"When you are thinking about going away for a long duration mission, it has to be part of your mindset that you're leaving your family, but it's for the right reasons, for good reasons, and hopefully helping humanity,'' US astronaut Sunita Williams who spent a total of 322 days in space on two missions to the International Space Station shares her experience with BBC's Christine Jeavans.
By Christine Jeavans
''So you settle yourself on that but you also have to prepare yourself. I call it tying up the ends of your life before you go because you never know what's going to happen.
''You want to make sure that when you leave, you feel at peace with everything. My first mission was six-and-a-half months. We weren't exactly sure how long it was going to be because I went up and back on the space shuttle which was dependent on weather for launch and landing.''
''So you might have to say goodbye a couple of times and you might get excited to come home and then have to wait. It was an emotional rollercoaster, particularly because it was my first space flight.''
''In space you need to stay as "usual" as possible. On the space station I would brush my hair every day. I'm not sure it made my hair look any better but it was one of those things that you do that you usually do on Earth so it keeps you normal.''
''Keep to a regular day is important as there have been studies that even a half-hour change to the normal 24-hour cycle starts to mess people up a little bit.
''There are sleep stations where you just close the door and it's dark and quieter. You can hear alarms in case something bad happens but it's generally pretty quiet. Most people have a little bit less sleep, there is always a feeling of nervousness, just because you're in a different environment and subconsciously you're always on edge a little bit.''