Unobtainium
In engineering, fiction, and thought experiments, unobtainium is any fictional, extremely rare, costly, or impossible material, or (less commonly) device needed to fulfill a given design for a given application. The properties of any particular unobtainium depend on the intended use. For example, a pulley made of unobtainium might be massless and frictionless; however, if used in a nuclear rocket, unobtainium would be light, strong at high temperatures, and resistant to radiation damage. The concept of unobtainium is often applied flippantly or humorously.
The word unobtainium is derived from unobtainable + -ium (the suffix for a number of elements). It pre-dates the similar-sounding IUPAC systematic element names, such as Ununoctium.Since the late 1950s, aerospace engineers have used the term "unobtainium" when referring to unusual or costly materials, or when theoretically considering a material perfect for their needs in all respects, except that it does not exist. By the 1990s, the term was in wide use, even in formal engineering papers such as "Towards unobtainium [new composite materials for space applications]." The word unobtainium may well have been coined in the aerospace industry to refer to materials capable of withstanding the extreme temperatures expected in reentry.Aerospace engineers are frequently tempted to design aircraft which require parts with strength or resilience beyond that of currently available materials.
Engineering origin
Later, unobtainium became an engineering term for practical materials that really exist, but are difficult to get. For example, during the development of the SR-71 Blackbird spy plane, Lockheedengineers at the "Skunk Works" under Clarence "Kelly" Johnson used unobtainium as a dysphemism for titanium. Titanium allowed a higher strength-to-weight ratio at the high temperatures the Blackbird would reach, but the Soviet Union controlled its supply and was trying to deprive the US armed forces of this valuable resource. Eventually, through a European front company, a large quantity of titanium found its way to the United States.
In the 1970s, bicycle magazines, such as Bike World, sometimes referred to exotic lightweight bicycle parts as being made of unobtanium, although while expensive they were commercially obtainable.
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