Manned mission to Mars

Artist's rendering of the proposed Mars Transfer Vehicle that would use NTR propulsion, inflatable habitat technology and the Orion MPCV.

A manned mission to Mars has been the subject of science fiction, engineering and scientific proposals throughout the 20th century and into the 21st century. The plans comprise proposals not only to land on but in the end for settling on and terraforming Mars, while exploiting its moons Phobos and Deimos.

Preliminary work for missions has been undertaken since the 1950s, with planned missions typically taking place 10 to 30 years in the future. 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.

Challenges

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

There are several key challenges that a human mission to Mars must overcome:

1. The health threat from exposure to high-energy cosmic rays and other ionizing radiation.
2. The negative effects of a prolonged low-gravity environment on human health, including eyesight loss.
3. The psychological effects of isolation from Earth and, by extension, the lack of community due to impossibility of real-time connections with Earth.
4. The social effects of several humans living under crowded conditions for over one Earth year.
5. The inaccessibility of terrestrial medical facilities.
6. Possible equipment failure of propulsion or life-support systems.

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 utilizing Martian H₂O (preferably as water ice instead of liquid water) and atmospheric CO₂ with mature technology.

Windows

One of the considerations when traveling to Mars from Earth or vice versa is that the energy needed to transfer between their orbits hits a low point every 26 Earth months (2 years and 2 months). So missions are typically planned to coincide with one of these windows. In addition, the energy needed in the low-energy windows varies on roughly a 15 year cycle. The easiest windows only need 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. However, typical Mars mission plans have round-trip flight times of 400 to 450 days. A fast Mars mission of 245 days round trip could be possible with on-orbit staging. Utillizing Hohmann transfer orbits is a common plan.

20th century proposals

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 (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 and 1960s)

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

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 the 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 NASAs 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.

Soviet mission proposals (1956 through 1970)

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.

Artist's depiction of TMK-MAVR

Heavy Piloted 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 TMK project was planned as an answer from the Soviet Union to the United States manned moon landings. 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 were powered by a 40 kW photovoltaic array.

NASA Design reference missions (1990s)

Main article: Design reference mission 3.0

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”

9) 1989 Zubrin, et.al*

10) 1994-99 Borowski, et. al

11) 2000 SERT (SSP)

12) 2002 NEP Art. Gravity

13) 2001 DPT/NEXT

14) 2009 DRA 5

21st century proposals

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 has been confirmed as of 2005. Design for the ship 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

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 travelling costs.

Project Constellation included an Orion Mars Mission.

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 taikonauts 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)

Since returning the astronauts from the surface of Mars is one of the most difficult parts of a Mars mission, 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!"

Main article: Mars to Stay

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.

MarsDrive mission design (2008)

The MarsDrive Organization has been working at a series of new human mission designs starting with Mars for Less. Their current design program under Director of Engineering Ron Cordes has discarded many of the Mars for Less elements and was reviewed as MarsDrive DRM 2.5 in June 2008. Some of their design philosophy is focused on using current or near term existing launch vehicle systems, permanent human settlement, conceptual EDL systems and enhanced surface ISRU. Their current design in 2012 is titled "Ready For Mars" and focuses on use of small Viking heritage landers to solve the Entry, Descent and Landing challenge. Their proposed methods of funding the mission are also an alternative to the current government funded plans with a private consortium approach being investigated.

NASA Design Reference Mission Architecture 5.0 (2009)

DRMA 5.0 "commuter" Mars base, Chemical Propulsion Option(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 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.^{[citation needed]}

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.

NASA/SpaceX 'Red Dragon' (2012)

Main article: Red Dragon (spacecraft)

Red Dragon is a proposed concept for a low-cost Mars lander mission that would utilize a SpaceX Falcon Heavy launch vehicle, and a modified Dragon capsule to enter the Martian atmosphere. The concept will be proposed for funding in 2012/2013 as a NASA Discovery mission, for launch in 2018. The primary objective would be the search for evidence of life on Mars (biosignatures), past or present; a substantially unmodified version of the crewed Dragon capsule could be used for payload transport to Mars, and would be a precursor to the ambitious long-term plans of a manned mission to Mars.

Mars One (2012)

Main article: Mars One

In 2012, a Dutch entrepreneur group revealed plans of a fund-raising campaign for a human Mars base to begin in 2023. One difference from other projects is that 'Mars One' is organized as a not-for-profit organization, strives to use worldwide suppliers, with no politics involved.

In 2016, a telecom orbiter would be sent, a rover in 2018, 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. Current plans specify that the entire mission is to be filmed and broadcast back to Earth as a media event.

The Mars Initiative (2013)

Main article: The Mars Initiative

This is a publicly funded international non-profit organization focused on space advocacy, space exploration, and the promotion of a human mission to Mars including exploration of Mars and the colonization of Mars.

Inspiration Mars Foundation (2013)

Main article: Inspiration Mars Foundation

In 2013, the Inspiration Mars Foundation founded by Dennis Tito plans a manned mission to flyby Mars in 2018.

