Low-pressure chamber

Preparation for the 2010 supersonic freefall involves lots of testing for Baumgartner and his equipment. Here, he and his pressure suit are being checked out in a low-pressure chamber at a U.S. Air Force base. (The white object in the lower-left corner of the window is his helmet.)

Because of the thin air in the vicinity of 120,000 feet and the limited movement provided by the pressurized suit, Baumgartner will have to choreograph his initial movements for when he exits the gondola. The Red Bull Stratos team says that although at that altitude he'll be above 99 percent of Earth's atmosphere, he'll still feel virtually the same gravity as on the ground--despite being in a near-space environment, he'll hardly be weightless. In fact, because of the weak resistance of the thin air, he'll plummet earthward much faster than he's used to in traditional, lower-atmosphere skydives.

"What we're counting on is that at the high altitude the air will be rarified, so shock waves won't have the same detrimental, concussive effect as they would down low," Dr. Jonathan Clark, Red Bull medical director, said in a statement. "But ultimately, this mission is a test flight, so we'll know a lot more afterward than we'll know beforehand."