How the International Space Station Works

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Space Exploration Pictures The International Space Station. See more pictures of space exploration.
Image courtesy of NASA

Imagine you wake up in the morning, look out your window and see the vast blue horizon of Earth and the blackness of space. Our world stretches out beneath you. Mountains, lakes and oceans pass by in a beautiful stream of rapidly changing scenery as you orbit the Earth every 90 minutes. Sounds like something unreal out of a science fiction novel, right? For the crews of the International Space Station (ISS), it's a reality.

In 1984, President Ronald Reagan proposed a permanently inhabited, government- and industry-supported space station be built by the United States in cooperation with several other countries. The U.S. along with 14 other countries -- Canada, Japan, Brazil, and the European Space Agency (United Kingdom, France, Germany, Belgium, Italy, The Netherlands, Denmark, Norway, Spain, Switzerland and Sweden) decided to bring Reagan's vision to fruition. After the fall of the Soviet Union, the United States invited Russia to cooperate in the ISS project, which was still in its planning stages, bringing the number of participating countries to 16.

NASA took the lead in coordinating the ISS's construction, and today the ISS serves as an orbiting laboratory for experiments in life, physical, earth and materials sciences. Its assembly in orbit began in 1998. The ISS has about 38 modules and requires at least 44 spaceflights to deliver the components into orbit. One-hundred sixty spacewalks, totaling 1,920 man-hours, are required to assemble and maintain the ISS. The ISS is scheduled for completion in 2011 and will have an anticipated life of 10 years after that. Cost estimates of this stellar project range from $35 billion to more than $100 billion [source: NASA ISS Reference guide and Boyle].

In this article, we'll look at the parts of the ISS, how it maintains a permanent environment for humans in space, how it's powered, what it's like to live and work on the ISS, and how, exactly, we'll use the ISS. First, we'll start with its parts and assembly.


Parts and Assembly of the ISS

The Japanese Kibo complex of the ISS and the space shuttle Atlantis docked to the station
The Japanese Kibo complex of the ISS and the space shuttle Atlantis docked to the station
Image courtesy of NASA

Building the International Space Station (ISS) is much like building a toy using a child's LEGO or K'nex building block set. There are more than 100 parts to the ISS and all of those parts are linked together. The parts can be categorized as follows:

  • Pressurized modules -- such as the Zarya, Zveda, Destiny, Columbus and Harmony -- provide breathable, warm environments for living quarters, equipment rooms and laboratories where the crews live and work.
  • Nodes link modules together and allow branching of the ISS structure.
  • Docking ports allow various space vehicles to attach to the ISS.
  • A long, linear truss lies above the pressurized modules, forming a girder framework where the solar panels and radiators attach. A mobile, robotic, servicing arm moves along the truss to haul cargo and experiment packages.
  • External Research Accommodations provide multiple mounting locations along the outside of the ISS for experiments that rely on full exposure to the space environment.
  • Spacecraft -- such as the Soyuz spacecraft and Progress supply ship -- dock with the ISS to transport astronauts and supplies to and from Earth.

Assembly of the ISS began in November of 1998 when a Russian proton rocket placed the first module, the Functional Cargo Block (Zarya), in orbit. A three-member crew, the ISS's first, was launched from Russia on October 31, 2000. The crew spent almost five months aboard the ISS, activating systems and conducting experiments. Since then, many spacecraft have delivered parts of the ISS into orbit and its assembly has progressed. During this time, the ISS has been manned continuously with 26 crews of astronauts (as of this writing). The astronauts have spent a cumulative total of 4,423 days in outer space. The current crew, Expedition 26, will spend 5 months in space and return to Earth in May 2011, and then Expedition 27 will begin.

With a scheduled completion date set for December 2011, there are seven remaining scheduled flights in 2011 to complete its construction. There will be three flights by Russian and European rockets to deliver supplies, two space shuttle flights and one Russian proton rocket will deliver large pieces of modules or equipment and the shuttle flight in April will change crews.