Preparedness

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

• The United States has a number of robotic missions currently exploring Mars, with a sample-return planned for the future. The US does not currently have a launcher capable of sending humans to Mars, however, the Space Launch System could be that vehicle.^{[citation needed]} The Orion spacecraft, currently under development by NASA, could ferry astronauts from the surface of Earth to join a Mars-bound expedition in Earth orbit and then back to Earth's surface once the expedition has returned from Mars. NASA has used the Haughton impact crater on Devon Island as a proving ground due to the crater's similarity with Martian geology. According to New Scientist, an argon plasma-based VASIMR rocket could reduce the transit time to less than 40 days.
• The European Space Agency has sent robotic probes, and has long-term plans to send humans but has not yet built a human-capable launcher. There is a proposal to convert ESA's existing Automated Transfer Vehicle (ATV) for crewed launches. It plans to launch an unmanned mission to Mars, ExoMars, in 2016.
• 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. A simulation of a manned Mars mission, called Mars-500, was completed in Russia in November 2011.
• Japan has sent one robotic mission to Mars, the Nozomi (のぞみ).
• China's mission to Mars, the Yinghuo-1 space probe, was lost with Russia's sample return mission to Phobos, Fobos-Grunt.
• India plans to launch an unmanned mission to Mars in November 2013, the Mangalyaan.^{[citation needed]}

Contamination concerns for surface missions to Mars

Summary

Further information: Colonization of Mars#Concerns

This section addresses questions about whether humans should visit Mars at all, especially, whether they should visit the Mars surface. It also discusses what precautions should be taken to protect the planet Mars, and to protect Earth, during or prior to human exploration of Mars. For other concerns see Colonization of Mars - Concerns

The debate over whether or not life existed, or indeed still exists on Mars has not been settled. Consequently, a manned mission could contaminate the Martian surface with foreign micro-organisms, and compromise the search for indigenous Martian lifeforms. A human mission to the Mars surface would not be permitted under the existing Outer Space Treaty for this reason.

Mars is one of the few places in our solar system where life similar to Earth life may be able to survive. This makes it of particular interest to us, but it also makes it a location of especial concern for human exploration.

Highly evolved Earth microbes might compete with any existing life on Mars. This is akin to introducing placental mammals to a continent of only marsupials. The vacuum of interplanetary space between Earth and Mars isolates the planets from each other for micro-organisms, as effectively as the barriers of sea that prevent animals crossing between continents. By competing in this way, Earth life might make some or all species of life on Mars extinct even before they are discovered.

Also introduced Earth life, in forms able to survive and reproduce on Mars, could consume any existing pre-biotic organic deposits, which may have survived on Mars from the early solar system due to its lack of continental drift. They could also make planet wide changes in the chemistry and composition of materials on the surface of Mars. This could obscure study of Early Mars conditions - which is of great interest whether or not life evolved there.

Then there's the possibility that Martian life might have evolved into forms capable of acting as human pathogens. Though multi-cellular life like us may be unlikely on Mars, it's known that some current human pathogens evolved independently of any multicellular host. Carl Sagan was extremely concerned about the possible contamination of Mars from Earth (forward-contamination), and of Earth from Mars (back-contamination).

The existing Outer Space Treaty, particularly Article IX, and the more detailed COSPAR guidelines would not permit human exploration of the surface. Given the issues of forward and backward contamination, it seems that this treaty should remain in place until we have a better understanding of the planet. This need not hold back human colonization efforts greatly however, since another option is to explore the surface of Mars via telepresence, with rovers operated by humans in orbit around Mars. This could lead to a rapid increase in understanding of the conditions on Mars, and so could lead sooner to a well informed decision about whether or not colonization of the surface is advisable, and what the effects would be of humans and all our associated microbiota on the Martian environment. It could also lead directly to colonies in orbit around Mars, mining resources from the Martian moons.

Details

Life on Mars

Life appeared on Earth within a billion years of its formation with the oldest probable traces of life dating back to within 700 million years of its formation, not long after the end of the late heavy bombardment period which kept the crust of the newly formed Earth molten. Mars enjoyed similar conditions during the Noachian period for a few hundred million years, and there was still abundant water in the form of catastrophic flooding through the Hesperian period. Also there is much evidence that suggests that life could be possible on Mars even today - see Possibility of Mars having enough water to support life.

So - whether life on Earth evolved directly or was brought to the planet via meteorites, the evidence suggests similar processes could happen just as easily on the early Mars.

Relict communities on Mars

Martian life forms could exist in small relict communities with their own unique biochemistry and eco-systems, similarly to the inhabitants of cold seeps, or black and white smokers on Earth, and so may not be easy to find during early robotic explorations of Mars. Some might even be restricted to just one location on Mars (like the relict community of Metasequoia in China).

Though some may be evolved from organisms transferred from Earth by meteorites millions of years ago,, the latest common ancestor is likely to be 65 million years ago (since only the largest impacts with Earth can send material to Mars) there's also the tantalising possibility of much earlier types of life, or proto-life that might have survived since the early days of Mars in some niche area.

Since over two thirds of the Martian surface is more than 3.5 Gyr old, the possibility exists that Mars may hold the best record of the events that led to the origin of life, even though there may be no life there today.

The proto-life could include the extremely small nanobes (just 20 nanometers in diameter) or other protobionts. Or there may be well preserved organic remains from those early times. That seems especially possible since Mars has had little or no continental drift, and even the oceans probably didn't span the entire planet. So any deposits left in an isolated ocean bed on Mars 4.4 billion years ago may still be there, or even actual revivable "living fossils" from those times, that perhaps "wake up" and propagate briefly during the more clement periods on Mars.

Modern studies of extremophiles suggest contamination is inevitable

Recent research suggests that contamination of Mars is inevitable if human astronauts visit the surface.

