To minimize the cost of travel, the mission should last at least 15 years because the most favorable alignments between Earth and Mars (shortest distance) occur only very rarely.
The shortest distance between two bodies is when Mars is in opposition, that is to say when the Earth comes between Mars and the Sun. These oppositions are held approximately every 780 days (26 months), but given the relative eccentricity of the orbits of Mars and Earth, the shortest distance between the Earth and Mars (55 million kilometers) does not return all 26 months. it will be necessary to wait the concordance between the perihelion of Mars and the opposition of the two planets, or 7 oppositions, i.e. 15 years.
In these favorable conditions, astronauts traveling 6 months to go and less than four months for the return, in the best conditions. Astronauts will be confined in a cramped box and the psychological aspect of this confinement is difficult to manage, all human beings are not capable, moreover very little will support. It will make a drastic selection of the candidates.
Live for months in complete autonomy in a capsule requires to take oxygen, water and food needed to travel. For a journey of nine months, the mass of oxygen, water and food needed is huge. Each day, a man consumes about 1 kg of food, 1 kg of oxygen and 3 kg of water. To optimize the load, so it will recycle water and waste and carry a mini terrestrial ecosystem that allows the survival of the crew during this long journey. For oxygen it will take the CO2 discharged and produce oxygen through photosynthesis of plants. For water, it will be necessary to recycle the urine. For food, it will be necessary to recycle organic waste and grow vegetables in the waste. In addition it must be ensured that no pathogen invades the capsule. The psychological balance between men and women will be strongly put to the test. Although astronauts will be confined in a cramped box, facing to their confinement, the outward journey remains the easiest part of the mission.
Upon arrival on the Martian soil, candidates must be autonomous and mostly stay healthy and this task is much more complex than it seems. The Martian atmosphere is hostile, the light is low, the solar radiations are harmful, there is no oxygen, there is no liquid water and the temperature reached average -60 ° C and can drop to -130 ° C. On the desert surface of Mars, nothing grows, it will be necessary to find water, produce energy, oxygen, water and food in mini heated greenhouses. To build this, it will require a lot of materials, absent on Mars. It will not be possible to carry the materials needed to build a power plant, a boiler, a water reservoir, a unit of wastewater treatment, a radio room, a laboratory, a workshop, offices, rooms, sports halls, a kitchen, a restaurant, a library, etc. As for the return to Earth, it is the most obscure part of the mission. We have to wait a giant technological leap forward to consider.
NB: MELiSSA (Micro-Ecological Life Support System Alternative) is a project whose objective is the study of an ecosystem of micro-organisms and plants. This tool allows to better understand the behavior of artificial ecosystems and the development of technology for a future regenerative life support system for manned space missions of long duration, for example a lunar base or a mission to Mars. The driving force of MELISSA is recovering the food , water and oxygen from wastes (faeces, urea), carbon dioxide and minerals. Based on the principle of "aquatic" ecosystem, MELISSA has 5 compartments colonized respectively by thermophilic anoxygenic bacteria, photohererotrophic bacteria, nitrifying bacteria, photosynthetic bacteria, higher plants, and the crew. Hazardous waste and air pollutants are processed using the natural function of plants that in their turn provide food and contribute to the purification of water and oxygen to revitalize the air.
Mission ISECG has identified a set of tasks required in the lunar vicinity and on the surface of the Moon, before considering a manned mission to Mars, for the years 2030.
Ten space agencies met in Kyoto August 30, 2011 under the ISECG (International Space Exploration Coordination Group) to discuss the development of a common roadmap for coordinated space exploration internationally. Before sending men to Mars, it will return to the Moon and send humans to an asteroid. Each of these objectives will allow space agencies to gradually acquire the necessary technologies to reach Mars. Roadmap to prepare for a possible manned mission to Mars, highlights efforts to achieve financial and technological leaps to cross by global governmental and non-governmental organizations. Sustainable exploration, affordable and productive of the surface of Mars by humans is a very long term goal. The global roadmap for the exploration of Mars, creates a framework for the coordination of preparatory activities. This global roadmap Mars exploration is linked to a set of priorities and goals of preliminary respect and there are not that technological objectives. Of course we need to develop exploration technologies and the infrastructure needed to live and work beyond low Earth orbit.
But we must also engage the public, to interactive manner, as in a common space exploration cause. Human missions beyond low Earth orbit are possible with a coordinated international participation because the pitfalls are considerable. It will take a lot of expertise to enhance safety, expand human presence beyond low-Earth orbit to continually increase the number of people on each destination, extending the duration of manned missions in self-sufficiency, reduce the risk of space environment on human health and the technological equipment and finally to highlight the benefits to the whole of humanity.
NB: Agencies involved in the development of a common roadmap for coordinated space exploration are: ASI (Italy), CNES (France), CSA (Canada), DLR (Germany), ESA (European Space Agency), JAXA (Japan), KARI (Republic of Korea), NASA (United States), Roscosmos (Russia), UKSA (UK).