Boeing 720 (N930NA)

NASA has flown zero-g flights on various aircraft for many years. In 1959, Project Mercury astronauts trained in a C-131 Samaritan aircraft, which was dubbed the "Vomit Comet".[6] Twin KC-135 Stratotankers were used until December 2004 but have since been retired. One, a KC-135A known as NASA 930, was also used by Universal Pictures and Imagine Entertainment for filming scenes involving weightlessness in the movie Apollo 13; that aircraft was retired in 2000 and is now on display at Ellington Field, near the Johnson Space Center. The KC-135A is estimated to have flown over 58,000 parabolas. The other (N931NA or NASA 931) made its final flight on October 29, 2004, and is permanently stored in the Pima Air & Space Museum in Tucson, Arizona. In 2005, NASA replaced the aircraft with a McDonnell Douglas C-9B Skytrain II that was formerly owned by KLM Royal Dutch Airlines and the United States Navy