- Total mass: The total mass of the craft in tonnes, including fuel.
- Dry mass: The mass of the craft in tonnes when the fuel has been expended.
- Fuel amount: The total amount of fuel in the fuel tanks in KSP units. Liquid fuel and oxidizer have the same weight per unit, so add them together.
- Engine Isp: The fuel efficiency of the engine in seconds. Provided values are for vacuum.
- Delta-V: The achievable change in velocity in metres per second. Check the delta-v map to see how much you need.
Let's look at the stock craft "Kerbal 2". It has the following properties:
- Total mass: 19.36t
- Fuel: 800 – The ship has a Rockomax X200-8 fuel tank which can hold 800 units of liquid fuel plus oxidizer.
- Fuel type: Liquid fuel+Oxidizer
- Isp: 310s – The engine is a RE-M3 "Mainsail" engine which has an Isp of 310s in vacuum.
The ship also carries monopropellant and RCS thrusters. Once we've burned up all our LF+Ox, we can go a little faster by using the RCS thrusters:
- Total mass: 15.36t – The total mass is is the dry mass from the previous calculation, since we burned up all our LF+Ox.
- Dry mass: 12.36t – The ship has a FL-R1 monopropellant tank which holds 3t of fuel. The dry mass is therefore 3t less than the total mass.
- Isp: 240s – The monopropellant engines are RV-105 RCS Thruster Blocks, which have an Isp of 240s in vacuum.
Please note: Unlike in the examples above, you should actually fire the least efficient engine first to get more total delta-v.