Mizar, a star in the Big Dipper's handle, has a tiny companion. This star, Alcor, was known to the ancients. The pair was popularly known as the "Horse and Rider."
In this series we are exploring NASA's top five challenges as detailed in its Civil Space Shortfall Ranking, which is basically NASA's Christmas wish list. These are the technologies that NASA believes we need to develop if we want to go to space…and stay there.

