Laboratory measurements indicatedthatprovidinga2.5mAreversecurrent,whichallowsthe"stuck" rotortorelease,couldessentiallydegaussalappedunit.Providingtoomuchreversecurrentresultedin re-magnetizing theHipercointhereversedirectionresulting,again,inaresidualmagnetictorque. KeyTestResults Thefollowing setsofdatawillbesummarized: theabilityofresidual magnetism toexhibittorques in excess oftherestoring torqueofthespring,theabilitytoreducetheresidual magnetism toaminimum by applying asmallcurrent ofthereverse polarity totheactuator, andtheabilitytomeasure thechange in residual magnetism duetothisreverse polarity degauss current bymeasuring backemf. SpareUnitRelease Current (PreLapping) Therelease current isthevalueofcurrent atwhichtheshutteropensduetothespring.Thetorquedueto frictionwasfoundtobenegligible duetothedesignoftheshutter mechanism. Measurements ofrelease current weremadeduringtheassembly process. Thedesired release current was1to1.5mA.Afterthe failureoccurred, itwasdetermined thattheassembly process couldhaveamajorimpactontherelease current. Machining tolerances werealsoshowntohaveasignificant effectonresidual torques. Better alignment andtabcontact between therotorandstatorlowers therelease current and,therefore, decreases thetorquemarginavailable toopentheshutter. Initialtesting oftherelease currents onthespareunits showed lowerbutacceptable release current values in somecases. Noneofthespareshutter assemblies or actuator components exhibited enough residual magnetism toovercome therestoring torqueofthespring. However, a spareunitwasthendisassembled andreassembled. Itwas notedthattheassembly process couldimpacttherelease current value.Afteroneparticular reassembly process, the assembly didfailtoopenwithzerocurrent onrare occasions. Figure11showsrelease currents forSideAand Bforthespareunit.Itshows theSideAactuator had intimate contact andbetteralignment between therotorand statorthanSideB.Themore"normal" release currents on SideBindicate lesstabcontact andpoorer alignment between therotorandstatorintheclosedposition. Thesemeasurements weremadeusingapowersupplyat roomtemperature. Approximately 60mAwasapplied tothe actuator causing theshutter toclose.Thecurrent wasthen decreased untiltheshutteropened. Thevalueoftherelease current wasthenrecorded. Itisimportant tonotethatonthe rareoccasions thatamechanism stuck,italways opened whenaslightreverse polarity current wasapplied. These reverse polarity currents reduced theresidual magnetism torquetoalevelbelowtherestoring torqueofthespring thusallowing themechanism toopen. Figure11.Spareshutter release c..rrp.nt.q Actuator torquecharacteristics andoptimal degauss currents (Boundinq theProblem) Afterthesensitivity tothenatureofthecontact between thetaboftherotortothestatorwasfully appreciated, wedecided toimprove thiscontact bylapping. Lapping caused thespareunittofailtoopen atzerocurrent consistently. However, themechanism stillreliably opened uponapplication ofaslight reverse polarity current. Weisolated theactuator components inatestset-uptosimplify measurement of actuator torque. Measurements oftorquegenerated verses applied current werethenmadeandare showninFigure12.Thesemeasurements wereperformed bothpreandpostlapping. Priortolapping of theactuator components, intimacy ofcontact between therotorandstatorwasnotgoodenough to generate significant residual magnetism torques. Afterlapping, measurements showed significant residual magnetism torques. Values oftwotothreetimestherestoring torque ofthespringwere NASA/C Pn2002-211506 21