This tutorial demonstrates how to calculate your mission fuel requirements using a spreadsheet and the rocket equation. I recently flew missions to Duna and Eve that each required orbital assembly in LKO. These ships were too large to fully assemble them in the VAB, and I realized that I didn’t have a method of determining how much fuel each mission would require. I’m sure there are plenty of other use cases where you may need something more than the VAB tools to determine your fuel require