Human mission to Mars

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NASA concept of the first humans on Mars, with a habitat and rover, 2019
NASA concept of the first humans on Mars, with a habitat and rover, 2019
Photo of the Martian surface, 2018
Concept for a Mars base, with ice home, pressurized rover, and Mars suits, 2016
Concept for a spacecraft capable of transporting a crew to Mars, 2004

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. Some have also considered exploring the Martian moons of Phobos and Deimos.[1] Long-term proposals have included sending settlers and terraforming the planet. Proposals for human missions to Mars came from e.g. NASA, Russia, Boeing, SpaceX, and the Inspiration Mars Foundation. As of 2022, only rovers have been on Mars. The farthest humans have been beyond Earth is the Moon.

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.[2] 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).[citation needed] By 2020, virtual visits to Mars, using haptic technologies, had also been proposed.[3]

Meanwhile, the unmanned 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. Andy Weir's 2011 novel The Martian and its popular 2015 film adaptation were a successful hard science fiction take on the concept.

Travel to Mars[edit]

The minimum distance between the orbits of Mars and Earth from 2014 to 2061, measured in astronomical units

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.[4] The next low-energy launch period occurs in 2033.[6]

Several types of mission plans have been proposed, including opposition class and conjunction class,[5] 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 500 days (16 mo) 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 245 days (8.0 months) 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]

Three views of Mars, Hubble Space Telescope, 1997

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.[14] (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[edit]

Insets depict observation and analysis to find a safe landing site

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

Orbital capture[edit]

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[edit]

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 and 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]


The largest limiting factor for sending humans to Mars is funding. In 2010, the estimated cost was roughly US$500 billion, though the actual costs are likely to be more.[18] Starting in the late 1950s, the early phase of space exploration was conducted as much to make a political statement as to make observations of the solar system. However, this proved to be both wasteful and 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.[citation needed]

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.[18]

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 many homes (in Western and developed countries) for the purpose of entertainment such as computer games, and booking travel/leisure tickets, the computing power of home devices skyrocketed and prices plummeted.[19]


Comparison of radiation doses – includes the amount detected on the trip from Earth to Mars by the RAD inside the MSL (2011–2013).[20][21][22] Vertical axis is in logarithmic scale, so the dose over a Mars year is about 15 times the DOE limit, not less than twice, as a quick glance might suggest. The actual dose would depend on factors such as spacecraft design and natural events such as solar flares.

Several key physical challenges exist for human missions to Mars:[23]

Artistic vision of spacecraft providing artificial gravity by spinning. (see also Centrifugal force)
  • Psychological effects of isolation from Earth and, by extension, the lack of community due to lack of a real-time connection with Earth (Compare Hermit)
  • Social effects of several humans living under cramped conditions for more than one Earth year, and possibly two or three years, depending on spacecraft and mission design
  • Lack of medical facilities
  • Potential failure of propulsion or life-support equipment

Some of these issues were estimated statistically in the HUMEX study.[36] Ehlmann and others have reviewed political and economic concerns, as well as technological and biological feasibility aspects.[37] 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 mature technology.[38]

Planetary protection[edit]

Robotic spacecraft to Mars are currently 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.[39][40] Otherwise there is a risk of contaminating not only the life-detection experiments but possibly the planet itself.[41]

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).[42] There have been several planetary workshops on this issue, but with no final guidelines for a way forward yet.[43] Human explorers would also be vulnerable to back contamination to Earth if they become carriers of microorganisms.[44]

Mission proposals[edit]

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.

20th century[edit]

Fuel is mined from Phobos with the help of a nuclear reactor.[45]

Over the last century, a number of mission concepts for such an expedition have been proposed. David Portree's history volume Humans to Mars: Fifty Years of Mission Planning, 1950–2000 discusses many of these.[4]

Wernher von Braun proposal (1947 through 1950s)[edit]

Wernher von Braun was the first person to make a detailed technical study of a Mars mission.[4][46] Details were published in his book Das Marsprojekt (1952, published in English as The Mars Project in 1962[47]) and several subsequent works.[48] Willy Ley popularized a similar mission in English in the book The Conquest of Space (1949), featuring illustrations by Chesley Bonestell. Von Braun's Mars project envisioned nearly a thousand three-stage vehicles launching from Earth to ferry parts for the Mars mission to be constructed at a space station in Earth orbit.[46][49] The mission itself featured a fleet of ten spacecraft with a combined crew of 70 heading to Mars, bringing three winged surface excursion ships that would land horizontally on the surface of Mars. (Winged landing was considered possible because at the time of his proposal, the Martian atmosphere was believed to be much denser than was later found to be the case.)

