Weightlessness in Outer Space: At What Altitude Does Weightlessness Happen? October 14, 2012: Austrian daredevil Felix Baumgartner jumps from 120,000+ feet Was Baumgartner weightless during his ride up into near-outer space in the Red Bull Stratos project? The answer is no, he felt normal weight throughout his ascent. At a height of 128,000 feet (39 km), the force of gravity is only 1% less than at the surface of the Earth. Before the jump, he was held up by the helium balloon and capsule, unlike the free-fall orbit of the International Space Station. The moment he jumped from his capsule, he was in free-fall and weightless, just like ordinary sky divers and bungee jumpers. He quickly built up speed as he fell, surpassing the sound barrier within half a minute, due to the lack of atmosphere.There was no sonic boom because the air is so thin at that altitude. As he reached lower altitudes, the atmosphere thickened and wind resistance built up, causing his falling speed to decrease. If you watched the fall, you probably noticed he started tumbling. The force of the thin atmosphere caused him to become unstable. As the air got thicker, he was able to balance himself against the wind like an ordinary skydiver. When he reached terminal velocity (about 100 MPH as he got closer to sea level), he felt normal weight because the force of wind resistance balanced the force of gravity. You might think that astronauts are weightless because they are far from the Earth. So you might ask, "What height above the Earth must astronauts reach to achieve weightlessness?" But it's not any particular height or altitude that makes them weightless. Gravity is almost as strong at the height of the International Space Station as on the surface of the Earth -- only a few percent weaker. It's not the height, but the motion of the spacecraft that causes weightlessness. Any object that is falling freely is weightless, no matter where it happens to be. This can be the International Space Station at a height of 200 miles, a NASA reduced-gravity airplane at a height of several thousand feet, a drop tower at several hundred feet, or you jumping off a chair at 3 feet. To answer the question, a spacecraft becomes weightless when the engines are shut off, irrespective of the altitude. More: Space Shuttle, International Space Station, and Sir Isaac Newton ©2009 Gray Chang