It occurred to me that when traveling in a vacuum the thrust pushes solely against the rocket, whereas in our atmosphere it would also push against the air. Would that difference result in greater thrust?
I’d assume that friction with the atmosphere would negate any benefit, but is there more force applied?
Comments
No, “pushing against” is the wrong way to think about rocketry. All of the thrust comes from the Newtonian principle of equal and opposite reactions. All atmosphere does is impose drag, unless you have a separate, air-burning engine.
Yes and no. Rocket engines are designed to be more efficient either in the vacuum of space or at atmospheric pressures, with the primary difference being the shape/size of the nozzle. Take a look and compare SpaceX’s Raptor engines on the Starship. It has three sea level Raptors and three vacuum Raptors. Nearly identical internal/combustion chamber, but vastly different nozzles.
The reason for the different nozzle shape is to maximize the exit velocity of the exhaust over its operational conditions. At sea level, the atmosphere pushes against the sides of the exhaust to keep it focused, whereas in a vacuum there is no atmosphere so the nozzle is needed (otherwise a lot of the momentum is lost as exhaust exits to the side and not contributing to the forward velocity). Ideally, if we could develop a reliable, cost effective light weight, continuously variable nozzle we could get away with one nozzle design.