The Air Force expects the results from its review on the Russian-made RD-180 first stage rocket engine around the end of May, service Secretary Deborah James told the House Appropriations defense subcommittee March 26.

Air Force Under Secretary Eric Fanning said recently the service was performing a “business case analysis” of how much it would cost to produce the RD-180 in the United States. Air Force Chief of Staff Gen. Mark Welsh told reporters after the subcommittee hearing the Air Force, which is part of the Defense Department’s study into the RD-180, said it would probably take roughly $1 billion and five years to develop and produce an alternative engine. The RD-180 is developed by NPO Energomash

 and is distributed in the United States by RD AMROSS, a joint venture of NPO Energomash and United Technologies Corp.– [UTX] division Pratt & Whitney. 

Though relying on a Russian engine for a critical national security capability like space launches has always been discussed, the RD-180 has become a hot topic on Capitol Hill since the current crisis between Ukraine and Russia developed recently. James said the Air Force has roughly a two-year supply of RD-180s and that the relationship between United Launch Alliance (ULA), which uses the engine in its Atlas V rockets, has survived various peaks and valleys.

“This partnership has weathered various storms in the U.S.-Russian relationships,” James said during a hearing on the Air Force’s fiscal year 2015 budget request. “That doesn’t mean I’m not worried, but we have seen ups and downs before.”

Fanning also said recently the Air Force would like to have a more varied supply of engines to minimize risk. ULA is a joint venture of Lockheed Martin [LMT] and Boeing [BA].