How does one measure velocity in space? Just what the title states. 
Velocity, by definition, is the distance covered in a defined amount of time. How does one measure the velocity of a spacecraft that is not in Earth Orbit? E.g. Beagle
EDIT:
I qualified the location as outside of Earth orbit so as to clear the frame of reference used sometime to measure velocity.
 A: You need a frame of reference to measure velocity. It doesn't mean anything without a frame. Please try to be more precise--- I have a rock floating through space, and a spaceship, and I want to measure the velocity of the rock relative to the spaceship. You can do this by bouncing light off it and measuring the Doppler shift.
A: Velocity is still measured the same way wherever you are. It doesn't need to have any connection to Earth's orbit.
We can't measure an absolute velocity anyway - should we measure against a point on Earth? well, it is rotating, and Earth is orbiting the Sun, which is orbiting the centre of the Milky Way, which is ... and so on.
Just use whatever reference point is useful, and measure the relative velocity.
A: I'll qualify this by saying it should be a comment to the question so please don't shoot me based on that...
taking the extended commentary of the question into account regarding using doppler shift, you would be measuring relative to the object or emmissions that produced the doppler shifted particles, which is a longer explanation of the accepted answer... without a reference, there is nothing to measure against, and distance (and perforce velocity) become irrelevant.
assuming dispersion of some reference from your spacecraft you could measure any change in velocity from the point of dispersion, but I'm not sure that's what you were after.
A: If a vessel in space has velocity, it will have kinetic energy.
Energy can be converted. Convert a part of it to rotational energy.
If you have no velocity, you cannot convert translational kinetic energy
into rotational kinetic energy.
