Human mission to Mars explained

The idea of sending humans to Mars has been the subject of aerospace engineering and scientific studies since the late 1940s as part of the broader exploration of Mars.[1] Long-term proposals have included sending settlers and terraforming the planet. Currently, only robotic landers and rovers have been on Mars. The farthest humans have been beyond Earth is the Moon, under the U.S. National Aeronautics and Space Administration (NASA) Apollo program which ended in 1972.

Conceptual proposals for missions that would involve human explorers started in the early 1950s, with planned missions typically being stated as taking place between 10 and 30 years from the time they are drafted. The list of crewed Mars mission plans shows the various mission proposals that have been put forth by multiple organizations and space agencies in this field of space exploration. The plans for these crews have varied—from scientific expeditions, in which a small group (between two and eight astronauts) would visit Mars for a period of a few weeks or more, to a continuous presence (e.g. through research stations, colonization, or other continuous habitation). Some have also considered exploring the Martian moons of Phobos and Deimos.[2] By 2020, virtual visits to Mars, using haptic technologies, had also been proposed.[3]

Meanwhile, the uncrewed exploration of Mars has been a goal of national space programs for decades, and was first achieved in 1965 with the Mariner 4 flyby. Human missions to Mars have been part of science fiction since the 1880s, and more broadly, in fiction, Mars is a frequent target of exploration and settlement in books, graphic novels, and films. The concept of a Martian as something living on Mars is part of the fiction. Proposals for human missions to Mars have come from agencies such as NASA, CNSA, the European Space Agency, Boeing, SpaceX, and space advocacy groups such as the Mars Society and The Planetary Society.

Travel to Mars

The energy needed for transfer between planetary orbits, or delta-v, is lowest at intervals fixed by the synodic period. For EarthMars trips, the period is every 26 months (2 years, 2 months), so missions are typically planned to coincide with one of these launch periods. Due to the eccentricity of Mars's orbit, the energy needed in the low-energy periods varies on roughly a 15-year cycle[4] with the easiest periods needing only half the energy of the peaks.[5] In the 20th century, a minimum existed in the 1969 and 1971 launch periods and another low in 1986 and 1988, then the cycle repeated. The last low-energy launch period occurred in 2023.[6]

Several types of mission plans have been proposed, including opposition class and conjunction class, or the Crocco flyby.[7] The lowest energy transfer to Mars is a Hohmann transfer orbit, which would involve a roughly 9-month travel time from Earth to Mars, about 500days at Mars to wait for the transfer window to Earth, and a travel time of about 9 months to return to Earth.[8] [9] This would be a 34-month trip.

Shorter Mars mission plans have round-trip flight times of 400 to 450 days,[10] or under 15 months, but would require significantly higher energy. A fast Mars mission of 245day round trip could be possible with on-orbit staging.[11] In 2014, ballistic capture was proposed, which may reduce fuel cost and provide more flexible launch windows compared to the Hohmann.[12] In the Crocco grand tour, a crewed spacecraft would get a flyby of Mars and Venus in under a year in space.[13] Some flyby mission architectures can also be extended to include a style of Mars landing with a flyby excursion lander spacecraft.[14] Proposed by R. Titus in 1966, it involved a short-stay lander-ascent vehicle that would separate from a "parent" Earth-Mars transfer craft prior to its flyby of Mars. The Ascent-Descent lander would arrive sooner and either go into orbit around Mars or land, and, depending on the design, offer perhaps 10–30 days before it needed to launch itself back to the main transfer vehicle. (See also Mars flyby.)

