135 While development testing had been conducted early on to validate the cleaning and bake- out efficacy , the  overall process was not 100% flight -like, and may account for the discrepancy in findings . A detailed  investigation of the hardware from FM2 ACA testing yielded a number of findings . The stringent precision  cleaning operation cleaned the surfaces so well that higher friction was exhibited between sliding surfaces   even during assembly operations . Inspection of components  from the suspect sample tubes  identified that  the bare 440C balls in the ball lock mechanisms had significantly oxidized , resulting in surface changes  contributing to higher friction. In addition, moly -disulfide dry film lubricat ion on ball lock mechanism surfaces  had degraded. Pin-on-disk tribometer testing was conducted using flight -like material combinations, which  confirmed friction increases of 1.5 to 2 times (reaching up to approximately 0.4) as a result of the bake- out.  Per analysis, this increase in friction could be detrimental to proper mechanism functionality, as observed  in test . This finding was very late in the project; therefore, a quick solution had to be identified  and  implemented.  

Ultimately, two corrective actions were implemented. The 350°C  bake- out in air for a minimum of 1 hour  was reduced to a 150°C  bake- out in vacuum f or 24 hours,  which  eliminate d the adverse material affects   previously observed . Concurrently, methods to reduce friction in the ball lock mechanisms were assessed.  As a result, the balls within the ball -lock mechanisms for the sample tubes, covers, and dis pensers were  modified with the addition of  a sputtered moly -disulfide dry film lubrication to help reduce friction. Pin-ondisk tribometer testing of these modifications showed a significant decrease in friction with results less than  0.1 (details of tribo logy findings in work for publication) . Implementing this change actually addressed  a few  concerns identified through design and test, such as the aforementioned L/D concern in the sample tube  ball lock mechanisms, and a concern with worn dry film lubricated surfaces observed in the seal dispensers   after test . Validation of these changes using both flight -like and the flight hardware was performed over  environments without issues . With the change in the bake- out criteria, additional cleaning steps w ere  implemented as required for PP and CC compliance just prior to the bake- out. 

Tight tolerances were used throughout the ACA, on the order of microns in a number of passive mechanism  locations required to ensure position accuracy could be achieved with SHA interactions . Working in microns  meant a lot of manufacturing challenges and discrepancies . Verification of tolerances was critical to ensure  hardware was acceptable to use and required very precise CMM (coordinate measuring machine)  inspection (on the order of less than 1 micron in some cases, and typically less than 3 microns) . When  working with tolerances so tight, verifying assembly -level dimensions may be warranted vs. relying on piece  part inspection data. This became apparent for hermetic seals w hich contain piece parts designed in 5  micron increments as required to meet sealing requirements . It was unknown that hermetic seal  components were expanding during seal assembly . This issue was not identified until hermetic seals failed  to dispense successfully into sample tubes during test . Root cause was identified as fit issues where the  seal was too large to fit within a sample tube. Seal-to-tube pairing takes into account a number of factors,  but ultimately the seal has to fit in the sample tube. Inspection of hermetic seal assemblies yielded larger  diameters for the components that must fit within a tube which had been CMM inspected previously .  Therefore, all hermetic seals were reinspected at the assembled state using optical measurement  equipment in the cleanroom to not compromise hardware cleanliness . With this information, the flight  hermetic seals were assessed against the flight sample tubes to ensure sufficient clearances exist for  dispensing, with ideal pairing arrangements identified for s urface operations.  

Dust accumulation on hardware can become a significant problem during operations . Accommodating  anticipated dust in the ACA during operations resulted in designs either attempting to provide a path for  dust to exit if possible, or the i mplementation of seals to prevent dust intrusion in the first place to protect  sensitive mechanisms (i.e., bearings , screw mechanisms, etc. ). Standalone dirty development testing was  conducted on ACA hardware that will be exposed to significantly dusty env ironments during the mission.  This testing include d the BC exterior mechanisms (i.e., docking assembly and upper door release), which  will not only be exposed to the dusty environment for the duration of the mission, but also susceptible to  debris strikes during the Rover landing event . These mechanisms  exhibited  robustness to excessively dusty  conditions . Dirty testing in the QMDT venue revealed significant dust accumulation on critical sample tube  and glove surfaces . While some dust accumulation on sample tube surfaces was expected and