71 In the CLUPI focus mechanism development , the mechanical environment  specification severity increased  drastically at a late stage of the project. This led to additional (and extensive) design iterations  at CSEM in  an already very tight schedule. Efforts were done to make sure that the mechanism would be compatible  with the interfacing structure. Further improvement s could have been implemented on the interfacing  structure to reduce its impact on the amplification of random levels.  

2. In Compliant Mechanisms , Avoid Poorly Constrained Intermediate Stages:  internal modes of the  guiding structure are often the root -cause to compl iant mechanism failure. While overall structural  modes are dampened by the assembled structure and the mobile stage modes are dampened by  a launch lock , intermediate stage modes cannot be easily locked an d are not dampened.  

In the CFM development , the intermediate stage mode (originally at 830 Hz) was an important source of  stresses in the mechanism. It is not damped by any phenomenon but the internal  material dampin g. Thus,   the intermediate stage arm behaves  as a tuning fork and stress es the blades above their limit. The solution  was to better constrain the arm with  a transverse blade. This solved the problem but could have been  implemented at an earlier stage of the project  thus saving the cost and time of developing further  breadboards.  

3. Most Compliant Mechanisms Need Launch Locks : This is especially true when the guiding rigidity  is low, which is needed achieve long strokes. In these cases, the development of launch locki ng  must be started early in  the development of the compliant mechanism. This allows for a better  integration of the locking system in the mechanism and may even allow for a locking of the  intermediate stages.  

At the very beginning of the CFM development n o launch lock was designed. Not that it was not foreseen  as necessary by the engineering team,  but because the cost of the launch lock development was not  included in the first feasibility study. Furthermore, the feasibility study  report  did not mention explicitly the  need for a launch lock . Due to this missing information,  the customer was misled to believe no launch lock  would be required. Thus, during mass budget negotiations , no allowance was made for such a system. It  was only shortly before the instrument delta  PDR that the need of a launch lock was identified  and flagged  as critical. T he late-coming launch lock design was  then highly constrained by an already very tight  schedule and mass budget.  

4. Test as You Fly, as Early as P ossible: While mission representative test s are ofte n associated with  extensive costs, they are the only way to anticipate issues with multiple root -causes.  

The failure of the CFM launch lock during qualification is a good example to justify the need for “test as you  fly” method: m any tests were performed to make sure that the unlocking would behave as expected:  

• Launch lock friction and force characterizati on measurements   successful  

• NEA te sted alone, with representative actuation current and low temperature  successful  

• Launch lock mechanism tested at ambient  with mechanical release representative   successful   

However,  the first time the launch locking system was tested integrally in -flight representative condition was  during the thermal vacuum qualification test , during which the system failed to unlock within an acceptable  duration.