Orbiting Earth for over two decades—with its oldest modules launched more than 20 years ago—the International Space Station (ISS) is aging. Astronauts will soon depart, but what becomes of this engineering marvel?
On November 2, 2000, NASA astronaut Bill Shepherd and Russian cosmonauts Yuri Gidzenko and Sergei Krikalev became the first crew to dock with the ISS. Born from post-Cold War collaboration, the station has hosted continuous human presence ever since. To date, 244 individuals from 19 countries have lived aboard, some multiple times, supporting more than 3,000 scientific investigations involving 108 nations.
Like any complex machine, the ISS requires ongoing maintenance, and crewed missions are costly. NASA alone invests about $4 billion annually. To fund ambitions beyond low Earth orbit, such as lunar and Mars missions, the agency must shift priorities. NASA plans to retire the ISS around 2030, but its structure cannot remain in orbit indefinitely.
At 400 km altitude, the ISS balances Earth's gravity against its orbital speed of 7.66 km/s. Trace atmospheric molecules cause drag, gradually slowing it. Periodic reboosts by visiting spacecraft keep it stable, with operations funded through at least 2024. NASA confirms the station can fly until 2028 or beyond if needed—but retirement looms.
From its assembly via 42 launches—including 37 by U.S. space shuttles—planners anticipated a controlled deorbit, with shuttles guiding reentry. But shuttles retired in 2011, prompting new strategies.
NASA is developing alternatives, though details remain preliminary. A 2017 NASA-Roscosmos study outlined a leading option: using Russian Progress cargo vehicles, which routinely dock and reboost the ISS with fuel transfers.
For deorbit, Progress craft would reverse this process, firing thrusters to lower the orbit predictably. This targets reentry over the Pacific Ocean's remote Point Nemo, minimizing risks.
The task is daunting. At 400 tons and nearly the length of a football field, much of the ISS may survive reentry. This echoes the 2001 deorbit of Russia's Mir station—but the ISS is three times heavier, amplifying challenges.
China's Tiangong ("Heavenly Palace") station is set to replace the ISS, launching core modules around 2023. Weighing nearly 100 tons across three modules, it will operate in low Earth orbit for at least 15 years. Taikonauts will conduct experiments and train for deep-space missions, with access open to all UN member states.
