They do share information, but it's a much different situation. It's not 100 days, NASA already does 100 day missions on the ISS, there's little NASA doesn't k

They do share information, but it's a much different situation. It's not 100 days, NASA already does 100 day missions on the ISS, there's little NASA doesn't know from direct experience that any navy could tell them. The most common scenario for a mission to Mars would involve 6 month trips with 18 month stays on the Martian surface, for a total of well over 2 years away from Earth. With a crew of maybe 4, on the low end. That's a situation that's completely unprecedented in history. Not only do you have extended isolation, but there's no way to get out of that isolation, no matter what happens. They are locked in to that extremely long term of isolation, there's no abort scenario to bring them back home sooner (in many mission designs anyway). The closest analogy on Earth isn't submarine voyages, it's actually prison. And that's a big reason why there's been a desire to study these sorts of things separately, without the extensive cost of space hardware in the picture. Because it is an unknown and it does have the potential to impact the potential success of a mission.