Master's Thesis Proposal

Rithvik Nagarajan

(Advisor: Prof. Lightsey)

"Numerical Studies on the Determination and Prevention of Roll Resonance in
Liquid Sounding Rockets"

Thursday, February 1 

11:00 a.m.

Weber Space and Technology Building 304

Abstract

Sounding rockets are suborbital vehicles designed to carry scientific payloads and perform experiments in the upper atmosphere. Recently, there has been a focus on reusable liquid sounding rockets to allow faster launch rates and lower costs per mission. Fin-stabilized sounding rockets tend to be designed with high length-to-diameter ratios for drag optimization. This leads to a susceptibility in roll-yaw resonance, where the vehicle spins close to the pitch natural frequency. Previous studies have shown the vehicle can exhibit abnormal rolling and yawing motion beyond predictions by linear theory. These phenomena are referred to as roll lock-in and catastrophic yaw respectively. These effects can destabilize the rocket and induce high structural loads.

This research investigates the susceptibility and consequences of roll lock-in and catastrophic yaw on liquid sounding rocket designs using a comprehensive 6DOF numerical model. Non-linear combustion, vehicle aeroelasticity, configurational asymmetries, and non-linear aerodynamics are incorporated into this model with Monte Carlo variables. Previous off-nominal Georgia Tech sounding rockets are studied with respect to roll resonance to validate this model. This numerical approach is used to validate a wellknown space-shot sounding rocket design and assess mission failure likelihood. The findings reveal a high susceptibility to roll resonance, prompting the proposal of a roll control scheme that takes advantage of liquid rocket pressurized gas. Four attitude control thrusters are fired in pairs, implementing a bang-bang roll control scheme tailored for liquid sounding rockets with elevated roll resonance risk. This research analyzes the effectiveness of the control system in mitigating roll resonance issues.

Committee

• Prof. Glenn Lightsey – School of Aerospace Engineering (advisor)
• Prof. Jonathan Rogers – School of Aerospace Engineering
• Prof. Jonnalagadda Prasad – School of Aerospace Engineering