Sierra Space, one of the leading pureplay commercial space companies building the first end-to-end business and technology platform in space, announced that it successfully tested a new 5,500 lbf. hypergolic rocket engine that promises to become a groundbreaking addition to its engine portfolio.

Employing pure hydrazine fuel and MON3 oxidizer in a staged combustion cycle, the new engine delivers a vacuum-specific impulse of over 339 seconds, making it very efficient for a storable engine. In addition, the engine is designed for continuous throttling from 5,500 lbf of thrust at 100% power down to 900 lbf at 17% power, allowing for precise control and maneuverability.

“This high-performance, re-usable bipropellant engine represents a major leap in space propulsion technology, setting new standards for efficiency, reusability, and versatility,” said Tom Vice, CEO of Sierra Space. “This engine is tailored for in-space applications where reusability, storability, throttling, and vehicle weight-saving are paramount, making it an excellent choice for landers, upper stages, transit vehicles, and extended-duration missions.”

The use of hydrazine as fuel provides commonality for spacecraft using hydrazine monopropellant thrusters for attitude control and maneuvering, thus simplifying overall propulsion system architecture.

The engine employs a highly innovative preburner – along with unique thrust chamber cooling – to provide high combustion efficiency and stability across the throttle range. Designed and developed by Agile Space Industries, the preburner underwent multiple hot-fire demonstrations in a standalone configuration prior to integration with the rest of the engine.

“In a timeline of 19 weeks, Agile was able to design, manufacture, test, iterate and deliver a reliable preburner,” said Agile Space Industries CEO Chris Pearson. “The timeline was extremely fast, especially given that this is the first time that we have been able to find, in the public record, that a high-flow hydrazine-rich preburner has been developed and used in an engine.  The initial prototype demonstrated stable operation across a 6:1 throttle range with high combustion efficiency.”

Following preburner development, the new VRM5500-H engine was tested at the US Army DEVCOM stand at Redstone Arsenal in Huntsville, Alabama. The engine exhibited efficient, stable combustion at all throttle points, with a minimum throttle ISP exceeding 339 seconds.

The teams at Sierra Space and Agile Space Industries executed the design, development, and testing of the prototype engine in just over nine months by employing rapid design-to-test cycles and heavy use of advanced additive manufacturing techniques to minimize fabrication time. The thrust chamber and preburner are fully 3D printed on common metallic printers, demonstrating Sierra Space’s commitment to pushing the boundaries of design and manufacturing technologies in the aerospace industry.

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