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Trepid Phase II Completed with First Successful Test Fire of Homemade High Power Motor

 

 

Meet the Propulsion Group, better known as Project Trepid, the newest and most intense addition to the LetSpace team. Trepid is, quite literally, our hottest and most explosive project to date. From the beginning, LetSpace has set its sights on designing, building, and launching a space-shot rocket capable of crossing the Karman line, 62 miles above sea level. While this goal was initially approached using commercial motors, it quickly became clear that a mission of this scale would demand a custom propulsion solution. That realization sparked the creation of Project Trepid.

 

To tackle this challenge, the project was structured into three phases. Phase I focused on designing and validating a low-power motor. Phase II advanced that work with the development of a high-power motor capable of producing reliable, repeatable thrust. Phase III will refine this design further and culminate in testing the motor during a full rocket launch.

 

This week marked a major milestone with the successful completion of Phase II. After months of design iteration and problem-solving, a J-class motor was successfully test-fired, with thrust data captured using the ARIES data logging system. This achievement represents a critical step toward fully custom propulsion and brings LetSpace one step closer to reaching the Karman line. More details on the motor design and testing are provided below.

 

                                         

Above: Image of Test Stand with Spent Motor After Test Fire

 

About the Motor:

 

The Trepid motors are composed of a mixture of Potassium Nitrate and Sorbitol, otherwise known as KNSB. These two chemicals are mixed at a ratio of about 65:35 to produce ideal burn rate characteristics (many thanks to Richard Nakka for providing us with much of the necessary background information to make this motor possible). After creating a proof-of-concept motor to determine if we could make this propellant ourselves, we scaled up by designing a J-class motor for real flight use. This also involved creation of a motor casing that could withstand rigorous testing and sudden pressure increases should one of the grains overpressurize. Recently, the avionics team has designed the ARIES system (see below) to measure and record data during these test fires. 

 

While design and casting of the motor had minimal obstacles, there was one major obstruction that prevented consistent ignition: humidity. Letourneau, and therefore LetSpace, is situated in east Texas, where humidity levels remain consistently around 80% during the day (increasing at night). KNSB motors are practical in many ways, but they also tend to be one of the most hygroscopic propellants. As a result, many of the intial test fires were unsuccessful simply because the motor would not ignite after being exposed to open air for more than five minutes. To overcome this challenge, a unique two-stage ignition system was created. Powdered KNSB mixed with black powder was placed in a thin tissue and wrapped tightly around the head of the igniter, then inserted into the motor. This created a longer spark, providing more time for the motor to potentially ignite. There are many commercial igniters that are also designed to provide a longer spark, but these have not yet been tested. Once implemented, this new system has been shown to light motors consistently, even in the high humidity of east Texas. 

 

About ARIES:

 

ARIES (Advanced Remote Ignition and Evaluation System) is the computer system designed to record data during static test fires of experimental motors. This was created to replace the previous Compact Remote Ignition System (CRIS), which had been destroyed in a testing incident. CRIS, though useful for ignition, did not have a means of logging data during a static test fire, so ARIES was also created to accomodate this need. 

 

 

Above: PCB Layout for ARIES System