NASA managers decided Tuesday to modify existing space station ammonia coolant hoses by welding shorter sections together to replace a longer hose design that failed a recent ground pressure test. If the work goes well - and the schedule is tight - NASA hopes to launch the shuttle Endeavour on Feb. 7 as planned to deliver a new module to the orbiting lab complex.

The Tranquility module was moved to the transportation canister Tuesday in preparation for delivery to launch pad 39A. Credit: NASA-KSC

The primary goal of the three-spacewalk mission is to attach a pressurized module known as Tranquility to the left side of the space station's central Unity module. Tranquility will be used to house critical life support systems and exercise gear that currently are located elsewhere in the laboratory.

NASA originally intended to attach Tranquility to Unity's Earth-facing port but later decided to mount it on the left side instead. Connectors needed to circulate ammonia coolant to and from Tranquility were not correctly positioned, or "clocked," for Tranquility to be attached to Unity's left-side port.

As a result, custom 14-foot-long hoses were ordered to compensate for the offset. But during a ground test last week, a hose ruptured below the required pressure level, throwing a potential wrench into NASA's schedule.

At a space station program requirements control board meeting Tuesday at the Johnson Space Center in Houston, NASA managers decided to replace the suspect hoses with shorter, flight-qualified lines that will be welded together to reach the required length.

At the same time, engineers will modify the hose design that failed in an attempt to make it strong enough to meet the design criteria. Those hoses will be used as backups.

NASA spokesman Kelly Humphries said the welded hoses and the modified longer lines are expected to be shipped to the Kennedy Space Center about five days before Endeavour's planned launching.

"Both sets of hoses are expected to be ready within a day or so of each other," he said.

If that schedule can be maintained, the astronauts should be able to fly a full-duration three-spacewalk mission, attaching and activating Tranquility as planned. But if additional problems develop, NASA flight controllers have developed fall-back plans to fly a scaled-back two-spacewalk mission that would defer some work until later.

Endeavour and its six crew members - commander George Zamka, pilot Terry Virts, Kathryn Hire, flight engineer Stephen Robinson and spacewalkers Robert Behnken and Nicholas Patrick - plan to fly to Florida Jan. 18 to review emergency procedures and participate in a dress-rehearsal countdown Jan. 21.

Shuttle program managers, meanwhile, will assess Endeavour's launch processing next week and senior managers will meet Jan. 27 for a flight readiness review that will include an update on the space station hose work. Endeavour's countdown is scheduled to begin Feb. 4 for a launch attempt at 4:39 a.m. EST on Feb. 7.

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