WASHINGTON — On the same day two Russian-made RD-180 rocket engines arrived in Alabama from Moscow, the U.S. Air Force issued a request for information on the possibility of weaning itself from those very engines.

Amid heightened tensions with Russia, the Defense Department has been making preliminary preparations for life without the RD-180, which powers the first stage of United Launch Alliance’s Atlas 5 rocket, one of two the company uses to launch military and other government satellites.

The request for information, posted to the Federal Business Opportunities website Aug. 20, is a step in that direction.

“The Government is seeking insight into booster propulsion and/or launch system materiel options that could deliver cost-effective, commercially-viable solutions for current and future National Security Space launch requirements,” the solicitation from Air Force Space Command says. “The Air Force needs this information to inform near term decisions about how to best ensure that future launch requirements are fulfilled by reliable, commercially-viable sources.”

Companies are being asked to respond by Sept. 19 to 35 questions. Among them: “What solution would you recommend to replace the capability currently provided by the RD-180 engine?”

Air Force officials have told Congress they only have a broad idea of how to replace the RD-180. Estimates of the investment in money and time necessary to field an American-built alternative vary widely.

Congress, meanwhile, is preparing bills that would fund a full-scale engine development program starting next year; the White House is advocating a more deliberate approach that begins with an examination of applicable technologies.

In the request for information, the Air Force says it is open to a variety of options including an RD-180 facsimile, a new design, and alternative configurations featuring multiple engines, and even a brand new rocket.

The Air Force is also trying to decide on the best acquisition approach. Options include a traditional acquisition or a shared investment as part of a public-private partnership.

The service is planning to host industry representatives for presentations on the potential development program Sept. 25 and Sept. 26.

Aside from securing its own launch capabilities, the Air Force hopes to stimulate the development of a more robust domestic commercial propulsion industry. Employment in the U.S. propulsion sector has declined in recent years, especially following the retirement of NASA’s space shuttle.

The RD-180 is built by RSC Energomash of Russia and sold to Denver-based ULA by RD Amross, a joint venture of Energomash and United Technologies Corp. When that arrangement was set up during the 1990s, the idea was to eventually set up a U.S. production line for the hardware.

However, the U.S. production line never materialized due in large part to cost considerations.

Russia has threatened to restrict RD-180 exports to the United States in retaliation for U.S. sanctions levied on certain Russian government officials following that country’s incursions into Ukraine. However, ULA says that engine deliveries continue without interruption, the latest evidence being the arrival Aug. 20 of two RD-180s at the rocket maker’s Decatur, Alabama, manufacturing plant.

That delivery brings to 15 the number of RD-180 engines in the United States. ULA is expecting delivery of 27 additional engines through 2017 under its current contract with RD Amross.

“We expect another shipment of three engines later this year,” ULA spokeswoman Jessica Rye said.

A 2015 defense authorization bill drafted in the U.S. Senate would prohibit U.S. space companies from entering new contracts or renewing existing contracts for launch vehicle supplies from Russia.

SpaceNews staff writer Dan Leone contributed to this story.