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scifi:spacecraft

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Spacecraft

YAGS SciFi is all about spacecraft and travel between worlds, so having a system for defining spacecraft is important.

The statistics used are simplified from real world values to make the maths of designing craft easier. Mostly, this involves including all the constants in the basic statistics.

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.

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.

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
F-1 (LOX/RP1) 5 7,770 260 1550 2.6 14
J-2 (LOH) 1 1,000 421 1000 4.2 2
Raptor (LOX/RP1) 1 2,400 380 2400 3.8 14
Merlin (Methane) 1 981 311 980 3.1 10
Nerva (H) 2 246 841 250 8.4 1

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.

Supplies

Crew need supplies, which counts as cargo. 1dt of supplies has a mass of 5,000kg, and will last 1 crew member 1,000 days. This includes food, water, air and other necessities. It is assumed water and air is recycled as much as possible, but 'loss' is included in the expendables.

Crew Quarters

How much space crew need depends on the duration of the flight.

  • Hours: ¼dT
  • Days: 1dT
  • Weeks: 2dT
  • Months: 4dT

Cramped quarters are about half this. Luxurious can be from twice to five times this.

scifi/spacecraft.1577022185.txt.gz · Last modified: 2019/12/22 13:43 by sam

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