We know all that!
You're not supposed to scientifically analyse every aspect of it. That's the worst thing you can do with the majority of science fiction - as soon as you start that, you've ruined it for yourself and the others you try to be a smarty pants to.
It's not a documentary, it's a Saturday evening TV show aimed at the masses. Sit back, don't think too deep into it, and enjoy the adventure, peril, and dilemmas.