This story was updated May 15

WASHINGTON — A consortium of three companies including propulsion provider Aerojet Rocketdyne has asked the U.S. Department of Defense about the possibility of obtaining production rights to United Launch Alliance’s Atlas 5 rocket, a military workhorse that ULA has designated for replacement by the end of the decade.

In theory, the consortium would use the Aerojet-designed AR1 engine to replace the controversial Russian-made RD-180 engine used on the Atlas 5 today.

The consortium includes Dynetics, the Huntsville, Alabama-based engineering company, and Shafer Corp., the Arlington, Virginia-based science and engineering contractor led by former NASA Administrator Mike Griffin.

Griffin co-authored a high-profile study last year that recommended that the Air Force immediately embark on a crash program to replace the kerosene-fueled RD-180 with an American-made engine. The study was triggered by a sharp deterioration in U.S.-Russian relations following Russia’s annexation of Crimea from Ukraine in February 2014.

Denver-based ULA said in a May 11 email to SpaceNews that the company has “no intention of selling or transferring” Atlas 5 production rights, a move that presumably would create a new competitor in the national security launch market. But the Atlas 5 was developed in part with Air Force funding, raising the question of whether the government has a say in the matter.

Sacramento, California-based Aerojet Rocketdyne, traditionally the dominant U.S. supplier of liquid-fueled rocket engines, has been scrambling of late to maintain and expand its foothold in the U.S. national security launch business, which is undergoing a tectonic shift with the arrival of SpaceX to challenge ULA’s monopoly and a congressional directive to discontinue using the RD-180. Congress has allocated $220 million this year to develop a U.S. engine that would be ready to replace the RD-180 by around 2019.

Aerojet Rocketdyne’s answer is the AR1, which the company says could be relatively easily integrated with the Atlas 5. But ULA has opted to go in a different direction, pursuing a new rocket dubbed Vulcan whose main stage would use the BE-4 engine being funded and developed by Blue Origin of Kent, Washington.

The BE-4 is fueled by liquid natural gas, which is less dense than kerosene and thus could not be plugged into the aft end of the Atlas 5 as currently designed. ULA officials have said they view the kerosene-fueled AR1 as a backup option in case Blue Origin stumbles on its engine.

In an April 29 letter to U.S. Defense Secretary Ashton Carter, the Aerojet-Dynetics-Schafer consortium said it was interested in exploring the launch rights and intellectual property associated with the Atlas 5. Defense Department officials did not immediately respond to a request for comment.

The letter argues that the lowest-cost and lowest-risk option for ending reliance on the RD-180 is to replace it with the AR1, according to a source familiar with the matter. Because an AR1-powered Atlas 5 would be relying on existing designs and infrastructure, that rocket could be certified more quickly than alternatives like the Vulcan, the source said.

Officials say there is precedent in replacing engines, a process they refer to as “re-engining.”

“We have a rocket engine problem, not a launch vehicle problem,” said Steve Cook, director of corporate development for Dynetics.

The proposal appears to be a nonstarter with ULA, a joint venture of defense giants Boeing and Lockheed Martin.

“United Launch Alliance holds the rights to build and launch the Atlas V, and we have no intention of selling or transferring them,” Christa Bell, a ULA spokeswoman, said in an email to SpaceNews. “The Vulcan launch system is expected to produce its first flight in 2019, with full certification in 2022-2023. We expect to launch Atlas 5 into the next decade as we work with customers to meet requirements and transition to the new launch vehicle, continuing our focus on mission success, one launch at a time.”

The Air Force in late April issued a draft request for proposals on launch vehicle development that responds to Congress’ directive to field a replacement for the RD-180-powered Atlas 5. In comments on the draft solicitation, Aerojet, which is teaming with Dynetics and Schafer, said its focus is too broad and should be narrowed to rocket engine development.

Aerojet Rocketdyne builds the RS-68 main engine for ULA’s other rocket, the Delta 4, but ULA intends to phase out that vehicle around 2018 because costs too much to build and operate. Aerojet Rocketdyne also supplies variants of the RL10 upper-stage engine that is used on the Atlas 5 and Delta 4 today, and also would be used in the initial version of the Vulcan.