Astronaut Jeffrey Hoffman remembers his friend and fellow astronaut Ron McNair, one of the seven people who were killed in the Challenger explosion on January 28, 1986. Hoffman gives a first-person account of his interaction with McNair, who earned a PhD at MIT before being selected as an astronaut. Hoffman flew five missions on the Space Shuttle, the last in 1996, and was one of the astronauts who helped fix the Hubble Space Telescope.