Rockets Up & Down

When engineers let their imaginations go--in a properly professional manner--they are apt to think about rockets, whose limit is above the sky. Last week a Manhattan meeting of the American Society of Mechanical Engineers heard Professor Hsue-shen Tsien, Chinese-born rocket expert from Caltech, on the prospects in rocketeering. Most of Dr. Tsien's paper was technical, e.g., how to keep the walls of combustion chambers from melting. But his conclusion was clear and startling: present-day technology is capable of building a transcontinental rocket ship.

Dr. Tsien's rocket liner would be 78.9 ft. long and 8.86 ft. in diameter, with a loaded weight of 96,500 Ibs. It would have small wings and a ramjet as well as a rocket motor. Its maximum speed, 9,140 m.p.h., would carry the ship 1,200 miles on an elliptical course outside the atmosphere. As it curved down toward the earth, it would meet the air again and turn into a non-powered glider. Coasting through the air for another 1,800 miles, it would land at 150 m.p.h.--not much more than the landing speed of many modern fighter craft. Duration of flight from Los Angeles to New York: one hour.

While hearing this piece of optimism, the A.S.M.E. also honored, as the year's best technical paper by an undergraduate, a piece of rocket-pessimism by George D. Lewis of the University of Connecticut. Engineer Lewis, who now works for Pratt & Whitney Aircraft Co., argued mathematically that a single-stage, chemically fueled rocket cannot escape from the earth's gravitation.

To escape into outer space, Lewis pointed out, requires an initial speed of 6.95 miles a second (25,020 m.p.h.). This requirement cannot be dodged by running the rocket motor slowly over a long period; that would only waste energy by forcing the ship to carry heavy fuel to a greater height.

To reach "escape velocity," the space ship's fuel must be used as economically as possible, and the efficiency of a rocket motor depends on the speed of the exhaust gases. Lewis calculated that a space ship carrying half its total weight in fuel would have to shoot out its exhaust gases at 9.95 miles a second (52,536 ft. per sec.).

Since the speed of the exhaust gases is proportionate to the temperature in the combustion chamber, Lewis next calculated what temperature such a rocket's materials would have to stand. The figure came out about 506,000DEG F., which is about 80 times more than enough to melt a combustion chamber made of any known substance.

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