[niky]

Acceleration is a direct product of power.

Here you describe thrust as power divided by speed.

Speed of what? Of the exhaust gases, correct? What do you measure the speed of the exhaust gases against out in deep space?

The spacecraft, of course. In free space, there are no other inertial frames to measure exhaust velocity by. Exhaust leaving the rocket at 100 mph relative to the nozzle will leave it at 100 mph relative to the nozzle regardless of the absolute velocity of the spacecraft at the time.

Again... we're talking about a craft launched from a planet embedded in a galaxy that is moving at over 100,000 miles per hour towards the Great Attractor. If absolute velocity actually affected acceleration, a rocket fired towards the Great Attractor would accelerate measurably slower (compared to the Earth) than one fired away from it. Which doesn't happen.