How is weightlessness produced?

Weightlessness is not a place but a state. Even at the orbital altitude of the space station, Earth still pulls strongly, with about 90 percent of its surface strength. The sensation of weight only arises when something counteracts that pull: the chair, the floor, the airplane seat. If everything falls freely at the same time, that counterforce is missing, and nothing presses anymore on the scale, the spine, or the inner ear. That is exactly what a crew in orbit experiences permanently, and for an instant, anyone who jumps.

A space station constantly falls toward Earth and never reaches it, because at the same time it flies very fast sideways. Its trajectory curves with the same intensity as the Earth's surface below. Strictly speaking, that is why microgravity reigns and not zero gravity: residual atmosphere brakes it, the station is large enough that small differences exist between its ends, and any movement on board—every fan, every docking maneuver—generates small accelerations. That is why sensitive experiments are suspended in a decoupled way and carried out during calm phases.

To run tests, no one needs to launch. In the drop tower, a capsule falls inside an evacuated tube; free fall lasts only seconds—at NASA's facility at the Glenn Research Center, 5.18 seconds—but that is enough for combustion or crystallization experiments. A parabolic flight aircraft climbs steeply and then follows the trajectory its own weight would describe, so that the cabin and its occupants fall together, for much longer than in the tower, about 20 to 30 seconds each time. Water tanks, on the other hand, do not generate weightlessness but buoyancy: they serve to practice maneuvers, not physics.