/sci/ - Science & Math

This isn't homework, just been bothering me for ages.

How would you accurately measure the mass of a large object in space without changing acceleration?

Like say, you wanted to control a variable mass space craft accurately, and you wanted to know your total mass at any given time to give you the best possible control.

Lets say you're a large object in zero g, vacuum ect.

How would you measure your own mass, without known velocity?

This isn't homework, I was wondering how computer controlled spacecraft could make highly accurate adjustments to their course if their mass was changing. Wasting fuel to watch changes in an accelerometer was all I could think of, and it seemed both inefficient and inaccurate, especially with large masses.