Mars Exploration Rover Potentiometer Problems, Failures and Lessons Learned  Mark Balzer*  Abstract  During qualification testing of three types of non-wire-wound precision potentiometers for the Mars  Exploration Rover, a variety of problems and failures were encountered. This paper will describe some of  the more interesting problems, detail their investigations and present their final solutions. The failures  were found to be caused by design errors, manufacturing errors, improper handling, test errors, and  carelessness. A trend of decreasing total resistance was noted, and a resistance histogram was used to  identify an outlier. A gang fixture is described for simultaneously testing multiple pots, and real time X-ray  imaging was used extensively to assist in the failure analyses. Lessons learned are provided.  Introduction  On the Mars Exploration Rover (MER), many angular positions required remote monitoring. An incomplete  list includes the angular positions of four Steering Actuators (WSA), the azimuth, elevation, elbow, wrist  and turret joints on the Instrument Deployment Device (IDD), and the azimuth and elevation axes of the  High Gain Antenna Gimbal (HGAG). On the MER Lander, knowledge of the angular position of the three  Lander Petals was also required. The MER avionics monitored these angular positions by reading the  digital, incremental, rotary, magnetic encoder on each of the fourteen electric motor shaft inputs to these  geared mechanisms. In case of encoder failure, or if avionics power and thus stored angular position data  was lost, all fourteen angular positions could be determined and tracked via backup precision analog  potentiometers (pots) configured to measure the output angles of the WSA, the IDD joints, the HGAG  axes and the Lander Petals.  Pots were also used in the MER suspension. The left and right rocker-bogie pivots each had one pot to  measure the relative angle between each bogie and its rocker arm, while a third pot in the MER differential  measured the relative angle between the left and right rocker arms. In conjunction with a three-axis  accelerometer providing the Rover's orientation with respect to a gravity vector, relative angle  measurements from these pots allowed the Rover's complete kinematic state to be determined. Though  the suspension pots were the sole source for this data, it was deemed non-critical for a nominal mission.  Pots are miniature electromechanical mechanisms and as such must pass a rigorous series of tests to be  considered flightworthy. This paper will describe some of the more interesting issues that arose during  qualification testing of the MER pots, detail their investigations and present their final solutions. Lessons  learned along the way will be pointed out.  Description of Pots  The Lander Petal, Bogie Pivot and Differential pots shared a common design based on MIL-PRF-39023;  single-turn rotary pots in a metal cup with a bearing-mounted input shaft. The HGAG and WSA pots were  each custom, single-turn rotary units designed to be mounted within their respective actuators, and thus  had no bearings of their own.  All pots used on MER were of the precision rotary nonwire-wound (conductive plastic) type. Since the pots  described in this paper (Figure 1) were provided by a single vendor, they shared basic design features  such as:  1) An aluminum alloy "cup" which served as the frame of the pot.  * Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA  Proceedings of the 3dh Aerospace Mechanisms Symposium, Langley Research Center, May 17- 19,2006  303