Russia, the U.S.' long-standing partner in space, is turning to China for its lunar ambitions.

Why it matters: The U.S. and Russia have been uneasy partners in orbit for decades, but as the two grow farther apart in space, their rift could reshape the geopolitical landscape above Earth — and on it — for years to come.

• "We're not going to see the same level of cooperation between the United States and Russia, compared to what we saw in the 1990s ... when Russia was broke, going through an economic catastrophe after the collapse of the Soviet bloc and was desperate," space policy expert Bleddyn Bowen told me.

Driving the news: Last week, China and Russia signed an agreement to work together to develop a lunar research station on or orbiting the Moon, allying Russia with a nation many see as in opposition to U.S. interests in space.

• The memorandum of understanding comes after Russia declined to sign NASA's Artemis Accords governing international cooperation and uses of the Moon, and after a Russian official criticized NASA's plans to build a small space station in lunar orbit.
• Russia was initially expected to provide an airlock for the small lunar space station, which is part of NASA's plans to land people on the Moon, but now "NASA will be pursuing other options for the provider of the airlock," NASA said in a statement.

The backstory: U.S.-Russia space relations began to sour in the early 2010s when Russia annexed Crimea.

• The two countries' space programs kept them talking via the International Space Station, but since then, Russia's public posture toward the U.S. on space issues changed, experts say.
• "We saw a marked change in how the Russians interacted in multilateral space forums," Brian Weeden of the Secure World Foundation told me. There was "a marked increase in the hostility of their language against pretty much anything the U.S. was proposing."

The intrigue: China's space program and industry is booming, with support from the government and a long-term vision of what the nation hopes to accomplish. Russia's star, on the other hand, is fading.

• Russia is losing a significant source of revenue as SpaceX flies astronauts to the space station, ending NASA's reliance on the Russian-made Soyuz rocket.
• This partnership with China will allow Russia to work with a nation on the rise when it comes to space, while China gets to take advantage of Russia's established technical acumen.

Just as important, if not more, the two powers together will wield geopolitical weight in forming international space policy.

• As Europe, Canada, Japan and others are already partnering with the U.S. on its Moon plans, this partnership between Russia and China could potentially pull in support from other nations, if the two nations decide they also want partners.

What to watch: It's not clear how high a priority the Russia-China lunar research station will have as China works to build its own space station orbiting Earth in the coming years.

• The division of labor for the two nations hasn't been laid out, and there isn't a clear funding source announced yet.
• And experts say that the door isn't necessarily closed for the U.S. and Russia to partner with one another in space in the future.