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.

NASA's Karen Nyberg explains how astronauts run in space while stationed on the ISS. The International Space Station was launch in 1998 and is staffed by astronauts from around the world in alternating shifts.

Astronaut Jim Lovell shares his memories from the Apollo 13 mission.