This video documents the design, construction, and static test fire of "Super 8," a 120-pound solid rocket motor intended for a future space shot. The narrative is driven by a critical manufacturing error that occurred during the propellant casting phase, resulting in several incompletely cured sections within the motor. The video details the entire fabrication process, including mixing the "Risky Batman" propellant formula, machining the aluminum case and multi-material nozzle, and spin-casting the protective internal liner. The central conflict arises from the discovery of the soft propellant, which posed a significant risk of catastrophic failure through over-pressurization or nozzle clogging. Despite these risks, the motor was test-fired, resulting in a successful 12-second burn that met performance goals. A detailed post-fire analysis of the cross-sectioned motor reveals how close the motor came to failure, yet ultimately validates the robustness of the design, concluding the propulsion development phase of the project.
Building and Firing a Flawed 120lb Rocket Motor
0:00:26 Propellant Formula: The motor uses 120 lbs of a custom propellant called "Risky Batman." It is an HTPB-based formula with aluminum powder as fuel and ammonium perchlorate as the oxidizer, designed for a slow, high-impulse burn suitable for a space shot.
0:03:47 Two-Day Mixing Process: Propellant production is intentionally split over two days. The first day involves mixing all components except the curative. This pause allows ammonia gas, a byproduct of the bonding agent's chemical reaction, to dissipate, preventing the formation of bubbles (voids) that would compromise the motor's performance.
0:05:05 Hardware Fabrication: Key components are custom-machined. This includes the 8-inch diameter 6061 aluminum case, the forward closure with its ignition system, and a multi-material nozzle combining an isomolded graphite throat (for temperature resistance), a phenolic midsection, and an aluminum carrier.
0:10:00 Liner and Casting Setup: A protective liner, called "mystery goo," is applied to the inside of the case using a custom-built spin-casting machine. The propellant is then cast into the motor in three separate 40 lb batches around a central mandrel that shapes the propellant's core.
0:13:26 The Critical Casting Error: A crucial mistake occurs during the casting of the propellant. The crane holding the mixing bowl could not tilt far enough, forcing the creator to scrape propellant from the sides of the bowl. This introduced small amounts of propellant that were not thoroughly mixed with the MDI curative.
0:16:22 Discovering the Flaw: After the propellant cured, the removal of the central mandrel revealed soft, gooey, uncured sections at the boundaries between the three casting batches. This defect creates a high risk of failure, as the uncured propellant could be ejected during the burn, increasing the burn surface area and chamber pressure to dangerous levels.
0:17:59 Decision to Fire: Despite the significant risk, simulations were run to model the flawed motor as three separate segments. The analysis suggested that the motor should remain within safe pressure limits. The decision was made to proceed with the test fire as the only way to gather real-world data.
0:20:39 Successful Test Fire: The "Super 8" motor is static fired and completes a successful and stable 12-second burn, achieving its primary objectives without catastrophic failure.
0:21:22 Performance Results: The motor delivered 112,000 Newton-seconds of total impulse with a peak thrust of almost 15 kilonewtons, meeting the performance requirements for the creator's space program.
0:21:40 Post-Fire Analysis: The motor case was cut into sections for detailed inspection. The analysis confirmed that the protective liner had burned away significantly more at the flawed boundaries—becoming "shockingly thin" in some spots—but ultimately held, preventing a burn-through. This successful test concludes the motor development phase of the project.