SKA RFS sounding rocket flight dynamics model validation based on flight data
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: FLIGHT DYNAMICS
GNC
AVIONICS
SIMULATIONS
VALIDATIONS

description: Sounding rocket flight simulation is an important aspect of the design process and pre-flight preparations. In the former case, it allows for estimating the rockets performance, its apogee, velocity and acceleration profiles, and in the latter, it is crucial to determine the launch safety by estimating the rockets trajectory and impact point and velocity. In both cases, an accurate mathematical and physical model of the rocket and the environment is required in order to precisely predict the rockets trajectory and behavior in flight. 
Every software tool used for the purpose of flight simulation requires verification and validation. Verification is a process of checking whether the prepared models were applied correctly, and validation is used to determine if the models themselves are correct. It is a process of determining whether and how accurately applied models represent reality. In order to do so, there is a need to establish metrics or thresholds for when to agree on the correctness of the model.
This paper will focus on the validation of the physical models implemented within the SKA Rocket Flight Simulation (SKA RFS) software, developed by the Rocketry Division of the Students Space Association at the Warsaw University of Technology since 2018. The validation will be based on the flight data from the sounding rockets developed by the Association. Each rocket is equipped with inertial and satellite sensors, which provide, via integration methods, information about the rockets state in flight in terms of position, orientation, velocity and acceleration. The collected information is transmitted as telemetry data during the flight and saved to the on-board computers memory for further post-processing.
SKA RFS is a 6DOF flight simulation tool able to simulate multi-staged rockets, equipped with multiple engines, multiple parachutes, and aerodynamic control systems. The software is entirely written in the MATLAB environment. It includes the models of steady and unsteady aerodynamics, including the possibility of using lookup tables to store data obtained from CFD calculations or aerodynamic tunnel measurements in the form of aerodynamic coefficients. The software also includes the International Standard Atmosphere model with altitude-variable wind and accounting for the local atmospheric conditions near the launchpad. The models of inertial sensors, servomotors and the on-board computer are also included. The dynamic model of the rocket used within the software also handles the variable inertial properties of the rockets. Dynamic equations of motion are solved with the assumption of the oblate and rotating Earth using the WGS-84 Earth model.
The flight data, gathered using on-board inertial, barometric and GNSS sensors, will be post-processed and then used to validate the software in terms of the accuracy of predicted accelerations, velocities and altitude profiles, as well as the rockets position and orientation.