ASTRONAUTS who take part in deep space travel might encounter psychological problems and loneliness which could provide a bigger barrier than technology to future missions, according to a French expert. At a major symposium on the future of human spaceflight in Strasbourg this week, Jacques Arnould, of the French space agency CNES, will argue that losing sight of Earth could be too traumatic for astronauts to bear, however highly trained they may be. Even a relatively short mission to Mars might tip some people over the edge, he warns. The barriers of the human mind are a frontier that must be approached delicately, but one that it is necessary to cross, Arnould said. ‘How will an inhabitant of Earth react when the image of his planet disappears from view? No answer exists at the present time.’ He added: ‘It may not be excessive to argue that this question alone offers a justification for human spaceflights to Mars.’