CÓMO FUNCIONA LA ISS

A self-sufficient city 400 km up

The International Space Station isn't a single spacecraft: it's a set of more than fifteen pressurized modules, built by different countries and assembled in orbit over more than a decade, that together form a laboratory and permanent home roughly the size of a football field. Everything the crew needs to breathe, drink, eat, work, and communicate with Earth is generated, recycled, or shipped inside that structure, with no outside help besides periodic cargo deliveries.

The modules that make it up

The station combines two major segments, one Russian and one led by the United States, physically joined but with independent life-support systems for safety. Among the most notable modules:

• Zarya (1998): the first module launched, of Russian origin, which provided the initial power and propulsion before anything else was in orbit.
• Zvezda (2000): the Russian service module, housing the main life-support system and the crew's first sleeping quarters.
• Destiny (2001): the US science lab, dedicated to physics, biology, and materials-science experiments.
• Columbus (2008): the European Space Agency's (ESA) laboratory.
• Kibo (2008-2009): the Japanese module (JAXA), the largest on the station, with its own external platform for experiments exposed to the vacuum of space.
• Cupola (2010): the seven-windowed observation dome, used for research, operating the robotic arm, and enjoying the view.

How it generates electricity

Power comes exclusively from the Sun: eight solar array wings, with a combined surface area of about 2,500 m², generate up to 120 kilowatts when fully lit. Since the ISS passes through Earth's shadow every orbit (about 16 times a day, for roughly 35 minutes each time), that surplus daytime energy is stored in lithium-ion batteries that keep systems running through the dark stretches. Those batteries replaced the older nickel-hydrogen batteries installed in the 2000s, swapped out via a series of spacewalks between 2017 and 2019.

How it produces air and recycles water

The life-support system, known as ECLSS (Environmental Control and Life Support System), generates oxygen through electrolysis: it splits water into hydrogen and oxygen using electricity from the solar panels. Carbon dioxide exhaled by the crew is captured and either vented or partly converted back into water. The water recovery system recycles roughly 90-98% of the station's water, including humidity from breathed air, sweat, and yes, urine, after a distillation and filtering process that makes it drinkable. Without this recycling, each crew member would need several tons of water shipped from Earth every year.

How it stays in orbit

At 400 km up there's still a very thin layer of atmosphere that slightly drags on the station, causing it to lose altitude little by little. To compensate, the ISS needs periodic "reboost" maneuvers, usually using the engines of docked Russian Progress cargo ships, though it can also use its own thrusters. Without these regular adjustments, the orbit would decay and the station would re-enter the atmosphere within a matter of years.

How it communicates with Earth

Most communications (voice, video, science data, and the live video feed you can watch on our live page) pass through NASA's TDRS (Tracking and Data Relay Satellite System) network, in geostationary orbit far higher than the ISS. This network keeps the station in near-constant contact, aside from brief gaps when the geometry between the station and relay satellites isn't favorable.

Quick questions

How long does it take to build a station like this?

Assembling the ISS took over a decade, from Zarya's launch in 1998 until its main configuration was completed around 2011, across more than 40 separate assembly missions.

Could the oxygen supply fail?

The system has multiple layers of redundancy: besides the main electrolysis generator, the station keeps reserves of compressed oxygen and backup chemical generators (lithium perchlorate candles) for emergencies.

Who pays for the ISS's upkeep?

The cost is shared among the five partner space agencies (NASA, Roscosmos, ESA, JAXA, and CSA) under international agreements that also determine which modules each one contributes and maintains.