In the 1980s, it was suggested that aerobraking at Mars could reduce the mass required for a human Mars mission lifting off from Earth by as much as half.[15] As a result, Mars missions have designed interplanetary spacecraft and landers capable of aerobraking.[15]

Landing on Mars

A number of uncrewed spacecraft have landed on the surface of Mars, while some, such as Beagle2 (2003) and the Schiaparelli EDM (2016), have failed what is considered a difficult landing. Among the successes:

Orbital capture

When an expedition reaches Mars, braking is required to enter orbit. Two options are available: rockets or aerocapture. Aerocapture at Mars for human missions was studied in the 20th century.[16] In a review of 93 Mars studies, 24 used aerocapture for Mars or Earth return.[16] One of the considerations for using aerocapture on crewed missions is a limit on the maximum force experienced by the astronauts. The current scientific consensus is that 5 g, or five times Earth gravity, is the maximum allowable deceleration.[16]

Survey work

Conducting a safe landing requires knowledge of the properties of the atmosphere, first observed by Mariner 4, and a survey of the planet to identify suitable landing sites. Major global surveys were conducted by Mariner 9, Viking 1 and two orbiters, which supported the Viking landers. Later orbiters, such as Mars Global Surveyor, 2001 Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter, have mapped Mars in higher resolution with improved instruments. These later surveys have identified the probable locations of water, a critical resource.[17]

Funding

A primary limiting factor for sending humans to Mars is funding. In 2010, the estimated cost was roughly US$500 billion, although the actual costs are likely to be more.[18] Starting in the late 1950s, the early phase of space exploration was conducted by lone nations as much to make a political statement as to make observations of the solar system. This proved to be unsustainable, and the current climate is one of international cooperation, with large projects such as the International Space Station and the proposed Lunar Gateway being built and launched by multiple countries.

Critics argue that the immediate benefits of establishing a human presence on Mars are outweighed by the immense cost, and that funds could be better redirected towards other programs, such as robotic exploration. Proponents of human space exploration contend that the symbolism of establishing a presence in space may garner public interest to join the cause and spark global cooperation. There are also claims that a long-term investment in space travel is necessary for humanity's survival.

One factor reducing the funding needed to place a human presence on Mars may be space tourism. As the space tourism market grows and technological developments are made, the cost of sending humans to other planets will likely decrease accordingly. A similar concept can be examined in the history of personal computers: when computers were used only for scientific research, with minor use in big industry, they were big, rare, heavy, and costly. When the potential market increased and they started to become common in businesses and later in homes (in Western and developed countries), the computing power of home devices skyrocketed and prices plummeted.[19]

Medical

See main article: Space medicine. Several key physical challenges exist for human missions to Mars:[20]

Some of these issues were estimated statistically in the HUMEX study.[37] Ehlmann and others have reviewed political and economic concerns, as well as technological and biological feasibility aspects.[38] While fuel for roundtrip travel could be a challenge, methane and oxygen can be produced using Martian H2O (preferably as water ice instead of liquid water) and atmospheric CO2 with sufficiently mature technology.[39]

Planetary protection

See also: Planetary protection. Robotic spacecraft to Mars are required to be sterilized. The allowable limit is 300,000 spores on the exterior of general craft, with stricter requirements for spacecraft bound for "special regions" containing water.[40] [41] Otherwise there is a risk of contaminating not only the life-detection experiments but possibly the planet itself.[42]

Sterilizing human missions to this level is impossible, as humans are host to typically a hundred trillion (1014) microorganisms of thousands of species of the human microbiota, and these cannot be removed. Containment seems the only option, but it is a major challenge in the event of a hard landing (i.e. crash).[43] There have been several planetary workshops on this issue, yet there are no final guidelines for a way forward.[44] Human explorers would also be vulnerable to back contamination to Earth if they become carriers of microorganisms.[45]

Mission proposals

See main article: List of crewed Mars mission plans.

Over the past seven decades, a wide variety of mission architectures have been proposed or studied for human spaceflights to Mars. These have included chemical, nuclear, and electric propulsion, as well as a wide variety of landing, living, and return methodologies.

A number of nations and organizations have long-term intentions to send humans to Mars.

Technological innovations and hurdles

Significant technological hurdles need to be overcome for human spaceflight to Mars.

