WASHINGTON — The U.S. Air Force awarded Sierra Space a $16 million contract extension to further develop and test its VR35K-A upper stage rocket engine, the Colorado-based aerospace company announced Feb. 12. The extension follows the successful completion of the engine’s integrated test campaign and builds upon a previous $22.6 million contract awarded in July 2023 to mature the engine design.
Sierra Space’s VR35K-A, a liquid-propellant engine that generates 35,000 pounds-force (lbf) of thrust, is aimed at military and commercial launch applications. The Air Force Research Laboratory’s Rocket Propulsion Division at Edwards Air Force Base, California, is overseeing the project as part of ongoing efforts to advance upper stage propulsion capabilities.
The Air Force has been actively investing in next-generation upper stage engine technology for more than a decade. Beginning in 2010, the service conducted market research to identify additional sources for upper-stage propulsion systems. In 2016, it awarded a $33.6 million contract to SpaceX to develop a prototype of its Raptor engine for potential use on the upper stages of the Falcon 9 and Falcon Heavy launch vehicles. Around the same time, Sierra Space — formerly Sierra Nevada Corporation — began working with the Air Force to adapt its proprietary Vortex engine technology for upper-stage applications.
The recent test campaign for the VR35K-A engine was conducted at Sierra Space’s Badger Propulsion Test Facility in North Freedom, Wisconsin. Florida Turbine Technologies, a subsidiary of Kratos Defense & Security Solutions, collaborated on the program, providing key turbomachinery components for the engine’s development.
Sierra Space is positioning the VR35K-A for the launch market but also for in-space propulsion use, including spacecraft orbital maneuvering and lander descent systems. The company’s Dream Chaser spaceplane, designed to deliver cargo to the International Space Station and other destinations in low Earth orbit, uses Vortex-based reaction control system thrusters.
A Sierra Space spokesman said that the company is in discussions with multiple launch providers about potential applications of the VR35K-A engine.
