In April 2004, the Space Shuttle Orbiter Reaction Control System (RCS) thruster serial number (S/N) 120 s injector was found to be cracked while undergoing a nozzle retrofit at the White Sands Test Facility (WSTF). The RCS is composed of safety-critical propulsion hardware elements used to control the attitude of the space shuttle orbiter during virtually all operational mission phases. Since a failure resulting from an RCS thruster burn-through (initiated from a crack) could be catastrophic, an official flight constraint was issued until flight safety could be adequately demonstrated. One recommendation was to reproduce the cracking in the laboratory to understand fully the driving environments. The Johnson Space Center (JSC) Materials & Processes (M&P) Branch initiated an effort starting in January 2005 to reproduce the cracking in the niobium injector. The results were successful. The specific conditions necessary to cause cracking were explicitly established and bounded. Each of the following conditions is necessary in combination: 1. A mechanically disturbed/cold-worked free surface (plastic deformation from machining, handling, fastener installation, etc.) 2. An externally applied sustained tensile stress near yield strength 3. Presence of fluorine-containing fluids on exposed tensile/cold-worked free surfaces 4. Sustained exposure to temperatures greater than 400 F
Johnson Space Center Material Laboratory Reproduction and Failure Analysis of Cracked Orbiter Reaction Control System Niobium Thruster Injectors
2007
48 pages
Report
Keine Angabe
Englisch