Analysis is made of the propulsive thrust and specific impulse attainable by cooling aircraft surfaces with liquefied or solidified gases having vaporization temperatures lower than the equilibrium surface temperature. It is found that for some coolants a net thrust is obtainable without further heat addition at all flight speeds if the vaporization temperature and heat of vaporization are sufficiently low.nUse of coolant vaporization as the sole means of propulsion yields low specific impulses at low speeds. As flight speed increases, the attainable specific impulse increases; if liquid hydrogen is used as coolant, specific impulses comparable to those of conventional liquid rocket propellants are theoretically attainable in the hypersonic speed range. This propulsion system provides the possibility of flight with cooled aircraft surfaces at extremely high Mach numbers.
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