Table of Contents

Water cycling in a microgravity environment

Objective

Using water cycling, this activity teaches students about phenomena considered normal on Earth, but which do not work or work differently in space.

Context

In a spacesuit, humidity caused by an astronaut’s perspiration can become a problem. The activity is designed to help students think about, in greater detail, the aspects that must be taken into account when designing a spacesuit.

Method

• The subject matter may be presented by the educator or printed for students to review themselves;
• Students, either alone or in teams, try to answer the questions asked;
• An answer sheet is available.

The importance of water cycling

Where there is water on Earth, it is usually in motion. This movement ensures the conditions favourable to the development of life.

From the oceans, through the atmosphere and to the land, large quantities of water are exchanged.

The oceans-atmosphere-land water cycle contains five steps

In brief:

The Sun causes water to be evaporated from lakes and oceans. The water vapour rises in the atmosphere. This is called evaporation.

In the upper atmosphere, where the air is cool, the water is condensed into small droplets?clouds. This is condensation.

The winds (caused by the unbalanced warming of the ground) push the clouds further away. This is transport.

When the clouds encounter cooler masses of air, the small droplets come together, forming large drops and resulting in rain (or snow). These are precipitations.

Depending on the geography, when precipitations fall to the ground, catchment areas that slowly return the water to lakes and oceans are formed. This is overland flow.

Transparency

In detail:

Evaporation

The Sun warms the water, especially in shallow areas. Since a warm liquid cannot dissolve as much gas as a cool liquid, the gas forms micro-bubbles. These micro-bubbles are lighter than equivalent volumes of water, causing them to change places with the water and rise to the surface (due to gravity). The water vapour is combined with the air. Since it has been warmed through its contact with the water, and since warm air is not as dense as cool air, it gives way to the cool air and rises. The water vapour rises with the warm air. Evaporation can also occur when the ground is humid and the air is warm.

Condensation

The air cools down as it rises and, unlike liquids, cannot contain as much water vapour as warm air. The water vapour forms very small droplets that reflect light in all directions: these are clouds. These droplets are so small that their insignificant weight does not pull them far enough downward to resist the air, causing the droplets to remain in suspension. The altitude of clouds varies according to atmospheric conditions, explaining the different types of clouds. Condensation can also occur when the warm air filled with humidity cools down (e.g. fog) or meets a cool object (e.g. dew).

Transport

Winds are caused by the fact that atmospheric pressure varies at different points of the Earth. Above a city, a forest, a desert or a shallow body of water, the air is warmer than it is above a field, a deep body of water or an area covered with snow. The warm air rises, is replaced by cool air, and winds start blowing. The Earth revolves and trends associated with motion appear. The clouds previously formed are pushed by the winds, causing them to move.

Precipitation

When the clouds meet cooler masses of air (because of other winds or because mountains force the air to rise abruptly), the droplets come together to form bigger drops. Cool air contains less water vapour than warm air. Since the larger drops can no longer remain in suspension, they overcome the air resistance and fall to the ground. Atmospheric conditions vary widely according to area and altitude, making it possible for water to reach the ground in the form of snow, ice pellets, sleet, rain or hail. For precipitations that fall into the oceans, this is where the cycle ends (and starts over).

Overland flow

Precipitations that fall at high altitudes stay in place if the weather is cold, are absorbed by the ground if it is porous, or cause an overland flow if the ground is impermeable or already saturated with water. This is how seasonal or permanent blankets of snow, water tables and brooks are created. Springtime causes the snow to melt, high water tables create downstream water sources, and brooks combine to form rivers and then streams, returning the water to the oceans. In cool regions, the water is returned to the oceans over very long periods of time through glaciers (rivers of ice). Since it takes time for water to descend the catchment areas, given that some land areas have small slopes and that precipitations occur regularly, some areas remain humid and favour all forms of life.

What if we were in a very low-gravity environment...

You read about water cycling in the previous section. The role played by gravity was clearly mentioned in certain cases, but it was not emphasized everywhere. Now, imagine what would happen if gravity were greatly reduced?not an easy task. Try to answer the following questions. Our answers are provided below.

Would there be evaporation caused by the Sun?
Would there be condensation in the upper atmosphere?
Would there be winds causing the clouds to move?
Would there be precipitations?
Would overland flow and infiltration still occur?
Would there be life?
What would happen?

Answers

Would there be evaporation caused by the Sun?

Yes and no. The gas would still escape from the warmed liquid, probably causing larger bubbles. For the escaped gas to place itself above the liquid, gravity is required. Without gravity, the gas bubble would not know in which direction to go. Instead of forming a lake, the liquid would form a ball. With very little gravity, the gas bubble would eventually “rise”.
Let’s think about the water vapour that would be formed close to the surface. The problem remains: the water vapour will not rise in the atmosphere. The water vapour rises because a volume of warm air filled with water vapour is not as heavy as an equal volume of cool air. But heaviness means weight, and therefore gravity. If there is no gravity, nothing moves. If there is very little gravity, the ascension is very, very slowly.

