The appearance of the Air Force’s top two officials on Capitol Hill keyed up an ongoing fight between lawmakers over continued use of the Russian-made RD-180 rocket engine.

An Atlas V at the Cape Canaveral launch range. Photo: ULA.
An Atlas V at the Cape Canaveral launch range. Photo: ULA.

The service is moving as quickly as it can to develop a replacement to the RD-180 engine, but until industry can produce an alternative it will need about 18 of the Russian engines to assure its access to space, Air Force Secretary Deborah Lee James told the Senate Appropriations defense subcommittee.

“Given the importance of space and the many, many complexities involved here, our strong desire for competition being right at the head of the pack, we need reasonable flexibility to access RD-180s over the next few years as we transition to these two domestically available commercial providers,” she said. “We think having access to a total of about 18 RD-180s is reasonable and prudent to maintain competition over these next few years.”

For a decade, United Launch Alliance (ULA), a joint venture of Lockheed Martin [LMT] and Boeing [BA], held a monopoly on national security spaceflight launches. ULA uses the RD-180 in its Atlas V launch vehicle. When the Air Force certified Space Explorations Technology Corp. (SpaceX) for launches in 2015, it created a competitive environment that the service is eager to preserve.

But lawmakers—most notably Senate Armed Services Committee Chairman John McCain (R-Ariz.) and Sen. Richard Shelby (R-Ala.) an appropriations committee member whose home state manufactures the Atlas V—vehemently disagree on how to reach that goal.

The 2015 and 2016 National Defense Authorization Acts helmed by SASC contained provisions that restrict use of the RD-180 and would ban it outright after 2019. The 2016 appropriations act eliminated the cap on the number of RD-180s the Air Force could purchase, but did not end the 2019 requirement to get off the engine.

“I’m concerned that some of my Senate colleagues may not fully appreciate the policy of assured access to space,” Shelby said during the hearing before asking James and Air Force Chief of Staff Gen. Mark Welsh to comment on its importance.

McCain, who was not present for the hearing, shot back on Twitter that two existing rockets with American engines could be used instead of the Atlas V—ULA’s Delta IV and SpaceX’s Falcon 9.

“We have that technology today,” he tweeted.

If access to the RD-180 is limited before a replacement engine is fielded, it could create a gap, said James, who implored senators for “reasonable flexibility.” Experts have told the service that industry could have a replacement ready by 2019.

“That’s what we’re charging toward, that’s what the law has told us to do,” she said. “It’s a risky proposition to have it done by ’19, but it’s possible.”

However, even after a company comes forward with a new engine, it will have to be integrated with the rocket, tested and certified. “So we project that it will be longer than FY ’19 before we have that total capability to power us into space.”

The Air Force could award funds for a RD-180 replacement engine within the next month, James said.

“We’ve obligated all of the dollars authorized and appropriated in ‘FY ’14 and $142 million of the $220 million provided in ’15, with the balance of that money to be obligated over the next month or so pending successful outcomes on final negotiations,” she said. The 2017 budget request includes $297 million to develop an RD-180 alternative.