AbstractThe international Mars Exploration community has been planning to return samples from Mars for many years; the next decade should see the plans becoming a reality. Mars Sample Return (MSR) requires a series of missions, first to collect the samples, then to return them to Earth, whilst preventing the contamination of both Earth and Mars. The first mission in the campaign, Mars 2020, will land at Jezero Crater in early 2021; samples should return to Earth sometime after 2032. The information to be derived from analysis of martian samples in terrestrial laboratories equipped with state-of-the-art instrumentation is more than recompense for the difficulties of the MSR campaign. Results from analyses of returned samples will enable increased understanding of martian geological (and possibly biological) evolution. They will facilitate preparations for human exploration of Mars and by providing a second set of absolute ages for a planetary surface will validate (or otherwise) application of the lunar crater-age scale throughout the Solar System. Mars Sample Return (MSR) requires a series of missions, first to collect the samples, then to return them to Earth, whilst preventing the contamination of both Earth and Mars. The first mission in the campaign, Mars 2020, will land at Jezero Crater in early 2021; samples should return to Earth sometime after 2032. The information to be derived from analysis of martian samples in terrestrial laboratories equipped with state-of-the-art instrumentation is more than recompense for the difficulties of the MSR campaign. Results from analyses of returned samples will enable increased understanding of martian geological (and possibly biological) evolution. It is essential, if we are to be certain that the samples returned to Earth can be interpreted as representative of the material that was collected on Mars, that analyses are performed of the material whilst it is in situ on Mars. 3 MSR Mission Design As currently planned, Mars Sample Return is not a mission, but a campaign of several missions; one possible architecture for the campaign, with the different component missions is shown in Fig. 2 . Fig. 2 Full size image Possible architecture for a Mars Sample Return Campaign (from Haltigin et al. 2018 ) In this scenario, the first mission is NASA’s Mars-2020 rover, due to launch in July 2020. Samples returned from the crater may contain evidence of martian life, even if at the biomarker level rather than as fossils (Summons et al. 2011 ). An additional benefit of studying a suite of samples from Jezero crater is that the results will allow reconstruction of an entire martian sedimentary system, from which it should be possible to apply the results to other sedimentary regions observed from orbit. 4.2 Using Returned Samples for Evaluation of Potential Hazards to Human Exploration The return of samples to Earth from Mars is also an important part of any Human Exploration programme (NASA 2009 ). Analysis of the returned samples, especially the airfall dust, would take place as part of the planetary protection procedures to determine whether there were any biological or geochemical hazards in the samples that might affect humans. “Breaking the chain of contact” when leaving Mars is currently a requirement for containment of all material returning from Mars including any mission items that have been exposed to the martian environment. The reaction steps required to determine the organic inventory of a sample, and the associated range of chemicals and temperature regimes There are five planetary protection categories defined by COSPAR; all Earth return missions are Category V and a Mars Sample Return mission is Category Vb (Restricted Earth Return), the requirements for which are given as follows: The absolute prohibition of destructive impact upon return, the need for containment throughout the return phase of all returned hardware which directly contacted the target body or unsterilized material from the body, and the need for containment of any unsterilized sample collected and returned to Earth. Post-mission, there is a need to conduct timely analyses of any unsterilized sample collected and returned to Earth, under strict containment, and using the most sensitive techniques. If any sign of the existence of a non-terrestrial replicating entity is found, the returned sample must remain contained unless treated by an effective sterilizing procedure (COSPAR 2011 ; Kminek et al. 2017 ). Design studies for an MSR Receiving and Curation Facility have examined facilities in which biohazardous material is stored on Earth. The most recent reports are Euro-CARES ( 2017 ) and MSPG ( 2019a , 2019b ). The most strictly-controlled of such facilities is BSL-4, where all possible precautions are taken to prevent material escaping (backward PP). Less attention is given to material coming into the laboratory (forward PP). Currently, there is no existing facility that maintains high level containment in both the backwards and forwards direction, hence the need for a specially-designed facility for returned martian samples. It has sometimes been the case in previous design studies that the requirements for PP have been seen to be in conflict with those of the science goals. Farmer, Silica deposits on Mars with features resembling hot spring biosignatures at El Tatio in Chile. Nat. Commun. 7 , 13554 (2016). https://doi.org/10.1038/ncomms13554 Article ADS Google Scholar J.D. Rummel, M.S. Race, D.L. DeVincenzi, P.J. Schad, P.D. Stabekis, M. Viso, S.E. Acevedo, A draft test protocol for detecting possible biohazards in Martian samples returned to Earth, Washington, DC (2002). https://planetaryprotection.nasa.gov/summary/DraftTestProtocol M.A. Sephton, O. Botta, Recognizing life in the Solar System: guidance from meteoritic organic matter. Int. J. Astrobiol. 4 , 269–276 (2005). https://doi.org/10.1017/S1473550405002806 Article ADS Google Scholar J.P. Smoot, T.K.

