U.S. Government Awards Contract to Sierra Space to Develop Powerful New Upper-Stage Rocket Engine

Sierra Space VR35K-A Hot fire

Company’s VORTEX® VR35K-A successfully completes full hot fire test testing, engine provides up to 30% more payload to orbit performance

LOUISVILLE, Colo. – July 26, 2023 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.


About Sierra Space

Sierra Space (www.sierraspace.com) is a leading, pure play commercial space company at the forefront of innovation and the commercialization of space in the Orbital Age®, building an end-to-end business and technology platform in space to benefit life on Earth. With more than 30 years and 500 missions of space flight heritage, the company is enabling the future of space transportation with Dream Chaser®, the world’s only commercial spaceplane, and is bringing LIFE® (Large Integrated Flexible Environment) to low-Earth orbit with its modular, three-story commercial habitation and science platform. Both Dream Chaser and LIFE are central components to Orbital Reef, a mixed-use business park in LEO being developed by principal partners Sierra Space and Blue Origin, which is expected to be operational by the end of the decade. Sierra Space also builds and delivers a host of systems and subsystems across solar power, mechanics and motion control, environmental control, life support, propulsion and thermal control, offering myriad space-as-a-service solutions for the new space economy.





Alex Walker
Sierra Space
(303) 803-2297

Lauren Quesada
Griffin Communications Group
(281) 744-7938


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