In support of space shuttle return-to-flight efforts, gear-scuffing tests were conducted by the Mechanical Components Branch at the NASA Glenn Research Center. A new test gear box was designed, fabricated, and installed in Glenn’s Gear Noise Test Facility to test flight gears from the shuttle rudder/speed brake power drive unit (PDU). Failure of these gears during flight could jam the rudder/speed brake, which is needed for steering and landing the shuttle, and cause a catastrophic failure. The objectives were to recreate scuffing damage similar to that found on the flight gears at conditions expected during back-drive, to document conditions that induce scuff, to demonstrate that scuffed PDU flight gears can be operated long enough to complete a shuttle mission, and to quantify the scuffing and tooth wear.
Space shuttle rudder/speed brake PDU flight gears installed in a test gear box for scuffing tests at Glenn.
Scuffing-like damage was found on the tooth surfaces of gears 5 and 6 of the shuttle rudder/speed brake PDU 2 after a transient back-driving event occurred in flight. Tests were conducted using a pair of unused space flight gears in a bench test setup (see the photograph) at operating conditions up to 2866 rpm and 1144 in.-lb at the input ring gear and 14,000 rpm and 234 in.-lb at the output pinion gear. This corresponds to a power level of 52 hp.
This test condition exceeds the maximum estimated conditions expected in the back-driving event that was thought to produce the scuffing damage. Some wear marks were produced, but they were much less severe than the scuffing damage produced during shuttle flight. These tests gave confidence to the Shuttle Project Office to proceed with the launch of space shuttle flight STS-114. If a future shuttle flight includes a back-driving event that produces gear scuffing, Glenn’s bench test rig could be used to assess the remaining life of gears that were scuffed in flight. Such an approach provides the most direct assessment method short of system-level testing.
Find out more about the research of Glenn’s Mechanical Components Branch: http://www.grc.nasa.gov/WWW/5900/5950/
Glenn contacts:
Margaret P. Proctor, 216-977-7526, Margaret.P.Proctor@nasa.gov; and Fred B. Oswald, 216-433-3957, Fred.B.Oswald@nasa.gov
Authors:
Margaret P. Proctor, Fred B. Oswald, and Dr. Timothy L. Krantz
Headquarters program office:
Space Operations
Programs/Projects:
Shuttle Project Office
Last updated: October 16, 2006
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