Space exploration programmes, currently under discussion in the US and in Europe, foresee human missions to Mars to happen
within the first half of this century. In this context, the European Space Agency (ESA) has conducted a study on the human
responses, limits and needs for such exploratory missions, the so-called HUMEX study (ESA SP-1264). Based on a critical assessment
of the limiting factors for human health and performance and the definition of the life science and life support requirements
performed in the frame of the HUMEX study, the following major critical items have been identified: (i) radiation health risks,
mainly occurring during the interplanetary transfer phases and severely augmented in case of an eruption of a solar particle event;
(ii) health risks caused by extended periods in microgravity with an unacceptable risk of bone fracture as a consequence of bone
demineralisation; (iii) psychological risks as a consequence of long-term isolation and confinement in an environment so far not
experienced by humans; (iv) the requirement of bioregenerative life support systems complementary to physico-chemical systems,
and of in situ resource utilisation to reach a closure of the life support system to the highest degree possible. Considering these constraints,
it has been concluded that substantial research and development activities are required in order to provide the basic information
for appropriate integrated risk managements, including efficient countermeasures and tailored life support. Methodological
approaches should include research on the ISS, on robotic precursors missions to Mars, in ground-based simulation facilities as well
as in analogue natural environments on Eart