The agg ressive mass bu dget and re stricted volume for this missio n cau sed the engin eering team to adopt   an integrated , four-ba r linkage app roach to the st and up deploy ment schem e. The existing rover bo dy  structure (Warm Electroni cs Box, or WEB), lander, and the su spension syste m were utili zed to creat e  three  of the  four li nks and two of the fo ur pivot s, reducing the number & volu me of th e parts and active  device s added to lift the ro ver.  

The RL M fun ctione d in two  modes:   • First, it provi ded the m otive force fo r lifting the ro ver in ad dition to fun ctioning a s the final link  necessa ry for the four-ba r system. That  is, it controlled two deg rees of freed om (vertical m otion an d  rotation i n pitch) when lifti ng in concert with the suspension syste m’s linkage. In this lifting phase, the  RLM supports the rover at two p oints: a shaped, Torlon pa d that contact s the flat rove r “bell y”, and a  Torlo n rolle r that is ins erted into a spe cially shap ed socket.  

• Secon d, latch es in the suspen sion system en gaged in two step s as the depl oyment reache d its a pex  and th e RLM  was reverse d, thus alteri ng the kinematics of the fo ur-bar linkage  by maki ng th e bridge  joint between  the front a nd rear rocke rs rigid. This second mode of operation th en requi red the RLM   to cont rol onl y one de gree of freedo m, vertical m otion. The di sengageme nt of rotational (pitch) control  is accomplished th rough passive m eans, by allowi ng the rear rover support to  simply fall a way while   the front rove r sup port roller rotate s in its so cket to permit the no w-rigid rover and ro cker system to   rotate abo ut a pivot on the rear b ogie. 

Actuator Selection  A trade  study early  in the  design process identified a linear a ctuato r as the preferred me ans of motivating   the lifting proc ess. The chief alternative, torque-ac tuated joints , was  found to require very high torque and  corre spondin gly high  mom ents appli ed to beams and plate-type structu ral mem bers. Thi s resulted  in an  unacceptabl e mass an d volume for a rotary actu ator, along with the inefficient  use of structural shapes.  Only small an gular joi nt excursio n wa s required.  

The actu ator assembly wa s sub contracted. A leadscrew type of actuator was assu med (but n ot specifie d)  in requests for proposal. Whe n pure linear motion i s desired fro m a lea dscrew actuato r, it is g enerally  prefe rred tha t its torq ue be reacted internally to  simplify the de sign of n eighborin g component s. Thi s  would requi re extra m ass, volume, an d engi neering effort h owever, so the mech anism’s linka ge was  designed to react the  leadscrew’s torque. We ulti mately sel ected a linear actuator from Ducomm unAmerican El ectro nics (A EI); they offe red an existi ng, qu alified motor-gea rhead with the  addition  of a  leadscrew ou tput module. Du comm un’s actuator m ade use of their elect ronically commutate d (brushle ss)  motor de sign. JPL had al ready u sed anothe r Ducomm un m otor of very ne arly the sam e desi gn in   previous  spacecraft, and it matc hed our drive elec tronics  with its  less-common c enter-t ap winding  config uratio n. 

The le adscrew an d thrust beari ng stage represented a new design. The le adscrew, a t wo-start type with   modified a cme threa d form, was custom made by Nook Indu stries. The completed Rover Lift Actuator  (RLA ) was q ualificatio n tested at the  vendo r on a linear-b earing dynamom eter that was fitted with cables  and wei ghts to permit app lication of loa ds up to 4,0 87 N (9 20 lbf ). The dyna mometer was placed in a  thermal cham ber that allo wed testing ov er the ra nge of -60° C (with  the aid of col d LN 2) up to + 35°C.  

Significant Design Fea tures  When Ducommun proposed a leadscrew-based li near actuator, we re quired th at it be p rovided with a dry,  self-lu bricatin g polymer nu t. The reason  was that th e RLM wa s likely to be expose d to powerful jets of   dust up on M ER’s lan ding and multiple boun ces on t he Ma rtian surface. But with a stroke o f about 244  mm (9.61 in ) in a cro wded spa ce, we coul d find no  viable desi gn for a prote ctive boot around the le ad  screw. We a ssume d that a  conventio nal metal nut with  wet lub rication wo uld attract dan gerous quantities  of Martian  dust to sti ck to  the ex posed leadscrew an d seriously di minish  the RLM’s lifting capacity o r jam  it altogethe r. Instea d of a fl exible bo ot, dense b rush wipers were ad ded to sweep  the screw ah ead of and  201