Conclusions from these workshops recognize that some degree of forward contamination associated with human astronaut explorers is inevitable.

This is made likely because of discovery of ordinary seeming micro-organisms with hidden extremophile capabilities - the most famous is Deinococcus radiodurans aka "Conan the bacterium" a remarkable organism with polyextremophile capabilities found in ordinary situations such as textiles and dung. It can survive high levels of ionizing radiation, also cold, vacuum, acid and dehydration. This lets it thrive in habitats as diverse as reactor cooling ponds, and dry granite in Antarctica. It might have acquired these adaptations from conditions on early Earth when conditions perhaps were similar to Mars for a few hundred million years. It can survive on Mars for millions of years below a few cm of soil. However as an obligate aerobe it needs oxygen to grow and reproduce.

There are many anaerobic extremophiles now known. The ones of special relevance for Mars include the psychrophiles (cold loving), the halophiles (salt loving), and the endoliths that live in stones. Many of these are autotrophs (or "primary producers") so that they can generate all they need from ingredients such as water, carbon dioxide, light, rock or hydrogen sulfide.

Knowledge of extremophiles is largely limited to cultivable extremophiles. There are many non cultivable extremophiles about which little is known at present, probably more species of non cultivable extremophiles than cultivable ones. For instance, many non cultivable extremophiles have been shown to live in spacecraft assembly cleanrooms.

In the case of the Archaea, because of the issues involved in cultivating them, it's not even known how many Phyla there are (a Phylum is at the same classification level as Chordate, a higher level than Vertebra which includes all creatures with backbones). Estimates vary from 18 to 23 Archaea Phyla with selected species from only 8 of those phyla cultivated and studied directly - see Species of Archaea.

Possible habitats for life on Mars

Midday soil temperatures as estimated by the Viking Orbiter occasionally got as high as 27 ⁰C. The Spirit rover regularly recorded daytime air temperatures in the shade well above 0 ⁰C, except in winter. It recorded a maximum temperature of 35 ⁰C. The other possible source of heat on Mars is geothermal. Although there have been no measurements yet of volcanic activity on Mars, there is clear evidence of activity within the last two million years; the planet is not yet geologically dead. There may therefore be some underground sources of geothermal heat near the surface that are hot enough to keep ice in liquid form as water but not quite hot enough to erupt to the surface as lava.

One possible location where life may flourish is in underground caves on Mars. Also deep down in the ice below 150 m (methanogens survive in Antarctic ice in similar conditions). Also, there are places on the surface of Mars where the atmospheric pressure is high enough to raise the boiling point of water to 10⁰C, well above its freezing point (which at 0⁰C is independent of atmospheric pressure). This is high enough so that thin films of water might form, especially in the form of brine (adding salt can reduce the freezing point considerably).

Another place they could possibly thrive on present day Mars is just below the surface of the soil. This habitat, if it exists, is particularly relevant for forward contamination of Mars as it is easily accessible from the surface, and widespread, as described in a recent paper (March 2012).

We find that thin films of near subsurface liquid water on Mars at –20°C could provide a viable niche for terrestrial psychrophilic halophiles.

The postulated psychrophilic halophiles there would be autotrophs - primary producers that just need CO₂ and water and other inorganic ingredients to thrive. So once established on Mars, they are limited only by the range of distribution on Mars of the habitat they need. The water would be liquid at this low temperature because of the presence of the martian salts, which can also help the terrestrial psychrophilic halophiles to survive at particularly low temperatures.

Terrestrial life may also be able to survive solely on humidity from the air. A recent experiment at DLR ( Germany's national research center for aeronautics and space)(April 2012) using a simulated Mars environment found that lichen and bacteria could survive on Mars in this way, particularly in cracks in the rocks.

During this period, the lichens and bacteria continued to demonstrate measurable activity and carry out photosynthesis (this is one of an on-going series of many experiments - see the original papers)

The water required for this process is present in the morning and evening of the Martian day, when humidity condenses as precipitation across the surface, and the organisms can absorb it. ... We must be extremely careful not to transport any terrestrial life forms to Mars, Otherwise they might contaminate the planet.

For more about possible habitats for life on present day Mars, see Possibility of Mars having enough water to support life.

Longevity of endospores and resistance to Mars surface conditions

Contamination of the surface is also made more likely by the extreme longevity and DNA self repairing capabilities of some organisms and of endospores, their ability to survive UV and vacuum, and the protection from UV provided by just a few mm. of soil.

The Expose E experiment on the International Space Station included a simulation of exposure to the Mars surface and produced stunning results. When they were in multi-layers, 5% of spores were able to survive on the surface for at least 125 days (3,000 hours) exposed to direct Martian daylight (simulated by filtering the direct light from the sun to Martian levels). An appreciable quantity of spores were able to survive the same period even in monolayers. Then 70-75% of the initial population survive the same period on the simulated Mars surface in shadows.

The spores used were of two species, Bacillus pumilus SAFR-032 isolated from an air lock of the spacecraft assembly facility at the Jet Propulsion Laboratory, which showed elevated resistance to UV radiation and hydrogen peroxide treatment compared to the wild-type strain, and Bacillus subtilis, which is found in soil and in the human gut.