Entry into the thin and shallow Martian atmosphere will pose significant difficulties with re-entry; compared to Earth's much denser atmosphere, any spacecraft will descend very rapidly to the surface and must be slowed.[54] A heat shield has to be used.[55] NASA is carrying out research on retropropulsive deceleration technologies to develop new approaches to Mars atmospheric entry. A key problem with propulsive techniques is handling the fluid flow problems and attitude control of the descent vehicle during the supersonic retropropulsion phase of the entry and deceleration.[56]

A return mission from Mars will need to land a rocket to carry crew off the surface. Launch requirements mean that this rocket could be significantly smaller than an Earth-to-orbit rocket. Mars-to-orbit launch can also be achieved in single stage. Despite this, landing an ascent rocket back on Mars will be difficult.

In 2014, NASA proposed the Mars Ecopoiesis Test Bed.[57]

Intravenous fluidOne of the medical supplies that might be needed is a considerable mass of intravenous fluid, which is mainly water, but contains other substances so it can be added directly to the human blood stream. If it could be created on the spot from existing water, this would reduce mass requirements. A prototype for this capability was tested on the International Space Station in 2010.[58]
Advanced resistive exercise deviceA person who is inactive for an extended period of time loses strength, muscle and bone mass. Spaceflight conditions are known to cause loss of bone mineral density in astronauts, increasing bone fracture risk. The most recent mathematical models predict 33% of astronauts will be at risk for osteoporosis during a human mission to Mars.[31] A resistive exercise device similar to an Advanced Resistive Exercise Device (ARED) would be needed in the spaceship but would not fully counteract the loss of bone mineral density.
  • Breathing gasesWhile humans can breathe pure oxygen, usually additional gases such as nitrogen are included in the breathing mix. One possibility is to use in situ nitrogen and argon from the atmosphere of Mars, but they are hard to separate from each other. As a result, a Mars habitat may use 40% argon, 40% nitrogen, and 20% oxygen.[59]
  • An idea for keeping carbon dioxide out of the breathing air is to use reusable amine-bead carbon dioxide scrubbers.[60] While one carbon dioxide scrubber filters the astronaut's air, the other is vented to the Mars atmosphere.

    Growing foodIf humans are to live on Mars, growing food on Mars may be necessary – with numerous related challenges.[61]

    Related missions

    Some missions may be considered a "Mission to Mars" in their own right, or they may only be one step in a more in-depth program. An example of this is missions to Mars's moons, or flyby missions.

    Missions to Deimos or Phobos

    Many Mars mission concepts propose precursor missions to the moons of Mars, for example a sample return mission to the Mars moon Phobos[62] – not quite Mars, but perhaps a convenient stepping stone to an eventual Martian surface mission. Lockheed Martin, as part of their "Stepping stones to Mars" project, called the "Red Rocks Project", proposed to explore Mars robotically from Deimos.[63] [64] [65]

    Use of fuel produced from water resources on Phobos or Deimos has also been proposed.

    Mars sample return missions

    An uncrewed Mars sample return mission (MSR) has sometimes been considered as a precursor to crewed missions to the Mars surface.[66] In 2008, the ESA called a sample return "essential" and said it could bridge the gap between robotic and human missions to Mars. An example of a Mars sample return mission is Sample Collection for Investigation of Mars.[67] Mars sample return was the highest priority Flagship Mission proposed for NASA by the Planetary Decadal Survey 2013–2022: The Future of Planetary Science.[68] However, such missions have been hampered by complexity and expense, with one ESA proposal involving no fewer than five different uncrewed spacecraft.[69]

    Sample return plans raise the concern, however remote, that an infectious agent could be brought to Earth. Regardless, a basic set of guidelines for extraterrestrial sample return has been laid out depending on the source of sample (e.g. asteroid, Moon, Mars surface, etc.)[70]

    At the dawn of the 21st century, NASA crafted four potential pathways to Mars human missions,[71] of which three included a Mars sample return as a prerequisite to human landing.

