In April 2018, a letter of intent was signed by NASA and ESA that may provide a basis for a Mars sample-return mission.[{{cite news |last=Rincon |first=Paul |date=April 26, 2018 |title=Space agencies intent on mission to deliver Mars rocks to Earth |publisher=BBC |url=https://www.bbc.com/news/science-environment-43907326}}][{{cite web |date=April 26, 2018 |title=Video (02:22) – Bringing Mars Back To Earth |url=https://www.youtube.com/watch?v=ie3-UwPLUho |url-status=live |archive-url=https://ghostarchive.org/varchive/youtube/20211222/ie3-UwPLUho |archive-date=2021-12-22 |publisher=NASA}}{{cbignore}} {{PD-notice}}] The agreement["Joint Statement of Intent between the National Aeronautics and Space Administration and the European Space Agency on Mars Sample Return," T. Zurbuchen and D. Parker, April 26, 2018. https://mepag.jpl.nasa.gov/announcements/2018-04-26%20NASA-ESA%20SOI%20(Signed).pdf, Mars Exploration Program Analysis Group, Retrieved January 28, 2023] came out of the 2nd International Mars Sample Return Conference in Berlin, Germany.[2nd International Mars Sample Return Conference, April 25–27, 2018. https://astrobiology.nasa.gov/events/2nd-international-mars-sample-return-conference/, Astrobiology at NASA, Retrieved January 28, 2023] The conference program was archived along with 125 technical submissions that covered sample science (anticipated findings, site selection, collection, curation, analysis) and mission implementation (Mars arrival, rovers, rock drills, sample transfer robotics, Mars ascent, autonomous orbit rendezvous, interplanetary propulsion, Earth arrival, planetary protection).["2018 International Mars Sample Return Conference Berlin." https://www.lpi.usra.edu/lpi/contribution_docs/LPI-002071.pdf, Lunar and Planetary Institute, Retrieved January 28, 2023] In one of many presentations, an international science team noted that collecting sedimentary rock samples would be required to search for ancient life.["Seeking Signs of Life on Mars: The Importance of Sedimentary Suites as Part of Mars Sample Return," iMOST Team (International MSR Objectives and Samples Team), MSR 2018 Berlin, https://www.lpi.usra.edu/lpi/contribution_docs/LPI-002071.pdf#page=103, Lunar and Planetary Institute, Retrieved 18 February 2023] A joint NASA-ESA presentation described the baseline mission architecture, including sample collection by the Mars 2020 Rover derived from the MAX-C concept, a Sample Retrieval Lander, and an Earth Return Orbiter.["Mars Sample Return Architecture Overview," C. Edwards and S. Vijendran, MSR 2018 Berlin, https://www.lpi.usra.edu/lpi/contribution_docs/LPI-002071.pdf#page=74, Lunar and Planetary Institute, Retrieved February 12, 2023] An alternative proposal was to use a SpaceX Falcon Heavy to decrease mission cost while delivering more mass to Mars and returning more samples.["Commercial Capabilities to Accelerate Timeline and Decrease Cost for Return of Samples from Mars," P. Wooster, M. Marinova, and J. Brost, MSR 2018 Berlin, https://www.lpi.usra.edu/lpi/contribution_docs/LPI-002071.pdf#page=172, Lunar and Planetary Institute, Retrieved February 12, 2023] Another submission to the Berlin conference noted that mission cost could be reduced by advancing MAV technology to enable a significantly smaller MAV for a given sample payload.["Mars Ascent Vehicle Needs Technology Development with a Focus on High Propellant Fractions," J. Whitehead, MSR 2018 Berlin, https://www.lpi.usra.edu/lpi/contribution_docs/LPI-002071.pdf#page=168, Lunar and Planetary Institute, Retrieved February 12, 2023]
