Prior to space flights, high-altitude flights were developed using experimental airplanes that brushed the stratosphere, notably military flights, including spy planes. Given the enormous altitudes at which they flew, pressure maintenance suits were created as precursors to modern astronaut suits. The Baklan suit, for instance, closely resembles the suit worn by Austrian adventurer Felix Baumgartner, the current parachute jump record holder. Despite aesthetic differences, their construction principles are quite similar.

The Baklan full-pressure suit was developed by Zvezda for the crew of high-altitude strategic aviation aircraft starting in 1970. The Strizh, derived from the Baklan suit, is a space suit initially developed for the crew of the Russian Buran space shuttle and resembles the Sokol space suit worn by Soyuz crew members. It was designed to protect cosmonauts during a potential ejection from the spacecraft at altitudes of up to 30 km and speeds of up to Mach 3.

Mach 3 is a dimensionless quantity representing the ratio of flow velocity past a boundary to the local speed of sound, defined by the equation M = u/c where:

• “M” is the Mach number,
• “u” is the local flow velocity relative to the boundaries (either internal, such as an object immersed in the flow, or external, like a channel), and
• “c” is the speed of sound in the medium.