GO IN DEPTH

Spaceship Earth

What You Need

 
Spaceship Earth

Purpose

To develop an understanding of our planet as a system by designing a very-long-duration space mission in which the life-support system is patterned after that of earth.


Context

This lesson was developed by Dr. Penny Firth, a scientist, and Mr. Bradley Smith, Director of the Strategic Environmental Research and Development Program of the Department of Defense, as part of a set of interdisciplinary Science NetLinks lessons aimed at improved understanding of environmental phenomena and events. Some of the lessons integrate topics that cross biological, ecological, and physical concepts. Others involve elements of economics, history, anthropology, and art. Each lesson is framed by plain-language background information for the teacher and includes a selection of instructional tips and activities in the boxes.

One of the really nice things about living on earth is all of the stuff we don't have to worry about. We don't have to worry about running out of oxygen. There is always plenty of water somewhere on the planet. And where the soils and climate are right, we can find or grow ample food for ourselves. In short, the earth functions as a massive life-support system for over six billion humans as well as the trillions of other life forms that share the planet with us. Click on the Earth Observatory site for a spectacular image of earth. The "blue marble" picture is the most detailed true-color image of the planet to date.

How does our planetary life-support system work? There is no real mystery to the broad outlines of the story (although scientists continue to refine our understanding of various bits): the requirements for human life are provided by organisms and their interactions with the non-living environment. Energy from the sun powers the food webs and the water cycle and all parts of the system are interconnected. Outputs from one part of the system are inputs for another part. This linked output-input setup is often called feedback, and feedback is what keeps the system from careening out of bounds like a soccer ball. For earth, out of bounds might mean runaway global climate change (such as ice ages), or catastrophic loss of important species leading to the collapse of vital ecosystems, or wildly unusual extreme weather patterns and the consequent loss of life and property.

This lesson is entitled Spaceship Earth to reinforce the idea that our planet is–in reality–like a spaceship hurtling through space on a long-duration mission. There is no resupply from outside sources. Recycling is as much a part of the natural order of things as is the sunrise everyday. Pollution occurs when there are outputs that cannot be used as inputs for something else. Pollution is harmful and can be downright dangerous. The connections between parts of the natural system are imperative to its normal operation. By actively thinking through what it takes to keep people alive on a spaceship, the students will come to understand more fully what it takes to keep people alive on this planet.

For prerequisite knowledge, common misconceptions, and benchmarks related to this lesson, see the Prerequisite Knowledge Teacher Sheet.

Note: You can contact Dr. Firth at pfirth@nsf.gov, or Mr. Smith at Bradley.Smith@osd.mil .


Planning Ahead

We have tried to provide you with several options for the hands-on part of teaching this lesson, recognizing that time is always limiting and you may wish to enjoy this lesson in something less than its full glory.

Option 1:
The first, original, and (we think) most fun option is to print out the Rescue Mission Planning packet and use the worksheets in constructing 3-D shadow boxes as described in the Development. The shadow boxes will represent subsystems (i.e., crew quarters, greenhouse, etc.) and will ultimately be connected to one another by colored yarn or ribbon (representing inputs and outputs).

So you will need several boxes, creative ideas for what the insides might look like (cotton balls dyed for compost, moss or twigs for the plants, etc.), and various colors of yarn or string. Also tape, glue, and similar construction items.

A shadow box, for those of you unfamiliar with the term, is a miniature diorama inside a box. A shoebox is about the smallest size that can be worked in easily. If your classroom has enough space to allow larger boxes, the students should be encouraged to use them. Because teams of students will work on each shadow box, they will need as much room to move as possible.

Option 2:
This option is faster than shadow boxes, but has the drawback of being in only two dimensions. Basically, you print out the Rescue Mission Planning packet and develop a good idea of what the inputs and outputs for each subsystem are. Then print out the Subsystem Posters Packet and place the posters on a bulletin board.

The students will then put inputs and outputs on each subsystem poster (they can glue on pictures if time allows) and, using push pins or similar attachments, connect the subsystem posters with yarn or ribbon of different colors.