In the 1956 revised vision of the Mars Project plan, published in the book The Exploration of Mars by Wernher Von Braun and Willy Ley, the size of the mission was trimmed, requiring only 400 launches to put together two ships, still carrying a winged landing vehicle.[50] Later versions of the mission proposal, featured in the Disney "Man In Space" film series,[51] showed nuclear-powered ion-propulsion vehicles for the interplanetary cruise.

U.S. proposals (1950s to 1970s)[edit]

Artist's conception of the Mars Excursion Module (MEM) proposed in a NASA study in 1963. Crew wear Mars suits on surface EVA from the module.

From 1957 to 1965, work was done by General Atomics on Project Orion, a proposal for a nuclear pulse propulsion spacecraft. Orion was intended to have the ability to transport extremely large payloads compared to chemical rocketry, making crewed missions to Mars and the outer planets feasible. One of the early vehicle designs was intended to send an 800-ton payload to Mars orbit. The Partial Nuclear Test Ban Treaty of 1963 made further development unviable, and work ended in 1965.[52]

In 1962, Aeronutronic Ford,[53] General Dynamics and the Lockheed Missiles and Space Company made studies of Mars mission designs as part of NASA Marshall Spaceflight Center "Project EMPIRE".[46] These studies indicated that a Mars mission (possibly including a Mercury and Venus fly-by) could be done with a launch of eight Saturn V boosters and assembly in low Earth orbit, or possibly with a single launch of a hypothetical "post Saturn" heavy-lift vehicle. Although the EMPIRE missions were never proposed for funding, they were the first detailed analyses of what it would take to accomplish a human voyage to Mars using data from actual NASA spaceflight, laying the basis for future studies, including significant mission studies by TRW, North American, Philco, Lockheed, Douglas, and General Dynamics, along with several in-house NASA studies.[46]

Following the success of the Apollo Program, von Braun advocated a crewed mission to Mars as a focus for NASA's crewed space program.[54] Von Braun's proposal used Saturn V boosters to launch NERVA-powered upper stages that would propel two six-crew spacecraft on a dual mission in the early 1980s. The proposal was considered by President Richard Nixon, but passed over in favor of the Space Shuttle.

In 1975, von Braun discussed the mission architecture that emerged from these Apollo-era studies in a recorded lecture, and while doing so suggested that multiple shuttle launches could instead be configured to lift the two nuclear thermal rocket engine-equipped spacecraft in smaller parts, for assembly in orbit.[55]

Soviet mission proposals (1956 through 1969)[edit]

The Martian Piloted Complex (MPK) was a proposal by Mikhail Tikhonravov of the Soviet Union for a crewed Mars expedition, using the (then-proposed) N1 rocket, in studies from 1956 to 1962. The Soviets sent many probes to Mars with some noted success stories, including Mars atmospheric entry, but the overall rate of success was low.[citation needed] (see Mars 3)

Heavy Interplanetary Spacecraft (known by the Russian acronym TMK) was the designation of a Soviet space exploration proposal in the 1960s to send a crewed flight to Mars and Venus (TMK-MAVR design) without landing. The TMK spacecraft was due to launch in 1971 and make a 3-year-long flight including a Mars fly-by, at which time probes would have been dropped. The project was never completed because the required N1 rocket never flew successfully. The Mars Expeditionary Complex, or "'MEK"' (1969) was another Soviet proposal for a Mars expedition that would take a crew from three to six to Mars and back with a total mission duration of 630 days.

