I am an aeronautical engineering student and at university with a group of friends we are are working on building a rocket aimed at getting past the Karman Line (boundary to space).

We will be starting with smaller rocket launched and building our way up to the final rocket. I am thinking about what the best method would be to scale our design. We could build a small liquid engine rocket and as we go on to build larger rockets, we would use the same liquid engine rocket but it would bigger in size or the alternative would be to use multiple small ones and multiple nozzles.

In short, what is a more scalable design, one large nozzle or multiple small nozzles?

I can understand that with using multiple smaller engines would be better since we would have tested, and launched them previously. Whereas if we were just to make the liquid larger, we wouldn't have launched them before.

I am not sure if I have explained my question clearly. Do comment if you want any other clarifications.

FYI: we are using a bi-propellant engine, with no turbo pump and regenerative cooling.

  • $\begingroup$ beware that scale increases exponentially and not linearly. higher = more fuel + structural components to carry the increased fuel + more fuel to carry the structural components... I suggest setting specific altitude targets and using data from each test to improve your (aerodynamic and otherwise) model as you go. I suspect multiple stages will win in the end... $\endgroup$
    – Abel
    Dec 26, 2021 at 19:35
  • $\begingroup$ @Abel thanks for that advice! Just to double check, in your last sentence you meant 'multiple stages' and not 'multiple engines'? $\endgroup$
    – Shapol
    Dec 26, 2021 at 19:42
  • $\begingroup$ Will you be getting supersonic flow after the combustion chamber? $\endgroup$
    – Solar Mike
    Dec 26, 2021 at 19:45
  • $\begingroup$ it would theoretically be possible to have stages that are purely fuel tanks, but the benefits of separate engines for each stage tend to be nice- engines designed for the load they carry and the ability to kick off your previous stage instead of only having low density air and your fuel products to satisfy conservation of momentum. $\endgroup$
    – Abel
    Dec 26, 2021 at 19:55
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    $\begingroup$ I'm voting to close because none of the necessary parameters are given. There are about 20 parameters needed to even begin thinking about this. That none are provided does not bode well. $\endgroup$
    – Phil Sweet
    Dec 27, 2021 at 22:25

1 Answer 1


In strictly practical terms, the quickest solution is to derive a good design for the small engine and then simply add more of them. Scaling up a rocket nozzle is a difficult process (lots of nonlinear effects that cannot be neglected) and after the scale-up, you would need to verify the new design through repetitive testing, which costs lots of money and takes lots of time.


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