Deep Space Network 70-Meter Antenna Elevation Bearing Failure Investigation

Antennas for the United States Deep Space Network (DSN) are vital to the success of the space program in providing tracking and communication with deep space probes. The three 70-meter antennas, located in California, Spain, and Australia, are the largest and most important link of the DSN network capability. These antennas were originally constructed at 64 meters in diameter, but were subsequently modified to 70-meter diameter to support the Neptune and Uranus encounters by the Voyager spacecraft. An increase in load on the supporting bearings accompanied this modification. It was determined that the bearings possessed the capacity to support this additional load; however, the load was not uniformly distributed. One of the elevation bearings on the antenna in Spain collapsed on December 13, 1989. This bearing functioned on the 70-meter antenna over an 18 year period. Four SKF 231/600 CAK C1 W33 SRB bearings support the DSN antenna assemblies which rotate very slowly over 160° once or twice daily. Bearing rolling contact components were manufactured from AISI 52100 steel. Rolling elements were produced with axially through-bore holes to facilitate the heat treat process. Failure investigation established that fatigue cracks initiated at the surfaces of center holes, progressed to fracture which led to lockup and culminated in overload of associated bearing components. Due to advancements in material development since the 1970s, solid rollers may be satisfactorily produced without center holes which can introduce sources for stress risers. Antenna operation was promptly restored by replacing the damaged bearing with a spare. Load equalization and nondestructive inspection of the remaining bearings were conducted. Fracture mechanics analysis was performed to estimate the remaining life of the bearings. Due to the critical nature of the DSN antennas, a recommendation was made to replace existing bearings with current state of the art solid roller bearings.