WASHINGTON — Sierra Space won an Air Force contract to continue development of an engine that could be used in the upper stage of future launch vehicles.

Colorado-based Sierra Space received a $22.6 million contract from the Air Force Test Center July 25 to mature the design of its VR35K-A engine. The contract will allow continued work on the engine, such as development of “flight-weight engine component design,” according to a Defense Department procurement notice.

Sierra Space and, previously, Sierra Nevada Corporation, have been working on the VR35K-A engine design for several years with support from the Air Force Research Laboratory. That included completing a critical design review for the engine in August 2022.

The engine, using liquid hydrogen and liquid oxygen propellants, is designed to produce 35,000 pounds-force of thrust. In a statement to SpaceNews, Sierra Space said the engine achieved “high thrust efficiency” during recent tests at a company facility in Wisconsin.

“Compared with other upper-stage engines currently on the market, the VR35K-A provides more thrust and higher performance in a smaller package,” said Rusty Thomas, Sierra Space’s chief technology officer and vice president and general manager for the company’s Space Applications business sector.

The company has previously outlined several advantages of the engine design, including its use of a fuel-rich staged combustion cycle for increased specific impulse, a measure of engine efficiency. The engine also uses thrust chamber assembly design called VORTEX for increased pressure in a smaller volume.

“Once complete, the VR35K-A will allow our launch vehicle teammates and partners to deliver up to 30% more payload mass to orbit,” Thomas said. “It will drive technology across all propulsion products at Sierra Space, from our applications and destinations sectors to space transportation with our Dream Chaser spaceplane.”

Sierra Space has not disclosed any customers for the VR35K-A engine. While intended for use on launch vehicle upper stages, companies designing or operating large launch vehicles today are either developing their own engines or are buying engines from other suppliers, as United Launch Alliance is with the RL10 engine from Aerojet Rocketdyne used on its Atlas, Delta and Vulcan vehicles.

At an investor conference June 27, though, Tom Vice, chief executive of Sierra Space, said the company was examining long-term options for developing propulsion systems that would allow Dream Chaser to reach orbit without relying on other companies’ launch vehicles.

“We’re thinking about investigating the right technologies in thermal and propulsion and materials that allows us to potentially think about the staging options that would allow us, for the first time, have horizontal takeoff,” he said, but didn’t offer a schedule or other details about those plans.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...