Speed of colonisation

Introduced Earth microbes, if they find a suitable habitat, could colonise all habitable regions throughout the planet with surprising rapidity. Martian winds have the potential to transport micro-organisms throughout the planet during dust storms (perhaps imbedded in a grain of dust so protected from UV), they can also be transported by dust devils. A human visit would introduce huge numbers of micro-organisms (skin flora of a human consists of an estimated 10¹² i.e. one trillion individual organisms). Combine this with the potential exponential growth of micro-organisms in a suitable habitat and if conditions are favourable e.g. in some of the caves or under the surface of the soil, then it might not take long at all to contaminate the entire planet.

Carl Sagan (et al.) calculated that:

A single terrestrial microorganism reproducing as slowly as once a month on Mars would, in the absence of other ecological limitations, result in less than a decade in a microbial population of the Martian soil comparable to that of the Earth's.

So, after a viable micro-organism arrives on Mars and starts a process of habitat limited exponential growth, it might not take a long time in decades before it colonizes all suitable habitats reachable by spores from the surface. If it doesn't happen quite so quickly, the extreme longevity of Endospores (hundreds of thousands or possibly millions of years) and UV resistance makes eventual contamination of the entire planet inevitable after a visit by humans, so long as there are habitats there suitable for them.

Has Mars been contaminated by Earth life already?

There is some concern that previous spacecraft missions to Mars might have contaminated Mars already. For instance the Mars Climate Orbiter- the one that famously crashed on Mars due to a mix up about metric and imperial units - was not intended to land on Mars, and so was only sterilized to Category III. Though it may have burnt up completely during entry, there is a possibility that some of it survived the entry and contaminated the surface of Mars. Many other historical Mars missions have crash landed and some of these crashes might have created other possible opportunities for forward contamination. Another fairly recent example from NASA is the Mars Observer, intended as an orbital mission, which also crashed on Mars.

Even the Viking missions, noted for the care taken to prevent forward contamination of Mars, still weren't sterilized to quite the same levels as modern missions to Mars. Some of the early Soviet Union missions which included several landers in the Soviet Union - Mars series, were probably sterilized to less than the Viking levels.

The COSPAR policy guidelines are based on probabilities, and in 1969 the guideline was that there should be a probability of less than 1 in 1000 of contaminating Mars during the period of biological exploration. However due to issues in the models used, the probability of contamination may be higher than this.

Also, none of the missions are completely sterilized inside and out, because some components such as computers wouldn't survive the heat treatment and other sterilization processes. To take MSL as an example - the core box of the rover with the main computer and other key components are sealed and vented through high-efficiency filters to keep microbes inside. This means that even a mission sterilized for the surface could contaminate Mars if the sealed units are breached during an impact event. A recent example where such a breach is a possibility is the case of the Mars Polar Lander, and there have been many such crashes of spacecraft to Mars from both the USA and Soviet Union.

Bearing all this in mind it is certainly possible that Mars has already been contaminated with Earth life. However, on the positive side, the surface of Mars is inhospitable for most forms of Earth life. Also though the Mars storms eventually degrade materials on the surface of Mars, this is a far slower process than on Earth. The sealed units are also likely to remain sealed over long timescales (except for the possible case of crashed spacecraft).

All of the spacecraft have brought some Earth life to the surface of Mars, particularly as spores within the encapsulated components, and in small quantities, on the surfaces of the spacecraft too. However, there seems a reasonable probability that this contamination is confined to the interiors and surfaces of the spacecraft, the crash debris that has landed on Mars, and the immediate vicinity of the spacecraft. It's also perhaps probable that it is in a permanently dormant state such as spores.

We haven't found any martian life, but there is life on Mars: life we sent there, says NASA's planetary protection officer, Catharine A. Conley. Bacteria, pollen spores, and other pieces of life have traveled millions of miles inside our spacecraft, and we have reason to believe they could have survived the journey (life on the outsides of the craft would have been killed by exposure to UV light outside of Earth's atmosphere), and are now persisting on the Red Planet. "The saving grace to all this," Conley says, "is that the surface conditions on Mars are pretty hostile to Earth life, so it's not very likely that those organisms could actually reproduce, or even survive if they came off the spacecraft." If they're doing anything at all, they're just sitting there.

The original aims of COSPAR are to protect Mars during the scientific exploratory stage, including the search for signs of life or proto-life on Mars. Christopher McKay has argued further, that until we understand the situation better, we must explore Mars in a way that is biologically reversible, so that if needed, we can remove all life forms carried to the planet by our explorations.

Previous missions to Mars, such as the Pathfinder mission and the two MER rovers, have carried microorganisms to the Martian surface where they remain dormant as long as shielded from ultraviolet radiation. To reverse this contamination already present on Mars, it would be necessary to collect all metal objects within which microbes could remain viable. Furthermore, the soil at crash sites and in the vicinity of landers that had come into contact with the spacecraft would have to be thrown up into the atmosphere where it would be exposed to sterilizing ultraviolet radiation.