    The rover Perseverance, which landed on Mars in 2021, is equipped with a device that allows it to collect rock samples to be returned at a later date by another mission.[72] Perseverance as part of the Mars 2020 mission, was launched on an Atlas V rocket on 30 July 2020.[73]

    Crewed orbital missions

    Starting in 2004, NASA scientists have proposed to explore Mars via telepresence from human astronauts in orbit.[74] [75]

    A similar idea was the proposed "Human Exploration using Real-time Robotic Operations" mission.[76] [77]

    In order to reduce communications latency, which ranges from 4 to 24 minutes,[78] a manned Mars orbital station has been proposed to control robots and Mars aircraft without long latency.[79]

    See also

    Further reading

    External links

    Notes and References

    1. News: Rich . Nathaniel . 25 February 2024 . Can Humans Endure the Psychological Torment of Mars? – NASA is conducting tests on what might be the greatest challenge of a Mars mission: the trauma of isolation. . live . https://archive.today/20240225110334/https://www.nytimes.com/2024/02/25/magazine/mars-isolation-experiment.html . 25 February 2024 . 25 February 2024 . The New York Times.
    2. Web site: JAXA. 2021-09-20. Japan Space Agency: Why We're Exploring the Moons of Mars. 2021-09-25. SciTechDaily. en-US.
    3. News: Von Drehle . David . Humans don't have to set foot on Mars to visit it . 15 December 2020 . . 16 December 2020 .
    4. David S. F. Portree, Humans to Mars: Fifty Years of Mission Planning, 1950–2000, NASA Monographs in Aerospace History Series, Number 21, February 2001. NASA SP-2001-4521.
    5. David S. F. Portree. Humans to Mars: Fifty Years of Mission Planning, 1950–2000, NASA Monographs in Aerospace History Series, Number 21, February 2001. Chapter 3, pp. 18–19. NASA SP-2001-4521.
    6. Mission design options for human Mars missions . free . free . Paul D.. Wooster. International Journal of Mars Science and Exploration. 2007. 3. 12. 10.1555/mars.2007.0002. 2007IJMSE...3...12W. etal. 10.1.1.524.7644.
    7. David S. F. Portree. Humans to Mars: Fifty Years of Mission Planning, 1950–2000, NASA Monographs in Aerospace History Series, Number 21, February 2001. Chapter 3, pp. 15–16. NASA SP-2001-4521.
    8. Web site: Hohmann transfer orbit diagram. The Planetary Society. en. 2018-03-27.
    9. Web site: Homann Transfers. Jim Wilson's Home Page. 2018-03-27.
    10. Wernher von Braun, Web site: March 1964 . Popular Science . 12 June 2015 . google.com . Bonnier Corporation.
    11. Web site: Folta . etal . 2012 . FAST MARS TRANSFERS THROUGH ON-ORBIT STAGING . Usra.edu.
    12. Web site: Williams . Matt . 28 December 2014 . Making A Trip To Mars Cheaper & Easier: The Case For Ballistic Capture . 12 June 2015 . io9 . Universe Today . en.
    13. Web site: Crocco. Tdf.it. 2015-11-03. 2017-12-01. https://web.archive.org/web/20171201034318/http://www.tdf.it/2006/2/crocco_en.htm. dead.
    14. To Mars by Flyby-Landing Excursion Mode (FLEM) (1966). Wired.
    15. Web site: Photo-s88_35629. https://web.archive.org/web/20070802140932/http://spaceflight.nasa.gov/gallery/images/exploration/marsexploration/html/s88_35629.html. dead. 2007-08-02. Spaceflight.nasa.gov.
    16. A Comparative Study of Aerocapture Missions with a Mars Destination. Diane. Vaughan. Bonnie F.. James. Michelle M.. Murk. Ntrs.nasa.gov. 26 April 2005. 16 March 2019.
    17. Web site: Anderson. Gina. 2015-09-28. NASA Confirms Evidence That Liquid Water Flows on Today's Mars. 2020-09-28. NASA.
    18. Book: Taylor, Fredric . The Scientific Exploration of Mars . Cambridge University Press . 2010 . 978-0-521-82956-4 . Cambridge, England . 306 . en-uk.
