Firebiter

On Nov 13th 2022, Firebiter, an 6-inch diameter, 64-inch long P-class solid rocket motor, was successfully fired, becoming the team’s first successful static fire since Spring 2019. The motor delivered a total impulse of 15,674 lbf-s, producing a maximum thrust of 1632 lbs. Firebiter was fired in a carbon-epoxy motorcase with a carbon-phenolic nozzle, all of which were designed and fabricated by USC students.

The purpose of this static fire was to certify a motor for use on Fireball, our upcoming 6” high-performance flight vehicle. The design of Firebiter began in September 2022, we started by designing the overall grain geometry and nozzle geometry by utilizing our proprietary motor simulation. After the design was completed the engineering leads compiled a comprehensive design review detailing both the design and planned manufacturing process. This design review was presented to both current members and lab alumni, and after considering all aspects of the design the team agreed to move forward with manufacturing.

The first component to be produced was the carbon-fiber filament wound case which is essential to containing the extreme internal pressure of the burning solid propellant. The design of the case was determined by our analysis team, using in-house developed scripts to analytically calculate the optimal wind angles and overall laminate design. After handing this design off to the composites team the winding could begin!

After hours of meticulous winding the case was placed in an oven in order to cure the epoxy. After curing overnight, the case was ready to be removed from the oven and taken off its mandrel, and the composites team were eager to inspect this first case of the year. Unfortunately, during inspection of the inside of the case a flaw was found, the part of the case responsible for sealing against the bulkheads had chipped. The cause of the defect was quickly determined to be a minor manufacturing oversight, and we were confident a new case wouldn’t have this same issue. However, a new case layup would be a formidable task, it takes nearly two full days to complete the entire process, and the composites team has to constantly supervise in order to ensure the layup is proceeding without error. So following the discovery of this defect a discussion was organized to talk about possible solutions/repairs to the chipping. Although, after careful consideration of possible solutions we came to the conclusion that any solution at this point would introduce unquantifiable risk of the seals failing, which would certainly result in the destruction of the case and the failure of the static fire. So we concluded that doing a whole new case layup would be the best course of action.

A few weeks later the new case layup began and with cautious optimism we hoped this case would turnout well. The winding began and we patiently watched as layer by layer the case began to take shape. Once the winding was complete, once again the case was placed in the oven and cured overnight. This time when the case was removed, we took it off it’s mandrel and we saw that the sealing surface was pristine, and the case looked amazing (pictured below).

The nozzle was the next component to be completed. The process began with our machining team creating the mold onto which the nozzle would be formed. The composites team then intricately wrapped layers of carbon phenolic in order to form the nozzle. After the wrapping was complete the nozzle was cured. Pictured below is the nozzle after it was finished curing and ready to be removed from its mold. Once the nozzle was demolded, it was handed to the machining team for final machining and completion.

The propellent grains were the next to be produced. RPL sets itself apart from other collegiate organizations in the fact that we cast our own solid propellant. To cast the grains the propulsion team has to travel out to a specialized off-site facility where we ultimately mix, cast, cure and then finally integrate said grains into the motor case.

For Firebiter the casting trips didn’t come without some difficulties, during one casting session an unforeseen lightning storm appeared in the skies, this presented a danger to the mixing operations and therefore was halted for the day and all personnel went home. Regrettably this meant all the propellent mixed that day was scraped. Despite this unfortunate complication the propulsion team bounced back and resumed production and before long all the grains were cast and ready to be integrated into the motor. Most excitingly the propulsion team had worked out a new process and formulation which allowed for the propellant to be easily pourable, a feat which had been in the works for the past few years but had been elusive till now. This pourable quality enabled the propellant to be packed more efficiently, and thus the propellant density was significantly increased.

When all parts were ready for final assembly, we drove out to the Reaction Research Society’s Mojave Test Area (MTA). Once at MTA we unpacked our trailer, and began our integration process.

Once the motor was fully-integrated on the pad and we got the all-clear from the on-site pyro-technician to proceed with the static fire. We retreated to the bunker with nervous anticipation. Standing in the bunker the Earthshaker static fire series loomed heavy in all our minds, the three consecutives failures of ESI, ESII, and ESIII gave discouraging prospects for this static fire but we all hoped Firebiter would break the streak. Once all respective leads had given the ‘GO’ for firing we readied ourselves.

The countdown began.…Three…Two…One…IGNITION

The motor erupted into a fury of fire and smoke. Everyone was captivated as the motor burned, and we watched with baited breath for whether it would end in a fiery explosion or successfully complete the burn.

Before long the raging exhaust yielded and the smoke cleared.

IT WORKED!

The bunker erupted into a frenzy of cheers and excitement. The success of this static fire was the culmination of months of hard work, and marked the end of a discouraging chain of failures.

Armed with this success we are moving forward with Fireball, our upcoming 6” flight vehicle. Look out for more information on Fireball in the upcoming months as we hope to launch in the coming spring.