DUBAI, United Arab Emirates — The Aerospace Corp. has begun evaluating, at the behest of the U.S. Air Force, U.S.-based alternatives to using Russia’s RD-180 engine to power the Atlas 5 rocket, a primary launch vehicle for U.S. military payloads, an Aerospace Corp. official said.

Ray Johnson, vice president for space launch operations at El Segundo, California-based Aerospace Corp., said estimates of how long it would take to field an RD-180 replacement for Atlas 5 vary widely.

“I see numbers all over the map,” Johnson said May 14 during the World Space Risk Forum here. “Some people say they could do it in five years. Others estimate it’s going to be longer than that, and that it could be eight.”

Aerospace Corp. work evaluating what it would take to develop a hydrocarbon engine to replace the RD-180 — if U.S.-Russia relations sour to the point where the engine is no longer available or wanted — “is literally just a few weeks old,” Johnson said.

Johnson said that despite U.S. technology-transfer restrictions that have limited the kinds of interaction that U.S. officials can have with RD-180 builder NPO Energomash of Russia, Aerospace has “gained a considerable amount of insight into the RD-180.”

“We go over to NPO Energomash. We do reviews of the hardware. We do reviews of the testing of the hardware and we get insight into their anomaly resolution methods,” Johnson said.

Technology transfer rules under the U.S. International Traffic in Arms Regulations prohibit Aerospace officials from offering Energomash any lessons from the center’s analysis of the RD-180.

“ITAR is very challenging for us and has to do particularly with the flow of information from us to them, not from them to us,” Johnson said. “So we can ask questions and get insight into what they’re doing. What we can’t do is make judgments and say, ‘You ought to do it this way.’”

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Peter B. de Selding was the Paris Bureau Chief for SpaceNews.