Colonization of Mars


Colonization of Mars
An artist's conception of the colonization of Mars, with a cutaway showing part of the interior

The colonization of Mars by humans is the focus of speculation and serious study because the surface conditions and availability of water on Mars make it arguably the most hospitable planet in the solar system other than Earth. The Moon has been proposed as the first location for human colonization, but Mars has a thin atmosphere, giving it the potential capacity to host human and other organic life. Both the Moon and Mars, as potential colonization sites, have the disadvantages of cost and risk associated with landing down deep gravity wells, which may make asteroids another option for early expansion of humans into the solar system.

Contents

Relative similarity to Earth

Space colonization
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The Earth is much like its "sister planet" Venus in bulk composition, size and surface gravity but Mars' similarities to Earth are more compelling when considering colonization. These include:

  • The Martian day (or sol) is very close to Earth's. A Mars solar day 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°, compared with 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.
  • Mars has an atmosphere. Although it is very thin (about 0.7% of Earth's atmosphere) it provides some protection from solar and cosmic radiation and has been used successfully for aerobraking of spacecraft.
  • Recent observations by NASA's Mars Exploration Rovers, ESA's Mars Express and NASA's Phoenix Lander confirm the presence of water ice on Mars. Mars appears to have significant quantities of all the elements necessary to support Earth-based life.[1]

Differences from Earth

  • The surface gravity on Mars is 38% of that on Earth. It is not known if this is enough to prevent the health problems associated with weightlessness.[citation needed]
  • Mars is much colder than Earth, with a mean surface temperature of −63 °C and a low of −140 °C. The lowest temperature ever recorded on Earth was −89.2 °C, in Antarctica.
  • There are no standing bodies of liquid water on the surface of Mars.
  • Because Mars is farther from the Sun, the amount of solar energy reaching the upper atmosphere (the solar constant) is less than half of what reaches the Earth's upper atmosphere or the Moon's surface. However, the solar energy that reaches the surface of Mars is not impeded by a thick atmosphere like on Earth.
  • Mars' orbit is more eccentric than Earth's, exacerbating temperature and solar constant variations.
  • The atmospheric pressure on Mars is ~6 mbar, far below the Armstrong Limit (61.8 mbar) at which people can survive without pressure suits. 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 a third and a whole bar.
  • The Martian atmosphere consists mainly of carbon dioxide. Because of this, even with the reduced atmospheric pressure, the partial pressure of CO2 at the surface of Mars is some 15 times higher than on Earth. It also has significant levels of carbon monoxide.
  • Mars has a very weak magnetosphere, so it deflects solar winds poorly.

Habitability

Conditions on the surface of Mars are much closer to habitability than the surface of any other known planet or moon, as seen by the extremely hot and cold temperatures on Mercury, the furnace-hot surface of Venus, or the cryogenic cold of the outer planets and their moons. Only the cloud tops of Venus are closer in terms of habitability to Earth than Mars is.[2] There are natural settings on Earth where humans have explored that match most conditions on Mars. The highest altitude reached by a manned balloon ascent, a record set in May 1961, was 34,668 meters (113,740 feet).[3] The pressure at that altitude is about the same as on the surface of Mars.[4] Extreme cold in the Arctic and Antarctic match all but the most extreme temperatures on Mars.

Terraforming

An artist's conception of a terraformed Mars (2009)

It may be possible to terraform Mars to allow a wide variety of living things, including humans, to survive unaided on Mars' surface.[5]

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.)[6] A three-year exposure to such levels would be close to the safety limits currently adopted by NASA. Levels at the Martian surface would be somewhat lower and might vary significantly at different locations depending on altitude and local magnetic fields.

Occasional solar proton events (SPEs) produce much higher doses. Some SPEs were observed by MARIE that were not seen by sensors near Earth due to the fact that SPEs are directional, making it difficult to warn astronauts on Mars early enough.

