Heinlein, Robert A – Have Space Suit will Travel

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.