Space: A New Setback for the Shuttle

Design flaw in Challenger's engines forces another launch delay

Ever since last November, the new space shuttle Challenger has been perched proudly on its Florida pad, pointing skyward like an anxious eagle. Last week NASA officials gloomily conceded that their $1 billion bird may have to sit in its nest a while longer. The latest delay involves the most serious problem yet encountered with the troubled Challenger: a basic defect in design that requires overhauling all three of the main engines. Unless the flaw can be quickly corrected, the problem could create a horrendous backup of civilian and military satellites waiting to be carried aloft and add millions of dollars to the cost of the shuttle program.

Ironically, the defect stems, at least in part, from NASA'S own supercaution. To improve performance, Challenger's engines were built to operate at 9% greater thrust than those of the first orbiter, Columbia, when the throttle is fully opened. Realizing that this extra power would vibrate the spacecraft more violently, NASA engineers at the Marshall Space Flight Center made a design change. They ordered reinforcement of the metal piping that carries hot, gaseous hydrogen fuel into the small chamber where the engines are first fired up and begin revving to their full 480,000 lbs. of thrust.

The modification took the form of a sleeve that was brazed, or soldered, around the pipes. Presumably, the added metal would have protected the fuel lines from chafing against other parts inside the crowded engine. After the brazing, however, the pipes became so rigid that they developed hairline cracks during test firings, allowing the highly combustible fuel to escape. Such leaks during a flight could cause a calamitous flash fire.

In testimony before a congressional subcommittee on science and technology last week, Air Force Lieut. General James A. Abrahamson, NASA'S associate administrator and boss of the shuttle program, said that discovery of the defect was a tribute to the space agency's quest for safety. He might have added that it was also because of an odd bit of luck. In late January, only days before Challenger's originally scheduled liftoff, NASA inspectors discovered that hydrogen was leaking from the No. 1 engine.

The seepage was traced to a ¾-in.-long crack in the engine's manifold, where hydrogen and oxygen come together under extremely high temperatures and pressures. That crack was the result of an inadequately hardened weld ordered up to repair some damage sustained during manufacture. But when the No. 1 engine was removed, its replacement also showed signs of leakage. This time oxygen was pouring out of a heat exchanger, a situation that might have triggered an explosion and fire.