Suspended 150 feet below a balloon, the capsule will protect Baumgartner from stratospheric temperatures reaching minus 70 Fahrenheit and offer a stable oxygenated and pressurized environment during the ascent so he has air to breathe and can avoid decompression sickness. The craft will also act as a stable base for his step-off into free fall.
The hostile environment presents a daunting challenge to the electronics, radio communications and camera systems vital to the capsule’s operation. Led by Art Thompson, the mission’s technical project director, the craft was designed and hand-constructed at Sage Cheshire Aerospace, Inc. in Lancaster, California.
Once the capsule has completed its ascent and Baumgartner has safely accomplished his mission, a remote triggering system will release the craft from the balloon. Tracked via a GPS system, a recovery parachute will bring the capsule slowly back to Earth, where the data can be extracted and evaluated.
The mission’s science team opted for a sealed capsule instead of a gondola used by the current record holder, Joe Kittinger, when he jumped from a height of 102,800 feet in 1960. The additional altitude of the Red Bull Stratos mission means that there are exponentially greater hazards from exposure to freezing temperatures, oxygen deprivation and low air pressure. The sealed capsule will protect Baumgartner. He will inflate his pressure suit only as he prepares to exit the craft.
The capsule testing program included initial evaluations at Sage Cheshire Aerospace, followed by a 2011 altitude chamber test verifying the vessel’s integrity in a real-time flight simulation to jump altitude. Following a final phase of egress training, Art Thompson confirmed that the capsule is ready to fly.
The capsule’s design incorporates four key components: the pressure sphere, the cage, the shell and the base with crush pads.
The pressure sphere, with a diameter of 6 feet, contains the flight control panel and instrumentation and is where Baumgartner will be seated during the ascent. It is molded from fibreglass and epoxy, while the door and windows are made of acrylic. The pressure sphere’s interior will be pressurized to 8 pounds per square inch (psi), the equivalent of 16,000 feet above sea level, to reduce the risk of decompression sickness during the ascent without requiring Felix to inflate his pressure suit.
The cage surrounds the pressure sphere and supports the capsule overall. It was made by welding together Chrome-Moly (chromium molybdenum) aircraft tubing/pipes, a strong steel alloy frequently used in motor sports and aerospace industries. The cage frame is the point at which the capsule attaches to the balloon and will bear the load for the parachute system and capsule touchdown.
The external shell, 11 feet high and 8 feet in diameter at its base, surrounds the pressure sphere and cage. It is a foam-insulated skin covered in fiberglass that provides protection and insulation against temperatures that may reach – 70 Fahrenheit or lower.
Base and crush pads
The 8-foot-diameter base comprises of a 2-inch thick aluminum honeycomb panel which protects the capsule from sharp objects during landing and provides a mounting for the balloon system control box and batteries. Attached to the base are the landing crush pads, made of a cell-paper honeycomb covered by a fibre glass/epoxy fairing. They are designed to handle as much as 8 Gs on impact. Taking more than 150 drop tests to develop, the crush pads can be used only once and must be replaced after every flight.