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Why LH2/LOX for lunar lander?
Why is NASA going with LOX/LH2 for the new lunar lander instead of the
seemingly more reliable hydrazine/NO4 Apollo LEM engines? It would seem that the more easily stored hydrazine/NO4 would make for more adaptable lengthy missions. I understand that there were major concerns about a LEM being stranded on the surface. Considering the hypergolic nature of the propellent, how could this happen? Does anybody have any info on the reliability of hydrazine based engies vs LOX/LH2 engines? |
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Why LH2/LOX for lunar lander?
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Why LH2/LOX for lunar lander?
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Why LH2/LOX for lunar lander?
In article .com,
wrote: Why is NASA going with LOX/LH2 for the new lunar lander instead of the seemingly more reliable hydrazine/NO4 Apollo LEM engines? They've always planned to use something somewhat more storable for lunar *ascent* propulsion. They would prefer to avoid N2O4/hydrazine and such, because those compounds are so toxic and so dangerous to handle that they dramatically run up costs. They'd originally hoped for LOX/methane, but budget trouble is pushing them back toward N2O4/hydrazine at last report. The reason for wanting to use LOX/LH2 for lunar *descent* is their aversion to in-orbit assembly. If you insist that everything (except perhaps the crew) must go up in one big launch, suddenly the total fueled mass of the lander matters a great deal. And within a given total lander mass, you can put a lot more payload on the lunar surface with LOX/LH2 descent propulsion than with LOX/methane or N2O4/hydrazine. Storing LH2 for the few days needed to get from the Earth to the Moon is not a big problem. Apollo might well have used a LOX/LH2 descent stage if it had started a little bit later. As it was, at the time the basic decisions had to be made, LOX/LH2 propulsion was still troublesome, and it seemed too risky. LOX/LH2 descent propulsion was penciled in for follow-on systems only. By the time the LM actually flew, only a few years later, LOX/LH2 was under control and the early decision looked overly conservative. (Note that the LM descent stage *did* use cryogenics -- the helium for tank pressurization was stored that way.) I understand that there were major concerns about a LEM being stranded on the surface. Considering the hypergolic nature of the propellent, how could this happen? Tank leaks. Helium leaks. Plumbing malfunctions. Overly-hard start damaging the engine (a real worry -- excessive pressure transients at startup were never entirely cured). Stage-separation problems. Does anybody have any info on the reliability of hydrazine based engies vs LOX/LH2 engines? Any propellant-choice effect is swamped by differences between different engines. The LOX/LH2 RL10 is one of the most reliable sizable rocket engines ever built, but they aren't all like that. -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
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Why LH2/LOX for lunar lander?
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#6
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Why LH2/LOX for lunar lander?
For all the right reasons, instead of LOx/LH they should be using the
likes of h2o2/c3h4o For their moon exit phase, a little kick start directly towards LL-1 and then the use of LRn--Rn--ion thrusters should do the trick. After all, there's hardly any logic in folks returning from the moon if their banked bone marrow is simply going to be too little too late in order to save their day. In other words, the gamma and secondary/recoil worth of hard-X-rays (especially by day) is going to insure that no human DNA is ever going to be unscaved. Aluminum is nearly transparent to gamma, and it's hardly worth moderating the likes of hard-X-rays. The usage of UHMW/Polyethalene or similar density to H2O is simply going to demand too much volume. - Brad Guth |
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