423 Conclusions and Lessons Learned  

Detent Design   Although the detent brake worked well and the add- on module that was designed proved capable of passing  all qualification tests, this solution adds  mass and complexity. In parallel, work was carried out by maxon  to make rotors with segmented magnets (rather than a one- piece ring magnet) and then shape the magnetic  field from those magnets to create the necessary detent. Making magnetic field simulations that correctly  predicted the obtained detent was difficult, which resulted in initial prototypes deliveri ng insufficient torque.  Follow -up prototypes achieved the targeted 10 mNm. The greatest difficulty encountered was fixing the  individual magnets to the rotor so that they were not susceptible to breaking under shock impacts.  Eventually it was decided that this presented too much risk, especially to the schedule if several attempts  were needed to find a workable solution. Despite not being chosen for the flight design, with further  development this is likely to be a more reliable (because of fewer parts) and compact solution that should  be investigated further.      Overheat ing Concern   The overheating concern has led to significant effort s in both analysis and implementation to reduce the  motor wire temperature below the allowable limits. For past missions, prot ecting the motors from  overheating entailed installing a PRT on  the case and operat ing under the assumption that the housing  temperature is well coupled to the wire temperature. Due to the outer rotating design  of the Mars 2020  motors , there is no external  location that  is thermally coupled.  However, a potential solution for both ground  testing and thermal model validation would be to implement a thermocouple (TC) directly into the windings  at the time of assembly and provide a path for those thermocouples to be moni tored, either through traces  in the board or hol es in the board that can be routed to the channel for the lead wires. These ther mocouples  can be set to a GSE thermal alarm or act like a switch. The TCs can monitor concurrently while running the  thermal model in multiple atmospheric environments to better ground the model in demonstrated  performance. An additional improvement to the design could be to thermally couple the wires to the stator  lamination stack instead of suspended between t wo PEEK en d caps.  

Teamwork between a Government -Funded Science Institut ion and a Commercial Company   A close collaboration between maxon and JPL was essential in developing the flight units, as it required a  combination of maxon’s decades of experience with industrial motor and gearbox design and JPL’s  decades of institutional experience in spacecraft design.  

For such a collaboration to work, it is necessary for both sides to understand each other’s motivation s and  methodologies . Commercial companies (especi ally those with limited previous space experience) need to  understand that organizations like JPL can (and do) place significant resources into issues that may be of   no importance  in an industrial setting, which is a result of  decades of hard learnt lessons where a single  small failure can terminate a mission. The space environment is very unforgiving of design or manufacturing  errors , which may never be noticed in a standard  Earth-based application. The education of contractor staff  on this history is a cr itical part of gaining acceptance for the space science mission method of working.  

In turn,  government -funded institutions need to understand how industrial manufacturing companies , such  as maxon,  usually have the goal of using their limited engineering resources as efficiently as possible to  keep the production lines filled with products that receive repeat orders. Thus, one-off high engineering  resource developments are often viewed as a disturbance to the series production goals of the company ;  however , this can be partially mitigated  by presenting the work as subsidized technology development and  being as open as possible in helping the commercial company obtain a marketing effect by publicizing the  work.  

Final Thoughts   During the three- year collaboration, significant resources were required from both organizations to resolve  the problems encountered and complexity involved in developing the Mars 2020 actuators . Even when the  basis of the design was a commercial product, the issues  encountered highlight  the importance of allowing