Thesis (Ph. D.)

Title: Attitude Control of a Remote Sensing Satellite in Underactuated Conditions

Abstract:
Underactuation poses a significant challenge to space mission control and performance. This dissertation investigates the non-linear attitude tracking control problem for a remote sensing satellite underactuated by a reaction wheel (RW) actuator fault. First, the fault detection and diagnosis strategy is based on the sliding mode and adaptive sliding mode observers in a finite-time decision window. The failed actuator is excluded from the control loop by forming the proposed reconfiguration window to transition from a 3 RWs configuration to 2 RWs. The underactuation fault-tolerant control is designed according to the active method, where the adaptive robust control law employed for the fault-free conditions is switched to the underactuated attitude tracking control. The structure of underactuated attitude tracking control is based on kinematic and adaptive backstepping dynamic controllers. The effect of unknown bounded external disturbances is considered with an adaptive estimation term. The asymptotic stability of the closed-loop control system is proved via Lyapunov theory in the presence of parametric uncertainty. Due to the underactuation, a new approach proposed in the prescribed performance function is interval error constraints, which include the pointing accuracy and stability requirements in imaging time intervals. System performance is presented for two actuator fault scenarios in a snapshot imaging mode to understand this case clearly. Numerical simulations confirm the satisfactory performance of the proposed strategy that underactuated case is diagnosed by injecting stuck and idle faults around 2.19 and 3.52 s. Furthermore, the results of the present work are validated using an air-bearing experimental test bed to illustrate a more realistic behavior of an underactuated satellite. The results confirm the applicability of the underactuation fault-tolerant control.

Publication:
1- Attitude path design and adaptive robust tracking control of a remote sensing satellite in various imaging modes, Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, Sage., Jan 2023.
2- Designing an adaptive robust observer for underactuation fault diagnosis of a remote sensing satellite, International Journal of Adaptive Control and Signal Processing, Wiley., Jul 2023.

Title: New Algorithm for GEO Communication Satellite Conceptual Design

Abstract:
This thesis describes a new methodlogy design approach for GEO geostationary communication satellite. This method has been developed to reduce the prohibitive cost and time of their conceptual design phase. The proposed method effectively conducts the design of GEO communication satellite lying in the range of 1–7 thousand kilograms. The main feature of the new methodlogy is to determine the design information of the conceptual design of satellite with both high performance time and acceptable accuracy. Using this method, one can readily extract the characteristics of structure, attitude determination and control, command and data handling, electrical power, and other subsystems of a satellite. The new method exploits a statistical design model (SDM) in the first instance to yield a rough estimation of the satellite, i.e., a rapid extraction of the budgets for mass, power, dimensions the satellite subsystems and its cost. Then, using the parametric design model (PDM) approach, it performs subsystems design more accurately and ascertains the components specifications of each subsystem in terms of a catalog of products with the corresponding manufacturers. A database of 382 GEO communication satellites launched from 2000 to 2017 has been used in this thesis to implement the SDM approach. This method developed in the Labview & Matlab & Exel software is capable of contributing to satellite design phases as a connection to the hardware simulators of different subsystems. Herein, after describing the general ideas utilized in the satellite design, we have introduced various relationships and parts of the methodlogy. The accuracy of new method was amply verified through a flight prototype, indicating the average error of 16.7% in the obtained results.

Publication:
1- FADSat: A system engineering tool for the conceptual design of GEO satellites platform, Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, May 2018.
2- An Effective Approach to Identify the Mass Properties of a Satellite Attitude Dynamics Simulator, Australian Journal of Mechanical Engineering, April 2018.
3- A software for establishing technical specifications of GEO communication satellites, Journal of Space Science and Technology (JSST), September 2017.
4- Statistical Design Model (SDM) of satellite thermal control subsystem,42st COSPAR Scientific Assembly Conference, Korea, September 2017.
5- Statistical design model (SDM) of communication satellites, 2015 7th International Conference on Recent Advances in Space Technologies (RAST), Turkey/Istanbul, January 2015.

6- Statistical Design Model (SDM) of power supply and communication subsystem’s Satellite,40st COSPAR Scientific Assembly Conference, Russia, August 2014.
7- Statistical design model and telecommunication satellites subsystems, 2013 6th International Conference on Recent Advances in Space Technologies (RAST), Turkey/Istanbul, January 2013.
8- Statistical model of power supply subsystem Satellite, 2013 6th International Conference on Recent Advances in Space Technologies (RAST), Turkey/Istanbul, January 2013.

