A space station is a large spacecraft designed to remain in orbit for months or years, providing a pressurized environment where crews can live and work in space. Unlike capsules or shuttles built for short trips, space stations serve as permanent outposts, equipped with life support systems, laboratories, and living quarters that allow people to stay in orbit for extended missions. The International Space Station, the largest ever built, stretches 356 feet end to end and orbits Earth at five miles per second with a crew of seven.
What Keeps a Space Station Running
Surviving in orbit means recreating everything Earth’s atmosphere and surface provide for free. A space station has to generate breathable air, supply drinkable water, regulate temperature, produce electricity, and remove waste, all inside a sealed structure hurtling through a vacuum where temperatures swing hundreds of degrees between sunlight and shadow.
Oxygen comes from splitting water molecules apart using electricity. The process yields oxygen for the cabin and hydrogen as a byproduct. That hydrogen gets fed into a reactor along with the carbon dioxide the crew exhales, producing water that goes right back into the system. It’s a loop: water becomes oxygen, the leftover hydrogen recaptures exhaled carbon dioxide, and the reaction yields water again. Trace contaminants from electronics, plastics, and human bodies are scrubbed from the air using charcoal beds and chemical filters.
Water recycling is equally aggressive. The station collects sweat, condensation from the air, and even urine, then purifies it all back into drinking water. Fresh supplies still arrive periodically from Earth, but the recycling systems dramatically reduce how much needs to be shipped up.
The ISS runs on eight large solar arrays capable of generating 84 to 120 kilowatts of electricity, enough to power more than 40 average homes. When the station passes into Earth’s shadow (which happens every 90-minute orbit), onboard batteries take over. About 60 percent of the power generated during sunlit periods goes toward charging those batteries.
Temperature control uses a combination of heaters, insulation, and loops of liquid ammonia that absorb excess heat from equipment and crew activity, then carry it to external radiators that release it into space.
How the ISS Is Structured
The International Space Station is a collection of pressurized modules connected by airlocks and docking ports. Modules like Destiny (a U.S. laboratory), Columbus (a European lab), and Zvezda (a Russian service module) each serve distinct purposes, from scientific research to crew sleeping quarters to engine control. The pressurized section where people actually live and work runs about 218 feet along its main axis. A 310-foot truss extends across the station’s exterior, holding the solar arrays and radiators. The whole structure weighs roughly 925,335 pounds.
Docking ports allow cargo ships and crew vehicles to attach to the station, delivering supplies and rotating personnel. The Russian Zvezda module houses engines that periodically boost the station’s altitude, since atmospheric drag slowly pulls it lower. Spinning gyroscopes help maintain the station’s orientation so its solar panels stay pointed at the sun and its antennas stay locked on communication satellites 22,000 miles above Earth.
Why Build a Lab in Orbit
The primary scientific value of a space station is microgravity. On Earth, gravity drives convection, sedimentation, and buoyancy, forces that interfere with many physical and biological processes. Remove gravity and diffusion becomes the dominant force in mixing, producing more uniform structures at the molecular level. This has practical applications across materials science, medicine, and manufacturing.
Protein crystals, for example, grow larger and more perfectly structured in microgravity, making it easier to study their shapes and develop targeted drugs. Researchers have used the ISS to test manufacturing a protein with potential applications for treating retinal blindness. Metal alloys, fiber optics, and advanced ceramics can also be produced with fewer defects when gravity isn’t pulling heavier components to the bottom of a mixture. Surface tension becomes more predictable without gravity interfering, allowing more precise layering of materials.
Beyond materials, the station serves as a testbed for understanding what long-duration spaceflight does to the human body, research that’s essential before sending crews to Mars.
What Living in Space Does to the Body
Without the constant pull of gravity, bones and muscles deteriorate quickly. Weight-bearing bones lose roughly 1% of their density for every month spent in space if astronauts don’t actively fight it. That rate is comparable to what someone with osteoporosis might experience over a full year on Earth.
To counteract this, crews exercise an average of two hours every day using specialized equipment: a treadmill with harnesses that pull them toward the belt, a resistance machine that simulates weightlifting, and a stationary bike. Even with this regimen, some bone and muscle loss still occurs, though it’s significantly reduced compared to early space missions when exercise protocols were less rigorous.
Space Stations Past and Present
The concept dates back to the early 1970s. The Soviet Union launched Salyut 1 in 1971, making it the first space station to reach orbit. The U.S. followed with Skylab in 1973, which hosted three crews before being abandoned in early 1974. The Soviets continued iterating through a series of Salyut stations, with Salyut 6 (launched in 1977) introducing a second docking port that allowed supply ships to visit while a crew was aboard. Salyut 7 launched in 1982.
The Soviet Mir station, which reached orbit in 1986, represented a major leap. It was the first modular station, built by launching a core and then attaching additional modules over time. Mir operated for 15 years and hosted international crews, proving that humans could live in space for many months at a stretch.
Today, two space stations are permanently crewed. The ISS, a collaboration among the U.S., Russia, Europe, Japan, and Canada, has been continuously occupied since November 2000. China’s Tiangong station (the name translates to “Sky Palace”) was completed in late 2022. It consists of three modules: the Tianhe core module at the center, flanked by the Wentian and Mengtian science modules. A separate space telescope module called Xuntian is planned to fly in a nearby orbit. Tiangong represents the final step in China’s crewed space program and operates independently of the ISS partnership.
What Comes After the ISS
NASA plans to operate the ISS through 2030, then decommission it. The process involves gradually lowering its orbit through natural atmospheric drag and intentional thruster burns, then executing a final large re-entry maneuver to guide the debris into an uninhabited stretch of ocean. A purpose-built U.S. Deorbit Vehicle will handle that final push. All crew will return to Earth before the re-entry burn.
The transition plan calls for commercially owned and operated stations to take over in low Earth orbit. Several private companies are developing modules and platforms intended to host both government-funded research and commercial manufacturing in microgravity.
Further out, NASA’s Gateway station will orbit the Moon rather than Earth. Planned for launch no earlier than 2027, its first habitable module will support lunar surface missions under the Artemis program and serve as a staging point for eventual crewed missions to Mars. Gateway will be much smaller than the ISS, designed for shorter stays rather than permanent occupation, but it extends the space station concept to deep space for the first time.