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Contents
- 1 Relative similarity to Earth
- 2 Differences from Earth
- 3 Conditions for human habitation
- 4 Radiation
- 5 Transportation
- 6 Communication
- 7 Robotic precursors
- 8 Early human missions
- 9 Economics
- 10 Possible locations for settlements
- 11 Advocacy
- 12 In fiction
- 13 See also
- 14 References
- 15 Further reading
- 16 External links
Relative similarity to Earth
| Space colonization |
- The Martian day (or sol) is very close in duration to Earth's. A solar day on Mars is 24 hours 39 minutes 35.244 seconds. (See Timekeeping on Mars.)
- Mars has a surface area that is 28.4% of Earth's, only slightly less than the amount of dry land on Earth (which is 29.2% of Earth's surface). Mars has half the radius of Earth and only one-tenth the mass. This means that it has a smaller volume (~15%) and lower average density than Earth.
- Mars has an axial tilt of 25.19°, similar to Earth's 23.44°. As a result, Mars has seasons much like Earth, though they last nearly twice as long because the Martian year is about 1.88 Earth years. The Martian north pole currently points at Cygnus, not Ursa Minor like Earth's.
- Recent observations by NASA's Mars Reconnaissance Orbiter, ESA's Mars Express and NASA's Phoenix Lander confirm the presence of water ice on Mars.
Differences from Earth
- While there are kinds of micro-organisms and lichens that survive in extreme environmental conditions, including simulations that approximate Mars, plants and animals generally cannot survive the ambient conditions present on the surface of Mars.[1]
- The surface gravity of Mars is 38% that of Earth. Although microgravity is known to cause health problems such as muscle loss and bone demineralization,[2][3] it is not known if Martian gravity would have a similar effect. The Mars Gravity Biosatellite was a proposed project designed to learn more about what effect Mars' lower surface gravity would have on humans.[4]
- Mars is much colder than Earth, with a mean surface temperature between 186 and 268 K (−87 °C and −5 °C).[5][6] The lowest temperature ever recorded on Earth was −93.2 °C, in Antarctica.
- There are no standing bodies of liquid water on the surface of Mars.[citation needed]
- Because Mars is farther from the Sun, the amount of solar energy entering the upper atmosphere per unit area (the solar constant) is less than half of that entering the Earth's upper atmosphere. However, due to the thinner atmosphere, more solar energy reaches the surface.
- Mars' orbit is more eccentric than Earth's, increasing temperature and solar constant variations.
- Due to the relative lack of a magnetosphere, in combination with a thin atmosphere – less than 1% that of Earth's – Mars has extreme amounts of ultra-violet radiation that would pose an ongoing and serious threat.
- The atmospheric pressure on Mars is ~7.5 mbar, far below the Armstrong Limit (61.8 mbar) at which people can survive without pressure suits. The atmospheric pressure on Earth, at sea level, is 1,013 mbar, 135 times that of Mars. Since terraforming cannot be expected as a near-term solution, habitable structures on Mars would need to be constructed with pressure vessels similar to spacecraft, capable of containing a pressure between 300 and 1000 mbar.
- The Martian atmosphere is 95% carbon dioxide, 3% nitrogen, 1.6% argon, and traces of other gases including oxygen totaling less than 0.4%.
