Parabolic flight experiments are conducted through NASA's Johnson Space Center (JSC) Reduced Gravity Program in Houston. This program provides the unique "weightless" or "zero-g" environment of space flight for test and training purposes. This is the perfect setting for a variety experiments, including spatial orientation, movement and balance control, motion sickness and adaptation.
The reduced gravity environment is obtained by flying a specially modified C-9 plane through a series of parabolic maneuvers, going up and down in such a way that the net force experienced by anyone onboard changes between reduced (weightlessness, 0 g), the 1g of straight and level flight (normal Earth gravity), and high (almost double, 1.8 g) gravity.
The maneuvers may be flown consecutively in a roller-coaster fashion or separated by breaks of straight and level flying. A typical mission is two to three hours long and consists of 30 to 40 parabolas. Lunar (0.6g) and Martian (0.38g) profiles are also available.