427 Mars 2020 Center Differential Pivot Restraint : Flexurized Spring System  Providing  Compliance for Rover  Mobility Deployment Prior to Landing  

Matthew Cameron* and Kevin Liu*  

Abstract  

The Center Differential Pivot Restraint (CDPR) for the Mars 2020 mission is designed to constrain motion  of the rover differential and to dampen out the load response during rover’s mobility deployment event in  Entry, Descent, and Landing (EDL)  phase of the mission . For Mars 2020, it was required to redesign the  mechanism to save minimum 33% of the mass from the previous Mars Science Laboratory  (MSL) design .  The new mechanism architecture used a monolithic spring- like flexure to act as the system compliance,   resulting in 50% mass savings from the MSL design.  Along the design and prototype testing process,  several mechanism design principles were re -affirmed as well as lessons learned about potential race  conditions.  

Introduction  

The Mars 2020 mi ssion is designed to land and traverse a newly improved rover  on Mars to gather soil  samples  that could  be returned to Earth for detailed study.  During  the EDL portion of the mission, the rover  is lowered from  the sky crane via three bridle connections while the rover’s mobility subsystem’s  rocker/bogie suspension on both side s of the rover deploys in preparation for surface touchdown  (Fig. 1).  During this deployment event, the CDPR absorbs and dampens out the induced load into the rover at the  chassis top deck interface in the event when the side- to-side suspension deployment becomes asymmetric.   Same as that of the MSL mission, the CDPR is mounted on the top deck of the rover chassis and located  directly aft of the rover differential assembly (Fig.  2).  

As improved upon the previous MSL CDPR [1], completely new design and architecture for the Mars 2020  CDPR were achieved by maintaining the same functionalit y, while reducing the restraint’s mass by 50%.  From conceiving the initial design in November 2015, through multiple design reviews and prototype testing,  to completing flight integration and qualification testing around early January 2020, the entire crad le-tograve process spanned over a 39- month period. This paper discusses details of the new Mars 2020 design  and mechanism features, its development process, key improvements from the previous MSL mission, and  the design validation testing campaign; highli ghting key lessons learned throughout the design and testing  process.   

Mars 2020 vs. MSL Design  

The design for Mars 2020 CDPR is composed of a spring- like flexure, constrained by a pyro pin- puller  attached to the mobility differential on one end and a shoulder bolt to a bracket bolted to the rover chassis  top deck on the other end (Fig. 2 ). Details o f its design and the deployable mechanism are presented in a  later section. For brevity and scope of this paper, see [1] for complete details of MSL’s CDPR design.  

In both designs, the mechanism’s function is the same and is described in three phases: (1)  rover mobility  deployment response dampening and motion constrain during EDL, (2) CDPR mechanism deployment,  and (3) remaining deployed for the remainder of surface operations. Major similarities of CDPR between  the two missions include how each deployabl e is constrained to the differential as well as the main passive  element in the deployment mechanism.  

* Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA  

Proceedings of the 45th Aerospace Mechanisms Symposium, NASA Johnson Space Center, 2020