WASHINGTON — The U.S. Air Force plans to spend $500 million over the next five years, with roughly $200 million to be committed in February, to develop a new liquid-fueled rocket engine to replace the Russian-made engine that currently launches many national security missions, according to new White House budget documents.

The spending plan also calls for the service to hold competitions for nine satellite launch contracts — two more than officials were planning for a year ago — and distinctly refrains from committing to future wideband and protected communications satellites.

The new engine is the most high-profile addition to the budget.

Last year, Congress set aside $220 million for a new rocket engine to help wean the department from the Russian-made RD-180 engine. Lawmakers said they would like a new engine by fiscal year 2019, a timetable Air Force officials have called aggressive. The new money came over objections from the White House and the Air Force, which to date has been slow in detailing how it will spend the money.

Now the Air Force says it plans to plans to award about $204 million worth of contracts in February to study concepts including alternate manufacturing processes, launch system architectures, risk reduction for key propulsion components, advanced propulsion technologies, and material and manufacturing development.

The spending plan calls for the Air Force to spend about $84 million on the project next year. A round of contracts worth a combined $74 million is tentatively slated for award in October, documents show.

Industry experts have said developing a new engine likely would cost around $1 billion. The budget documents indicate the Air Force is willing to chip in for about half of that cost and said the service would follow a “shared investment approach.”

Meanwhile, the Air Force plans to competitively award up to nine satellite launch contracts by the Sept. 30 end of the fiscal year in 2017, which opens more of the national security market to SpaceX.

At this time last year, the Air Force said seven missions would be put up for bid through 2017, a reduction from the previously announced number of 14 that triggered a lawsuit by SpaceX. The Hawthorne, California, company recently dropped its lawsuit, which challenged a large sole source rocket order with United Launch Alliance, after the Air Force agreed to make more competitive awards.

The Air Force’s plan now calls for three competitive launch contracts in 2016 and four in 2017. The service also said it has funding for two competitive launch contracts in fiscal year 2015. In addition, ULA will receive two sole-source missions in 2016 as part of its 2013 contract with the Air Force for three dozen rocket cores.

Beginning in 2018, every national security launch is expected to be open for competition, Air Force officials said.

The new budget request also leaves open several possibilities for the Air Force’s next-generation satellite communication programs.

In its 2015 budget request, the Air Force said it would delay buying the seventh and eighth satellites in its Advanced Extremely High Frequency secure communications system. In the 2016 request, those satellites do not appear in the five-year planning horizon, and the Air Force said it does not expect to need replacements until 2027.

Instead, the Air Force requested $174 million to study next-generation technologies for secure communications, including work on a protected tactical waveform demonstration and inserting new capabilities into clones of the current satellites.

The budget also leaves open questions about what will follow the Air Force’s Wideband Global Satcom constellation. The five-year funding outlook has just $11 million earmarked 2019 and nothing in 2020.

Air Force officials have said they expect to begin an official analysis of alternatives on potential follow-on programs in 2016, but Gen. John Hyten, the commander of Air Force Space Command, has said the service needs to start making decisions before the 2017 budget request is prepared, a process that begins in earnest this summer.

Commercial satellite operators are positioning themselves for an increased share of Pentagon.

Other highlights of the budget request include: