9.9 Elective Option - Space Science

Senior Science

9.9 Elective Option - Space science

Section 3

Effect of Space

on the Body

Section 3 :: Effect on the Body

Reduced gravity in space impacts can have short-and long-term effects on body functions

INGESTION AND GRAVITY

Ingestion is the taking of food and drink into the body

Food does not fall into your stomach. You can eat and swallow food while standing on your head. This means that gravity is not assisting food reaching your stomach. Of course, people tend to eat when upright. In this situation ingestion is helped by gravity

In humans, ingestion can occur without the assistance of gravity because food is pushed into your stomach by a “wave of muscular contractions”. The process is called peristalsis. Circular muscles in the wall of the oesophagus just behind the food contract. This squeezes the food towards the stomach. The muscles contract so that the region of contraction stays just behind the food. This constantly pushes the food towards the stomach.

Notes Questions

1. ActivityPlace a tennis ball just inside a long stocking. How can you get the ball to the other end of the stocking?
2. Explain why the tennis ball can be moved in terms of muscular contractions of the hand.
3. Describe how this is similar to the muscular contractions in the stomach.

Notes Questions (for next page)

1. Why is it possible to pour liquids on Earth?
2. Is it possible to pour liquids in space?
3. In space, what shape does a floating blob of liquid form?
4. Identify one problem associated with drinking in space.
5. Name two pieces of equipment needed to drink in space.

PROBLEMS WITH DRINKING

On earth, drinking involves holding a container to our lips and pouring the liquid into our mouths. The fluid passes down our oesophagus because of the muscular contractions (by peristalsis) and assisted by gravity. On earth, pouring a liquid is possible because gravity causes the liquid to fall down (away from the container).

Can you pour a liquid in a micro-gravity environment?

Can a liquid be tipped out of a glass in a micro-gravity environment?

Can you get the liquid out of a glass container in a micro-gravity environment?

What happens if liquid is “spilt” while drinking?

Diagram

a. Pouring on earthb ‘Pouring’ in micro-gravity

Note – You cannot pour in space. Why? – no gravity & you would not have an open container. The diagram is hypothetical.

In a micro-gravity environment, both the cup and liquid are falling together around the earth. When the liquid container is tipped ‘over’ the liquid does not fall out. It mostly stays where it is – in the container. Therefore, liquids cannot be poured in a micro-gravity environment. It would be impossible (or at least not easy to pour) to pour a liquid into your mouth while in space.

To get the liquid out of the cup you could quickly pull the cup away from the opening. This would leave the liquid floating. The floating blob of liquid would form a sphere because of the force of attraction between water molecules. [Remember from Lifestyle Chemistry – the surface tension produces the smallest surface area possible – a sphere] Obviously, a problem associated with drinking in space is liquid can just end up floating around inside the space capsule. This is a nuisance and potentially dangerous.

Therefore, there are THREE problems associated with drinking in space. These are:

• How to store the liquid
• How to get the liquid from the container to the mouth
• How to prevent the liquid escaping and then floating in a micro-gravity environment.

How Do Astronauts Drink?

To drink in space, astronauts use a method similar to drinking from a “Poppa”. A light, aluminium pouch is used to hold the liquid. A straw is used to sip the drink. Muscular action in the oesophagus squeezes the liquid into the stomach, without the assistance of gravity. The straw has a clamp to prevent the liquid from escaping when the astronaut is not drinking.

PACKAGING OF FOOD FOR THE SPACE SHUTTLE

There are a number of factors that affect how food is packaged and eaten for a space mission.

• Reducing weight - total weight of the spacecraft must be kept at a minimum for a successful launch. For a typical ten day mission, only 1.7 kg of food is taken on board for each astronaut.

• Preserving stored food - bacteria and fungi grow very quickly in a micro-gravity environment. So food needs to be stored to ensure preservation of food. An important means of doing this is by dehydrating food.

• Preventing spillage in weightless conditions- any food or drink that escapes from its container while being eaten in space may cause great danger to the space shuttle if it floats into the instrumentation etc. Short circuits could mean a major equipment failure and cause the crew to not be able to return from space. Problems can also occur if the escaped ‘floaters’ are inhaled. Consequently, all food and drink is prepared and stored in containers that will prevent spillage.

