The rocket equation [0] disagrees: "In what has been called 'the tyranny of the rocket equation', there is a limit to the amount of payload that the rocket can carry, as higher amounts of propellant increment the overall weight, and thus also increase the fuel consumption"
The pure, theoretical rocket equation still scales linearly, the tyranny lies in the hard limit of how much mass you can theoretically accelerate out of a gravity well per unit off fuel.
But bigger rockets can get closer to that theoretical optimum because some dead weight components remain fixed-size and because some masses scale with surface instead of volume. Rockets can scale better than linearly with size, but they will never exceed the rocket equation.
I'm having a mental blockage on this, as you can always launch 10 rockets at the same time and get 10 times the payload. Having those 10 rockets strapped together should not change the payload of them flying independently.
What am I missing here -- I'm sure I'm overlooking something.
If you strap 10 rockets together, you don't need to keep all 10 copies of some components. You don't need 10 computers, or ten emergency abort systems, or ten communications systems, etc. One large tank will have less mass/volume than 10 small ones, etc.
Interestingly there are couple rockets that are close to "strapping couple rockets together" for various reasons:
The R7 rocket
- mostly to avoid engine ignition in flight & due to having a lot of nozzles you need to fit on a rocket
- this was then kept for Soyuz even after an additional stage has been added that is started in flight
- Soyuz 2V uses a more efficient engine & uses only the central stage
The proton Rocket
- the central tank has the maximum diameter you can ship via rail from the factory to Baykonur
- by mounting smaller tanks around it that are shipped separately you can avoid building an overly long rocket, that could be fragile and unstable
Saturn 1/1B
- basically a stop gap using existing Jupiter and Redstone rocket tankage tooling
- strap 8 Redstone tanks around 1 Jupiter tank and you get the S-I first stage
Delta IV Heavy/Falcon Heavy
- you have a rocket that can launch by itself with smaller payload or by strapping 3 first stages together can launch a bigger payload
- better economies of scale as you can doe more with a single rocket design instead of maintaining 2 separate one (big and small)
- in Falcon Heavy case you can also save all the first stages from more demanding trajectories where you would otherwise have to expend the regular F9 first stage
OTRAG
- make dirt cheap and as simple as possible standardized "rocket tubes"
- strap a lot of them together
- fire and jettison in the right order to achieve orbit (check your staging! ;-) )
While this does work, the Falcon Heavy has convinced Elon not to go into that direction again. Its actually not that simple to strap these together and just making a bigger tank is actually easier.
Poorly for the current market using a FH makes sense, but to break to another level, building one big rocket is better. Both the US Saturn 5 and the Soviet N1 were big single tube vehicles.
Correct. You can (super¹)linearly increase launch mass by adding fuel. The rocket equation hits when you're trying to go farther, rather than more massive.
¹ Superlinear because tank mass scales with a lower exponent than tank volume.
You aren't missing anything, the comment you are responding to is confusing the per unit of fuel payload limit to be the total limit of the rocket. You can add more engines/ use bigger ones which would allow for more fuel and thus more payload( in theory at least).
That's correct so far. Now think further: a single, larger rocket has the advantage of leaving away the tank walls that would be in the inside now. Less mass needed for the tank walls (the outer walls need to become stronger though), more available for payload, extra fuel and oxidizer or extra stuff like things needed for reusability.
Rocket efficiency scales infinitely with size.