WASHINGTON — United Launch Alliance is set to make a decision this year on whether a Blue Origin or Aerojet Rocketdyne engine should power its Vulcan launch system. The outcome hinges on a series of hot-fire tests that will prove whether Blue Origin's BE4 works, ULA's chief executive told Defense News on April 6.

"It's a big decision, and you only get to make it once, and if you pick the wrong engine it's very difficult to come back from that, so we're going to be very, very careful," Tory Bruno, ULA's president and CEO, said.

ULA — a joint venture of Lockheed Martin and Boeing — is leaning toward the BE4 because much of the engine's development has been self-funded and it will be certified as early as 2017, two years earlier than Aerojet's AR1, Bruno said.

However, the BE4 is the first rocket engine of its size to use methane as a propellant, which introduces the possibility of combustion instability. For that reason, ULA is waiting until after fire-testing to make its final down-select, he said.

Blue Origin already has constructed its first full-scale BE4, which has been shipped to its West Texas facility for ground testing. The hot-fire tests will take place over several weeks later this year, allowing Blue Origin to collect data over multiple test events where the power level will gradually be increased and then sustained for longer periods of time.

"Finally you're at full power running long enough to be steady state, and you know what you've got," Bruno said. "Then, we will know what we have, and we'll be able to pick an engine."

ULA will not be making a final selection alone. The company has established an independent team of experts to advise it, and Congress has chartered its own group — comprised of engineers and scientists from NASA’s Marshall Space Flight Center — to give lawmakers guidance. Bruno also expects the Air Force to provide input.

"If all four groups say the same thing, it will be a very easy decision. If there are any differences, we’ll resolve them, and then we’ll pick an engine," he said.

Bruno hopes to make an engine selection before ULA submits its final proposal for the Air Force’s launch service agreement competition, the Evolved Expendable Launch Vehicle (EELV) follow-on program that will help fund the development of new launch systems. But with the final request for proposals likely coming out in summer, ULA may have to structure its bid to accommodate both the AR1 and BE4 while continuing to develop both engines, as a down-select is slated for later..

Bruno characterized the AR1 as the lower-risk but higher-priced entrant. Aerojet is currently "making excellent progress" conducting component testing, he said. Aerojet’s AR1, like the RD-180 currently employed by ULA’s Atlas V, will be fueled by a combination of kerosene and liquid oxygen, making combustion instability less of a concern.

"It's not zero risk, because it's going to be our first oxygen-rich staged combustion engine developed

here in the States, but much less risk" than the BE4, Bruno said.

Unlike Blue Origin, Aerojet has yet to sign a contract with ULA because the design is not yet mature enough to set a firm price.

"What they're doing instead is doing cost modeling, forecasting the price as they work through the design. They have a price target that they're trying to drive to," Bruno said, adding that those estimates show that a set of BE4 engines will be cheaper than both the RD-180 and the AR1.

Aerojet Rocketdyne officials maintain that the AR1 will be lower cost and lower risk than its competitor, and that the engine’s performance will replicate the battle-tested RD-180 that powers ULA’s Atlas V. Even if the BE4 manages to make it through hot-fire testing, there will still be added uncertainty involved because Blue Origin still has not chosen a production facility for the BE4, meaning manufacturing processes aren’t solidified, Julie Van Kleeck, its vice president of advanced space and launch programs and strategy, said during an April 3 briefing.

"To truly certify, you don't have to [just] certify the design, you certify the processes that are built in a certain factory. You have to certify the whole thing to really know you have a certified engine," she said.