摘要: For the past 30 years, NASA Lewis Research Center's ground-based reduced-gravity facilities have supported numerous investigations for several research disciplines. Lewis' two drop towers and its DC-9 aircraft have provided a low-... 展开 For the past 30 years, NASA Lewis Research Center's ground-based reduced-gravity facilities have supported numerous investigations for several research disciplines. Lewis' two drop towers and its DC-9 aircraft have provided a low-gravity environment (gravitational levels that range from 1 percent of Earth's gravitational acceleration to onemillionth of that measured at the Earth's surface) for brief periods of time. 'Zero gravity,' the weightless condition also known as microgravity, can be produced in these facilities by creating a free-fall or semi-free-fall condition where the force of gravity on an experiment is offset by its linear acceleration during a 'fall' (a drop in a tower or a parabolic maneuver by an aircraft). The low-gravity environment obtained 'on the ground" in NASA facilities is the same as that of a spacecraft in orbit around the Earth. 收起