THE UNIVERSITY OF QUEENSLAND Bachelor of Engineering Thesis Analysis of Aerodynamic Loading on a Rocket and Design Student Name: Adam YARROW Course Code: MECH4500 Supervisor: Mr Sholto Forbes-Spyratos Submission date: 27 October 2017 A thesis submitted in partial fulfilment of the requirements of the Bachelor of Engineering degree in Mechanical and Aerospace Engineering. UQ Engineering Faculty of Engineering, Architecture and Information Technology Abstract The University of Queensland’s Centre for Hypersonics are investigating the viability of a reusable three-stage, rocket-scramjet-rocket based access to space system, aimed at reducing the cost to orbit for small satellites (Preller & Smart, 2015). The final stage of this system is a conventional liquid fuelled rocket, designed to carry the satellite into its final orbit after being released from the second stage scramjet (Preller & Smart, 2015). Previously, the third stage vehicle was designed for exo-atmospheric operations, but new trajectories place the separation point well within the atmosphere, exposing the vehicle to high dynamic pressures (up to 50 kPa), at large angles of attack (10 degrees) (Forbes-Spyratos, Kearney, Smart, & Jahn, 2017; Preller & Smart, 2015). The large angle of attack on the vehicle resulted in lift dominating the aerodynamic forces, as opposed to in a conventional rocket where drag dominates. As such, it was hypothesised that conventional rocket design literature may not be applicable for the design of the third stage vehicle (Benson, 2014). The purpose of this thesis was to evaluate this hypothesis, to determine if rocket based design and optimisation literature could be adapted to a lift dominated, rocket like structure, in particular, the third stage vehicle. Phase One of this thesis involved reviewing available rocket design and optimisation literature and adapting it to develop a parametric CAD model of the third stage vehicle. The CAD model consisted of two main assemblies, an external aeroshell and the internal structure. Due to the atmospheric release point of the vehicle, the protective aeroshell needed to resist all aerodynamic loads, making it a critical component of the current design which needed to be validated. Phase Two then involved undertaking finite element analysis on the third stage to evaluate the applicability of using conventional rocket optimisation literature in the design of the third stage vehicle. To achieve this goal, static and buckling simulations of the third stage aeroshell were undertaken in ANSYS for freestream dynamic pressures ranging from 30 to 50 kPa (to simulate different release altitudes). For the dynamic pressures tested the aeroshell was statically 3.6 to 6.0 times stronger than necessary. Buckling was also not a critical failure mode. It was concluded that the restrictions imposed on the stringer and backing thicknesses of the aeroshell, due to the literature optimisation techniques implemented, resulted in the vehicle being heavily overdesigned for the applied loads. This suggested that the adaption of conventional rocket optimisation methods for the vehicle in this thesis was not the most effective method to optimise the load bearing structure. The final optimised configuration of the aeroshell weighed 281 kg, but to further reduce the safety factors and vehicle mass, evidence suggested that the backing and stringer thicknesses of the third stage vehicle needed to be reduced. i Acknowledgements I would first like to acknowledge Mr Sholto Forbes for his guidance and direction whilst supervising me throughout this thesis. Without his support, help and data provided this project would likely have not been completed. My parents, for their encouragement, support and patience not only through this thesis, but also the past four years of my degree – I could not have got through this without you. My brother, thank you for your help dealing with the intricacies of Creo and putting up with my frequent moods, it was greatly appreciated. I would also like to thank all my friends from UQ Engineering, without you, we would never have made it through, your advice, jokes and support will forever be appreciated. I would also like to acknowledge Dr Juan Torres and Dr Bill Daniel for their help debugging my ANSYS model. Finally, I would like to thank my grandparents and Allan, for their interest and encouragement throughout my degree. ii Table of Contents Abstract ........................................................................................................................................ i List of Figures ............................................................................................................................. 1 List of Tables .............................................................................................................................. 5 List of Acronyms, Symbols and Definitions .............................................................................. 7 1 Introduction ........................................................................................................................ 9 1.1 Objectives .................................................................................................................. 11 1.1.1 Phase 1: Initial Structural Design ....................................................................... 11 1.1.2 Phase 2: Analysis of the Structural Design Subject to Aerodynamic Loading .. 11 1.2 Scope .......................................................................................................................... 12 1.3 Methodology .............................................................................................................. 13 1.4 Chapter Overview ...................................................................................................... 14 2 Literature Review ............................................................................................................. 16 2.1 Introduction ................................................................................................................ 16 2.2 SPARTAN Launch System ....................................................................................... 16 2.3 Similar Launch Systems ............................................................................................ 18 2.4 Spacecraft Loading .................................................................................................... 22 2.4.1 Loads .................................................................................................................. 22 2.4.2 Failure Modes ..................................................................................................... 24 2.4.3 Safety Factors ..................................................................................................... 25 2.5 Spacecraft Structural Elements .................................................................................. 27 2.5.1 Payload Fairings ................................................................................................. 27 2.5.2 Payload Adaptors ................................................................................................ 31 2.5.3 Propellant Tanks ................................................................................................. 34 2.6 Stiffening Structures .................................................................................................. 37 2.6.1 Overview of Potential Structures ........................................................................ 37 2.6.2 Design and Optimisation of Isogrid Structures .................................................. 42 2.6.3 Design and Optimisation of Stringer Stiffened Structures ................................. 46 iii 2.7 Thrust Structures ....................................................................................................... 51 2.8 Spacecraft Materials .................................................................................................. 54 2.8.1 Commonly Used Materials and Applications .................................................... 54 2.8.2 Materials Summary ............................................................................................ 59 3 Structural Design of the Third Stage Vehicle .................................................................. 62 3.1 Design Overview ....................................................................................................... 62 3.2 General Assumptions and Requirements .................................................................. 63 3.3 Aeroshell ................................................................................................................... 64 3.3.1 Cylinder .............................................................................................................. 66 3.3.2 Nose Cone .......................................................................................................... 74 3.3.3 Attachment Points .............................................................................................. 84 3.3.4 Flanges ............................................................................................................... 87 3.4 Internal Structure ....................................................................................................... 88 3.4.1 Payload Adaptor ................................................................................................. 89 3.4.2 Thrust Structure.................................................................................................