Iqbal Shareef, Ph.D., CMfgE , P.E. Bradley University, Peoria, Illinois (309) 677-2981

1. International Space Station SARJ Race Ring Damage Simulation and Durability TestFor Life Extension Presented at NASAAcademy of Aerospace Quality Workshop Cape Canaveral, Florida March 22, 2012 Iqbal Shareef, Ph.D., CMfgE, P.E. Bradley University, Peoria, Illinois (309) 677-2981 Shareef@bradley.edu

2. 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

3. 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 2011with operations to continue until at least 2015, and likely 2020+ • ISS is the largest artificial satellite that has ever orbited the Earth, it can be seen with a naked eye

5. ISS is much longer than the length of Boeing 777. It is larger than 5BR house, weigh ~ 1 million lbs, and its16 solar panelsgenerate ~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

6. Port SARJ Starboard SARJ Solar Panels Pressurized Modules International Space StationAs seen from the departing SpaceShuttleAtlantis on May 23, 2010

7. Space Station SARJ (Solar Alpha Rotary Joint) The SARJ is a mechanism and is a structural assembly that transfers electricity from the arrays.

8. SARJ Assembly Overview

9. SARJ Race Rings and Rollers - Design Details Affecting the Tribology • 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)

10. 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.

11. Inspection of Starboard SARJ by Astronaut(After 83 days of operation)

12. Trundle Bearing Assemblies and Race Rings A B Cross Section View Trundle Bearing Assembly SARJ C Starboard SARJ Race Ring

13. Alignment of Rollers with Race Ring Fs Fs Fs Ft Ft≈0 Ft ≥ 0 Enlarged View of Misaligned Roller Enlarged View of Aligned Roller Overall Race Ring with Roller

14. Why is Roller Misalignment Important ? Axial Force (thrust force) Thrust Force for 3 lubrication conditions and varying misalignment angle - vacuum ~ 5x10-6Torr

15. Why is Roller Misalignment Important ? ( roller tipping ) Roller Axis of Rotation Camber Axis Roller Roller Roller Race Ring Race Ring Race Ring Case “A” Axial Force= 0 Case “C” Large Axial Force Case “B” Moderate Axial Force

16. Laboratory Observation of Roller Tipping Image from NASA/CP-2010-216272 (Almon, Wilkinson, Loewenthal),

17. Contact Pressure Contour plot of calculated pressure distribution for SARJ roller and raceway operating with a 4500 N normal load and 800 N axial load

18. Contact Pressure in Vacuum Roller Rig Roller contact simulation and contour plot of calculated pressure distribution in GRC VRR operating with a 780 N normal load

19. Condition of the Nitrided Roller • After the Damage Propagation Test Location 1 Location 2

20. Profile Inspections of the Nitrided 15-5 Roller at Circumferential Position #4.

21. NASA GRC Vacuum Roller Rig

22. NASA GRC Vacuum Roller Rig - Schematic

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 • contact passing frequency on VRR ~60X greater compared to SARJ • entraining velocities; VRR at 10 rpm ~ 19 mm/sec ; SARJ ~ 1.9 mm/sec • space radiation, atomic oxygen • residual “atmosphere” in VRR (at 5 x 10-6Torr) • space thermal conditions • gravity effects ?

24. Testing Goals / Approach • 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)

25. Normal Force, Thrust Force and Ratio of Ft/Fn for LIT 1-9

26. Normal Force, Thrust Force and Ratio of Ft/Fn for LIT 10-19

27. Normal, Thrust, Ft/Fn from LIT3

28. Normal, Thrust, Fs/Fn from LIT3

29. Normal, Thrust, Ft/Fn from LIT18

30. Normal, Thrust, Ft/Fn from LIT16-17

31. Summary of 19 LIT Test Results

32. Conditions of Rollers after LIT9 and LIT19 Nitrided 15-5PH 440C Gold After LIT9 Nitrided 15-5PH 440C Gold After LIT19

33. Roughness and Wear After LIT 9 micrometer micrometer

34. Roughness and Wear After LIT 18

35. A Test Plan to Investigate Influence of “Strategic Pauses”(this required actions at odd hours; special thanks to Mr. Richard Manco)

36. Normal, Thrust, Ft/Fn from LIT19

37. 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 10-18 experiments the average number cycles for lubricant to become ineffective was 60,400 cycles.

38. 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 10-19 there were more than 850,000 rotations without significant damage to render the rollers functionless. Note: SARJ makes nearly 96,000 rotations per year.

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

40. 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

41. Thanks For Your Attention

42. Back up Slides

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

44. References “Investigation Of The Vacuum Tribological Property Of Damaged Surfaces In Presence Of Grease,” 2011 STLE Annual Meeting & Exhibition, Control ID: 980140, Category: Grease, Atlanta GA, May 15-19, 2011. by Timothy Krantz and Iqbal Shareef. NASA CP-2010-216272 (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

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?

46. Dr. Iqbal Shareef and Michael Freeman