How does artificial weightlessness work?

There is no machine that switches off gravity. What laboratories and training facilities produce is free fall: the cabin, the experiment and the person fall together, so that nothing presses against a surface anymore. NASA calls this state microgravity, because people and objects appear weightless without gravitational pull having actually disappeared. On Earth, that time window is brief, and its duration determines which experiments are even possible.

In a parabolic flight, an aircraft climbs steeply and then follows the trajectory of a thrown object. According to NASA, the crew and equipment are in free fall for about 20 to 30 seconds at the top of each parabola; a single flight strings together dozens of these arcs, with load peaks between each window. Drop towers offer shorter but far more stable conditions. The ZARM drop tower in Bremen reaches 4.7 seconds in drop mode and up to 9.3 seconds when the capsule is launched upward by catapult, with quality better than 10⁻⁶ g.

Immersion pools don't produce weightlessness, but an imitation of it: buoyancy supports the suit and tools, which allows training of maneuvers for extravehicular activities, while blood and body fluids keep behaving as they do on the ground. Rotating structures work the opposite way: they generate artificial gravity because the wall pushes the crew inward, and they are considered a possible countermeasure against the effects of long flights. Permanent weightlessness therefore remains tied to an orbit in which a vehicle falls freely around Earth, not to a ground-based facility.