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Friday, 28 December 2007

NASA Sets Plan for Shuttle Sensor Fix

NASA engineers will remove parts of a suspect fuel tank connector for analysis and repair, work that will likely further delay the planned January launch of the shuttle Atlantis, the agency's shuttle chief said Thursday.

Space shuttle program manager Wayne Hale told reporters that engineers will replace external components of an oversized electrical socket on Atlantis' fuel tank before setting a new launch date.

"This is probably going to not allow us to fly on Jan. 10," Hale said in an afternoon teleconference. "We're probably going to be a little bit after that."

A few extra days, or possibly weeks, will be required to complete the troubleshooting work, he added.

Atlantis' STS-122 construction flight to the International Space Station (ISS) has been delayed since December, when fuel gauge-like sensors failed standard countdown tests during two separate launch attempts. The sensors are vital, since they serve as a backup system to shut down a shuttle's three main engines before their fuel supply runs out.

Engineers tracked the intermittent glitch to a so-called "pass-through" connector that serves as a bridge for electrical connections running from the interior of Atlantis' fuel tank to the orbiter's aft-mounted avionics bay. The connector consists of internal and external electrical sockets that plug into a central glass plate with embedded metal pins.

"We believe we are experiencing intermittent electrical system open circuits in this arrangement," Hale said, adding that the glitch occurs only when Atlantis' fuel tank is fueled with its super-chilled liquid hydrogen and liquid oxygen.

On Saturday, engineers will remove the pass-through connector's central plug and exterior wiring for additional tests in early January, Hale said.

"After the first of the year, when we start getting the first of these lab reports in, we will begin to have a handle on our no earlier than launch date," he added.

The leading repair option under discussion is a soldering method that will fuse the exterior electrical connections in the pass-through plug, which will avoid open circuits caused by the movement of pins when the fuel tank is fueled. A similar fix was used on Atlas-Centaur rockets when they experienced engine cutoff sensor glitches, Hale said.

"We have a high degree of confidence that that will solve our problems," he added.

Commanded by veteran shuttle flyer Stephen Frick, Atlantis' seven-astronaut crew is tasked with delivering the European Space Agency's Columbus laboratory to the ISS during a planned 11-day mission. The spaceflight will be the first of possibly six NASA shuttle flights slated for 2008.

"We're taking this one step at a time," said Hale, adding that any changes to the 2008 shuttle flight schedule are secondary to fixing the current sensor glitch. "Obviously, we'd like to fly as soon as it's practical and safe to do so."



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