For example, apparently nothing can prevent degeneration of bones in weightlessness. All these might imply that space flights for people cannot be sufficiently long even to reach close planets, not speaking about more distant places in space. We cannot create sufficiently big gravitational attractor as the Earth is. And so, it might look as people cannot inhabit space stations for a really long stay. Simply, human organisms demands weight and it is our destiny to remain close to a big planet, as we are now.
Weight is a vital condition for our life to go normally.
The devorce between gravitational force and weight can be discovered in a debate and motivate students to explore the way to create weight in space. Recent studies shows the weightlessness is a state of potential dangerous for humans. It might look as preventing people from space explorartion. The problem can be solved basing on th efact that weight is a concept which is different from the gravitational force. Weight can be created in a specially dezigned stations or ships.