Sally Ride was a 27-year-old Ph.D. candidate, looking for postdoctoral work in astrophysics, when an item in the Stanford University newspaper caught her eye. NASA was looking for astronauts. She was one of only six women to be accepted, out of 8,000 applicants. She joined NASA in 1977, and underwent years of rigorous physical and scientific training. In 1983 she became the first American woman in space, flying a six-day mission on the Space Shuttle Challenger. Her second mission lasted eight days, contributing to her career total of 343 hours in space. She was scheduled for a third mission at the time of the Challenger explosion in 1986. She served on the Presidential Commission investigating the accident, and participated in long-term planning at the space agency's headquarters in Washington until her retirement from NASA. From 1989, she was a Professor of Physics at the University of California, San Diego, where her research interests centered on the theory of non-linear beam-wave interactions. She also served as a Science Fellow of the Center for International Security and Arms Control at Stanford University and as Director of the California Space Institute. A passionate advocate for science education, she created the Sally Ride Club and Sally Ride Science Camps to encourage young girls interested in mathematics, science and technology. She was inducted into the Astronaut Hall of Fame in 2003, exactly 20 years after her historic flight. Sally Ride died of cancer in 2012, at the age of 61.