During ascent and descent, space shuttle astronauts wore the classic orange ACES pressure suit:
In this picture:
What is the nylon strap going from crotch to neck for, and why is it attached via a pulley to a cable looped around the suit’s collar?
It’s to keep the neck seal away from the astronaut’s neck when putting it on. It prevents the seal from compressing the neck and helps keep the area open for proper ventilation and for later attaching the helmet and life-support connections. It basically just holds the neck opening “forward.”
My guess is that it helps hold their position in a seated position while the suit is under pressure.
Theoretically, pressure suits are made with constant volume joints so changing position doesn’t increase pressure, making it harder. Practically, it might be the case that it still is difficult to bend at the waist. That strap would pull neck to crotch.
That makes more sense. You wouldn’t want the neck collar ring tight to the throat.
By “neck seal”, are you referring to the hard circular ring that the helmet attaches to, or the flexible material that appears to be gathered snugly around the wearer’s neck? Presumably the former, because it wouldn’t make sense to try to pressure-seal anything against the wearer’s flesh. But now that I’ve said that, what exactly is all that material bunched up against the wearer’s neck? Is this so the ACES functions as a dry suit (even without a helmet) in the event of a water landing/egress?
Yes, the hard ring.
I believe the suit is not completely waterproof. It’s insulated and protects from cold air and water temperatures, and it’s water resistant, but not waterproof. They do train in them underwater to simulate microgravity, so the level of resistance is probably pretty high.
AIUI, the underwater training for microgravity activities is done with an EMU suit rather than an ACES suit:
This is in part what it does (also keeping the helmet forward so it doesn’t smack into the occupant’s face) but it also serves to help compress the torso longitudinally during external depressurization. Because this is a ‘soft’ suit, when depressurized the suit will puff out and without that restraint the helmet and neck ring will basically try to shoot upward with the user essentially ‘hanging’ by their armpits. These suits are really designed just as emergency depressurization suits and are not intended for EVAs. so they lack the internal structure of the semi-rigid A7L EVA suit and the precisely fitted design to each individual astronaut.
This material is a called a “neck dam”, and its purpose is to prevent water intrusion during egress. The suit is watertight (as long as valves are closed) and the dam is to assure that water does not fill through an open helmet during water landing and egress, drowning the astronaut the way Gus Grissom almost did. (Grissom’s suit had a neck dam but because of the sudden sinking of the Liberty 7 he did not have time to properly deploy it.) The suits have an attached harness for a floatation system as well as the parachute and were designed to allow the astronauts to survive water exposure for several hours before rescue.
Stranger
So I was right!
Yeah but not just for the seated position. If anything, it is even more important when standing.
Stranger
It probably did kill Victor Prather in the Strato Lab V flight. He fell in the water, his suit flooded and he drowned.
For those (like me) unfamiliar with “Strato Lab”:
Wow. 'Nads of steel.
Years ago I nearly witnessed a similar event that happily didn’t actually occur. But came very close.
The scene is USAF water survival training. Then held in the shallows off Homestead Florida. One of the tasks is to be hoisted aloft in a parasail behind a speedboat. But unlike the fun tourist ride, you’re wearing a full set of flight gear including helmet & oxygen mask, a USAF standard parachute harness, with the inflatable 1-person dinghy/lifeboat hanging on a lanyard ~30 feet below you.
Once towed up to about 300 feet you were pretend you’d just ejected, disconnect from the tow rope and free-descend under the parachute, do your procedures to land successfully in the water, deploy your inflatable “water wings” type flotation device, get out from underneath the canopy, get into your life raft, begin signalling for help, and await “rescue” by another boat nearby.
We were using a very slightly modified standard ejection seat canopy as a “parasail”. So when you cut loose, you went more or less straight down and at a good clip. In light winds the canopy settled directly on top of you and getting out from underneath it without being tangled in it before it sank was a big deal. To up the difficulty level the CO2 cartridges in your flotation were used, not new. So inoperative and you had to blow into the red tube to inflate. After getting out from under the canopy.
No biggee if you kept your wits about you; all this had been rehearsed ad nauseum in safer places.
So far no disaster.
By luck my class had about 10 guys like me, 23 yo indestructible cocky Lieutenants fresh out of pilot training on our way to train to fly an F-whatever. And two ancient well-worn 35yo Majors who were going to the U2/SR-71 program and would be doing the exact same drill, except wearing their pressure suit without a helmet. Simulating that they’d discarded the helmet earlier in their descent from stupid-high in the stratosphere. To improve their odds, they were also supposed to have water wings with live CO2 carts.
Yup, there was a mix-up on whose water wings were put onto who. Some newbie greenhorn (not me), got the water wings with live carts, and one of the space-suit majors got the dead ones.
He did not drown, but it was a very close call. Keeping the suit’s neck ring above water was not at all easy, and the more water than got inside, the harder it got. Good thing the rescue boat was extra close by.