Hydropos

Could that be because it's really not that complicated to calculate?

Just to play devil's advocate on this, the brain is extremely adaptable in young kids. The sooner you can get them familiar with academic practices, the better (in terms of how much they can learn).

Interestingly, you may actually see a gain in the amount of water on board, as water is a metabolic byproduct of carbohydrates (food). Not sure how this balances against other sources of loss, though.

Not so much "keep it under wraps" as "not confirm it officially", as it would make the program look unprofessional. Religious conservatives might see it as an excuse to try and pull funding. Some of the astronauts who have lived on the ISS and replied to this question structured their responses like "Officially, no. No sexual activity is permitted aboard the ISS". In other words, it's likely a "don't ask don't tell" sort of deal.

It's been a while though, and I have an extremely sensitive throat - coughing after vaping - so I haven't done it recently.

Something a friend of mine found: adding a single drop of a nicotine-free, high-menthol vape juice to a "dose" (~30mg) of DMT makes it much easier on the throat and lungs.