How the International Space Station Works

By: Craig Freudenrich, Ph.D. & Mark Mancini
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Updated: Feb 5, 2021

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. Four years later, the U.S. joined forces with Canada, Japan and the European Space Agency (a program then co-managed by the United Kingdom, France, Belgium, Italy, the Netherlands, Denmark, Norway, Spain, Switzerland, Sweden and West Germany) to make this station a reality [source: NASA].

The list of participating countries would grow during the 1990s as Russia and Brazil joined the project, although Brazil would eventually cut ties with the ISS in 2007 [source: Gizmodo Brazil].

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 — and it’s been continuously occupied by astronauts since 2000 [source: NASA].

The ISS contains a vast array of interconnected airlocks, docking ports and pressurized modules [source: NASA]. As of November 2019, a grand total of 222 spacewalks have been conducted at the station [source: NASA].

The ISS will continue to receive funding until at least 2024. So far, this stellar project has cost participating nations more than $100 billion — and NASA spends $3 to $4 billion on it per year [source: Greenfieldboyce].

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.

Building the International Space Station (ISS) is much like building a toy using a child’s LEGO or K’nex building block set. But whereas those playthings tend to be small in scale, the ISS contains thousands and thousands of parts [source: Hollingham].

Some of the major components are listed below:

Assembly of the ISS began in November 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 Oct. 31, 2000. The crew spent four months and 17 days 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 — as of this writing, 61 astronaut expeditions have successfully reached the station.

The station’s current crew took over Oct. 3, 2019. Those brave men and women are the members of ISS Expedition 61 and they’re scheduled to remain in space until February 2020. At that point, they’ll hand over the reins to Expedition 62 [source: NASA].

As home offices go, the ISS is pretty darn big. At 357 feet (108.8 meters) in length, the aforementioned truss is almost as long as an American football field. The ISS also contains multiple sets of broad, rectangular solar panels with 240-foot (73-meter) wingspans. Weight-wise, the station tips the scales at 925,335 pounds (419,725 kilograms). And it has 13,696 cubic feet (388 cubic meters) of habitable space aboard, a figure that increases every time another vessel docks there [source: NASA].

Traveling at the breakneck speed of 17,227 miles per hour (27,724 kilometers per hour), the ISS orbits at an average altitude of 248 miles (400 kilometers) above the Earth’s surface [sources: Conners and Howell].

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 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 all need oxygen, so the ISS has several methods of providing it. One technique is to have oxygen delivered from Earth via spacecraft. Supply shuttles periodically arrive with fresh oxygen in tow; the life-giving element is deposited into pressurized tanks aboard the ISS [source: Starr].

The ISS also has systems that make breathable oxygen from recycled water. Using electrolysis, some of these devices split water into hydrogen and oxygen gas. Then, the former is combined with an undesirable compound: carbon dioxide (CO2). Humans naturally exhale this colorless gas, but breathing in too much of it is hazardous to your health.

On Earth that usually isn’t a problem because plants absorb CO2. Yet gardening space is limited on the ISS, which forced engineers to devise other means of removing excess carbon dioxide. After the electrolysis process kicks in, some of the hydrogen reacts with the accumulating CO2. A byproduct of this interaction is methane gas, which gets vented into space. Meanwhile, reclaimed oxygen enters the ISS air supply [source: Starr].

While that’s going on, drinking water gets recycled as some of these very mechanisms repackage exhaled air. Water is also reclaimed by collecting sweat, condensation and urine. (Plus, some crew-members get water from reusing toilet and shower water.) As astronaut Douglas H. Wheelock told The New York Timesin 2015, when you’re aboard the ISS, “Yesterday’s coffee is tomorrow’s coffee” [source: Schwartz].

According to the European Space Agency, as much as 80 percent of the water aboard the ISS is recycled. Right now, the ESA and NASA are tinkering with closed-loop life support systems that — if perfected — might totally eliminate the need for water and oxygen shipments to the ISS. Cracking this technology could become the key to long-distance space travel in the future [source: ESA].

OK, so what about food? Well, apart from some edible plants that are grown onboard, the crew depends on routine deliveries for most of its food supply. Lots of menu items come in specially-designed packets that get affixed to dining surfaces with Velcro, lest they float away in the low-gravity environment [sources: Lemonick and Preston].

