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--- scifi:spacecraft [2019/11/23 22:47] – sam
+++ scifi:spacecraft [2019/11/24 14:27] – sam
@@ Line 26: / Line 26: @@
 **Total Wet Mass** is equal to the ship **Mass**, plus the mass of fuel times its density.
+==== Mass ====
+In //Traveller//, mass is measured in //displacement tonnes//, which is actually a volume based on one tonne of liquid hydrogen - equal to 14m³.
+**YAGS SciFi** also uses //displacement tonnes// as the basic rating for a ship, but a ships //actual mass// is how massive it is in //tonnes//.
+Each //displacement tonne// is considered to be about 1,000kg in mass. A ship is mostly space, being a mix of pipes, electronics, living space, hull and structural support. There are two parts of the ship though which have much higher mass.
+=== Cargo ===
+The first is cargo space, which when full will count as 10,000kg per //displacement tonne//. It is assumed that most cargo is efficiently packed and sealed in individual containers. Some types of cargo may have different mass ratings (such as metal ores, which could be 5 - 20 times this).
+Each dt of cargo being carried therefore counts as +10dt to the ship's actual mass.
+=== Fuel ===
+The second is fuel, which is often a liquid (sometimes solid) which completely fills the fuel tank with no space left over. Like cargo, fuel also has a density and so a full fuel tank increases the mass of the ship. Water counts as +14 per dt (14m³ of water has a mass of 14 tonnes, by definition), other fuels will count differently.