More Words, Deeper Hole

You want to determine how badly the rocket will show up against the 3K background. Two equations come to mind, the Stefan-Boltzmann law:

Power = sigma * effective radiating area * (temperature ^ 4)

and

Power = 1/2 * mass * exhaust velocity * acceleration

Of course, if you're past Earth's orbit, you will want some part of your spacecraft at ~300 K anyway. And inside Earth's orbit, refrigeration becomes interesting. But the rocket is going to be the power hog.

Carlos