Twin KC-135 Stratotankers were used until December 2004, but later retired. One, a KC-135A registered N930NA (also known as NASA 930, formerly USAF serial no. 59-1481), flew more than 58,000 parabolas after NASA acquired it in 1973, before being retired in 1995. It is now on display at Ellington Field, near the Johnson Space Center. The other (N931NA or NASA 931, formerly AF serial no. 63-7998) was also used by Universal Pictures and Imagine Entertainment for filming scenes involving weightlessness in the movie "Apollo 13"; it made its final flight on October 29, 2004, and is permanently stored in the Pima Air & Space Museum in Tucson, Arizona.