Maintaining a habitable temperature is another big concern. The ISS has to withstand temperatures of -128 degrees Celsius (-200 degrees Fahrenheit) and 93 degrees Celsius (200 degrees Fahrenheit) on the dark and sunlit sides of our planet, respectively.

Among other things, the ISS uses heaters, insulation and liquid ammonia-circulating loops to regulate the internal temperature. Radiators help release excess heat generated by some of the machinery aboard the station [source: NASA].

Like any home, the ISS must be kept clean. This is especially important in space, where floating dirt and debris could present a hazard. Astronauts use various wipes, detergents and vacuums to clean surfaces, filters and themselves. Trash is collected in bags, stowed in a supply ship and returned to Earth or incinerated [sources: Anderson and NASA].

Fire is one of the most dangerous hazards in space. During astronaut Jerry Linenger’s stay on Mir, a fire broke out. The Mir crew extinguished the fire, but not before the station was damaged. To detect and suppress fires, the ISS has smoke detectors, computerized alarm systems, fire extinguishers and portable breathing devices [source: Frost].

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 240 feet (73 meter) long and — cumulatively-speaking — they cover an area of around 27,000 square feet (2,500 square meters) [source: NASA].

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 [source: NASA].

Like a grid on Earth, the arrays generate primary power — approximately 84 to 120 kilowatts of electricity, enough to keep the lights on at over 40 homes. NASA reports that while the ISS absorbs sunlight, around 60 percent of the electricity produced in this process goes to recharging batteries aboard the station [source: NASA].

Originally, the ISS was fitted with nickel-hydrogen batteries. But in 2017, after 18 years of service, those were swapped out for two dozen lithium-ion replacements. On top of being cheaper, these upgraded batteries are smaller and more efficient [source: Nield].

At the station’s orbiting altitudes, Earth’s atmosphere is extremely thin, but still thick enough to drag on the ISS and slow it down. Therefore, the ISS must be boosted every so often, lest it veer off-course and lose altitude by decelerating.

The Russian Zvezda service module has engines that can be used to boost the ISS. However, it’s the Progress supply ships that do most of the reboosting. Each reboosting event requires rocket engine burns [sources: Pappalardo and NASA].

These same technologies could also be used to steer the vessel away from floating space debris (which is fairly common these days). Besides, it’s sometimes necessary to adjust the station’s orientation so it can link up with supply vessels.

Not only does the ISS crew need to know their precise whereabouts, but they’ve also got to locate other objects — and figure out how to get from Point A to Point B, especially during reboosts.

To discern its speed and location, the ISS uses Russian and U.S. global positioning systems (GPS). Also, there are multiple spinning gyroscopes that help the station maintain its desired orientation. Additionally, the ISS monitors the whereabouts of various stars, satellites and ground stations — as well as the sun — in order to navigate [source: NASA].

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

To stay in touch with Earth, the station uses Tracking and Data Relay Satellites (TDRS) located 22,000 miles (35,400 kilometers) above the Earth. Signals containing voice, video and scientific data are relayed through these devices, which facilitate contact between the ISS and NASA’s mission control in Houston (by way of the White Sands Complex in New Mexico) [source: 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 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].

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 PJs, 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].

After waking up, each astronaut has a post-sleep period to prepare for the day. During this time, the astronauts can shower, eat and read the Daily Summary Report (which — fun fact — includes the occasional cartoon) [source: ESA].

Exercise is important; in microgravity, bones lose calcium and muscles lose mass. So, astronauts set aside plenty of time for workouts. On the ISS, crew members spend 2.5 hours a day — for six days a week — rigorously exercising. While they’ve got a treadmill, an exercise bike, and weightlifting gear at their disposal, these items look pretty far removed from the equipment you’d see at a YMCA. (For crying out loud, the weightlifting device uses suction to create resistance — and the bike doesn’t even have a seat.) [source: Grush].

For actual work, astronauts conduct experiments or maintenance. Like most people, they stop to eat lunch at midday. Then, once the workday wraps up, there’s an evening planning conference between the crew and ground control centers. When that’s over, the astronauts are free to hang out, grab dinner and engage with social media.

Speaking of leisure time, the ISS has been known to hold crew-wide movie nights. In 2016, Gizmodo reported that the astronauts had access to over 500 films and TV shows, including “Modern Family,” “Pulp Fiction” and Alfred Hitchcock’s “Notorious.” One year later, Expedition 54 set the twitterverse abuzz when they were treated to a screening of “Star Wars: The Last Jedi” aboard the ISS [sources: Novak and NASA].

