Reactor for Space

The project for which the Middletown, Conn., plant was first built has been abandoned; U.S. authorities no longer feel driven to solve the enormously difficult design problems of a nuclear-powered aircraft. But the Pratt & Whitney engineers who sweated over the complexities of the atom plane's engine are still determined to get some sort of nuclear reactor aloft. They are working for AEC now, and last week the commission allowed them to give a glimpse of their top-secret labs.

White-Hot Metal. The most striking Middletown project is SNAP-50, a lightweight nuclear-power reactor designed to operate in space. Incorporating technical know-how gained on the airplane-engine project, this SNAP (for Systems for Nuclear Auxiliary Power) contains liquid lithium and gaseous potassium, tricky fluids that would drive most engine designers to seek liquid solace. Molten lithium is frightening stuff; it corrodes almost anything, and bursts into flame on contact with oxygen. Gaseous potassium, while not quite so bad, is hot and explosive too.

The liquid lithium flows through the hot reactor core and emerges at 2,000DEG F. The tubes that carry it, made of zirconium-columbium alloy, run at near white heat. The lithium is piped through a heat exchanger and turns liquid potassium (boiling point, 1,400DEG F.) to high-pressure gas that runs a turbine producing 300 kw. to 1,000 kw. of electricity. The potassium gas goes to a wide, flat condenser to be turned back into a liquid (see diagram).

Radiation Cooling. Pratt & Whitney chose to work with these unpleasant fluids because building a nuclear engine for space requires a solution for one overriding problem: how to get rid of heat from the condenser. There is no air to cool it by convection; the only cooling comes from radiation, which increases sharply with temperature. If the working fluid were steam, an enormous condenser would be needed to radiate its low-grade heat. The lithium-potassium combination runs so hot that a fairly small condenser does the job.

The strange fluids demanded new alloys to contain them and new kinds of pumps and valves to move them around. Whole technologies had to be developed to make them behave properly. Pratt & Whitney scientists are confident that SNAP-50 will be well tested by 1965. When it finally takes to space, it will find plenty of important work: providing electricity for long-distance radar and communication, working the spacecraft's instruments and internal machinery, running an ion propulsion engine to change course while cruising through deep space.

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