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I'm specifically looking for an answer to whether a pressure fed or pump fed engine would be more feasible considering a mass of over 50T(metric, of course), and a single stage to descend and then re-fire the engines to ascend again.

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    $\begingroup$ Define "best" / "more feasible" for a meaningful answer. Cost? Schedule? Mass? $\endgroup$ Jan 12, 2023 at 0:03
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    $\begingroup$ For an ascent stage, I'd think "reliability" would be the deciding criteria for declaring something the best. $\endgroup$
    – Mark
    Jan 12, 2023 at 3:55
  • $\begingroup$ @OrganicMarble Unfortunately I may have to answer "all" to your suggestions. Mass, Cost, Workability with storable propellants, etc. I should perhaps re-fraise my question slightly, but I think basically an answer that is perhaps not definitive but provides extensive information on WHY I would choose different engine cycles. thanks (: $\endgroup$ Jan 13, 2023 at 6:16
  • $\begingroup$ @Mark certainly, however my question is intended specifically for a vehicle that can achieve a landing and an ascent to LLEO (low lunar equatorial orbit). This is so that, theoretically, I could deliver cargo, load a small payload from a surface base, such as waste, used batteries, or people, and then ascend to an orbiting station. I agree however that reliability is a big factor. I had thought previously that pressure fed storable would be best, but given a lower ISP etc., I thought I had better ask. Thanks! $\endgroup$ Jan 13, 2023 at 6:20
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    $\begingroup$ "Optimize everything!" is not a winning strategy. You might be interested in the paper linked in this answer to learn about some of the tradeoffs. space.stackexchange.com/a/43155/6944 $\endgroup$ Jan 13, 2023 at 13:13

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I would argue a simple pressure-fed engine cycle is a good option.

These are low complexity and reliable, which are very attractive properties for a lunar landing system. They can not have high chamber pressure nor do they have particularly high thrust (50t on the moon does still not demand high thrust), but this these drawbacks are much less felt than in the first stages of orbital launch systems.

Restarting pressure-fed engines is also conceptually simpler since this is simply a question of vales, where restarting turbo pumps or for that matter any other pump system can be much trickier.

Much more than that can't be said without knowing the specific requirements.

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    $\begingroup$ @ikrase Sea Dragon was going to be pressure-fed $\endgroup$ Jan 26, 2023 at 5:37
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    $\begingroup$ Space.SE: The only place where Sea Dragon is an anchor point for "reasonable". $\endgroup$ Jan 26, 2023 at 6:36
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    $\begingroup$ @SE-stopfiringthegoodguys how in the hell would they have tested that engine? $\endgroup$ Feb 1, 2023 at 18:56
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    $\begingroup$ @OrganicMarble Just attach fifty F-1 engines pushing in the other direction to keep it still. ez. $\endgroup$ Feb 1, 2023 at 19:35
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    $\begingroup$ As to testing the sea dragon engine it would have been placed in a test stand, I think. Just pointing up slightly. Thus it won't carry the entire testing facility into the air. (: $\endgroup$ Feb 7, 2023 at 4:31

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