Responding to US and European sanctions over the crisis in Ukraine, Russia says it would consider ending its cooperation on the International Space Station. But its options are limited, say experts.

The safe landing in Kazakhstan Wednesday of a Russian Soyuz capsule returning three astronauts from the International Space Station suggests that for all the thunder and fury coming from Moscow about the future of the station, operations are continuing on a business-as-usual basis, at least for now.

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On Tuesday, Russian Deputy Prime Minister Dmitri Rogozin announced that the country would consider ending its participation in the space-station program in 2020; would prohibit the US military's use of a rocket motor that powers the Atlas V, one of two launch workhorses for defense and intelligence satellites; and would close down global-positioning-satellite monitoring stations in Russia unless it was allowed to build comparable monitoring stations in the US for its navigation satellites.

All of these threatened steps are in response to sanctions the US and Europe have imposed on influential Russians including Mr. Rogozin over Russia's annexation of Crimea and its efforts to destabilize eastern Ukraine.

Tuesday's announcement represents a shot across the bow for the US space program, says Roger Handberg, a political scientist at the University of Central Florida in Orlando who specializes in space and defense policy.

But, if no further actions or statements come out of Moscow "indicating that this is going to get pushed seriously, then I think we'll just go on as we are," he says.

NASA has no other choice, he says, and in some ways, neither do the Russians.

In January, the US agreed to extend its participation in the space station program to 2024 instead of 2020, an extension that US partners sought after studies showed that the modules, especially the most recent additions from Europe and Japan, would be capable of lasting at least until 2024, and likely well beyond. The moves Rogozin threatened regarding the space station would affect all of the major partners and put Moscow in the unexpected position of being tarred as an unreliable partner for spaceflight activities.

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International Space Station: How serious are Russias threats?