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u International Space Station SARJ Race Ring Damage Simulation and Durability Test For Life Extension Iqbal Shareef, Ph.D., CMfgE, P.E. Bradley University, Peoria, Illinois (309) Presented at NASA Academy of Aerospace Quality Workshop Cape Canaveral, Florida March 22, 2012
u Outline Overview of the International Space Station SARJ (Solar Alpha Rotary Joint) SARJ mechanism, tribology and contact mechanics SARJ degradation and remedy Lab experiments to simulate and study the ongoing tribology condition of the SARJ –Goals of the experiments –Description of the test rig and test parameters –Typical test results and insights gained from experiments Summary 2
u International Space Station (ISS) is a research facility assembled in low Earth orbit. (~220 miles or 354 km from Earth) The ISS project is a multi-national effort led by United States, with partners from Russia, Canada, the European Union, Japan, and others. Construction of the ISS began in 1998 and completed in 2011 with operations to continue until at least 2015, and likely ISS is the largest artificial satellite that has ever orbited the Earth, it can be seen with a naked eye
u ISS is much longer than the length of Boeing 777. It is larger than 5BR house, weigh ~ 1 million lbs, and its 16 solar panels generate ~84 kW and cover more than 3 times the US Senate Chamber Since First Launch Nov 20, 1998 –More than 1.8 billion statute miles on the odometer. –~10 round trips to the Sun –~70,000 orbits around the Earth –More than 105 launches to ISS –More than 200 visitors to ISS from 8 different countries –67 Russian vehicles, 36 space shuttles, 2 European, 1 Japanese –More than 150 Spacewalks
u International Space Station As seen from the departing Space Shuttle Atlantis on May 23, 2010 Starboard SARJ Port SARJ Pressurized Modules Solar Panels
u 7 Space Station SARJ (Solar Alpha Rotary Joint) The SARJ is a mechanism and is a structural assembly that transfers electricity from the arrays.
u 8 SARJ Assembly Overview
u SARJ Race Rings and Rollers - Design Details Affecting the Tribology 9 12 rollers (following members) ~ 63 mm diameter, gold-plated 440C steel Race ring (driving member) ~ 3.2 meter diameter, Nitrided 15-5 steel Normal load ~4.4 kN, nominal line contact length 21.5 mm Ring speed 1 revolution per orbit (~ 92 minutes) Initially operated without liquid lubricants Now operating with a grease (perfluorinated polyether type base oil + moly- disulfide)
u Problem Statement and Objective ~ 83 days of operation, Starboard SARJ exhibited increased drive motor current and structural vibrations. EVA showed nitrided Starboard SARJ race ring had extensive damage. To reduce damage effect, astronauts lubricated the race ring with grease that significantly reduced drive motor current and structural vibrations. GRC simulated the race ring damage in dry running condition. GRC investigated the life of the lubricant in a simulated VRR. Objective is to find the # of cycles it takes for the grease to lose its effect.
u Inspection of Starboard SARJ by Astronaut (After 83 days of operation) 11
u Trundle Bearing Assemblies and Race Rings 12 Cross Section View Starboard SARJ Race Ring A B C Trundle Bearing AssemblySARJ
u Alignment of Rollers with Race Ring Overall Race Ring with Roller Enlarged View of Aligned Roller Enlarged View of Misaligned Roller Ft≈0 Fs Ft Fs Ft ≥ 0 Fs
u 14 Why is Roller Misalignment Important ? Thrust Force for 3 lubrication conditions and varying misalignment angle - vacuum ~ 5x10 -6 Torr Axial Force (thrust force)
u 15 Why is Roller Misalignment Important ? ( roller tipping ) Case “A” Axial Force = 0 Camber Axis Case “B” Moderate Axial Force Case “C” Large Axial Force Roller Race Ring Roller Axis of Rotation Roller Race Ring
u 16 Image from NASA/CP (Almon, Wilkinson, Loewenthal), Laboratory Observation of Roller Tipping
u Contact Pressure 17 Contour plot of calculated pressure distribution for SARJ roller and raceway operating with a 4500 N normal load and 800 N axial load
u Contact Pressure in Vacuum Roller Rig 18 Roller contact simulation and contour plot of calculated pressure distribution in GRC VRR operating with a 780 N normal load
u 19 Condition of the Nitrided Roller After the Damage Propagation Test Location 1 Location 2
u Profile Inspections of the Nitrided 15-5 Roller at Circumferential Position #4. 20
u 21 NASA GRC Vacuum Roller Rig
u NASA GRC Vacuum Roller Rig - Schematic 22
u 23 Use of the NASA GRC Vacuum Roller Rig to Simulate Ongoing Tribology Condition of SARJ Certain tribology conditions were matched well material type and manufacturing processes same type of grease able to match Hertz contact pressure misalignment angle of “X” on SARJ matched by ~”2X” angle on VRR Certain tribology conditions were not completely matched Xcontact passing frequency on VRR ~60X greater compared to SARJ Xentraining velocities; VRR at 10 rpm ~ 19 mm/sec ; SARJ ~ 1.9 mm/sec Xspace radiation, atomic oxygen X residual “atmosphere” in VRR (at 5 x Torr) Xspace thermal conditions Xgravity effects ?
