Agreed. I’m not sure where your earlier 50G came from, but it’s probably more than we need to subject our test monkey to.
Stapp (he of the insanely large brass balls) may not have died of his tests, but that’s not to say he was uninjured by them. A few days in the hospital recovering was sorta par for the course.
Which is incompatible with the other part of the OP: that the pilot do something useful once delivered onto orbit ASAP.
50 gees over 16 s gets you to 8 km/s–roughly orbital velocity. You could reduce this, but your accelerator length grows quadratically, and it’s already 64 km (the remainder of the 200 km is to keep a nice vacuum). 50 is in the ballpark of Stapp’s tests so I thought it was a reasonable goal.
I’d say it’s unknown, but not implausible that with better protection, our pilot might do well enough to do something useful post-delivery. Stapp’s conditions weren’t ideal. The reversed direction of acceleration is an obvious one, though forced lung pressurization might help even further.
No, I’m referring to free divers, who take a breath of air at the surface and then dive to depths exceeding 800’.
Doesn’t change the picture–every surface of their bodies is still at 10 atm, gas or liquid. The volume of the air in their lungs has gone down by 90%, but it isn’t being pushed out and there’s still some free volume.
The atmosphere in the hypothetical capsule is at 1 atm, though, while the inside of the lungs is at (say) 1.25. I don’t think a person can hold in that kind of pressure, though maybe I’m wrong about that. I suspect it’ll just be forced out under acceleration. The pilot’s probably blacked out and not in a position to be holding his breath anyway.
An overpressured helmet, restrained mechanically (attached to a snug-fitting shirt, for instance), could maintain the right pressure balance, but it seems tricky.
Thinking on it more, a space activity suit is almost exactly what we want here–it uses mechanical pressure to allow the lungs to be overpressured (compared to the environment) without popping the astronaut. The suit needs to be built such that the mechanical pressure drops off rapidly with distance; as our accelerating astronaut’s lungs shrink, the suit reaches a new equilibrium such that external pressure force + acceleration force = internal pressure force. The lung volume would just decrease slightly, not go to zero.
SASes aren’t quite mainstream tech yet, but we don’t need a full-fledged version here, just something good enough for a short launch.
Conventional aviator oxygen masks & regulators provide positive pressure breathing at high altitude.
The standard design mixes ambient air with an increasing percentage of pure O2 as the altitude goes up to maintain the same partial pressure of O2 as has ordinary air at sea level pressure. Once the altitude exceeds ~25,000 even 100% O2 at ambient pressure is less than sea level atmospheric O2 partial pressure.
At that point the mask/regulator system, clamped snugly to the face, begins to apply positive pressure. It’s mildly challenging to breath, and a PITA to talk under positive pressure. In normal breathing, relaxing your diaphragm muscles causes an exhale and you pull with those muscles to inhale.
Under pressure breathing that’s reversed; relaxing allows the mask to inflate the lungs and you inhale. It takes a positive shove on your part to exhale against the pressure. At very high altitude it’s significant unfamiliar work just to breath, much less talk.
The practical limit for this system is ambient pressures up around 50,000 foot altitude equivalent. Higher than that the pressures needed would be great enough to damage the lung’s plumbing and alveoli.
I don’t know how well a system like that would work as a G[sub]x[/sub] countermeasure. But it’d be worth something. It doesn’t help at all for more typical fighter maneuvering G[sub]z[/sub] loads and isn’t used AFAIK.