evangotlib :

p. Ha.  Win.

Unobtainium is also used, in an ironic sense, for materials that are practical and really exist, but are difficult to get. For example, during the development and service period of the SR-71 Blackbird spy plane, engineers working for Lockheed Corporation at the Skunk Works used the term unobtainium as a dysphemism for titanium. Titanium was required because of the high temperatures that the SR-71 airframe reached. Although at room temperature, titanium alloys have a strength-to-weight ratio similar to that of aluminum alloys, at the operating temperature of jet engines, titanium maintains much of its strength, whereas aluminum weakens dramatically. At the time, titanium was very difficult to obtain because Soviet Union had cornered the market in this material and was trying to prevent the American military from obtaining it.[nb 1] Eventually, through a European front company, a large quantity of titanium found its way to the United States. Since the discovery of the FFC Cambridge process in 1996, titanium is more readily obtained.[nb 2]