Comment by jlgreco | Hacker News Reader

Comment by jlgreco | Hacker News Reader

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Part of the problem with reusing SSMEs was that they burned hydrogen and hydrogen embrittlement basically ensured that any sort of fast or cheap turn around with SSMEs was impossible.

Hydrogen is a pain in the ass to work with if you want a reusable rocket. The Space Shuttle was really only nominally reusable, the engines had to practically be rebuilt every time to make sure everything was alright (the SRBs were hardly any better, though at least they were simpler.) (Really, hydrogen is just a pain in the ass in general though. It isn't very dense and needs to be kept much cooler than LOX to boot (requiring all that foam on the external tanks), which is why the Shuttle external tank had to be so goddamn big. The massive efficiency of LOX/LH2 are somewhat mitigated by these factors.)

If SpaceX can get their F9R working well, that will likely be the first properly reusable rocket (first stage anyway). Those will burn RP-1 which won't suffer from hydrogen embrittlement.

The Soviets would have been better off continuing to neglect LH2/LOX and focus on the fuels they did best with (basically what they have done ever since they discontinued Energia). Also, while the Energia would have been suboptimal for non-Buran loads, it still would have been the heaviest lifting rocket they ever had, able to put 32,000kg into TLI (compared to the Saturn V's 47,000kg and the N1's never realized 23,500 kg). The Shuttle stack wasn't merely suboptimal for that sort of thing, it was worthless.

Yeah, the SSME's were never as reusable as projected but their efficiency helped to mitigate somewhat the massive cost in weight of the shuttle. If you are committed to a shuttle design you might as well choose a very efficient partially reusable engine over one with RP-1 or a less efficient lox/h20 engine with lower total costs. That isn't an argument in favor of the shuttle just a reasonable design choice.

>>The Soviets would have been better off continuing to neglect LH2/LOX and focus on the fuels they did best with (basically what they have done ever since they discontinued Energia).

I have to disagree with this. The soviets began developing LH2/LOX technologies immediately after the N1 failure for the same reason that the Saturn V used LH2/LOX as an upper stage fuel: it is hard to make the math work for massive rockets that only consume RP-1. The weight penalty on the upper stages is just too large to be cost effective. You might as well pay the cost of LH2/LOX development if you intend to launch super heavy payloads.

>>Also, while the Energia would have been suboptimal for non-Buran loads, it still would have been the heaviest lifting rocket they ever had, able to put 32,000kg into TLI (compared to the Saturn V's 47,000kg and the N1's never realized 23,500 kg). The Shuttle stack wasn't merely suboptimal for that sort of thing, it was worthless.

If the criteria for deciding between SLS/Buran-Energia is which one can launch the most payload then, yes, you would choose Energia. This wasn't an intended benefit of Energia and was simply due to reliability concerns about reusing rocket engines(especially with fuel sources that the Soviets didn't have experience with).

It is hard to evaluate the cost of reusing Energia technology and developing a new booster that would be more optimal going forward. If the Soviets had the money and the political foresight to cancel Buran they might have been able to do it and use Soyuz and Energia together.

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