The Mars Sample Return (MSR) Campaign must meet a series of scientific and technical achievements to be successful. While the respective engineering responsibilities to retrieve the samples have been formalized through a Memorandum of Understanding between ESA and NASA, the roles and responsibilities of the scientific elements have yet to be fully defined. In April 2020, ESA and NASA jointly chartered the MSR Science Planning Group 2 (MSPG2) to build upon previous planning efforts in defining 1) an end-to-end MSR Science Program and 2) needed functionalities and design requirements for an MSR Sample Receiving Facility (SRF). The challenges for the first samples brought from another planet include not only maintaining and providing samples in pristine condition for study, but also maintaining biological containment until the samples meet sample safety criteria for distribution outside of biocontainment. The MSPG2 produced six reports outlining 66 findings. Abbreviated versions of the five additional high-level MSPG2 summary findings are: Summary-1. A long-term NASA/ESA MSR Science Program, along with the necessary funding and human resources, will be required to accomplish the end-to-end scientific objectives of MSR. Summary-2. MSR curation would need to be done concurrently with Biosafety Level-4 containment. This would lead to complex first-of-a-kind curation implementations and require further technology development. Summary-3. Most aspects of MSR sample science could, and should, be performed on samples deemed safe in laboratories outside of the SRF. However, other aspects of MSR sample science are both time-sensitive and sterilization-sensitive and would need to be carried out in the SRF. Summary-4. To meet the unique science, curation, and planetary protection needs of MSR, substantial analytical and sample management capabilities would be required in an SRF. Summary-5. Because of the long lead-time for SRF design, construction, and certification, it is important that preparations begin immediately, even if there is delay in the return of samples.

A preliminary planetary protection compliance assessment shows the Earth Return Vehicle containment architecture as a critical design driver that requires 420 kg allocation. The proposed architecture has an estimated mission cost of $3.0–6.0 billion, which is a potential cost reduction compared with similar remaining elements of the current campaign by the National Aeronautics and Space Administration/European Space Age (NASA/ESA) Mars Surveyor (MSR) campaign (estimated to be $5–8 billion without accounting for the already-operational Perseverance rover). This study identifies a mass-critical but physically plausible pathway for near-term Mars sample return at the conceptual design level while acknowledging that significant technology maturation and high fidelity design validation and advance to Phase A requires a possible launcher upgrade. Published in Frontiers in Astronomy and Space Sciences The present study fills this gap by coupling all four elements within a unified mission framework, enabling cross-subsystem trade studies not possible in decoupled analyses. Planetary protection requirements for Mars sample return missions have been well analyzed. The COSPAR Planetary Protection Policy ( COSPAR, 2021 ) classifies MSR as Category V Restricted Earth Return, requiring break-the-chain containment to avoid uncontrolled release of Martian material to the Earth’s biosphere. Containment verification needs have been analyzed by Summons et al. (2014) , and the mass and complexity implications of a triple-containment architecture for Earth-return vehicles have been analyzed by Muirhead et al. (2020b) . These requirements impose severe mass and design requirements that must be modeled into any credible MSR architecture study. Surface communications for Mars robotic operations have been examined in the context of multi-robot coordination. Fong et al. (2013) showed surface communication relay ideas for planetary exploration, and