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 will study its effects on living organisms along with shielding techniques.[7] There is some evidence that this kind of low level, chronic radiation is not quite as dangerous as once thought; and that radiation hormesis occurs.[8] The consensus among those that have studied the issues is that radiation levels, with the exception of the SPEs, that would be experienced on the surface of Mars, and while journeying there, are certainly a concern, but are not thought to prevent a trip from being made with current technology.[9]

Transportation

Interplanetary spaceflight

Mars (Viking 1, 1980)

Mars requires less energy per unit mass (delta V) to reach from Earth than any planet except Venus. Using a Hohmann transfer orbit, a trip to Mars requires approximately nine months in space.[10] Modified transfer trajectories that cut the travel time down to seven or six months in space are possible with incrementally higher amounts of energy and fuel compared to a Hohmann transfer orbit, and are in standard use for robotic Mars missions. Shortening the travel time below about six months requires higher delta-v and an exponentially increasing amount of fuel, and is not feasible with chemical rockets, but would be perfectly feasible with advanced spacecraft propulsion technologies, some of which have already been tested, such as VASIMR,[11] and nuclear rockets. In the former case, a trip time of forty days could be attainable,[12] and in the latter, a trip time down to about two weeks.[13] Another possibility is constant-acceleration technologies such as space-proven solar sails and ion drives which permit passage times at close approaches on the order of several weeks. Both of these propulsion systems have been deployed and could readily obtain a constant acceleration of 0.1 g.[citation needed]

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 male persons 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.[14]

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.[15] 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.[16]

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 men and material on Mars.[17] A space elevator on Phobos has also been proposed.[18]

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,[19] 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.[20]

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 asteroids, which could pose a severe risk to any satellite.[21]

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.[22] 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 and Opportunity. 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.

Early human missions

Early human missions to Mars, 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 plan, advocated by Robert Zubrin.[13] 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

Iron-nickel meteorite found on mars surface

As with early colonies in the New World, economics would be a crucial aspect to a colony's success. The reduced gravity well of Mars and its position in the solar system may facilitate Mars-Earth trade and provide the rationalization for continued settlement of the planet.

Mars' reduced gravity together with its rotation rate makes it possible for the construction of a space elevator with today's materials, 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.

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.[23] 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.[24] 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.

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.

Heating requirements could be lowered if the colonists use domes to trap solar heat, especially for greenhouses.

Possible locations for colonies

Mars can be considered in broad regions for discussion of possible colony sites.

Polar regions

Mars' north and south poles once attracted great interest as colony 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 colony locale. Like Earth, Mars sees a midnight sun at the poles during local summer and polar night during local winter.

Equatorial regions

Mars Odyssey found what appear to be natural caves near the volcano Arsia Mons. It has been speculated that colonists could benefit from the shelter that these or similar structures could provide from radiation and micrometeroids. Geothermal energy is also suspected in the equatorial regions.[25]

Midlands

Eagle Crater, as seen from Opportunity (2004)

The exploration of Mars' surface is still underway. The two Mars Exploration Rovers, Spirit and Opportunity, have encountered very different soil and rock characteristics. This suggests that the Martian landscape is quite varied and the ideal location for a colony would be better determined when more data becomes available. As on Earth, seasonal variations in climate become greater with distance from the equator.

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.[26]

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. Another group is MarsDrive, which is dedicated to private initiatives for the exploration and settlement of Mars.

Concerns

Besides the general criticism of human colonization of space (see space colonization), there are specific concerns about a colony on Mars:

  • Mars has a gravity 0.38 times that of the Earth and a density of the atmosphere of 1% that on Earth.[15] The stronger gravity than the Moon and the presence of aerodynamic effects makes it more difficult to land heavy, crewed spacecraft with thrusters only, yet the atmosphere is also too thin to get very much use out of aerodynamic effects for braking and landing. Landing piloted missions on Mars will require a braking and landing system different from anything used to land crewed spacecraft on the Moon or robotic missions on Mars.[16]
  • The question of whether life once existed or exists now on Mars has not been settled, raising concerns about possible contamination of the planet with Earth life. See Life on Mars.
  • Advocates of a return to the Moon say the Moon is a more logical first location for a first planetary colony, perhaps using it as practice for future manned missions to Mars.[27] However, in several ways experience gained on the moon would not be applicable to the task of colonizing Mars. The moon has no atmosphere, no analogous geology and a much greater temperature range and rotational period. These differences mean that Mars has more in common with Earth than Earth has with the Moon. Antarctica or desert areas of Earth provide much better training grounds at vastly lesser cost. Also, the Moon is extremely poor in several of the key elements required for life, most notably hydrogen, nitrogen and carbon (50 – 100 ppm)[citation needed], and has only 47.2% of the delta-v requirement for launching to orbit that Mars has.[28]
  • It is unknown whether Martian gravity can support human life in the long term (all experience is at either ~1g or zero gravity). Space medicine researchers have theorized on whether the health benefits of gravity rise slowly or quickly between weightlessness and full Earth gravity. One theory is that sleeping chambers built inside centrifuges would minimize the health problems. The Mars Gravity Biosatellite experiment was due to become the first experiment testing the effects of partial gravity, artificially generated at 0.38 g to match Mars gravity, on mammal life, specifically on mice, throughout the life cycle from conception to death.[29] However, in 2009 the Biosatellite project was cancelled due to lack of funds.
  • Mars' escape velocity is 5 km/s, which, though less than half that for Earth, is reasonably high compared to the Moon's 2.38 km/s or the negligible escape velocity of most asteroids.[30] This could make physical export trade from Mars to other planets and habitats less viable economically.
  • There is likely to be little economic return from the colonization of Mars while Lunar and Near Earth Asteroid industry is likely to be exporting to Earth.[31]
  • Mars has dust storms which can reduce solar power. The largest of these storms can cover much of the planet.

