LE BOURGET, France (AFP) - The European Space Agency (ESA) on Tuesday called for applications for one of the most demanding human experiments in space history: a simulated trip to Mars in which six "astronauts" will spend 17 months in an isolation tank on Earth. Their spaceship will comprise a series of interlocked modules in an research institute in Moscow, and once the doors are closed tight, the volunteers will be cut off from all contact with the outside world except by a delayed radio link. They will face simulated emergencies, daily work routines and experiments, as well as boredom and, no doubt, personal friction from confinement in just 550 cubic metres (19,250 cubic feet), the equivalent of nine truck containers. Communications with the simulated mission control and loved-ones will take up to 40 minutes, the time that a radio signal takes to cross the void between Earth and a spaceship on Mars. Food will comprise mainly the packaged stuff of the kind eaten aboard the International Space Station (ISS). The goal is to gain experience about the psychological challenges that a crew will face on a trip to Mars. Four of the crew will be Russian, and two will come from countries that are members of ESA, agency and Russian officials said at the Paris Air Show in Le Bourget. In all, 12 European volunteers are needed. A precursor 105-day study is scheduled to start by mid-2008, possibly followed by another 105-day study, before the full 520-day study begins in late 2008 or early 2009. Backup for the two volunteers taking part in each of these simulations means that 12 Europeans are needed. "The selection procedure is similar to that of ESA astronauts, although there will be more emphasis on psychological factors and stress resistance than on physical fitness," ESA said in a press release. Men and women who think they have the right stuff can download the application form on (http://www.spaceflight.esa.int/CallforCandidates). The terrestrial Mars-stronauts will not get much glory for their confinement, nor will they get particularly rich. They will get paid 120 euros (158 dollars) a day, said Marc Heppener of ESA's Science and Application Division. Viktor Baranov of Russia's Institute of Biomedical Problems, where the experiment will take place, said his organisation had received about 150 applications, only 19 of which came from women. "The problem is that it is very difficult to find healthy people for this kind of experiment," he said. Assuming that Mars and Earth are favourably aligned, with their closest distance of 56 million kilometres (35 million miles), it would take 250 days to get there, 30 days spent on site to conduct experiments and 240 days for the return, said Baranov. A trip to Mars is not an early prospect. The United States has set plans to return to the Moon by 2018 and later head to Mars, but without setting a date. The trip is fraught with many technical challenges, many of which are outranked by the question of keeping the crew healthy and sane.