Imaginatively called "Build It Yourself: Satellite! Game"
http://www.jwst.nasa.gov/build.html
Web based and all... Now we can all be rocket scieneticians.

if I see my design go up into space, I want royalty fees & stuff.

edit: build your own satellite? more like click a bunch of options that you have no choice but to click & build the satellite they want you to build.

lame. I was hoping to create a mega super satellite of doom. :(