Shuttle Program Frequently Has Suffered Engine Problems

The space shuttle’s main engines, one of which cut off prematurely during launching Monday, have repeatedly experienced problems during the first four years of the shuttle program. The difficulty Monday occurred when a sensor detected overheating in a turbo-pump that boosts the pressure of hydrogen flowing into the engine’s main combustion chamber.

A year ago, a valve failure in an engine aborted a shuttle launching seconds before takeoff. A similar shutdown occurred earlier this month, although the cause has not yet been determined.

The shuttle engines, which are designed for 55 launchings, have not performed up to that life expectancy. The National Aeronautics and Space Administration has continually had to juggle engines among its three operational shuttles to maintain its flight schedule. At one point, it had only enough working engines to fly one shuttle, although it had three craft in the hangars.

On Monday, it was not clear whether the pump was in fact overheating or whether the heat sensor was defective. But the computer that monitors the engine’s operation took no chances and ordered the engine shut down. Challenger and its crew of seven made it into orbit by burning the remaining two engines longer than planned.

The space shuttle is designed to be lofted into space atop more than 7 million pounds of thrust delivered from three main engines in the tail of the spaceship augmented by two booster rockets strapped alongside.

When everything goes right, the booster rockets burn solid fuel for approximately two minutes and then parachute into the ocean, where they are recovered for future use. The main engines, fueled by liquid hydrogen and liquid oxygen from the 184-foot external tank that towers over the shuttle, fire for about eight minutes and should cut off when the ship is traveling at 17,440 miles an hour, just short of its orbital velocity of 17,500 m.p.h.

When the propellants enter each engine, they pass through a maze of plumbing and a series of chambers and pumps designed to increase the pressure and yield maximum thrust. The high-pressure turbo-pump, which operates at about 30,000 revolutions a minute, is 22 inches wide and 44 inches long.