Case for Mars (1981–1996)[edit]

Following the Viking missions to Mars, between 1981 and 1996, several conferences named the Case for Mars were held at the University of Colorado at Boulder. These conferences advocated human exploration of Mars, presented concepts and technologies, and held a series of workshops to develop a baseline concept for the mission. It proposed use of in-situ resource utilization to manufacture rocket propellant for the return trip. The mission study was published in a series of proceedings volumes.[56][57] Later conferences presented alternative concepts, including the "Mars Direct" concept of Robert Zubrin and David Baker; the "Footsteps to Mars" proposal of Geoffrey A. Landis,[58] which proposed intermediate steps before the landing on Mars, including human missions to Phobos; and the "Great Exploration" proposal from Lawrence Livermore National Laboratory, among others.

NASA Space Exploration Initiative (1989)[edit]

Artist's conception of a human mission on the surface of Mars
(1989 painting by Les Bossinas of Lewis Research Center for NASA)

In response to a presidential initiative, NASA made a study of a project for human lunar- and Mars exploration as a proposed follow-on to the International Space Station. This resulted in a report, called the 90-day study,[59] in which the agency proposed a long-term plan consisting of completing the Space Station as "a critical next step in all our space endeavors," returning to the Moon and establishing a permanent base, and then sending astronauts to Mars. This report was widely criticized as too elaborate and expensive, and all funding for human exploration beyond Earth orbit was canceled by Congress.[60]

Mars Direct (early 1990s)[edit]

Because of the greater distance, the Mars mission would be much more risky and expensive than past Moon flights. Supplies and fuel would have to be prepared for a 2- to 3-year round trip and the spacecraft would need at least partial shielding from ionizing radiation. A 1990 paper by Robert Zubrin and David A. Baker, then of Martin Marietta, proposed reducing the mission mass (and hence the cost) by using in situ resource utilization to manufacture propellant from the Martian atmosphere.[61][62] This proposal drew on concepts developed by the former "Case for Mars" conference series. Over the next decade, Zubrin developed it into a mission concept, Mars Direct, which he presented in a book, The Case for Mars (1996). The mission is advocated by the Mars Society, which Zubrin founded in 1998, as practical and affordable.

International Space University (1991)[edit]

In 1991 in Toulouse, France, the International Space University studied an international human Mars mission.[63] They proposed a crew of 8 traveling to Mars in a nuclear-powered vessel with artificial gravity provided by rotation.[63] On the surface, 40-tonne habitats pressurized to 10 psi (69 kPa) were powered by a 40 kW photovoltaic array.[63]

NASA Design reference missions (1990s)[edit]

NASA Mars habitat concept for DRA 1.0, derived from the Mars Direct Architecture, 1995

In the 1990s, NASA developed several conceptual-level human Mars exploration architectures. One of these was NASA Design reference mission 3.0 (DRM 3.0) to stimulate further thought and concept development.

Selected other US/NASA studies (1988–2009):[64]

  1. 1988 "Mars Expedition"
  2. 1989 "Mars Evolution"
  3. 1990 "90-Day Study"
  4. 1991 "Synthesis Group"
  5. 1995 "DRM 1"
  6. 1997 "DRM 3"[65]
  7. 1998 "DRM 4"
  8. 1999 "Dual Landers"

21st century[edit]

Artist's concept of crew members setting up weather monitoring equipment on the surface of Mars

NASA Design reference missions (2000+)[edit]

The NASA Mars Design Reference Missions consisted of a series of conceptual design studies for human Mars missions, continued in the 21st century. Selected other US/NASA plans (1988–2009):[64]

  1. 2000 SERT (SSP)
  2. 2001 DPT/NEXT
  3. 2002 NEP Art. Gravity
  4. 2009 DRA 5[66]

MARPOST (2000–2005)[edit]

The Mars Piloted Orbital Station (MARPOST) is a Russian-proposed crewed orbital mission to Mars, using a nuclear reactor to run an electric rocket engine. Proposed in October 2000 as the next step for Russia in space along with participation in the International Space Station, a 30-volume draft project for MARPOST was confirmed as of 2005.[67] Design for the ship was proposed to be ready in 2012, and the ship itself in 2021.[68]

ESA Aurora programme (2001+)[edit]

Artwork featuring astronauts enduring a Mars dust storm near a rover

In 2001, the European Space Agency (ESA) laid out a long-term vision of sending a human mission to Mars in 2033.[69] The project's proposed timeline would begin with robotic exploration, a proof of concept simulation of sustaining humans on Mars, and eventually a crewed mission. Objections from the participating nations of ESA and other delays have put the timeline into question, and currently ExoMars, delivered an orbiter to Mars in 2016, have come to fruition.

