Just learned of the Sea Dragon proposal from back in 1962. From the Wikipedia entry

The first stage was to be powered by a single enormous 80,000,000 pounds-force (360 MN) thrust engine burning RP-1 and LOX (liquid oxygen). The fuels were pushed into the engine by liquid nitrogen, which provided a pressure of 32 atm for the RP-1 and 17 atm for the LOX, providing a total pressure in the engine of 20 atm (~300 psi) at takeoff.

That's a huge amount of thrust, especially for a single engine. Although the design proposal was never further investigated, would an engine this large be possible to fabricate today? Has any research into actually producing anything larger than the F1 been seriously carried out?

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    $\begingroup$ Good grief if they ever started that engine it would be the biggest Sodastream in history... $\endgroup$
    – Andy
    Commented Jun 23, 2016 at 15:48
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    $\begingroup$ @Andy I wonder what the wake from starting that thing underwater would have been like! $\endgroup$ Commented Jun 23, 2016 at 17:55
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    $\begingroup$ Indeed - and bubbling sea can sink ships because the bubbles reduce the overall density of the water. (I assume they considered such effects for launches and test firings...) $\endgroup$
    – Andy
    Commented Jun 24, 2016 at 8:01
  • $\begingroup$ new SciShow Space video Meet the Sea Dragon: The Biggest Rocket Ever Designed $\endgroup$
    – uhoh
    Commented Jul 13, 2019 at 2:35

1 Answer 1


Has any research into actually producing anything larger than the F1 been seriously carried out?

The M-1 was a hydrogen engine just a little larger than the F-1. Parts of it were built and tested and the engine would likely have worked just fine if completed and flown. Lack of need for a super-heavy lift vehicle larger than a Saturn V prevented it from being developed further.

The RD-170/171 is comparable to the F-1 -- heavier but more compact, and just a bit more powerful.

Although the [Sea Dragon] proposal was never further investigated, would [Sea Dragon's first-stage engine] be possible to fabricate today?

Probably. The design was fairly conservative for all its size, pressure-fed rather than pump-fed, with quite low chamber pressure. As mentioned in the Wikipedia article, the general design was reviewed and considered sound by TRW; I assume that includes the engines.

The main problem I'd expect to see would be combustion instability -- conventional wisdom says that's a bigger problem in large chambers than small ones, and this is certainly a large chamber. This Q/A discusses that problem.

However, the original Aerojet-General proposal suggests that the resonant frequencies of such a large chamber would be so low that feedback instability wouldn't be sustained:

With regard to combustion stability, an analysis on the basis of sensitive time lag theory (perhaps the best theory so far developed) indicates that the Sea Dragon thrust chamber will operate well outside the region of combustion instability. One of the primary advantages of sea based development testing is that it permits early experimental evaluation of combustion stability on a full scale basis without an exorbitant outlay for facilities.

In other words "we don't think it's a problem, but, hey, at least if one of those engines blows up in the ocean it won't hurt anything."

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    $\begingroup$ Great answer! It seems that multiple engines are all the rave these days, so a single gargantuan engine would be amazing to have seen. $\endgroup$ Commented Jun 24, 2016 at 13:07
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    $\begingroup$ For one big engine to make sense, you have to commit fully to the Big Dumb Booster concept - you only use it for frequent launches of low value, fungible cargo (e.g. food or propellant) and you expect to lose one every once in a while. $\endgroup$ Commented Jun 24, 2016 at 15:28
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    $\begingroup$ Testing the engine would be ...interesting. $\endgroup$ Commented Jun 26, 2016 at 2:29

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