Human mission to Mars

Crewmembers setting up weather monitoring equipment on the surface of Mars (artist's concept).

A human mission to Mars has been the subject of science fiction, engineering, and scientific proposals since the 19th century. The plans comprise proposals to land on Mars, eventually settling on and terraforming the planet, while utilizing its moons, Phobos and Deimos.

The exploration of Mars has been a goal of national space programs for decades. Preliminary work for missions that would involve human explorers has been undertaken since the 1950s, with planned missions typically being cited as taking place 10 to 30 years in the future when they are drafted. The list of manned Mars mission plans in the 20th century shows the various mission proposals that have been put forth by multiple organizations and space agencies in this field of space exploration. Nonetheless, a human mission to Mars has been criticized for minimizing the "harsh realities and bitter truths that underlie the dream".

In terms of the current U.S. space program, NASA's long-term program Orion has a projected pace of development such that, as of late 2014, human spaceflight to Mars is anticipated in about 2035. That mission will be preceded by shorter flights for the up to four-person capsule involved, with experiments taking place to better the technologies protecting Mars-bound astronauts from the radiation of deep space. In October 2015, NASA presented the next steps in the effort in more detail, as well as a related health hazards report.

In fiction, the concept of humans traveling to and terraforming Mars has been explored in books, graphic novels, and films. Examples include: Robinson Crusoe on Mars (1964 film), Total Recall (1990 film), Kim Stanley Robinson's Mars trilogy (1993-1996), Mission to Mars (2000 film), Red Planet (2000 film), Doctor Who's The Waters of Mars (2009 TV episode) and The Martian (2015 film and 2011 book). The appeal of space-travel to the planet is a major aspect to Mars in fiction.

Travel to Mars

Three views of planet Mars, the "red planet"

Closest approaches of Mars to Earth, 2014-2061. Communication times are slightly shorter when it is closest.

The energy needed for transfer between planetary orbits, or "∆V", is lowest at intervals fixed by the synodic period. For Earth / Mars trips, this is every 26 months (2 years and 2 months), so missions are typically planned to coincide with one of these launch windows. The energy needed in the low-energy windows varies on roughly a 15-year cycle with the easiest windows needing only half the energy of the peaks. In the 20th century, there was a minimum in the 1969 and 1971 launch windows and another low in 1986 and 1988, then the cycle repeated.

Several types of mission plans have been proposed, such as the opposition class and conjunction class, or the Crocco flyby. The lowest energy transfer to Mars is a Hohmann transfer orbit; a mission to Mars using Hohman transfer involves an approximately 9 month travel time from Earth to Mars, about five hundred days at Mars to wait for the transfer window to Earth, and a Hohmann transfer of about 9 months to return to Earth.

Shorter Mars mission plans have round-trip flight times of 400 to 450 days, but requiring a higher energy. A fast Mars mission of 245 days round trip could be possible with on-orbit staging. In 2014 Ballistic capture was proposed, which may reduce fuel cost and provide more flexible launch windows compared to the Hohmann.

In the Crocco grand tour, a "humanned" spacecraft would get a flyby of Mars and Venus for under a year in space. Some flyby mission architectures can also be extended to include a style of Mars landing with a flyby excursion lander spacecraft. Proposed by R. Titus in 1966, it involved extending a flyby mission with a short stay lander. Basically, a short stay lander-ascent vehicle would separate from a "parent" Earth-Mars transfer prior to its flyby of Mars. The Ascent-Decent 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)

Challenges

Comparison of radiation doses - includes the amount detected on the trip from Earth to Mars by the RAD inside the MSL (2011 - 2013). The 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 a number of factors such as design of the spacecraft and natural events such as Solar flares.

Logistical

The estimated cost of sending humans to the red planet is roughly 500 billion U.S. dollars, though the actual costs are likely to be more. The largest limiting factor for sending humans to Mars is funding. In the late 1950s, rivalry between the Soviet Union and the United States stimulated a national priority to send humans to the moon. Under the current global geopolitical climate, however, government funding of these programs has decreased. Recent participation of private companies in space travel and participation by new nations such as India may present new opportunities.