In fiction

A few instances in fiction provide detailed descriptions of Mars colonization. They include:

See also

References

  1. ^ nasa.gov
  2. ^ http://gltrs.grc.nasa.gov/reports/2002/TM-2002-211467.pdf
  3. ^ centennialofflight.gov
  4. ^ sablesys.com
  5. ^ Technological Requirements for Terraforming Mars
  6. ^ http://hacd.jsc.nasa.gov/projects/space_radiation_marie_references.cfm MARIE reports and data
  7. ^ bnl.gov
  8. ^ Zubrin, Robert (1996). The Case for Mars: The Plan to Settle the Red Planet and Why We Must. Touchstone. pp. 114–116. ISBN 0-684-83550-9. 
  9. ^ Zubrin, Robert (1996). The Case for Mars:The Plan to Settle the Red Planet and Why We Must. Touchstone. pp. 117–121. ISBN 0-684-83550-9. 
  10. ^ http://www.phy6.org/stargaze/Smars1.htm
  11. ^ NASA Tech Briefs - Variable-Specific-Impulse Magnetoplasma Rocket
  12. ^ http://www.newscientist.com/article/dn17476-ion-engine-could-one-day-power-39day-trips-to-mars.html?full=true
  13. ^ a b Zubrin, Robert (1996). The Case for Mars: The Plan to Settle the Red Planet and Why We Must. Touchstone. ISBN 0-684-83550-9. 
  14. ^ NASA: Space radiation between Earth and Mars poses a hazard to astronauts.
  15. ^ a b Dr. David R. Williams (2004-09-01 (last updated)). "Mars Fact Sheet". NASA Goddard Space Flight Center. http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html. Retrieved 2007-09-18. 
  16. ^ a b Nancy Atkinson (2007-07-17). "The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet". http://www.universetoday.com/2007/07/17/the-mars-landing-approach-getting-large-payloads-to-the-surface-of-the-red-planet. Retrieved 2007-09-18. 
  17. ^ This is from an archived version of the web: The Space Elevator - Chapters 2 & 7 http://web.archive.org/web/20050603001216/www.isr.us/Downloads/niac_pdf/chapter2.html
  18. ^ Space Colonization Using Space-Elevators from Phobos Leonard M. Weinstein
  19. ^ marsrovers.jpl.nasa.gov
  20. ^ http://onlinelibrary.wiley.com/doi/10.1196/annals.1370.007/pdf
  21. ^ http://www.stk.com/downloads/resources/user-resources/downloads/whitepapers/0201_sun_mars_lib_pts.pdf
  22. ^ "A Novel Interplanetary Communications Relay" (PDF). http://strathprints.strath.ac.uk/25836/2/Macdonald_M_-_strathprints_-_A_novel_interplanetary_communications_relay_Aug_2010.pdf. Retrieved February 14, 2011. 
  23. ^ Landis, Geoffrey A. (2008-04-24 (last updated)). "Meteoritic steel as a construction resource on Mars". NASA Goddard Space Flight Center. http://www.sciencedirect.com/science/article/pii/S009457650800266X. Retrieved 2011-05-26. 
  24. ^ Lovelock, James and Allaby, Michael, "The Greening of Mars" 1984
  25. ^ http://www.users.globalnet.co.uk/~mfogg/fogg1996.pdf
  26. ^ G. E. Cushing, T. N. Titus, J. J. Wynne1, P. R. Christensen. "THEMIS Observes Possible Cave Skylights on Mars". http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1371.pdf. Retrieved June 18, 2010. 
  27. ^ WayBackMachine archive of Space Frontier Foundation
  28. ^ HANDBOOK of CHEMISTRY and PHYSICS, 64TH EDITION (c)1983, page F-133
  29. ^ Mars Gravity Biosatellite
  30. ^ Welcome to the Planets
  31. ^ The Case For Space

Further reading

External links


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