ESA/Russia plan (2002)[edit]

Another proposal for a joint ESA mission with Russia is based on two spacecraft being sent to Mars, one carrying a six-person crew and the other the expedition's supplies. The mission would take about 440 days to complete, with three astronauts visiting the surface of the planet for a period of two months. The entire project would cost $20 billion and Russia would contribute 30% of these funds.[70]

USA Vision for Space Exploration (2004)[edit]

On 14 January 2004, George W. Bush announced the Vision for Space Exploration, an initiative of crewed space exploration. It included developing preliminary plans for a return to the Moon by 2012[71] and establishing an outpost by 2020. By 2005, precursor missions that would help develop the needed technology during the 2010s were tentatively outlined.[72] On 24 September 2007, Michael Griffin, then NASA Administrator, hinted that NASA would be able to launch a human mission to Mars by 2037.[73] The needed funds were to be generated by diverting $11 billion[74] from space science missions to the vision for human exploration.

NASA has also discussed plans to launch Mars missions from the Moon to reduce traveling costs.[75]

Mars Society Germany – European Mars Mission (EMM) (2005)[edit]

The Mars Society Germany proposed a crewed Mars mission using several launches of an improved heavy-lift version of the Ariane 5. Roughly five launches would be required to send a crew of five on a 1200-day mission, with a payload of 120,000 kg (260,000 lb). Total project cost was estimated to be 10 to 15 billion euros.[76]

China National Space Administration (CNSA) (2006)[edit]

Sun Laiyan, administrator of the China National Space Administration, said on July 20, 2006, that China would start deep-space exploration focusing on Mars over the next five years, during the Eleventh Five-Year Plan (2006–2010) program period.[77] The first uncrewed Mars exploration program could take place between 2014 and 2033, followed by a crewed phase in 2040–2060 in which crew members would land on Mars and return home.[78] The Mars 500 study of 2011 prepared for this crewed mission.

Mars to Stay (2006)[edit]

The idea of a one-way trip to Mars has been proposed several times. In 1988, space activist Bruce Mackenzie proposed a one-way trip to Mars in a presentation at the International Space Development Conference,[79] arguing that the mission could be done with less difficulty and expense without a return to Earth. In 2006, former NASA engineer James C. McLane III proposed a scheme to initially colonize Mars via a one-way trip by only one human. Papers discussing this concept appeared in The Space Review,[80] Harper's Magazine,[81] SEARCH Magazine[82] and The New York Times.[83]

NASA Design Reference Mission 5.0 (2007)[edit]

NASA released initial details of the latest version conceptual level human Mars exploration architecture in this presentation. The study further developed concepts developed in previous NASA DRM and updated it to more current launchers and technology.

Martian Frontier (2007–2011)[edit]

Mars 500, the longest high-fidelity spaceflight simulation, ran from 2007 to 2011 in Russia, and was an experiment to assess the feasibility of crewed missions to Mars.[84]

NASA Design Reference Mission Architecture 5.0 (2009)[edit]

Concept for NASA's Design Reference Mission Architecture 5.0 (2009)

NASA released an updated version of NASA DRM 5.0 in early 2009, featuring use of the Ares V launcher, Orion CEV, and updated mission planning. In this document.[85]

NASA Austere Human Missions to Mars (2009)[edit]

Extrapolated from the DRMA 5.0, plans for a crewed Mars expedition with chemical propulsion. Austere Human Missions to Mars

Mars orbit by the mid-2030s (2010)[edit]

In a major space policy speech at Kennedy Space Center on 15 April 2010, Barack Obama predicted a crewed Mars mission to orbit the planet by the mid-2030s, followed by a landing. This proposal was mostly supported by Congress, which approved cancelling Project Constellation in favor of a 2025 Asteroid Redirect Mission and orbiting Mars in the 2030s.[86] The Asteroid Redirect Mission was cancelled in June 2017 and "closed out" in September of the same year.[citation needed]

Russian mission proposals (2011)[edit]

