The Design
The balloon and capsule for the Breitling Orbiter were both built by Cameron Balloons Ltd. in Bristol, England. The "rozier" design, named for its original inventor French physicist Francois Pilatre de Rozier, comprises a double skin, or envelope, and contains both hot air and helium gas.
The advantage of this design is that, instead of having to store and jettison burdensome ballast at sundown in order to slow its descent, hot-air burners can be switched on to stabilize the craft's altitude, with only a tiny amount of propane required to heat the helium.
A safe, inert gas, helium is thus contained in a sphere located inside the hot-air balloon proper. At the start, the sphere is only half-filled with helium. As the balloon ascends, lessening pressure and the heat of the sun cause the gas to expand to its "cruising" volume. Thus, the "rozier" balloon travels by solar power during the day and propane gas at night.
If the balloon experienced a major loss of helium, it would remain aloft, turning itself into a classic hot-air balloon. If a catastrophe occurred, the balloon fabric would double as a giant parachute, keeping the balloon's descent rate at about 16 feet per second. The crew members will also have access to strap-on parachutes for emergency back-up.
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