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Mars is the focus of much speculation and serious study about possible '''human colonization'''. Its surface conditions and the likely availability of water make it arguably the most hospitable of the planets in this solar system, other than Earth . 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. 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 would require an exponentially increasing amount of delta V, and are not feasible with standard Chemical Rocket s, but could become feasible with more advanced propulsion technologies, such as Nuclear Rocket s, which could feasibly cut the trip time down to about two weeks.1 RELATIVE SIMILARITY TO EARTH While Earth is most like neighboring Venus in bulk composition, Mars similarities to Earth are arguably more compelling when considering colonization. These include:
DIFFERENCES There are differences, of course, between Earth and Mars:
HABITABILITY Physiologically, Mars' atmosphere may be considered a Vacuum . An unprotected human being would lose consciousness in about 20 seconds and would not survive more than a minute or so on the surface of Mars without a Space Suit . Still, conditions on Mars are much closer to habitability than the extremely hot and cold temperatures on Mercury , the furnace-hot surface of Venus , or the Cryogenic cold of the Outer Planets . Only the cloud tops of Venus are closer in terms of habitability to Earth than Mars is. There are natural settings on Earth where humans have explored that match most conditions on Mars. Extreme cold in the Arctic and Antarctic match all but the most extreme temperatures on Mars. On March 21 , 2007 , in remarks at JPL's High-Tech Conference for Small Business, NASA Deputy Administrator Shana Dale said, "We also hope to discover if Mars can provide a second home for humans – an extension of our civilization – 40 million miles from Earth." 2 Terraforming of Mars Mars]] See Also: Terraforming of Mars Some groups have speculated that Mars might one day be transformed so as to allow a wide variety of living things, including humans, to survive unaided on Mars' surface.http://www.users.globalnet.co.uk/~mfogg/zubrin.htm The practicality of Terraforming is still unclear, and its Ethics are disputed. RADIATION Mars has no global Geomagnetic Field comparable to Earth's. 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 0.8 gray per year). 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 Event s (SPEs) produce much higher doses. Astronauts on Mars could be warned of SPEs by sensors closer to the Sun and presumably take shelter during these events. Some SPEs were observed by MARIE that were not seen by sensors near Earth due to the fact SPEs are directional. This would imply that a network of spacecraft in orbit around the Sun might be needed to ensure all SPEs threatening Mars were detected. 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 Accelerator s to simulate space radiation. The facility will study its effects on living organisms along with shielding techniques. 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.3 The general 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 whilst journeying there, are certainly a concern, but are not thought to prevent a trip from being made with current technology.4 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 Satellite s. While these will eventually wear out, additional orbiters with communication relay capability are likely to be launched before any colonization expeditions are mounted. The round trip communication delay due to the Speed Of Light ranges from about 6.5 minutes at closest approach to 44 minutes at superior conjunction. Real-time conversation with Earth, such as Telephone is not possible, but other means of communication, such as E-mail and Voice Mail pose no difficulty. 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. It should be remembered that the vast majority of exploration and colonization of Earth was conducted without the benefit of real-time communication with "home". Also a satellite at either of the Earth-Sun L4/L5 Lagrange Point s could serve as a relay during this period. Ordinary for such communications. In any case, a constellation of communications satellites, perhaps including a Lagrangian Point satellite located to avoid difficulties during superior conjunction, would be a minor expense in the context of a full-blown Mars colonization program. ROBOTIC PRECURSORS The path to a Mars colony will be prepared by Robotic systems such as the Mars Exploration Rover s Spirit and Opportunity. These systems will help locate resources, such as ground water or ice, that will help a colony to grow and thrive. The lifetimes of these systems will 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. Robotic systems will 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 MANNED BASES As with the first manned missions to the Moon, early manned missions to Mars may be tentative steps, sometimes referred to as Flags and Footprints. A real progression towards colonization will be the establishment of permanent bases which begin to establish an infrastructure from which other activities can grow. One proposal for early manned landings on Mars with a live-off-the-land approach is Mars Direct as advocated by Robert Zubrin .5 An active effort is also underway to simulate these early bases with the Mars Analogue Research Station Programme at Devon Island in Canada and with a more frequently used site in Utah , USA. ECONOMICS As with early colonies in the New World , economics are a crucial aspect to a colony's success. Whereas North American Colonies established a trade in timber, furs, and other raw materials, the early Martian colonies will need to develop local resources both for internal consumption and, perhaps, for export. These resources will certainly include water and/or ice. In the slightly longer term, the reduced gravity well of Mars versus that of the Earth may improve the economics of lifting materials from the surface. This reduced gravity together with Mars' rotation rate makes possible the construction of a Space Elevator , although there is the problem of the low orbit of its moon Phobos . 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 Latitude s 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. Midlands , as seen from ''Opportunity'' ]] The exploration of Mars' surface is still underway. The two Mars Exploration Rover s, ''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 become available. As on Earth, the further one goes from the equator, the greater the seasonal climate variation one encounters. 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. The canyon runs roughly east-west, so shadows from its walls should not interfere too badly with solar power collection. River channels lead from the canyon, indicating it was once flooded. Martian moons While not strictly part of Mars itself, the moons are attractive for some kind of presence. The Delta-v from the moons to an Earth return trajectory is low, and the moons may possess rocket propellant such as water ice in the rock. If so, they could act as refueling points for vehicles returning to Earth, and would be economically viable to periodically return propellant and other material to Cislunar Space . This could help pay for Martian surface settlement. CONCERNS Besides the general criticism of human colonization of space (see Space Colonization ), there are specific concerns about a colony on Mars:
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