Before any NASA craft is cleared for liftoff, it must undergo exhaustive testing in one of the administration’s 42 major wind tunnels, which range from just a few inches wide to cavernous enough to contain a full-sized airplane.

With an aircraft model held on a stationary post, air is accelerated through the tunnel by fans, allowing engineers to study the effects of different designs on flight characteristics such as lift, drag and stability.

NASA’s earliest wind tunnel predates NASA itself, and was built in 1920 at the Langley Research Center, then under the auspices of the National Advisory Committee for Aeronautics (NACA).

As flight technology became more advanced and complex, so did the testing facilities. Specialized tunnels were developed to simulate subsonic, transsonic, supersonic and even hypersonic speeds — five times the speed of sound. Some tunnels can approximate the fiery heat of atmospheric re-entry, while others can test the effects of ice buildup at high altitudes. Some newer facilities can magnetically suspend aircraft models in midair, eliminating aerodynamic interference from support structures.

Today, NASA-operated wind tunnels are routinely used to test and tweak military and civilian aircraft.