Several Mars mission concepts and proposals have been put forth by Russian scientists. Stated dates were for a launch sometime between 2016 and 2020. The Mars probe would carry a crew of four or five cosmonauts, who would spend close to two years in space.[citation needed]

In late 2011, Russian and European space agencies successfully completed the ground-based MARS-500.[87] The biomedical experiment simulating crewed flight to Mars was completed in Russia in July 2000.[88]

2-4-2 concept (2011–2012)[edit]

In 2012, Jean-Marc Salotti published a new proposal for a crewed Mars mission. The '2-4-2' concept is based on a reduction of the crew size to two astronauts and the duplication of the entire mission. Two astronauts are in each space vehicle, four are on the surface of Mars, and two are once again in each return vehicle. If one set of hardware runs into trouble, the other astronauts are ready to help (two for two). This architecture simplifies the entry, descent, and landing procedures by reducing the size of the landing vehicles. It also avoids the assembly of huge vehicles in LEO. The author claims that his proposal is much cheaper than the NASA reference mission without compromising the risks and can be undertaken before 2030.[89][90]

Boeing Conceptual Space Vehicle Architecture (2012)[edit]

In 2012, a conceptual architecture was published by Boeing, United Launch Alliance, and RAL Space in Britain, laying out a possible design for a crewed Mars mission. Components of the architecture include various spacecraft for the Earth-to-Mars journey, landing, and surface stay, as well as return. Some features include several uncrewed cargo landers assembled into a base on the surface of Mars. The crew would land at this base in the "Mars Personnel Lander", which could also take them back into Mars orbit. The design for the crewed interplanetary spacecraft included artificial gravity and an artificial magnetic field for radiation protection. Overall, the architecture was modular to allow for incremental R&D.[91]

Mars One (2012-2019)[edit]

In 2012, a Dutch entrepreneur group began raising funds for a human Mars base to be established in 2023.[92] The mission was intended to be primarily a one-way trip to Mars. Astronaut applications were invited from the public all over the world, for a fee.

The initial concept included an orbiter and small robotic lander in 2018, followed by a rover in 2020, and the base components in 2024.[92] The first crew of four astronauts was to land on Mars in 2025. Then, every two years, a new crew of four would arrive. Financing was intended to come from selling the broadcasting rights of the entire training and of the flight as a reality television show, and that money would be used to contract for all hardware and launch services. In April 2015, Mars One's CEO Bas Lansdorp admitted that their 12-year plan for landing humans on Mars by 2027 is "mostly fiction".[93] The company comprising the commercial arm of Mars One went bankrupt in January 2019.[94]

Inspiration Mars Foundation (2013)[edit]

In 2013, the Inspiration Mars Foundation founded by Dennis Tito revealed plans of a crewed mission to fly by Mars in 2018 with support from NASA.[95][96] NASA refused to fund the mission.

Boeing Affordable Mission (2014)[edit]

On December 2, 2014, NASA's Advanced Human Exploration Systems and Operations Mission Director Jason Crusan and Deputy Associate Administrator for Programs James Reuthner announced tentative support for the Boeing "Affordable Mars Mission Design"[clarification needed] including radiation shielding, centrifugal artificial gravity, in-transit consumable resupply, and a lander which can return.[97][98] Reuthner suggested that if adequate funding was forthcoming, the proposed mission would be expected in the early 2030s.[99]

Mars Semi-Direct Revisited (2016)[edit]

As the Earth Return Vehicle was deemed very heavy, Robert Zubrin proposed in 1993 a "semi-direct" scenario, in which the outbound trip is still direct to the surface but the return is split into two steps, first going back to Mars orbit using a relatively small ascent vehicle in order to join a return vehicle that is sent there a long time in advance. As the return is not direct anymore, the scenario is called "semi-direct". In 2016, Jean-Marc Salotti made new calculations and revisited the architecture of the mission, showing that 4 heavy launches of the heaviest version of the NASA Space Launch System would be sufficient for its implementation[100]

NASA's Journey to Mars and Moon to Mars Programs (2015–present)[edit]

Artist's rendering of SLS Block 1/Orion

On October 8, 2015, NASA published its strategy for human exploration and sustained human presence on Mars. The concept operates through three distinct phases leading up to sustainable human presence.[101]