To prevent crumbs forming, tortillas are preferred to bread but sandwiches can be eaten early in the mission to ensure freshness and a tendency to not form crumbs.

To prevent food floating away, foods are generally made with a sauce or gravy to hold the food together. If any food does escape, the liquid will maintain the food as a large drop due to cohesion.

Where does the water comes from for drinking and rehydrating food?

The supply of fresh water on the space shuttle is never a problem because it is constantly being made as a bi-product of the fuel cells which produce electricity by the combination of hydrogen and oxygen (which forms water). The international space station, however, does not possess fuel cells for making electricity but takes advantage of solar arrays. Consequently, the continual supply of water on the space station must be ensured by:

• recycling of the water in urine, exhaled air, etc.
• not requiring the addition of water to foods which are in a dehydrated form.

KINDS OF PACKAGING

In the early days of space flight, Mercury astronauts squeezed processed food from aluminium toothpaste tubes. They also ate sandwich cubes coated in unflavoured gelatin that kept the bread crumbs from making a mess in the tiny spacecraft cabins. The food, though nutritious, was not very appetising. It lacked the look and feel that make eating pleasurable on Earth.

After many experiments with food types, packaging, and preparation, NASA reached an important conclusion. It was possible and safe to carry normal foods into space and eat them in an almost normal way. The big difference was how foods were packaged and prepared in orbit.

At first, a lot of food was packaged in rigid, square containers. These containers caused problems due to the large amount of rubbish created. Flexible, plastic packets replaced these rigid containers. They have a valve for inserting water to rehydrate the food inside. These are also much easier to be pack down in the rubbish compactor.

Foods for Space Shuttle astronauts come in many forms. Some are freeze-dried while others are thermally stabilized, dried, or eaten in natural form.

• Natural form foods, such as peanuts or dried apricots, are packed in vacuum sealed plastic bags. The packages are cut open with scissors and the food is eaten as is.

• Foods such as tuna or salmon come in metal cans with panel pull-back lids like those snack-food cans found at supermarkets.

• Dinner entrees, such as beef stew or smoked turkey, are packed in foil and plastic pouches. They are heated in the Shuttle’s oven and eaten when ready.

• Dried food is packed in special plastic containers with flexible lids. Hot or cold water must be added to make the food ready for eating.

• The beverage packages are made from foil and a plastic laminate, in order to provide longer shelf life.

Notes Questions

1. Identify three factors that need to be considered for containers used in space.
2. How much food is provided per astronaut for a ten-day mission?
3. Name two reasons why it is necessary to prevent the spillage of food in space.
4. How was food packaged on the Mercury missions?
5. What conclusion did NASA reach about the food suppled for space missions?
6. ResearchWhat is meant by rehydrate?
7. Name three types of packages used for space missions.
8. What is the advantage of flexible, plastic packets compared to rigid, square containers?

TYPES OF SPACE FOOD

Space food on the space shuttle may belong to one of the following categories:

• Rehydratable food -- the water has been removed i.e. the food has been a dehydrated in a process known as freeze drying. eg beverages and hot cereal.

• Thermostabilised food -- has been heat processed and canned to destroy bacteria and fungi allowing the food to be stored at room temperature. e.g. pudding, fruit and tuna fish in cans.

• Intermediate moisture food -- some of the water has been taken out of the food to maintain the soft texture and reduce the potential for growth of bacteria and fungi. As a result, the food can be directly eaten without the need for preparation. eg. dried fruit

• Natural form food -- stored in a flexible pouch and ready to eat e.g. nuts, biscuits and health bars

• Irradiated food -- beef steak and smoked turkey are the only foods so far to be sterilised by ionising radiation which allows them to be kept at room temperature.

• Frozen food -- a food may be quick frozen to maintain freshness and texture of the food. eg. casserole

• Fresh food -- e.g. apples and bananas are not preserved or processed but are generally best eaten early in the mission.

• Refrigerated food -- requires cool temperatures to prevent spoiling e.g. cream cheese

Most of food to be used on the international space station will be frozen, refrigerated or thermostabilised to reduce the use of valuable water.

Source

Notes Questions

1. Name one example of each of the following

a) rehydratable foodb) natural form food c) thermo stabilised food.

1. How is food thermo stabilised?
2. When is it best to eat freah food?
3. Why is some food refrigerated?

Selecting Food for a Space Mission

A good dinner is important for astronauts for both health and relaxation.