Title: Under-Actuated Spacecraft Fault Tolerant Attitude Control Design and Its
Implementation on the Spacecraft Simulator

Abstract:
The presented dissertation employs a novel control method for the spacecraft de-tumbling mode. This mode is associated with under-actuated spacecrafts which tumble because of unknown events. The control method contains two stages: de-tumbling and pointing. In the detumbling stage, the spacecraft angular velocity and attitude error decrease by a quaternion
feedback regulator (QFR) to pre-defined lower bounds. The QFR control input is determined by the invers kinematics of the nominal model and Lyapunov stability theory. In the next stage, fine pointing is achieved by the tube-based model predictive controller (TMPC) and the attitude steers to the arbitrarily small neighborhood of the origin. According to the proposed TMPC methodology, at the first step, a reference attitude trajectory is determined by considering the terminal constraints, control input saturation and uncertainties. Next, an ancillary nonlinear model predictive controller maintains the attitude in the small neighborhood of the reference attitude trajectory. Furthermore, according to the under-actuated control procedure, linear matrix inequality (LMI) and generalized likelihood ratio (GLR) as the fault detection and identification (FDI) methods have been proposed to detect the fault occurrence and the unactuated control axis. Software simulations by MATLAB show that the proposed control method can recover the spacecraft attitude in the given time with the limited control effort. In order to check the capability of the controller on the operating aerospace systems, the equipping and initializing of two satellite attitude control simulators have been presented. Verification process has been done by the 3-axis stabilization method with thrusters and reaction wheels.
After confirming the quality of the 3-axis attitude control, the under-actuated controller has been implemented. The results figure out the right assessing of the under-actuated controller depends on the quality of the simulator. Unfortunately, at the level of testing the under-actuated controller, the unacceptable quality of some elements such as thrusters and some uncertainties such as simulator moment of inertia, undesired large deviations are produced which encounter the collision between the simulator hands and air bearing stand and disturbs the assessing process consequently.

Publication:
1- Attitude Control of an Underactuated Spacecraft Using Quaternion Feedback Regulator and Tubebased MPC, Acta Astronautica, November 2016.
2- Attitude control of an underactuated spacecraft using tube-based MPC approach, Aerospace Science and Technology, September 2015.
3- Passive fault-tolerant sliding mode attitude control for flexible spacecraft with faulty thrusters, Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, December 2013.

Title: Launch Vehicle Conceptual Design by Using Holistic Concurrent Design (HCD)

Abstract:
The principle goal of this Thesis is presenting the framework of Holistic Concurrent Design (HCD) and Reliability based Launch Vehicle Conceptual Design (RLVCD) under the integrated algorithm. The suggested algorithm had two main design cycles as follows:
The first design cycle concerned with reliability based design and load analysis: this cycle assist us to achieve the main design parameters and load analysis for structural design.
The second design cycle concerned with sub-system design (disciplinary design): this cycle assist us to achieve the values of design variables belong to subsystems (structure and propulsion sub-system) with overall satisfaction.
The most important different between this and previous research can be stated as reliability allocation, reliability assessment and generation of integrated code for design of structure and Engine sub-system and load analysis and also development of modular design model and sharing the designer technical knowledge in design optimization.
The verification and Validation of suggested methodology has been performed based on exist launch vehicle and other design models. For example, the most important step of HCD methodology is the establishment of fuzzy rule sets. This step can be verified by closed form model of design disciplines. And also reliability assessment based on Monte Carlo Simulation can be verified by bayesian network (analytical Model of reliability assessment) and etc. The obtained result has been presented and published some papers in prestigious (ISI, Scientific and Research) journals and also international external and internal conference.
Some of contribution of thesis has been listed as follow:
• Present the application of Holistic Concurrent Design (HCD) framework for expendable launch vehicle (the first time)
• Present the algorithm of Reliability based Launch vehicle Conceptual Design (RLVCD) (the first time)

Publication:
1- A multi-objective, multidisciplinary design optimization methodology for the conceptual design of a spacecraft bi-propellant propulsion system, Journal of Structural and Multi-disciplinary Design Optimization, 2015.
2- Multi-objective Multidisciplinary design of Space Launch System using Holistic Concurrent Design, Journal of Aerospace, Science and Technology, 2014.
3- Liquid propellant engine conceptual design by using a fuzzy-multi-objective genetic algorithm (MOGA) optimization method,
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2014.
4- A Bayesian Networks Approach to Reliability Analysis of a Launch Vehicle Liquid Propellant Engine, Journal of Aerospace Science and Technology (JAST), 2012.
5- Numerical and Experimental Investigation of Vortex Breaker Effectiveness on the Improvement in Launch Vehicle Ballistic Parameters, Journal of Mechanical Science and Technology, 2010.
6- A Variational Approach in Determination of Explicit Neighboring Optimal Guidance Law for Injection into Orbit, the Journal of International Review of Automatic Control (I.RE.A.CO.), 2008.
7- A Bayesian Networks Approach to Reliability Analysis of a Space Vehicle Separation Sub-system, 6th International Conference on Recent Advances in Space Technologies (RAST), Istanbul/Turkey, 2013.
8- A Bayesian Networks Approach to Reliability Analysis of a Launch Vehicle GN&C, METU, Ankara International Aerospace Conference (AIAC), Ankara/Turkey, 2011.
9- An Analytic Hierarchy Process based Reliability Allocation Method (ARAM), International Symposium on the Analytic Hierarchy Process, Sorento/Italy, 2011.
10- Study of Using Vortex Breakdown in Vortical Flow Field at the Outlet of Propellant Tanks, Ninth International Congress of Fluid Dynamics & Propulsion, Alexandria/Egypt, 2008.