NASA Slips Shuttle Launch Again
Feb 10, 2009
By Frank Morring, Jr.
Launch of the space shuttle Discovery with the fourth and final Boeing-built solar array wing for the International Space Station in its payload bay won't come until Feb. 22 at the earliest, to give engineers more time to complete safety testing.
Managers already had slipped the STS-119/15A mission, originally set for Feb. 12, to Feb. 19 for additional testing at NASA facilities across the country. Engineers are wrapping up impact tests designed to determine if a suspect hydrogen valve might send a broken-off fragment into a gaseous hydrogen line with enough force to cause a leak.
The valves - one in each of the three engines in a shuttle orbiter - keep enough gaseous hydrogen in the system to maintain a pressure of at least 32 psi in the shuttle's main liquid-hydrogen tank. But post-flight inspection after the most recent shuttle mission revealed a tiny fragment had broken off one of the valves in the shuttle Endeavour, allowing pressure in the system to drop slightly.
In that case the other two valves were able to maintain adequate pressure for safe engine operation. The cause of the problem was traced to unexpected metal fatigue caused by vibrations from gaseous hydrogen flowing over the valve hardware.
Now that the phenomenon is understood, shuttle program managers want more data before developing a flight rationale. The valves in Discovery have flown in their present positions before, and did not show signs of wear or fatigue in electronic microscope inspections ordered after the problem on the Endeavour valves was found.
Impact tests are under way at Glenn Research Center, Stennis Space Center, Marshall Space Flight Center and the NASA facility at White Sands, N.M., using compressed air to send tiny metal fragments simulating broken valve pieces down lengths of pipe that mimic the gaseous hydrogen lines in a shuttle stack. So far, the testing has not damaged the simulated hydrogen lines, according to an agency spokesman.
Final results from the tests are due for final review by shuttle program managers on Feb. 13. If the data support a flight rationale, the formal flight readiness review for the STS-119 mission will be held Feb. 18, which could set up a launch attempt as early as the predawn hours of Feb. 22.
Discovery photo: NASA
