Exactly muslim observe fasting still through the sun movment. Thats why the timing varies region to region. Now If you have ever lived in Iceland you would know what is the sun situation there. In summer it is more than 20 hours of day light and in winter less than 4 hours.
About the outer space yes I would like to know the answer to that and where would be qibla in outer space... up side down?
I would surely like to contact a scholar for these issues.
I am going to kid a little with you...so don't feel bad.
Worry about it when you get to space!!..:)
At any rate whenever I find no direct ruling on any situaion:
I do whatever I see most logical, conforming to common sens.......... and closer to any direct ruling that exists!
So in space (if I ever get there)....I wouldn't worry about Qibla direction at all.
If it makes you feel comfortable....assume up side down position!!!:D
It always amuses me when people come with unusual questions and answer equally unusal answer.
Many times the question makes no real sense since the questioner is actually not wanting to learn but in essence is asking just to ask a question.
Now a little kid goes to his mommy!!!
Mommy what if you were not married to daddy..what would have happened to me? I am talking about these kind of questions!!
Same thing: why ask question when you have not gone to space or everyone knows there is no direct ruling on it so the person is free to choose with all his own judgement.
This comes from trusting Allah. He in all his mercy will not make you or anyone responsible for answering the questions which were not revealed by him through his messangers!!!
Coming to the topic:
Fasting is for those who are otherwise physically healthy.
BTW: No need to follow ANY religious ruling if mentally ill :D
If dehydration is deemed dangerous for someone (by an authentic qualified physician without cheating) then I think based on what I know that the person is exempt from fasting. Just give Kuffara....
If during fasting a person is dangerously dehydrated....got diarrhea, heat stroke or whatever.............It is quite OK to terminate fasting.
One should avoid getting in to situations as much as possible when fasting wich could lead to serious dehydration..
Kidneys and brain work miraculously.
Body makes so many chemicals/hormones which regulate salt and water content of the body. Its a great training for kidneys and part of brain like hypothalamus/Pitutary gland to make these chemicals and work a little harder in case water is not consumed for a while.
I personally do not think drinking plenty of water before and after fasting is good. Drink enough so your thirst is satisfied. Perhaps an extra glass.
Why I said that? Kidneys and brain in situation like drinking too much water adjust their chemicals in such a way that kidneys cannot hold water any longer and the person actually goes to bathroom either for a long time or several times till body fluid viscosity gets to normal range again. This may overshoot and the person may actually lose valuable salt and water content of the body unnecessarily.
So all extra water is down the drain anyway so why drink gallons of water before and after fasting? Let your thirst center in brain work itself and don't try to mess with it.
Anyway if one is still worried then small sips periodically..enough to replenish water but not to disturb thirst center too much while not fasing is all one can do.
Please read about brain thirst center/antidiuretic hormone/hypothalamus/aldosterone/Pitutary gland/hormonal functions of renal cortex etc.
Smartest cortex in the body is not in brain.....its in the kidneys...:)
I have not even touched spiritual side of it which others did so well.