While scientists and space experts understand the value in sending humans to Mars, critics argue the immediate benefits of establishing a human presence on Mars are more esoteric than practical. Yet proponents of human space exploration contend that while the short term benefits will be academic, the symbolism of establishing a presence in space may garner public interest to join the cause and spark global cooperation. Furthermore, experts maintain that a long-term investment will be necessary for humanity’s survival.

In the artistic vision, the spacecraft provides artificial gravity by spinning. (see also Centrifugal force)

Physical

There are several key physical challenges for human missions to Mars:

• Health threats from exposure to high-energy cosmic rays and other ionizing radiation. In May 2013, NASA scientists reported that a possible mission to Mars may involve a great radiation risk based on the amount of energetic particle radiation detected by the RAD on the Mars Science Laboratory while traveling from the Earth to Mars in 2011-2012. The calculated radiation dose was 0.66 sieverts round-trip. The agency's career radiation limit for astronauts is 1 sievert.
• Negative effects of a prolonged weightlessness environment on human health, including eyesight visual impairment. (Depends on mission and spacecraft design)
• Psychological effects of isolation from Earth and, by extension, the lack of community due to impossibility of real-time connections with Earth. (compare Hermit)
• Social effects of several humans living under crowded conditions for more than one Earth year, possibly two or three years, on the mission to Mars, and a comparable length of time on the return to Earth. (Depends on spacecraft and mission design)
• Inaccessibility of terrestrial medical facilities.
• Potential failure of propulsion or life-support equipment.
• Forward contamination of potential habitable zones.
• Back contamination of Earth with possible Martian microbes. (Depends on mission design)
• Development of proper equipment to allow safe locomotion in a low gravity environment (See Locomotion in Space)

Some of these issues were estimated statistically in the HUMEX study. Ehlmann and others have reviewed political and economic concerns, as well as technological and biological feasibility aspects. 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.

Mission proposals

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

20th century

Main article: List of manned Mars mission plans in the 20th century

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.

Wernher von Braun proposal (1947 through 1950s)

Wernher von Braun was the first person to make a detailed technical study of a Mars mission. Details were published in his book Das Marsprojekt (1952, published in English as The Mars Project in 1962) and several subsequent works, and featured in Collier's magazine in a series of articles beginning March 1952. A variant of the Von Braun mission concept was popularized in English by Willy Ley 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. 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. Later versions of the mission proposal, featured in the Disney "Man In Space" film series, showed nuclear-powered ion-propulsion vehicles for the interplanetary cruise.

U.S. proposals (1950s, 1960s, and 1970s)

Artist's conception of the Mars Excursion Module (MEM) proposed in a NASA study in 1963.

File:VenusFlybyCutaway.jpg

Apollo era interplanetary spacecraft

In 1962, Aeronutronic Ford, General Dynamics and the Lockheed Missiles and Space Company made studies of Mars mission designs as part of NASA Marshall Spaceflight Center "Project EMPIRE". These studies indicated that a Mars mission (possibly including a 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 only studies, and never proposed as funded projects, these were the first detailed analyses of what it would take to accomplish a human voyage to Mars using data from actual NASA spaceflight, and laid much of 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.

Following the success of the Apollo Program, von Braun advocated a manned mission to Mars as a focus for NASA's manned space program. Von Braun's proposal used Saturn V boosters to launch nuclear-powered (NERVA) upper stages that would power two six-crew spacecraft on a dual mission in the early 1980s. The proposal was considered by (then 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 spacecrafts in smaller parts, for assembly in-orbit.

Soviet mission proposals (1956 through 1969)

Main articles: Martian Piloted Complex and TMK

The Martian Piloted Complex or "'MPK'" was a proposal by Mikhail Tikhonravov of the Soviet Union for a manned Mars expedition, using the (then proposed) N-1 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 ratio was low and their space program struggled through disasters like the lost Salyut 1 crew and explosions of their N-1 rocket (see Mars 3)

Heavy Interplanetary Spacecraft (known by the Russian acronym TMK) was the designation of a Soviet Union space exploration proposal in the 1960s to send a manned flight to Mars and Venus (TMK-MAVR design) without landing. The TMK spacecraft was due to launch in 1971 and make a three-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)

Following the Viking missions to Mars, between 1981 and 1996 a series of 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. The baseline concept was notable in that it proposed use of in-situ resource utilization to manufacture rocket propellant for the return trip using the resources of Mars. The mission study was published in a series of proceedings volumes published by the American Astronautical Society. Later conferences in the series presented a number of alternative concepts, including the "Mars Direct" concept of Robert Zubrin and David Baker; the "Footsteps to Mars" proposal of Geoffrey A. Landis, 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)

Main article: Space Exploration Initiative

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 project. This resulted in a report, called the 90-day study, 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.