Though it seems reasonably likely that Mars remains pristine, there is enough uncertainty in the level of planetary protection achieved so far that we can't say with 100% confidence that our efforts to protect the planet have succeeded. If we do detect life on Mars, follow up observations will be needed to make sure it isn't life previously introduced by earlier missions to Mars. If it ever does turn out that despite our best efforts, Earth life has been introduced to Mars, it is still important not to introduce any more new species to the planet until we understand better what the implications are (e.g. for terraforming or for research into the geology of Mars). Following our analogy of higher animals and continents, after the discovery that rabbits have been inadvertently introduced to a continent, it is even more important to be careful about introduction of other species such as Cane Toads.^{[citation needed]}

Human missions cannot fulfill the COSPAR guidelines for planetary protection

The variety of life in a human occupied spacecraft is vast. In skin flora alone there are 1,000 known species in 19 phyla. Then there are all the extremophiles isolated from spacecraft assembly cleanrooms, and the many micro-organisms in our food, in the air, etc. Since there is no way to study non cultivable archaea in any detail, it's impossible at present levels of technology to do an exhaustive inventory of them all, to determine their requirements for survival and their extremophile capabilities.

It is impossible for a human mission to fulfill the current COSPAR guidelines for planetary protection applied to robotic missions to Mars. These require amongst other things at least Viking level of sterilization of the spacecraft and contents if there is any possibility of contamination of the surface in case of a hard landing compromising the spacecraft. Human occupied spacecraft can never achieve this because a hard landing would deposit human bodies with all the associated human microbiomes on the surface of Mars.

NASA currently follows COSPAR guidelines of planetary protection for Mars. For an up-to-date discussion of possible future developments of the guidelines see the report of the 2012 workshop

Risks of pathogens from Mars

Another risk of human exploration is return of dangerous organisms from Mars to Earth - it's been established that micro-organisms hazardous to humans can evolve without any animal host (examples include Legionnaire's disease, and toxic food contaminants such as Ergot), so it's possible that existing Mars life could be hazardous to humans.

Carl Woese, who first classified the Archaea, the third domain of life said in an interview:

When the entire biosphere hangs in the balance, it is adventuristic to the extreme to bring Martian life here. Sure, there is a chance it would do no harm; but that is not the point. Unless you can rule out the chance that it might do harm, you should not embark on such a course.

Carl Sagan wrote:

Precisely because Mars is an environment of great potential biological interest, it is possible that on Mars there are pathogens, organisms which, if transported to the terrestrial environment, might do enormous biological damage - a Martian plague, the twist in the plot of H. G. Wells' War of the Worlds, but in reverse. This is an extremely grave point. On the one hand, we can argue that Martian organisms cannot cause any serious problems to terrestrial organisms, because there has been no biological contact for 4.5 billion years between Martian and terrestrial organisms. On the other hand, we can argue equally well that terrestrial organisms have evolved no defenses against potential Martian pathogens, precisely because there has been no such contact for 4.5 billion years. The chance of such an infection may be very small, but the hazards, if it occurs, are certainly very high.

More recent research has suggested that biological contact between the planets can occur via transfer of life on meteorites. However this doesn't undermine his conclusion, because, firstly, new species introduced in this way might well have caused extinctions in the past, as such an extinction would be hard to recognize in the fossil record - and secondly, there may well be species on Mars that never made the transition successfully, if indeed any did.

This scenario also raises the possibility of forward contamination of Mars leading to later backward contamination of Earth - that life introduced to Mars by human astronauts could evolve through adaptive radiation into new life hazardous to humans for future visits to Mars and then returned to Earth later.^{[citation needed]} The organisms evolving through adaptive radiation would be the microbial equivalents of the likes of the Tenrecidae, the "Lemur versions of hedgehogs, mice, otters etc", filling ecological gaps on Mars occupied by other microorganisms on the Earth. Evolution could be rapid because of the short generation time of micro-organisms, other factors such as horizontal gene transfer that speed up evolution of micro-organisms, and the possibly vast extent of suitable regions for extremophiles (especially if survival beneath the soil is possible). The diversity of habitats on Mars (variations in detail depending on climate, rock type, shadowing, depth of the habitat in the soil, etc.) would contribute towards adaptive radiation, and rapid evolution, similarly to that observed in modern experimental evolution.

Risks of "accidental terraforming"

There's also the risk of "accidental terraforming". This has been explored particularly by Christopher McKay in his thoughtful article on the ethics of terraforming Mars. In his conclusion he says:

Until we know the nature life on Mars and its relationship – if any – to life on Earth, we must explore Mars in a way that keeps our options open with respect to future life. I have argued elsewhere that this means that we must explore Mars in a way that is biologically reversible.

Terraforming Mars is thought to be a process that requires care, especially when it comes to introduction of living organisms. Successful terraforming would depend on the planet developing its own feedback loops and its own biosphere just like the Earth.

On Earth the global temperature, the salinity of the sea, the oxygen level in the atmosphere, the amount of CO₂ in the atmosphere, and many other factors are kept in balance by many feedback cycles involving life. This is the weak Gaia hypothesis that most scientists accept.

It may take a great deal of care and understanding and research before we can set up similar feedback cycles on Mars. The cycles could as easily work in the opposite direction of the one desired (e.g. remove oxygen or CO₂ from the air, or form clouds that cool the planet). An easy example to use here is the risk of inadvertently introduced aerobes like Deinococcus radiodurans - these could "wake up" and thrive and remove oxygen from the atmosphere when we attempt to make it oxygen rich. Getting the cycles to work correctly may be a delicate matter of introducing the right life forms in the correct order. For instance one suggestion is to introduce methanogens first, then oxygen producing organisms that work via photosynthesis and then finally aerobes as a final step - a sort of sped up version of what happened in the early atmosphere of the Earth.

