What are the differences between a project sponsor and a project champion? Can the project sponsor and project champion be the same person? If so, what are the risks? Did the Iridium Project have a...

What are the differences between a project sponsor and a project champion? Can the project sponsor and project champion be the same person? If so, what are the risks? Did the Iridium Project have a project sponsor, project champion, or both? If you believe that both existed, then who filled each position?