What problems do manned space flights have to overcome?
Its more concern with the physical well being of the astronauts and cosmonauts during long term space missions than anything. Getting to Mars itself would be relatively easy, keeping the crew fit and fed is the big problem. I feel however that our current ideas are heading in the wrong direction tho. An old idea comes to mind here, oneil rings. A ship designed as an oneil colony could be built, used as a space station, and refitted for a trip to mars within 20 years. A ship big enough to support triple redundancy in all areas, its own food processing, and a crew so large that there wouldnt be psychological effects on them. Gravity would not be a problem in the ship as it would feel natural to the crew. Technicians, medics, maintenance people, scientists, etc could co-habit-ate the ship easily for 6 months. This would also allow going to and from the Martian surface studying the planet for future in habitation. The ISS should be scrapped immediately and rethought!
