American spy satellites and classified military spacecraft are routinely launched into orbit with help from Russian rocket engines developed in the Soviet era. That is no secret to anyone in the world of national security space launches.

The big question is whether this intimate technological relationship can continue given the political fallout from Russia’s actions in Ukraine. Already, a top Kremlin official has threatened to ban the export to the United States of powerful RD-180 engines unless Russia is guaranteed that they won’t be used by the U.S. military.

U.S. military officials and space-industry experts say it’s high time the United States had an industrial base that produced rocket engines that can do what the Russian engines do. Congress is in the process of authorizing money for such an effort. In theory, it’s a no-brainer: Why rely on Russians for such an integral ­element of the U.S. national security program?

But everything is highly inertial in the world of rocket science. The creation of powerful rocket engines in the United States could take several years at least. If the supply of Russian engines were cut off in the meantime, the U.S. launch program would face delays, with attendant costs to taxpayers of billions of dollars, according to a recent U.S. Air Force study.

The United States is planning 38 launches of the Atlas V, the main stage of which uses the Russian-made, liquid-fueled RD-180 engine, but it has only 16 of those RD-180s in the stockpile, the study said.

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Another complication is that the United States and Russia have enjoyed doing space-related business with each other for a number of years. The Russians like the hard currency coming into their country, and American aerospace companies like the reliable, robust Russian hardware.

Although the central planners of the Soviet Union struggled to create simple consumer goods, they excelled at ordering up large things like military weaponry and rocket engines. After the collapse of the Soviet Union, U.S. policy encouraged government agencies and aerospace companies to snap up Russian hardware and keep the Russian engineers busy, lest they find employment in countries hostile to U.S. interests.

Long-term U.S. plans to produce a domestic cousin to the RD-180 never got off the ground. The aerospace sector discovered that it was comfortable with the workhorse Russian engines when it came time to launch sensitive missions such as spy satellites. The Atlas V rocket has made more than 50 consecutive successful launches using the RD-180. NASA and other government agencies rely on the Atlas V for some of their scientific payloads.

“The former Soviet Union invested in technology. Our country has not invested in that technology for now going on 30 years,” said Mike Gass, chief executive of United Launch Alliance, the ­50-50 partnership of Lockheed Martin and Boeing that owns the Atlas V and Delta IV rockets and has a virtual monopoly on national security launches.

“One thing about the Russians: It may not be the most elegant and subtle design, but man, the thing works. It’s a tank,” said another executive in the U.S. launch industry, who spoke on the condition of anonymity because of the delicate nature of the issue.

The United States and Russia continue to cooperate in operating the international space station with their other partners. But on May 13, Russian Deputy Prime Minister Dmitry Rogozin, who is in charge of the country’s space sector, said at a media briefing that his country would no longer sell rocket engines to the United States for military purposes. On his Twitter account he made a reference to the U.S. reliance on Russian rockets to send astronauts to and from the international space station, saying the United States should consider using a trampoline.

The Air Force and the White House have both signaled that they have heard nothing official from the Russian government about a blockade on engine sales. It’s possible, experts say, that Rogozin’s angry comments were simply political bluster and did not indicate a new Russian policy.

“I think this is a time to pause and find out if that is an official position,” Gen. William Shelton, head of the Air Force Space Command, told reporters recently in Colorado Springs at the 30th Space Symposium. “Industry to industry, I think there are some indications that business as usual is what we’re talking about.”

Not happy with business as usual are certain members of Congress — including Sen. John McCain (R-Ariz.), who is pushing for bans on new purchases of Russian engines to go along with a boost in domestic engine production.

Meanwhile, Elon Musk, head of the start-up space company SpaceX, has been intensifying his efforts to capture a chunk of the national security launch business and is also competing to win NASA’s upcoming contract to send astronauts to the space station. Musk has pointedly cited the reliance of his competitors on Russian engines; SpaceX uses American-made hardware.

SpaceX recently sued the Air Force to reopen the bidding on a 36-launch contract already awarded to United Launch Alliance. This battle between what is informally known as “New Space” (SpaceX) and “Old Space” (ULA) is moving through the courts.

SpaceX President Gwynne Shotwell said last month that the launch industry’s long-standing reliance on Russian engines is a “terrible strategy.”

But Gass, the ULA chief, said that his company had long planned for a potential disruption in the supply of Russian hardware and that one option is to rely more heavily on Delta IV rockets, which do not use the Russian engines.

“We’re looking at all kinds of alternative engines,” Gass said. “This country should be investing in propulsion technology.”