[MarianaM (OP)]

David asks...

Would the biological clock change to a longer period of activity and less sleep when in space and weightlessness, and so thus less energy is needed to survive?

What do you think?

[alancalverd]

In the absence of a solar cycle, the human body seems to adopt something like a 25 - 30 hour cycle. In the absence of gravity we certainly don't need to consume as much energy to walk and carry stuff, but it is important to exercise in order to prevent bone demineralisation, so it's a question of roundabouts and swings.

Sleep is essential regardless of physical effort as the brain needs to shut down and clear itself from time to time. 

[evan_au]

Given the energy cost of accelerating a kilogram of food or water or oxygen to 11km/sec to achieve low-Earth orbit, it won't be energetically efficient to live in space any time soon.