I use a spreadsheet to design my stages before I build them so that I am assured they are the lightest and cheapest designs for the job. I've been asked to explain how the process works and have some free time this morning... so here goes.
I will demonstrate the process in 4 specific cases:
1) low thrust vacuum stage
2) medium thrust upper launch stage
3) high thrust liquid fuel booster stage
4) high thrust solid propellant booster stage
I will try to explain the un