WASHINGTON — United Launch Alliance has signed contracts to study potential replacements for the Russian-made RD-180 engine that powers the first stage of its Atlas 5 rocket, and hopes to select a single concept for development this year.

In a press release June 16, Denver-based ULA said it had signed contracts with multiple U.S. companies to study next-generation liquid-oxygen/hydrocarbon propulsion concepts.

Jessica Rye, a spokeswoman for ULA, declined to identify the study contractors, citing nondisclosure agreements. She declined to detail the number of contracts or their value, calling the information proprietary.

The selected companies will study the technical feasibility of engine concepts, and lay out schedules along with cost estimates and technical risks, the release said. ULA hopes to select a supplier by the fourth quarter of this year, with a first launch targeted for 2019, the release said.

“As the nation’s steward of the launch industrial base and the only company certified to launch our nation’s most critical missions, it is incumbent upon ULA to bring forward the best solutions to preserve that capability for the future,” Michael Gass, ULA president and chief executive, said in a statement. “While the RD-180 has been a remarkable success, we believe now is the right time for American investment in a domestic engine.”

Momentum for developing a large liquid-fueled rocket engine in the United States has been building rapidly in Congress and elsewhere since Russia’s annexation of Crimea and continued threat to the rest of eastern Ukraine. The RD-180-powered Atlas 5 is one of the Pentagon’s two main satellite-launching workhorses, but a top Russian government official has threatened to bar the use of Russian-made engines for launches of U.S. national security satellites.

The RD-180 is built by NPO Energomash of Russia and sold to ULA by RD-Amross, a joint venture between Energomash and United Technologies Corp. ULA currently has 15 of the engines in its inventory.

U.S. Air Force officials have begun taking steps to preserve the Atlas 5 for those missions that require its unique capabilities. The single-core version of the Atlas 5 is more powerful than that of the Delta 4, meaning it can handle some of the larger Defense Department satellites that otherwise would require the triple-core — and very expensive — Delta 4 Heavy.

A recent report by an expert panel said the consequences of losing access to the RD-180 would be significant and urged the Air Force to begin work on a U.S. alternative. “Regardless of RD-180 viability, U.S. needs to develop a domestic engine,” the report said.

A pair of defense bills in the House have proposed spending $220 million next year to develop a new liquid-fueled rocket engine that would debut in 2022. A bill in the Senate authorizes up to $100 million for that activity and says the engine should be ready by no later than 2019.

In the statement, George Sowers, ULA’s vice president of advanced programs, said the company had a “number of very promising alternatives” to choose from. Sowers, who was previously the chief systems engineer for the Atlas 5, will lead the activity.

“There are many exciting advanced technologies that are mature and can be used to enhance our capabilities and our competitiveness,” Sowers said.

ULA said it would continue to work with RD-Amross on the long-term viability of the RD-180 in competition with the new engine. ULA raised the possibily of funding a new engine either privately or through a public-private partnership.

The pool of likely U.S. engine suppliers to ULA is a small one. At the top of the list is Aerojet Rocketdyne of Sacramento, California, which is the dominant U.S. supplier of large liquid-fueled rocket engines. ULA has also worked with XCOR Aerospace on engine development.

Space Exploration Technologies Corp. builds liquid-fueled engines in house for its Falcon 9 rocket, but the company’s relations with ULA are highly antagonistic as the two square off for future Air Force business.

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Mike Gruss is a senior staff writer for SpaceNews. He joined the publication in January 2013 to cover military space. Previously, he worked as a reporter and columnist for The Virginian-Pilot in Norfolk, Va. and The Journal Gazette in Fort Wayne, Ind. He...