Technically, a parachute would work at any height except beyond the atmosphere of a planet (i.e. in space). As proved by Felix Baumgartner, you can even fall from 120,000 feet. However, because of his weight, he had to let himself fall before using his parachute. Since our payload (approximately 800 grams) is not nearly as heavy as a human being, the parachute will be enacted as soon as the balloon pops and it falls. The parachute will already be hanging next to the payload. There are many misconceptions about parachute inversion. It isn’t like an umbrella in the wind where it flips completely inside out (although it could happen), but the general definition is when one part of the parachute passes through the lines of another part and flips partially inside out. There is also temporary inversion, where the part of the parachute comes back out of inversion extremely quickly, sometimes in less than 0.1 of a second. There are three main causes found over the many years:
1. Movement of the parachute skirt- During the launch and/or early inflation, random movement can cause various parts of the parachute skirt to move inwards and to the opposite side.
2. Cross wind deployments- Cross wind deployments result in the relative wind trying to push the “up wind” aside of the parachute skirt against and under the “down wind” side, leading to an inversion.
3. Uneven canopy skirt- An uneven canopy skirt, such as when a group of suspension lines or risers become entangled, encourages inversion.
Note from Kevin – Think also about how thin the atmosphere is at that altitude. The parachute will become much more effective when the train (payload + chute + balloon) gets down to an altitude where the atmosphere is thick enough to provide some real resistance. This is the same reason that aerodynamics don’t matter at all for a satellite in orbit.