Whichever option you choose, we have developed an Online Teaching Tool that you can use to help walk the students through the various interconnections between the subsystems. Although each part of this is fairly simple, the final product is definitely a pile of spaghetti! We strongly encourage you to familiarize yourself with the various outputs and inputs before you get too far along in connecting up your subsystems, whether you decide to use the 2-D (subsystem posters) or 3-D (shadow boxes) approach.

Note: We have also made the Online Teaching Tool available in a version that can be easily printed for quick reference: Printable Teaching Tool.

Remember, the message here is that the many subsystems of the spaceship are simple models of the same subsystems that we have here on earth.


Motivation

Present students with the following scenario and then brainstorm possible solutions. It is important that you don't "give away" the underlying concept too soon: the spaceship being designed is really a model of our planet Earth. Let students figure this out by themselves!

The Scenario
A spaceship and its crew have been accidentally transported to a far galaxy, beyond radio communication. Your mission is to design and mount a rescue. Your rescue ship will be in space for at least 20 years, or until you graduate from high school. You will not have the ability to carry all of the consumable things that you will need with you (i.e., food, water, etc.). You can assume that NASA engineers have developed an on-board energy and propulsion system that will take you as far as you need to go–and get you home again, with lights and heating/cooling all the way. You can assume that you have artificial gravity and protection from harmful radiation. You can also assume that re-supply is not going to be possible: you must bring everything with you (see Cardinal Rules below). You (the class) are the crew.

Cardinal Rules for Rescue Mission Spaceship Planning:

  • Nothing goes in. Nothing goes out.
  • Every output must be an input.
  • Every input must come from an output.

Development

What do human beings really need? And what do they want?
In the closed spaceship system, as mentioned in the Cardinal Rules, nothing goes in and nothing comes out. The class must think about recycling everything. The system must be designed so that everything that is produced (output) must be used as a source (input) for another process. A process is something that takes place over time, such as breathing, eating, photosynthesizing, and reading comic books.

Distribute the Rescue Mission Planning packet to each team of students and start brainstorming by thinking about what human beings need as inputs. Have students fill in the inputs on Student Sheet 1 of the Rescue Mission Planning Packet. With any luck, the students will list food, water, and oxygen.

Then start thinking about the outputs. Some of these will be obvious (urine, feces) and others may require prompting (water, carbon dioxide). Have students fill in the outputs on Student Sheet 1 of the Rescue Mission Planning packet.

The student sheet might look something like this:

Rescue Mission Planning Student Sheet 1 (example)

HUMAN INPUTS
 
HUMAN OUTPUTS
Food
 
Feces
Water
 
Urine
Oxygen
 
Carbon dioxide
   
Water (perspiration, exhalation, washing, food preparation)
Crew Quarters
Have a team of students build a shadow box of the crew quarters on the spaceship. This is the place where the crew will spend most of their time: eating, sleeping, recreating, studying, and exercising. It might require several different rooms. Don't forget a bathroom! Explain to them that this is one of several subsystems that they will construct as part of the spacecraft.

Make large, clearly-labeled arrows for each of the inputs and outputs listed on the worksheet (i.e., carbon dioxide, food, etc.) and glue, tape, or otherwise fix the arrows pointing into (inputs) or out of (outputs) the crew quarters shadow box. Later in the lesson, the arrows to and from this shadow box will be connected by yarn or ribbon to the arrows to and from other shadow boxes.


Food: If Pizza, Then Life
Once you have listed the inputs and outputs for the crew, have the class look at the "Food" input. Ask them how they would produce their food. What kinds of foods do they like? What kinds of foods do they need? Should they plan for both kinds? They may suggest various types of plants and animals as sources of food. Plants and animals have inputs and outputs also. The Leafy Green Astronauts article on the Science@NASA site is about plants but also deals with the wider issues of cycling material. It is good background.

Perhaps some students may suggest that food will come from a "replicator" like the ones on Star Trek. While technology may some day yield such a marvelous device—and perhaps this very class of students may invent it—it will still need raw materials to make the food. These raw materials will be in the form of protein, sugar, and fats, which will have to come from somewhere, i.e., plants and animals.


So, let's have students brainstorm the inputs and outputs for plants using Student Sheet 2 in the Rescue Mission Planning packet.

