As the race to the moon receded, American and Soviet astronauts met and shook hands in space for the first time in 1975. The United States and Russia continued to work together in outer space, looking beyond their hostilities on Earth, culminating in the 1990s with the two nations jointly building and operating a laboratory in space.
The future of that cooperation grew uncertain on Tuesday as the new head of Russia’s space agency announced that Russia would leave the International Space Station after its current commitment expired at the end of 2024.
“The decision to leave the station after 2024 has been made,” said Yuri Borisov, who was appointed this month to run Roscosmos, a state-controlled corporation in charge of the country’s space program.
Mr. Putin’s response: “Good.”
With tensions between Washington and Moscow rising after Russia’s invasion of Ukraine in February, Russian space officials including Dmitry Rogozin, Mr. Borisov’s predecessor, had made declarations in recent months that Russia was planning to leave. But they all left ambiguity about when it would happen or whether a final decision had been made.
If Russia follows through, it could accelerate the end of a project that NASA has spent about $100 billion on over the last quarter-century and set off a scrambling over what to do next. The space station, a partnership with Russia that also involves Canada, Europe and Japan, is key to studying the effects of weightlessness and radiation on human health — research that is still unfinished but needed before astronauts embark on longer voyages to Mars. It has also turned into a proving ground for commercial use of space, including visits by wealthy private citizens and the manufacturing of high-purity optical fibers.
NASA did not respond to a request for comment. An official at the White House said the United States had not received any formal notification from Russia that it would withdraw from the space station, although officials have seen the public comments.
“We are exploring options to mitigate any potential impacts on the I.S.S. beyond 2024 if in fact Russia withdraws,” said John Kirby, a spokesman for the National Security Council.
Ned Price, the State Department spokesman, said during a briefing on Tuesday that “I understand that we were taken by surprise by the public statement that went out,” and added that Russia’s announcement was “an unfortunate development.”
NASA has said that it intends to continue operating the space station through the end of 2030. The “after” in “after 2024” in Mr. Borisov’s words provides wiggle room for Russia to extend its participation beyond its current commitment.
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“This could be bluster from the Russians,” said Phil Larson, a White House space adviser during the Obama administration. “It could be revisited, or it could come to fruition.”
But experts say the announcement clouds the prospect of keeping the station going through the end of the decade.
“The withdrawal will take some time,” said Pavel Luzin, a Russian military and space analyst. “Most likely, we need to interpret this as Russia’s refusal to extend the station’s operation up until 2030.”
Speaking from orbit to a conference about the space station’s research, Kjell Lindgren, one of the NASA astronauts on the I.S.S., said nothing had changed up there, yet.
“That is very recent news,” he said, “and so we haven’t heard anything officially. Of course, you know, we were trained to do a mission up here, and that mission is one that requires the whole crew.”
For nearly half of a century, beginning with a meeting of American and Soviet astronauts in orbit in 1975 during the Apollo-Soyuz mission, cooperation in space has been seen as a way to build positive relations between the two countries, even when diplomatic tensions remained. The decades of space collaboration have weathered numerous ups and downs in relations between the United States and Russia.
From 1995 to 1998, NASA’s space shuttles docked at Russia’s Mir space station, and American astronauts lived on Mir.
In 1994, President Bill Clinton recast efforts to build Freedom, a space station proposed by President Ronald Reagan a decade earlier, as the International Space Station, and Russia was added as one of the main participants.
The decision was a symbol of post-Cold War cooperation between the world’s two space superpowers, which competed to launch rockets and astronauts to orbit during tense stages of their global competition and later engaged in the moon race that led to the Apollo landings of the 1960s and 1970s. But American policymakers in the 1990s also made a cold calculation that building the space station would provide work for Russian rocket engineers who might otherwise have sold their considerable expertise to countries that were seeking to build missiles, like North Korea.
The station’s first module was launched in 1998, and astronauts have lived there since 2000. Russian and American crewmates flew together in Soyuz capsules and the space shuttles for journeys to orbit from the Baikonur Cosmodrome and the Kennedy Space Center. They shared meals and holidays, collaborated on the repair and maintenance of the station and discussed the politics roiling their nations on the surface.
NASA officials, who want to extend operations of the space station through 2030, have expressed confidence that Russia will remain, despite recent shifts in the broader political relationship.
However, this month, NASA strongly criticized Russia after Roscosmos distributed photographs of the three Russian astronauts on the space station holding the flags of Russian backed separatists in two provinces of Ukraine.
How long the station could operate without Russia’s involvement is uncertain. The outpost in orbit consists of two sections, one led by NASA, the other by Russia. The two are interconnected. Much of the power on the Russian side comes from NASA’s solar panels, while the Russians provide propulsion to periodically raise the orbit.
It is conceivable that Russia might be willing to sell its half of the station to NASA or a private company. NASA is also looking at whether American spacecraft could take over some of the tasks of raising the orbit of the space station. But because of the location of NASA’s docking ports, the American vehicles would be less well-suited for adjusting the orientation of the space station.
Russia has plans for its own space station, but Roscosmos has been lacked the money to do so for years. After the retirement of the U.S. space shuttles in 2011, NASA had to buy seats on the Soyuz rockets, providing a steady stream of money to the Russians. That revenue dried up after SpaceX started providing transportation for NASA astronauts two years ago. Russia lost additional sources of revenue as a result of economic sanctions that prevented European and other nations’ companies from launching satellites on its rockets.
“Without cooperation with the West, the Russian space program is impossible in all its parts, including the military one,” Dr. Luzin said.
Russia is also looking to cooperate more with China’s space program, which launched a laboratory module on Sunday to add to its space station, Tiangong. But Tiangong is not in an orbit that can be reached from Russia’s launchpads, and many of the discussions between the two countries have focused on cooperating on lunar exploration.
“The prospect of cooperating with China is a fiction,” Dr. Luzin said. “The Chinese have looked at Russia as a prospective partner up until 2012 and have stopped since then. Today, Russia cannot offer anything to China in terms of space.”
Not too long ago, it was the United States that wanted to end the International Space Station after 2024.
In 2018, the Trump administration proposed ending federal financing for the space station, hoping to move its astronauts to commercial stations. That initiative petered out a year later, when NASA shifted its attention to accelerating plans to send astronauts back to the moon.
NASA is still trying to jump-start a market for future commercial space stations. In December, it awarded contracts worth a total of $415.6 million to three companies — Blue Origin of Kent, Wash.; Nanoracks of Houston; and Northrop Grumman of Dulles, Va. — to develop their designs.
Paul Martin, the inspector general for NASA, however, has warned that even if the International Space Station continues through 2030, commercial follow-ups might not be ready in time, and there could be a gap where NASA has no orbiting laboratory to conduct research, especially on the long-term health effects of zero gravity and radiation on astronauts.
If Russia’s decision leads to abandonment of the I.S.S., then China might possess the only space station in orbit. China has offered to fly astronauts from other nations to Tiangong. Astronauts from the European Space Agency have already trained with Chinese astronauts. In general, NASA is prohibited from working directly with China.
The new turmoil could also highlight another unsolved issue: how to safely dispose of something that is the size of a football field and weighs close to a million pounds. In a report released in January, NASA discussed a plan to push the station into the atmosphere so that anything that survived re-entry would splash into the Pacific Ocean. The detailed logistics are yet to be worked out.
Peter Baker and Michael Crowley contributed reporting from Washington.