WASHINGTON – Facing congressional pressure to begin work on an American replacement for the Russian-built main rocket engine used today to launch most U.S. national security payloads, the U.S. Air Force quietly unveiled the initial steps in a procurement strategy that has been complicated by a key industry player’s own plans.

The announcements, released late April 24, detail what Gen. John Hyten, commander of Air Force Space Command, acknowledged April 28 is a “complicated” and “difficult” acquisition strategy, one that may produce an American-made rocket engine by 2019, as Congress has directed. But speaking with reporters at a breakfast here, Hyten said it likely would take at least two more years to integrate the engine into a rocket.

Hyten is among the Air Force leaders scheduled to testify before the Senate Armed Services Committee April 29 in a hearing in which lawmakers are expected to grill witnesses about plans to replace the Russian-built RD-180 engine, the main powerplant on United Launch Alliance’s workhorse Atlas 5 rocket.

Congress mandated last year that the Defense Department develop a kerosene-fueled main rocket engine to replace the RD-180, also kerosene fueled, by 2019. While Air Force officials have raised doubts they can meet that deadline — Hyten called it an “enormous” technological challenge — service leaders have nonetheless been working for months on an acquisition strategy.

Part of the reason for taking so long, Hyten said, is that the Air Force had to shift gears last fall after Denver-based ULA announced it would work with Blue Origin on a new engine fueled by liquid-natural-gas rather than kerosene. Following that announcement, the Air Force decided to broaden the scope of its search to include engines that, like Blue Origin’s BE-4, are not necessarily designed to plug into the first stage of the Atlas 5.

One of the service’s first steps under the new strategy is to award six to eight contracts with a combined value of $31 million for companies to work on booster propulsion technologies, according to a draft broad agency announcement released April 24. The individual contract awards will range between $500,000 and $8 million, the notice said. Companies will be eligible for multiple awards so long at the total value does not exceed $16 million.

The money for these contracts will be drawn from the $40 million Congress reprogrammed in 2014 and the $220 million lawmakers appropriated in 2015 for the engine development effort, Hyten said. The Air Force has spent $50 million of that money so far, Hyten said, although how that money was used is unclear.

Also unclear is how the Air Force would spend the remaining two thirds of the money, at least over the next year or so.

The Air Force is looking at two specific areas: reducing the cost of booster propulsion components and subsystems through the use of new materials and additive manufacturing; and advanced technologies such as alternative propellants and architectures. All of the technologies the Air Force will consider are expected to be within two years of maturity, the posting said.

The service is asking for white papers on the subject before May 8. After an Air Force review of those papers, selected respondents will be invited in June to bid for development contracts.

A second, but overlapping, step is to develop a design for a complete new engine, according to another draft solicitation released late April 24. The idea, is to “take us to [preliminary design review] with a prototype plan,” Hyten said.

The design could be a main- or upper-stage engine, the solicitation said. The document did not detail how much the government intends to spend on this part of the effort, but did say that industry co-funding will be expected.

A formal request for proposals for the second phase is expected by the end of May, Hyten said, and the service hopes to have proposals back from industry by the end of June.

Interestingly, Kent, Washington-based Blue Origin has told the Air Force it has no interest in taking government money for its BE-4 development effort, Hyten said. SpaceX, the Hawthorne, California, company challenging ULA for a share of the national security launch market, has expressed a similar sentiment, he said.

In a third step, to take place at what was described only as “a later time,” but likely before 2018, the Air Force will invest in development and “secure launch service commitments” from those companies selected during the second phase, the solicitation said.