WASHINGTON — The U.S. Air Force awarded three small research contracts Dec. 14 as part of a broader effort to end U.S. reliance on a Russian rocket engine for launching national security missions, according to posts on the Federal Business Opportunities website.

The contracts are the second round of deals as the service aims to replace the RD-180 engine, which powers United Launch Alliance’s Atlas 5 rocket, used to launch a majority of U.S. national security satellites.

The second-round contract recipients are: $902,000 for microelectronic design firm Tanner Research of Monrovia, California; $935,000 for the Johns Hopkins University of Baltimore; and $728,000 for component manufacturer Moog Inc. of East Aurora, New York.

The Dec. 14 postings did not include any details of the technologies engineers would study with the contract money.

The Air Force has said it wants improvements to rocket propulsion technology that can be completed in less than two years. The service has indicated that initial research efforts would focus on reducing the cost of propulsion components and subsystems through the use of new materials and additive manufacturing.

The Air Force has said it plans to award a total of six to eight contracts with a combined value of $35 million aimed at developing lower-cost propulsion components. In November, the service said it would make awards, ranging between $500,000 and $8 million in value, through February 2016.

In November, the Air Force awarded the first of those contracts to the Johns Hopkins University’s Whiting School of Engineering, a $545,000 contract to study additive manufacturing techniques to make cooling chambers for liquid rocket engines.