In July 2019, a mission architecture was proposed.[{{cite news |last=Foust |first=Jeff |date=July 28, 2019 |title=Mars sample return mission plans begin to take shape |publisher=SpaceNews |url=https://spacenews.com/mars-sample-return-mission-plans-begin-to-take-shape/}}][{{cite web |last=Cowart |first=Justin |date=August 13, 2019 |title=NASA, ESA Officials Outline Latest Mars Sample Return Plans |url=http://www.planetary.org/blogs/guest-blogs/2019/nasa-esa-latest-msr-plan.html |publisher=The Planetary Society}}] In 2019, JPL authors summarized sample retrieval, including a sample fetch rover, options for fitting 20 or 30 sample tubes into a {{convert|12|kg|adj=on}} payload on a {{convert|400|kg|adj=on}} single-stage-to-orbit (SSTO) MAV that would use hybrid propellants, a liquid oxidizer with a solid wax fuel, which had been prioritized for propulsion technology development since 2016.["Mars Sample Return Lander Mission Concepts," B. Muirhead and A. Karp, 2019 IEEE Aerospace Conference, March 2019.] Meanwhile, the Marshall Space Flight Center (MSFC) presented a comparison of solid and hybrid propulsion for the MAV.["Development Concepts for Mars Ascent Vehicle (MAV) Solid and Hybrid Vehicle Systems," L. McCollum et al., 2019 IEEE Aerospace Conference, March 2019.] Later in 2019, MSFC and JPL had collaborated on designing a two-stage solid propellant MAV, and noted that an unguided spinning upper stage could reduce mass, but this approach was abandoned at the time due to the potential for orbital variations.["A Design for a Two-Stage Solid Mars Ascent Vehicle," A. Prince, T. Kibbey, and A. Karp, AIAA 2019–4149, AIAA Propulsion and Energy Forum, August 2019.]
Early in 2020 JPL updated the overall mission plan for an orbiting sample package (the size of a basketball["Bold plan to retrieve Mars samples takes shape," D. Clery and P. Voosen, Science, 366: 932, November 22, 2019.]) containing 30 tubes, showing solid and hybrid MAV options in the range {{convert|400|to|500|kg}}.["Mars Sample Return Mission Concept Status," B. Muirhead, A. Nicholas, and J. Umland, 2020 IEEE Aerospace Conference, March 2020.] Adding details, MSFC presented designs for both the solid and hybrid MAV designs, for a target mass of {{convert|400|kg}} at Mars liftoff to deliver 20 or 30 sample tubes in a {{convert|14|to|16|kg|adj=on}} payload package.["Mars Ascent Vehicle Solid Propulsion Configuration," D. Yaghoubi and A. Schnell, 2020 IEEE Aerospace Conference, March 2020.]["Mars Ascent Vehicle Hybrid Propulsion Configuration," D. Yaghoubi and A. Schnell, 2020 IEEE Aerospace Conference, March 2020.] In April 2020, an updated version of the mission was presented.[{{cite web |last=Clark |first=Stephen |date=April 20, 2020 |title=NASA narrows design for rocket to launch samples off of Mars |url=https://spaceflightnow.com/2020/04/20/nasa-narrows-design-for-rocket-to-launch-samples-off-of-mars/ |access-date=April 21, 2020 |work=Spaceflight Now}}] The decision to adopt a two-stage solid rocket MAV was followed by Design Analysis Cycle 0.0 in the spring of 2020, which refined the MAV to a {{convert|525|kg|adj=on}} design having guidance for both stages, leading to reconsideration of an unguided spin-stabilized second stage to save mass.["Integrated Design Results for the MSR DAC-0.0 Mars Ascent Vehicle," D. Yaghoubi and P. Ma, 2021 IEEE Aerospace Conference, March 2021.]
