OH BOY, SIT DOWN AND STRAP IN
YOU'VE ACTIVATED MY AUTISTIC TRAP CARD
Okay so aside from the blips mentioned above I was thinking Weir knew what he was doing because he seemed pretty knowledgeable but as someone who went on an entire mountaineering disasters special interest binge about a year ago this is causing my brain to record scratch.
The Hail Mary is at 40% of standard atmosphere. For context, the summit of Mt Everest is at 33% of the air pressure of sea level.
MT EVEREST, WHICH IS FAMOUS FOR BEING COVERED IN CORPSES LONG BEFORE YOU EVEN GET THAT HIGH!
Long before you even get there, many people have died from the low pressure due to their lungs filling with blood and fluid, or their brains swelling up. Even with supplemental oxygen people struggle in the death zone at 8KM and up. Many struggle before they even get there. Lots of people die because at that height there's so little air a rescue helicopter can't get up there because there isn't enough air for the blades to bite and push down; only once in history has a helicopter been as high as the summit.
Mt Everest is nearly nine kilometres high. For 40%, that's about 7.25 KMs high, according to a graph I found online. This is less than a kilometre under the death zone, which is where your lifespan is measured in hours or days without extra oxygen depending on your biology. This is two kilometres higher than the highest settlement on earth where the locals have explicitly evolved to survive, where the air pressure is 55% of sea level atmosphere. Oh, and those populations are still prone to chronic mountain sickness from living at high altitude for too long despite their genetic advantages.
The record on earth is two years at 5,900 metres. Grace has lived at about 7,250 metres for three or four years while in a coma that's already putting his body under considerable strain.
Like. Let's give Weir the benefit of the doubt and assume that that 40% pressure is pure oxygen to compensate. Now you have a massive fire risk (because that would mean double the amount of oxygen you'd have at sea level, where it's about 20% of 1atm to the Hail Mary's 100% at 0.4), and you don't want that in an enclosed area in space where evacuation is impossible, emergency services don't exist and there's electrical circuits everywhere that can cause a spark. One short circuit or misaligned cable and everyone is dead.
There's no reason why Weir can't have had him in a normal standard atmosphere and make him hang out in a decompression chamber for a few hours instead if he wanted to commit to modern day scientific and technological abilities, this is a bizarre narrative decision.
ETA: Wait this would explain the air resistance thing. Grace is still wrong I think, I don't think density negates air resistance, but there WOULD be less air resistance even on top of the increased gravity at 40%.