Training to become an astronaut requires an applicant to endure physically demanding and stressful tests – various machines and simulators measure each trainee's response to the rigors of space travel. Today, an entirely unrelated industry uses many of these simulators and other devices for a different purpose – entertainment. Zero gravity is a condition of weightlessness referring to the absence of a gravitational force (g-force or Gs) - a measurement of the acceleration due to gravity that causes weight. A body in a “zero gravity” (or “microgravity” - a state of near weightlessness) environment is acted upon only by gravity, with no reactionary forces exerted by its surrounding matter, the person therefore enters a state of freefall where all objects in that given space are falling at the same rate.
The way the flight works is fairly simple: the plane flies in a series of parabolas, or peaks and valleys. Initially, the aircraft pulls up and increases thrust at a 45-degree angle. During this portion of the flight, passengers actually feel extra gravity – around 1.8 Gs. Then, the plane reduces thrust and lowers its nose, just before reaching the top of the peak. It’s at this moment that the plane, and everyone inside, shift into free fall. So in reality, you’re not floating so much as falling, like a skydiver surrounded by a plane. After half a minute, the plane then starts to pull up again and the process is repeated.
The Zero-G has not abandoned its main purpose, however, which is to provide a handy gravity-free environment for scientists to conduct experiments.
"It is a beautiful opportunity," notes Jean-Louis Thonnard, a professor at Belgium's Université Catholique de Louvain who is researching gravity's effect on upper-body movement. "By studying the manipulation of objects in different gravity fields, we understand how important gravity is on Earth," he explains. "We are gravity dependent."
Sticking a scientist on a parabolic flight is considerably cheaper than sending them to the International Space Station, and many of the world's top space centers use Zero-G as a venue for the early stages of experimentation.