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There are two known examples of fuel crossfeed: The Space Shuttle and the Atlas. The Space Shuttle had fuel lines running from the ET to the main engines. Meanwhile, the Atlas fed fuel from a main tank to the sustainer and booster engines, the latter being dropped mid-flight. Presumably when the booster section was dropped, the lines running to the engines would be closed to prevent fuel leakage.

So if the US already has developed the technology for asparagus staging, why isn't it ever used, and why hasn't NASA studied it yet? I already know that crossfeed is risky/complicated but the technology is already out there. Has NASA or any other agency given a real study for asparagus/fuel crossfeed?

Edit: The targeted duplicate is asking if it is realistic/possible. I'm mainly asking for if any space agency has done a study on asparagus staging or any other form of fuel crossfeed. I know SpaceX studied crossfeed on Falcon Heavy but they never implemented it and I cannot find any papers about the study.

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    $\begingroup$ According to Wikipedia, Falcon heavy was initially designed with crossfeed, ”However, due to its extreme complexity this feature was cancelled in 2015 leaving each of the three cores to burn its own fuel. Later evaluations revealed that the propellant needed for each side booster to land (reuse) are already close to the margins so there is really no advantage to crossfeed.” This explanation doesn’t make sense to me, but it may hold a clue to why crossfeed is not popular. $\endgroup$
    – Woody
    May 4 at 15:39
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    $\begingroup$ It's a lot of plumbing, which adds weight, complexity and risk if it goes wrong. The costs outweigh the benefits. $\endgroup$
    – GdD
    May 4 at 16:17
  • $\begingroup$ American rockets has a tradition of using solid boosters $\endgroup$ May 4 at 17:00
  • $\begingroup$ @OrganicMarble no, not a dupe. The targeted question is asking if it is realistic/possible. I'm mainly asking for if any space agency has done a study on asparagus staging or any other form of fuel crossfeed. I know SpaceX studied crossfeed on Falcon Heavy but they never implemented it and I cannot find any papers about the study. $\endgroup$ May 4 at 17:06
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    $\begingroup$ The answers to the duplicate clearly explain why it isn't used. But now that you have changed the question (thereby invalidating the answer that was already posted, negative style points for you on that one) agree it is no longer a duplicate. $\endgroup$ May 4 at 17:18

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The big problem with asparagus staging is that it only works for vehicles that have multiple liquid tanks in the same stage. The problem with this is that multiple smaller tanks weigh more than 1 bigger tank (since surface area scales faster than volume). As such, asparagus staging is a total pain to implement, and the gain is relatively minor so people don't use it.

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    $\begingroup$ Are there any liquid-fueled vehicles that don't have multiple liquid tanks in the same stage? $\endgroup$ May 4 at 16:22
  • $\begingroup$ is there a better way of phrasing this? What I meant was multiple tanks of the same fuel type which I'm pretty sure Falcon heavy is the only modern one that does it. $\endgroup$ May 4 at 17:17
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    $\begingroup$ If you mean of the same fluid, it would seem that a reasonable clarification would be including that fact in the answer. However, I still don't see what multiple tanks of the same liquid in the same stage have to do with asparagus staging - which involves multiple bodies - so when you edit, some clarification on that would be great. However, the OP has changed the question so that this is no longer an answer to it. They now want to know if studies have actually been done, which this does not address. $\endgroup$ May 4 at 17:21
  • $\begingroup$ @OrganicMarble I haven't really changed the question that I'm asking, I've just changed the title and a bit of the contents to focus more on it. $\endgroup$ May 5 at 12:37
  • $\begingroup$ @fasterthanlight if you're asking why it doesn't work, it's a duplicate. If you're asking for the history of studies, you've invalidated this answer. $\endgroup$ May 5 at 12:42
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As far as I am aware, asparagus staging has not yet been attempted by any space agency. However, Vladimir Chelomey proposed the so called 'UR-700' Rocket as an alternative to the N1 Soviet Moon Rocket.

The UR-700 would have had fuel crossfeed from its three liquid booster-pairs to the core stage - 'onion staging'. It was never built, and I do not know how realistic and well thought-out this design really was, but this is the closest I can get you.

Link to Astronautics here

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