Shuttles grounded by two sets of leaks.

Shuttles grounded by two sets of leaks

It proved a double blow to proud NASA. As astronomers pondered the consequences of an apparently misshapen mirror that significantly reduced the Hubble Space Telescope's ability to explore the distant heavens, engineers at Kennedy Space Center in Florida discovered yet another hydrogen leak in a space shuttle. A month ago, the space agency delayed the flight of Columbia because of such a leak. This time, Atlantis revealed a similar and possibly related leak.

NASA, which had already postponed Columbia's mission until at least August, reacted to this second potentially lethal problem by indefinitely suspending flights by the three shuttle craft. William B. Lenoir, NASA's chief of space flight, said the shuttles would remain grounded until engineers found, understood and fixed the leaks.

No one ventured a specific date when the shuttle fleet might fly again.

Liquid hydrogen and liquid oxygen serve as the propellants for the shuttle orbiter's three powerful main engines that help drive the craft into space. The two supercold fluids fill the huge external fuel tank that clings to the underside of the astronaut-carrying orbiter and flow through a complex system of pipes and valves to the main engines. The fuel mixture is highly explosive.

Hydrogen has no scent or color, and spotting hydrogen leaks requires special detectors. It is far more difficult to locate a leak and repair it than to simply confirm that one exists. Engineers have been conducting tests of each craft's external tank and its piping, as well as of the "umbilical" connecting hoses and the fittings used to fill the tanks.

The leak studies now focus on four themes, Lenoir says. One involves a detailed analysis of how the pieces that make up the propellant-storage and delivery components were made. A second concentrates on how this equipment was handled, assembled and shipped. A third line of investigation is devoted to step-by-step data analysis of the system, checking to make sure engineers haven't overlooked some possible leak source. And the fourth, reminiscent of the Challenger investigation, creates and follows "fault trees" designed to anticipate subtle flaws--in design, fabrication or other aspects--that might trigger equally disastrous consequences.

Columbia had been scheduled for a May launch to carry Astro-1, a four-telescope observatory that will study the sky from the shuttle's cargo bay rather than from a "free-flying" satellite like the Hubble Space Telescope. Atlantis had been scheduled to deploy a classified satellite for the Department of Defense.