When completed, the ISS will be 243 ft (74m) long and 361 ft (110 m) wide. It will have a mass of 925,000 lbs (420 metric tons) and a pressurized volume of 33,023 ft3 (935 m3); the pressurized volume will be about the cabin size of a 747 jet. It will be in orbit at 217 to 285 miles (362 to 476 km), inclined 51.6 degrees relative to the equator [source: ISS Facts and Figures and NASA ISS Reference guide].

Those are some pretty impressive specs -- but perhaps even more impressive is how the ISS maintains a livable environment.

Sustaining a Permanent Environment in Space

Sustaining a permanent environment in space requires things many of us take for granted here on Earth: fresh air, water, food, a comfortable (and habitable) climate -- even waste removal and fire protection. First, let's talk air. We need oxygen so the ISS has several systems for providing it. One system is to have oxygen delivered from Earth via spacecraft. This oxygen is stored in external tanks; similarly, these spacecraft deliver nitrogen gas, which makes the ISS air supply. The ISS also has a generator that makes oxygen from recycled water. Using electricity, it splits water into hydrogen and oxygen by electrolysis. The hydrogen gas gets vented into space and the oxygen goes into the ISS air. And finally, the ISS has a solid fuel oxygen generator that burns oxygen candles to release oxygen into the ISS air. Fans circulate the air within the ISS modules. The circulated air gets passed through various filters to remove particles and microbes. The composition of the air is constantly monitored and regulated throughout the station.

On Earth, plants remove the carbon dioxide we exhale, which is poisonous to us. In the ISS, it's removed chemically from the air by various "scrubbers" that absorb carbon dioxide and react it with other chemicals. In addition to carbon dioxide, we also breathe out water vapor. Aboard the ISS, this excess water vapor gets condensed into liquid and is recycled. But this isn't the only source of water. Like oxygen, water gets delivered to the ISS. In fact, there are various methods to transport supplies to the space station. The Russians have the Progress supply ships, European Space Agency has the automated transfer vehicle and Japan has the Kounotori2 or HTV2. Water is a byproduct of the fuel cells that the shuttle uses to generate electricity and water is even recovered from the crew's urine, which gets filtered and treated to make water for drinking, hand-washing and showers. The water gets stored in bags and containers throughout the station. Food is also delivered to the ISS by spacecraft. And the ISS has a kitchen with a food preparation area, food warmers and a table where the crew can eat.

The electronics aboard the ISS make more than enough heat to warm the station. In fact, the problem is getting rid of excess heat. So there are various methods to distribute heat evenly throughout the station. The temperature control system uses electric heaters, insulation and liquid ammonia pipes (heat distributors) to control the internal temperature. Radiators on the station's outside help eliminate the heat to outer space.

Like any home, the ISS must be kept clean. This is especially important in space, where floating dirt and debris could present a hazard. For general housecleaning, astronauts use various wipes (wet, dry, fabric and disinfectant), detergents and wet/dry vacuum cleaners to clean surfaces, filters and themselves. Trash is collected in bags, stowed in a supply ship and returned to Earth for disposal. Solid waste from the toilet is handled in a similar manner after it has been compacted, dried and bagged.

ISS: Power, Propulsion and Communications

The ISS is basically a large spacecraft. As such, it must be able to move about in space, its crew must maintain communications with controllers on the ground and it needs power to accomplish all of this.

We take for granted having electrical power to operate our homes. For example, to use your coffee maker, you simply plug it into the wall without a second thought. Like in your home, all of the onboard systems of the ISS require electrical power. Eight large solar arrays provide electrical power from the sun. Each array is 239 feet (73 m) long and covers an area of 24,187 ft2 (approximately 2,247 m2), or about one-half acre. On each array are two blankets of solar cells. Each blanket is on one side of a telescoping mast that can extend and retract to fold or form the array. The mast turns on a gimbal so that it can keep the solar cells facing the sunlight. The Russian modules also have 80- to 97-foot (24- to 30-m) solar arrays that provide power [source: NASA ISS Facts and Figures].

Like a power grid on Earth, the arrays generate primary power -- approximately 160 volts of DC electricity. The primary power gets converted by a secondary transformer to provide a regulated 124-volt DC current to be used by the station's equipment. There are also power converters onboard to meet the different currents required by U.S. and Russian equipment. The primary power is also used to charge the ISS's three nickel-hydrogen battery stations, which provide power when the ISS passes through the Earth's shadow in each orbit.

