K-36RB (K-36M-11F35) seats and the Strizh full-pressure suit, qualified for altitudes up to 30,000 m and speeds up to Mach three. Buran flew only once in fully automated mode without a crew, thus the seats were never installed and were never tested in real human space flight. Ejection capsule An alternative to ejection seats was an escape crew capsule or cabin escape system where the crew ejected in protective capsules, or the entire cabin is ejected. Such systems have been used on several military aircraft. The B-58 Hustler and XB-70 Valkyrie used capsule ejection, while the General Dynamics F-111 and early prototypes of the Rockwell B-1 Lancer used cabin ejection. Like ejection seats, capsule ejection for the shuttle would have been difficult because no easy way existed to exit the vehicle. Several crewmembers sat in the middeck, surrounded by substantial vehicle structure. Cabin ejection would work for a much larger portion of the flight envelope than ejection seats, as the crew would be protected from temperature, wind blast, and lack of oxygen or vacuum. In theory an ejection cabin could have been designed to withstand reentry, although that would entail additional cost, weight and complexity. Cabin ejection was not pursued for several reasons: Major modifications required to shuttle, likely taking several years. During much of the period, the vehicle would be unavailable. Cabin ejection systems are heavy, thus incurring a significant payload penalty. Cabin ejection systems are much more complex than are ejection seats. They require devices to cut cables and conduits connecting the cabin and fuselage. The cabin must have aerodynamic stabilization devices to avoid tumbling after ejection. The large cabin weight mandates a very large parachute, with a more complex extraction sequence. Air bags must deploy beneath the cabin to cushion impact or provide flotation. To make on-the-pad ejections feasible, the separation rockets would have to be quite large. In short, many complex things must happen in a specific timed sequence for cabin ejection to be successful, and in a situation where the vehicle might be disintegrating. If the airframe twisted or warped, thus preventing cabin separation, or debris damaged the landing airbags, stabilization, or any other cabin system, the occupants would likely not survive. Added risk due to many large pyrotechnic devices. Even if not needed, the many explosive devices needed to separate the cabin entail some risk of premature or uncommanded detonation. Cabin ejection is much