Rithvik Nagarajan
(Advisor: Prof. Lightsey)
will propose a master’s thesis entitled,
Numerical Studies on the Determination and Prevention of Roll Resonance in Liquid Sounding Rockets
On
Thursday, February 1 at 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 a 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 well- known 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
•                    f Aerospace Engineering