How the International Space Station Functions

Picture yourself waking up in the morning, gazing out your window to behold the vast blue expanse of Earth and the infinite darkness of space. Below you, our planet unfolds. Mountains, lakes, and oceans drift by in a mesmerizing flow of rapidly changing landscapes as you circle the Earth every 90 minutes. It may sound like something from a science fiction novel, but for the crew aboard the International Space Station (ISS), it’s an everyday reality.

In 1984, President Ronald Reagan put forward the idea of constructing a space station, permanently inhabited, and supported by both the government and industries, to be built by the United States in partnership with several other nations. Four years later, the U.S. teamed up with Canada, Japan, and the European Space Agency (a project that was co-managed by the United Kingdom, France, Belgium, Italy, the Netherlands, Denmark, Norway, Spain, Switzerland, Sweden, and West Germany at the time) to turn this vision into reality [source: NASA].

Throughout the 1990s, the number of nations involved in the ISS project grew, with Russia and Brazil joining. However, Brazil severed its relationship with the ISS in 2007 [source: Gizmodo Brazil].

NASA took charge of organizing the ISS's construction, which has since become a space-based research hub for experiments across a variety of scientific fields, including life, physical, Earth, and materials sciences. Its assembly in space began in 1998, and astronauts have lived aboard it continuously since 2000 [source: NASA].

The ISS boasts an extensive network of connected airlocks, docking ports, and pressurized modules [source: NASA]. As of April 2022, a total of 248 spacewalks have been conducted at the station [source: NASA].

The ISS is slated to receive funding at least until 2030, as confirmed by the Biden administration on December 31, 2021. To date, the cost of the project for the participating countries exceeds $100 billion, with NASA contributing $3 to $4 billion annually [source: Greenfieldboyce].

This article explores the components of the ISS, how it ensures a stable environment for humans in space, its power sources, the daily life and work aboard, and the ways we utilize the ISS. Let's begin by examining its structure and assembly.

The Assembly and Construction of the International Space Station

Building the ISS is comparable to constructing a toy using a child's LEGO or K'nex set. While these toys are small in size, the ISS features an enormous number of parts [source: Hollingham].

Here are some of the primary elements that make up the International Space Station:

The assembly of the ISS began in November 1998 when a Russian proton rocket launched the first module, the Functional Cargo Block (Zarya), into orbit. The first crew, consisting of three astronauts, was sent to the ISS on October 31, 2000. They spent four months and 17 days aboard, activating systems and conducting experiments.

Since its initial assembly, numerous spacecraft have delivered additional ISS components into orbit, and its construction continues. The station has been continuously staffed with astronauts — as of now, 66 astronaut expeditions have successfully reached the station.

Expedition 67 commenced with the departure of Soyuz MS-19 on March 30, 2022, with NASA astronaut Thomas Marshburn assuming the role of ISS commander [source: NASA].

When it comes to home offices, the ISS is quite large. Stretching 357 feet (108.8 meters) in length, the truss is nearly as long as a football field. The station also features multiple solar panels with wingspans of 240 feet (73 meters). The ISS weighs 925,335 pounds (419,725 kilograms) and offers 13,696 cubic feet (388 cubic meters) of habitable space, which increases each time a new vessel docks there [source: NASA].

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

These specifications are certainly impressive, but what's even more remarkable is how the ISS ensures a habitable environment for its crew.

Maintaining a Sustainable Environment in Space

Maintaining a permanent environment in space requires essential resources that many of us take for granted on Earth: fresh air, water, food, a comfortable climate — and even systems for waste removal and fire safety.

Let's begin with air. Oxygen is a necessity for all living beings, and the ISS has multiple methods of ensuring a steady supply. One such method involves delivering oxygen from Earth via spacecraft. Periodic supply missions bring fresh oxygen, which is stored in pressurized tanks on the station [source: Starr].

Additionally, the ISS employs systems that generate breathable oxygen from recycled water. These systems use electrolysis to break water into hydrogen and oxygen. The hydrogen then combines with carbon dioxide (CO2), a gas humans naturally exhale but cannot breathe in excess of.

On Earth, plants naturally absorb CO2, but the ISS has limited space for gardening. To manage excess CO2, engineers developed methods to remove it. After electrolysis, some of the hydrogen reacts with the CO2, producing methane gas, which is vented into space, while the oxygen produced is added to the station's air supply [source: Starr].

Simultaneously, water is recycled through systems that collect exhaled air, sweat, condensation, and even urine. In fact, some astronauts even reuse water from the toilet and shower. As astronaut Douglas H. Wheelock said to The New York Times in 2015, aboard the ISS, "Yesterday's coffee is tomorrow's coffee" [source: Schwartz].

