# Calculating the Specific Power (W/kg) of Ion Engines

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I'm thinking about diving deeper into the ion engines of KSP. Not only can I understand them better for KSP fanworks, in which the engine math would be described in great detail, but I can apply these principles for real-life.

As a KSP example, the given values of the IX-6315 "Dawn" engine are:

Values I can easily calculate are:

• Mass flow rate for xenon propellant (kg/s)
• Exhaust velocity (m/s)
• Beam power (watts)
• Wet-to-dry mass ratios for certain dV requirements
• For certain phases, some parts will be jettisoned (e.g. I'm not going to carry an Apollo-style landing craft back home if I've already used it).

Using this engine as an example, how do I calculate the specific power (W/kg) for it? With that value, I can divide it by the input power to get the mass of the power supply system required.

• Example: an engine with an Isp=2000s and a Thrust = 0.2 N.
• A value of 100 W/kg was given for the specific power, but I have no idea how they got it.
• mass of power supply system = (Power required in W) / (specific power in W/kg)

This might not matter so much in KSP, but it does for real-life calculations. Plus, as an aerospace engineering major, I want to better understand what goes into xenon-powered spacecraft. If someone could help me, that would be nice.

Edited by Mars-Bound Hokie
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Ion engines in KSP are not even close to being correct, for gameplay reasons.

I'm not sure what you are asking for here. Are looking for the power to operate the engine?

It looks like you are focusing on the wrong thing. You need to figure out how much power the thruster needs. Ex. If you figure out that it needs 200W, then you know the mass of the power supply is 200W/100W/kg or 2 kg.

Edited by mikegarrison
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