Mars Direct (early 1990s)

Main article: Mars Direct

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

International Space University (1991)

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

NASA Design reference missions (1990s)

Main article: Mars Design Reference Mission

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). It was a study performed by the NASA Mars Exploration Team at the NASA's Johnson Space Center (JSC) in the 1990s. Personnel representing several NASA field centers formulated a "Reference Mission" addressing human exploration of Mars. The plan describes a human mission to Mars with concepts of operations and technologies to be used as a first cut at an architecture. The architecture for the Mars Reference Mission builds on previous work, principally on the work of the Synthesis Group (1991) and Zubrin's (1991) concepts for the use of propellants derived from the Martian atmosphere. The primary purpose of the Reference Mission was to stimulate further thought and development of alternative approaches, which can improve effectiveness, reduce risks, and reduce cost. Improvements can be made at several levels; for example, in the architectural, mission, and system levels.

Selected other US/NASA plans (1988–2009):

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"

7) 1998 "DRM 4"

8) 1999 "Dual Landers"

21st century

NASA Design reference missions (2000+)

Concept for NASA Design Reference Mission Architecture 5.0 (2009)

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):

11) 2000 SERT (SSP)

12) 2002 NEP Art. Gravity

13) 2001 DPT/NEXT

14) 2009 DRA 5

MARPOST (2000–2005)

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

ESA Aurora programme (2001+)

Main article: Aurora programme

The European Space Agency had a long-term vision of sending a human mission to Mars in 2033. Laid out in 2001, the project's proposed timeline would begin with robotic exploration, a proof of concept simulation of sustaining humans on Mars, and eventually a manned mission; however, objections from the participating nations of ESA and other delays have put the timeline into question.

ESA/Russia plan (2002)

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.

USA Vision for Space Exploration (2004)

Main article: Vision for Space Exploration

Project Constellation included an Orion Mars Mission. (then United States President) George W. Bush announced an initiative of manned space exploration on January 14, 2004, known as the Vision for Space Exploration. It included developing preliminary plans for a lunar outpost by 2012 and establishing an outpost by 2020. Precursor missions that would help develop the needed technology during the 2010-2020 decade were tentatively outlined by Adringa and others. On September 24, 2007, Michael Griffin, then NASA Administrator, hinted that NASA may be able to launch a human mission to Mars by 2037. The needed funds were to be generated by diverting $11 billion 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.

Mars Society Germany - European Mars Mission (EMM) (2005)

The Mars Society Germany proposed a manned Mars mission using several launches of an improved heavy-lift version of the Ariane 5. Roughly 5 launches would be required to send a crew of 5 on a 1200 days mission, with a payload of 120,000 kg (260,000 lb).

China National Space Administration (CNSA) (2006)

Main article: Chinese space program § Mission to Mars and beyond

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. The first uncrewed Mars exploration program could take place between 2014–2033, followed by a crewed phase in 2040-2060 in which crew members would land on Mars and return home. The Mars 500 study of 2011 prepared for this manned mission.

The One-Way Trip Option (2006); Mars to Stay (2006)

Main article: Mars to Stay

The idea of a one-way trip to Mars has been proposed several times. Space activist Bruce Mackenzie, for example, proposed a one-way trip to Mars in a presentation "One Way to Mars - a Permanent Settlement on the First Mission" at the 1998 International Space Development Conference, arguing that since the mission could be done with less difficulty and expense if the astronauts were not required to return to Earth, the first mission to Mars should be a settlement, not a visit. 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, Harper's Magazine, SEARCH Magazine and The New York Times.

