NASA makes 3d models of spacecraft and other space objects freely available

You can now download for free many 3d models in .stl or Blender format from NASA-s official repository. There are satellites, spacecraft, asteroids, planets and other cool stuff.

Models are scaled to approximately 4 inches (100 mm) in the longest dimension and are probably not optimized for your home 3d printer, so you will probably have to work on them. 

Still, it is very cool move from NASA. Sharing IS caring.
NASA 3d resources page:

http://nasa3d.arc.nasa.gov/models/printable