    19. Web site: How SpaceX, Virgin Galactic, Blue Origin and others compete in the growing space tourism market. Michael. Sheetz. September 26, 2020. CNBC.
    20. News: Regis . Ed . Let's Not Move To Mars . September 21, 2015 . . September 22, 2015.
    21. Web site: Scharf . Calib A. . 20 January 2020 . Death on Mars – The martian radiation environment is a problem for human explorers that cannot be overstated . 20 January 2020 . Scientific American.
    22. Saganti . Premkumar B. . Cucinotta . Francis A. . Wilson . John W. . Cleghorn . Timothy F. . Zeitlin . Cary J. . Model calculations of the particle spectrum of the galactic cosmic ray (GCR) environment: Assessment with ACE/CRIS and MARIE measurements . Radiation Measurements . October 2006 . 41 . 9–10 . 1152–1157 . 10.1016/j.radmeas.2005.12.008 . 2006RadM...41.1152S .
    23. Shiga . David . Too much radiation for astronauts to make it to Mars . . 2726 . 2009-09-16 .
    24. Fong, MD . Kevin . The Strange, Deadly Effects Mars Would Have on Your Body . 12 February 2014 . . 12 February 2014.
    25. Gelling . Cristy . Atom & cosmos: Mars trip would mean big radiation dose: Curiosity instrument confirms expectation of major exposures: Atom & cosmos: Mars trip would mean big radiation dose: Curiosity instrument confirms expectation of major exposures . Science News . 29 June 2013 . 183 . 13 . 8 . 10.1002/scin.5591831304 .
    26. Web site: Scott . Jim . Large solar storm sparks global aurora and doubles radiation levels on the martian surface . 30 September 2017 . . 30 September 2017 .
    27. Siew, Keith . et al. . Cosmic kidney disease: an integrated pan-omic, physiological and morphological study into spaceflight-induced renal dysfunction . 11 June 2024 . . 15 . 4923 . 10.1038/s41467-024-49212-1 . live . https://archive.today/20240613124840/https://www.nature.com/articles/s41467-024-49212-1 . 13 June 2024 . 13 June 2024 . 11167060 .
    28. News: Cuthbertson . Anthony . Human missions to Mars in doubt after astronaut kidney shrinkage revealed . 12 June 2024 . . live . https://archive.today/20240613125402/https://www.yahoo.com/news/human-missions-mars-doubt-astronaut-090649428.html?guccounter=1 . 13 June 2024 . 13 June 2024 .
    29. Dr. Matt Midgley, Would astronauts’ kidneys survive a roundtrip to Mars?, University College of London. 11 June 2024. Retrieved 13 June 2024.
    30. https://news.yahoo.com/news/human-missions-mars-doubt-astronaut-090649428.html Human missions to Mars in doubt after astronaut kidney shrinkage revealed
    31. 10.1371/journal.pone.0226434. A human mission to Mars: Predicting the bone mineral density loss of astronauts. 2020. Axpe. Eneko. Chan. Doreen. Abegaz. Metadel F.. Schreurs. Ann-Sofie. Alwood. Joshua S.. Globus. Ruth K.. Appel. Eric A.. PLOS ONE. 15. 1. e0226434. 31967993. 6975633. 2020PLoSO..1526434A. free.
    32. Mader . Thomas H. . Gibson . C. Robert . Pass . Anastas F. . Kramer . Larry A. . Lee . Andrew G. . Fogarty . Jennifer . Tarver . William J. . Dervay . Joseph P. . Hamilton . Douglas R. . Sargsyan . Ashot . Phillips . John L. . Tran . Duc . Lipsky . William . Choi . Jung . Stern . Claudia . Kuyumjian . Raffi . Polk . James D. . Optic Disc Edema, Globe Flattening, Choroidal Folds, and Hyperopic Shifts Observed in Astronauts after Long-duration Space Flight . Ophthalmology . October 2011 . 118 . 10 . 2058–2069 . 10.1016/j.ophtha.2011.06.021 . 21849212 . 13965518 .
    33. Web site: Puiu . Tibi . Astronauts' vision severely affected during long space missions . November 9, 2011 . Zmescience.com . February 9, 2012.
