>>10876008Building a bigger rocket lets you take better advantage of certain parts of the rocket equation, specifically the parts to do with wet mass vs dry mass. A bigger rocket is easier to build closer to the bare minimum structural mass required to handle the forces and other requirements involved. It's a simple concept, a propellant tank twice the size doesn't need an insulation layer twice as thick, that part stays the same thickness. Ditto for any wires (longer but proportionally thinner) paint (larger surface area but proportional layer thickness goes down) etc.
Also, the rocket equation only runs away from you if you are trying to get more and more delta V, NOT more payload. A rocket with twice the overall mass of a rocket with equal efficiency will in fact get twice the payload to orbit. Imagine a 100 ton rocket gets 1 ton into orbit, at 7 km/s. Now imagine a 200 ton rocket. The 200 rocket will be able to get 2 tons into orbit, no problem. What the 200 ton rocket CANNOT do, is accelerate a 1 ton payload to 14 km/s. In order to get that 1 ton payload up to 14 km/s, the rocket would need to be far more than twice as big, in fact (using the same 1 to 100 payload ratio) it would need to weigh 10,00 tons! Why the huge jump?
It's because in order to get up to 14 km/s, the rocket is going to have to accelerate to 7 km/s, then accelerate again by another 7 km/s. That seems trivial, but consider what the ramifications are. The 100 ton rocket from the original case could push 1 ton of payload to 7 km/s. If that rocket started off already moving at 7 km/s, then it would reach 14 km/s. However, in order to push that entire 100 ton rocket up to 7 km/s, you're going to need a rocket stage that is bigger by the same factor of size difference between the original rocket and its payload. That means you need a new rocket that weighs 100 times more than the 100 ton rocket, giving it a starting mass of 10,000 tons, in order to get 1 ton of payload up to 14 km/s.