Huntsberger et al. (2003) studied autonomous multi-robot coordination schemes applicable to sample retrieval missions. TABLE 1 Element Function Heritage basis TRL Heavy-lift launcher Mars transfer injection Falcon Heavy (flight proven) 9 Capsule-class vehicle Cruise, EDL, surface platform Crew capsule heritage, Red Dragon studies 4–5 MA-ERV Stage 1 (liquid) Mars ascent (lower) NTO/MMH engine heritage ( Huzel and Huang, 1992 ) 4–5 MA-ERV Stage 2 (solid) Mars ascent (upper) Small solid rocket motor (SRM) heritage ( Sutton and Biblarz, 2017 ) 5–6 MA-ERV Stage 3 (EP) Mars escape, Earth transfer SPT-140 Hall thruster ( Hofer and Gallimore, 2006 ) 5–6 Earth Return Vehicle Sample containment, Earth entry Stardust, Hayabusa2 ( Yada et al., 2021 ) 5 Quadruped robots (×3) Surface sample retrieval Spot ( Boston Dynamics, 2024 ) and ANYmal ( Hutter et al., 2017 ) 3–4 ISRU system (×4) CH 4 /O 2 production MOXIE ( Hoffman et al., 2022 ) and Sabatier demos ( Zubrin et al., 2013 ) 3–4 General purpose heat source–radioisotope thermoelectric generator (GPHS-RTG) (×2) Electrical and thermal At Stage 2 burnout, the remaining 640 kg comprises the Stage 2 structure (181 kg), the Stage 3 electric propulsion system (155 kg), the Earth Return Vehicle with sample containment (420 kg), and the interstage adapter hardware (estimated at 15 kg, included in Stage 2 structural mass). This residual mass enters a 200 km circular Mars orbit at approximately 3.45 km/s orbital velocity, ready for the Stage 3 low-thrust spiral escape. At Stage 1 burnout, T/W increases to , which is acceptable. Stage 2 ignition at 2,446 kg initial mass with SRM thrust of approximately 50 kN yields T/W = , which is appropriate for an upper stage in near-vacuum conditions. 9.4 Planetary protection compliance Mars sample return missions fall under COSPAR Category V Restricted Earth Return ( COSPAR, 2021 ), which imposes very strict requirements for avoiding uncontrolled release of Martian material into the Earth’s biosphere. The most important requirements and their design consequences are described in the following. 9.4.1 Triple containment The returned samples should be encapsulated in three independent containment barriers, each of which is proven to be free of failure in all mission environments (launch loads, thermal cycling, Mars surface exposure, and Earth entry). However, the outside surfaces of the tubes have been exposed to the Martian environment. The sample loading mechanism must either: (a) sterilize the outside of loading tubes prior to loading them into the OS container, or (b) treat the inside of the OS container as “Mars-exposed” and rely on the primary, secondary, and tertiary containment barriers. 9.4.3 ERV mass allocation The ERV mass allocation of 420 kg tabulated in Table 22 includes the following details. 9.4.4 Abort and breach scenarios Two critical scenarios require analysis: 9.4.4.1 Containment breach during Mars ascent In the event of a failure of the OS container seal during MA-ERV launch vibration, samples will stay inside the ERV shell (tertiary containment). Leak detection sensors on the OS container can check the integrity of the seal in LMO before committing to return to Earth. 9.4.4.2 ERV breakup during Earth entry For entry into Earth to occur during return from Mars, the ERV must survive entry at approximately 12 km/s (direct return from Mars). TPS failure could contaminate Earth’s atmosphere with Martian material. 9.5 Communications architecture Surface operations that require autonomous robot coordination over a range of 4.6 km use a layered communications architecture as described in Section 6.5 . The most critical issues that remain open are described in the following subsections. 9.5.1 Latency There is a 4–24 min one-way light time between Earth and Mars, which would prevent real-time teleoperation. All sample retrieval operations are to be autonomous with ground-in-the-loop supervisory control limited to strategic decisions (sortie planning, path selection, and abort commands).