Reduced gravity aircraft

A reduced-gravity aircraft is a type of fixed-wing aircraft that provides brief near-weightless environments for training astronauts, conducting research and making gravity-free movie shots.

Versions of such airplanes, officially nicknamed Weightless Wonders, were operated by the NASA Reduced Gravity Research Program. The unofficial nickname "vomit comet" became popular among those who experienced their operation.

Parabolic flights as a way of simulating weightlessness was first proposed by the German aerospace engineer Fritz Haber and the German physicist Heinz Haber in 1950. Both had been brought to the US after World War II as part of Operation Paperclip.

Parabolic flights are also used to examine the effects of weightlessness on a living organism. While humans are by far the most common passengers, non-human animals have occasionally been involved in experiments, including a notable experiment on how weightlessness affected a Domestic cat's righting reflex and a pigeon's attempts to navigate in a weightless state.

The aircraft gives its occupants the sensation of weightlessness by following a parabolic flight path relative to the center of the Earth. While following this path, the aircraft and its payload are in free fall at certain points of its flight path. The aircraft is used in this way to demonstrate to astronauts what it is like to orbit the Earth. During this time the aircraft does not exert any ground reaction force on its contents, causing the sensation of weightlessness.

Initially, the aircraft climbs with a pitch angle of 45 degrees using engine thrust and elevator controls. The sensation of weightlessness is achieved by reducing thrust and lowering the nose to maintain a neutral, or "zero lift", configuration such that the aircraft follows a ballistic trajectory, with engine thrust exactly compensating for drag. Weightlessness begins while ascending and lasts all the way "up-and-over the hump", until the craft reaches a downward pitch angle of around 30 degrees. At this point, the craft is pointing downward at high speed and must begin to pull back into the nose-up attitude to repeat the maneuver. The forces are then roughly twice that of gravity on the way down, at the bottom, and up again. This lasts all the way until the aircraft is again halfway up its upward trajectory, and the pilot again reduces the thrust and lowers the nose.

...
Wikipedia