Chapter 3 of RAH's (Robert Heinlein) Have Space Suit will Travel, Scribner's Juvenile from the 1950's in which hero Kip in great expository RAH style refurbishes a used space suit. A great book along with A Door into Summer for a young engineer of any age.
""But I didn't get tired of it; a space suit is a marvelous piece of machinery-a little space station with everything miniaturized. Mine was a chrome-plated helmet and shoulder yoke which merged into a body of silicone, asbestos, and glass-fiber cloth. This hide was stiff except at the joints. They were the same rugged material but were "constant volume" -when you bent a knee a bellows arrangement increased the volume over the knee cap as much as the space back of the knee was squeezed. Without this a man wouldn't be able to move; the pressure inside, which can add up to several tons, would hold him rigid as a statue. These volume compensators were covered with dural armor; even the finger joints had little dural plates over the knuckles.
It had a heavy glass-fiber belt with clips for tools, and there were the straps to adjust for height and weight. There was a back pack, now empty, for air bottles, and zippered pockets inside and out, for batteries and such.
The helmet swung back, taking a bib out of the yoke with it, and the front opened with two gasketed zippers; this left a door you could wiggle into. With helmet clamped and zippers closed it was impossible to open the suit with pressure inside.
Switches were mounted on the shoulder yoke and on the helmet; the helmet was monstrous. It contained a drinking tank, pill dispensers six on each side, a chin plate on the right to switch radio from "receive" to "send," another on the left to increase or decrease flow of air, an automatic polarizer for the face lens, microphone and earphones, space for radio circuits in a bulge back of the head, and an instrument board arched over the head. The instrument dials read backwards because they were reflected in an inside mirror in front of the wearer's forehead at an effective fourteen inches from the eyes.
Above the lens or window there were twin headlights. On top were two antennas, a spike for broadcast and a horn that squirted microwaves like a gun-you aimed it by facing the receiving station. The horn antenna was armored except for its open end.
This sounds as crowded as a lady's purse but everything was beautifully compact; your head didn't touch anything when you looked out the lens. But you could tip your head back and see reflected instruments, or tilt it down and turn it to work chin controls, or simply turn your neck for water nipple or pills. In all remaining space sponge-rubber padding kept you from banging your head no matter what. My suit was like a fine car, its helmet like a Swiss watch. But its air bottles were missing; so was radio gear except for built-in antennas; radar beacon and emergency radar target were gone, pockets inside and out were empty, and there were no tools on the belt. The manual told what it ought to have-it was like a stripped car.
I decided I just had to make it work right.
First I swabbed it out with Clorox to kill the locker-room odor. Then I got to work on the air system.
It's a good thing they included that manual; most of what I thought I knew about space suits was wrong.
A man uses around three pounds of oxygen a day-pounds mass, not pounds per square inch. You'd think a man could carry oxygen for a month, especially out in space where mass has no weight, or on the Moon where three pounds weigh only half a pound. Well, that's okay for space stations or ships or frogmen; they run air through soda lime to take out carbon dioxide, and breathe it again. But not space suits.
Even today people talk about "the bitter cold of outer space"-but space is vacuum and if vacuum were cold, how could a Thermos jug keep hot coffee hot? Vacuum is nothing-it has no temperature, it just insulates.
Three-fourths of your food turns into heat-a lot of heat, enough each day to melt fifty pounds of ice and more. Sounds preposterous, doesn't it? But when you have a roaring fire in the furnace, you are cooling your body; even in the winter you keep a room about thirty degrees cooler than your body. When you turn up a furnace's thermostat, you are picking a more comfortable rate for cooling. Your body makes so much heat you have to get rid of it, exactly as you have to cool a car's engine.
Of course, if you do it too fast, say in a sub-zero wind, you can freeze- but the usual problem in a space suit is to keep from being boiled like a lobster. You've got vacuum all around you and it's hard to get rid of heat.
Some radiates away but not enough, and if you are in sunlight, you pick up still more-this is why space ships are polished like mirrors.
So what can you do?
Well, you can't carry fifty-pound blocks of ice. You get rid of heat the way you do on Earth, by convection and evaporation-you keep air moving over you to evaporate sweat and cool you off. Oh, they'll learn to build space suits that recycle like a space ship but today the practical way is to let used air escape from the suit, flushing away sweat and carbon dioxide and excess heat-while wasting most of the oxygen.
There are other problems. The fifteen pounds per square inch around you includes three pounds of oxygen pressure. Your lungs can get along on less than half that, but only an Indian from the high Andes is likely to he comfortable on less than two pounds oxygen pressure. Nine-tenths of a pound is the limit. Any less than nine-tenths of a pound won't force oxygen into blood-this is about the pressure at the top of Mount Everest.
Most people suffer from hypoxia (oxygen shortage) long before this, so better use two p.s.i. of oxygen. Mix an inert gas with it, because pure oxygen can cause a sore throat or make you drunk or even cause terrible cramps. Don't use nitrogen (which you've breathed all your life) because it will bubble in your blood if pressure drops and cripple you with "bends." Use helium which doesn't. It gives you a squeaky voice, but who cares?
You can die from oxygen shortage, be poisoned by too much oxygen, be crippled by nitrogen, drown in or be acid-poisoned by carbon dioxide, or dehydrate and run a killing fever. When I finished reading that manual I didn't see how anybody could stay alive anywhere, much less in a space suit.
But a space suit was in front of me that had protected a man for hundreds of hours in empty space.
Here is how you beat those dangers. Carry steel bottles on your back; they hold "air" (oxygen and helium) at a hundred and fifty atmospheres, over 2000 pounds per square inch; you draw from them through a reduction valve down to 150 p.s.i. and through still another reduction valve, a "demand" type which keeps pressure in your helmet at three to five pounds per square inch-two pounds of it oxygen. Put a silicone-rubber collar around your neck and put tiny holes in it, so that the pressure in the body of your suit is less, the air movement still faster; then evaporation and cooling will be increased while the effort of bending is decreased. Add exhaust valves, one at each wrist and ankle-these have to pass water as well as gas because you may be ankle deep in sweat.
The bottles are big and clumsy, weighing around sixty pounds apiece, and each holds only about five mass pounds of air even at that enormous pressure; instead of a month's supply you will have only a few hours-my suit was rated at eight hours for the bottles it used to have. But you will be okay for those hours-if everything works right. You can stretch time, for you don't die from overheating very fast and can stand too much carbon dioxide even longer-but let your oxygen run out and you die in about seven minutes. Which gets us back where we started-it takes oxygen to stay alive.""