Random Vibration Failure Mechanism ofaConrad Bearing usingCrown Bali-Retainer KlausEngel,Regina Kwiatkowska ,andMihaiVladimirescu Abstract Instrument ballbearings utilizing a"snap-over" crownretainer arewellknowninspaceapplications. Although thereissomeanecdotal historyofretainer ejection following extreme vibration orshock,such events arerareandsparsely documented. Acasestudyispresented inwhichsuchabearing failure occurred duringvibration testofarotarycoaxial cableswitchdesigned foruseinatelecommunications satellite payload. Thestudyaddresses thefailuremechanism, itssubsequent analysis, andthepractical resolution. Theoccurrence isnotable because itcannotbepredicted usingthestandard bearing selection method basedonstaticanddynamic load-carrying capacity. Introduction Thepaperdealswithararetypeoffailurespecific tothebearings usingcrowntypeball-retainer. The crownball-retainer iswidely usedinminiature bearings (deepgroove-Conrad, angular-contact or self-aligning) forspaceapplications, because ofitssimplicity andlowdragproperties. Thecapabilities and behaviors ofthesebearings arewellunderstood andselection criteria arebroadly accepted and documented. Despite thisfamiliarity wehave,inaseemingly mundane application, afailurethatdefies prediction. Immediately following, wedescribe theswitchmechanism, itssupported load,thedynamic boundary conditions thatdefinethevibration exposure, andthespecial testregime adopted tovalidate switches for thisenvironment. Subsequent sections focusontheeventsofthetestfailure,evidence obtained, analysis performed andconclusions. Theanalyses explore theproblem intermsofconventional bearing criteria andalsoexamine possible failureexplanations related todynamic modes. Theoutcome provides some practical adviceandopportunities forfurtherexamination bybearing specialists. Application Description TheCOMDEVhighpowerT-Switch isadiscrete electro-mechanical deviceusedtorouteradiofrequency (RF)signals incoaxial cablenetworks. The"T"designator indicates afourportdevice capable of selectively connecting anyporttoanyotherport.Thesixpossible connections areengaged twoatatime, givingthedevicethreedistinct mechanical states. The"highpower" designator identifies ascaled-up variant (approximately twicestandard size)thathaslargeinternal clearances toavoidRFinduced voltage breakdown. Thisversion hasaneightyearspaceheritage withseveral thousand devices operating in orbit,including manyinconfigurations similartothepresent case. TheT-Switch hasamodular design basedonaunique, patented actuation mechanism (USPatent 5,499,006/Mar. 12,1996).Figure1showstheoperating concept andFigure2presents across-section through theswitch.Sixelectrical conductors intheRFmodule, eachfittedwithasmallmagnet, arefreeto reciprocate between opencircuitandclosedcircuitpositions. Theactuator module supports arotating disc withsixmagnets (magnetic cam)oriented totoggle, byattraction orrepulsion according tothedisc orientation, conductors inthesixpossible paths.Therotaryactuator resembles abrushless DCmachine withthree(60°angular separation) phases. Switching isaccomplished bysupplying theselected motor phasewithadiscrete DCcommand pulse.Afterthepulse,havingacquired thecorrect position, theswitch remains magnetically latched initsselected statewithout theapplication ofanyelectrical current. Corporate R&D,COMDEVInternational, Cambridge, Canada. **COMDEVSpaceGroup,Cambridge, Canada. Proceedings ofthe36thAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002. NASA/CP--2002-211506 291