In 2009, following a series of space shuttle missions to complete major portions of the International Space Station, the crew size aboard the orbiting laboratory expanded to six. The number of crew members aboard the station has, more or less, remained steady since then, with Russia providing half the crew while NASA and its international partners provide another three astronauts.

But, in a surprise announcement, Russia is considering scaling back its crew complement from three to two. According to Russian media reports, Sergei Krikalev, the director of human programs for Roscosmos, said the move was made to lower Russia's ongoing costs to service the station. By reducing the number of its crew members, Russia will need to fly fewer Progress cargo ships, which deliver food and supplies to the Russian side of the station.

Roscosmos already spends considerably less on station operations than NASA does. Russian media report that Roscosmos plans to spend about $4.1 billion from 2016 through 2025 for station maintenance. That's just a little more than NASA's annual expenses for station operation and transportation, which were $3.7 billion in fiscal year 2016.

In a statement on Monday, NASA confirmed that Russia is considering dropping back to two crew members. However, the agency did not provide any additional information.

According to NASA:

Any questions about the near-term Russian Space budget or Russian ISS expedition size should be directed to the Roscosmos press office. Roscosmos has joined NASA and other International Space Station partners in extending support for the orbiting laboratory to at least 2024, and the current level of research of both NASA and the international partners on ISS is at an all-time high.

Future crew sizes

The Russian decision raises questions about future space station crew sizes and the lifetime of the space station. In regard to crew size, NASA is discussing how to handle its own crew complement on the US side of the station—the US Orbital Segment—should Russia scale back. At present NASA has three slots, generally filled by two of the agency's astronauts and one crew member from the European Space Agency, Canada, or Japan. Several scenarios are being considered, but Ars has learned that the most likely option is keeping the NASA complement the same, which would reduce the overall crew size aboard the station to five.

In some sense, that would represent a step backward to a time before May 29, 2009, when Roman Romanenko, Frank de Winne, and Bob Thirsk arrived on the station, expanding the crew size to six, which also marked the first time all of the ISS partners were represented on board. Before that, dating back to October 2000, three crew members were aboard the station. The only exception was a brief period after the Columbia accident when NASA had to fall back to a “caretaker” mode of two crew members, due to the grounding of the shuttle.

The other big question is what this potential move might signal about Russia’s future commitment to the station. Although NASA and its partners have signed agreements to continue flying and supporting the station until 2024, the US space agency has talked openly about the possibility of flying it until 2028, or possibly even beyond then. Russia, however, has made noises about breaking with the international partnership no later than 2024, if not earlier, and building its own orbiting station.

NASA’s pursuit of its commercial crew program—promoted as “Launch America”—further complicates matters. NASA currently relies on Russia for crew transport to the space station. When Boeing and SpaceX begin flying crew vehicles in a couple of years, Russia will lose the half a billion dollars the US agency currently pays Roscosmos annually for Soyuz seats. This fiscal pressure may also be adding to Russia’s desire to scale back its investment in the station.

In any case, the multi-decade space station program that has bound US and Russian interests in space, coming after the Cold War and 1960s space race, has been one of the great diplomatic achievements of recent decades. Even as US-Russia tensions escalated following the Ukraine crisis, the two partners have worked well together in space. It would be disappointing to see that partnership unravel in less than a decade.