How much fuel does a rocket need for a round trip?

In Spaced Out! you see a rocket's range once its modules are built and fuelled. The rocket range planner answers before that. You pick an engine, the fuel and oxidizer you can load, the distance in hexes and the landings on the way, and it returns the fuel the trip needs and whether the load covers it.

A round trip to a target four hexes away is eight hexes, and the planner adds one step of fuel for each landing, so two landings make ten steps. Each engine burns a fixed amount per step. The Steam Engine burns 15 kg of Steam, the Small Petroleum Engine 45 kg of Petroleum and the Petroleum Engine 90 kg.

The Steam Engine needs no oxidizer and holds 150 kg of steam in its own tank, exactly ten steps. The Small Petroleum Engine holds 450 kg of fuel, also ten steps, but burns it only with oxidizer. In the planner Oxylite burns twice its mass in fuel and Liquid Oxygen four times, so ten steps take 225 kg of Oxylite or 112.5 kg of Liquid Oxygen.

Each engine also caps the rocket's height, at 25 for the Steam Engine, 20 for the Small Petroleum Engine and 35 for the Petroleum Engine. The Petroleum Engine carries no fuel of its own and draws from Large Liquid Fuel Tank modules of 900 kg each.

A rocket can only fly to hexes that have been analyzed with a Telescope or a Cartographic Module. Once the first target is analyzed, count its hexes on the starmap, enter the distance and landings, and load the fuel and oxidizer the planner asks for before launch.