As reported by the European Space Agency, approximately 80 percent of the water aboard the ISS is recycled. Currently, the ESA and NASA are working on closed-loop life support systems that, if perfected, could eliminate the need for water and oxygen shipments to the station. Mastering this technology could be the key to enabling long-duration space travel in the future [source: ESA].

What about food, you ask? Aside from a few edible plants grown onboard, the crew relies on regular supply missions for most of their meals. Many items are packaged in special containers that are attached to surfaces with Velcro to prevent them from floating away in the station's low-gravity environment [sources: Lemonick and Preston].

Keeping a stable temperature is a significant challenge. The ISS must endure temperature extremes, ranging from -128 degrees Celsius (-200 degrees Fahrenheit) on the side facing away from the Sun, to 93 degrees Celsius (200 degrees Fahrenheit) on the sunlit side of the planet.

To manage this, the ISS relies on a combination of heaters, insulation, and liquid ammonia-circulating loops to regulate its internal temperature. Radiators help dissipate excess heat generated by the station's equipment [source: NASA].

Like any home, cleanliness aboard the ISS is essential. This is especially true in space, where floating particles and debris can pose risks. Astronauts use a variety of wipes, cleaning agents, and vacuums to clean surfaces, filters, and themselves. Trash is collected in bags, stored in supply ships, and either returned to Earth or incinerated [sources: Anderson and NASA].

ISS: Energy, Propulsion, and Communications

The ISS functions as a massive spacecraft. Therefore, it must be capable of maneuvering in space, ensuring constant communication between its crew and mission control, and having a reliable power source to operate these systems.

We often take for granted the electricity we use to power our homes. For instance, using your coffee maker is as simple as plugging it into the wall. Similarly, every system aboard the ISS relies on electrical power. This power is generated by eight massive solar arrays, each measuring 240 feet (73 meters) long. In total, these arrays cover an area of approximately 27,000 square feet (2,500 square meters), harnessing energy from the sun [source: NASA].

Each solar array consists of two blankets of solar cells. These blankets are mounted on telescoping masts that can extend or retract to adjust the array's position. The masts rotate on a gimbal to ensure the solar cells continuously face the sunlight [source: NASA].

Much like an electrical grid on Earth, the arrays generate primary power, producing between 84 and 120 kilowatts of electricity — enough to power more than 40 homes. NASA reports that while sunlight is absorbed by the ISS, approximately 60 percent of the electricity produced is used to recharge the station's batteries [source: NASA].

The ISS was originally equipped with nickel-hydrogen batteries, but in 2017, these were replaced with 24 lithium-ion batteries. These new batteries are not only more cost-effective but also smaller and more efficient than their predecessors [source: Nield].

At the ISS's orbital altitude, Earth's atmosphere is thin but still exerts enough drag to slow the station down. To prevent it from losing altitude and veering off-course, the ISS requires periodic boosts to maintain its orbit and momentum.

The Zvezda service module, operated by Russia, is equipped with engines capable of boosting the ISS. However, most of the reboosting is performed by the Progress supply ships, which carry out the necessary rocket engine burns during these events [sources: Pappalardo and NASA].

These propulsion technologies also help steer the ISS away from drifting space debris, which is increasingly common. Additionally, the station's orientation must sometimes be adjusted to facilitate docking with supply vessels.

In addition to knowing its exact location, the ISS crew also needs to track other objects and determine the best route from one point to another, especially during reboost maneuvers.

To monitor its speed and position, the ISS utilizes both Russian and U.S. global positioning systems (GPS). It also employs a series of gyroscopes that assist in maintaining the station's orientation. Furthermore, the ISS tracks various stars, satellites, ground stations, and even the sun to help with navigation [source: NASA].

Now that you understand how the ISS remains in space, it's time to explore what life and work are like aboard the station.

Life Aboard the ISS

Ever wondered what it's like to live and work in space? To provide insight, Expedition 18 flight engineer Sandra Magnus penned a series of journal entries during her time aboard the ISS. She observed one key detail: an astronaut's schedule is meticulously planned in advance by a team on the ground.

"Onboard, we have a scheduling program that provides all the details we need to carry out our tasks for the day. It tells us when to sleep, when to wake up, when to exercise, when to eat, and when we need specific information to complete our work" [source: NASA].

Although the schedule might seem rigid, Magnus points out that there is some flexibility — not every task needs to be done exactly when the schedule says.

Microgravity creates a challenging environment. Whether sleeping, changing clothes, or working, everything around you in the ISS floats unless secured. Even simple tasks, like getting dressed, become complex. Imagine opening your closet only to have everything float out. As Magnus explains, "When I take off my pajamas, they float around the crew quarters until I gather them up and secure them behind a band or something. It's easy to lose things up here!" [source: NASA].

