430 The reduction in effective torsional stiffness and mass reduction did come with a trade- off, however . The  linear spring of the CDPR would be less stiff , yet still had the same amount of  time to dampen out the  resultant load at the center of the differential . While the load to dampen out from an asymmetric deployment  would start -off lowe r, the more compliant linear spring would not be able to dampen out as much load as  the MSL CDPR. This resulted in a higher load at the time of pin-puller firing for the Mars 2020 compared to  MSL. From worst case ADAMS models with the softer Mars 2020 restraint system, the peak load (torque  about the CDP axis or rover z -axis as denoted by “Mz”) at the time of release was roughly 56% higher, but  still within the capability of the pin- puller (Fig. 3). 

Figure 3. Moment about CDP of MSL vs. Mars 2020 showing the maximum torque through the CDP at  the time of CDPR pin- puller firing: (a) MSL loads showing an initial higher peak mobility deployment load  and a lower pin- puller firing load, (b) Mars 2020 loa ds showing an initial lower peak mobility deployment  load and a higher pin- puller firing load.  

Flexure Design and Development   With the  target torsional stiffness about the CDP  set, the design and placement of the spring- like flexure   that would act  as the damper  for the CDPR was the first component of the CDPR to be fully prototyped and  tested.  The flexure design began with a simple cantilever beam concept.  The multi-looped feature was then  implemented and modeled by placing several cantilever beams in series to form a linear spring.  In the early  design phase, a MATLAB optimization program was created to determine the placement and sizing of the  flexure  in order to minimize mass while also achieving the target equivalent tor sional stiffness about the  CDP.  A structurally optimum and mass efficient location of the flexure was determined to be the same as  that of MSL; having the pin- puller attaching to the flexure 180.5  mm aft of the CDP axis.  After this  optimization determining rough sizing of flexure dimensions, the design transitioned to higher fidelity Finite  Element Analysis (FEA) modeling to close in on a more final design of the flexure.  

There were challenges in the initial design of the flexure to strike a  balance between required material   strength and structural buckling margin as well as target flexure compliance.  To begin, Maraging 300 steel  was selected as candidate material for the flexure due to its superior strength properties and high strength   vs. stiffness ratio as material strength was the first design constraint to satisfy followed by structural  compliance.  To arrive to the first prototype design, extensive analytical iterations via FEA were performed  in order to meet a rather narrow design window of stress, buckling, and stiffness requirements . Findings  from the structural analysis indicated that peak stress  magnitudes and distribution  as well as overall flexure  stiffness are highly sensitive to the width  of the flexure loops followed by stem of the loops  (Fig. 6).  

Prior to Detailed Design R eview  (DDR) , a flexure prototype out of the flight material specification and same  lot of flight material was subjected to a series  of structural characterization testing.  Objectives of this testing  was to statically characterize the flexure’s  uniaxial tension and compression stiffness  at room temperature  and qualification level hot (+40°C) and cold ( -55°C) temperature up to CDPR’s flight limit load (FLL) . A final  test would be conducted to determine the flexure’s  tensile residual strength capability at room temperature.