The KC-135 is a NASA airplane which provides a special opportunity to perform experiments in microgravity. The plane flies in parabolas, 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 0-g experiments, as well as for astronaut training. A typical week of flying will be 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".
The UCSD Physiology/NASA lab has conducted several experiments aboard the KC-135 plane.
Most recently, they conducted a study on the deposition of small aerosol particles in the lung. The subject breathed continuously through a mouthpiece connected to a valve system from which breathed either room air or aerosol. The aerosol concentration and flow rate were measured by a photometer and pneumotachograph (flow meter). In the first set of flights, four different aerosol sizes, from 0.5 micron to 3 micron, were used, and a comparison was made looking at how much deposition occurred as a function of gravity level for each particle size. The particles used were spherical latex particles, so they were non-toxic and harmless to the lung.
View some pictures from these flights.