Do bigger rocket work better?

Do bigger rockets work better? for example, if a rocket had 5 times the engines of the Saturn 5 and 5 times the fuel could it take 5 times the payload into orbit? Could it take more, or would it take less?

• I feel like this question is better served by the Space Exploration Stack Exchange, but you might want to examine the Tsiolkovsky Rocket Equation. Commented Sep 6, 2020 at 5:13
• In a nutshell the answer is no beyond a certain point they don't work that well. If you want to launch more mass into orbit the most practical option is to make the rocket reusable rather than bigger. Throwing millions of dollars of precision engineering into the ocean after every launch is not a very practical solution. Commented Sep 6, 2020 at 5:21
• jdunlop, thanks for pointing me in the direction of space exploration stack exchange. I did not know it existed. Commented Sep 6, 2020 at 5:43
• @Slarty reuse is easier with larger rockets. The mass of things like heat shielding increase with the surface area while overall vehicle mass increases with volume, so the overhead of carrying them is smaller for larger vehicles. There are physical limits, but even SpaceX's Starship isn't close to them. Commented Sep 6, 2020 at 15:34
• What you're talking about is the concept known as the big dumb booster. Sea Dragon was an interesting proposal, but it never went anywhere for a reason(namely cost and lack of anything to launch, though it might have still beat the shuttle). This clip from the Apple series For All Mankind shows what it might have looked like if it had ever launched. The cool part is that it would have launched from the ocean, as it was a safer way to launch given the level of thrust. Commented Sep 7, 2020 at 5:19

2 Answers

To some extent it depends how you arrange the rocket, but whichever way you do it there will be big problems.

You could just make the rocket taller, but then the pressure on the lower part of the rocket will increase and it will need to be strengthened adding mass. There will also not be enough room for extra engines at the bottom unless they stick out which will increase air resistance in the atmosphere.

You could just make the rocket wider providing more room for engines, but the pressure inside the propellant tanks will still increase and require a more massive tank.

You could just strap n multiple rockets of the same size together side by side, this would theoretically give you n times the payload capability of a single rocket. But it also presents some major control and stability issues which will rapidly increase in as n increases.

You could break the rocket up into multiple stages so empty propellant tanks can be discarded as you get higher, but this does not solve the problem of increased pressure on the lower stages at lift off and adds considerable additional complexity.

Fundamentally you always have to contend with the “tyranny” of the rocket equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

A key factor is the ratio of the mass of the rocket propellant to the mass of the rest of the rocket (payload, tanks, engine etc). The velocity that you can reach is related to this mass ratio by a logarithmic function so you rapidly reach a point of diminishing returns as there are physical limitations on how much propellant can be contained in a given mass of tankage. Rockets today are already 90% giant propellant tank so there is little room for improvement.

There have been designs considered for super-heavy post-Saturn launch vehicles in real life, so the idea isn't merely confined to fantasy. Consider the Boeing MLLV, Sea Dragon, and a bunch of really interesting 1960-era "Nova" designs, each of which were intended to be several times as large, carry several times as much payload, and generally be cheaper per unit of payload to orbit as well.

The Saturn V's payload fraction was just over 4%; if the estimated mass figures for these are to be taken seriously, these giant launchers were designed for something in the 3-5% range, which seems comparable enough that the reduced cost per ton (economies of scale) could make it worth it.

Of course, the per-unit cost of these launchers was prohibitive, and NASA really didn't have any need for super-heavy payloads after Apollo, especially with their gradual defunding, so none of the designs came to fruition. Odds are they would have encountered all kinds of unforeseen problems... but clearly people at least thought about the idea, and it made enough physical sense to put research into it.

One of the more obvious concerns is "what happens if it explodes?" Chemical launch vehicles usually have around a 1% failure rate, so sooner or later one's going to blow up on the pad — and if fifteen thousand tons of fuel are exploding, how many people are in danger from the blast? How long would it take to clean everything up? Accidents of this sort seriously hindered the Soviet N1 program, after all.