Mars to Stay proposes that astronauts sent to Mars for the first time should stay there indefinitely, both to reduce mission cost and to ensure permanent settlement of Mars. Among many notable Mars to Stay advocates, former Apollo astronaut Buzz Aldrin is a particularly outspoken promoter who has suggested in numerous forums "Forget the Moon, Let's Head to Mars!" In June 2013, Aldrin wrote an opinion, published in The New York Times, supporting a manned mission to Mars and which viewed the moon "not as a destination but more a point of departure, one that places humankind on a trajectory to homestead Mars and become a two-planet species." In August 2015, Aldrin, in association with the Florida Institute of Technology, presented a "master plan" for NASA consideration proposing astronauts with a "tour of duty of ten years" colonize Mars before the year 2040.

NASA Design Reference Mission 5.0 (2007)

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.

NASA 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.

NASA Austere Human Missions to Mars (2009)

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

USA's Mars orbit by the mid-2030s (2010)

In a major space policy speech at Kennedy Space Center on April 15, 2010, U.S. President Barack Obama predicted a manned Mars mission to orbit the planet by the mid-2030s, followed by a landing:

By the mid-2030s, I believe we can send humans to orbit Mars and return them safely to Earth. And a landing on Mars will follow. And I expect to be around to see it.

The United States Congress has mostly approved a new direction for NASA that includes canceling Bush's planned return to the Moon by 2020 and instead proposes asteroid exploration in 2025 (Asteroid Redirect Mission) and orbiting Mars in the 2030s.

Russian mission proposals (2011)

A number of 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 to five cosmonauts, who would spend close to two years in space.

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

2-4-2 concept (2011–2012)

In 2011, Jean-Marc Salotti published a new proposal for a manned Mars mission, with a release in 2012. The 2-4-2 concept is based on a reduction of the crew size to only 2 astronauts and the duplication of the entire mission. There are 2 astronauts in each space vehicle, there are 4 on the surface of Mars and there are 2 once again in each return vehicle. In addition, at every step of the mission, there are 2 astronauts ready to help the 2 others (2 for 2). This architecture simplifies the entry, descent and landing procedures, which are known to be very risky, thanks to a significant reduction of 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.

Conceptual Space Vehicle Architecture for Human Exploration of Mars (2012)

In 2012, Conceptual Space Vehicle Architecture for Human Exploration of Mars, with Artificial Gravity and Mini-Magnetosphere Crew Radiation Shield was released, laying out a possible design for a human 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 a several unmanned 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 manned interplanetary spacecraft included artificial-gravity and an artificial magnetic field. Overall, the architecture was modular and to allow for incremental R&D.

Mars One (2012)

Main article: Mars One

In 2012, a Dutch entrepreneur group proposed a fund-raising campaign for a human Mars base to begin in 2023. One difference from other projects is that it would be a "one-way" mission, i.e., there will be no return trip to Earth. Astronaut applications were invited from the public all over the world.

In 2018, a telecom orbiter would be sent, a rover in 2020, and after that the base components and its settlers. The base would be powered by 3,000 square meters of solar panels. The SpaceX Heavy rocket would launch flight hardware. The first crew of 4 astronauts would land on Mars in 2025. Then, every two years, a new crew of 4 astronauts would arrive. Current plans specify that the entire mission is to be filmed and broadcast back to Earth as a media event, revenues from which would help fund the program. In April 2015, Lansdorp admitted that their 12-year plan for landing humans on Mars by 2027 is mostly fiction.

Inspiration Mars Foundation (2013)

Main article: Inspiration Mars Foundation

In 2013, the Inspiration Mars Foundation founded by Dennis Tito revealed plans of a manned mission to fly by Mars in 2018 with support from NASA.

Boeing Affordable Mission (2014)

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" including radiation shielding, centrifugal artificial gravity, in-transit consumable resupply, and a lander which can return. Reuthner suggested that if adequate funding was forthcoming, the proposed mission would be expected in the early 2030s.

NASA's Journey to Mars: Pioneering Next Steps in Space Exploration (2015)

Artist's rendering of a Block 1 SLS

On October 8, 2015, NASA published its official plan for human exploration and colonization of Mars. The plan operates through three distinct phases leading up to fully sustained colonization. The first stage, already underway, is the "Earth Reliant" phase. This phase continues utilizing the International Space Station until 2024; validating deep space technologies and studying the effects of long duration space missions on the human body. The second stage, "Proving Ground," moves away from Earth reliance and ventures into cislunar space for most of its tasks. This is when NASA plans to capture an asteroid (planned for 2020), test deep space habitation facilities, and validate capabilities required for human exploration of Mars. Finally, phase three is the transition to independence from Earth resources. The "Earth Independent" phase includes long term missions on the lunar surface which leverage surface 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.

