Optical Diagnostics of the BOLT-1B Flight Experiment

The Bolt-1b flight experiment launched in September 2024 from the Andoya Space Centre, Norway. A team from UniSQ recorded optical tracking data of the engine burn phase from two ground stations located approximately 2 km from the launchpad, as well as spectral images from a closer station. This work presents a methodology for launch vehicle optical trajectory reconstruction, and compares results to the best estimated trajectory (BET) informed by on-board sensors. Optical tracking measurements are processed using an Unscented Kalman Filter (UKF), Rauch-Tung-Striebel (RTS) smoother, and maximum a posteriori (MAP) parameter estimation. This algorithm was implemented using the JAX library, which enabled direct evaluation of filter likelihood derivatives using its automatic differentiation capability. Gimbal orientation and camera misalignment errors were the dominant source of measurement error, and were corrected by estimating a series of small SO(3) rotation alignment parameters. Velocity of the reconstructed trajectory is within 2% of the BET value during dual-station tracking, and differences are within expected uncertainty bounds. Key features of the acceleration profile were reconstructed; however, higher frequency vehicle dynamics in the initial seconds of flight were not resolved. Despite some limitations to measurement accuracy in the current work, results demonstrate that portable optical tracking equipment can complement on-board sensors, and provide redundancy when the performance of these systems is not guaranteed. Processed spectral measurements from an imaging spectrograph and novel differential spectrometer are also presented. These spectral results include narrowband peaks in plume composition as well as continuum emissions at the nozzle. The campaign provided insights into the planning and execution of in situ optical diagnostic campaigns, and the effectiveness of a variety of instruments, which are discussed.