If the students are knowledgeable enough—perhaps they help out around the family garden—they might list some of the components of fertilizer, such as nitrogen, phosphorus, and potassium. If they don't, not a problem. But they should be led to the concept that plants do not live on water and air alone. Fertilizer in nature is part of the soil and when people compost, they are simply renewing the fertility of the soil, a process that takes place constantly around the planet.

The student sheet might look something like this:

Rescue Mission Planning Student Sheet 2 (example)

PLANT INPUTS
 
PLANT OUTPUTS
Carbon dioxide
 
Oxygen
Water
 
Water (transpired water vapor)
Fertilizer
 
Food (i.e., seeds, fruits, leaves, roots)
   
Non-food plant material
Space Greenhouse
Have a team of students build a shadow box of the greenhouse that will supply the plants for the expedition. Explain to them that this is another one of the subsystems that they will construct as part of the spacecraft.

Students should make clearly-labeled arrows for each of the inputs and outputs listed on the worksheet (i.e., carbon dioxide, food, etc.) and glue, tape, or otherwise fix the arrows pointing into (inputs) or out of (outputs) the shadow box.


After the plants are under control, start brainstorming the animals (Student Sheet 3 of the Rescue Mission Planning packet). Will they be vertebrates, like fish and birds? Is this where boneless chickens will be invented? Or will people get a little adventurous and suggest some invertebrates, such as insect larvae and worms? This is an exceptional time to allow students in the class free range across the spectrum of gross but edible animals. Ask the class what inputs all animals have in common. How about outputs?

The student sheet might look something like this:

Rescue Mission Planning Student Sheet 3 (example)

ANIMAL INPUTS
 
ANIMAL OUTPUTS
Food
 
Feces
Water
 
Urine
Oxygen
 
Carbon dioxide
    Water (perspiration, exhalation)
    Food (i.e., meat)
   
Non-food animal parts
Space Barnyard
Now have a team of students build a shadow box of the facility that will supply the animals for the expedition. Again, this is one of several subsystems that they will construct as part of the spacecraft.

If they have decided to include fish, be sure that they build in some aquaria. NASA has explored the idea of using Tilapia, a tasty fish that lives on the waste products of plants.

Again, make large, clearly-labeled arrows for each of the inputs and outputs listed on the worksheet and glue, tape, or otherwise fix the arrows pointing into or out of the shadow box.


Water: Water, water everywhere, if you're seeking in the air
Now you have spent some time discussing and building crew quarters and the sources of food for the crew. Let's turn our attention to water and how it will move around the spaceship. Remember that the water that the mission starts out with is it. It may change form (liquid water, water vapor, ice) and may spend time in and as a part of the bodies of different plants, animals, microbes, and humans, but there is not going to be any resupply of water.

The Water on the Space Station article discusses the problems with water on the International Space Station and the recycling systems that have been developed to deal with these problems.

One thing to recall at this point is that the water released by plants (transpiration) and animals (exhalation, perspiration, urine, wash water) cannot be directly drunk by humans. In the case of exhaled, transpired, and perspired water, it is very pure, but in vapor form. In the case of urine, well, nobody I know would drink it short of desert desperation. So, if we want to use it and the wash water for human or animal drinking water, it will need purification.

Urine is more than 95% water. The five percent that isn't water contains salts and other nutrients that are necessary for life. The class may wish to simply dilute the urine with pure water and use it directly to water the plants. Alternatively, the water in the urine can be extracted through a variety of processes and then used for human or animal drinking water. The wash water and water that has been used in food preparation can be purified as well.

Although water vapor in the air is perfectly pure, and there is a lot of it, it is not particularly helpful for drinking, food preparation, washing, or plant watering. Brainstorm with the class about how to get the water out of the air. They should come up with the idea of condensation in some form, i.e., the water drops that form on the side of a cold soda-pop can in the summer. Because power on the spaceship is not a problem, the students can plan a cooler to extract the water from the air through condensation and turn it into a liquid.

To help the students think about the water cycle on board, use Student Sheet 4 of the Rescue Mission Planning packet to guide them in brainstorming the sources and uses for water. As they brainstorm, be sure that they list the form that the water is in (vapor or liquid).

