I'm coming from a background of Kerbal Space Program, so I'm not 100% sure all of this applies to real-life but I'm asking in the hopes someone might tell me that. Yes, I know, it's not real space travel and it doesn't accurately simulate all physics perfectly, but it's a good approximation and the core concepts are unchanged, so I consider it a good way to get introduced to concepts which one can then go and research further.
One thing that becomes pretty apparent from the start is that to get to orbit you need engines. To power these engines you need fuel, but fuel has mass, so you need more fuel and eventually things get pretty large and expensive. Each engine has a specific impulse and a craft (as we understand it to be a collection of payload, fuel, and engines) has a certain amount of delta-V, or the change in velocity possible.
Every maneuver, ascent, or powered landing the craft makes eats away at this budget of velocity change. From playing around it seems to be that making the following changes has the following effects:
- Adding more fuel:
- The thrust to weight ratio decreases. In orbit this doesn't appear to matter, but when landed it must be greater than 1 to have enough thrust to lift the craft.
- The amount of time the engines can burn for increases, but does this mean the delta-v only increases if you assume you are not ascending/landing and therefore do not need a TWR > 1?
- Adding more engines:
The TWR increasesThe thrust increases (and this usually increases the TWR, but not if the engine is exceptionally heavy in relation to the thrust produced), but the amount of time the engines can burn for decreases as more fuel is burnt in the same amount of time.
- I am unsure how delta-v changes here. It seems like adding more engines without adding more fuel does not increase it, it just means the same amount can be expended in a shorter time.
So when constructing a spacefaring vehicle (in reality), is there a mathematical or "proper" way to determine the optimum balance between fuel and engines? Furthermore, is such a method dependant on the celestial body/bodies you are within the Hill sphere of?