The flags of the countries representing the crew members of Soyuz TMA-12M are seen at the Russian Mission Control Center in Korolev, Russia, March 28, 2014.

The escalating tensions between the U.S. and Russia over Ukraine have reached a new altitude: space.

In the aftermath of the Cold War, the two super powers set aside their mistrust and agreed to build a massive orbiting outpost as a symbol of a new era of cooperation in space exploration. But now that partnership is under serious strain.

After Russian Deputy Prime Minister Dmitry Rogozin this week said his nation might no longer allow U.S. astronauts access to its launch vehicles and may use the International Space Station without American participation, the House Science, Space and Technology Committee on Thursday pressed NASA for answers about the how the U.S. could respond.

Since the retirement of the space shuttle, Russia has provided launches for U.S. astronauts, for $71 million each.

“Dropping out of ISS is a high-profile move on Russia’s part,” said Marco A. Caceres, space analyst for the aerospace research firm Teal Group Corp. of Fairfax, Va. “They’re pulling the rug out from under the Americans. It’s a move of national pride that plays well in Russia.”

Indeed, after railing against U.S. sanctions in response to Russia’s annexation of Crimea, Rogozin, chief of the Russian space and defense sectors, suggested that “the U.S.A. ... bring their astronauts to the International Space Station using a trampoline.”

Rogozin’s threat is too significant for the U.S. to ignore, said Loren B. Thompson, an aerospace and defense expert at the Lexington Institute, a Washington-based think tank.

“The central assumptions of the Obama administration space policy are no longer valid,” he said.

The space station is just one example of how the mess in Ukraine is undermining aerospace trade between the two leaders in space travel. Russia has threatened to suspend exports of rocket engines, which are used to help launch U.S. Air Force satellites. And it has threatened to suspend cooperation on navigational systems that depend on outposts in Russia.

The U.S. helped fund the Russian program in the aftermath of the collapse of the Soviet Union. And when the shuttle Columbia burned up on re-entry in 2003, killing seven, the Russians agreed to help ferry U.S. astronauts back and forth to space.

The $100-billion orbital outpost, often cited as the most expensive machine ever built, has a series of modules and power systems, some Russian, some American and others from a range of international partners. The U.S. hardware produces most of the station’s electricity, but the Russian propulsion system helps keep the station in orbit.

Now, that combination of hardware could cause a major headache. Under legal agreements, the U.S. has an upper hand in controlling the space station, but Rogozin said his nation could operate its modules independently of the U.S.

In a House hearing at the end of March, NASA Administrator Charles Bolden said the agency’s partner is not Russia itself, but rather the Russian space agency, a distinction that many analysts dismissed.

The House science committee sent a letter to Bolden on Thursday seeking an assessment of a Russian withdrawal from the space station program after 2020. While the partnership is not yet broken, the committee wants to know what options the U.S. has if Rogozin’s threats become reality.

The issue involves broad engineering and legal issues that may be new: Could the space station be separated into two parts? Who owns key systems? What would happen to life science research and how would such a breakdown in cooperation affect political support for human space flight?

When the U.S. and Russia agreed to build the station in 1993, neither country had the political will to build such an ambitious project by itself. For years the space station has been considered a symbol of how cooperation among nations may yield bigger results than any single effort.

But that was then.

“This is a step back toward the Cold War days,” Caceres said of the current climate. “It’s the beginning of a freeze on a great relationship that’s been forged over the last two decades.”

NASA ultimately wants private companies to take astronauts to the station by 2017, but that hardware is still in development.

Officials with NASA said they did not yet have a response to the committee’s letter but issued a statement, which said in part:

“NASA has not received any official notification from the government of Russia on any cessation or changes in our space cooperation at this point. Operations on the ISS continue on a normal basis with the safe return of the Expedition 39 crew May 13 and the expected launch of another crew in two weeks.”

Separately, Rogozin has said Russia intends to stop supplying the U.S. with rocket engines that are used in launching military satellites into orbit.

United Launch Alliance, a joint rocket venture of aerospace giants Boeing Co. and Lockheed Martin Corp., uses a Russian-made engine on its Atlas V rocket.

The RD-180 engine provides the main thrust for the rocket, which launches the government’s pricey, school-bus-sized national security satellites for spying, weather forecasting, communications and other, experimental purposes.

In the wake of Russia’s seizure of Crimea, the Pentagon asked the Air Force to review United Launch Alliance’s use of the engine.

United Launch Alliance said it was not aware of any restrictions. But even if an embargo on selling the engines takes effect, the company says it has stockpiled a two-year supply. It also has another family of rockets, called Delta IV, which uses all U.S.-made rocket engines.

“We are hopeful that our two nations will engage in productive conversations over the coming months that will resolve the matter quickly,” Jessica Rye, a company spokeswoman, said.