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Heat Sink and Sources an Astronaut Could Encounter Cody O’Riley Thomas Edison State College
Space is the final frontier of human exploration. This is due to the environment we have to survive in, and we can do so with very complicated suits and technology. The environment is 100% lethal to humans, and this is due to what we take for granted. An astronaut is exposed to a variety of heat sources and heat sinks, but all are not the same nor do they behave the same. Space is very, very cold and the temperature is -454.81 degrees Fahrenheit. Now for comparison, the absolute zero is –459.67 degrees Fahrenheit. This is the absolute lowest temperature, and space is very close to this. Therefore heat transfer as we know it will not work in our favor anymore. The human body on planet Earth gain heat from the atmosphere. Generally speaking when it is over 100 degrees Fahrenheit we are gaining heat from the environment and not losing any. When the temperature outside is not that, we are below our body temperatures, but given our clothes, fat, and temperature we aren’t loosing much heat. This is because our atmosphere is conducive to us, until it becomes really cold. Generally speaking winter would kill humans without the aid of furs, coats, or heaters. That is because at those temperatures the atmosphere is sucking heat out of us like a sponge is to water. Even with all of the above, we will eventually die in over -200 degrees Fahrenheit. Humans are incapable of maintaining their own body temperatures in any extreme environments. This is due to our body’s innate ability to perform all three heat transfer types at once without build in cooling system called sweat. This is
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what makes space so deadly to us, we need a stable environment to survive, and space is the extreme opposite of earth. In space we must identify where heat is produced. The answer is all the stars around us generate heat, especially our sun. There will be heat coming off the space craft including electronics around you. The astronaut himself generates heat. In space a human being is a heat source. There are then random bouts of radiation and flares from stars that you have to worry about heat wise. It is to be noted the sun is not friendly in space when it’s facing you directly; it can cause your suits temperature to fluctuate. This is due to your suit trying to keep the perfect temperature range, and is very delicate to any changes in the extreme environment. With many of the heat sources one must wonder what exactly a heat sink is here. That is simply everything else around you, even your suit and body. Your body is a heat sink to the heat produced via his suit. While the suit can absorbs both heat sources at a small rate due to the ultimate heat sink space being around it. That means that everything else your suit touches is also a heat sink. So unless you’re on the sun side of earth, you’re pretty much the only heat source in the surrounding area, next to your space craft. This temperature in the space suit is helped by the pressure generated inside the suit; it keeps your fluids from boiling into gases. Though it is to be noted that the pressure in the suit is only .29 atm, which is .71 atm below earth pressure. This pressure is essential because of how liquids behave at low pressure ranges. Liquids boil in space, so it is a good idea to pressurize the suits. However we cannot achieve full earth pressure due to the oxygen an astronaut breathes is pure oxygen. Earth has only 20% oxygen in its atmosphere. It really is just enough to keep us alive. This breakdown of heat sources and heat sinks help to show exactly how harsh an environment and shows that what we experience on earth is really easy to survive.
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The suit works as an insulator, a heat source, and a heat sink as well. This is due to how many layers the suit actually makes up. The suit has to act as a heat sink due to the built in heat source and heat production of the human, but is has to be tempered with great insulation for heat loss. This begins with what the first layer an astronaut actually wears. They wear a cloth suit that is specially woven with tubes throughout the suit. This allows for water to flow through the tubes to keep the astronaut cool. This is because the astronaut can be under some pretty hot conditions due to the human body’s heat source. One such factor is due to the sun itself. These people can be looking at a temperature over 250 degrees Fahrenheit in space. So it is no wonder why they have to be cooled so effectively in some scenarios. This is where the space suit and the cloth suit work together. The fluids the run through the tubes of the cloth suit also run through a built in heat exchanger in the back of the suit. This transfers the heat out through a thin layer of generated ice that gets vaporized into space. This is what makes the suit a heat sink, because in and of itself has a heat sink built into it. This is what allows for such an efficient insulator of the suit. The person would quite literally fry in the suit without this heat sink functioning correctly. The actual heat source of the suit is a little confusing. Despite the environment of space being so frigid, the space suit doesn’t come with an actual heater unit. The suit system relies on the human body to generate the heat, which in managed by the advanced cooling system in the suit. This sounds odd, but makes perfect sense in regards to heat transfer and space. Convection does not work in space, not like on Earth. The only way for any significant heat transfer in space to occur is radiation heat transfer, which is extremely slow. This is why the suit has such an efficient insulator; the suit uses your heat to produce the perfect environment. This is why they wear the cloth suit with micro tubes in it; it drags the heat off of you in water, and heats the air in
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the suit with it. Due to extreme heat in space that can occur, that is where the built in heat exchanger comes in handy to reduce the heat in the suit. The suit also has its own water system in the suit, so one does not have to worry about becoming dehydrated from the loss of their bodily fluids. The heating source of the suit comes with a very dangerous risk. This specifically relates to using the body as the suits heating source. Human bodies are meant to operate within a pretty fine line limit. This temperature range lies usually within the 98 degrees Fahrenheit to 100 degrees Fahrenheit. There are some oddballs, but most fall into this limit. This temperature is maintained with environmental temperatures between 68 degrees Fahrenheit to 130 degrees Fahrenheit. The human body is literally built to lose heat off of itself. We conduct heat through touching other materials, we have heat convection, we radiate heat, and our perspiration cools us down even more effectively. All this happens at once here on Earth where we have a really huge open space with other heater and cooler elements. The space suit has no such space. There is a cooling system but no heat system aside from the potential blast of 250 degrees from a sun ray or blast of radiation from the cosmos. That is exactly why using our bodies as the heat source is so dangerous. This is due to the lack of space, the lack of area for the heat to dissipate into. The body could literally cook itself without proper cooling, hence why we can generate a fever. Well we can generate more than just a fever in this scenario. Heat Exhaustion becomes a very real possibility to a poorly cooled body. Dehydration can happen due to a failure in the water system of the suit. This puts the human body under incredible circumstances where it could very easily die. This is assuming the body over heats itself, but any external heating source could send the body over its limit.