The first stage, already underway,[when?] is the "Earth Reliant" phase, which continues using the International Space Station until 2024, validating deep space technologies and studying the effects of long-duration space missions on the human body.[citation needed][102]

The second stage, "Proving Ground", moves away from Earth reliance and ventures into cislunar space for most of its tasks. The proposed Lunar Gateway would test deep-space habitation facilities, and validate capabilities required for human exploration of Mars.[103]

Finally, phase three is the transition to independence from Earth resources. The "Earth Independent" phase includes long-term missions on the Martian surface with habitats that only require routine maintenance, and the harvesting of Martian resources for fuel, water, and building materials. NASA is still aiming for human missions to Mars in the 2030s, though Earth independence could take decades longer.[104]

In November 2015, Administrator Bolden of NASA reaffirmed the goal of sending humans to Mars.[105] He laid out 2030 as the date of a crewed surface landing on Mars, and noted that the 2021 Mars rover, Perseverance would support the human mission.[105]

In March 2019, Vice President Mike Pence declared, "American astronauts will walk on the Moon again before the end of 2024, 'by any means necessary'."[106] This reportedly prompted NASA to accelerate their plans to return to the Moon's surface by 2024. NASA says it will use the Artemis lunar program in combination with the Lunar Gateway as stepping stones to make great scientific strides "to take the next giant leap - sending astronauts to Mars".[107]

SpaceX Mars transportation infrastructure (2016–present)[edit]

In 2016, SpaceX announced that it planned to send a Red Dragon capsule for a soft landing on Mars by 2018,[108] but they halted the effort by mid-2017 in order to focus engineering resources to the effort that would later become known as "Starship."[109]

SpaceX has publicly proposed a plan to begin the colonization of Mars by developing a high-capacity transportation infrastructure. As discussed in 2016, the ITS launch vehicle conceptual design was to be a large reusable booster topped by a spaceship or a tanker for in-orbit refueling.[110] The aspirational objective at that time was to advance the technology and infrastructure such that the first humans to Mars could potentially depart as early as 2024.[111][needs update]

As the top development priority of SpaceX became developing a larger and more capable launch vehicle after 2018, Elon Musk has continued to articulate aspirational plans for early Mars missions as one objective of that program. In September 2017, Musk announced an updated vehicle design for the Mars mission at the International Astronautical Congress. The vehicle for this mission was called BFR (Big Falcon Rocket) until 2018, when it was renamed "Starship".[112][better source needed] Starship is planned to provide the capability for on-orbit activity like satellite delivery, servicing the International Space Station, Moon missions, as well as Mars missions. Cargo flights to Mars would precede crewed flights.

  • As early as 2024, pathfinder Starship cargo vehicles could be sent to Mars.[113]
  • Crewed Starship vehicles would follow, at the earliest in 2026, two years after the first cargo flights.[114]

Mars Base Camp (2016)[edit]

Mars Base Camp is a US spacecraft concept that proposes to send astronauts to Mars orbit as early as 2028. The vehicle concept, developed by Lockheed Martin,[115] would use both future and heritage technology, as well as the Orion spacecraft built by NASA.

Deep Space Transport (2017)[edit]

Artist impression of the Deep Space Transport, about to dock with the Lunar Gateway

The Deep Space Transport (DST), also called Mars Transit Vehicle,[116] is a crewed interplanetary spacecraft concept by NASA to support science exploration missions to Mars of up to 1,000 days.[117][118][119] It would be composed of two elements - an Orion capsule and a propelled habitation module.[120] As of April 2018, the DST is still a concept to be studied, and NASA has not officially proposed the project in an annual U.S. federal government budget cycle.[121][122]

The DST vehicle would depart and return from the Lunar Gateway to be serviced and reused for a new Mars mission.[118][123][124]

Current intentions by nations and space agencies[edit]

Artist's rendering of the planned Orion/DSH/Cryogenic Propulsion Module assembly.

