400 the gear wheels as observed after vibration testing (see Figure 19 ) is still not underst ood and shall be  further investigated (see last chapter "Outlook").  2. When we initially saw those areas of lubrication loss on the gear wheels (see Figure 11) we were  sure that this was the end of the story. Thanks to  ESTL, who had great confidence in their sputtering  process and was confiden t according to measur ements performed to still have sufficient MoS 2 on the  teeth to survive the life test, we decided to c ontinue. The life test was a success. Those observed  areas increased but the residual MoS 2 layer survived. It is the intent ion to continue the life test on the  pre-QM (see last chapter "Outlook")  3. Witness samples for process control for any ki nd of surface layer generation should be of the same  material and should have been exposed to the same processes and sequence of processes as the  units to be treated. In some cases where geometry  has also an impact on the surface treatment, the  witness sample should have also a similar geometry.    4. Keeping MoS 2 surfaces either in a dry environment or  ideally in vacuum or in constant N 2 atmosphere  is state of the art knowledge to prevent moisture absorption of the MoS 2. Permanent purging of  mechanism elements like bearings is one of the me thods applied if the outer environment is not  adequate. In the vicinity of optical surfaces at temperatures below those of the mechanism (cold  traps), purging or even open venting hole s might allow particles from the MoS 2 to escape from the  mechanism and to pollute the optical surfaces. As  seen from the life test, particle generation cannot  be avoided. Consequently the purging process, purg ing direction and venting hole definition needs to  be properly planned at the beginning of the project to prevent pollution effects.  

Outlook   In a very short time frame of 7 months a dry-lubr icated actuator for ambient and cryo application was  developed with a complete new combination of materials. Though the development was a success, some questions are still open and shall be further investigated.   As outlined in the lessons learned, the material tr eatment process does have an important impact on the  sputtering process success. The observed partial lo ss of lubricant on the gear wheels is still not  understood. From the pin-on-disc test results, we do have clear indications that the electro-polishing is of negative influence but the physical or chemical nature of such an effect is still not completely understood.  Other effects like the order of hardening and polishing might be also of influence. These effects need to be assessed also for different standard gear box or b earing materials. Astrium wants to initiate a program  with ESA, ESTL and further technical surface coating experts to fu rther investigate this issue.   Though we did initially lose some lubricant on the gear surfaces, they survived the life test and it would be  of interest to determine the final life of such surfaces in the gear box. So Astrium will continue the life test  on the pre-qualification models (both the MoS 2 and the lead lubricated ones). Life test stop criteria will be  a certain current threshold (still TBD) which would be equivalent to a certain increase of the friction torque  of the unit (e.g., 50%). A dedicated inspection program of the units will follow the life test and results shall be reported at the next ESMATS to be held at Astriu m premises in Friedrichshafen in September 2011. 

Acknowledgment 

Astrium would like to thank their partners in this development program for their utmost efforts they  provided in terms of technical quality, adherence to the very tight schedule and their expertise support at  any phase of this project.  - Phytron GmbH   - motor development and the overall assembly and functional testing  - Gysin AG   - gear box components - GRW    - bearing manufacturing and Cronidur ® hardening  - ESR   - MoS 2 and lead lubrication  NASA/CP-2010-216272