They say they’ve closed the loop on the propulsion system for the Lynx. Sounds like they still have to improve it to get needed performance, but that’s a breakthrough. One of the long poles, as well as the wings.
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There’s something a little weird here. I thought they closed the loop at least once before. But that may also have be more to do with _efficiency_ of the result.
No, pretty sure this is a first, based on a discussion I had last week.
You may be thinking of the XCOR hydrogen engine.
Nope, not thinking of the hydrogen engine, but I’d need to look back at some old Reports and perhaps other files re the “is this the first time” question.
Charles, don’t forget that XCOR is working on two different engines with closed-loop pump drive: The Lynx engine which burns LOX and kerosene, and the liquid hydrogen engine. It’s possible you’re thinking of something you may have heard a while back about the hydrogen engine.
Rand, I’d guess one of the things they want to have a little additional efficiency in hand for is so they can trade some away as they compact and simplify the mass of plumbing showing in that test-stand picture so it’ll fit inside the back of Lynx.
Did this have to fly Lynx Mk 1 or is this an achievement for a higher performing successor?
Lynx has been planned around this engine from early days; the engine and airframe have been developed in tandem. They could probably make Lynx fly with some sort of open-loop alternate version engine, but the performance hit would be quite large.
Rand, what does “closed the loop” mean in this context? I’ve seen the term used but not defined.
They’re talking about engine propellant feed pumps driven entirely by waste heat from the engine, via a closed helium heat-transfer loop. This is a high-efficiency rocket engine cycle that as far as I know has never been done before.
So, no heavy high-pressure propellant tanks for a “pressure-fed” engine, no heavy high-pressure gas tanks to drive the pumps as in XCOR’s previous X-Racer, and no throwing roughly 10% of the propellant energy overboard via a “gas-generator” to run the pumps.
Potentially 98-99% of the energy in the rocket propellant can actually come out as thrust here. The only other types of rocket engine that could do that up till now were “staged-combustion” (like Shuttle main engines or the Russian RD-180) or “expander-cycle” like the old RL-10 upper stage engine.