In October 2020, the MSR Independent Review Board (IRB) released its report["Mars Sample Return (MSR) Program: Final Report of the Independent Review Board (IRB)," https://www.nasa.gov/sites/default/files/atoms/files/nasa_esa_mars_sample_return_final_report_small.pdf#page=10, NASA reports website. Retrieved July 6, 2023] recommending overall that the MSR program proceed, then in November NASA responded to detailed IRB recommendations.["Summary of NASA Responses to Mars Sample Return Independent Review Board Recommendations," https://www.nasa.gov/sites/default/files/atoms/files/nasa_esa_mars_sample_return_final_report_small.pdf#page=1, NASA reports website. Retrieved July 6, 2023] The IRB noted that MSR would have eight first-time challenges, including the first launch from another planet, autonomous orbital rendezvous, and robotic sample handling with sealing to "break-the-chain".["Mars Sample Return (MSR) Program: Final Report of the Independent Review Board (IRB)," Notes below Chart 33, https://www.nasa.gov/sites/default/files/atoms/files/nasa_esa_mars_sample_return_final_report_small.pdf#page=42, NASA reports website. Retrieved July 6, 2023] The IRB cautioned that the MAV will be unlike any previous launch vehicle, and experience shows that the smaller a launch vehicle, the more likely it is to end up heavier than designed.["Mars Sample Return (MSR) Program: Final Report of the Independent Review Board (IRB)," Chart 42 and notes below it, https://www.nasa.gov/sites/default/files/atoms/files/nasa_esa_mars_sample_return_final_report_small.pdf#page=51, NASA reports website. Retrieved July 6, 2023] Referring to the unguided upper stage of the MAV, the IRB stated the importance of telemetry for critical events, "to allow useful reconstruction of a fault during second stage flight."["Mars Sample Return (MSR) Program: Final Report of the Independent Review Board (IRB)," Chart 43 and notes below it, https://www.nasa.gov/sites/default/files/atoms/files/nasa_esa_mars_sample_return_final_report_small.pdf#page=52, NASA reports website. Retrieved July 6, 2023] The IRB indicated that the most probable mission cost would be $3.8 to $4.4B.["Mars Sample Return (MSR) Program: Final Report of the Independent Review Board (IRB)," Chart 57 and notes below it, https://www.nasa.gov/sites/default/files/atoms/files/nasa_esa_mars_sample_return_final_report_small.pdf#page=66, NASA reports website. Retrieved July 6, 2023] As reported to the NAC-SC in April 2021, the Planetary Science Advisory Committee (PAC)["NASA Planetary Science Advisory Committee website," https://science.nasa.gov/researchers/nac/science-advisory-committees/pac, Retrieved July 4, 2023] was "very concerned about the high cost" of MSR, and wanted to be sure that astrobiology considerations would be included in plans for returned sample laboratories.[{{Cite report |url=https://smd-cms.nasa.gov/wp-content/uploads/2023/04/FINALScienceCmteMeetingMinutes_Signed_April2021.pdf |title=NASA Advisory Council Science Committee April 14–15, 2021 Meeting Report |date=2021 |location=Washington, DC |page=3}}]
Early in 2022 MSFC presented the guided-unguided MAV design for a {{convert|125|kg|adj=on}} mass reduction, and documented remaining challenges including aerodynamic complexities during the first stage burn and coast to altitude, a desire to locate hydrazine steering thrusters farther from the center of mass, and stage separation without tip-off rotation.["Integrated Design Results for the MSR SRC Mars Ascent Vehicle," D. Yaghoubi and S. Maynor, 2022 IEEE Aerospace Conference, March 2022.] While stage separation and subsequent spin-up would be flight tested, the authors noted that it would be ideal to flight test an entire flight-like MAV, but there would be a large cost.
