Development ofaFineSteering MirrorAssembly RubenNalbandian*and JeffWilliams* Abstract Inter-satellite andterrestrial lasercommunications depend ontheabilitytoreliably directalaserbeam, withextremely highpointing accuracy, lowpower, andsufficient bandwidth toallowrejection of environmental disturbances. Toaddress thesedemanding requirements, MoogChatsworth Operations hasdeveloped aminiature FineSteering Mechanism (FSM),usedforspacelasercommunications, thatismoreefficient thanvoicecoilactuated devices andiscapable ofmoretravelthanpiezoelectric actuated devices. Thedesignchallenge wastodevelop alightweight, compact, highbandwidth, lowpower,thermally stable two-axis FineSteering mechanism, capable of62.4degree angular range. Thispaperoutlines thedesign, development, andtesting ofthetwo-axis FineSteering Mechanism assembly, withparticular emphasis placedonthemagnetic designandthegimbagflexure development andtesting. Introduction Inorderforthenewlyemerging lasercommunications tobefeasible forbothinter-satellite andlandbasedtelecommunications, aFineSteering Mirror-tilting deviceisneeded todirectthelaserbeamfrom thetransmitting sourcetothereceiving target.Pointing abeamatatargetmirrorseveral kilometers away, therefore, requires apositional accuracy ontheorderofone(1)microradian. Atthesametime,thedevice mustbecapable ofmoving themirrorasmuchas62.6degrees toprovide adequate pointing coverage of thesteered beam.Thedevicealsomusthavesufficient control bandwidth torejectdisturbances caused byenvironmental factors andmachinery vibrations. Forsmallsignaldisturbances ofabout0.01degrees, thedevicebandwidth mustbeabout200Hz.Obviously largerdisturbances mustberejected atlower bandwidths. Twotechnologies areconsidered foractuation offaststeering mirrors: voice-coils andpiezoelectric actuators. Voice-coils offerlargerstrokeforrelatively lowpower;however, theyarelimitedinbandwidth andstiffness. Piezoelectric actuators ontheotherhandofferhighbandwidth andstiffness, butarelimited inposition outputrange.TheFineSteering Mechanism presented inthispapercombine thebenefits of bothtechnologies, resulting inarelatively highbandwidth, lowpower, relatively largedisplacement mechanism ofcompact dimensions. Principle ofOperation Theprinciple ofoperation ofthismechanism iselectromagnetic. Anarrayoffour(4)identical electromagnetic circuits ispositioned with90degrees angular separation fromeachotheraround the periphery ofacircle.Theelectromagnetic design differsfromthatofconventional voice-coil actuated systems inthatfourpermanent magnets aremounted tothemoving mirrorplatform, whilethe corresponding coilsandthecoilcores,whichconstitute themoremassive parts,residewithinafixed housing. Duetothemagnetic pullforceofthepermanent magnets ontheferromagnetic coilcores,the mirrorplatform iscontinuously underapullforce.Amagnetic returnstructure surrounding thecoils creates aclosed magnetic circuit.Themagnetic fluxinthecircuitistheresultant ofthatduetothe permanent magnet andthatduetocurrent. Bychanging thecurrent andpolarity inonecoil,amagnetic MoogInc.,Chatsworth Operations, Chatsworth, CA Proceedings ofthe36thAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/C P--2002-211506 207