The past Nov 18 was the last launch, of Starship. The things didn't happen as planned. But all of us know that soon or later Spacex will make it a successful. It will be a long time before it can be reliable to carry a load similar to James Space Webb.

My question is: Why Spacex Starship is not a modular rocket ? Currently all the heavy lift rocket category are built in modular way, like:

Falcon_Heavy with 3 modules of 9 engines each one. ULA delta 4 heavy with three RS-68 engines one in each booster. Angará A-5 consists of one URM-1 core and four URM-1 boosters. Arianne 5, one core plus two solid fuel boosters. China Long March 5, one core and 4 boosters.

Is there any physics constraint related with the payload and the kind of mission for which it was designed ?

Because is really complicated feed and deliver oxygen and propellant to 33 engines.

And of course is more easy to do it if you have 3 block with 11 engine each, or 4 with 9 engines. Also short construction times. because you can have 3 hangars with many personnel working at the same time.

The company plain that the rocket is intended to be fully reusable, With 3 or 4 block the inertia moment in case of a vertical land is totally different. It even increases the likelihood of having a successful landing. And if one engine explode after separation at least you can recover the other boosters.

Can somebody give some what could be the technical reasons? I would ask Elon directly but I lost his phone number.


  • $\begingroup$ I don't think this question needs to be closed, I just think it needs to be rewritten. It is a somewhat interesting question; worth answering - even if the answer may be fairly simple. $\endgroup$ Commented Nov 20, 2023 at 2:21
  • $\begingroup$ It may just come down to "someone" wanting to prove a concept: that such a rocket can be made & that it could be successful. $\endgroup$
    – Fred
    Commented Nov 20, 2023 at 4:56

1 Answer 1


The main factor is the intended full reusability, with short turn-around time necessary to perform the orbital refueling for departure to Mars.

Falcon Heavy is an outlier, a Kerbal style contraption integrating 3 monolithic Falcon 9 boosters and non-recoverable second stage into one launcher. All the rest you mentioned is non-recoverable, so nobody cares if they scatter all over ocean after separation. Starship must be able to re-launch quite soon after landing, because otherwise the cryofuel in the ship awaiting in orbit will boil off. There's no time for complex re-integration process.

Also, while individual boosters may be easier, integration is difficult.

It actually ended up being way harder to do Falcon Heavy than we thought. At first it sounds real easy; you just stick two first stages on as strap-on boosters. How hard can that be? But then everything changes. [the loads change, aerodynamics totally change, tripled vibration and acoustics, you break the qualification levels on all the hardware, redesign the center core airframe, separation systems] ... Really way, way more difficult than we originally thought. We were pretty naive about that. src

So, building four blocks with 9 engines each may be easier than building a monolithic 36-engine booster. Integrating them into one launch platform - not really.

  • 5
    $\begingroup$ Also, the same volume spread across three tanks has more tank wall area and thus more mass than when consolidated into one tank. The reason why Falcon Heavy and the other triple-stick boosters exist is because they are low launch rate variants of their single-stick counterparts, not because they are inherently better. $\endgroup$ Commented Nov 20, 2023 at 13:44
  • $\begingroup$ As well as that quote, I seem to remember them saying that it was almost as much work to develop Falcon Heavy as just developing a brand new rocket from scratch would have been. $\endgroup$
    – Kaz
    Commented Nov 21, 2023 at 16:34
  • 2
    $\begingroup$ @Kaz: Apparently, Elon Musk was so frustrated that he was ready to shut down the whole R&D project, only months before the successful Demo mission. Gwynne Shotwell stopped him, arguing that they had already sold launches to paying customers who wouldn't wait for Starship to be operational. $\endgroup$ Commented Nov 21, 2023 at 21:44
  • 1
    $\begingroup$ @JörgWMittag Awesome. Another point in favour of "SpaceX works so well because there's someone like Shotwell who's able to check Musk's impulses and channel them in useful directions for the company". $\endgroup$
    – Kaz
    Commented Nov 22, 2023 at 16:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.