Our sister planet has no "Gaia" established yet to help out if we make a mistake (just in the sense of the weak Gaia hypothesis there). Without a careful step by step approach, and guidance and research, Mars might set up its own version of "Gaia" - but maybe one that favours some organism that we would call an extremophile with feedback loops that resist changes away from that extremophile favouring habitat. Or it might never successfully form a self-regulating environment for life like that on Earth, and after a period of instability and swings in the conditions there (as life interacts with the atmosphere and Mars surface), revert to something close to its current state.

So seeding Mars inadvertently with whatever micro-organisms are able to "hitch a ride" on human occupied spaceships might not be the best way to start the process of terraformation, if we decide it is the right thing to do. It is also something that should be thought over and decided, whether to transform the climate of Mars long term. There are many ethical issues involved that need thought. As Christopher McKay of the NASA Ames Research Center wrote in the conclusion to his article:

It is important to have the long-term view of life on Mars and the possibilities of planetary ecosynthesis. This affects how we explore Mars now. Mars may well be our first step out into the biological universe, it is a step we should take carefully.

Risks of sample return to the Earth's surface

Sample return to the Earth surface itself has all those risks mentioned by Carl Woese above, as the container could rupture if the parachute fails during the landing (rupture of a sample container has already occurred during the sample return of the Genesis capsule). Then, if it does return safely to the Earth's surface, it is hard to contain extremophiles, especially ones not studied yet (unknown hazards) - because at this stage knowledge of the sample will be limited. It could for instance contain uncultivatable archaea, also ultramicrobacteria. It might even contain Martian nanobacteria if such exist (nanobacteria are controversial but ultramicrobacteria are well established to exist).

In current advance planning for the Mars Sample Return facility on Earth it is recognised that the risks can't be reduced to zero.

Consequently, risk-mitigation strategies will focus on eliminating the hazard and/or reducing the probability of a negative event. Both will lead to a risk that is considered acceptable, since achieving zero risk is not possible.

That makes it an ethical issue. There is a risk, though it may be very small. Is it right to take this risk, especially at early stages when our level of knowledge of the sample is limited? As we've seen, there is at least a small chance that it may include pathogens humans are not yet immune to, and at our present level of knowledge of the planet, it may even contain dormant states of life unrelated to any organisms on Earth, possibly even based on novel life chemistry

Another concern is the possibility of human error, or management decisions compromising the safety precautions. This happened during the attempt to quarantine the astronauts and Moon samples for the first Apollo 11 return from the moon.

Risks of Mars sample return to a lunar base or large orbital station

Carl Sagan was also deeply concerned about return of the samples to a lunar base or to a large orbital station. Writing in 1976 in his book The Cosmic Connection: An Extraterrestrial Perspective he said:

It is no use arguing that samples can be brought back safely to Earth, or to a base on the Moon, and thereby not be exposed to Earth. The lunar base will be shuttling passengers back and forth to Earth; so will a large Earth orbital station. The one clear lesson that emerged from our experience in attempting to isolate Apollo-returned lunar samples is that mission controllers are unwilling to risk the certain discomfort of an astronaut – never mind his death – against the remote possibility of a global pandemic. When Apollo 11, the first successful manned lunar lander, returned to Earth – it was a spaceworthy, but not a very seaworthy, vessel – the agreed-upon quarantine protocol was immediately breached. It was adjudged better to open the Apollo 11 hatch to the air of the Pacific Ocean and, for all we then knew, expose the Earth to lunar pathogens, than to risk three seasick astronauts. So little concern was paid to quarantine that the aircraft-carrier crane scheduled to lift the command module unopened out of the Pacific was discovered at the last moment to be unsafe. Exit from Apollo 11 was required in the open sea.

There is also the vexing question of the latency period. If we expose terrestrial organisms to Martian pathogens, how long must we wait before we can be convinced that the pathogen-host relationship is understood? For example, the latency period for leprosy is more than a decade. Because of the danger of backcontamination of Earth, I firmly believe that manned landings on Mars should be postponed until the beginning of the next century, after a vigorous program of unmanned Martian exobiology and terrestrial epidemiology. I reach this conclusion reluctantly. I, myself, would love to be involved in the first manned expedition to Mars. But an exhaustive program of unmanned biological exploration of Mars is necessary first. The likelihood that such pathogens exist is probably small, but we cannot take even a small risk with a billion lives. Nevertheless, I believe that people will be treading the Martian surface near the beginning of the twenty-first century.

This was written soon after the Apollo landings, when space scientists were full of optimism for future space exploration. As we know there hasn't yet been a vigorous program of unmanned Martian exobiology and terrestrial epidemiology of the type he describes.

We have only just started on such a program with the Mars Science Laboratory (the "Curiosity" rover), the first rover since Viking to directly search for biosignatures, which landed on Mars on August 5, 2012. It's just a beginning as, for instance, its "hand lens", though high resolution of 14.5 micrometers per pixel, can't observe endospores or other dormant states directly, can't dig far beneath the surface, and has no modern equivalent of the Viking nutrient experiments (instead, it searches for the signatures of life by techniques such as firing a laser at the sample, X-ray spectroscopy and the like). Also it's level of sterilization is not high enough under COSPAR guidelines to study habitats where life might occur in present day Mars (due to the extra costs that would add to the mission), and it was intentionally sent to an area of Mars where present day life is extremely unlikely to be observed due to the aridity of the soil. So, though impressive compared with what came before, it is only a start. There are many other rovers planned for the future that will build on its results.

