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The International Space Station Solar Alpha Rotary Joint Anomaly InvestigationThe Solar Alpha Rotary Joint (SARJ) is a single-axis pointing mechanism used to orient the solar power generating arrays relative to the sun for the International Space Station (ISS). Approximately 83 days after its on-orbit installation, one of the two SARJ mechanisms aboard the ISS began to exhibit high drive motor current draw. Increased structural vibrations near the joint were also observed. Subsequent inspections via Extravehicular Activity (EVA) discovered that the nitrided case hardened steel bearing race on the outboard side of the joint had extensive damage to one of its three rolling surfaces. A far-reaching investigation of the anomaly was undertaken. The investigation included metallurgical inspections, coupon tests, traction kinematics tests, detailed bearing measurements, and thermal and structural analyses. The results of the investigation showed that anomaly had most probably been caused by high bearing edge stresses that resulted from inadequate lubrication of the rolling contact. The profile of the roller bearings and the metallurgical properties of the race ring were also found to be significant contributing factors. To mitigate the impact of the damage astronauts cleaned and lubricated the race ring surface with grease. This corrective action led to significantly improved performance of the mechanism both in terms of drive motor current and induced structural vibration.
Document ID
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Harik, Elliot P.
(Boeing Co. Houston, TX, United States)
McFatter, Justin
(Boeing Co. Houston, TX, United States)
Sweeney, Daniel J.
(NASA Johnson Space Center Houston, TX, United States)
Enriquez, Carlos F.
(Boeing Co. Houston, TX, United States)
Taylor, Deneen M.
(NASA Johnson Space Center Houston, TX, United States)
McCann, David S.
(Boeing Co. Houston, TX, United States)
Date Acquired
August 25, 2013
Publication Date
January 1, 2010
Subject Category
Spacecraft Design, Testing And Performance
Report/Patent Number
Meeting Information
Meeting: 40th Aerospace Mechanisms Symposium
Location: Cocoa Beach, FL
Country: United States
Start Date: May 12, 2010
End Date: May 14, 2010
Distribution Limits
Public Use Permitted.
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