    34. Web site: Breaking News Videos, Story Video and Show Clips – CNN.com . CNN . 12 June 2015.
    35. News: Strickland . Ashley . Astronauts experienced reverse blood flow and blood clots on the space station, study says . 15 November 2019 . . 22 November 2019 .
    36. Marshall-Goebel, Karina . et al. . Assessment of Jugular Venous Blood Flow Stasis and Thrombosis During Spaceflight . 13 November 2019 . . 10.1001/jamanetworkopen.2019.15011 . free . 2 . 11 . e1915011 . 31722025 . 6902784 .
    37. 10.1016/j.asr.2005.06.077 . 37 . General human health issues for Moon and Mars missions: Results from the HUMEX study . 2006 . Advances in Space Research . 100–108 . Horneck . Gerda. 1 . 2006AdSpR..37..100H .
    38. 10.1016/j.actaastro.2005.01.010 . 56 . Humans to Mars: A feasibility and cost–benefit analysis . 2005 . Acta Astronautica . 851–858 . Ehlmann . Bethany L.. 9–12 . 15835029 . 2005AcAau..56..851E .
    39. Book: 10.1109/AERO.2005.1559325 . Preliminary system analysis of in situ resource utilization for Mars human exploration . 2005 IEEE Aerospace Conference . 2005 . Rapp . D. . Andringa . J. . Easter . R. . Smith . J.H. . Wilson . T.J. . Clark . D.L. . Payne . K. . 319–338 . 0-7803-8870-4 . 25429680 .
    40. Web site: Queens University Belfast scientist helps NASA Mars project . "No-one has yet proved that there is deep groundwater on Mars, but it is plausible as there is certainly surface ice and atmospheric water vapour, so we wouldn't want to contaminate it and make it unusable by the introduction of micro-organisms." . BBC News . 23 May 2014 . live . https://web.archive.org/web/20231105093701/https://www.bbc.co.uk/news/uk-northern-ireland-27526981 . Nov 5, 2023 .
    41. Web site: dead . COSPAR Planetary Protection Policy . https://web.archive.org/web/20130306111646/https://science.nasa.gov/media/medialibrary/2012/05/04/COSPAR_Planetary_Protection_Policy_v3-24-11.pdf . 2013-03-06 . 20 October 2002 . 24 March 2011.
    42. Book: http://www.nap.edu/openbook.php?record_id=11937&page=95 . 7 Planetary Protection for Mars Missions . free . An Astrobiology Strategy for the Exploration of Mars . The National Academies Press . 2007 . 10.17226/11937 . 978-0-309-10851-5 . 12 June 2015 . live . https://web.archive.org/web/20150911082501/http://www.nap.edu/openbook.php?record_id=11937&page=95 . Sep 11, 2015 .
    43. Web site: When Biospheres Collide – a history of NASA's Planetary Protection Programs . Michael . Meltzer . May 31, 2012 . Chapter 7, "Return to Mars" – final section: "Should we do away with human missions to sensitive targets" . NASA . live . https://web.archive.org/web/20221017114212/http://www.nasa.gov/connect/ebooks/when_biospheres_collide_detail.html . Oct 17, 2022 .
    44. Web site: Rummel . J. D. . Race . M. S. . Kminek . G. . 2015 . Planetary Protection Knowledge Gaps for Human Extraterrestrial Missions . live . https://web.archive.org/web/20231108213826/https://www.hou.usra.edu/meetings/ppw2015/pdf/1010.pdf . Nov 8, 2023.
    45. Book: http://www.nap.edu/openbook.php?record_id=10360&page=37 . 37 . free . 10.17226/10360 . 5. Potential Hazards of the Biological Environment . Safe on Mars: Precursor Measurements Necessary to Support Human Operations on the Martian Surface . 2002-05-29 . National Academies Press . 978-0-309-08426-0 . Washington, D.C. . Martian biological contamination may occur if astronauts breathe contaminated dust or if they contact material that is introduced into their habitat. If an astronaut becomes contaminated or infected, it is conceivable that he or she could transmit Martian biological entities or even disease to fellow astronauts, or introduce such entities into the biosphere upon returning to Earth. A contaminated vehicle or item of equipment returned to Earth could also be a source of contamination. . live . https://web.archive.org/web/20150911125821/http://www.nap.edu/openbook.php?record_id=10360&page=38 . Sep 11, 2015 .
