WHAT WE FOUNDThe primary constraint and driver for Mars 2020 development is the Projectís planned July 2020 launch date. An optimal 20-day launch window for a trip from Earth to Mars occurs every 26 months. Missing the 2020 launch window would result in significant additional costs related to overhead, stand-by work force, replacement of degraded parts and components, and storage while waiting for the next launch opportunity. Although Mars 2020 Project management has taken appropriate steps to address risks inherent in using heritage technology and several issues identified on the MSL mission, we identified several schedule-related issues that could indicate the Project is overly optimistic, including a condensed development schedule for five of the seven instruments, a shorter development timeframe than MSL, and less detailed Integrated Master Schedule for assigning timelines to all required tasks than MSL.The largest risk to the Mars 2020 schedule is the Projectís Sample and Caching Subsystem (Sampling System), which will collect core samples of Martian rocks and soil and place them on the planetís surface for retrieval by a future robotic or human mission. At Preliminary Design Review (PDR), three of the Sampling Systemís critical technologies were below technology readiness level (TRL) 6, meaning the prototype had not yet demonstrated the capability to perform all the functions required. Projects are evaluated during PDR to ensure they meet all system requirements with acceptable risk and within cost and schedule constraints. The immaturity of the critical technologies related to the Sampling System is concerning because, according to Mars 2020 Project managers, the Sampling System is the roverís most complex new development component with delays likely to eat into the Projectís schedule reserve and, in the worst case scenario, could delay launch. As of December 2016, the Project was tracking the risk that the Sampling System may not be ready for integration and testing Ė the period when a spacecraft is built, undergoes final testing, and is prepared for launch Ė in May 2019, as planned.The Mars 2020 Project also does not appear to be on track to meet the 90 percent metric for release of engineering drawings by the February 2017 Critical Design Review (when a project demonstrates its design is sufficiently mature to proceed to full-scale fabrication, assembly, integration, and testing). Engineering drawings communicate to manufacturers the details of a productís design and are considered a good measure of a projectís stability. Failure to achieve this metric could affect the Projectís ability to ensure design stability, achieve technical objectives, and meet schedule and cost expectations.In addition to the risks associated with the Sampling System and the engineering drawings, we also identified several other challenges confronting Mars 2020 Project managers, including late delivery of actuators (the components responsible for moving and controlling parts and instruments on the rover); foregoing an engineering model of the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) designed to assess the feasibility of producing oxygen on Mars as a cost savings measure; ensuring the rover does not exceed its designed mass limit of 1,050 kilograms; and addressing foreign partner funding issues that may affect their ability to timely deliver components to the Project. WHAT WE RECOMMENDEDTo assist the Mars 2020 rover mission in achieving its technical objectives, meeting Project milestones, and controlling costs, we recommended the Associate Administrator for Science require the Mars 2020 Project Manager to (1) ensure the TRL of critical technologies and the rate of releasable engineering drawings meet established criteria before the Project completes Critical Design Review; (2) develop alternative plans to minimize changes to the overall science mission, Project cost, schedule, and scope if current risks to the actuators, mass growth, MOXIE, and Sampling System are realized; (3) assess the effectiveness of using a less detailed Integrated Master Schedule and make timely adjustments if required; and (4) continue to work with partners facing funding issues.NASA concurred with our recommendations and described planned actions. We find the actions responsive and will close the recommendations upon verification the Agency has taken the action.