WASHINGTON – A key U.S. House member said Feb. 24 that the Air Force’s plan to invest more than $1 billion in a new rocket would violate the 2015 defense authorization law and that instead, the service should place a higher priority on developing a new rocket engine.

The remarks, from Rep. Mike Rogers (R-Ala.), the chairman of the House Armed Services strategic forces subcommittee, are the latest in an ongoing back-and-forth between the Hill and the Air Force over how to end reliance on the Russian RD-180 rocket engine.

The RD-180 powers United Launch Alliance’s Atlas 5 rocket, which launches a majority of national security satellites. Since the crisis in Crimea in February 2014, ending the use of that engine has become a top priority for Defense Department leaders and lawmakers. But figuring out exactly how to do so has been a repeated point of contention.

“Let me be clear. We have a Russian engine problem,” Rogers said here during a budget forum organized by FiscalTrak and the Air Force Association. “But we do not have a launch vehicle problem. I’m extremely concerned the Air Force is taking on too much risk in what may amount to be a very expensive endeavor.”

In its budget request for fiscal year 2017, the Air Force said it plans to spend $1.2 billion over the next five years on a next generation launch system. This would include investing in upgrades to existing rockets or investing in entirely new systems from domestic launch providers such as SpaceX, Orbital ATK and United Launch Alliance.

Rogers’ concern comes from the fact that “the Air Force doesn’t actually know what it wants to build yet,” he said. “The budget request is so undefined it’s as if the Air Force is asking for a blank check from Congress on the scope of the effort.”

Just six days earlier, Lt. Gen. Samuel Greaves, commander of the Air Force Space and Missile Systems Center, emphasized during a breakfast here that investments in new launch technologies have followed the letter of the law and that further investments would come with the cooperation of Congress.

Defense Department leaders including Greaves; Frank Kendall, the Pentagon’s acquisition chief; and Deborah Lee James, the secretary of the Air Force, have repeatedly said a new engine is not enough to maintain assured access to space.

“Just replacing the RD-180 engine with a new engine will not deliver the same performance of the current design of any rocket,” Greaves said. “In fact, it may result in a system that delivers less payload to orbit at a higher cost.”

The debate is likely to continue next month during a budget hearing before Rogers’ subcommittee, which provides oversight of military space issues.

Rogers contends the Air Force is planning to use money set aside for a new engine for “an expressly different purpose” than lawmakers intended.

Congress has given the Air Force $444 million over the past two years to end reliance on the RD-180. But the National Defense Authorization Act for fiscal year 2015 explicitly says the Air Force is to use money only for a rocket engine and not for development of a new launch vehicle.

“The Air Force is planning a program that violates current law,” he said.

But during a question-and-answer session Rogers offered a twist to his position that may leave room for middle ground.

“My priority is to keep a focus on the engine. If the Air Force or DOD choose to, in addition to that, put money into launch, I don’t care,” he said. “I just don’t want to take my foot off the pedal on getting an American-made engine and anything that diverts money away from that, I’m against. If they want to put on top of that (money) for a launch system, they can knock themselves out.”