The Pentagon has launched a review to determine whether using a Russian-built rocket engine to launch military satellites has any national security implications, following Russia’s seizure and annexation of Crimea.

The review, which defense officials expect to wrap up in late May, will examine the security risks, as well as the costs of developing and producing a replacement for the RD-180 engine used in the Atlas V rocket.

Air Force Chief of Staff Mark A. Welsh told reporters last month that domestically developing and producing an alternative engine would take about five years and cost $1 billion — a steep sum for a department struggling to grapple with a downturn in spending.

“If we decided to produce this engine domestically, clearly we have a big bill to pay,” Senate Defense Appropriations Subcommittee Chairman Richard J. Durbin, D-Ill., said at a hearing last week.

United Launch Alliance, the Boeing-Lockheed Martin joint venture behind the launches, estimates it has a two-year supply of the engines.

The ULA estimates it would take four to five years to produce an alternative engine, creating a potential gap if the Pentagon opted to stop procurement of the engines altogether. There are another 29 RD-180s under contract, the first of which would be delivered in November.

“The last thing we’d want to do is cut off our noses to spite our faces,” said Mark Bitterman, a ULA spokesman.

But lawmakers and Pentagon officials nonetheless want to weigh their options for the future.

The Russian-American partnership on the program has “weathered various storms,” Air Force Secretary Deborah Lee James told the House Defense Appropriations Subcommittee on March 26. “That doesn’t mean I’m not worried about it. I am.”

James has specifically said she wants to ensure there are adequate spare parts in the inventory. And she has also stressed that ULA has the option of using its other rocket — the Delta IV, which does not use the RD-180 engine — as a fallback option for at least some of the launches.