CAPE CANAVERAL, Fla. -- Shuttle Endeavour will blast off Nov. 29 on a mission to the International Space Station -- if, that is, engineers can convince managers that it's safe to land the ship with wheels that might be corroded.
With four astronauts and the next full-time station crew onboard, Endeavour is scheduled to blast off at 7:44 p.m. EST Nov. 29 (0044 GMT Nov. 30) from Kennedy Space Center.
The launch date and time were firmed up during a traditional flight readiness review held here Thursday at NASA's coastal Florida spaceport.
Engineers, however, will spend the next two weeks trying to prove that the shuttle can land safely despite minor corrosion that has been uncovered on the wheels of other shuttles.
"I think they feel like this is not going to be a safety issue. But they've got to prove it," said KSC spokesman George Diller. "They've got to have engineering data to prove it."
Here's the situation:
Small amounts of corrosion were discovered on shuttle wheels earlier this year during routine inspections at the manufacturer, B.F. Goodrich Co. of Troy, Ohio.
Specifically, corrosion was found around holes where 18 bolts are used to connect the front and back halves of the split wheels, which are made of aluminum.
The discovery prompted NASA to send 17 of the 30 wheels in the agency's fleet-wide inventory back to the manufacturer for tests, and similar amounts of corrosion have been found on all the wheels.The worst case so far has been a rust spot that measured 0.04 inches (0.1 centimeters) deep, 0.09 inches (0.2 centimeters) long and 0.005 inches (0.01 centimeters) wide.
NASA and contractor engineers, however, are not entirely certain what is causing the corrosion, and the six wheels on Endeavour's main landing gear and nosewheel landing gear cannot be inspected while the shuttle is poised for liftoff at KSC's launch pad 39B.
There is some concern, meanwhile, that corrosion could cause the wheels to crack or fracture when a 100-ton shuttle makes a 225 mph (360 kilometer per hour) landing.
Engineers, consequently, are conducting tests aimed at determining whether the type of corrosion found during inspections potentially could cause a wheel to fracture upon landing. Metallurgical analysis is being done, engineers are evaluating machining processes used to manufacture shuttle wheels and destructive testing also is on tap.
An analysis aimed at determining the root cause of the problem also is under way. To that end, engineers are reviewing a variety of potential causes, including the possibility that:
- Corrosion protection materials applied to the wheels might be damaged when wheels are installed on shuttles.
- Exposure to rain, or the environment that wheels are stored in, might be the culprit.
- Galvanic interaction between the different metals that are used to make wheels and wheel bolts might trigger corrosion.
Also a possible cause: Cleaning materials used on the wheels.Engineers are expected to brief senior shuttle program managers on the progress of their efforts over the next two weeks, and a formal decision on whether to proceed with launch is expected to be made during a management meeting two days prior to the planned launch.
Senior shuttle managers, meanwhile, cleared suspect turbopumps on two of Endeavour's three liquid-fueled main engines.
A small crack recently was discovered on a turbine blade within an identical engine pump that flew on a July 1999 shuttle mission. But engineers determined that Endeavour's pumps could operate without problems even if they had a similar flaw.
NASA's 107th shuttle flight will involve ferrying a fourth full-time crew to the international station. Led by veteran Russian cosmonaut Yuri Onufrienko, the so-called Expedition Four crew includes American flight engineers Daniel Bursch and Carl Walz.
The trio will replace current outpost commander Frank Culbertson and his two cosmonaut colleagues -- Vladimir Dezhurov and Mikhail Turin, who have been onboard the station since August and will return to Earth Dec. 10 aboard Endeavour.
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