The KC-135 is a NASA airplane which provides a special opportunity to perform experiments in microgravity. The plane flies in a parabolic trajectory, resulting in 2-g during the pullout, and 0-g for a period of 25-30 seconds over the top. The plane is used for microgravity experiments, as well as for astronaut training. A typical week of flying consists in 40 parabolas a day, four flights per week. To those who have experienced the thrill of floating, the KC-135 is fondly known as the "Vomit Comet."

To learn more about what it's like to go through NASA's Microgravity Program read this excellent article by Peter Yost.

Currently, the UCSD Physiology/NASA lab is conducting a new set of experiments aboard the KC-135. These experiments are a continuation of previous studies investigating aerosol transport and deposition in the human lung in altered gravity levels. A summary of the previous studies can be found in our “past research” section. 

In the present experiment, we are using 1 µm-diameter particles as a means to study convective mixing mechanisms in the alveolar region of the lung. Because particles with a diameter of 1 µm have very low intrinsic motions, they act as a non-diffusing gas and they may be used to trace convective and bulk processes. In this particular experiment, we are studying the complex mixing induced by the reversal of the flow during a breathing cycle. Subjects breath through a mouthpiece and perform a predefined breathing maneuver. During the inspiration phase, a small amount of aerosol, an aerosol 'bolus', is introduced so that it is transported to a predetermined depth within the lung. The inspiration is followed by a breath-hold period and a maximal expiration. During the breath-hold, small flow reversals are induced by a mechanically driven piston. The reversibility of flow in the lung can be studied in this manner.