August 13, 1999
Web posted at: 11:02 a.m. EDT (1502 GMT)
By Robin Lloyd
CNN Interactive Senior Writer
(CNN) -- The next space shuttle launch has been postponed at least three weeks to give inspectors time to remove Endeavour's massive payload and inspect dozens of miles of cables for potential short circuits like one that popped during a July shuttle launch.
The short circuit occurred five seconds after the space shuttle Columbia's July 23 launch because electricity arced between a stripped screw and an exposed wire, NASA said this week.
The possibility of a similar problem on Endeavour, which had been set for a September 16 launch for a radar mapping mission aboard, prompted NASA managers to put off the launch to no sooner than October 7 to give technicians time to inspect its wiring.
"We think it's appropriate that we take out the cargo bay and inspect the entire length of cable trays," said shuttle team supervisor and astronaut Don McMonagle.
The short circuit on Columbia was the result of a one-time incident, he said, when a technician inadvertently pressed a packet of wires against the stripped screw, rubbing off a wire's insulation. The wire and its insulation are about as thick as a paper clip.
Launch vibrations on July 23 shook the wire to the point that it made contact with the screw, causing the arc, engineers believe. The short knocked out power to two of the three engines on the shuttle, but back-up systems took over. A second short circuit would have meant a permanent loss of power to at least one engine, forcing an emergency landing in Florida or Africa and putting astronauts' lives at risk.
Photo showing the worn section of shuttle wiring and burn marks from the short
Second exposed wire prompted delay
The source of the short was discovered Saturday and Sunday. The next day, technicians inspected the rest of Columbia and another shuttle in the fleet, Atlantis. On Columbia, they found one other wire with rubbed-away insulation. No such wires were found on Atlantis, which is younger than Columbia.
Given the discovery of the second exposed wire on Columbia, managers decided it was "prudent" to inspect Endeavour as well before launch. The rest of the shuttle fleet also will be inspected.
"Because of the finding of damage of a similar nature, that led us to believe that there is at least one credible scenario that could cause us to have damage in more than this one isolated incident," McMonagle said.
Lab tests showed that the insulation on the Columbia wire that had a short circuit had worn away before launch during an isolated incident, not over time. The wire is one of several bundled in a metal tray -- like a gutter with a cover -- where the floor of the payload bay meets one of its walls, said NASA spokesman Joel Wells.
During a Thursday meeting at the Kennedy Space Center, managers, engineers and technicians decided to inspect Endeavour's wiring, rather than moving it as planned from its hangar to the Vehicle Assembly Building in preparation for launch.
Engineers think the wire was pressed against a burred screw head by a worker stepping on the wire, resting an elbow against it or bracing to move upward, Wells said.
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