Re: How could you measure the mass of an object in space?

Measuring mass in space, or any condition with little or no gravity can be done
by measuring vibrations/oscillations of a system.  

One example, I read out in Scientific American can be used to measure mass.

A metal rod of known mass and distribution is rigidly attached to a larger
structure.  The rod is then made to vibrate/oscillate and the frequency
recorded.

Then the object (better if is small) is affixed to the rod near the free end. 
The rod and attached mass now are made to oscillate again and the new frequency
is recorded.  

If you can come up with the moment of inertia of the rod and the moment of
inertia of the combined system, then you can solve for the frequency of the
vibrating/oscillating system under the assumption of small vibration as a
function of mass (really mass distribution).

I gloss over this a bit because in reality this can be very difficult to do in
practice -- especially if the mass if a large object.

Sincerely,

Tom "Space Jiggler" Cull