there is no weight in space

Actually, mass always keeps its properties. This of course is why we use grams, or pounds mass when trying to accurately describe something. Weight is pretty relative, even on our own planet. Because of the oblateness of the Earth, gravity is not consistent around the globe. Now in space, it gets even worse. Since everything continuously exerts a force on everything, you can't just look at "weight" in terms of the earth or what ever large mass you are closest to. This is commonly referred to "non-two body" or "J2 perturbations.

Unless you are approaching the speed of light then it does some funny stuff... Unless you assume you are using a super/sub luminal space model in which case Einstein was wrong about mass getting exponentially large at relativistic velocities.

Maybe I went off the deep end of the topic, but I spend pretty much my whole day around this sort of stuff, so its fun to share!

Actually it can depend on the observer such as in the case of a Lorentz contraction using spatial relativity. But again this is assuming that the theory of spatial relativity is correct. (Not general relativity)

As I said before, using a super/sub luminal model, which rather elegantly explains quantum singularities, dark matter, and gravity, then yes, mass does always keep its properties. The more and more research we do, the less and less likely it is the Einstein was right, but since it is something most everyone is at least passingly familiar with I figured I would toss it in.