The student sheet might look something like this:

Rescue Mission Planning Student Sheet 4

Inputs to Water Facility  
Water Sources:
Form:
Human breathing
vapor - pure
Animal breathing
vapor - pure
Perspiration
vapor - pure
Plant transpiration vapor - pure
Urine liquid - polluted
Used wash water liquid - polluted
Used cooking water
liquid - polluted

Outputs from Water Facility  
Water Uses:
Form:
Irrigation water
liquid - pure
Drinking water
liquid - pure
Cooking Water
liquid - pure
Wash water liquid - pure
Water World
Have a team of students build a shadow box of the facility that will handle the water needs of the spaceship and crew. It is responsible for two processes, for which it will need two kinds of technology: 1) a condenser unit of some sort to change water vapor to liquid water and 2) a purification unit to clean up urine and used wash water and cooking water.

The students can represent these units any way they wish in the shadow box. For example, empty thread spools connected by pipe cleaners could be a purification unit. The condenser might be a small, clear plastic bottle of the sort that bottled water comes in. If you leave a little water in the bottom, it will likely acquire a realistic bit of condensation on the inside.

If there is space, time, and inclination, the students might wish to equip the water facility with tanks for water storage. The tanks might be labeled "pure water" and "polluted water." The tanks could be made from cut-down cereal boxes or anything else that the students think of.

The large arrows for the water facility should point in for "water vapor" and "polluted water" and out for "pure water."


Solid Waste: Solid as a…
Remembering the cardinal rules of rescue mission spaceship planning (every output must be an input, every input must come from an output), your class will probably notice that we have not accounted for all of the outputs and inputs. Although it may not be as pleasant to think about as food and water, we need to give a little time to solid waste. Solid waste on the spaceship will include human and animal feces, as well as non-food plant parts (stems, skins, inedible roots, etc.) and non-food animal parts (scales, bones, skin, hair, etc.). What to do with this revolting stuff?

Have the students brainstorm how they can turn these outputs into inputs, especially the one input that is in short supply: plant nutrients (fertilizer).

As far as non-food plant and animal mass is concerned, hopefully the students will suggest composting. This is an excellent solution. In case they have heard that animal waste should not be composted in our gardens here on earth, reassure them that the reason for this is to avoid attracting rats and other vermin. Unless they bring rats along (avoid 7th grader jokes at this point), they won't have this problem on the spaceship. The compost will make an excellent source of fertilizer for the plants and clear up that pesky input-output problem we had.

Your students may offer that the animal feces (manure) can be used to fertilize the plants. This is a pretty good idea. They may balk at the idea of using human feces for the same purpose. This also reflects good common sense. Human waste may be contaminated and spread disease if used directly. With the spaceship's unlimited source of energy, the human and animal feces can be sterilized before they are placed in the compost bin.

Just a brief word about the compost bin. It is important to remember who is doing the work: microbes. At the right temperature, and given a little oxygen and a variety of food sources, bacteria, fungi (molds and others), and similar kinds of organisms will rapidly decompose almost all organic matter to a clean, easily used soil-like material: compost. The microbes that perform this work will produce carbon dioxide gas as they do their work.

To help the students think about the solid waste-related pathways on board, use Student Sheet 5 of the Rescue Mission Planning packet to guide them in brainstorming what these materials are and what form they are in.

The student sheet might look something like this:

Rescue Mission Planning Student Sheet 5

Inputs to Solid Waste Facility  
Human feces
solid
Animal feces
solid
Non-food plant parts
solid
Non-food animal parts solid
Oxygen gas

Outputs from Water Facility  
Compost
solid
Carbon dioxide
gas
Solid Waste Facility
The final shadow box is the facility that will handle the solid waste. It is responsible for two processes, for which it will need two kinds of technology: 1) a sterilizer unit of some sort to purify the feces and 2) a composting unit to convert the sterile feces and the remaining solid waste into compost for the plants.

