On last Friday’s episode of Battlestar Galactica, the crew of the Galactica finally ran up against a problem that is the bane of aerospace engineers: metal fatigue. Fatigue can affect anything built with metal that is subjected to stress, but airplanes and spacecraft can be particularly vulnerable. As shown on BSG, metal fatigue starts with tiny cracks you can’t see. Subjected to repeated cycles of stress, these microscopic cracks grow. Left unchecked, they can cause a structural member to fail abruptly, sometimes with catastrophic results.
As explained in Georgeo Bibel’s terrific book Beyond The Black Box: The Forensics of Airplane Crashes , metal fatigue has been behind a number of aviation disasters, including the loss of two de Havlilland Comets in 1954. The British de Havlilland Comet was the world’s first commercial jetliner, and those crashes taught engineers a hard-bought lesson.
Until then, engineers had not fully appreciated how vulnerable aircraft are to fatigue problems. This vulnerability arises from the fact that jetliners are big pressurized tubes that are subject to a host of stresses. These stresses are then applied every time the plane takes off and lands, and the more cycles a piece of metal experiences, the more cracks grow (and there are always microscopic cracks, because there always some flaws in the atomic lattice of the metal). Thus metal in a plane “ages” much faster than a similar piece of metal in, say, a building, even if both pieces are expected to carry similar loads. More recently, in 2002, NASA had to ground the entire shuttle fleet when cracks were found in fuel lines that fed hydrogen to the main engines. Even unpressurized unmanned spacecraft that don’t have to worry about repeated take offs and landings can still find themselves subjected to many cycles of stress, due to things like vibrating engines or the clockwork moving in and out of Earth’s shadow as the spacecraft travels in orbit.
As Bibel points out, because there will always be microscopic cracks, if nothing was done, all planes would sooner or later come apart due to to metal fatigue. This is why airplanes are subject to such a rigorous routine of preventative maintenance. By catching small cracks before they become big ones–as the chief did on BSG–components can be swapped out before they threaten the safety of the vehicle.