Bolden speech (2015)

In November 2015, the administrator of NASA re-affirmed the goal of sending humans to Mars. He laid out 2030 as the date of a manned surface landing, and noted that planned 2020 Mars rover would be in support of the human mission. Also discussed was the use of robotics to prepare an underground habitat for the arriving people. He noted the advantages of living underground on Mars, especially that it eliminates the need to construct above ground shielding. Top surface activity was not excluded however, just that the crew would "probably live underground for the most part". Living underground on Mars offered many advantages in regards to human survivability. The underground base would be prepared in advance by an armada of robots, robotic precursors to human presence.

Current intentions

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

Planting a U.S. flag on Mars

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

• The United States has a number of robotic missions currently exploring Mars, with a sample-return planned for the future. On December 5, 2014 NASA successfully launched and tested the Orion Multi-Purpose Crew Vehicle (MPCV), the first component of NASA's planned Mars mission program. The Orion MPCV will serve as the launch/splashdown crew delivery vehicle, in combination with a Deep Space Habitat module, which will provide additional living-space for the crew on the 16-month-long journey from Earth to Mars and back. The first manned Mars Mission, which will include sending astronauts to Mars, orbiting Mars, and a return to Earth, is currently scheduled for the 2030s.
• The European Space Agency has long-term goal to send humans but has not yet built a manned spacecraft. It has sent robotic probes, and plans to launch an unmanned ExoMars in 2016 and 2018.

A Soyuz landing on Earth in 2015

• Russia (and previously the Soviet Union) has sent a large number of probes. It can send humans into Earth orbit and has extensive experience with long-term manned orbital space flight due to its space station programs, including Mir and its predecessors. A simulation of a manned Mars mission, called MARS-500, was completed in Russia in November 2011. Its previous missions to Mars, including Mars 96 and Phobos-Grunt were unsuccessful; a budget proposal has been submitted to re-launch Phobos-Grunt in 2024. Russia has shown itself capable of working with other nations in space, especially the United States via such programs as Shuttle-Mir and the International Space Station.
• India successfully placed an unmanned Mars Orbiter Mission (also called Mangalyaan) satellite in Mars orbit on 23 September 2014.
• Japan has sent one robotic mission to Mars, the Nozomi, but it failed to achieve Mars orbit.
• China's mission to Mars, the Yinghuo-1 space probe, was lost with Russia's sample return mission to Phobos, Fobos-Grunt. China claims to have built and tested a functioning EmDrive prototype, which could reduce Mars' interplanetary transit time. The EmDrive spacecraft propulsion technology is also being investigated in the United States, despite it being criticized as pseudoscience.

Technological innovations and hurdles

Depiction of plants growing in a Mars base. NASA plans to grow plants in space to help feed astronauts, in support of pioneering space.

NASA has stated that robots will prepare an underground base for a human surface mission

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 and for a spacecraft of the weight needed to carry humans, along with life support, supplies and other equipment. Should a heat shield be used, it would need to be very large. Retro rockets could be used, but would add significant further weight.

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. Reentry for a large rocket will be difficult.

One of the medical supplies that may be needed is intravenous fluid, which is mostly water but contains other things so it can be added directly to the human blood stream. If it can be created on the spot from existing water then it could spare the weight of hauling earth-produced units, whose weight is mostly water. A prototype for this capability was tested on the International Space Station in 2010.

While it is possible for humans to breathe pure oxygen, a pure oxygen atmosphere was implicated in the Apollo 1 fire. As such, Mars habitats may have a need for additional gases. One possibility is to take nitrogen and argon from the atmosphere of Mars; however, they are hard to separate from each other. As a result, a Mars habitat may use 40% argon, 40% nitrogen, and 20% oxygen.

Another concept for breathing air is to use re-usable amine bead carbon monoxide scrubbers. While one carbon monoxide scrubber filters the astronauts air, the other is vented to the Mars atmosphere.

Precursor 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' moons, or flyby missions.