After waking up, astronauts have a brief time to prepare for the day. During this period, they can shower, eat, and read the Daily Summary Report (which — fun fact — includes an occasional cartoon) [source: ESA].

Exercise is crucial; in microgravity, bones lose calcium, and muscles lose mass. So astronauts dedicate ample time to exercise. On the ISS, crew members spend 2.5 hours a day — six days a week — working out. They have access to a treadmill, an exercise bike, and weightlifting equipment, but these are quite different from the gear you'd find at a YMCA. The weightlifting machine uses suction for resistance, and the bike doesn't even have a seat! [source: Grush].

Astronauts spend their workday conducting experiments or performing maintenance tasks. Like anyone, they break for lunch around midday. Once the day’s work is complete, there's a conference with ground control centers to plan for the evening. Afterward, the astronauts are free to relax, enjoy dinner, and interact on social media.

When it comes to leisure, the ISS crew often gathers for movie nights. According to Gizmodo in 2016, astronauts had access to over 500 films and TV shows, including "Modern Family," "Pulp Fiction," and Alfred Hitchcock’s "Notorious." In 2017, Expedition 54 made headlines when they watched "Star Wars: The Last Jedi" aboard the ISS, sparking excitement across social media [sources: Novak and NASA].

In an ideal scenario, astronauts are meant to get 8.5 hours of sleep each night. However, due to the constant hum of machinery, some astronauts prefer to wear earplugs while they sleep [source: ESA].

Work Aboard the ISS

The ISS facilities are available for researchers from various sectors, including governments, industries, and academic institutions. But why would they be interested? The ISS offers a unique platform for scientific research in microgravity. Gravity influences many processes on Earth, such as how atoms bond to form crystals. In the microgravity environment of the ISS, scientists are able to grow larger and more perfectly structured crystals than what can be achieved on Earth. These advancements could lead to more effective drugs for treating diseases or enhanced technologies for detecting radiation [source: ISS: U.S. National Laboratory].

Microgravity also causes intriguing changes to fire behavior. On Earth, striking a match causes gravity to pull the cooler, denser air downward, allowing the hot gases to rise and create a teardrop-shaped flame. However, in the weightlessness of the ISS, flames form as small bluish spheres. This phenomenon has significantly deepened our understanding of combustion. In the future, experiments with fire aboard the ISS may help engineers develop more efficient burners while also reducing air pollution [source: NASA].

Extended exposure to weightlessness results in the loss of calcium from bones, muscle tissue deterioration, and the depletion of bodily fluids. These effects — such as muscle weakening and osteoporosis — are similar to the effects of aging. As such, microgravity could provide valuable insights into the aging process and related treatments.

Indeed, experiments involving NELL-1 — an experimental protein that helps combat osteoporosis by promoting bone regeneration — have shown promising results in lab mice aboard the ISS [source: Smith].

Astronauts aboard the ISS also have the opportunity to test ecological life support systems. Within their orbiting workplace, they can cultivate a variety of plants that release oxygen, absorb carbon dioxide, and even produce food. Mastering these gardening techniques will be crucial for long-duration space missions, like those destined for Mars.

While orbiting above Earth's atmosphere, the ISS crew uses specialized instruments and telescopes to monitor various phenomena on the planet's surface, such as glacier distribution, and in its atmosphere, like the formation of hurricanes. Additionally, they can observe the sun, stars, and distant galaxies without the atmospheric distortion that typically affects telescopic observations on Earth.

For more information on specific projects and experiments, you can visit NASA's Space Station Experiments website. Now, let's explore the future of the ISS.

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 2030. And major changes are already in motion. NASA announced in July 2019 it would open the ISS to commercial and private companies, as well as private astronauts on U.S. spacecraft, in keeping with Reagan's original plan. And April 8, 2022, that vision was realized when SpaceX and Axiom Space sent four citizens on the first all-commercial mission. Dubbed AX-1, the four-man crew is commanded by Michael López-Alegría, a former NASA astronaut. 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, former 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 discussions continue among participating nations about the future of their shared off-world laboratory, China has been advancing its own space station projects. The Tiangong-1 and Tiangong-2 prototypes, which completed their missions in Earth's orbit in 2018 and 2019, respectively, laid the foundation for an even more ambitious endeavor: a larger space station, similar to the ISS, consisting of three modules. The Chinese government plans to complete this new station in the early to mid-2020s [source: Jones].

Regardless of the future of the International Space Station, it remains a remarkable achievement in space engineering — and, as of now, holds the record for the longest manned space mission in history.