Hoofs of Hydrogen

After five years and $325 million worth of frustration, a snow-white Centaur rocket flashed its hoofs high over Cape Kennedy last week and galloped into orbit. As its Atlas booster fell away, the Centaur's own nozzles bloomed with a blue, barely visible flame: the high-energy signature of burning hydrogen.

Up by the Bootstraps. Designed to hurl more than a ton of instrument payloads all the way to the moon, the 28 1/2-ft. Centaur generates 30,000 Ibs. of thrust with its two restartable Pratt & Whitney engines. The hydrogen fuel they burn has been the key--and the curse--of the Centaur system from the time it was born on engineers' drawing boards. As early as 1909, U.S. Rocket Pioneer Robert Goddard noted that hydrogen (in liquid form, known as LH.,) might prove to be the optimum chemical rocket fuel. Its light molecular weight, less than half that of standard liquid fuels, gives it 35% more thrust per pound. But LH2 begins to boil above --423 DEGF., and because it is so cold, engineers usually find it too hot to handle. Most metals shiver to pieces when they come in contact with it, and its extreme volatility makes it flash into explosive gas at the gentlest slosh.

In 1958", when Pratt & Whitney engineers set out to develop the Centaur's engines, they boldly planned to turn that touchy temperament to their advantage. In the final product, frigid LH2 does two jobs as it courses toward ignition. First, it is pumped through an outer jacket where it cools the thrust chamber's fierce 6,000DEG heat, and in the process vaporizes itself for ultimate burning. But before it reaches the chamber, the gas is expanding fast enough to spin an auxiliary turbine, which pumps more fuel and oxidizer into the cooling jacket. Thus the LH2 practically lifts itself by its own bootstraps.

Out of the Stable. After more than 700 ground firings, the engine seemed ready for a test in the weightless environment of space. But the crucial first shot ended in naming failure before the engines could ignite. Just 55 seconds after liftoff, a weather shield tore loose, followed by a blazing rupture in a hydrogen fuel tank. With Centaur already 18 months behind schedule and Congressmen crying inept management NASA shifted the program from Marshall Space Flight Center, where Wernher von Braun's team was primarily concerned with the Saturn program, to the Lewis Research Center in Cleveland. There tough-minded Director Abe Silverstein, 55, took charge.

At Lewis, extensive design changes quickly reshod the limping space horse. Fuel-tank baffles were added to cut down sloshing; a new separation system was developed to cut Centaur loose from its first-stage Atlas; a critical operation in the engine-start procedure was cut from 24 to four seconds. Last week, in new harness, the second Centaur charged out of its stable and into space without a hitch. Its engines burned clear and blue for the programmed 380 seconds, sent the rocket tumbling into an elliptical orbit ranging from 340 to 1,050 miles above the earth. But it was not the orbit that mattered, nor the fact that the 10,200-lb. Centaur was the largest U.S. satellite orbited to date. By proving that hydrogen engines would burn in space, Centaur showed that the U.S. space effort is on a sound propulsive track. The multistage Saturn boosters that will sling U.S. astronauts to the moon will also burn liquid hydrogen in their upper stages.

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