429 The deployable for MSL and Mars 2020 are both constrained in place by a 9.5- mm ( 3/8-inch)  diameter pinpuller pyro device. The pin-puller is  in the same location relative to the Center Differential Pivot ( CDP ) and  differential  (Fig. 2). The MSL’s CDPR  dampened out the response from the asymm etric load using two  mirrored stacks of b elleville spring washers  within  a crank -slider mechanism  [1]. A titanium linkage   (weigh ing approximately 150 grams)  coupled the pin -puller to the belleville spring washers . Immediately  after the pin- puller was fired, only the  titanium  linkage was deployed and constrained in place by two torsion  springs [1]. For Mars 2020, a steel spring- like flexure replaces  the titanium linkage and the entire belleville  spring assembly.  Immediately after the pin-puller is fired , the steel flexure ( weigh ing approximately 1500  grams) is deployed to a final stowed position  and is also  driven by two torsion springs . This is where the  similarities between MSL and Mars 2020 CDPRs end.  

Since the mass of the deployable for Mars 2020 was 10 times greater  than that of MSL , a heavy emphasis  on CDPR’s ability to deploy  its flexure  and to ensure it remains  deployed  was put forth during the re- design  process.  As a result, t his drove to four major mechanis m design changes from MSL to Mars 2020. A  summary of these changes are as follows :   • Size and strength increase of the torsion springs in order to achieve the required release torque   • Installment of a kickoff spring as a  tertiary flexure release aid   • Installment of a magnetic latch into the deployable hard stop to further ensure the flexure to remain  at a fully and final deployed position   • Having the spring element being between the spherical bearings  ensured  moment decoupl e or  pure axial load transfer which  eliminate d alignment concerns that lead to several issues in the  MSL’s mechanism [1]      Details of the aforementioned mechanisms and structural features are discussed in later sections .  

Lastly, even though the location of the CDPR relative to the differential was similar between MSL and Mars  2020, the mechanical  interface between the rover chassis top deck had to be redeveloped.  Part of what  drove the MSL design was the shear pin interfac e between the CDPR and the top deck that not only  required a time-consuming match drilling process but  was also set by the time the compliant MSL CDPR  had to be developed [1] . For the Mars 2020 design, this interface was renegotiated to avoid using match  drilled shear pins and allowed for easier integration to the chassis top deck. Instead, a singular shear feature  was created.  The shear  feature is a monolithic planar extrusion with a t ightly toleranced diameter from the  bottom of the chassis bracket that mated to a pocket on the rover chassis top deck.  Along with the four  bracket mounting fasteners, the designed size and fitment tolerance of the shear boss were intended to  take the enti re shear load through the CDPR if the frictional cap ability of the preloaded interfaces common  to the four bolts was compromised . This newly designed shear feature ensured  full shear capability and  eliminated  any risk of  joint interface slippage.  This design feature allowed for easy integration and avoided  a high risk and precise match drilling operation on the major top deck  component. This was a good reminder  of a design engineering principle to value design for assembl y. The interface between the CDPR and the  mobility differential utilized the same match drilled shear pins and interface as MSL’s design due to mobility  differential remaining nearly heritage from MSL.  Despite this particular interface still being match dr illed,  the re- designed shear boss feature of chassis bracket to top deck interface still required less time and effort.  

Flexure Conceptualization and Trade -off for Mars 2020  

As with MSL, the structural and compliant aspect for the Mars 2020 CDPR  mechanism was to create a  theoretical torsi on spring about the CDP [1] . Unique for the Mars 2020 CPDR  was to accomplish this with  a lower torsional spring stiffness and overall assembly mass i nstead.  As determined by simulation of  EDL  sequence in ADAMS , a reduced torsional stiffness about the CDP coupled with a reduced CDPR mass  would linearly  reduce the peak  flight loads transferred into the rover chassis and mobility system.  This  finding was set forth as the design objective for the Mars 2020 CDPR where  MSL’s torsional stiffness of  200,000 N -m/rad [1] was halved to 100,000 N -m/rad to become the new Mars 2020 design parameter  for  the CDPR .