An astronaut's choice of food, which is checked by a dietician, must reflect:

• food liked by the astronaut.
• variety - rehydratable foods allow a greater variety of meal
• a balanced diet (five food groups; food pyramid; 1, 2, 3, 4, 5+ food plan)
• energy considerations (measured in kilojoules & about 3000 kJ daily)
• amount of food needed (a maximum weight of 1.7 kg).

Other factors include

• Preparation requirements
• Potential for spillage
• Wastage (food and packaging)

Typical menu for two days of an astronaut's mission

Source: NASA Educational Briefs (EB-90-7(E)

Notes Questions

1. List all the foods in the table above that are natural form foods.
2. Name the foods that need water to be added before they are eaten.
3. List the foods that are possibly packaged in a metal can.
4. How are beverages stored?
5. How do astronauts drink beverages?

GRAVITY AND BONE HEALTH

Bone is living tissue. Bone tissue is constantly being renewed - broken down and built up. This process allows bones to grow and to mend (when bones are broken)

• In children more bone tissue is being built up than is being removed. This allows bone growth.
• Normally, in adults the build up of bone tissue is about the same as the loss of bone tissue. Adults stay about the same size.
• In old age, the build up of bone tissue is less that the break down of bone tissue. This helps explain why older people seem to get smaller.

An important aspect of bone health is the uptake of calcium. Strong bones require calcium. Calcium needs to be deposited in bone tissue as part of the renewing process. If calcium levels are not maintained bones become brittle and break more easily. The maintenance of bone health means that the deposit of calcium in bone tissue is sufficient to maintain growth in children or at least balances the removal of calcium in adults.

Maintaining calcium levels in bone tissue depends on at least two factors.

• One factor is having enough calcium in the diet.
• The other is participating in weight bearing exercise (ie the role of gravity)

Studies have shown that eating calcium rich foods is not enough. The uptake of calcium by the bones is greatly increased by exercise. This exercise needs to be “weight-bearing” exercise. Weight bearing activities involve the body working against the pull of gravity. On earth, walking and running are good examples of such activities. Every time a step is taken (and the heal ‘hits the ground) helps the heal bone and other leg bones to absorb calcium and maintain bone health. Swimming, where the body is supported by water, is not such a good activity for maintaining bone health.

The importance of gravity has been made obvious by studying bone mass losses by astronauts. It has been discovered that prolonged periods of “weightlessness” can cause serious calcium depletion in astronauts. This makes the bones become brittle, lose strength and increases the possibility of fractures. Cosmonauts on the Salyut 6 for 175 days, for example, lost eight percent of the calcium in their bones. To reduce calcium loss from bone tissue astronauts must maintain an exercise program. In space (a micro-gravity environment), there is no point walking for exercise since the body is not working against the pull of gravity. The exercises must be load bearing – that is, the muscles need to work against a resistance.

Notes Questions

1. Explain why people can get smaller as they get old?
2. Name the main factor that is important in maintaining calcium levels in bones.
3. Outline problems associated with the loss of calcium from bones.
4. How can bone health be maintained on space missions?

GRAVITY AND MUSCLE TONE

Muscle tone relates to the condition where muscle fibres are slightly contracted to keep the body in good shape and not flabby.

Muscle tone, size and strength increase by exercising against a resistance (called resistance training). On earth, the resistance is provided mostly by the pull of gravity – ie weight. Muscle size and strength decrease when people stop exercising. A good example of this is when someone breaks their leg and gets a plaster cast. The lack of exercise can result in a significant decrease in the size of the leg muscles. Living on earth means you are always affected by the gravitational pull. This helps maintain muscle tone.

In the micro-gravity environment most activities require less effort. The heart, blood vessels, and muscles weaken because weightlessness involves less work for the body than working against the pull of gravity. As a result muscles lose tone and strength. Most of the loss is thought to occur in the leg bones and spine that are responsible for erect posture and locomotion. Soviet researchers found that cosmonauts who spent just one month in space lost between 10% to 20% of their muscle strength in their arms and legs.

Muscle and bone problems are insignificant in a short duration shuttle mission but it is of great concern for long stays in space on the space station and eventually for a trip to Mars. Sore muscles may be the end result of a space shuttle mission but there is a serious threat to an astronaut’s health from long duration space travel.