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Basic Human Needs in Space

Above: Image © Public Domain

Three of the basic needs of humans on Earth are food, air and water. Humans in space need these things as well. For astronauts on the International Space Station (ISS), these basic needs are met with materials either sent from Earth or recycled on the ISS (air and water). In the future, growing plants such as tomatoes on the ISS could play an important role in meeting all three basic human needs, just like on Earth.

What Happens Now on the International Space Station?

Food

Food gives us energy from protein, fat and carbohydrates. Food also provides vitamins and minerals that our bodies need to work properly.

Food for the ISS astronauts is sent from Earth on resupply spacecraft. Most of the food is ready-to-eat or pre-cooked (see Figure 1). The meals are customized to provide enough energy and essential nutrients to keep the astronauts healthy during their mission.

Air

Breathable air contains nitrogen, oxygen and very little carbon dioxide. We need oxygen in order for our cells to get energy from the food we eat; this process is called cellular respiration. Carbon dioxide is a waste product of cellular respiration that we breathe out. Carbon dioxide is a toxic gas and can be fatal if there is too much in the air we breathe.

The ISS orbits Earth in a vacuum, which means that there is no naturally available air to breathe. A machine called the Environmental Control and Life Support System (ECLSS, see Figure 2) produces breathable oxygen for the astronauts onboard. The oxygen comes from separating water molecules into hydrogen and oxygen gases. The ECLSS also removes carbon dioxide from the air inside the ISS using filters or chemical reactions. The ECLSS is not the only system responsible for breathable air on the ISS. The Russian Elektron system makes oxygen and the Russian Vozdukh system removes carbon dioxide.

Water

On Earth, we use around 350 litres of water per person per day for drinking, cooking, washing, flushing toilets, etc. Astronauts on the ISS use only 12 litres per person per day. It is critical that they conserve water because there is no natural source of water in orbit. Some water is sent from Earth on resupply spacecraft. But water is heavy, so it’s not practical to send all the water that astronauts need for a long mission.

Water recycling is very important in the closed environment of the ISS. The ECLSS recycles 93% of the water that is used and produced by ISS astronauts (See Figure 2). Water used for washing is cleaned to make drinking water. Excess water vapour in the air onboard the ISS is condensed into liquid water. Even astronauts’ sweat and urine is collected and recycled into drinking water.

How Would a Space Garden Help With Life Support?

Food

Only a limited amount of fresh food can be sent to the ISS from Earth because it has to be eaten before it spoils. A space garden would let astronauts harvest fresh fruit and vegetables continuously. Seeds are ideal to send to the ISS as cargo on a resupply spacecraft because they are small and lightweight.

Plants get the energy they need by making their own food in a process called photosynthesis. During photosynthesis, plants use carbon dioxide, water and light energy to make oxygen and sugar. Sugar is a simple carbohydrate that provides energy to plant cells. Plants can also turn sugar into complex carbohydrates such as starch. Carbohydrates from plants are an important food energy source for humans (See Figure 3).

In August 2015, astronauts on the ISS ate lettuce that they had grown onboard the station. This was the first time space-grown vegetables were eaten in space. NASA scientists are working on gardening systems to get more food plants, including tomatoes, to grow on the ISS.

Air

On Earth, plants are essential for making breathable air. Plants use carbon dioxide and produce oxygen during photosynthesis, improving the quality of the air we breathe. Growing plants on the ISS would help to make oxygen for the astronauts to breathe and remove carbon dioxide from the air (See Figure 3).

Water

Plants lose water to the environment by transpiration, which is evaporation from small pores, or holes, in leaves. It is possible that plants on the ISS could be watered with undrinkable wastewater, and the water vapour that is lost from the leaves could be collected and turned into pure drinking water through condensation (See Figure 3). By themselves, plants could not supply all of the pure water needed for a mission, but they could work along with the water-recycling component of the ECLSS.

Glossary

Carbon dioxide

A gas used by plants for photosynthesis; a gas produced as waste by animals during cellular respiration. Plants also make carbon dioxide through cellular respiration, but they use more during photosynthesis than they make during cellular respiration.

Carbohydrate

One of the main kinds of nutrients in food and a source of food energy; energy comes from the carbohydrates sugar and starch. Sugar is a simple carbohydrate and starch is a complex carbohydrate made from many sugar molecules linked together.

Condensation

A change in state of matter from a gas to a liquid.

Evaporation

A change in state of matter from a liquid to a gas.

Fat

One of the main kinds of nutrients in food and a source of food energy. Dietary fat is also required to absorb some vitamins. Extra food energy is stored in the body in the form of fat.

Oxygen

A gas used by animals during respiration; a gas produced by plants during photosynthesis.

Photosynthesis

The process used by plants to change light energy into biochemical energy (sugar). Light energy is used to change carbon dioxide and water chemically into oxygen and sugar.

Protein

One of the main kinds of nutrients in food and a source of food energy. Dietary protein is broken down into its building blocks, called amino acids. These amino acids can be used by the body to grow and repair tissues and organs. 

Cellular Respiration

The process used by plants and animals to get energy from sugar molecules. Cellular respiration changes oxygen and sugar chemically into carbon dioxide and water and heat.

Transpiration

The process of water movement through plants and eventual evaporation from small pores, or holes, in leaves.

Water Vapour

Water molecules in the form of gas.

References