Several me chani sms were con sidered for the hing es in the syste m inclu ding twist cap sules and slip rings.  In all other ca ses considered, either fri ction or spring rate were fo und to be difficult to mitigate early in the   design proce ss. Ideal Rol amite joints we re found to m eet the requirement s of the system while  minimizing   complexity. Significa nt electri cal po wer and data harn essing co uld be passed acro ss the joint while   maintaini ng the de sired m inimal sprin g rate an d fric tion pe rform ance by routi ng electri cal co nductors in  like fashio n to the syn chronizi ng tap es. Also, the inco rporation of additional fu nction ality ap peared to be   straightforwa rd given the a vailable volu me within  and at either en d of the Rola mite cylinde rs. 

Design 

The current p oint de sign i s an isol ation system fo r a 25-kW sol ar array. Mass p roperties of the sub system  to be isolated  have been assume d for a thin-film sola r array with an averag e areal mass den sity of 0.25   kg/m2. Natu ral frequ ency estimate s for the array we re ba sed on previo us work as referenced in [1] for a   100-kW array  and scaled acco rdingly. Perform ance requirements for the isolation system were impo sed  based on typi cal spa cefligh t requireme nts wh erever a pplicable. Assum ed re quirement s we re impo sed o r  derive d if in  the course of  design, no requi rements had yet been established.  Assume d requirement s  were in many  cases imp osed in ord er to bracket the achievable p erforman ce of the isolation  system in to   establi sh the scalability of the isol ation system. 

Isolation system req uirements relev ant to joint performan ce in clude;  1. Pass p ower harne ssing requi red for a 25-kW sol ar array ope rating at 300 V.  2. Pass d ata harne ssing as typically re quired for a sol ar array.  3. Impart no more tha n T/n parasiti c torque into t he isolatio n syste m whe re T is the equivale nt worstcase ine rtial force of the sy stem tran smitted to the host and n is the numb er of joi nts in the syst em.  4. Position  the solar array and i solation system to  a comman ded location  and orientation. Ea ch joint  must be moto rized an d abl e to be driven .  5. Transmit force s resulting from grav ity gradient  and sola r radi ation pre ssure to the host (to be  reacted by th e host attitud e cont rol sy stem) while still  isolating subsystem vibration.  6. Self-rigidi ze (lo ck) for safe mode o peration. Safe mode lo cking  must occu r within 30 second s and   subsequently requi re no power to re main in eithe r safe mode or norm al operational mod e. Safe   mode lo ads resultin g from  a 0.003 -g acceleration in any orie ntation mu st be reacte d thro ugh th e  isolatio n syst em.  7. Package compa ctly for laun ch an d deploy once in orbit. 

Three distin ct modes of op eratio n beco me appa rent; pa ssive i solation, drive and safe mod e. In order to  accom plish a ll requi red fu nction ality while still main taining de sired perfo rmance, additional mechani sm  had to b e package d withi n the Rolami te. Specificall y, a method to drive the j oint as well as a l ocking  mechani sm was requi red.  

The de sign o f the Rolamite prog ressed  by investigat ing ea ch fun ctional mo de requi red of the isol ation   system and subsequ ent joi nt requirements. The m ajority of the o perational life  of the isolati on sy stem i s  expecte d to be in passive i solatio n and t herefore was investigate d first. Also, addi ng drive an d safe mod e  function ality wa s dete rmined to be a straightforwa rd design progression.  

Passiv e Isolation Mode 

Passive isola tion mode must exhibit zero sp ring rate and near ze ro friction i n the intende d degre e of  freed om and be stiff in the remai ning five deg rees of free dom. Maxi mum pa rasitic torq ue is on  the orde r of  1E-5 Nm. Ma ximum sp ring rate is o n the ord er of 5 E-6 Nm/rad. A Rola mite wit h two cylin ders and two   oppo sing serpentine tap es requires an  external fo rce to balance  the resulta nt coupl e pro duced by the  displaced lin es of action of each t ape (the tape s can not be routed i n the same plane o r pass through th e  same point).  In order to  achieve a balan ced syst em, at least three tapes are requi red; two tapes   straddlin g a center tape ro uted in oppo site se rpentine fashio n. Since el ectrical harne ssing would req uire  signifi cant cyl inder length, two set s of synch ronizing tape pairs we re loca ted at either en d of the joint to   enforce syn chronization. The lengt h of the Rolamit e could then  be scaled to accommo date harne ss  requirements betwe en the synchroni zing tapes.   165