Star Citizen Discussion Thread v11

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If there are any flight sim developers on CIG's payroll, then they either need a trout to the face or to hang their heads in shame/bewilderment. How the hell does an atmosphere affect a self contained thruster's efficiency (has to be self contained or it doesn't work in space)?....there is just so much "wrong" in that statement, whoever wrote it should get thrown into a propeller as a lesson.
Weeeeeell… there are some effects on specific impulse that depend on the pressure difference between the interior and exterior of a combustion chamber, and that will obviously depend on altitude in atmo, up to and including being in a vacuum. It's not a “drastic difference”, however, but a continuum going from a minimum at the surface to a maximum in open space. It sounds more like someone at CI¬G opened up the KSP wiki and started copying ideas… :D

e: Or to just steal the wikipedia entry:
Wikipedia said:
In rocketry, the only reaction mass is the propellant, so an equivalent way of calculating the specific impulse in seconds is used. Specific impulse is defined as the thrust integrated over time per unit weight-on-Earth of the propellant:
{\displaystyle I_{\rm {sp}}={\frac {v_{\text{e}}}{g_{0}}},}


{\displaystyle I_{\rm {sp}}}
is the specific impulse measured in seconds,
is the average exhaust speed along the axis of the engine (in ft/s or m/s),
is the standard gravity (in ft/s2 or m/s2).

In rockets, due to atmospheric effects, the specific impulse varies with altitude, reaching a maximum in a vacuum. This is because the exhaust velocity isn't simply a function of the chamber pressure, but is a function of the difference between the interior and exterior of the combustion chamber. Values are usually given for operation at sea level ("sl") or in a vacuum ("vac").
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Another 10,000 posts, so it's time for a new thread!

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