The syn chronizing tape s enforce joint kinematics a nd re sult in one de gree of freedom a s well a s one  relatively low stiffness di rection. As the synchroni zing tapes pa ss from on e cyli nder to the next throug h  the line of rolling co ntact b etwee n the cylinders, the mechani cal advantage of the tape s decreases to ze ro  to rea ct a force throug h the centers of the Rol amite cylinde rs and actin g away from the li ne of rolli ng  conta ct (a te nsile f orce). This l ow stiffness di rection is addressed via the l ocking  and safe m ode  mechani sms discu ssed lat er. Synch ronizing tap es on the engin eering unit ha ve been fab ricated u sing  Elgiloy, a highly-processe d cold rolled nick el ste el with very high tensil e mod ulus. 

Since th e isol ation sy stem must b e repe atedly cycl ed, fatigue mu st also be co nsidered in man y aspe cts of  the de sign. Electri cal harnessing must be pa ssed across th e joint in simil ar fashion a s the synch ronizing  tapes. In ord er to maintai n zero sp ring rate and nea r zero friction , the electrica l harne ssing must rem ain  elasti c to the greatest extent possi ble throu ghout a range of strain rate s and te mperatures. Furthe r, each   elect rical co nducto r mu st be fully insul ated to prev ent arcing to  adjacent ci rcuits o r grou nding to the  structure. A compo site mo dulus of ela sticity sufficie nt to pre clude fatigue failu re and mi nimize  visco elastic  losse s became a si gnificant de sign challen ge. Th e cu rrent en ginee ring joint hard ware unde r test i s  comprised of six Kapton -laminated flex circuit s using acrylic a dhesive. Cree p and viscoel astic loss of the   acrylic at upper tempe rature extrem es has been i dentified as a con cern and demo nstrated in the  hardware. L ow temp eratu re emb rittleme nt of cycle d polymers is also a concern,  but ca n be mitigated via  active or p assive the rmal manag ement. Thermal function al testing is underway on th e engin eering  hardware to establi sh a d ata point on perfo rmance of  the harne ssing. Co nductor material must have a n  infinite fatigue life while transmitting electri cal po wer at low loss.  Harn ess ten sioning is onl y intended to   ensure that the harne ss dynamics are tightly couple d to the joint and do not indu ce additio nal vibration   mode s of th e isol ation system. Ha rness ten sioning and stiffne ss are th erefore m uch lo wer than the  synchroni zing tapes and do  not react extern al load s across the join t. Heritage co nductor mate rial su ch as  copper is not suitabl e for re peated cyclin g even at very  low load s. A Beryllium coppe r alloy was foun d that   adeq uately met infinite fatigue life and l ow resistivity requi reme nts. Additional insulating techniqu es are  currently und er investig ation to minimize cree p an d visco elastic loss. In order to minim ize fun ctional   changes due to thermal expan sion at temperature extreme s, synchro nizing tap es as well as harne ss flex  circuit tape s are terminate d on the Rol amite cyli nders via low sp ring rate de coupling sp rings. 

Drive Mode 

The drive m echanism is capabl e of tra nsmitting torq ues b etween the host an d sub system to rea ct small  distu rbance force s as well  as those re quired for su bsyste m rep ositionin g. Solar ra diation p ressure a nd  gravity gradie nt are sou rces of disturb ance force s considered here and are two orde rs of mag nitude lowe r  than that req uired for sub system re positioning. A pa ssive du al dri ve mecha nism has bee n desi gned that  requires only one a ctuato r.  

A drive drum is locate d on one end of one Rolamite cylinder with tape s routed i n belt drive fa shion to th e  other Rolamit e half (see Fi gure 1). A ste pper motor i s coupl ed to th e drive d rum though a ve ry low sprin g  rate spiral spring. The step per motor win ds the sprin g to achi eve th e desired to rque, and  the sprin g allows  the joint to oscillate in vibra tion isolatio n mode wit hout significant ch ange s in to rque thereby re acting small ,  nearly con stant distu rbance force s. A local control  loop is de signed to null  comma nded torque an d  measured to rque at an update rate multiple time s slower than the lowe st natural fre quency of th e  subsystem (for averagin g). This aspe ct of the vibratio n isolatio n system di ffers from ac tive c ontrol in that   the update rate band width does not scal e clo sely wi th subsystem freque ncy an d must only a ccomm odate   for relative d rift between th e sub system and ho st.  

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