Lessons Learned andConclusions Fortheselection ofamotorredundancy concept, ananalysis ofthepossible failuremodesonaframeless motor(FMECA) haspointed outguidelines tobefollowed: Theuseofpermanent magnets shouldbeprohibited if(l)themagnet maximum acceptable temperature isnotsecured bydesignmargins, and(2)ifthebraking torquecreated byafailedshort-circuited main winding cannotbemanaged bytheredundant path. Common thermal pathsbetween mainandredundant motorpartsshouldbeprohibited. Nevertheless, withthehighperformance required forspaceapplications (i.e.,mass,efficiency), itappears thatmotortechnologies prohibiting theuseofpermanent magnets canrarelybeconsidered ifweexcept "niche"applications wherereduced performance isacceptable. Asaconsequence, thedesignofredundant motorsmustintegrate theideaofincorporating magnets andnottrytoavoidthispractical reality. Fiveredundant designoptions areidentified andthefollowing comments canbemade: Thefullmechanical redundancy concept Thisisthebestsolution iftheriskofhavingasinglepoint failurebetween themainandredundant pathsisacriticaldesignconcern, especially intermsof potential thermal stresses. Nevertheless, this"awkward" designsuffersfromitsverylimited performances andleadstoasignificantly higherrecurring motormanufacturing coststobebalanced withtheotheroverallprojectcosts. Th_Dartialmechanical redundancy concept Thisisacompromised designbetween theprevious reliable options andtheotherefficient options. Thisoptionislessefficient andlessreliable andthus marginally considered ; Thetwo-sector electrical redundancy concept Asfortheotherelectrical redundancy concepts, therisk ofhavingathermal singlepointfailureneedstobecarefully considered inthiscase.Onthispointof view,itisthemostoptimal designamongtheelectrically redundant options. Asadrawback, for saturated motorsthatarehighlymagnetically loaded(typically stepper motors), thedesignsuffersfrom alimitedtorque/powercapability. Ingeneral, thisoptionispreferable withthebrushless DCmotor technology. Theshared-slots electrical redundancy concept Thisoptioncanbeconsidered asanalternative tothe previous oneforapplications requiring animproved torquecapability, unreachable duetoexcessive magnetic saturation andformotordesigns thatcannotconsider theprevious optionformagnetic design reasons (whereby theslotscannotbesharedinanyadequate way). _'Thetwowires-in-parallel electrical redundancy concept Thisoptioncouldbeconsidered asan alternative tothelastifthemotor's designcan'treflectthetwoprevious options formagnetic reasons again(slotscannotbesharedinanyadequate way). Finally, statistics wereprovided regarding thetypeofredundancy concept selected forvarious space programs (>100mechanisms), whichseemtodemonstrate thathalfofthemechanisms haveimplemented non-redundant motors. Theotherhalfconsider mostlyelectrically-redundant options, thesharebetween the three"electric options" beingratherbalanced withaslightpreference forthe"two-sectors" options. Mechanical redundancy options seemnottobewidelyconsidered. References 1.Favre,Ericetal."European electricspaceratedmotorshandbook", Proceedings ofthe8_European Symposium onSpaceMechanisms andTfibology, (Sept.1999),ISBN92-9092-752-6, pp.159-165. 2.ETELAerospace Inc."Stepper motorperformance datasheet-type#AERSM01", 4909Nautilus Court North,Boulder, CO80301,USA. 3.ETELAerospace Inc."Listofmainspacecontracts", Boulder, CO80301,USA. 186