# Was DAWN's power-limited propulsion really limited by power used to accelerate the ions?

The discussion here uses the DAWN mission as a reference for the argument that the power used to accelerate the ions is what's important.

I'm curious how many watts were actually used to accelerate DAWN's ion thrust (e.g. $$P = IV$$), and how it compares to how many watts were actually used to sustain the plasma and unrelated to accelerating the ions.

My hunch is that the power for acceleration was actually trivially small compared to the power used to ionize and sustain the plasma, but I'd be happy to shown otherwise quantitatively.

According to wikipedia each Nustar engine on Dawn used 2100W, and achieved 92mN of thrust with an exhaust velocity around 30 km/s. So from the thrust and the exhaust velocity we can compute the Xenon mass flow as $$0.092/30000 = 3\times 10^{-6} kg/s$$.
Now each kilogram of Xenon has a kinetic energy of $$1/2 \times 30000^2 = 4.5\times 10^8 J/kg$$ so the power converted to KE of the ions is simply the product of these: 1350 W.