Manned flyby

An example of this is Inspiration Mars, which could be compared to the Manned Venus Flyby (NASA) mission proposal of the 1970s, but for Mars.

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 - 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.

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

Mars sample return missions

Artist concept of SCIM passing through the Martian atmosphere. This was a simpler sample return architecture that achieved being one of four semi-finalists in the 2002 Mars Scout selection. That mission slot was ultimately won by the Phoenix lander

Sample return mission concept

An unmanned Mars sample return mission (MSR) has sometimes been considered to be an essential precursor to crewed missions to Mars' surface by the 21st century. The ESA noted that a sample return as being essential and 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. Mars sample return was the highest priority Flagship Mission proposed for NASA by the Planetary Decadal Survey 2013-2022: The Future of Planetary Science. However, such missions have been hampered by complexity and expense, with one ESA proposal involving no less than five different unmanned spacecraft.

A difficulty in sample return plans is the concern that, however remote, something could be brought back that could infect life on the Earth. Regardless, a basic set of guidelines for extraterrestrial sample return have been laid out depending on the source of sample (e.g. asteroid, Moon, Mars surface, etc.) Hardware and mission parameters are designed following planetary protection protocols so mission concepts can proceed forward in an orderly way without causing undue concern over remote chances. The issue of sample protection is another factor that increases the difficulty of sample return, both to keep the sample from getting contaminated with Earth material or life, and achieving a rational approach to keeping the Mars sample from "contaminating" Earth.

At the dawn of the 21st century, NASA crafted four potential pathways to Mars human missions. Of those four, three included a Mars sample return as a prerequisite to human landing, however one did not.

Crewed orbital missions

Landis and Lupisella proposed to explore Mars via telepresence from human astronauts in orbit.

A similar idea, was the proposed "Human Exploration using Real-time Robotic Operations" (HERRO) mission.

Another proposed mission was the Russian Mars Piloted Orbital Station.

Cyanobacteria for ecopoiesis and on-site production processes

The Mars Ecopoiesis Test Bed showing its transparent dome to allow for solar heat and photosynthesis, and the cork-screw system to collect and seal Martian soil together with oxygen-producing Earth organisms. Total length is about 7 cm.

In 2014, Techshot, a company based in Greenville, Indiana, worked on a NASA Institute for Advanced Concepts (NIAC) program to develop sealed biodomes that would employ colonies of oxygen-producing cyanobacteria and algae to produce oxygen (O₂) from Martian soil. An initial test, the Mars Ecopoiesis Test Bed, would be done on a small scale on Mars. If the experiment is successful, they will propose building large, closed ecological systems to produce and harvest oxygen for a future human mission to Mars' life support systems. Being able to create oxygen on Mars would provide considerable cost savings to NASA, and allow for longer human visits to Mars than would be possible if astronauts had to transport their own heavy oxygen tanks. This biological process would be isolated in contained areas, and is not intended as a type of global planetary engineering for terraforming of Mars' atmosphere, but NASA states that "This will be the first major leap from laboratory studies into the implementation of experimental (as opposed to analytical) planetary in situ research of greatest interest to planetary biology, ecopoiesis and terraforming." The planetary protection protocols for such a mission, however, would be difficult.

Some scientists suggested a wider role for cyanobacteria in the development of self-sustainable manned outposts on Mars. They propose that cyanobacteria could be used directly for various applications, including the production of food, fuel and oxygen, but also indirectly: products from their culture could support the growth of other organisms, opening the way to a wide range of life-support biological processes based on Martian resources.

See also

• Artificial gravity
• Delta-vs between Earth, Moon and Mars
• Exploration of Mars
• Health threat from cosmic rays
• Human spaceflight
• Interplanetary spaceflight
• Life on Mars
• Mars analog habitat
• Mars Design Reference Mission
• Nuclear propulsion
• Space medicine
• Space weather

External links

• Human Exploration of Mars: The Reference Mission Design Reference Mission 1.0
• Reference Mission Version 3.0, Addedum to Human Exploration of Mars Design Reference Mission 3.0
• Mars Expeditions & Flybys & Selected Flybys List of most manned mission projects to Mars
• a longer bibliography can be found in the bibliography of Portree's book, available in pdf format from NASA.