WASHINGTON – Aerojet Rocketdyne has held discussions with at least two unnamed launch providers, in addition to United Launch Alliance, who have an interest in using the AR1 rocket engine the company is developing, Aerojet’s president said March 1.

The U.S. Air Force announced Feb. 29 it was investing $115 million this year, and with options, as much as $536 million over the next five years, in AR1, a new liquid oxygen- and kerosene-fueled main-stage engine. The contract award is part of an Air Force initiative to end reliance on the Russian-built RD-180 engine that powers ULA’s Atlas 5 workhorse rocket.

The Air Force said in a Feb. 29 announcement that its AR1 investment is being made with the intent that it would power ULA’s next-generation rocket, known as Vulcan.

But ULA executives have said their top choice for an engine is Blue Origin’s BE-4, and that they are continuing to work with Aerojet Rocketdyne on the AR1 as a backup plan.

Eileen Drake, Aerojet Rocketdyne’s chief executive, said in March 1 interview with SpaceNews that the Air Force could continue to fund work on the AR1 even if ULA chooses to move forward with the BE-4.

“Each year is a different discussion,” she said of the contract’s options. “The ULA downselect is not a condition” of continued funding.

ULA is expected to make a decision between the two engines later this year, but has said Blue Origin is the frontrunner.

Aerojet Rocketdyne declined to disclose further information on the other launch companies they had discussed the new engine with, including whether they are based in the United States.

“This engine will be available for use on the Atlas 5, Vulcan and other launch vehicles currently in development,” Drake said.

Aerojet Rocketdyne executives say they plan to test the first AR1 development engine in 2017, followed by additional testing in 2018 and to provide a certified engine in 2019.

For the upcoming year, Aerojet Rocketdyne will use the Air Force funding to work toward a critical design review in the fourth quarter of 2016 and toward the purchase of some long-lead items, Drake said.

After Aerojet Rocketdyne found itself in a competition with Blue Origin to develop a new engine in late 2014, the company increased its internal investment on AR1. For fiscal year 2015, Aerojet Rocketdyne spent nearly $48 million on the program, Drake said. She expects the company to spend a similar amount this year.

The Pentagon’s Feb. 29 release said Aerojet Rocketdyne’s total investment could reach about $268 million.

Drake said “a small portion” of the $115 million Air Force investment will go toward previously completed work on the engine.