Sierra Space Successfully Tests Advanced Throttling on Hypergolic Rocket Engine

Sierra Space has successfully tested its new VRM5500-H hypergolic rocket engine, which has the potential to revolutionize space propulsion systems. The engine operates on hydrazine fuel and MON3 oxidizer in a staged combustion cycle, delivering a vacuum specific impulse of over 339 seconds. What sets this engine apart is its ability to continuously throttle from a maximum of 5,500 lbf down to 900 lbf at 17% power, making it highly adaptable for various space missions.

Sierra Space CEO Tom Vice describes the engine as a “major leap” in space propulsion technology, offering efficiency, reusability, and versatility. Its design aligns well with in-space applications where reusability, storability, throttling, and weight-saving are crucial factors. This makes it an ideal choice for landers, upper stages, transit vehicles, and extended-duration missions.

© Sierra Space

One notable feature of the VRM5500-H engine is its use of hydrazine as fuel. This not only ensures high efficiency but also promotes commonality with spacecraft that use hydrazine monopropellant thrusters for attitude control and maneuvering. This strategic decision simplifies the overall propulsion system architecture, enhancing operational coherence and efficiency.

The development of this engine involved collaboration with Agile Space Industries, particularly in creating an innovative preburner that ensures high combustion efficiency and stability across the throttle range. Agile Space Industries’ CEO Chris Pearson highlights the achievement of designing, manufacturing, testing, iterating, and delivering a reliable preburner in just 19 weeks. This rapid development, especially of a high-flow hydrazine-rich preburner, demonstrates stable operation across a 6:1 throttle range with high combustion efficiency.

The VRM5500-H engine underwent rigorous testing at the US Army DEVCOM stand at Redstone Arsenal in Huntsville, Alabama. The testing confirmed its efficient and stable combustion at all throttle points, validating its performance claims. Sierra Space and Agile Space Industries were able to design, develop, and test the prototype engine in just over nine months, thanks to advanced design-to-test cycles and the use of additive manufacturing techniques. The thrust chamber and preburner were fully 3D printed on common metallic printers, showcasing Sierra Space’s commitment to innovating aerospace design and manufacturing technologies.

The successful testing of the VRM5500-H engine marks a significant advancement in space propulsion technology. Its high efficiency, versatility, and innovative design approach demonstrate Sierra Space’s commitment to pushing the boundaries of space exploration and travel. This development not only showcases the capabilities of Sierra Space and its partners but also sets a precedent for future advancements in space propulsion systems.