up during landing could significantly increase the drag. Due to the configuration of the mechanism, if the  follower bearing were to drag and twist the bar, addi tional torsion would be imparted to the bearing  potentially causing even more drag and a lockup situation could be created.   

To exclude debris from  the follower bearing, a  careful seal design  was implemented.  Initially labryinth-type  convolutions were  envisioned to exclude  debris and impart the  minimum amount of  drag to the motor.  Following the critical  design review this  design was modified to  focus more on debris  exclusion and less on  motor drag. The seals  are risky because of  the –70 °C operating  temperatures and the  large amount of play in  the bearing. A plastic seal with enough contact pressu re to seal the bearing in one position may provide  too much contact force when very cold and in a differ ent relative position of inner to outer races. The  solution was to use a thin metal shield with a relati vely long cantilever. The stiffness of the metal changes  much less with temperature and the long cantilever pr ovided adequate deflection. On  the inner side of the  bearing a more convoluted labyrinth seal was selected which added no additional drag.  and of  Follow er end:  Single  row  radia l follower  bearin g avoids  over-constraint  fers  minimal drag  Driven end:  Duplex bearing s in  actuator carry  loads  at driv en end Perman ently  installed torque  tube spans end to end  Driven end  “Diaphra gm”  avoids o verconstraint of  bearin g  Both ends:  Combination  launch lock - hard stop  Figure 13.  Cam era Bar Driv e Mechanism  

Mini- TES Driv e 

The fifth mechanism is the Mini-TES Mirror Rotation Dr ive. The Mini-TES is an Infrared spectrometer that  is located below the Rover deck. The PMA serves as a periscope to enable the Mini-TES to look around  from a higher vantage point. The Mini-TES mechanism rotates a mirror so that the instrument can look up  and down and provides an enclosed calibration target. The Azimuth drive described earlier provides the  left/right motion. 

Basic Requirements:   Support the mirror and provide an elevation axis of rotation  Move the mirror at 5.7 degrees/sec with a pointing error of 1 mrad  Provide an enclosed calibration target of known temperature  Incorporate a rotating baffle that will exclude light and limit debris when closed 

There are two 45 degree angled mirrors inside the head of  the PMA.  One mirror is fixed and the MiniTES rotation drive controls the other. Light enter s the PMA through an opening in the top “T” section,  reflects off the moveable mirror and travels to the fixed mirror and then travels down the mast to the  instrument as shown in Figure 14. A custom DC mo tor with custom hybrid planetary – harmonic gearhead is located in the top of the PMA and drives t he first angled mirror about the horizontal or elevation  axis. This elevation axis together wi th the mast azimuth drive provides  the capability to point the Mini-TES  field of view.  

To limit the complexity and weight of the system t he mirror is mounted directly on the gear-motor with no  additional support. The mirror is cantilevered off the motor shaft and does not include a launch lock  element or brake mechanism. There was concern that  the launch vibration environment might cause the  cantilevered mirror to rotate even though it is rotationally balanced. Deflection of the cantilevered mass  under load effectively unbalances the system. In a rich  vibration environment this configuration could  272