With the development of the International Space Station and plans for future missions to Mars, astronauts are likely to spend ever longer periods in space. However, little is known about how the female body is affected by weightless conditions. This is because most previous ground-based studies have been carried out on male volunteers and because relatively few women have flown in space to date.

The new study is a joint venture between ESA, NASA and the French and Canadian space agencies. It will be carried out by the French Institute for Space Medicine and Physiology at a hospital in Toulouse, France. Volunteers must be non-smokers aged between 25 and 40, less than 185 cm in height, and have no addictions to drugs or alcohol. They should be fluent in French or English and citizens of the European Union, Norway, Switzerland or the US. They will earn a total of €15 200, which will be paid in instalments over a four-year period.

The 24 test subjects will be split into three groups of eight. One -- the control group -- will have no extra stimulus over the 60-day best-red period. The second group will carry out an exercise regime whilst in bed. The third group will be fed a nutritional supplement during the 60 days. An international team of scientists, doctors and nurses will look after the women, whose fitness, heart and muscle function, mood, hormonal status, nutritional requirements, reflexes, balance and immune system will all be monitored. Volunteers will be videoed during the entire study and will have to carry out three-week long tests before and after the period in bed.

ESA hopes to use the results in its plans for human space exploration. It already wants to send astronauts to the Moon before launching a manned mission to Mars by 2035 as part of its ambitious Aurora programme. According to ESA, lying in bed for extended periods induces changes similar to those experienced by astronauts during and after space flight -- including poorer blood circulation, weaker muscles, changes in gait and balance, and a reduced ability to perform physical exercise. Tests will start in January 2005.