Rocket fuel

On the moon the tank is half empty, and you wonder whether it is enough to get back. The avionics does not know the answer – but it provides everything you need to work it out yourself.

How much fuel is on board?#

Mass is the total mass with fuel and cargo, DryMass the mass without fuel. The difference is the fuel:

lbn mass AVIONIK HASH("Avionik") Mass Average
lbn dry AVIONIK HASH("Avionik") DryMass Average
sub fuel mass dry         # kg of fuel on board

Mass costs fuel: the heavier the rocket, the more it uses to get to another place. And the thrust-to-weight ratio ThrustToWeight depends on gravity – the same rocket has a different value on every celestial body. If it is small, the rocket uses more during launch and landing. Below 1 it does not lift off at all, because the thrust does not carry its own weight.

The fuel ratios#

The rocket's tanks are gas capsule tanks with Pressure, TotalMoles and the usual gas ratios. Only what comes together in the right ratio can burn. For hydrogen and oxygen, combustion in the game requires two parts hydrogen to one part oxygen. Whatever is left over flies along as dead weight.

lbn h2 TANK HASH("Treibstoff") RatioHydrogen Average
lbn o2 TANK HASH("Treibstoff") RatioOxygen Average
div tmp h2 o2
sap tmp tmp VERHAELTNIS TOLERANZ   # 2 : 1, 10 % leeway

sap with a relative tolerance is right here – a ratio of two readings never hits exactly 2.

Planning the return flight#

In this game version no device provides a value “fuel for the way back”. The LogicType ReturnFuelCost exists, but no device outputs it. So the chip plans itself: it remembers the supply at launch and reports when a fixed share has been used. The workshop turns back at 55 % – half for the way back, plus a reserve.