COLORADO SPRINGS, Colo. — Aerojet Rocketdyne’s Julie Van Kleeck pitched the AR1 rocket engine to a roomful of reporters Tuesday morning as the only direct replacement for the reliable but politically polarizing Russian engine that powers the Atlas 5 rocket.

The U.S. Air Force awarded Aerojet Rocketdyne a contract in February worth up to $534 million over five years to certify and start delivering flight-ready AR1 engines in 2019. Aerojet Rocketdyne says it already has kicked in $70 million, with its total investment expected to exceed $250 million over the life of the contract.

Van Kleeck, vice president of Aerojet Rocketdyne’s advanced space and launch business unit, said the Air Force contract — the largest of several propulsion-related awards the service has made in recent months — is a sign of the Air Force’s confidence in the AR1’s ability to provide an expedient replacement for the RD-180 engine the Defense Department is under pressure from Congress to stop using.

United Launch Alliance, however, has anointed Blue Origin’s methane-fueled BE-4 engine as the front runner to replace the RD-180 by serving as the main engine for the Denver company’s next-generation rocket Vulcan.

“The AR1 engine can fly both on an Atlas and Vulcan and it’s the only engine that can do so,” Van Kleeck said.

While ULA continues to work with Aerojet Rocketdyne on the AR1, ULA executives have said the BE-4, whose development is being bankrolled by Amazon.com founder Jeff Bezos, is several years closer to flight readiness.

Van Kleeck challenged that assertion.

“When you introduce new propellants such as methane to the solution you not only have to have a totally different vehicle architecture but you also have to make costly changes to ground infrastructure and operations and in the end you have no more capability than you had with Atlas and have substantially increased cost and decreased reliability,” she said.

ULA has said it expects to make a decision on Vulcan’s engine sometime around the end of the year. If ULA chooses BE-4 over AR1, will Aerojet Rocketdyne continue to fund the engine’s development?

“We believe the AR1 is going to fly,” Van Kleeck said.

On Atlas 5, Vulcan or something else?

“We believe the AR1 is going to fly,” Van Kleeck repeated.