Apollo’s PLSS And The Science Of Keeping Humans Alive In Space
upstart writes for SoyCow1984:
Our bodies are fairly fragile biological systems. The human body operates within a fairly small temperature range, requires regular access to water and food and above all oxygen. It has a low tolerance for pollutants like carbon dioxide (CO2) which is a natural byproduct of its metabolism. Rising CO2 levels in the air one breathes eventually leads to hypercapnia (CO2 poisoning).
When it comes to keeping a human alive in a low-oxygen, low-temperature environment such as a mountain climber would experience, we usually reach for warm clothes and thermal underwear to retain as much body heat as possible. For oxygen one would use an oxygen tank and a mask - essentially breathing pure oxygen, or environmental air mixed with extra oxygen. We had the most to learn from deep sea diving which comes closest to the experience of breathing in space. Divers use the open-circuit system, or an advanced 'rebreather' system that scrubs CO2 from the air breathed out by the diver.
For Yuri Gagarin, his SK-1 (DDDNDDDN DD3/4ND1/4DNDNDDD^1 #1: "Skafandr Kosmicheskiy" or "Space Diving Suit") spacesuit was pressurized, supplied with fresh oxygen and scrubbed of excess CO2 by the systems built into the spacecraft, with the SK-1 suit connected up to them using hoses. Even then, descending to Earth in a Vostok spacecraft required the cosmonaut to eject at 7 km altitude and parachute down to the surface, as the landing of the spacecraft's descent module was not deemed survivable due to the extreme deceleration.
In the end, Yuri managed to stay conscious throughout the entire mission, making it safely back onto the Earth's surface. This showed that manned space missions in Earth orbit are definitely survivable.
Following a number of firsts achieved in Yuri's historical mission, both the Soviets and the Americans gained experience at keeping their cosmonauts and astronauts alive and comfortable in Earth orbit. In addition to umbilical cord systems to the spacecraft's oxygen generating, CO2 -scrubbing and temperature regulating facilities, the Soviets developed for Voskhod 2 an open-circuit oxygen-providing backpack good for about 45 minutes. The next big challenge was to take the spacecraft's complete life support system and turn it into a portable system.
EVAs (extra-vehicular activities) at the time involved staying quite near the spacecraft, but these were all for short flights in orbit. There was no question that using an open-circuit system on the Moon would be exceedingly wasteful and impractical. Using an umbilical cord to the landing craft would also be impractical for many fairly obvious reasons. The picked solution would become the Apollo Portable Life Support System (PLSS).
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