WASHINGTON — The US Air Force has awarded Orbital ATK and Elon Musk's SpaceX contracts to develop prototypes of rocket engines as a part of the government's ongoing effort to end reliance on the Russian RD-180 booster for military space launch.

Orbital ATK nabbed a $47 million contract to develop three rocket propulsion system prototypes intended for use on an Orbital ATK next-generation launch vehicle, the Pentagon announced Wednesday. The total potential value of the contract, including all the options, is $180 million.

Specifically, the contract includes development of prototypes of Orbital ATK's GEM 63XL strap-on solid rocket motor, the Common Booster Segment solid rocket motor and an Extendable Nozzle for Blue Origin's BE-3U engine. Blue Origin, founded by Amazon.com's Jeff Bezos, has been pushing its Blue Engine (BE) class of engines as a homegrown alternative to the RD-180.

SpaceX, meanwhile, won a $33.6 million contract to develop the Raptor rocket engine prototype for the company's Falcon 9 and Falcon Heavy launch vehicles, according to the Pentagon. The potential value of the award, including all options is $61 million.

Both contracts are part of the Air Force's Evolved Expendable Launch Vehicle program, intended to ensure US access to space.

Aerojet Rocketdyne, another rocket engine manufacturer, was notably missing from Wednesday's contract announcement. However, that does not mean the company is out of the running, as the Air Force is still in negotiations with other industry players.

"The Air Force is still in negotiations with the remaining offerors and subsequent awards, if any, will occur over the next few months," according to a Jan. 13 service statement.

The Pentagon currently relies on the RD-180 to power the Atlas V rocket, built by United Launch Alliance, a joint venture of Boeing and Lockheed Martin. Efforts to develop a domestic solution gained new urgency when Congress banned the use of the RD-180 for military space launch as a response to Russia's annexation of Crimea.

Lawmakers recently relaxed the ban as part of the 2016 omnibus spending bill, but officials are still pressing industry to find a homegrown alternative.

Twitter: @laraseligman