COLORADO SPRINGS, Colo. – Although United Launch Alliance maintains Blue Origin's BE-4 is the engine of choice for its next-generation Vulcan launch system, Aerojet Rocketdyne continues to push its AR-1 engine as the best domestic solution to propel rockets into space.

The AR-1 is "the most logical solution" to ending US reliance on the Russian RD-180 for space launch, said Julie Van Kleeck, Aerojet Rocketdyne vice president of space and launch systems, here during the Space Foundation's annual National Space Symposium.

Van Kleeck billed the AR-1 engine as the lowest risk and lowest cost solution to the taxpayer, and said it solves the problem on the shortest schedule. Further, she claimed the AR-1 is the only solution that fits on ULA's Atlas V vehicle, currently powered by the RD-180, while still providing flexibility for use on future launch vehicles, for example ULA's next-generation Vulcan rocket.

"All other solutions are more risky, bring no added value from a performance or capability standpoint and do cost more," Van Kleeck said April 12.

Aerojet Rocketdyne and its partner Dynetics plan to certify and deliver AR-1 flight engines in 2019, Van Kleeck said. The AR-1's next major design review is schedule for this fall after the companies complete risk reduction and manufacturing demonstrations, Van Kleeck said. This will allow the team to proceed into integrated testing and engine production, she said.

However, ULA president and CEO Tory Bruno contradicted many of Van Kleeck's claims. He said the AR-1 is "the long pull" to power the Vulcan launch system, telling Defense News the company is scheduled to receive BE-4 about 16 months earlier than the Aerojet Rocketdyne engine.

If ULA ends up choosing the BE-4, the Vulcan will first fly in 2019, with certification two or three years later, Bruno said during an interview here on Wednesday. If ULA goes with the AR-1, the Vulcan would fly first in 2020, with certification two or three years after that.

If Aerojet Rocketdyne can compress its schedule so that ULA can receive the AR-1 before the BE-4, the company may reconsider its first choice, Bruno said. ULA may also consider using the AR-1 ahead of the BE-4 if Aerojet Rocketdyne can improve its business case, he said – in other words, make the engine cheaper.

ULA and Blue Origin will do a full-scale static firing of the BE-4 at the end of the year, a test that will help ULA make a final judgment on which engine to use, Bruno said.

"At that point I'll look at a selection criteria that's got obvious stuff in it: Does it work? Then we would know. When is it going to be available? So the rest of the schedule going forward. And then, what is it going to cost?" Bruno said. "And then of course finally, what performance does it have?"

The Vulcan will eventually replace both the Atlas V and ULA's Delta IV to launch the heaviest payloads.

Twitter: @laraseligman