The ISS orbits the Earth at an altitude of 217 to 285 miles (362 to 475 km). At this altitude, the Earth's atmosphere is extremely thin, but still thick enough to drag on the ISS and slow it down. As the ISS slows down, it loses altitude. In addition to atmospheric drag, solar flares also slow the station down and cause it to lose altitude. So, the ISS must be boosted periodically to maintain its proper altitude. The command and service modules have rocket engines that can be used to boost the ISS. However, the Progress supply ships will do most of the reboosting. Each reboosting event requires two rocket engine burns. During the burns, work on the ISS is suspended. After the burns, station life returns to normal.

The ISS must be able to know precisely where it is in space, where other objects are and how to go from one point in space to another, especially during reboosting. To know where it is and how fast it is moving, the ISS uses both U.S. and Russian global positioning systems (GPS). To know which way it is pointing, its attitude, the ISS has several gyroscopes. The combination of all this information helps the ISS move from one point to another in space. In addition, the Russian navigation system uses sighting on the stars, sun and Earth's horizon for navigation.

Now that you know how the ISS stays in space, let's see what it's like to live and work there.

Life Aboard the ISS

Astronaut Sandra Magnus poses with free-floating stowage containers in the Destiny laboratory of the ISS.
Astronaut Sandra Magnus poses with free-floating stowage containers in the Destiny laboratory of the ISS.
Image courtesy of NASA

What's it like to live and work in space? To answer such questions, Expedition 18 flight engineer Sandra Magnus, wrote a series of journal entries about her stay aboard the ISS. She notes one important thing: An astronaut's day is planned well in advance (years actually) by many people on the ground. "Well we have a scheduling program on board that has in it all of the details that we need to know in order to do the day's work. It tells us when we should go to sleep, when we should get up, when we should exercise, when to eat our meals, when and what information we need to do our tasks " [source: NASA, Magnus Journal]. Although this does sound extremely rigid, Magnus notes that there is some flexibility in that not every task has to be carried out at the exact time the schedule dictates.

Microgravity presents a challenging environment. Whether you're sleeping, changing clothes or working, unless it's secured in place, everything in the ISS around you floats. Even something as seemingly simple as getting up in the morning and getting dressed isn't all that simple. Imagine opening up your closet only to have its contents come flying out at you. On getting ready in the morning, Magnus states, "When I take off my PJ's, they float around in the crew quarters until I gather them up and immediately fasten them down behind a band or something. Suffice it to say it is easy to lose things up here!" [source: NASA, Magnus Journal].

After waking up, each astronaut has a post-sleep period to prepare for the day. During this time, the astronauts can shower, eat, exercise and get ready for work. Exercise is important; in microgravity, bones lose calcium and muscles lose mass. So, astronauts must exercise for set times. Magnus preferred to exercise first thing in the morning, alternating daily between the stationary bike and treadmill. Next, there's a morning conference, where they discuss with crew members and ground controllers everyone's duties for the day. After the conference, they set out to work.

For work, astronauts conduct experiments or maintenance. Like most working people, they stop to eat lunch -- but their lunch breaks are a little different. The food on the ISS is mainly frozen, dehydrated or heat-stabilized, and drinks are dehydrated. Astronauts collect food trays and utensils, locate their individually-packaged meal from a storage compartment, prepare the items (rehydrating if necessary), heat the items, place them in the tray and eat. After the meal, they place the used items in a trash compactor, and clean and stow the utensils and trays.

After lunch, the scheduled activities continue. At the end of the work day, there's an evening conference followed by a 2-hour pre-sleep period. During this time, the astronauts eat dinner, complete any unfinished tasks and wind down. According to Magnus, there are plenty of options for filling this 2-hour period, "There is also email, phone calls, news, photos to review, and other activities which occupy this time. Friday is movie night and sometimes Saturday too" [source: NASA, Magnus Journal].

