Thus the invention of high temperature fuels will enable us to consider cores which are radiation cooled; such cores would be surrounded by large tanks (cooled by water) which in turn would be penetrated by beam holes. The beam holes themselves would probably have to be made of "unobtanium". (This "unobtanium" is a word coined at Atomics International to describe the material needed to make reactor projects feasible.) In between the radiation cooled reactors and the water cooled reactors is a regime suitable for liquid metal (including boiling liquid) cooled reactors. Once again "unobtanium" is needed.
Source: wiktionary
In order to illustrate some of the features of data processing under ideal conditions, a set of simulated data was generated and is presented in the last four columns of Table II. The hypothetical material is called Unobtainium.
Source: wiktionary
The names of materials presently used in aerospace applications are familiar: magnesium, aluminum, titanium, and so on. Propulsion scientists call the ideal material for turbine engines "Unobtainium," because it does not exist.
Source: wiktionary
As early as 1969, during the initial Phase A studies, Lockheed had taken the initiative in proposing a two-stage fully-reusable design with both stages built of aluminum and using silica tiles for thermal protection. [...] Though that company indeed was in the forefront in developing such tiles, they were items for laboratory research. A design that specified their use had no more intrinsic credibility than one that proposed to use the miracle metals Unobtanium and Wishalloy.
Source: wiktionary
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