WASHINGTON — The willingness of United Launch Alliance’s parent companies to fund a next-generation rocket hinges on winning relief from the ban on the Russian-made engine that powers its current government workhorse, the Atlas 5, ULA executives say.

In separate appearances, ULA Chief Executive Tory Bruno and Chairman Craig Cooning tied investment in ULA’s planned Vulcan rocket to the congressionally imposed ban on the future use of Russian-made engines to launch military payloads. The Atlas 5 is used today to launch most U.S. military payloads and virtually all of the nation’s scientific satellites.

The ban, imposed in the National Defense Authorization Act for 2015, permits ULA to use just five RD-180 engines for upcoming competitive phases of the U.S. Air Force’s Evolved Expendable Launch Vehicle program. The initial round, in which Denver-based ULA will square off against emerging rival SpaceX, gets underway this year and includes nine launches.

ULA, which is phasing out its Delta 4 rocket because of its high cost, expects the Vulcan, featuring a main engine developed and funded by the privately held Blue Origin venture, to debut in 2019 and win certification to launch military payloads in 2022. ULA says that to stay in the game until then, it needs to have at least 14 RD-180s available for the upcoming competitions.

The House and Senate have drafted different versions of the 2016 defense authorization bill that relax the ban. But while the House version permits ULA to use the 14 engines it says it needs for the near-term competitions — of which there are two — the Senate version clears no more than nine.

Developing the Vulcan, essentially an Atlas 5 with a new first stage in its initial version, will require an unspecified but substantial investment from ULA’s parent companies, Boeing and Lockheed Martin. ULA’s board of directors, composed of Boeing and Lockheed Martin executives, has yet to approve that full investment.

During a speech at Boeing media event May 19 in Los Angeles, Cooning said the RD-180 ban in its current form undermines the business case for investing in new launch capabilities. Cooning is president of Boeing Network and Space Systems and currently holds the ULA chairmanship, a position that rotates between Boeing and Lockheed Martin.

Cooning’s remarks were quoted by Flightglobal.com and confirmed by Boeing spokesman Robert Sterling.

The board has approved ULA’s target Vulcan milestones for the year, but for now will only commit investment funds on a quarterly basis.

In an emailed statement, Sterling said part of the business case for that investment is RD-180 availability. “Those engines must be available until a new launch vehicle is ready,” he said. “The Air Force has told Congress that the plan for phasing out the RD-180 needs to be modified. We fully support that position.”

Lockheed Martin spokesman Matthew Kramer confirmed that Sterling’s statement represents the board’s position.

In a luncheon speech here May 21, Bruno seconded the board’s motion. “It is currently unclear whether we will be allowed to use the RD-180 to continue flying the Atlas long enough to reach the new American engine, and that in itself is a significant impediment to making the investment,” he said. “When I talked about how important it was for the country to introduce the next generation of engine technology — it could be either the AR1 or the BE-4 — it is essential for Congress to allow us to cross that valley until the new engine is ready or it’s not going to happen.”

The BE-4, being developed by Kent, Washington-based Blue Origin, is ULA’s primary choice for an RD-180 replacement. Should Blue Origin falter, ULA has a backup option in the AR1 being developed by Aerojet Rocketdyne of Canoga Park, California.

Bruno cited the RD-180 as one of a number of market uncertainties facing ULA. Another is an expected decline in military demand — a “slump,” as he described it — from the current number of 10-12 missions annually to around five in the next couple of years.

That smaller number likely would be divvied up with SpaceX of Hawthorne, California, which is poised to end ULA’s current monopoly in the national security market when it wins certification, expected in June, for its Falcon 9 rocket. That means ULA will have to win substantial civil and commercial business — currently it is barely a bit player in the commercial market — to be viable.

Aerojet Rocketdyne, meanwhile, is part of a three-company consortium that has inquired about obtaining the production rights to the Atlas 5, which Bruno said are jointly owned by ULA and Lockheed Martin. Kramer said Lockheed Martin owns the elements of the Atlas 5 design created prior to ULA’s 2006 establishment and, like ULA, has no intention of transferring that intellectual property.

ULA also confirmed that 12 members, or 30 percent, of its executive-level staff had accepted buyouts and would be leaving the company. “It is important for ULA to move forward early in the process with our leadership selections to ensure a seamless transition and our continued focus on mission success,” ULA spokeswoman Jessica Rye said in a statement.