Living in space
Essential human requiremtns
Basic human needs
To travel in space the basic requirements for human survival are exactly the same as those requirements on Earth - air, water and food.
A human needs a balanced diet containing enough energy for each day's activities, and a suitable environment.
Energy for humans
A totally sedentary human needs a minimum of about 2000 Calories of food energy per day in order to survive (plus small, but essential, amounts of vitamins and minerals).
One food Calorie (with a capital "C") is actually equal to 1000 calories of heat energy (i.e. 1 Cal = 1kcal) Calories are fine for comparing the energy content of food products but not really very useful for scientific work. For scientific applications we use an energy unit called the joule (J).
1Cal = 4.2kJ
We can calculate that a human needs about 2000 x 4.2 kJ of energy, or
about 8.4 MJ per day |
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A balanced diet with enough kilojoules
A balanced diet is one which contains the following:
- Water
- Sufficient kilojoules of energy, primarily from carbohydrates
- Proteins
- Carbohydrates
- Fats - Essential for metabolizing some vitamins as well as to provide "stored" energy
- Vitamins
- Mineral salts
- Fibre
Click here to VIEW a copy of Canada's Food Guide
Click here to view and PRINT a copy of Canada's Food Guide (a printer-friendly version of the guide)
You can also explore other aspects of Canada's Food Guide – background information, access to copies in 10 different languages, a tracking facility, information for educators maintaining healthy habits by going to the Health Canada website.
How many kilojoules does a person need each day?
The answer depends upon three factors:
- One's basal metabolic rate (BMR)
- The level of physical activity undertaken during the day
- The environmental temperature
Basal metabolic rate (BMR)
The basal metabolic rate is the rate of metabolism of a resting individual and is determined by the rate of oxygen consumption. The BMR depends upon the species, age and sex of the individual. In general, BMR decreases gradually as we grow older. At any given age females tend to have a lower BMR than males.
Aerobic Respiration: An important by-product of respiration is the release of energy, mostly as heat.
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One's BMR is a measure of the rate at which energy is expended (kilojoules "burned") while resting. Vigorous activity such as running, or physical work, increases our metabolic rate. The need for more oxygen, and to expel excess carbon dioxide, causes us to "pant".
Daily energy requirements due to activity
The chart below shows some typical daily energy requirements for humans. An astronaut requires about 14 000-15 000 kJ per day (depending upon the work schedule).
| Category |
Energy (kJ) per day |
| Babies less than 2 months old |
2000 |
| Pre-school children (both sexes) |
5000-6000 |
| Teenage (female) |
9000-10000 |
| Teenage (male) |
11000-14000 |
| Adult (sleeping BMR) |
1500-2500 |
| Adult (clerical) |
10000-12000 |
| Astronaut (shuttle) |
14000-15000 |
| Adult (construction) |
14000-16000 |
Temperature considerations
Humans, like all mammals, are warm blooded and need to maintain a constant body temperature in order to survive. Ideal body temperature varies slightly from mammal to mammal, but for humans it is 37.5°C. Deviations of more than few degrees from this temperature within the body core (chest cavity) are dangerous. We get "chills" and shiver, or we get hot and feverish.
Placed in a cold environment the body responds by increasing its basal metabolism, thereby generating more heat. Arctic and Antarctic travelers require a much higher kilojoule intake than travelers in more temperate climates, doing the same amount of work.
A suitable environment
The conditions for a suitable environment include:
- air to breathe, containing oxygen, water vapour and relatively free of carbon dioxide and other gases, except for nitrogen or inert (non-reactive) gases such as argon and helium.
- a suitable temperature, ideally about 20-22°C.
- protection from external hazards.
- sufficient space for both physical and psychological comfort.
- suitable lighting.
Carbon dioxide, oxygen, and water vapour
For short term missions into space the problem of maintaining a suitable atmosphere is solved simply by removing unwanted gases (by pumping the air through scavenging filters), and adding oxygen as required, then recirculating the air. All waste materials are simply discarded when the mission returns to Earth. You can learn more about some of the efforts to recycle waste water by clicking on the NASA website.
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For long term missions the problem is much harder to deal with, since one cannot easily travel with an unlimited supply of either gas filters, water, food, or oxygen. Water vapour also creates a problem. If the air is too dry it is uncomfortable to breathe for long periods. If the air is too moist condensation occurs in cold places creating possible corrosion and electrical problems.
Plants (given sufficient light) will consume carbon dioxide.
In either a space vehicle, or a planet-based habitat, green plants may be used to help manage air quality.
The release of oxygen and the reduction of carbon dioxide are extremely helpful in maintaining a comfortable and healthy atmosphere within a closed environment.
The cycle to the left does not appear complete, since carbon (C) seems to disappear into the plant. To make the cycle truly complete, the human would eat the fruit from the plant, thereby completing the cycle of carbon (in carbohydrates). |
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In addition to consuming carbon dioxide during photosynthesis, green plants also produce water vapour.
A moderate amount of water vapour is important in creating a comfortable environment.
Equally important is the fact that the water vapour - which plants yield to the air through the process of transpiration, is pure. Condensing this water vapour produces clean drinking water, even when the plants are watered with impure water.
It may be possible to use plants to facilitate the purification of human waste water. |
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Summary
A complete recycling of resources is shown in the diagram to the right.
In a perfect system, oxygen and food would be produced at a rate that balances the consumption of carbon dioxide and water (a state of dynamic equilibrium).
To make the system function, however, energy must flow through the system, entering as light and eventually emerging as heat.
Note: chemical formulae are used as abbreviations only. The chemical process is not balanced. |
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Student activity
Attached is the 16-day rotating menu used by Dr. Robert Thirsk while he was on board the International Space Station for 187 days in 2009. Notice the legend +which describes the FORMAT of the various foods.
- Which day would be your favourite day in the 16-day cycling of the menu. Provide reasons for your choice.
- Why do you think that many of the foods are either irradiated or thermostabilized? Why don’t they just put the food in the refrigerator?
- Why do you think astronauts on board the International Space Station would really be welcoming when a shuttle from the USA or flight from Russia arrives (as it relates to food)?
- Take a day and analyze the menu for the day in terms of the nutritional value of the food for the astronauts. Although the menu does not provide amounts, indicate whether or not the menu is in line with the requirements of Canada’s Food Guide for Healthy Living.
- Identify any foods with which you are NOT familiar and research to find about that food, how it is prepared and the nutritional value for astronauts.
- Which day’s menu would be closest to a menu that you might experience at home? If none of the day’s menus are close to those you might experience, suggest reasons for this difference.
- You will notice that the “daily menu” is not broken up into specific meals. Suggest reasons why this might be the case.
- You will notice that the “daily menu” is not broken up into specific meals. Suggest reasons why this might be the case.
Plan an Investigation
Discuss the importance of water vapour in creating a comfortable environment and the role of green plants in contributing water vapour through the process of transpiration. Ask students to "brainstorm" a list of questions they have about the transpiration process. (e.g. how can we prove plants transpire? which parts of the plant yield water vapour? how much water vapour is released?)
Divide the class into small groups. Ask each group to decide upon a question they wish to investigate. Discuss with students the process to follow in planning and carrying out their investigation.
Distribute an Investigation Plan sheet to each group. Groups should submit their plans for approval before beginning their investigations.