    46. News: Wall . Mike . 27 August 2019 . Astronauts Will Face Many Hazards on a Journey to Mars – NASA is trying to bring the various risks down before launching astronauts to Mars in the 2030s. . 27 August 2019 . Space.com.
    47. News: Nasa's Orion spacecraft prepares for launch in first step towards crewed Mars mission . The Guardian . 1 Dec 2014 . . 2014-12-03.
    48. Web site: We're sending humans to Mars! Watch our #JourneytoMars briefing live today at 12pm ET: #Orion . Dec 2, 2014 . NASA . Twitter . 2014-12-02.
    49. Web site: NASA's Orion Flight Test and the Journey to Mars . 2014-12-01 . NASA website . 2014-12-02 . https://web.archive.org/web/20141202072856/http://www.nasa.gov/content/nasas-orion-flight-test-and-the-journey-to-mars/index.html#.VH62pTGVJK8 . dead .
    50. News: Berger . Eric . Why Obama's "giant leap to Mars" is more of a bunny hop right now . . 2016-10-12 . 2016-10-12.
    51. Johnston, Ian. "'Incredibly brave' Mars colonists could live in red-brick houses, say engineers", The Independent (April 27, 2017).
    52. Web site: ExoMars rover . 2023-04-10 . The Planetary Society . en.
    53. Web site: Foust . Jeff . 2022-11-29 . ESA's ExoMars plans depend on NASA contributions . 2023-04-10 . SpaceNews . en-US.
    54. Web site: Coates . Andrew . Decades of attempts show how hard it is to land on Mars – here's how we plan to succeed in 2021 . The Conversation . 2 December 2016 . 24 April 2021.
    55. Web site: Spinning heat shield for future spacecraft . University of Manchester . August 9, 2018 . ScienceDaily . 24 April 2021.
    56. News: Morring. Frank Jr. . NASA, SpaceX Share Data On Supersonic Retropropulsion : Data-sharing deal will help SpaceX land Falcon 9 on Earth and NASA put humans on Mars . subscription . 2014-10-18 . Aviation Week . 2014-10-16 . the requirements for returning a first stage here on the Earth propulsively, and then ... the requirements for landing heavy payloads on Mars, there's a region where the two overlap—are right on top of each other ... If you start with a launch vehicle, and you want to bring it down in a controlled manner, you're going to end up operating that propulsion system in the supersonic regime at the right altitudes to give you Mars-relevant conditions..
    57. News: Mars Ecopoiesis Test Bed. Hall. Loura. 2017-03-24. NASA. 2018-03-05. en . live . https://web.archive.org/web/20200809091435/https://www.nasa.gov/content/mars-ecopoiesis-test-bed/ . Aug 9, 2020 .
    58. Web site: A Solution for Medical Needs and Cramped Quarters in Space IVGEN Undergoes Lifetime Testing in Preparation For Future Missions . NASA . May 10, 2012 . Mike . Giannone . 12 June 2015 . 12 April 2016 . https://web.archive.org/web/20160412152906/http://www.nasa.gov/mission_pages/station/research/news/IVGEN.html . dead .
    59. Web site: The Caves of Mars – Martian Air Breathing Mice . https://web.archive.org/web/20070724100724/http://www.highmars.org/niac/niac02.html . 24 July 2007 . High Mars . Denise . Murphy . 12 June 2015.
    60. Web site: Suiting Up for the Red Planet. IEEE Spectrum . Rachel . Courtland . 30 September 2015 . live . https://web.archive.org/web/20170702054743/https://spectrum.ieee.org/aerospace/space-flight/suiting-up-for-the-red-planet . Jul 2, 2017 .