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The other factor to the body overheating is working too much. The space suits are not merely just a space suit, but also a space ship. There is a system designated SAFER on the suit, which is the propulsion system. This is for if the astronaut gets separated from the ship and needs to fly back to it. This system also helps an astronaut maneuver around in space. That help is what also keeps the astronauts body temperature lower. The other enemy for overheating is raising the body’s temperature by simply working on something, or moving around too much. The astronauts would have a heat stroke potentially by being allowed to move too much in the suits. This means their travel time has to be limited and well monitored. This helps to further explain why a simple spacewalk is considered to be pretty dangerous. The next real big risk is radiation. This can be random bursts or unknown bursts on any radiological elements. Aside from the obvious health risks, this could result in various heat increases inside the suit depending on what radiation it specifically is. Other sources of radiation can be heat born. The sun is not the only hot object in the sky and because of there is a certain degree of risk in running into an unexpected hot spot. The idea of using your body as the heating source does in and of itself create a nice warm environment you are comfortable with is a seemingly great idea. The reality is there is so many pressures to that stable temperature, that it is a real risk for your health.
The suit as we know has a heavy insulator in it. This is known to be multiple alternating layers of Kapton and Glass fiber cloth to produce the light weight super insulator (Dover, 1994). This combination leads the suit to be able to keep the temperature produced by a human being well contained and barely able to leave the suit itself. It will still have heat transfer outbound via radiation of the suit, but at a tremendously slow rate. This puts all the heat management on the
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built in heat sink to the suit. This in and of itself provides several risk factors. The cooling of the person requires them to be hydrated. This is due to the cooling liquid of the suit being performed by the sweat of the human body, which is why the suits come with a drinking pouch. Dehydration is a tremendous risk factor for the suit to even function correctly. The sweat collects in the cloth suit and travels along the build in mini pipes of the cloth suit. This travels throughout the suit cooling the human body down. The heat from this process is extracted through a heat exchanger in the space suit itself. The problem here become if the mini tubes were to ever breakdown or collapse. They are made out of collapse resistant material, but if it were to happen the astronaut would be in danger. The next danger is the heat exchanger itself. It works by transferring the het into a small amount of liquid that is frozen over by the coldness of space and then evaporates into space. This is a concern because if it were to clog, than there would be no more cooling going on in the suit. The suit is completely dependent on the heat exchanger because it is grossly unable to perform heat transfer like we can on Earth. Conduction and convection don’t really work in the vacuum of space. So because of this only one type is possible, radiation the slowest form of heat transfer. This is why the single heat exchanger unit is so important to the survival of the astronauts in the space suit. The space suit cannot deliver any heat to its environment except for the slow radiation output of it. This means we are limited to where we can actually travel. This brings up a very odd fact. Our suits are able to operate in ranges that deal with the radiation of the sun. This means we have to be careful of areas without any heat radiation like the dark side of the moon. This place is feasibly colder than our understanding. These places are those who are so far away from any heat radiation it is close to absolute zero, or at it. Those areas would be the points of no travel for humans in a space suit do it being so cold it might increase the radiation
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loss of heat through a space suit. That is the danger these suits run, they can only potentially lose heat one way. Heat does in deed travel through space. It can only travel by means of radiation heat transfer, but it is still a traveling mean. This radiation heat transfer is done on the infrared level, which means we cannot see it. All heats sources generate heat on this level. Due to the vacuum of space it is the only means. There are no particles close enough to allow for conduction, nor is any water in existence because it all boiled away due to the low pressure. Conduction through physical touch would not work due to the insulator used by the space suit, nor could it even in the low pressure. Heat in space just simply works one way, and it has to be a pretty powerful source to radiate any significant heat as far as Earth is away from the sun. The phenomenon that makes it hard for heat transfer makes it very easy to prevent heat flow. Since there is only one kind of heat transfer to stop, all we needed to do was supply an insulator which limits the radiation heat transfer to as small as possible. This effectively stops most heat transfer since space suits are only heated by us. There is a way to stop heat flow, which is the only way to prevent heat flow. This is to move all heat sources so far away from each other that there is no heat flow in space. There is no way to prevent the heat loss of the space suits through radiation. As it was stated above, we can limit radiation heat transfer to where it is but a trickle, but we cannot fully stop it. A spacewalk is one of the most dangerous events a human being can undertake. This is fundamentally due to how heat transfer works in space and how significant a heat sink and heat source works. Heat transfer exists in space much like it does earth, but the methods are far more
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extreme in their sources, which leads to some concerns, and also brings up how heat is moved and prevented from moving.
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Fazekas, A. (2013, December 20). Top 5 Space Station Repair Spacewalk Dangers. Retrieved August 20, 2015, from http://voices.nationalgeographic.com/2013/12/20/top-5-space-station-repairspacewalk-dangers/ Price, S., Philips, T., & Knier, G. (2001, March 21). Staying Cool on the ISS. Retrieved August 20, 2015, from http://science.nasa.gov/sciencenews/science-at-nasa/2001/ast21mar_1/ Shlosinger, A. (1969, October 1). HEAT PIPE DEVICES FOR SPACE SUIT TEMPERATURE CONTROL. Retrieved August 20, 2015, from http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690029106.pdf