Would there be condensation in the upper atmosphere?

Yes, if the temperature is low. Assuming that the humid air can reach a high altitude where it is cooler, condensation will occur, resulting in the appearance of clouds. However, the atmosphere may not be as thick if there is very little gravity. The atmosphere’s molecules would rise due to the low gravity and could escape because of the reduced release speed or because collisions with solar wind particles would slowly cause a breakdown. This is probably what happened with the gases that escaped from the surface of the Moon: they eventually escaped its gravity.

Would there be winds causing the clouds to move?

There would probably not be much wind in altitude. The air would be warmed at ground level, and the differences in local pressure would be the greatest sources of wind. If there were little gravity, the wind would not travel far, since the air would rise very slowly. Atmospheric imbalances would quickly be corrected.

Would there be precipitations?

Yes, but they would probably be very rare and of low intensity.

Would overland flow and infiltration still occur?

Yes, but very slowly. Wetlands would multiply, brooks would probably not come together as much, and there would be less large rivers and streams, flowing at a very low rate.

The egg and the bottle – How not to "crack" under pressure

Objective

During this activity, students are taught about variations in pressure caused by changes in the temperature of gases by observing that a hard-boiled egg can be sucked in through the neck of a bottle when the air in the bottle cools down.

Context

Gay-Lussac’s Law states that the volume occupied by a gas is directly proportional to its temperature when the pressure is constant. The corollary of this is that at a given volume, the pressure of a gas is directly proportional to its temperature. When, in a closed environment, the temperature of a gas increases, its pressure also increases while it tries to expand. Inversely, if the temperature decreases, the pressure drops as the gas contracts.

This phenomenon is important for astronauts. Spacesuits can be considered a closed environment with a relatively constant volume (the flexibility of the suit is controlled to limit its expansion under internal pressure). To maintain a constant pressure for the astronauts’ comfort, the temperature in the suit must absolutely be stable. To ensure this stability, the insulation of the suit must be optimized and its atmosphere controlled using sophisticated air-conditioning systems.

Equipment required

• A hard-boiled egg in its shell
• A bottle whose neck is slightly smaller than the largest part of the egg
• Wooden matches

Time required for the experiment

10 minutes

Method

• Remove the egg from its shell;
• Place the bottle on a table;
• Light three or four matches and let them fall in the bottle;
• Quickly place the egg on the neck of the bottle;
• Wait for the matches to burn out and for the air to start cooling in the bottle, then see what happens.

Observations

The matches warm the air in the bottle, causing it to expand. The egg acts somewhat like a one-way valve. Part of the warm air under pressure exits the bottle, making its way between the neck of the bottle and the egg. When the matches burn out, the air inside the bottle starts to cool and contract. This contraction corresponds to a drop in pressure in the bottle which, after a moment, becomes lower than the atmospheric pressure. This causes the egg, which is relatively flexible, to be sucked into the bottle.

Subjects for discussion

How would you go about removing the egg from the bottle?

Pascal scales – Understanding pressure measurements

Objective

During this activity, students are taught the basic principles of pressure, learning that the weight of an object, as indicated by a scale, decreases when this weight is distributed over more than one scale.

Context

One of the very important concepts of the science of spacesuits is the pressure that must be maintained artificially inside the spacesuits. But what exactly is pressure? This activity makes it possible to show the basis of this concept, helping students better understand the notions that will follow.

Equipment required

Two scales, identical if possible
Two pieces of wood of 10x10 cm and 2 cm thick
A wooden board approximately 1 m long

Time required

5 minutes for the experiment

Method

• Weigh yourself on each of the scales and record the results;
• Place the scales side by side, leaving a gap of approximately 70 cm;
• Place a piece of wood on each scale;
• Place the board on the pieces of wood, forming a bridge between both scales;
• Step onto the middle of the board and ask a friend to record the weight indicated on each scale.

Observations

Pressure is the relationship between a force and the surface on which this force is applied. The weight?or mass?is a force caused by applying weight to an object. In this experiment, we see that the force caused by the weight results in a pressure that it reduced by half when the force is distributed over two scales.

Subjects for discussion

Why is it possible to walk on snow with snowshoes without sinking?

Make your own barometer

Objective

During this activity, students will make a Torricelli barometer that uses water (rather than mercury), observing, over many days, fluctuations in atmospheric pressure. Students should learn that air under pressure exerts a very real force on surfaces with which it comes in contact, especially when it is confined in a closed environment.

