That a flight to Mars is a reality is beyond question. Its duration has also been calculated - using the optimum trajectory it will take 350 days there and 350 to get back, plus 20 to 30 days spent on the planet's surface. But the exact date is still only a guess. Optimists say 2017-2018 is the nearest "ballistic window" for an Earth-Mars mission, but pessimists consider it unrealistic, above all for technological reasons: a spacecraft must be built, engines developed, and the whole mass weighing hundreds of tons placed on a path to Mars.

Nevertheless a manned expedition to Mars is being prepared with such a schedule in mind. In Russia it is part of the Federal Space Program.

An advanced development project called "A Manned Expedition to Mars" was drafted in 2005. Vitaly Semyonov, chief designer at the Keldysh Center and one of the project developers, said the research already conducted has revealed one important feature: the schedule and costs of a Martian mission depend mainly on the type of propulsion unit.

Scientists have considered different options, including liquid rocket engines burning oxygen and hydrogen; nuclear rocket engines with liquid hydrogen as working medium; and nuclear and solar power units to drive electric propulsion engines. The choice fell on the solar unit with thin film elements based on amorphous silicon. The nuclear unit is viewed as a possible alternative.

Initially, it is planned to mount five expeditions using the same orbital spacecraft. All expeditions will include a multiple solar-powered tug. Their aim will be to select and prepare the site for a Martian base.

Scientists believe that the location of the site must above all meet the requirements of safe landing and take-off. Another important factor is the terrain on which a habitable facility will be located to ensure its anti-radiation protection. The terrain must also make easier the monitoring of asteroid-cometary impacts and their dangers for base residents.

A further essential requirement is the presence of liquid water at shallow depths. Lastly, an analysis of geological data from Mars has pinpointed the most likely spots with traces of life. It is not inconceivable that these areas will be most attractive for siting the first extra-terrestrial base.

But before the mission gets off the ground, scientists will have to solve, in addition to engineering challenges, a multitude of medical and biological problems. In a strategy for and the planning of a manned expedition to Mars the human factor is the top priority. It is the weakest and most exposed link of the mission, crucial for the whole project. Medical and biological aspects of the expedition therefore pose a new challenge to scientists.

Many of the established principles, methods and means of space travel are unacceptable for a manned Mars mission. What sets it apart is different communications techniques with the Earth, a variety of gravity effects, a limited period of adaptation to gravity before landing on Mars, enhanced radiation, and the absence of a magnetic field.

The 438-day flight aboard the Mir orbiter by physician Valery Polyakov at the end of last century showed that there are no fundamental medical or biological restrictions to extended space missions. Radiation, however, is another matter. Its effects intensify manifold when the vehicle leaves the protection of the Earth's magnetosphere. This demands a special anti-radiation facility. It might be a radiation shelter that would absorb charged particles or an artificial electromagnetic field built up around the craft.

Presently, the developers are inclined to opt for structural protection by placing tanks with fuel, water and other supplies around the living quarters. This affords a rate of protection of about 80-100 g/sq cm.

Another problem is food. It would seem years of practice have taken care of it, and there is no need to reinvent the wheel. The crew of a space ship will use freeze-dried products which need a little water and heating before being put on the table. But, fine and delightful as such dishes may be, they should be mixed with some normal food.

The idea of keeping caged fowl aboard the vehicle for cosmonauts to eat their eggs, quail eggs preferably, had to be abandoned. Experiments showed that newly hatched chicks never adapted to zero gravity. Fish and shellfish fared better, but they grow too slowly, and so cosmonauts are unlikely to eat fresh fish on their way to Mars. What is certain is that the interplanetary ship will have a greenhouse, though a small one. The optimum choice of crops will be crucial.

It has been calculated that a cosmonaut needs 2.5 liters of water daily, which means the vehicle will have to have a supply of several tons. Some of the water will be recirculated. An ideal arrangement would be a closed-circuit physical and chemical system to ensure cycles of substances. But this appears to belong to a distant future.

Other problems are psychological. With great distances involved, a radio signal will take 20 to 30 minutes to travel each way. Mission Control will simply have no time to intervene in an emergency. The Earth will at best provide advice, but all decision-making will be the responsibility of the spacecraft. But before a crewed Martian expedition lifts off, scientists will try to solve many of these problems during the Mars-500 mission.

It will be an imitation, not a real flight: a crew of six will spend 520 days in a ground facility consisting of five hermetically sealed communicating modules. One of them will imitate the Martian surface. The modules are loaded with devices to register various parameters inside and to monitor the health of the test subjects. Scientists need to know how human beings act in teams and handle non-standard situations.

All results - starting with the behavior pattern of the crew and ending with their diet - will be examined by specialists. This will take care of most likely situations and ways of dealing with them during the flight. A crew is currently being recruited for the "ground interplanetary mission". Ninety volunteers from 19 countries have already stepped forward. They are mainly men, with only eight women and one married couple.

The explanation appears simple: physiologically and psychologically women have fewer chances than men to be among the first to step on Mars. The experiment will involve six people, although a real mission to the planet will have a crew of four.

Remarkably, soon after Russia announced the Mars-500 experiment, the United States, too, began inviting volunteers for an imitation flight. The American experiment is scheduled to begin on May 1, 2007. Test subjects will spend four months on it.

The European Space Agency is developing its own concept of an expedition to Mars, so far uncrewed. China has plans to explore and utilize Mars. In short, a space race is getting off the start line again. The only question is, why should we fly to Mars at all?

"Most scientific achievements in space are credited to automatic devices, not manned missions," says Lev Zeleny, director of the Russian Academy of Sciences Space Research Institute. He believes, however, a human being is bound to land on Mars, even if the event makes no rational sense. The sensations of a person stepping down on the surface of another planet are so precious as to have no value scale to appreciate them.

Related Links
Mars News and Information at MarsDaily.com

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