> for the extremely hard problem of getting a super-large vehicle out of Earth’s gravity well into orbit
Why does it need to be super-large? To simulate gravity?
Why does it need to be super-large? To simulate gravity?
The rocket is already 90+% propellant (fuel & oxydizer), with the few percent left being the engines, structure and payload. So if you want the rocket to have a meaningful payload, it needs to be big.
For example the Falcon 9 weights 350 tons and can place 22 tons to low earth orbit (LEO). So about 6% of initial launcher weight ends up in orbit.
If you want to place the 100+ tons estimated for a reasonable Mars trip, your launcher will be either huge or you will need to do a lot of launches and assemble your ship in orbit with all the overhed that requires.
Starship also aims to be fully reusable, which will eat to your payload yet again but provides a huge benefit of not throwing away any part of your rocket, just burning a lot of propellant, which is dirt cheap compared to rocket hardware (estimates say about 5% of conventional rocket launch is fuel, the less is hardware that you normally simply crash into the ocean after use).
So in short - big payload -> big rocket. Reusable rocket with big payload -> humungous rocket that is really really cheap to operate.
In space vehicles, that means everything gets really, really big.
Launch vehicles tend to scale payload capacity at a greater rate than dry mass. So a small launch vehicle like RocketLab's Electron might have a wet mass of 12,000kg at launch and an LEO payload capacity of 225kg (225/12000 ~ 1.8% payload), the SpaceX Falcon9 has a wet mass of 550,000kg and an LEO payload capacity of 22,800kg (22800/550000 ~ 4.1% payload).
This just tends to mean that, very generally and with exceptions, larger vehicles can get mass into space with less fuel.
Rocket efficiency scales infinitely with size.
[0] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
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.
What am I missing here -- I'm sure I'm overlooking something.
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! ;-) )
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.
¹ Superlinear because tank mass scales with a lower exponent than tank volume.
I'm confused here. How are they not both cubic?
On the other hand, ten fuel tanks will mass more than a single fuel tank with ten times the volume.