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In fiction, engineering, 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. For instance, unobtainium is described as being stronger than helium, and lighter than air. 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. An alternative spelling, unobtanium is sometimes used (for example, for the crypto-currency Unobtanium), based on the spelling of metals such as titanium. == Engineering origin == Since the late 1950s,〔Since at least the 1950s: (Hansen, James R. (1987) "Engineer in Charge: A History of the Langley Aeronautical Laboratory, 1917–1958." The NASA History Series, sp-4305. ) Chapter 12, recounting an October 1957 meeting, mentions the problems caused by "the lack of a superior high-temperature material (which the Langley structures people dubbed 'unobtainium')" This paragraph in turn cites Becker, John V. "(The Development of Winged Reentry Vehicles, 1952–1963 )," unpublished, dated 23 May 1983.〕 aerospace engineers have used the term ''"unobtainium"'' when referring to unusual or costly materials, or when theoretically considering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 The word ''unobtainium'' may well have been coined in the aerospace industry to refer to materials capable of withstanding the extreme temperatures expected in re-entry.〔 Aerospace engineers are frequently tempted to design aircraft which require parts with strength or resilience beyond that of currently available materials. 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, Lockheed engineers 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. In the 1970s, bicycle magazines, such as ''Bike World,'' sometimes referred to exotic lightweight bicycle parts as being made of unobtainium, which, while expensive, were commercially obtainable. In the same period, driver and engineer Mark Donohue claimed unobtainium was used in the construction of Penske race cars. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「unobtainium」の詳細全文を読む スポンサード リンク
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