Williams first launched into space in 2007 and spent 195 consecutive days in space, setting a record for the longest single spaceflight by a female astronaut. On Wednesday, she'll celebrate her birthday in space.
Sally Ride was very private, but she inspired a generation of female scientists with her historic shuttle flight in 1983. Sally Ride, a physicist, proved that women could be equal partners with men in space.
On Thursday, NASA handed the world's most traveled space shuttle over to the Smithsonian. Visitors won't be able to walk its decks, but they will be able to experience the shuttle's interior through interactive images.
In this image provided by NASA, the space shuttle Endeavour is ferried by NASA's Shuttle Carrier Aircraft (SCA) over the Kennedy Space Center in the early morning hours of Sept. 19, 2012, as it departs for California.