Ordinarily I would have posted that in the "News And Chat" forum, but since that seems to have disappeared, this is the next best place.

NASA have a available a whole bunch of 3D models of their spacecraft and other equipment http://www.nasa.gov/multimedia/3d_resources/index.html. And like anything funded by the US Federal Government, they are public-domain (copyright-free), so they can be used, copied and redistributed for any purpose.

Previously these models have been in interchange formats like 3DS, OBJ and (ptui) FBX. But lately, it seems, they've started using Blender to do their modelling, so some models are directly downloadable in .blend format. For example, the Mars Odyssey model , Messenger, Mars Global Surveyor, Pioneer, and lots of other recent ones. Looks like they might even be using Blender exclusively for their newer models (from earlier this year).