Sierra Space has successfully completed the test campaign for the company’s fully integrated VR35K-A upper stage engine, under contract with Air Force Research Laboratory’s (AFRL), Rocket Propulsion Division at Edwards Air Force Base in California, marking a major step forward in the development of the firm’s advanced propulsion systems.
In addition, the company has been awarded a $16 million, firm-fixed-price contract from AFRL to continue upper stage engine maturation to fulfill future National Security Space Launch (NSSL) missions. This is a follow-on to a $22 million plus contract awarded to Sierra Space in July of 2023 by the Air Force Test Center at Edwards Air Force Base in California.
The VR35K-A is a high-performance, liquid oxygen (LOX)/liquid hydrogen (LH2) engine that employs a fuel-rich staged combustion cycle, an innovative turbopump architecture and a VORTEX® combustion chamber to produce 35,000 lbf of thrust at a higher performance than any engine currently on the market. Sierra Space’s patented VORTEX technology enables efficient and stable combustion while providing active cooling for the combustion chamber, ensuring high performance and reliability.
Additional key attributes of the VR35K-A include:
- Simplified Operation: A single-shaft turbopump assembly for streamlined functionality, including start-up and shut-down
- Mechanically-Coupled Mixture Ratio Control: Ensuring precise fuel and oxidizer balance.
- Additive Manufacturing: Reducing production costs and lead times for complex components.
The engine underwent a rigorous test campaign in 2024 at Sierra Space’s Badger Propulsion Test Facility in North Freedom, Wisconsin, and achieved all objectives, including: stable, efficient thrust chamber operation, robust and efficient turbomachinery operation, mixture ratio control, throttle demonstration and high overall engine efficiency.
Sierra Space partnered with Florida Turbine Technologies, a subsidiary of Kratos Defense & Security Solutions, Inc., to develop and test the turbomachinery used in the VR35K-A engine. The single-shaft main turbopump assembly provides for simplified and reliable operation—including start-up and shutdown—and mechanically-coupled mixture ratio control. Prior to integrating the turbomachinery into the engine, Sierra Space completed a comprehensive turbomachinery standalone test campaign to validate operating points and predicted performance.
The VR35K-A engine will support larger payload delivery to LEO and beyond. Sierra Space is also applying its VORTEX combustion chamber technology to engines and thrusters to support in-space propulsion for spacecraft orbital maneuvering and extraterrestrial landers.
“This partnership with Sierra Space has been highly successful and represents a cornerstone of our long-term strategic initiatives,” said Stacey Rock, President of Kratos’ Turbine Technologies Division