Ideally, crewmembers are supposed to get 8.5 hours of sleep per night. Due to the humming machinery, some astronauts wear earplugs while they doze [source: ESA].

Researchers from governments, industries 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 the blue planet we call home. For example, gravity alters the way that atoms come together to form crystals. Aboard the ISS, experimenters can develop bigger and better-structured crystals than they could on Earth. Such crystals could help us devise more efficient drugs to combat diseases — or improve radiation-detecting technologies [source: ISS: U.S. National Laboratory].

Also, microgravity does some interesting things to fire. When you strike a match here on Earth, gravity pulls cool, dense air downwards as hot gasses rise up — resulting in a teardrop-shaped flame. But on the ISS, flames take the form of tiny bluish spheres. These have already revolutionized our understanding of the combustion process. Down the road, ISS flame experiments could help engineers design more efficient burners and simultaneously reduce air pollution [source: NASA].

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 — such as decreased muscle strength, osteoporosis — are similar to the effects of aging. So, exposure to microgravity may give us new insights into the aging process and associated treatments.

Indeed, trial runs of NELL-1 — an experimental protein that fights osteoporosis by (among other things) forming replacement bone — on lab mice aboard the station have yielded some encouraging results [source: Smith].

ISS astronauts can also test ecological life support systems. In their orbiting workplace, it’s possible to grow various plants that release oxygen, absorb carbon dioxide and provide food. Those gardening skills will be important for long interplanetary space voyages, such as a trip to Mars.

Orbiting above the Earth’s atmosphere and equipped with special instruments and telescopes, the ISS crew can monitor lots of different things on the planet’s surface (like glacier distribution patterns) and in its atmosphere (like developing hurricanes). 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 NASA’s Space Station Experiments website. Now let’s take a look at the future of the ISS.

Knowledge rarely comes cheap. With its $100 billion cumulative price tag, the ISS is one of the most expensive undertakings in human history. And for years, financial considerations have raised questions about its long-term future.

The ISS will continue to receive funding from participating nations through the year 2024. But some major changes may be on the horizon. Recently, NASA has floated the idea of opening the station to private companies, in keeping with Reagan’s original plan. Maybe — at some point — commercial interests will assume partial or total control of day-to-day operations. Yet it remains to be seen if the ISS will ever become privately owned, as some politicians hope [sources: Greenfieldboyce and NASA].

Space may be the final frontier, but by now, the station’s orbital domain has become familiar territory. Once again, NASA is setting its sights on the moon: The ongoing Artemis program is supposed to land “the first woman and the next man” on Earth’s natural satellite by the year 2024 [source: NASA].

So where does that leave the ISS? Some administrators and scientists think research conducted aboard the station is vital to the success of future lunar — and Martian — exploration efforts. Still, money questions always rear their ugly heads. Does the ISS divert too much cash away from other spacefaring projects — or vice versa? On July 31, 2019, NASA administrator Jim Bridenstone announced that the agency wouldn’t take any money out of its ISS budget to fund new lunar landing tech. “If you cannibalize science, if you cannibalize the ISS, you will never achieve the end state you desire,” he opined [sources: Matthews and Redd].

While participating governments discuss their off-world laboratory’s fate, China has been creating space stations of its own. Two prototypes — Tiangong-1 and Tiangong-2 — ended their runs in planet Earth’s orbit in 2018 and 2019, respectively. Both vessels were used to help develop a bigger and better project: A large, ISS-like craft with three modules. According to the Chinese government, it’ll be completed in the early to mid-2020s [source: Jones].

No matter what tomorrow holds for the International Space Station, it remains a marvel of space construction — and as of this writing, it’s the longest manned space mission ever undertaken.

Much of the ISS engineering research and development goes toward studying the effects of the space environment on materials and developing new technologies for space exploration, including new construction techniques for building things in space, new satellite and spacecraft communications systems, and advanced life-support systems for future spacecraft.

The space environment has unique hazards (micrometeoroids, cosmic rays, atomic oxygen) that affect materials such as those used in spacecraft. Materials can be placed on the ISS in open platforms, exposed to the space environment for years and readily analyzed. The information retrieved will help design better materials for making satellites last longer in the space environment.

Originally Published: Dec 6, 2019

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