KOUROU, French Guiana – A new round of U.S. and European sanctions leveled at Russia’s rising aggression against Ukraine could slow a key decision this year on Moscow’s participation in the International Space Station (ISS) beyond 2020.

For now, mounting political tensions are "more or less" not affecting day-to-day operations aboard the orbiting outpost, says Alexey Krasnov, head of human spaceflight at Russian space agency Roscosmos. Speaking to reporters here on the eve of the Europe’s fifth and final Automated Transfer Vehicle (ATV-5) launch to the ISS, Krasnov said personnel at NASA are doing "everything they can to make sure politics do not affect our ability to work together."

However, with Moscow set to approve a new space road map this year for the period 2016-2025, Roscosmos needs to know now whether to budget for ISS hardware purchases that could keep the Russian elements of the space station functioning beyond 2020. Given rising political tensions over the escalating conflict in eastern Ukraine, Krasnov says it is unclear whether Moscow will approve Russia’s continued role in the ISS any time soon.

"We were told there would be support for the 2024 date, but our arguments were generated before April," when U.S. sanctions against Russian individuals and entities were put into force, he says.

Led by NASA, the ISS remains the largest international technology undertaking in history, one in which the U.S., Russia, Europe, Canada and Japan expect to have invested more than $100 billion by the end of the decade. As the lead ISS nation, the U.S. announced plans earlier this year to continue space station operations four years beyond a previously planned retirement in 2020.

However, Russia and Europe have not agreed to continue participating in the program after that date. With the threat of additional sanctions looming, the space station’s future appears increasingly murky.

William Gerstenmaier, NASA’s head of human spaceflight and operations, is confident Russia will stick with the ISS through 2024, though the current geopolitical climate suggests they may be reluctant to unveil such plans.

"Where before I was thinking Russia probably would step up first, that may not be the case now, and we have to be prepared for that," Gerstenmaier told reporters here July 29. "But if the U.S. can stay strong and we can still articulate why it makes sense to extend, then I think that also lets all the other partners think about this process and move forward."

Gerstenmaier said even if Russia does not plan for ISS extension this year, benefits of continued participation remain, should Moscow reach a decision within the next couple of years.

"There’s an opportunity lost by not knowing the station is going to be extended fully," Gerstenmaier said. "Having a 10-year research horizon is pretty important to them. Now, what this has done is put some uncertainty as to whether this 10-year horizon is going to happen. I think it will, but if it gets delayed two years, the benefit isn’t as real."

In the meantime, tonight’s final ATV mission will leave Moscow responsible for key aspects of the orbiting outpost. Slated to lift off this evening at 8:47 p.m. local time, the retirement of ATV makes Russia’s Progress transport vehicles the sole means of propulsive support to the ISS, including the ability to refuel the Russian Zvezda module, reboost the space station’s degrading altitude and occasionally maneuver it from the path of space debris.

Space station partners already rely on Russia’s Soyuz vehicle as the only form of crew transport to and from the ISS. With the final ATV, Progress becomes the lone spacecraft capable of deorbiting the space station at the end of its mission life, a retirement that is expected to occur within a decade.

With no more ATVs to deliver fuel to the ISS, Russia will be charged with managing propulsive support to the station, as well as for its eventual deorbit, a controlled re-entry that will send the 450-metric-ton structure into the Pacific Ocean.

"We are working on different deorbit scenarios," he said, including emergency evacuation of the ISS. "Two or three Progress vehicles can do this," he says.

Gerstenmaier says the partners have ample time to determine how to retire the space station.

"I have a long time to do this," he said, adding that ISS nations are likewise prepared for an emergency evacuation of the station. "But you’re multiple failures away before you get there," he said.

While NASA is the lead partner on ISS, all five members share responsibility for deorbiting the space station on a pro-rata basis determined by each member’s percentage of hardware mass.

But with relations deteriorating among the governments of the space station’s top three partners, one of the primary goals of the ISS agreement – the potential to use the station as a springboard for cooperative space exploration – appears in doubt.

"This could affect our ability to explore together beyond low Earth orbit," Krasnov said, though Gerstenmaier says the multinational partnership could offer common ground on which governments can build trust.

"Even though it’s an uncertain time, that basis for exploration is still there," Gerstenmaier said. "When these crises occur between countries, it’s important to have something you can talk about that you mutually agree is supportable by all countries. And having the space station as this multilateral engineering achievement, that offers the politicians an avenue for communication."