Context

There is (practically) no atmosphere in space outside a spacesuit. However, pressure used to reproduce the atmospheric pressure felt on Earth is artificially maintained inside spacesuits. Although this pressure is approximately three times less than what it is at ground level, it is enough to ensure an appropriate comfort level for astronauts and keep them from suffering from certain illnesses. In contrast, this pressure is also responsible for “inflating” the suit. This phenomenon makes the suit stiffer, restricting the astronauts’ movements.

Equipment required

• A beaker or a glass with straight sides
• A 30-cm transparent plastic ruler
• 30 cm of transparent plastic aquarium tubing of small diameter
• Transparent tape
• Playdoh or chewing gum
• Water
• Food colouring

Time required

Building: 15 minutes
Observation: 10 days

Method

• Stick the ruler vertically against the inside of the beaker or glass, making sure the scale is visible;
• Tape the tubing to the side of the ruler inside the glass, making sure to leave 1 cm between the bottom of the glass and the end of the tubing;
• Fill half the glass with water and add one or two drops of food colouring;
• Suck a bit of water in the tube. When the water level reaches approximately 20 cm on the ruler’s scale, block the end of the tubing with your tongue. Block the opening of the tubing permanently with a piece of playdoh or gum;
• Record the exact water level in the tube as well as the weather (warm or cold, sunny or cloudy, calm or windy);
• At the same time every day, record the water level in the tubing as well as the weather.

Observations

Fluctuations in atmospheric pressure do not occur fast enough to be observed over short periods. However, significant changes should occur every twenty-four hours. Usually, when the sky is covered, the “weight” of the air decreases above the barometer. The pressure exerted at the water surface decreases accordingly, lowering the water column. Inversely, when the nice weather returns, the atmospheric pressure increases, causing the water column to rises in the tubing.

Subjects for discussion

What would happen to the barometer’s water column if we took it atop Mount Everest? And what if we took it into space, at the altitude of the International Space Station?

Design a functional thermometer

Objective

During this activity, students will make a bulb thermometer that uses water (rather than mercury), learning how exchanges of heat between two bodies affect the state of liquids, such as their volume. Students should also learn that variations caused by adding heat to or removing heat from a body also apply to gas.

Context

The temperature of a body represents its heat at a given time. Heat is a physical phenomenon related to, among others, the activity of the body’s molecules. The more active the molecules are, the warmer the body, and the more its temperature?which we measure using a thermometer?increases. But how does a thermometer measure temperature? A body’s heat energy is seen mostly by comparing the body to another body with a different temperature. In this case, part of the heat from the warmest body is transferred to the other. In theory, this transfer continues until both bodies have the same temperature. Without this phenomenon, thermometers would not work.

A bulb thermometer usually contains a small amount of mercury at a certain temperature. When the thermometer is placed in a sink filled with hot water, the balance between both bodies starts taking place. The water transfers part of its energy to the mercury (it warms it up), whereas the mercury transfers part of its “absence” of energy to the water (it cools it down). The quantity of mercury in a thermometer is so minute that the cooling it causes on the water is insignificant. In contrast, the heat brought by the water to the mercury is very noticeable. Through the heat energy received from the water, the mercury molecules become active and the temperature increases. This increase in temperature causes the mercury to dilate (increase in volume), making it rise in the glass tube. The same phenomenon occurs when the thermometer is placed outside, in free air. In this case, it is the ambient air rather than the water that interacts with the mercury.

Heat energy is not the only thing that causes a body’s molecules to become active. The direct radiation, such as the Sun’s, also has this effect. A thermometer exposed directly to the Sun will indicate a higher temperature than that of the ambient air.

In space, there is no atmosphere, and therefore no ambient air. Away from all direct radiations, temperatures, in theory, are close to absolute zero. Absolute zero can be described as the complete absence of heat or the temperature at which all molecular activity ceases in matter. However, a body can reach temperatures near 150 °C when it is exposed to solar radiation. These differences in temperature pose very real problems to engineers responsible for developing materials used to make spacesuits. The suits must be protected against the effects of extreme temperature variations existing outside. It is also important to make sure that these variations do not affect the temperature of the atmosphere inside the suit.

Equipment required

• A glass container of small diameter with a watertight lid
• A drill or a hammer and a large nail
• A transparent or translucent straw of the smallest diameter possible
• Playdoh or chewing gum
• Water (very cold and very hot)
• Food colouring

Time required

Building: 15 minutes
Observation: 15 minutes

Method

• Make a hole in the lid of the container using the drill or the hammer and nail. The diameter of the hole should be just big enough for the straw;
• Insert the straw until half of its length is in the hole. Seal around the straw, using the playdoh or gum, above and below the lid;
• Fill the container to the edge with the very cold water (almost ice cold), add a few drops of colouring and stir;
• Tighten the lid on the container; some water may enter the straw;
• Place the container in a plugged sink and run the hot water.

