Stripped screw caused shuttle malfunction
Team studies whether to delay next launch
A hydrogen fuel leak, visible in the |
lower image, was one of the problems
encountered during Columbia's July 23
By Robin Lloyd
CNN Interactive Senior Writer
August 10, 1999
Web posted at: 3:37 p.m. EDT (1937 GMT)
(CNN) -- Technicians have identified a metal bur raised on a Phillips-head screw by a power tool as the cause of a short circuit five seconds into space shuttle Columbia's launch last month, a NASA spokesman said Tuesday.
The short circuit, which knocked out two of the six computers controlling the shuttle's rocket engines, along with a hydrogen leak in one of Columbia's engine nozzles, marred the otherwise successful launch on July 23 from NASA's Kennedy Space Center.
"That little bur on the top of an appropriately and firmly installed screw head and a wire, in the vicinity over 26 flights and 20 ferry flights on back of a 747, vibrated so much in that environment it finally wore through a wire," said Joel Wells, a Kennedy Space Center spokesman.
"It kind of lacerated the insulation of the wire," he said. The exposed wire and stripped screw created an opportunity for an electrical arc, Wells said.
If the short circuit had continued to knock out computers, it could have forced an emergency landing in Florida or Africa.
NASA managers, engineers and technicians were to decide late Tuesday whether the finding and a subsequent inspection for similar screws on another spacecraft in the shuttle fleet will force a delay in Endeavour flight set for September 16. That flight involves a radar mapping mission.
A team of technicians working in the shuttle's payload bay easily identified the cause of the short circuit Saturday and Sunday, Wells said. By tracing the bundled wires, they found evidence of electrical arcing, as well as burn marks on the screw and the wire.
"It's very clear to them that this was the cause of the short," Wells said.
Technicians started looking over Columbia as soon as it landed July 27, but equipment in its payload bay got in the way of a full inspection.
Last week, they pulled out the framework that had been used to hold in a booster rocket attached to the Chandra X-ray Space Observatory into orbit. The shuttle mission successfully released that space telescope currently orbiting Earth.
Now the question is whether there are other screws similarly stripped, either during the shuttle fleet's construction by what is now Lockheed Martin or during servicing in the past four years by the Boeing-led consortium called United Space Alliance.
"It's likely that that is a situation that could have existed for many, many years," said KSC spokesman Bruce Buckingham.
This week, technicians have studied Columbia and one of its three virtual twins, Atlantis. They may study Discovery as well. Along with engineers, they will make a prediction on whether the problem is likely to exist on Endeavour and should force a delay of its upcoming mission.
Technicians were set to roll Endeavour from its hangar to KSC's Vehicle Assembly Building Tuesday, but that has been delayed until Wednesday due to the screw finding.
At its next stop, the shuttle would be mated to the huge, orange, external fuel tank and boosters. It is set for installation on its launch pad on August 18.
If engineers recommend looking at Endeavour for stripped screws, the launch would be delayed, Wells said. Its payload is installed, its payload doors are closed and it has been checked for leaks.
"If you start opening things up you are not only impacting your schedule, you are also compromising areas you already have prepared for flight. You don't want to do that unless you have to," he said.
Columbia is the oldest orbiter in the shuttle fleet, while Endeavour, a replacement for the Challenger shuttle, which exploded just after launch in 1986, has logged only 13 flights.
Engineers will make a recommendation and meet with managers Tuesday at 4 p.m. to decide whether to go forward with the Endeavour schedule or postpone its move to the Vehicle Assembly Building -- and therefore the launch, Wells said.
It is unclear when the Shuttle Radar Topography Mission would fly if it were postponed, Wells said. A Hubble Space Telescope maintenance mission is set for October, with an International Space Station assembly mission to follow in December. Those missions are unlikely to be pushed back so the SRT mission might be postponed into 2000.
NASA engineers who probed the potentially hazardous hydrogen gas leak in the space shuttle Columbia's right main engine in July said it arose when a loose pin fell and weakened three stainless steel cooling tubes ringing the nozzle when the engines started.
A rupture followed, making the engine run 100 degrees hotter than planned and use more propellant. That left Columbia about seven miles short of its intended orbit. But the problem, as well as the short circuit, did not affect the overall mission.
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