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Life Support in Space
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In space, supporting life is a challenging task. The environment of space lacks the basic amenities of food, air and water - things we take for granted here on Earth.
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Living on Earth is easy. If you are hungry, a jaunt to the local grocery store is all you need to do to satiate your appetite. If you thirsty, tap water is almost always at hand. Oxygen is freely available to breathe and the carbon dioxide you exhale is, in turn, ‘inhaled’ by trees and plants. Thanks to modern plumbing, waste disposal facilities such as bathrooms are ubiquitous in most households and garbage disposal is conveniently taken care of by a service.
In space, however, supporting life is a much more complex and challenging task. The environment of space lacks the basic amenities of food, air and water - things we take for granted here on Earth. Every little detail, from how much food is consumed to how much oxygen is breathed, must be diligently tabulated and taken into account when planning a space mission. As the duration of a space mission lengthens, so does the complexity of the life support system needed for the mission.
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This dwarf wheat is grown in space. Photo courtesy NASA |
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So how exactly does a life support system work in space? Let’s start with food first. Today, astronauts rely on prepackaged food. While this food is palatable and satisfies the basic nutritional requirements of astronauts, it isn’t very appetizing and it wouldn’t be ideal for extended space missions. Instead, producing food in space is a more appealing option. Plants can be grown successfully in microgravity, although a long-term space mission would ideally have an artificial gravity system. Not only are plants are a source of food, but they remove carbon dioxide from the air and produce oxygen to breathe.
Much research has gone into the growth of a variety of plants in small confinements. The greater the edible yield of a plant, the greater the growth density of that plant, and the shorter the growth period of a plant, the more suitable that plant is for growth in space. Crops of potatoes, soybeans, lettuce, carrots, wheat, rice are suitable prospects for growth in space. Scientists are even selectively breeding these plants to be dwarf-like in size but high-yielding; characteristics that would maximize production of food in limited spaces. Even microbes are being investigated as a potential source of food in space. The amount of food consumed by astronauts depends on how strenuous their daily life is.
Water even more important need than food when it comes to human survival. The average human drinks approximately 4 kg of drinking water and 26 kg of washing water per day. Although the amount of washing water could potentially be reduced by imposing stringent restrictions on water usage, the amount of water consumed will remain constant. The perfect life support system would recycle the water from washing and urine into potable drinking water. Unfortunately, nothing is perfect and some water loss from a life support system is unavoidable. The engineering challenge is to minimize water loss. Many different and effective water recycling systems have been designed for use in space and the technology these systems require is readily available. Fuel cells are commonly used in modern space shuttles to produce water from the reaction of oxygen with hydrogen.
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Astronaut Catherine G. Coleman works with a small plant seedling on Columbia's flight deck. Plants could be a valuable source of food on a long space mission. Photo courtesy NASA |
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Another important factor in a life support system is the supply of breathable air and the removal of carbon dioxide. An average of 1.76 pounds of oxygen is used per space crew member per day (NASA). When the length of a space mission increases from a matter of days and weeks to months and years, a constant supply of oxygen becomes all the more critical. The Mir space station produces oxygen through the electrolysis of water.
As for the control of carbon dioxide levels, plants are an effective method of converting carbon dioxide to the useable constituents of water, food and oxygen. Reactors are another way of converting carbon dioxide. They use concentrated carbon dioxide filtered from the air and convert it to water through a series of steps. The composition of the air in a space habitat should consist of a mixture of oxygen and nitrogen in order to reduce the chances of fire as oxygen is flammable.
Integrating all the different elements of life support into one massive, reliable, functioning system is the most challenging barrier that stands in the way of long-duration space missions.
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The temperature and humidity of the air in a life support system are also important. The temperature can vary according to the comfort levels of humans, but the optimal temperature ranges for growing plants should be taken into consideration. Humidity levels are important because they play a role in water reclamation. When water vapor in the air condenses, it can be recollected and used for a variety of purposes aboard a space vehicle.
Finally, the disposal and recycling of waste is yet another component of a life support system. In our day-to-day lives, we leave a trail of waste behind us. From human metabolic wastes to garbage, the disposal of these wastes on Earth is a simple affair compared to on a space habitat with a life support system. Cargo space is limited on missions to space because of prohibitive launch costs. For this reason, the recycling of waste products into useable materials is necessary. There are a number of methods of recycling various forms of waste. Grey water produced from washing can be used to water plants, although residue from soap can be detrimental to the health of plants over the long-term. Human and organic waste can be purified to remove water and can be composted to use as plant soil. Other miscellaneous forms of trash can be burned to give off carbon dioxide, water and ashes. In all cases, the conservation of useful material is the main priority of recycling waste.
Integrating all the different elements of life support into one massive, reliable, functioning system is the most challenging barrier that stands in the way of long-duration space missions.
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