- Martian air has a partial pressure of CO2 of 7.1 mbar, compared to .31 mbar on Earth. CO2 poisoning in humans begins at about 1 mbar. Even for plants, CO2 much above 1.5 mbar is toxic. This means Martian air is completely toxic to both plants and animals even at the reduced total pressure .[citation needed]
Conditions for human habitation
Based on evidence collected by satellites, static landers and rovers such as Curiosity, conditions are not hospitable to humans or life as we know it. Antarctica has temperatures that are comparable (though Mars is colder), but other environmental circumstances that are very unlike those of Earth would be deadly to all life as we know it (except for perhaps some extremophilic microorganisms that have been shown to grow under simulated conditions).[7] These include greatly reduced air pressure, an atmosphere composed of 96% carbon dioxide (0.03% on Earth) and 0.1% oxygen (21% on Earth), reduced gravity, and no liquid water (although amounts of frozen water have been detected). Despite this, some consider Mars to be habitable. However, this would require that highly complex life support measures be taken. Humans would need to live in artificial environments. Humans may one day set foot on Mars for exploration, but it is unknown if they could ever adapt to living on Mars as permanent residents.Terraforming
Main article: Terraforming of Mars
It may be possible to terraform Mars to allow a wide variety of living things, including humans, to survive unaided on Mars' surface.[8]In April 2012, it was reported that some lichen and cyanobacteria survived and showed remarkable adaptation capacity for photosynthesis after 34 days in simulated Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the German Aerospace Center (DLR).[7][9][10]
Radiation
Mars has no global magnetic field comparable to Earth's geomagnetic field. Combined with a thin atmosphere, this permits a significant amount of ionizing radiation to reach the Martian surface. The Mars Odyssey spacecraft carried an instrument, the Mars Radiation Environment Experiment (MARIE), to measure the dangers to humans. MARIE found that radiation levels in orbit above Mars are 2.5 times higher than at the International Space Station. Average doses were about 22 millirads per day (220 micrograys per day or 0.08 gray per year.)[11] A three-year exposure to such levels would be close to the safety limits currently adopted by NASA.[citation needed] Levels at the Martian surface would be somewhat lower and might vary significantly at different locations depending on altitude and local magnetic fields. Building living quarters underground (possibly in lava tubes that are already present) would significantly lower the colonists' exposure to radiation.Occasional solar proton events (SPEs) produce much higher doses. Some SPEs were observed by MARIE that were not seen by sensors near Earth because SPEs are directional, making it difficult to warn humans on Mars early enough.[citation needed]
Much remains to be learned about space radiation. In 2003, NASA's Lyndon B. Johnson Space Center opened a facility, the NASA Space Radiation Laboratory, at Brookhaven National Laboratory, that employs particle accelerators to simulate space radiation. The facility studies its effects on living organisms along with shielding techniques.[12] Initially, there was some evidence that this kind of low level, chronic radiation is not quite as dangerous as once thought; and that radiation hormesis occurs.[13] In 2006 it was determined that protons from cosmic radiation actually cause twice as much serious damage to DNA as previously expected, exposing astronauts to grave risks of cancer and other diseases.[14] Because of radiation, the summary report of the Review of U.S. Human Space Flight Plans Committee released on 2009 reported that "Mars is not an easy place to visit with existing technology and without a substantial investment of resources."[14] NASA is exploring alternative technologies such as deflector shields of plasma to protect astronauts and spacecraft from radiation.[14]
Transportation
Interplanetary spaceflight
During the journey the astronauts are subject to radiation, which requires a means to protect them. Cosmic radiation and solar wind cause DNA damage, which increases the risk of cancer significantly. The effect of long term travel in interplanetary space is unknown, but scientists estimate an added risk of between 1% and 19%, most likely 3.4%, for men to die of cancer because of the radiation during the journey to Mars and back to Earth. For women the probability is higher due to their larger glandular tissues.[19]
Landing on Mars
Mars has a gravity 0.38 times that of the Earth and the density of its atmosphere is 1% of that on Earth.[20] The relatively strong gravity and the presence of aerodynamic effects makes it difficult to land heavy, crewed spacecraft with thrusters only, as was done with the Apollo moon landings, yet the atmosphere is too thin for aerodynamic effects to be of much help in braking and landing a large vehicle. Landing piloted missions on Mars will require braking and landing systems different from anything used to land crewed spacecraft on the Moon or robotic missions on Mars.[21]If one assumes carbon nanotube construction material will be available with a strength of 130 GPa then a space elevator could be built to land people and material on Mars.[22] A space elevator on Phobos has also been proposed.[23]
Communication
Communications with Earth are relatively straightforward during the half-sol when the Earth is above the Martian horizon. NASA and ESA included communications relay equipment in several of the Mars orbiters, so Mars already has communications satellites. While these will eventually wear out, additional orbiters with communication relay capability are likely to be launched before any colonization expeditions are mounted.The one-way communication delay due to the speed of light ranges from about 3 minutes at closest approach (approximated by perihelion of Mars minus aphelion of Earth) to 22 minutes at the largest possible superior conjunction (approximated by aphelion of Mars plus aphelion of Earth). Real-time communication, such as telephone conversations or Internet Relay Chat, between Earth and Mars would be highly impractical due to the long time lags involved. NASA has found that direct communication can be blocked for about two weeks every synodic period, around the time of superior conjunction when the Sun is directly between Mars and Earth,[24] although the actual duration of the communications blackout varies from mission to mission depending on various factors - such as the amount of link margin designed into the communications system, and the minimum data rate that is acceptable from a mission standpoint. In reality most missions at Mars have had communications blackout periods of the order of a month.[25]
A satellite at either of the Earth-Sun L4/L5 Lagrange points could serve as a relay during this period to solve the problem; even a constellation of communications satellites would be a minor expense in the context of a full colonization program. However, the size and power of the equipment needed for these distances make the L4 and L5 locations unrealistic for relay stations, and the inherent stability of these regions, while beneficial in terms of station-keeping, also attracts dust and asteroids, which could pose a risk.[26] Despite that concern, the STEREO probes passed through the L4 and L5 regions without damage in late 2009.