    61. News: Scoles . Sarah . 27 November 2023 . Mars Needs Insects – If humans are ever going to live on the red planet, they're going to have to bring bugs with them. . subscription . live . https://archive.today/20231128053332/https://www.nytimes.com/2023/11/27/science/mars-needs-insects.html . 28 November 2023 . 28 November 2023 . The New York Times.
    62. Book: Bosanac . Natasha . Manned sample return mission to Phobos: A technology demonstration for human exploration of Mars . Diaz . Ana . Dang . Victor . Ebersohn . Frans . Gonzalez . Stefanie . Qi . Jay . Sweet . Nicholas . Tie . Norris . Valentino . Gianluca . 1 March 2014 . CaltechAUTHORS . 9781479955824 . California . 1–20 . en-us . 10.1109/AERO.2014.6836251 . 3 November 2015 . https://web.archive.org/web/20151022201956/http://authors.library.caltech.edu/59437/ . 22 October 2015 . dead . Fraeman . Abigail . Gibbings . Alison . Maddox . Tyler . Nie . Chris . Rankin . Jamie . Rebelo . Tiago . Taylor . Graeme.
    63. Geoffrey A. Landis, "Footsteps to Mars: an Incremental Approach to Mars Exploration", Journal of the British Interplanetary Society, Vol. 48, pp. 367–342 (1995); presented at Case for Mars V, Boulder Colorado, 26–29 May 1993; appears in From Imagination to Reality: Mars Exploration Studies, R. Zubrin, ed., AAS Science and Technology Series Volume 91, pp. 339–350 (1997).
    64. Larry Page. Deep Space Exploration – Stepping Stones builds up to "Red Rocks: Explore Mars from Deimos".
    65. Web site: One Possible Small Step Toward Mars Landing: A Martian Moon . Space.com . 20 April 2011 . 12 June 2015.
    66. Web site: European Space Agency . Mars Sample Return: bridging robotic and human exploration . Esa.int.
    67. Web site: Jones . S. M. . etal . 2008 . Ground Truth From Mars (2008) – Mars Sample Return at 6 Kilometers per Second: Practical, Low Cost, Low Risk, and Ready . September 30, 2012 . USRA.
    68. Web site: Science Strategy – NASA Solar System Exploration . NASA Solar System Exploration . 2015-11-03 . https://web.archive.org/web/20110721054020/http://solarsystem.nasa.gov/2013decadal/ . 2011-07-21 . dead .
    69. Web site: Mars Sample Return. Esa.int.
    70. Web site: Archived copy . 2015-11-05 . https://web.archive.org/web/20151117020758/http://www.congrexprojects.com/docs/default-source/13c06_docs/session-1-rebuffat.pdf?sfvrsn=0 . 2015-11-17 . dead .
    71. Web site: Next On Mars. Spacedaily.com.
    72. Web site: Touchdown! NASA's Mars Perseverance Rover Safely Lands on Red Planet . 2021-02-19 . NASA's Mars Exploration Program . en-us.
    73. Web site: Launch Windows . 2021-02-19 . mars.nasa.gov . en-us.
    74. Landis . G. A. . 2008 . Teleoperation from Mars Orbit: A Proposal for Human Exploration . Acta Astronautica . 62 . 1 . 59–65 . 2008AcAau..62...59L . 10.1016/j.actaastro.2006.12.049.
      presented as paper IAC-04-IAA.3.7.2.05, 55th International Astronautical Federation Congress, Vancouver, British Columbia, Oct. 4–8, 2004.
    75. M. L. Lupisella, "Human Mars Mission Contamination Issues", Science and the Human Exploration of Mars, January 11–12, 2001, NASA Goddard Space Flight Center, Greenbelt, Maryland. LPI Contribution, number 1089. Accessed 11/15/2012.
    76. George R. Schmidt, Geoffrey A. Landis, and Steven R. Oleson NASA Glenn Research Center, Cleveland, Ohio, 44135, HERRO Missions to Mars and Venus using Telerobotic Surface Exploration from Orbit, . 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition. 4–7 January 2010, Orlando, Florida.
    77. 1 of 4 Geoffrey Landis – HERRO TeleRobotic Exploration of Mars – Mars Society 2010 . en . 2024-05-13 . www.youtube.com.
    78. Web site: Time delay between Mars and Earth – Mars Express . 2024-05-13 . en-US.
    79. Web site: Marpost . 2024-05-13 . www.astronautix.com.