A modified Boeing jet transport aircraft that was used by NASA for weightless training. The four-engine plane flew in parabolas, which produced 25 to 30 seconds of weightlessness over the top of the course. At that time, astronauts (who have named the plane the ‘Vomit Comet’) practised using different types of space shuttle equipment, as well as eating and drinking. Each week there were normally four flights of 40 parabolas each, with training sessions lasting between one and two hours. The KC-135 was also used for zero-gravity experiments. The aircraft made its final flight on 29 October 2004 and is permanently stored in the Pima Air & Space Museum in Tucson, Arizona.