Observations

The difference in temperature between the water in the container and the water in the sink is quite noticeable. As soon as the container is immersed in the hot water, the transfer of heat begins to take place. The water in the container heats up gradually, whereas the water in the sink gets slightly colder. The new source of heat to the water in the container causes it to increase in volume and rise in the straw.

Inflated gloves – Exploring the challenges of working with pressurized gloves in an environment where the external pressure is zero

Objective

Students learn about the obstacles faced by astronauts who must work in pressurized suits by trying to perform tasks while wearing dish gloves containing air under pressure.

Context

The human body is made to function normally at the pressure that exists at sea level, i.e. approximately 101 kPa. The absence of all atmospheric pressure at the altitude at which astronauts work during extravehicular activities must be compensated for. Spacesuits are therefore pressurized in order to maintain a viable environment. Although the pressure applied mechanically inside the suit is approximately three times less than the pressure at ground level, it is enough to have quite an undesirable effect. Since spacesuits are made of relatively flexible material, they have a tendency to expand, or inflate, when positive pressure is applied inside. This causes astronauts to move, to a certain extent, as if in an inflated balloon, which makes everyday tasks that much harder to perform.

Equipment required

• Two dish gloves
• Two large elastics
• Two small straws

Time required for the experiment

Approximately 15 minutes

Method

• Put one of the gloves on;
• Place an elastic around your wrist so that the glove is very tight;
• Insert a straw in the glove, under your wrist, with one end at the palm of your hand and the other outside the glove;
• Blow in the straw to inflate the glove, and quickly remove the straw;
• Repeat the same steps on the other hand;
• With both of your hands in the gloves, perform everyday tasks: take a pencil and write, handle tools, tighten a bolt, etc.

Observations

We know it is not easy to perform simple tasks when wearing winter gloves, for example. This experiment shows that things are even more difficult if positive pressure is applied inside the gloves. At present, it remains a necessary evil in the case of spacesuits.

Subjects for discussion

What methods do you think could be used to reduce the negative effects of applying positive pressure inside a spacesuit?

Note

It is best to perform this activity in teams in order to get help inflating the gloves and removing the straws.

If the gloves are available in many sizes, take the “large” size. Although students are usually more comfortable with small-size gloves, the large ones will make it possible to inflate the fingers, whereas the small ones may be too tight.

The tighter the elastics are, the less loss of pressure there is. However, there are risks of blocking the blood circulation. It is therefore important to make sure that students do not wear the gloves for extended periods.

Balloons suffer "the bends"

Objective

During this activity, students will learn about the effects of decompression on the human body, as well as the symptoms associated to caisson disease.

Context

A body is subject to decompression when the pressure to which it is submitted drops. This phenomenon is potentially dangerous for the human body when it occurs suddenly. Scuba divers, for example, are subject to decompression every time they come back up to the surface after being deep underwater. If they come back up too quickly, they are likely to suffer from a serious illness: caisson disease, also called decompression sickness (commonly known as “the bends”).

Caisson disease is characterized by the forming of nitrogen bubbles in the organic tissues and liquids. These bubbles result from the expansion of nitrogen that saturates the body when it is submitted to sudden decompression. Gases have this characteristic of increasing in volume when the pressure applied to them decreases.

Caisson disease can also affect astronauts: astronauts are subjected to significant decompression when they leave the environment of the orbiter or space station to perform extravehicular activities in space. The pressure inside the suit is approximately three times less than the pressure maintained in the spacecraft or space station. Measures must therefore be taken for the astronaut to undergo gradual decompression that can take place over a few hours.

Equipment required

• An inflatable balloon
• A bottle with a large opening, making it possible to inflate the balloon
• A straw
• Playdoh

Time required for the experiment

10 minutes

Method

• If you wish, draw eyes and a mouth on the sides of the balloon using a felt pen;
• Inflate the balloon inside the bottle, blowing through the neck. Make a knot and let the balloon fall in the bottle;
• Create a large and thick ring around the straw using the playdoh, and place the ring on the bottle opening;
• Work the playdoh so as to seal the bottle tightly?air should not be able to enter or escape the bottle by any other means than the straw;
• Place yourself in front of a mirror to observe the balloon. Making sure there are no air leaks, vigorously suck the air out of the bottle using the straw.

Observations

By vigorously sucking the air out of the bottle, the balloon undergoes rapid decompression. The air in the balloon expands when the pressure to which it is subjected decreases. Due to this expansion, the balloon seems to inflate.

Note

This activity may also be done in teams because it is difficult for the student sucking the air out through the straw to see the results at the same time if no mirror is available.

Here is an alternative that increases the effect:
Before sucking the air out through the straw, students can blow into it (increasing the pressure and reducing the volume of the balloon) and then inhale at once, increasing the depressurization and volume.