In April 2022, the United States National Academies released the Planetary Science Decadal Survey report for 2023-2032, a review of plans and priorities for the upcoming ten years - after many committee meetings starting in 2020, with consideration of over 500 independently submitted white papers, more than 100 regarding Mars, including comments on science and technology for sample return.["Planetary Science and Astrobiology Decadal Survey 2023-2032," https://www.nationalacademies.org/our-work/planetary-science-and-astrobiology-decadal-survey-2023-2032, National Academies of Sciences, Engineering, and Medicine. Retrieved February 26, 2023] The published document noted NASA's 2017 plan for a "focused and rapid" sample return campaign with essential participation from ESA, then recommended, "The highest scientific priority of NASA's robotic exploration efforts this decade should be completion of Mars Sample Return as soon as is practicably possible."["Origins, Worlds, and Life. A Decadal Strategy for Planetary Science and Astrobiology 2023–2032," https://nap.nationalacademies.org/catalog/26522/origins-worlds-and-life-a-decadal-strategy-for-planetary-science, https://doi.org/10.17226/26522, National Academies of Sciences, Engineering, and Medicine, Space Studies Board, National Academies Press, 2022; {{ISBN|978-0-309-47578-5}}. See pages 22-7 to 22-9. Retrieved February 26, 2023] Decadal white papers emphasized the importance of MSR for science,["Why Mars Sample Return is a Mission Campaign of Compelling Importance to Planetary Science and Exploration," https://mepag.jpl.nasa.gov/reports/decadal2023-2032/MSR%20science%20white%20paper-final4.pdf, MEPAG website. Retrieved July 5, 2023] included a description of implementing MSR,["Mars Sample Return Campaign Concept Architecture," https://mepag.jpl.nasa.gov/reports/decadal2023-2032/Decadal%20White%20Paper%20MuirheadBrianK.pdf, MEPAG website. Retrieved July 5, 2023] and noted that the MAV has been underestimated despite needing flight performance beyond the state of the art for small rockets,["The Challenge of Launching Geology Samples off of Mars is Easily Underestimated, Due to Tempting Misconceptions," https://mepag.jpl.nasa.gov/reports/decadal2023-2032/WhiteheadMisconceptionsMAV2020Oct11.pdf, MEPAG website. Retrieved July 4, 2023] needs a sustained development effort,["Mars Ascent Vehicle needs a Sustained Development Effort, Regardless of Sample Return Mission Timelines," https://mepag.jpl.nasa.gov/reports/decadal2023-2032/WhiteheadSustainMAV2020Oct11.pdf, MEPAG website. Retrieved July 4, 2023] and that technology development for a smaller MAV has the potential to reduce MSR mission cost.["Technology Development Can Lead to Smaller Mars Ascent Vehicles, for Multiple Affordable Sample Returns," https://mepag.jpl.nasa.gov/reports/decadal2023-2032/WhiteheadSmallerMAV2020Oct11.pdf, MEPAG website. Retrieved July 4, 2023] Decadal Survey committee meetings hosted numerous invited speakers, notably a presentation from the MSR IRB.["Decadal Survey on Planetary Science and Astrobiology: Steering Group Seventh Meeting Revised Final Agenda," https://www.nationalacademies.org/documents/embed/link/LF2255DA3DD1C41C0A42D3BEF0989ACAECE3053A6A9B/file/DE1EC51702FEF69877C024F38B3437AA2CD7C9F72218?noSaveAs=1, National Academies of Sciences, Engineering, and Medicine. Retrieved July 6, 2023]
As of March 2022, separate landers were planned for the fetch rover and the MAV, because together they would be too large and heavy for a single lander. A cost-saving plan as of July was to send only one lander with the MAV, and rely on the Perseverance rover to pass sample tubes to the MAV in the absence of a fetch rover.[Foust, Jeff (July 27, 2022) "NASA and ESA remove rover from Mars Sample Return plans," https://spacenews.com/nasa-and-esa-remove-rover-from-mars-sample-return-plans/ Space News. Retrieved December 21, 2023] Two new lightweight helicopters on the MAV lander would serve as a backup for moving the samples on Mars.["Mars choppers displace fetch rover in sample-return plan," J. Foust, Space News, August 2022, p. 6-7.]