Space colonization: spacewalk and other questions.
Alexander V. Bagrov ( «Authors»)
Generally speaking, space colonization is a huge and multifaceted process that can’t be done without answering thousands of seemingly small, “private” questions. For example, how many people should be in space colonies that it could exist independently, without constant support from the Earth? What should be the greenhouses to support the food needs of colonies? What crops are the most suitable to be grown in space greenhouses? How to ensure that the soil fertility in the greenhouses is not depleted and the crops – not degenerated? What to do with space industry waste? How to protect yourself from dangerous space radiation? A lot of questions, they can’t be listed. But it is necessary to answer to them, and with our publications we will do it, not only in scientific articles by scientists in the section “Scientific Publications “, but in the exhibit to the journal’s application “Brief Notes”, responding to questions from our readers. Further, there are a lot of space fantasies and misconceptions, for example, in [1-3] it was asked about what happens to a man in space without a spacesuit? This question has spawned many misconceptions on the part of those who started responding to it. In this regard, we will continue the crusade started by doctor Bogachev from LPI  [5, 6] against space-related misconceptions, horrors and dismemberments. Thus, it is often for phenomena usual for earthly residents to take a very different shade in space.
Let’s start with the question: will be an astronaut trapped in outer space without a spacesuit freezed or roasted? Sun’s rays heat the surface of any bodies near the Earth to a temperature of 130 ° C, and unexposed surfaces cool to space radiation temperature of -180 ° C. So, an astronaut trapped between the stove and freezer, will be fried on one side, while the other side will be frozen, as if he had been dipped in liquid nitrogen. Probably, no organism will survive in space without a spacesuit, even if we imagine that due to the wonders of genetic engineering it can withstand the vacuum of space. Incidentally, the same thing is not only true for a living organism, but also for any device launched in the space. But not every unit can stand it! Both people and devices need to be protected from such extreme temperatures. People got used to protect themselves from a bad weather with clothes. And what clothes suit people the best? It seems clear: warm during severe cold and light-weight during heat. But what if on one side the sun heats the suit to a temperature of 130 ° C, and from the other side it cools down to -180 ° C? The easiest option comes to mind: heaters and coolers have to be built in a spacesuit. Where it is “hot”, turn on the cooler, and where it is “cold”, turn on the heater. It turns out that this solution is not the best. An astronaut is not a weathercock, which will always turn a part of the suit with a cooler to the Sun; he must move and work freely in space.
Is it really necessary to make a suit as a chessboard, consisting of alternating coolers and heaters? Of course not. A key to the problem lies in the thermal conductivity. Everyone knows that the hot pan from the stove should be taken not with the bare hand, but with a hand clad in a thick mitten: the heat of the pan does not immediately reach the palm, and while the mitten is warming, the pan can be put on a non-combustible support and let it stand. During this time, the palm will feel the heat coming from the pan, but not get burned. The Same mitten saves hands from cold, if it’s necessary to take a cold piece of metal. Therefore, if the suit is made of a material with low heat conductivity, it will allow enduring the cold and the heat of the space, but for a very short time. Now, if the astronaut in his spacesuit can rotate quickly, placing one side, then the other side to sunlight, then the suit by the rapid alternation of heating and cooling would keep a constant temperature inside. But there are no trifles in the space! What the “constant” temperature will be in a spacesuit? If the body gets as much heat as it gives away, its temperature will be “equilibrium”. The amount of heat coming from the Sun can be calculated knowing the flow of its thermal energy and its share, which is not absorbed by the spacesuit (reflected from it). Radiated thermal energy, i.e. the cooling rate depends on the area of the suit and the fourth power of its temperature.
Near the Earth, at a distance of 150 million km from the Sun, the equilibrium temperature is close to -35 ° C. On the orbit of Mercury, it will be 150 ° C, and near Saturn – will drop to -150 ° C. So, near Mercury we will need to use an additional parasol, and next to Saturn – keep the suit heated all the time. Spin as on a spit not to be fried in the sun and do not freeze to death in the shade, is a bad option too. Engineers came up with a very simple solution for the suit. Inside of it, through tubes laid according to very precise calculations, a fluid with large heat capacity circulates. It is heated where it’s hot and gives the accumulated heat where it’s cool. So, it creates comfortable conditions around the astronaut, regardless of his orientation relative to sunlight. And when astronaut falls into shadow, and the influx of solar heat falls, the liquid is heated to the desired temperature.
By the way, that’s why the question of the shadow is so important to learn and use, for example, discussed in . And again – in space there are no trifles! Not only astronauts, but also delicate scientific equipment and even simple mechanics often need favorable thermal conditions. Steel frozen to the space temperature becomes brittle as glass, and semiconductor devices heated to a hundred a degrees and above stop working. A processor in any computer has a cooling system, and in some cases a simple radiator with a fan is not enough, and special coolers are used.
Equipment in space should work smoothly both in the sun and in the cold earth’s shadow! And it appears that the thermal control system of spacecraft – are masterpieces of engineering solutions. Each of us has a household refrigerator. It takes a lot of space, and weighs tens of pounds. Can we reduce it to the size of a matchbook? It’s Possible, but very difficult. And this should be done: nowadays, miniature devices are launched in the space (because each kilogram of payload launched into space, worth tens of thousands of dollars), and each of them should work in such an environment in which it will work for many years. This is especially important for microsatellites, which dimensions do not exceed the dimensions of road soapbox. That is why we believe that such developments are essential elements of space colonization, worthy of being published in our journal.
The author thanks the American astronomer and a talented artist Walter Myers  for permission to use his space art.