used engines used H2?

Ariane 5 and 6, and the upper stages of previous Ariane rockets

https://en.wikipedia.org/wiki/Rocket_propellant#Current_cryo...

Edit: Long March 9 will be mostly methane, with hydrogen upper stage.

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njarboe 886 days ago
Even more so in the era of re-usable rockets. Cheap fuel and reliability are now the focus.
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