Legal Protection of Earth and Mars from forward and backward contamination

With so many proposed Mars missions, from different countries and even private sponsors, any legal protection clearly has to be an international effort. We have a good precedent to follow though, the Antarctic Treaty. as Hurtak and Egan point out:

Clearly as an international document, the achievement of the Antarctic Treaty (1961) was an unprecedented landmark in political diplomacy in landing a virgin environmental area never touched by civilization and showing pristine landscapes. An entire continent was reserved for free and nonpolitical scientific investigation.

The Outer Space Treaty, particularly Article IX, is another international effort which is the basis for current measures for planetary protection.

"Article IX: ... States Parties to the Treaty shall pursue studies of outer space, including the Moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter and, where necessary, shall adopt appropriate measures for this purpose...

In the case of Antarctica, no exploitation is permitted until at least 2048 when the treaty will be reviewed - see the Protocol on Environmental Protection to the Antarctic Treaty. Visitors to Antarctica have to take special precautions to prevent contamination, and that includes tourists - their visits have to be short duration and carefully supervised. For instance tourists are not permitted to bring non-native species to Antarctica.

An even closer analogy in Antarctica is the case of Lake Vostok. Great care is taken to avoid contaminating the water, an extreme environment with fifty times the oxygen content of normal fresh water on our planet. It's of great scientific interest, and has been isolated from the surface probably for hundreds of thousands of years. The recent Russian drilling project was the subject of much legal discussion under the Antarctica treaty provisions. Some authors felt that the existing provisions are insufficient and that the legislation needs to be strengthened further.

A similar international treaty could protect Mars. A proposal for such a treaty has been drafted by Hurtak and Egan, using the Antarctica treaty as a model.

Enforcing a Mars Treaty

As is the case with Antarctica, such a policy might not be hard to police if the need for it is well understood. Mars is far more inaccessible than Antarctica, of less interest to tourists, of no immediate commercial interest for mineral exploitation, and when it comes to colonization, there are other targets that are actually more natural first targets for colonization if it is accepted that the surface of Mars is temporarily off limits for colonization.

• It is of no interest for commercial extraction of minerals in the near future. The likely first targets for mineral extraction are the Moon and the NEOs. For details, see Moon - Exporting material to Earth and asteroid mining.

• For space tourism, the Moon, and LEO are of far more interest than Mars in the near future. The "fast round trip" travel time to Mars is set at 245 days. This "fast trip" is also only achievable every 2 years and 2 months.

• For colonization, Mars seems like a natural target at first sight. However if Mars is temporarily off limits for colonization until Carl Sagan's suggested "vigorous program of unmanned Martian exobiology and terrestrial epidemiology" is complete, then there are other targets for colonization that have many advantages over Mars.

• Mars is often perceived as "Earth like" by potential colonists. However this is a misconception; most images of Mars are adjusted to simulate daylight illumination on the Earth to assist geologists in rock type identification. Unadjusted images are a near uniform dim muddy red-brown in colour. Mars near the equator has an average temperature similar to the Antarctic interior at -55 °C (-67 °F). However, the day-to-night Martian temperature swings of typically 60-80°C are much greater. This makes typical night temperatures on Mars far lower than the lowest temperatures for the Antarctic interior (see Climate of Mars - Temperature). The "atmosphere" counts as a vacuum on Earth and so requires spacesuits, and pressurised buildings to grow crops. Light levels are lower due to distance from the sun, and occasional planetary dust storms keep much of the Mars surface in darkness for months on end (see Concerns about Colonization of Mars).

• The poles of the Moon particularly are more "Earth like" than Mars according to most criteria. The Moon and NEOs are safer first targets for space colonization (with the long journey times from Earth to Mars a disadvantage for re-supply of damaged components or return of ill astronauts). With discovery of ice at the Moon's poles, the Moon in particular seems a viable alternative first target for space colonization, with many of the resources that a new space colony needs in situ.

That leaves those who wish to explore Mars for the sake of exploration rather than to settle there. It's been suggested that Mars can be explored more thoroughly and for less cost by telepresence, using humans in orbit around the planet. This provides a solution to the backward and forward contamination issues. It also provides an excellent motivation for establishing a human presence in orbit around Mars, and for sending human missions to Mars.

Exploration of the surface from orbit, via telerobotics and telepresence

This is an approach proposed in several recent mission profiles. It depends on human presence in orbit around Mars, leads to more rapid exploration of the surface than is possible with remote exploration from Earth, and permits human exploration of the surface of Mars in a more thorough way than is possible for human explorers on the surface, for a far lower budget than a surface mission. It also does this without the contamination issues mentioned above.

The reason that orbital missions are so favourable to exploration of the surface is that the delta v needed to reach a Mars capture orbit from LEO is only 5.2 km/second. This compares with 10.7 km/second needed to reach the surface. Indeed in terms of delta v Mars orbit is more accessible than the surface of the Moon which has a delta v of 5.93. See Delta-v budget. This makes it possible to consider ambitious manned missions to Mars orbit that would require a much higher budget, for less science return, if carried out on the surface of Mars. For long timescale operations such as supply of materials and fuel both ways, the difference is even more marked, as transfer to and from orbit can be achieved using the Interplanetary Transport Network.

An early suggestion of this type is Zubrin's Athena double flyby mission (with a crew of just two astronauts).