Recent work by the University of Strathclyde's Advanced Space Concepts Laboratory, in collaboration with the European Space Agency, has suggested an alternative relay architecture based on highly non-Keplerian orbits. These are a special kind of orbit produced when continuous low-thrust propulsion, such as that produced from an ion engine or solar sail, modifies the natural trajectory of a spacecraft. Such an orbit would enable continuous communications during solar conjunction by allowing a relay spacecraft to "hover" above Mars, out of the orbital plane of the two planets.[27] Such a relay avoids the problems of satellites stationed at either L4 or L5 by being significantly closer to the surface of Mars while still maintaining continuous communication between the two planets.
Robotic precursors
The path to a human colony could be prepared by robotic systems such as the Mars Exploration Rovers Spirit, Opportunity and Curiosity. These systems could help locate resources, such as ground water or ice, that would help a colony grow and thrive. The lifetimes of these systems would be measured in years and even decades, and as recent developments in commercial spaceflight have shown, it may be that these systems will involve private as well as government ownership. These robotic systems also have a reduced cost compared with early crewed operations, and have less political risk.Wired systems might lay the groundwork for early crewed landings and bases, by producing various consumables including fuel, oxidizers, water, and construction materials. Establishing power, communications, shelter, heating, and manufacturing basics can begin with robotic systems, if only as a prelude to crewed operations.
Mars Surveyor 2001 Lander MIP (Mars ISPP Precursor) was to demonstrate manufacture of oxygen from the atmosphere of Mars,[28] and test solar cell technologies and methods of mitigating the effect of Martian dust on the power systems.[29]
Early human missions
See also: Vision for Space Exploration
In 1948, Wernher von Braun described in his book The Mars Project
that a fleet of 10 spaceships could be built using 1000 three-stage
rockets. These could bring a population of 70 people to Mars.All of the early human missions to Mars as conceived by national governmental space programs—such as those being tentatively planned by NASA, FKA and ESA—would not be direct precursors to colonization. They are intended solely as exploration missions, as the Apollo missions to the Moon were not planned to be sites of a permanent base.
Colonization requires the establishment of permanent bases that have potential for self-expansion. A famous proposal for building such bases is the Mars Direct and the Semi-Direct plans, advocated by Robert Zubrin.[18]
Other proposals that envision the creation of a settlement have come from Jim McLane and Bas Lansdorp (the man behind Mars One, which envisions no planned return flight for the humans embarking on the journey ),[30] as well as from Elon Musk whose SpaceX company, as of 2013, is funding development work on a space transportation system called the Mars Colonial Transporter.[31][32]
The Mars Society has established the Mars Analogue Research Station Programme at sites Devon Island in Canada and in Utah, United States, to experiment with different plans for human operations on Mars, based on Mars Direct. Modern Martian architecture concepts often include facilities to produce oxygen and propellant on the surface of the planet.
Economics
A major economic problem is the enormous up-front investment required to establish the colony and perhaps also terraform the planet.
Some early Mars colonies might specialize in developing local resources for Martian consumption, such as water and/or ice. Local resources can also be used in infrastructure construction.[33] One source of Martian ore currently known to be available is reduced iron in the form of nickel-iron meteorites. Iron in this form is more easily extracted than from the iron oxides that cover the planet.
Another main inter-Martian trade good during early colonization could be manure.[34] Assuming that life doesn't exist on Mars, the soil is going to be very poor for growing plants, so manure and other fertilizers will be valued highly in any Martian civilization until the planet changes enough chemically to support growing vegetation on its own.
Solar power is a candidate for power for a Martian colony. Solar insolation (the amount of solar radiation that reaches Mars) is about 42% of that on Earth, since Mars is about 52% farther from the Sun and insolation falls off as the square of distance. But the thin atmosphere would allow almost all of that energy to reach the surface as compared to Earth, where the atmosphere absorbs roughly a quarter of the solar radiation. Sunlight on the surface of Mars would be much like a moderately cloudy day on Earth.[35]
Nuclear power is also a good candidate, since the fuel is very dense for cheap transportation from Earth. Nuclear power also produces heat, which would be extremely valuable to a Mars colony.