Work Aboard the ISS

The candle flame on the left is in normal gravity and the candle flame on the right is in microgravity.
The candle flame on the left is in normal gravity and the candle flame on the right is in microgravity.
Image courtesy of NASA

Researchers from governments, industry and educational institutions can use the facilities on the ISS. But why would they want to? The ISS is used mostly for scientific research in the unique environment of microgravity. Gravity influences many physical processes on Earth. For example, gravity alters the way that atoms come together to form crystals. In microgravity, near-perfect crystals can be formed. Such crystals can yield better semi-conductors for faster computers or for more efficient drugs to combat diseases.

Another effect of gravity is that it causes convection currents to form in flames, which leads to unsteady flames. This makes the study of combustion very difficult. However, in microgravity, simple, steady, slow-moving flames result. These types of flames make it easier to study the combustion process. The resulting information could yield a better understanding of the combustion process, and lead to better designs of furnaces or the reduction of air pollution by making combustion more efficient.

Long-term exposure to weightlessness causes our bodies to lose calcium from bones, tissue from muscles, and fluids from our body. These effects of weightlessness are similar to the effects of aging (decreased muscle strength, osteoporosis). So, exposure to microgravity may give us new insights into the aging process. If we can develop countermeasures to prevent the degrading effects of microgravity, perhaps we can prevent some of the physical effects of aging. The ISS provides long-term exposure to microgravity that could not be obtained by using other spacecraft.

The ISS allows us to test ecological life support systems that are similar to the way that the Earth provides life support. We can grow plants in large quantities in space to make oxygen, remove carbon dioxide and provide food. This information will be important for long interplanetary space voyages, such as a trip to Mars or Jupiter.

Orbiting above the Earth's atmosphere and equipped with special instruments and telescopes, the ISS crew can observe and take various measurements of the Earth's surface (amount of vegetation, temperature, water) and the Earth's atmosphere (carbon dioxide content, lightning strikes, hurricane development). Crew members can also use telescopes to observe the Sun, stars, and galaxies without distortion from the Earth's atmosphere.

For details on specific projects and experiments, you can check out the ISS Facility and Experimentation Web site. Now let's take a look at the future of the ISS.

Future of the ISS

The ISS is scheduled to be completed in 2011. The station is expected to be operational for another 10 years after that. Crews of astronauts will exchange out during that time. However, how that will happen is still unclear. The U.S. space shuttle fleet is being retired next year after 30 years of service. NASA's plans for returning to the Moon aboard the new Orion CEV spacecraft have been placed on hold as the Obama administration has cancelled the program. Although the Orion CEV spacecraft itself is still being developed, the Ares launch vehicle was cancelled. So, the future of the U.S. manned space program is uncertain at this time. NASA continues to develop new rocket technology to replace the shuttle. But exactly when this will be ready is unknown.

Once the shuttle fleet is retired, the United States will have no way of putting astronauts into space for a while. So, manned missions to the ISS will have to be transported using the Russian Soyuz spacecraft and resupplied using the Progress supply ships.

The ISS is not without its problems. With any machine as large and complex as the ISS, equipment breaks down and requires maintenance. However, given the projected price tag (more than $100 billion), many people have asked the question, "Is the ISS worth the money?" The criticism surrounds these basic points:

  • Is the science information gained worth the high price tag?
  • The ISS has little purpose in the future of space exploration. Critics have said that it exists to give the shuttles some place to go and the shuttles exist to service the ISS. The ISS isn't a launch platform to the moon, Mars or planets, no new rocket technology is being developed aboard it, and it does not fit into any long range plans of space exploration.
  • The ISS budget diverts funds away from highly successful unmanned space probes and space telescopes, which produce valuable scientific information.
  • The ISS budget diverts funds away from other manned space projects like missions to the moon or Mars.

Only time will tell about the benefits and costs of the ISS. In the meantime, it remains a marvel of space construction and the longest manned space mission undertaken.


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  • Boyle, Alan. "What's the cost of the space station?" MSNBC, accessed Jan. 28, 2011,
  • Launius, RD, Space Stations: base camps to the stars, Smithsonian Books, Washington, DC, 2003
  • NASA, Astronaut Sandra Magnus Expedition 18 Journals, accessed Dec. 26, 2010,
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