Propulsion provider Aerojet and partner Florida Turbine Technologies (FTT) have completed preliminary design of the turbopump assembly for a new upper-stage rocket engine under consideration by the U.S. Air Force, Aerojet said in a Nov. 28 press release.

The next-generation engine would replace the venerable RL10 cryogenic upper-stage engine currently used on the Air Force’s workhorse Atlas 5 and Delta 4 rockets. The service in September 2010 issued a request for information for the next-generation engine, arousing interest from both Sacramento, Calif.-based Aerojet and its main rival in liquid-fueled rocket engines, RL10 builder Pratt & Whitney Rocketdyne of Canoga Park, Calif.

Aerojet said the preliminary design of its turbopump passed muster with a team of independent experts. The project leverages the company’s past work on programs including the Air Force’s Integrated High Payoff Rocket Propulsion Technology demonstration program.

Aerojet’s current work on the next-generation engine is funded internally, Aerojet spokesman Glenn Mahone said.

Based on a 50-year-old design, the hydrogen-fueled RL10 has been upgraded over the years, but Pratt & Whitney Rocketdyne officials have said there is little more that can be done to boost its performance. In its request for information, the Air Force said it hoped to have an RL10 replacement available by 2017, but the service has yet to commit funding to the proposed effort.

“We are looking forward to a future open [next-generation engine] competition that focuses on modern and affordable design and manufacturing approaches that are critical to long-term launch vehicle propulsion sustainability,” Julie Van Kleeck, Aerojet vice president of space and launch systems, said in a prepared statement. “It has been decades since there has been an open engine competition in this country, which has not been good for U.S. competitiveness or its propulsion industrial base.”