Boeing has rejected the offer of rocket engine maker Aerojet Rocketdyne to purchase the United Launch Alliance (ULA) — the premier rocket launch provider for the United States Air Force. Boeing is one of the parent companies of ULA, along with Lockheed Martin, and executives for the company say they are completely uninterested in handing the rocket venture over to someone else. "The unsolicited proposal for ULA is not something we seriously entertained," Boeing spokesman Todd Blecher said, according to Reuters.

Last week Aerojet made a cash offer bid of $2 billion to buy ULA. The move was a way to make sure Aerojet's engines would be used in future ULA rockets. Right now, ULA desperately needs to replace the Russian-built RD-180 engine in its Atlas V rocket. After Russia annexed Crimea last year, Congress banned the RD-180 from being used to launch Air Force satellites. Since the Air Force is one of ULA's biggest customers, the compnay is faced with finding a new engine or losing a big source of revenue.

"The unsolicited proposal for ULA is not something we seriously entertained."

Aerojet is working on an engine, the AR-1, that ULA could use instead. If Aerojet owned ULA, then the company could mandate its use. But ULA wants to take a different route. Last week, the company announced a partnership with Blue Origin — the private spaceflight company helmed by Amazon founder Jeff Bezos. The two companies are working together to develop and test Blue Origin's BE-4 engine, which will eventually be used in ULA's next generation rocket Vulcan.

Despite this public rejection, Reuters says Aerojet is still interested in ULA and will put together another more detailed proposal to buy the company soon. Lockheed Martin declined to comment on the negotiations, but Reuters says the company rejected Aerojet's offer along with Boeing.