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

  • The United States has several robotic missions currently exploring Mars, with a sample-return planned for the future. The Orion Multi-Purpose Crew Vehicle (MPCV) is intended to serve as the launch/splashdown crew delivery vehicle, with a Deep Space Habitat module providing additional living-space for the 16-month-long journey. The first crewed Mars Mission, which would include sending astronauts to Mars, orbiting Mars, and a return to Earth, is proposed for the 2030s.[2][125][126][127] Technology development for US government missions to Mars is underway, but there is no well-funded approach to bring the conceptual project to completion with human landings on Mars by the mid-2030s, the stated objective.[128] NASA is under presidential orders to land humans on Mars by 2033, and NASA-funded engineers are studying a way to build potential human habitats there by producing bricks from pressurized Martian soil.[129]
  • The ESA has a long-term goal to send humans, but has not yet built a crewed spacecraft. It has sent robotic probes such as ExoMars in 2016 and plans to send the next probe in 2022.
  • Russia plans to send humans in the 2040–2045 timeframe.[130]
  • China plans to send humans in 2033.[131]

Technological innovations and hurdles[edit]

Depiction of plants growing in a Mars base. NASA plans to grow plants for space food.[132]
NASA has stated that robots will prepare an underground base for a human surface mission.[105]

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 with much denser atmosphere, any spacecraft will descend very rapidly to the surface and must be slowed down.[133] Heat shield has to be utilized.[134] 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.[135]

A return mission to Mars will need to land a rocket to carry crew off the surface. Launch requirements mean that this rocket would 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 on Mars will be difficult. Re-entry for a large rocket will be difficult.[citation needed]

In 2014, NASA proposed the Mars Ecopoiesis Test Bed.[136]

Intravenous fluid

One 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.[137]

Advanced resistive exercise device

A person who is inactive for an extended period of time loses strength and muscle and bone mass. Spaceflight conditions are known to cause loss of bone mineral density in astronauts, increasing bone fracture risk. Last mathematical models predict 33% of astronauts will be at risk for osteoporosis during a human mission to Mars.[30] A resistive exercise device similar to ARED would be needed in the spaceship.

Breathing gases

While humans can breathe pure oxygen, usually additional gases such as nitrogen are included in the breathing mix. One possibility is to take in situ nitrogen and argon from the atmosphere of Mars, but they are hard to separate from each other.[138] As a result, a Mars habitat may use 40% argon, 40% nitrogen, and 20% oxygen.[138]

An idea for keeping carbon dioxide out of the breathing air is to use reusable amine-bead carbon dioxide scrubbers.[139] While one carbon dioxide scrubber filters the astronaut's air, the other is vented to the Mars atmosphere.[139]

Precursor missions[edit]

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[edit]

Many Mars mission concepts propose precursor missions to the moons of Mars, for example a sample return mission to the Mars moon Phobos[140] – 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.[58][141][142]

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

Mars sample return missions[edit]

Artist concept of SCIM gathering a sample of the Martian atmosphere
Sample return mission concept

An uncrewed Mars sample return mission (MSR) has sometimes been considered as a precursor to crewed missions to Mars's surface.[143] In 2008, the ESA called a sample return "essential" and said it could bridge the gap between robotic and human missions to Mars.[143] An example of a Mars sample return mission is Sample Collection for Investigation of Mars.[144] Mars sample return was the highest priority Flagship Mission proposed for NASA by the Planetary Decadal Survey 2013–2022: The Future of Planetary Science.[145] However, such missions have been hampered by complexity and expense, with one ESA proposal involving no less than five different uncrewed spacecraft.[146]

Sample return plans raise the concern, however remote, that an infectious agent could be brought to Earth.[146] 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.)[147]

At the dawn of the 21st century, NASA crafted four potential pathways to Mars human missions,[148] of which three included a Mars sample return as a prerequisite to human landing.[148]

Currently, the rover Perseverance is equipped with a device that will allow it to pick up and seal samples of rock from Mars, to be returned at a later date by another mission. Perseverance as part of the Mars 2020 mission was launched on top of an Atlas V rocket on 30 July 2020 at (11:50 UTC).[149] Confirmation that the rover had landed on Mars was received on 18 February 2021 at 20:55 UTC.[150]

Crewed orbital missions[edit]

Starting in 2004, NASA scientists have proposed to explore Mars via telepresence from human astronauts in orbit.[151][152]

A similar idea was the proposed "Human Exploration using Real-time Robotic Operations" mission.[153][154]

See also[edit]


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Further reading[edit]

External links[edit]