Is an open expander (bleed-off) cycle engine that uses the gasified cryogenic oxidizer instead of the gasified fuel to drive the turbo pumps technically feasible?

I was thinking of a first stage open expander cycle rocket engine. Usually they're driven by H2, like in the case of the RL-10, RL-60 (I know they're actually closed cycles) or the LE-5 (those run actually open expander cycles). But H2 is very difficult to handle, as we've seen recently on the SLS. The next best fuel would be methane, but bleeding that off would get me into trouble with environmentalists since it's a great greenhouse gas. So why not using the oxygen in a Methane/LOX combination to drive the turbine of the turbo pumps?

I know, you'd probably waste more LOX by mass than by using H2, but is it really that bad? Since we're talking first stage applications here, the mass penalty isn't as bad as in the case with second stage propulsion, is it?

What would be the technical challenges that you would face in that setup?

Thanks for your answers.


1 Answer 1


Because warmed oxygen, as warmed metal would see it, is EXTREMELY CORROSIVE .

If your (admittedly first-) stage is lit for seconds like an interceptor missile, then those few seconds might just have everything hold together. However, you must also test any launcher stage if you expect anyone to trust their payload on it. How many tests- four? three? two? If you think the answer is zero, then either you’re military and can test by batch/QE due to your extended production run. Or, you know nothing of mission assurance, and (assuming you’re speaking of an orbital launcher, not a human-scale missile) we won’t be trusting our expensive programs to your concept:


It’s true that the Soviets did stuff in “sour” (oxidizer-rich) mixtures, including launch. Chiefly these used ceramics. However, you’re speaking of a turbine, and a room temp/cryo cycling one at that, which is a pretty lousy place to put brittle structures.

  • $\begingroup$ I see the corrosion problem but can't you solve that with smart metallurgy? I assumed that since there are working oxygen rich staged-combustion rocket engines corrosion should be a solvable problem. $\endgroup$ Jan 21 at 21:33
  • $\begingroup$ You still don’t get it YOUSTILLDONTGETIT. We do not invest our time, money, expertise, and pride/sense of accomplishment to make payloads that are “blowuppable.” Even the missile people want a hit, not a firework. So too should you have the pride to make any engine of your “unblowuppable”- but seems like no. Seems like you invested no time, money, expertise, etc., or you think you did. We want to have our payloads get there, and “there” is not the bottom of the sea. We are not interested in your brilliant idea, and will not pay for your brilliance, much less ego stroking. $\endgroup$ Jan 25 at 21:07
  • $\begingroup$ Akin’s Law #4: Your best design efforts will inevitably wind up being useless in the final design. Learn to live with the disappointment. Einstein: “Strive not to be a success, but to be of value.” What value does some new turbine bring- what problem does it solve, other than stroking your ego for coming up with it? We have viable rockets, does your turbine solve a problem, shift to a different problem, or ADD a problem? The problem is getting us there, yet lowering cost, risk, etc.- yet when challenged, you responded with no analysis, no test data, no plan forward: ‘Solve it for me’ $\endgroup$ Jan 25 at 21:15
  • $\begingroup$ I told you sour mixtures (not even pure O, but OH-) were handled via ceramics. Ceramics which make bad turbines in general, and increasingly so with size. When challenged with this, your answer is “I assume” smart people will solve it for you ? It’s our responsibility to stroke your brilliance- la idee fixe ? $\endgroup$ Jan 25 at 21:18

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