Overview and Purpose

Luna was a 50 lbf thrust static hybrid rocket engine operated from 2017 to 2021, firing for a total of 149 seconds over 20 test attempts. It was retired in November, 2021, to be replaced by the Proxima engine. It was Eclipse’s third Hybrid engine, following the Mk I and Titan I, respectively.

After a series of anomalies with the Mark I engine, the team decided in Fall 2017 to create a more stable and versatile testing platform, which became the Luna hybrid rocket engine. The most dramatic change from the Mark I was that Luna was mounted vertically in its test stand.

Luna was used as an education and testing platform for multiple aerospace design components, such as fuel grain composition, injector plate design, nozzle design, thrust vector control (TVC), and more. Optimizing these components allowed the team to conduct research and learn more about hybrid engine design and operation. To that end, the purpose of the project was not to be used for competition, but rather for obtaining knowledge about hybrid rocketry and further researching the theory behind hybrid engines. Experimental data and institutional knowledge gained by operating the Luna testing program played an invaluable role in informing the team’s decisions when developing the Titan II engine.

Design Components

Luna was designed to be 222 N (50 lb) thrust engine with a maximum burn time of 10s. The engine was a hybrid utilizing solid HTPB (Hydroxyl-terminated Polybutadiene) and liquid nitrous oxide. After igniting the HTPB grain in the combustion chamber, a valve would actuate, enabling self pressurizing nitrous oxide in the oxidizer tank to flow through a length of plumbing, past a pressure transducer to a bulkhead. The bulkhead housed the injector plate and was secured to the combustion chamber by bolted flanges that extended from the outer diameter of the bulkhead. The combustion chamber included an ablative cardboard liner to aid in thermal management. The nozzle at the end of the combustion chamber included a primarily aluminum body with a graphite insert covering the length of the converging and diverging ends of the nozzle. The nozzle bolted directly to the combustion chamber using identical flanges as the bulkhead. The nozzle was not secured directly to the test stand to allow for measurement of lateral force and to allow the combustion chamber to expand freely throughout the burn. The bulkhead was mounted directly to the test stand structure. The commercial nitrous supply and run tank was kept secured inside of a wooden box away from the engine to protect it against a potential anomaly.

The Test Stand

The purpose of the test stand was to provide a stable platform to test and record data from firing Luna. This data included axial thrust measurements from the main engine burn as well as radial thrust measurements from the engine's nitrogen-injection thrust vector control system. The test stand supported the weight of the engine and restrained its thrust to preserve safety and provide accurate thrust measurement during testing.

Testing

Luna was tested twenty times between December 2017 and November 2021. The engine suffered two catastrophic anomalies, in February 2020 and April 2021, for separate reasons. Analyzing the causes of these critical anomalies proved difficult as it became obvious that, since Luna’s design heritage dated back to the earliest days of the club, it was simply not robust, precise, or reliable enough to produce data that was useful enough to be worth the time and energy required to operate its testing program. For these reasons, Luna was officially retired following a scrubbed hot fire in November 2021. The Luna team then kicked off development of Luna’s successor, Proxima.

Luna saw the team’s knowledge of hybrid engines grow exponentially over its four year operation lifespan. It allowed the team to freely experiment with new concepts and ideas without risking our flagship engines, provided up-close and hands-on education in rocket propulsion to members both new and old, and taught the team how to operate a rocket engine’s hot fire campaign safely and efficiently.