Engine manufacturer Aerojet Rocketdyne announced today that its AR1 engine, which its building for the United Launch Alliance (ULA) — the military’s primary launch provider — has passed a major critical design review. That means the company will continue to develop the engine further to get ready for full-scale testing in 2017. But while Aerojet is making the AR1 for use in ULA's rockets, ULA hasn't said if it's actually going to use the engine or not.

The AR1 is being built as a replacement for the Russian RD-180 engine, which ULA uses in its flagship Atlas V rocket. Recently, ULA was forced to get rid of the RD-180, after Congress banned the Air Force from using Russian-made engines to launch satellites. Right now, ULA will lose the military's business — its main source of income — if it doesn't update its rocket engines.

ULA hasn't said if it's actually going to use the engine or not

Aerojet says it has the solution for ULA: just put the AR1 in the Atlas V. The company says the engine could easily be incorporated into the rocket and it will be ready by 2019 — the same year ULA has to stop using RD-180 engines for military launches. But ULA seems less interested in re-tooling the Atlas V's engines and more interested in making an entirely new rocket. ULA is working with Blue Origin to create a new engine, the BE-4, for a brand new rocket to be called Vulcan.

Still, Vulcan won't be ready for launches until 2022 or 2023. ULA is going to need to replace the Atlas V engines if it wants to keep launching Air Force satellites beyond 2019. It's possible that the Air Force may sway ULA's hand. Congress has set aside money for the military to subsidize the development of an RD-180 replacement. The Air Force hasn't decided how it's going to spend that money yet, but a glowing design review could make the AR1 an attractive investment option. And if the Air Force puts money into the AR1's development, ULA may be pressured to incorporate the engine into the Atlas V.

Of course, if the new omnibus bill is passed, the whole issue could be averted. A new provision in the bill lifts the ban on Russian-made rocket engines, so it's possible that ULA may not have to worry about replacing its Atlas V engines at all.