The RD-180 engine powers ULA's workhorse Atlas 5 rocket. Credit: NASA

WASHINGTON (Reuters) – United Launch Alliance, a joint venture of Lockheed Martin Corp. and Boeing Co. on Wednesday said it had ordered 20 more RD-180 rocket engines from Russia, on top of 29 engines ordered before Russia’s invasion of the Crimea region of Ukraine last year.

ULA said it would use the Russian engines on its Atlas 5 rockets to serve existing and potential civil and commercial launch customers until a new U.S.-built engine was developed and certified.

ULA spokeswoman Jessica Rye said deliveries on the new batch of engines would start once ULA received all of the previous order. ULA received eight RD-180 engines this year, she said.

The new order came days after the enactment of a massive U.S. spending bill that eased a ban on using Russian engines to launch U.S. military and intelligence satellites for fiscal 2016, which ends Sept. 30.

Congress banned military use of the engines after Russia annexed Crimea last year, but a provision in the fiscal 2016 spending measure leaves competition for launch contracts open to companies regardless of the origin of their engines.

ULA, the monopoly provider of military launches since its founding in 2006, last month declined to bid against SpaceX, a private company founded by the billionaire Elon Musk, to launch a next-generation GPS satellite for the U.S. Air Force.

At the time, the company said it lacked Russian-built RD-180 engines for its Atlas 5 rocket and did not have the accounting systems needed to comply with the rules of the competition.

The Pentagon’s chief arms buyer, Frank Kendall, told Reuters on Tuesday the Pentagon remained committed to ending its reliance on the Russian engines, but the spending bill provision would allow the U.S. military to use both the Atlas 5 rockets and SpaceX’s Falcon 9 for satellite launches until a new U.S.-built engine was ready.

ULA said it was moving forward with two companies developing their own U.S. engines, Blue Origin and Aerojet Rocketdyne Holdings, but such development programs were difficult and took years to complete.

(Reporting by Andrea Shalal; Editing by Dan Grebler and Alan Crosby)