The KC-135 is an aircraft used by the military as a tanker that has been modified by NASA into a platform for low-gravity studies. It is very aptly nicknamed the"Vomit Comet", since about 70% of first time fliers end up getting sick, even after taking the suggested medication. Reactions to low gravity can range from no symptoms to becoming violently sick. Comments made by students after their first flight include "Not for all the tea in China will I get back on that plane", "My organs hurt", and "Can I change my thesis topic?".

The plane usually flies forty parabolas per day, each consisting of a 1.8 pullup, a low gravity period of about 25 s, then a 1.6 g pullout. A typical profile showing the acceleration perpendicular to the floor of the aircraft is shown below for one parabola:

The pullup usually starts at about 24,000 ft and the top of the parabola occurs above 32,000 ft–imagine a two mile high roller coaster. A typical flight week consists of a Test Readiness Review and loading on Monday, two hour flights on Tuesday through Friday, then off-loading on Friday afternoon. We usually fly two to three weeks per year.

More information on the KC-135 can be obtained from the NASA web site http://jsc-aircraft-ops.jsc.nasa.gov/kc135/index.html.