Space: How does the ISS continue to function despite the weight of the years?

A steel giant that has been hurtling above our heads at 28,000 km/h for nearly a quarter of a century. Russia and the United States announced on Thursday, July 31, that they intend to jointly extend the operation of the International Space Station (ISS) until 2028. Until then, the ISS's future is safe. More than twenty-five years after its launch into orbit, the station has never stopped rotating. Still inhabited. Still operational, despite signs of fatigue and successive postponements of its decommissioning: a symbol of extraordinary space cooperation.

The ISS was launched in 1998, at a time when Russia and the United States were collaborating closely in space, despite geopolitical tensions on Earth. It was born from the merger of two competing projects: the Russian Mir-2 space station and the American Freedom. The first module launched into orbit, named Zarya (Russian for "dawn"), was followed a few weeks later by the American Unity module, which linked them.

Then, year after year, new modules were added, like so many Lego pieces: the American Destiny laboratory (2001), the European Columbus module (2008), the Japanese Kibo laboratory, and the Russian Zvezda segment. In total, around fifteen main modules were assembled in space, sometimes during missions requiring up to five extravehicular activities.

But aging in space is not without consequences. The materials are subjected to severe stress: extreme temperature variations (from -150 to +120°C between shadow and light), micrometeorite impacts, cosmic radiation, and the constant expansion and contraction of metal walls. Added to this is the wear and tear of seals, sealing systems, and welds. To remain habitable, the station therefore requires constant maintenance.

Supply cargo ships (Progress, Crew Dragon , Cygnus, etc.) regularly arrive to deliver food, water, spare parts, or fuel for the thrusters. But it is mainly the astronauts themselves who maintain the station. When a part breaks down, a solar panel needs replacing, or a cable deteriorates, they put on their pressurized suits and step out into the vacuum of space, attached to the station by a safety cable. These outings, called extravehicular activity , often last six to eight hours.

In January 2024, two NASA astronauts replaced an ammonia pump in the thermal control system, carefully handling tools specially designed to be handled with thick gloves in zero gravity. Each mission is meticulously planned, rehearsed on the ground in giant pools to mimic weightlessness, and coordinated in real time from Houston or Moscow.

Some repairs are more complex than others. For several years, an air leak has persisted in the Russian Zvezda module. It was located inside an airlock, at the level of a cracked metal coating. Several attempts to seal it have been made: first with adhesive tape designed to withstand high pressures, then with an epoxy coating (a type of resin) injected directly onto the crack. The internal pressure remains stable, but engineers acknowledge that the repair is only partial.

Despite the incidents, the station is holding firm. It is equipped with powerful robotic arms, such as Canadarm2, a 17-meter articulated arm capable of moving entire modules or catching cargo arriving in orbit. This arm is controlled remotely, from the station or from Earth, and can also serve as a mobile platform for astronauts during repairs. The European ERA arm, installed on the Russian Nauka module, allows similar operations in the Russian segment.

On the ground, hundreds of technicians and engineers monitor the station 24/7 from control centers in Houston and Moscow. Every onboard system—ventilation, pressure, oxygen levels, power generation, and orientation—is analyzed in real time. Even the slightest anomalies are detected in advance so that rapid intervention can be made. Sensors also measure the impact of micro-space debris or structural deformation. With this information, agencies can decide whether to adjust the station's altitude to avoid a collision or schedule repairs before a failure becomes critical.

But the countdown has begun. By 2030, the station is scheduled for a controlled deorbit . This means a thruster module will deliberately push it into the dense layers of the atmosphere, where it will largely disintegrate. The remaining debris will fall into an uninhabited area of the Pacific, nicknamed the "satellite graveyard" or Point Nemo . This maneuver is essential: without it, the station would sooner or later end up falling uncontrolled, with risks for inhabited areas.

In the meantime, NASA is banking on new private players, such as Axiom Space and Blue Origin , to build commercial space stations capable of taking over. Low Earth orbit could soon accommodate smaller, more modern, and more cost-effective modular laboratories.