Differences

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--- scifi:spacecraft [2019/12/22 13:43] – sam
+++ scifi:spacecraft [2020/04/26 10:27] (current) – sam
@@ Line 7: / Line 7: @@
 ===== Definitions =====
-**Mass**: Total size of the vehicle, in //displacement tonnes//. Each dt is 14m³ (one tonne of liquid hydrogen), and is assumed to have an actual mass of 1 tonne.
+**Displacement**: Total size of the vehicle, in //displacement tonnes// (dT). Each dT is 14m³ (one tonne of liquid hydrogen), and by default is assumed to have an actual mass of 1 tonne, though this can vary depending on the configuration.
+**Mass**: The actual mass of the vehicle in metric tonnes. This can get complicated, because mass can vary depending on both fuel and cargo load. //Dry mass// is the mass of the ship without any fuel. //Wet mass// is the mass fully fuelled. A //loaded// ship which is full of cargo will also have different masses depending on the amount and type of cargo.
 **Thrust**: How powerful a drive is, per displacement tonne. The higher this is, the faster a spacecraft can accelerate. This is based on Newtons of force produced by the drive, multiplied by a magic number.
 **Impulse**: How efficient a drive is. The higher this is, a spacecraft can accelerate for longer. This is based on the specific impulse (seconds) of the drive, multiplied by a magic number.
+**Delta-vee**: The maximum velocity the ship can achieve after being fully fuelled. There will often be values for this based on unloaded and loaded mass.
 The **Total Thrust** is the thrust of the engines times their total mass.
 The **Acceleration** is the **Total Thrust** divided by the **Ship Mass**, in m/s².
 ^ Engine           ^ Mass (dt) ^ Thrust (kN) ^ SI (s) ^ Thrust ^ Impulse ^ Density ^
@@ Line 26: / Line 31: @@
 **Total Wet Mass** is equal to the ship **Mass**, plus the mass of fuel times its density.
+Full statistics for some future designs are available here:
+  * [[./spacecraft/drives/chemical]]
 ==== Mass ====
-In //Traveller//, mass is measured in //displacement tonnes//, which is actually a volume based on one tonne of liquid hydrogen - equal to 14m³.
+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** considers this the ship's displacement, which is basically its volume.
-**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.
+Some craft are //Weak//, in which case total dry mass (including engines, living quarters, cargo hold etc) is multiplied by 0.75. This also has a negative impact on the hull strength of the ship (base soak x0.50).
+Some are //Fragile//, in which case their total dry mass is multiplied by 0.65. It improves performance, but they really suffer on punishment (base soak x0.25).
 === 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).
+The first is cargo space, which when full can contain 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.
+An empty cargo hold has a mass of 100kg per dT, since it is mostly empty space. When loaded with cargo, the mass of the cargo is in addition to this.
 === 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.
+An empty fuel tank has a mass of 100kg per dT, again since it is mostly empty space.
 === Supplies ===