The team of students can represent these units any way they wish in the shadow box. For example, the sterilizer unit could be a toilet tissue roll painted or covered with foil. The composting unit could be a small milk carton covered with foil or construction paper. The student team might also want to include a bin for finished compost. They could dye cotton balls brown and pile them in the bin to represent clean compost ready for use in the greenhouse.

The large arrows for the solid waste facility should be labeled as in the student sheet to be sure that everything is represented.


Air: How long can you hold your breath?
We know that oxygen is produced by green plants in the process of photosynthesis (photo "light" and synthesis "combination to form a whole"). As long as your greenhouse has a sufficient number of healthy plants, the spacecraft will have enough oxygen. The class might want to speculate about the balance of plants to produce oxygen versus those that will be harvested for food. What might happen if they harvested all of their plants at one time?

The important feedback to remember here is that the carbon dioxide produced by the human and animal passengers is a necessary input to the process of photosynthesis by plants. Keeping the oxygen and carbon dioxide in balance is very important to the success of the mission. The Breathing Easy on the Space Station article looks at how the real-life International Space Station is handling air.

There is no shadow box to make here, because the conversion of oxygen to carbon dioxide and carbon dioxide to oxygen is taking place in all of the other shadow boxes. You should have the class check, however, to be sure that the large input and output arrows include these gases for every shadow box.

Connections: A Big Pile of Spaghetti
The next step is to have students begin to make the connections between the inputs and outputs. Refer to the Online Teaching Tool for help with seeing the connections.

Note: We have also made the Online Teaching Tool available in a version that can be easily printed for quick reference: Printable Teaching Tool.

If you can, use a different color of yarn or ribbon to represent different materials or forms of materials (e.g., oxygen, food, liquid water, water vapor). It may be simplest to start with the gases oxygen and carbon dioxide. Make sure that you attach the yarn end to the output and that it goes to an input on another shadow box. Some outputs will flow to multiple inputs and vice versa.

Step back, take a deep breath, and look at your masterpiece. What a complicated pile of spaghetti! This should give students some feel for how complex and interconnected the life-support process is.

The Spaceship Earth: The Whole System
At this point, students are justifiably proud of their skill in design and their accomplishments in construction (if they have made the shadow boxes). They probably have become very engrossed in the process and the results without really standing back and realizing not only how complicated life support is, but how the earth provides all the facets of life support.

This is the point at which you can ask them to draw parallels between their self-sufficient spaceship and earth. Try to bring them to suggest the following points:

  • Life support is complicated.
  • In order to work properly, everything must be interconnected.
  • Every output must be an input to something else. Otherwise, the material that makes up the output simply piles up, becomes a pollutant, and may become a hazard. Also, you run out of inputs!
  • The earth is a closed system, just like the spaceship.

Assessment

The Naming Ceremony
A twenty-year mission in a custom-built spacecraft deserves a little ceremony. To celebrate the conclusion of the design and construction phase, you might have a little naming ceremony for the spaceship. We like the name "Spaceship Earth" for obvious reasons. The class may decide on something that sounds more spacey, like "Galactic Super Cruiser," or racy, like "Cosmos Express." It doesn't really matter, but make sure the cookies and punch are tasty!

Bring closure to this lesson and assess student understanding with the following questions:

  • Are there any human needs that are NOT met by the spaceship life-support system?
    (Hint: Think about intangibles such as social interaction, forms of expression, diversity in experience. Also consider spices, fragrances, clothing, exercise facilities, medical facilities and band-aids, music, libraries, and maybe pets.)
  • Would you like to serve on the mission? Why or why not?

Extensions

The National Aeronautical and Space Administration (NASA) has an extensive set of websites that deal with this subject. Some of these are included here:

Dr. John Graf of NASA's Johnson Space Center, and colleagues, have developed a fairly comprehensive listing of Life Support Systems for the Space Environment: Basic Tenets for Designers . This 14-point inventory is somewhat technical, but full of interesting tidbits on how the space environment differs from planetary environments, the importance of human interfaces with technology, and how design challenges constrain what can be done. It is worth reading even if you do not take your class to it.

The Orbital Space Settlements Online Course is for teachers and students who want to participate in the NASA Space Settlement Design Contest. It contains a wealth of information on life-support systems.


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