User:Jlmr

From Kerbal Space Program Wiki
Revision as of 23:52, 22 October 2012 by Jlmr (talk | contribs) (Units of measure)
Jump to: navigation, search

KSP is just what I have been looking for! A creative space simulator! Now if the team at Squad would just add little things like, ships, air balloons, zeplins, bombs, guns, missiles, subs, lasers, ground combat, animals, city/nation building, multiplayer, space colonies, space docks, space construction yards, asteroid mining, resources/economy... Hey, I can hope right? =)

Kerbals at War = OMG!!! *drools*

My stuff

Units of measure

  • While units of mass and thrust are not specifically labeled in-game, a bit of logic can quickly determine that thrust is measured in kilonewtons (kN) and mass in metric tons (t). For example, if measured in kilograms(kg), a "9 kg" Rockomax X200-16 Fuel Tank on Kerbin, having a surface gravity of 9.81 m/s2, would be roughly the size of a 48 oz coffee tin and only hold about 1.5 L of fuel. If measured in metric tons, a 9 t Rockomax X200-16 Fuel Tank under the same gravity would be about 0.67 m tall and 2 m in diameter, easily capable of holding the advertised 1600 L of fuel. Only a rocket engine with a thrust around 100 kN could have any chance to lift a 9 t fuel tank.
  • Thrust to weight ratio at sea level on Kerbin is calculated by the following equation, which applies only to liquid or solid fuel rocket engines, jet engines use a complicated formula on a vehicle to vehicle basis.

where:

is the thrust is the thrust obtained from the engine, in kilonewtons.
is the weight of the engine at sea level on Kerbin's surface.
is the mass of the engine in metric tons (t).
is the acceleration at sea level on Kerbin's surface, in m/s² (≈9.807 m/s²).
  • Specific impulse at sea level on Kerbin is is calculated by the following equation.

Justification for t and kN (or 1000's kg and 1000's of N)

  • An official NIST/SI publication: http://physics.nist.gov/Pubs/SP330/sp330.pdf states that kilonewton (kN) is a valid SI unit to represent 1000 N and ton (t), while historically a non-SI unit, has been accepted for use in the SI system by CIPM as a valid unit to represent 1000 kg for just over a century.
  • We already know that the game uses SI units. These are specifically labeled: meters for units of distance, meters/sec for acceleration, liters for fuel volume, and liters/sec for fuel consumption.
  • We know that the Mk1-2 Command Pod weighs 4 "units" from the in-game description. The command pod is roughly 2 m in height and 2 m in diameter. Calculating it's total volume gives us about 2.09 m3. Let's assume the capsule has 0.05 m (2 in) thick walls and subtract the interior void to get only the volume of the capsule walls. This gives us a volume of 1.80 m3.
    • Knowing the volume of the walls, we can calculate the density of the material making up the capsule, taking the 4 in-game units to mean kg, this comes out to be about 13.79 kg/m3. Unfortunately, is about 72.29 times less dense than water at room temperature and closer in density to most gasses! Perhaps Kerbals have discovered a super strong gas-like substance to make spaceships from? =)
    • However, if we take the 4 in-game units to mean metric tons, we get a density of around 13793.10 kg/m3, well within the range of the density of real building materials.
  • The wikipage on Kerbin states it has a surface gravity of 9.81 m/s2, roughly that of Earth.
    • Given this we can calculate the following. If measured in kilograms(kg), a "9 kg" Rockomax X200-16 Fuel Tank on Kerbin, having a surface gravity of 9.81 m/s2, would be roughly the size of a 48 oz coffee tin and only hold about 1.5 L of fuel. Unfortunately for our intrepid Kerbals, 1.5 L of fuel would not provide enough energy to lift a 9 kg payload through 75,000 m of atmosphere, much less a few hundred meters.
    • If measured in metric tons, a "9 t" (9,000 kg) Rockomax X200-16 Fuel Tank under the same gravity, being about 0.67 m tall and 2 m in diameter, gives a volume of 2104.87 L, more than enough to hold the advertised 1600 L of fuel. Only a rocket engine with a thrust around 100 kN (100,000 N), could have any chance of lifting the 9 t (9,000 kg) fuel tank.
    • Similarly, a substance weighing only 8 kg with a volume of 1,600 L has a density of 5 kg/m3, only about three times greater than the density of gaseous oxygen, and would not make an efficient fuel. Whereas, a fuel weighing 8 t with a volume of 1,600 L has a density of 5000 kg/m3, closer to a realistic rocket fuel.