In the Athena plan .... upon approaching Mars on a low-energy trajectory after a 9 month voyage, the piloted spacecraft is targeted to perform a gravity assist maneuver which changes its Earth to Mars .elliptical orbit into a circular orbit mimicking than of Mars, but sìightly inclined to the plane of Mars’ orbit. The spacecraft will then shadow Mars for about a year, never moving much more than about one light minute of distance from the Red Planet, with several months spent within 10 iight seconds. During this time the crew will be able to command a dispersed set of small rovers that have been landed on Mars, with command and response times about 100 times faster than would be possible from Earth. At the end of a year of shadowing Mars, the spacecraft’s trajectory will cause it to closely approach Mars again, at which time a Mars gravity assist can be used to transform its Mars like orbit into a Mars-to-Earth transfer elliptical trajectory.

HERRO (Human Exploration using Real-time Robotic Operations)

Another proposal of this type, presented by Landis and by Lupisella is to explore Mars via telepresence from human astronauts in orbit or on, say Deimos. They would be close enough to operate robots on the surface in real time (i.e., with only a short round-trip delay time), and this would also engage public interest as well.

A similar idea, this time based on a station in a slowly precessing nearly-sun-synchronous 12 hour Molniya orbit around Mars (to reduce the delta v required to a minimum) has been presented as a proposed mission for NASA called HERRO, which stands for "Human Exploration using Real-time Robotic Operations". In their abstact the authors write:

..., HERRO provides the cognitive and decision-making advantages of having humans at the site of study for only a fraction of the cost of conventional human surface missions. It is very similar to how oceanographers and oil companies use telerobotic submersibles to work in inaccessible areas of the ocean, and represents a more expedient, near-term step prior to landing humans on Mars and other large planetary bodies.

Results suggest that a single HERRO mission with six crew members could achieve the same exploratory and scientific return as three conventional crewed missions to the Mars surface.

This is a "win win" situation. The science return is increased, and it costs less. The orbiting spacecraft could eventually develop into an orbiting colony supplied from Deimos, the Mars surface and Earth. All the time this builds up an infrastructure of rovers, fuel generation plants etc. on Mars, and a valuable support facility in orbit around Mars, that could be useful for any future colonists on the surface, once the scientific studies are complete, and the effects of introducing Earth life to Mars and to any existing native Mars lifeforms are well understood.

The technologies developed for HERRO are directly relevant to later human surface missions. When the nation decides to develop the systems needed to send crews to the surfaces of the Moon and Mars, a good portion of the technological infrastructure will already be in place.

A short preliminary discussion of some of the possible outcomes of the scientific studies (indigenous life, sterile Mars, or life related to Earth life) and the ethical and practical issues involved in human colonization for each case can be found in Christopher McKay's article.

A similar mission has been proposed in Russia (as part of a suggested international effort with US participation for the landers) called the Mars Piloted Orbital Station. Another similar mission has been suggested by Lockheed Martin as part of their "Stepping stones to Mars" project, called the "Red Rocks Project" - this time the target is Deimos rather than an orbiting station about Mars. As with the other missions, the plan is to explore Mars via telepresence.

Telepresence and telerobotics are fields that are evolving rapidly right now, with many projects underway including those in Japan and the ones sponsored by the US military, and developments in software and hardware for computer gaming - so that soon it may be possible to nearly exactly simulate the experience of walking on the surface of Mars via tele-presence from an orbiting spacecraft or habitat.

There are suggestions for mining the substance of Deimos to support exploration and colonization. The moon might hold carbon and water ice. Determining what material is available from Deimos and Phobos is a high priority for humanity's progress in outer space. Deimos and Phobos pose no hazards from dust storms or corrosion as does the surface of Mars. Even in the case of these moons some caution may be needed to avoid contamination.

Phobos and Deimos themselves are generally considered extremely unlikely to harbor any living entity, be it indigenous or imported from Mars. However, this conclusion remains open to revision depending on what their in-situ exploration might reveal, particularly in relation to any subsurface ice that might be associated with preserved biological materials ... Phobos and/or Deimos can play a key PP role in the human exploration of Mars and need to be explored in depth by robotic precursors.

In an orbital colony around Mars, only the gravity is missing, which would need to be supplied using a tether system in the near term, or using a rigid rotating spacecraft (as in the HERRO proposal). At later stages of an orbital colony around Mars, gravity could be supplied by constructing a rotating habitat like the Stanford torus.

Mars analogs

Main article: List of Mars analogs

Technologies

Producing intravenous fluid from water could allow not having to carry this medical supply. A prototype for this concept was tested on the International Space Station in 2010.

Space bread has proved elusive because of a variety of challenges. By 2012 a method was suggested where dough is leavened by dissolved CO2 (as opposed to yeast) and cooked by a low temperature process. This could allow fresh baked bread from bulk ingredients on future spaceflights.

Mars habitats may use 40% Argon, 40% Nitrogen, and 20% Oxygen. Nitrogen and Argon can be taken from Mars air but are hard to separate from each other.

See also

• Artificial gravity
• Settlement of Mars
• Exploration of Mars
• Effect of spaceflight on the human body
• Health threat from cosmic rays
• International Mars Society
• Inspiration Mars
• Interplanetary spaceflight
• Life on Mars
• List of manned Mars mission plans in the 20th century
• Manned Venus Flyby
• MARS-500
• Mars in fiction
• Mars to Stay
• Nuclear propulsion
• Space medicine
• Space weather
• Terraforming of Mars
• Zero gravity

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.