Remember when NASA sent a women to space...

[Humpthree]

...for only six days and they gave her one hundred tampons.

One hundred tampons.

And asked, 'Will that be enough?'

Cause they didn't know if that was enough...These are our world's greatest minds. They are literally rocket scientists.

100 tampons. One hundred tampons...

I'd have expected if your cycle is usually heavy enough to need a change every 60-90 mins for 6 days straight, the Dr & medical team with NASA should already have taken this on as a medical consideration rather than leaving it up to an engineer to guess.

The actual truth of it seems to be that one engineer asked, and it because a joke.

Whilst weight is important on space flights for someting relatively lightweight like tampons the issue is more weight distribution that absolute weight (you do not want an unbalanced load), so NASA does over-provision a lot of things to do with crew welfare (eg. a five day mission will have 7-8 days food and water, maybe 10 days air).

There also might have been an element of the unknown, what actually happens in space, it impacts almost everything, your body dumps water in zero/micro gravity, meaning you wee a lot, that might impact period flow in some way as well, even sweat composition changes.