A Related Comment
One of the main reasons for returning home has always been to visit with friends and relatives. Modern technology does not require physical proximity for that to happen. This same technology also means space voyagers will br far less lonely than on sea voyages of the past. I honestly think the pshycological factors issues are vastly overblown when judged in the context of what historic explorers endured. Maybe we're softer now due to far easier lives, but we know humans are capable of enduring psychological stresses greater than those expected on a mission to Mars. Psychological factors are important in optimizing mission performance, but I don't think they are mission killers.
Regards,
Mark