Sierra Space, a leading commercial space company building the first end-to-end business and technology platform in space, today announced it has been awarded a $22,605,083 firm-fixed-price contract for maturation of their Advanced Upper Stage Engine (VR35K-A). The company successfully completed a 100% hot fire test campaign of this new VORTEX engine this spring, marking a significant maturation milestone for the upper-stage engine that Sierra Space is developing in conjunction with the Air Force Research Laboratory.

According to the U.S. Department of Defense, this contract provides for “leveraging the test data from the first Phase III Small Business Innovation Research component and integrated breadboard engine test to develop flight-weight engine component designs.” The Air Force Test Center at Edwards Air Force Base in California awarded the sole-source acquisition contract.

The VR35K-A is a liquid oxygen (LOX)/liquid hydrogen (LH2) engine that produces 35,000 lbf of thrust. The engine achieved high thrust efficiency during recent testing at the company’s propulsion test facility outside of Baraboo, Wisc. VORTEX technology will serve a critical industry need for engines that can support in-space propulsion for spacecraft orbital maneuvering and extraterrestrial landers.

“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 Space Applications business sector. “Think of it like gas mileage – how much thrust can you get out of a given amount of propellant? Once complete, the VR35K-A will allow our launch vehicle teammates and partners to deliver up to 30% more payload mass to orbit. 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.”

The VR35K-A is rooted in Sierra Space’s patented VORTEX engine design technology, which promotes efficient, stable combustion while also cooling the combustion chamber. Key system attributes providing high performance and low recurring cost include innovative single-shaft turbopump assembly for simplified operation and mechanically-coupled mixture ratio control, fuel-rich staged combustion cycle to drive high chamber pressure and subsequent compactness, vortex main propellant injector to increase overall cooling capacity and heavy use of additive manufacturing to reduce production costs and schedule of complex parts.

In August 2022, Sierra Space announced the VR35K-A had passed its Critical Design Review, which allowed the company to advance into the hot fire testing campaign. Next, Sierra Space will continue to advance the VR35K-A engine by completing build of the flight-weight prototype engine to demonstrate capability and performance, and ultimately move into full engine qualification testing.