Sierra Space and Agile Space collaborate on the Largest Hydrazine Preburner for Space Travel

Agile Space Industries, a specialist in additive manufacturing, has designed, developed, manufactured, tested and delivered the AX19 experimental preburner for Sierra Space in 19 weeks.

This project is believed to set a public record as it may be the first development and application of a hydrazine-rich preburner in an engine. The first prototype demonstrated stable performance over a 6:1 throttle range with high combustion efficiency, highlighting Agile Space’s ability to develop new technologies in record time.

Large, efficient rocket engines, such as those used in larger spacecraft, require a power source to drive the pumps that convert the propellants from the low pressure tanks to the high pressure required for engine operation. The AX19 preburner facilitates this by combining all of the engine’s hydrazine propellant with a portion of the engine’s MON-3 oxidizer to break down hydrazine into primarily hydrogen, ammonia, nitrogen and water. This hot gas drives the engine’s high-pressure pumps.

Hydrazine is a mono-fuel that does not require any oxidizing agents for combustion. This is a challenge when designing a fuel-rich preburner, as partial combustion as in kerosene, methane or hydrogen engines is not possible. The AX19 was designed to use as little catalyst as possible while still maintaining stable combustion. First, a small portion of the hydrazine is decomposed in a catalyst reactor and then fed into the main combustion chamber of the pre-combustor as a hot mixture of ammonia, nitrogen and hydrogen. At the same time, the remaining liquid hydrazine is injected into the combustion chamber, where it burns completely together with the oxidizer.

The AX19 preburner was successfully tested as a stand-alone component in October 2022 in Durango, Colorado, on Agile’s Animas test rig. After the initial runs, it was handed over to Sierra Space for further testing and successfully operated both standalone and coupled to the full VRM-5500H engine in the first and second quarters of 2023. These tests covered the entire throttle range and confirmed the stable function of the preburner and the successful operation of the VRM5500-H engine.

This project demonstrates Agile Space’s potential and efficiency in developing breakthrough technologies in the space sector and underlines the importance of innovation in rocket engine technology.