u Testing Goals / Approach 24 Keeping in mind the differences of VRR and SARJ, a parametric study was completed to determine relative effects and give qualitative understanding of expected SARJ behavior as grease loses effectiveness Parameters were varied systematically Rotating speed Normal load Misalignment angle Volume of grease applied 19 “lubrication interval tests” were completed (LIT1 – LIT19)
u Normal Force, Thrust Force and Ratio of Ft/Fn for LIT 1-9
u Normal Force, Thrust Force and Ratio of Ft/Fn for LIT 10-19
u 27 Normal, Thrust, Ft/Fn from LIT3
u 28 Normal, Thrust, Fs/Fn from LIT3
u 29 Normal, Thrust, Ft/Fn from LIT18
u 30 Normal, Thrust, Ft/Fn from LIT16-17
u 31 Summary of 19 LIT Test Results
u 32 Conditions of Rollers after LIT9 and LIT19 Nitrided 15-5PH 440C Gold After LIT9 Nitrided 15-5PH 440C Gold After LIT19
u 33 Roughness and Wear After LIT 9 micrometer
u Roughness and Wear After LIT 18
u 35 A Test Plan to Investigate Influence of “Strategic Pauses” (this required actions at odd hours; special thanks to Mr. Richard Manco)
u 36 Normal, Thrust, Ft/Fn from LIT19
u Results of the LIT Tests During LIT 1-9 the average number cycles for lubricant to become ineffective was 29,200 cycles using first pair of rollers. During LIT experiments the average number cycles for lubricant to become ineffective was 60,400 cycles.
u Results of the LIT Tests During the LIT1-9 experiments there were more than 885,000 rotations using the first pair of rollers. During LIT there were more than 850,000 rotations without significant damage to render the rollers functionless. Note: SARJ makes nearly 96,000 rotations per year.
u 39 Summary SARJ was vulnerable to inadequate lubrication Large friction can produce SARJ roller tipping Relative effects of operating parameters were studied by test Loss of lubrication effectiveness was determined from the rise of the axial force to a critical value The most influential parameter was the mass of grease applied “Strategic pauses” were effective to extend lube effectiveness in the VRR and be an effective strategy for SARJ
u Acknowledgements Dr. Alice Smith Professor and Chair of IE at Auburn Dr. Timothy L. Krantz Scientist S&T Division at NASA GRC Dr. Phil Abel Asst. Chief, S&T Division at NASA GRC Dr. Jim Zakrajsek Chief of S&T Division at NASA GRC, Dr. Richard Johnson Dean College of E&T at Bradley University 40
u Back up Slides 42
u 43 Condition of rollers after lab testing to simulate SARJ ring operating with a combination of "tipped" and "not tipped" rollers Ref: NASA Technical Memorandum, to be published, draft manuscript under review
u References “Investigation Of The Vacuum Tribological Property Of Damaged Surfaces In Presence Of Grease,” 2011 STLE Annual Meeting & Exhibition, Control ID: , Category: Grease, Atlanta GA, May 15-19, by Timothy Krantz and Iqbal Shareef. NASA CP (Conference Proceedings, includes three reports related to SARJ) “Roller Testing to Mimic Damage of the ISS SARJ Ring and Durability Test to Simulate Fifteen Years of SARJ Operation Using the Damaged Surface”; NASA TM (under technical review) by Krantz; Elchert; DellaCorte, Dube and Stanford “The ISS SARJ Bearing Failure and Recovery: Technical and Project Management Lessons Learned”; NASA TP (under technical review) by DellaCorte, Krantz, and Dube 44
u 45 Spacewalks to Clean and Lubricate the SARJ Mechanisms were Successful, and Systems are Operating Well Will the SARJ mechanism require additional applications of grease ? Can we expect “warning signs” that the lubrication condition is becoming inadequate?