Standalone version of the Oni Assistant tool. Pick an engine, cargo and target distance to see the fuel, oxidizer and mass impacts.
The calculator uses in-game values for tank capacities, oxidizer bonuses and weight penalties. Adding cargo, research or boosters makes the distance curve fall off quickly, so smaller rockets with fewer modules tend to be more efficient.
Steam engines are simple: they carry built-in water tanks and need no oxidizer, but they top out quickly. Petroleum rockets reach further but need balanced fuel and oxidizer storage. Hydrogen rockets remain the lightest option and benefit the most from LOX.
The solid booster adds a burst of distance but also extra wet mass. Try toggling boosters on a heavy rocket to see when it stops paying off.