Mars' reduced gravity together with its rotation rate makes it possible for the construction of a space elevator with today's materials,[citation needed] although the low orbit of Phobos could present engineering challenges. If constructed, the elevator could transport minerals and other natural resources extracted from the planet.
Economic drivers
Space colonization on Mars can roughly be said to be possible when the necessary methods of space colonization become cheap enough (such as space access by cheaper launch systems) to meet the cumulative funds that have been gathered for the purpose.Although there are no immediate prospects for the large amounts of money required for any space colonization to be available given traditional launch costs,[36][full citation needed] there is some prospect of a radical reduction to launch costs in the 2010s, which would consequently lessen the cost of any efforts in that direction. With a published price of US$56.5 million per launch of up to 13,150 kg (28,990 lb) payload[37] to low Earth orbit, SpaceX Falcon 9 rockets are already the "cheapest in the industry".[38] Advancements currently being developed as part of the SpaceX reusable launch system development program to enable reusable Falcon 9s "could drop the price by an order of magnitude, sparking more space-based enterprise, which in turn would drop the cost of access to space still further through economies of scale."[38] SpaceX' reusable plans include Falcon Heavy and future methane-based launch vehicles including the Mars Colonial Transporter. If SpaceX is successful in developing the reusable technology, it would be expected to "have a major impact on the cost of access to space", and change the increasingly competitive market in space launch services.[39]
Alternative funding approaches might include the creation of inducement prizes. For example, the 2004 President's Commission on Implementation of United States Space Exploration Policy suggested that an inducement prize contest should be established, perhaps by government, for the achievement of space colonization. One example provided was offering a prize to the first organization to place humans on the Moon and sustain them for a fixed period before they return to Earth.[40]
Possible locations for settlements
Broad regions of Mars can be considered for possible settlement sites.Polar regions
Mars' north and south poles once attracted great interest as settlement sites because seasonally-varying polar ice caps have long been observed by telescope from Earth. Mars Odyssey found the largest concentration of water near the north pole, but also showed that water likely exists in lower latitudes as well, making the poles less compelling as a settlement locale. Like Earth, Mars sees a midnight sun at the poles during local summer and polar night during local winter.Equatorial regions
See also: Caves of Mars Project
Mars Odyssey found what appear to be natural caves near the volcano Arsia Mons.
It has been speculated that settlers could benefit from the shelter
that these or similar structures could provide from radiation and
micrometeoroids. Geothermal energy is also suspected in the equatorial
regions.[41]Midlands
Valles Marineris
Valles Marineris, the "Grand Canyon" of Mars, is over 3,000 km long and averages 8 km deep. Atmospheric pressure at the bottom would be some 25% higher than the surface average, 0.9 kPa vs 0.7 kPa. River channels lead to the canyon, indicating it was once flooded.Lava tubes
Several lava tube skylights on Mars have been located. Earth based examples indicate that some should have lengthy passages offering complete protection from radiation and be relatively easy to seal using on site materials, especially in small subsections.[42]Advocacy
Making Mars colonization a reality is advocated by several groups with different reasons and proposals. One of the oldest is the Mars Society. They promote a NASA program to accomplish human exploration of Mars and have set up Mars analog research stations in Canada and the United States. Also are MarsDrive, which is dedicated to private initiatives for the exploration and settlement of Mars, and, Mars to Stay, which advocates recycling emergency return vehicles into permanent settlements as soon as initial explorers determine permanent habitation is possible. An initiative that went public in June 2012 is Mars One. Its aim is to establish a fully operational permanent human colony on Mars by 2023.[43]In fiction
Main article: Mars in fiction
A few instances in fiction provide detailed descriptions of Mars colonization. They include:- Aria by Kozue Amano
- Axis by Robert Charles Wilson
- Icehenge (1985), the Mars trilogy (Red Mars, Green Mars, Blue Mars, 1992–1996), and The Martians (1999) by Kim Stanley Robinson
- First Landing (2002) by Robert Zubrin
- Man Plus (1976) by Frederik Pohl
- "We Can Remember It for You Wholesale" (1966), by Philip K. Dick
- Mars (1992) and Return to Mars (1999), by Ben Bova
- Climbing Olympus (1994), by Kevin J. Anderson
- Red Faction (2001), developed by Volition, published by THQ
- The Platform (2011) by James Garvey
- "The Destruction of Faena" (1974) by Alexander Kazantsev
- The Martian Chronicles (1950) by Ray Bradbury
- The Sands of Mars (1951) by Arthur C. Clarke
- Total Recall (1990) by Paul Verhoeven
- Mars Trilogy (1993–96) by Kim Stanley Robinson
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