COLORADO SPRINGS — United Launch Alliance is prepared to select Blue Origin’s BE-4 engine for its Vulcan launch vehicle this year if the engine passes an upcoming series of tests, the company’s chief executive said April 5.

In an interview during the 33rd Space Symposium here, Tory Bruno said that tests of the BE-4 engine, scheduled to begin “very soon” at Blue Origin’s test site in West Texas, are the last major hurdle the engine must clear before ULA decides to use it on Vulcan.

“The economic factors are largely in place now and the thing that is outstanding is the technical risk,” Bruno said. “That’s why we keep talking about the engine firing.”

A major aspect of the engine tests, he said, is to determine the degree of combustion instability the BE-4 has when the engine starts. “Any time when you are developing a new rocket engine, any time you change the scale or the fuel, you are at risk of this phenomenon,” he said. The BE-4 engine is the largest engine developed to date that uses methane as fuel, rather than more common alternatives like kerosene or liquid hydrogen.

“We look first to the combustion instability as the chief technical risk that must be retired before we’d be able to pick an engine,” Bruno said. He anticipated a series of tests, lasting for several weeks, where the engine’s thrust is gradually increased to measure its performance and determine if it suffers from combustion instability.

Bruno said he was encouraged by tests of some key engine components, including the preburner, a smaller version of the main engine that powers the engine’s turbomachinery. “The good news is the preburner is running like a top,” he said. “We’re starting to get more and more confidence that we’re going to have a good experience when we run a full-scale engine.”

If the tests all go as planned, Bruno said ULA could be ready to formally select the BE-4 in as soon as 60 to 90 days. “But it could take longer,” he added. “It’s not on the calendar.”

Rob Meyerson, president of Blue Origin, confirmed in an April 5 interview that test of the BE-4 will start in the next several weeks. One engine is already at the company’s test site, with two more shipping there soon.

“We wanted to go into the test program hardware-rich,” he said. With those engines and other equipment at the test site, “we can move through the test program quite rapidly.” He said that testing would continue after ULA made its decision, with final certification of the BE-4 planned for late 2018 or early 2019.

While Bruno will make the decision about the engine, he will get plenty of advice. He said he recently established an independent non-advocate review (INR) team of outside experts to review the overall engine evaluation process. That team includes former Secretary of the Air Force Sheila Widnall; retired Air Force Maj. Gen. Susan Mashiko, former deputy director of the National Reconnaissance Office; and Ray Johnson, former vice president for space launch operations at the Aerospace Corp.

Bruno said Congress also established a separate INR team, comprised of engineers from NASA’s Marshall Space Flight Center, to review the engine selection process. “I was actually happy to hear that they did that,” Bruno said, adding that this team had access to the same data as ULA’s own review team.

Bruno added that he expected the Air Force would also seek access to the test data and provide ULA with its own opinion about the engine. “I will hear all of those opinions and it will be super easy if everybody says the same thing,” he said. “If they do not, then we will resolve that. And then we will make a choice.”

Aerojet Rocketdyne’s AR1 engine remains the alternative for Vulcan should the BE-4 run into technical problems. Development of the AR1 is 18 to 24 months behind the BE-4, he said, because it started later. “I have confidence they can get their engine to work” because of its use of a more conventional fuel, kerosene.

Blue Origin, though, has the financial edge. Bruno said ULA already has a firm fixed-price deal with Blue Origin for “a large enough quantity” of engines that covers initial Vulcan missions. Those engines will be produced initially at Blue Origin’s factory in Kent, Washington.

“Their production capability actually looks quite good,” Bruno said of those initial BE-4 engine plans. “My INR heads came back to me and said they are very comfortable with that production capability already.”

Later engines will be built at a separate facility Blue Origin plans to develop in the next few years that will be designed to produce dozens of engines a year. “We’re in the process of site selection for a full production site,” Meyerson said. He declined to identify the locations being considered, but said a decision should be made in the next six months.

Bruno said that he expected to decide on the Vulcan engine this year, but wouldn’t be rushed into one. “I get to make this decision, like, once. This is a big decision and if you don’t get it right, it’s very hard to come back from that,” he said. “So I’m going to take my time and listen to all these experts and stakeholders and then do it.”