The ideal group of people to review this topic would be Senior Avionics and Flight Dynamics Engineers.
Abstract
This analysis details the rapid fabrication and subsequent failure of the "Machua" high-power rocket, designed to achieve Mach 2 and test advanced avionics systems. The project focused on resolving chronic telemetry and Global Navigation Satellite System (GNSS) reliability issues through rigorous antenna testing using a Vector Network Analyzer (VNA), confirming that performance degradation stemmed primarily from poorly tuned, commercially supplied antennas. The custom AVA flight computer, utilizing a Kalman filter for state estimation, was responsible for roll control via an asymmetrical trim tab and parachute deployment. The flight abruptly terminated prematurely at Mach 1.3 following the detection of a false apogee condition. Root Cause Analysis identified a critical, rushed software logic error (a misplaced conditional check within the Kalman filter update loop) that permitted descent-specific, low-fidelity barometric speed data to corrupt the high-speed velocity estimate during boost, resulting in the erroneous zero-velocity trigger for pyro deployment.
Analysis of the Machua Rocket Flight and Failure
0:00 Project Overview and Design Constraints: The "Machua" rocket was conceived as a 4-day accelerated build utilizing spare components, targeting a Mach 2 flight profile with an L1000 motor. Primary objectives included testing new roll control mechanisms, a novel GPS chip, and resolving long-standing telemetry failures.
1:05 Structural and Control Systems: Fins were 3D-printed with 100% infill for strength and incorporated an asymmetrical trailing edge tab controlled by a single servo for roll stabilization.
3:08 Asymmetrical Control Justification: The use of a single roll tab was justified by the significant difference in mass moment of inertia (MOI) between the pitch and roll axes; pitch MOI was calculated to be over 400 times greater than roll MOI, rendering the asymmetric pitch coupling negligible during rolling maneuvers.
5:26 Diameter Classification: The structural approach involved attaching fins directly to the motor case, which was philosophically argued to represent "True Minimum Diameter," though the addition of a forward airframe section (7:56) created a hybrid structure.
11:55 RF System Reliability Investigation: Chronic telemetry and GPS inconsistencies were investigated using a VNA. Analysis demonstrated that off-the-shelf antennas exhibited poor tuning, with Standing Wave Ratios (SWR) reaching 1.6:1 to 2.5:1 at the 915 MHz operating frequency, confirming component quality was the root cause of prior RF failures.
15:04 Antenna Performance Baseline: A well-tuned antenna demonstrated an SWR of 1.073:1 at 915 MHz, indicating minimal reflected power and an ideal impedance match, which informed the component selection for Machua.
18:48 Pre-Flight Systems Check: Ground testing confirmed unprecedented telemetry and GPS performance, with the AVA flight computer acquiring 13-21 satellites and achieving sub-meter accuracy with zero packet loss prior to launch.
20:32 Flight Failure Event: The rocket experienced a catastrophic failure shortly after ignition, with the parachute deployment charge firing prematurely while the vehicle was under high thrust and still ascending.
24:49 Flight Dynamics and Error Condition: Post-flight data confirmed deployment occurred at an estimated velocity of 450 m/s (approximately Mach 1.3). The event was triggered because the AVA flight computer's Apogee detection logic registered the velocity estimate crossing below zero.
25:30 Root Cause Analysis (Software Logic Error): The primary cause was traced to a logical error in the AVA flight code written in the days leading up to launch.
27:27 Kalman Filter Corruption: A rushed if-else structure intended to enable descent speed measurements from the barometer was incorrectly gated. When the rocket velocity exceeded Mach 1, a conditional statement failed, allowing low-fidelity, slow-interval barometric speed estimates (effectively zero velocity during boost) to be incorporated into the high-fidelity Kalman filter, artificially flattening and then forcing the velocity estimate negative.
28:46 Conclusion of Failure: The incident highlights the danger of injecting untested, low-trust sensor data (barometric speed updates) into a critical state estimator (Kalman filter) under high dynamic conditions (boost phase) when code logic fails to maintain proper sensor gating.
29:23 Component Recovery: Both the upper avionics section and the booster were recovered, though the upper section sustained damage from the high-speed impact (estimated 24 m/s impact velocity). The parachute sailed away separately.