Small Satellite Attitude Control and Simulation

This paper deals with simulations of the attitude control system of the imaginary Artificial Satellite β by use of MATLAB/Simulink with possible extensions to satellite hardware testing. And also I was instructed to design a PID controller that will ensure that the Artificial Satellite achieves a particular desired angle, and meet the performance index that comprises system overshoot and settling time. This report gives an introduction of Attitude Control, and Simulation of an Artificial (test) Satellite. It gives an insight of the mathematical modelling for satellite attitude dynamics for 3 degrees of freedom. By the different limitations of how the Artificial Satellite operates, these models are adjusted accordingly. A set of strategies for controlling the attitude is presented. Through an explanation of PID controllers and their behaviors, the control codes and various laws are also adopted to work with the satellite. SIMULINK, a companion program to MATLAB, were used to Model, Simulate, and analyze the satellite’s dynamic systems. And thus the Simulink model was constructed. Combined, these findings are put to use in the form of a complete Simulink simulator for the satellite in orbit. Results with different control strategies to achieve the desired angle and meeting the performance index, are given. Keywords: Attitude Control, Simulation, Artificial Satellite, MATLAB, Simulink, PID Controller, Orbital Control, Transfer Function, Attitude Determination

1987

This paper gives the results of a dynamical analysis of the Globesat gravity gradient stabilized satellite in a 500 km circular orbit. The linearized equations of motion are developed and the stability of the satellite is investigated. The satellite is equipped with magnetic torquers for the purpose of providing attitude correction torques. These correction torques can be used to effect large changes in orientation and for producing small impulses for damping residual librational motions. The analysis shows that such a satellite can be captured into a gravity gradient stabilized mode, and that residual motions can be damped to small steady state values.

INCAS BULLETIN, 2012

The paper presents some aspects for synthesis of small satellites attitude control. The satellite nonlinear model presented here will be with six degrees of freedom. After movement equation linearization the stability and command matrixes will be established and the controller will be obtained using gradient and gradient method. Two attitude control cases will be analysed: the reaction wheels and the micro thrusters. The results will be used in the project European Space Moon Orbit-ESMO founded by European Space Agency in which the University POLITEHNICA of Bucharest is involved.

Proceedings of 5th International Conference on Recent Advances in Space Technologies - RAST2011, 2011

The paper purpose is to present some aspects regarding the calculus model and technical solutions for small satellites attitude control. Mathematical model is put in nonlinear and linear form. The linear form is used for attitude control system synthesis. The attitude control system obtained is used in nonlinear form in order to maintain desired attitude. A few numerical simulations are made for standard input and the satellite behavior is obtained. The satellite model presented will be with six DOF and use Cartesian coordinates. At this item, as novelty of the work we will use the rotation angles to describe the kinematical equations. Also this paper proposes a Fourier linearising of Trigger Schmidt element used for applying the command moment. The results analyzed will be the rotation angles of the satellite as well the rotation velocity. The conclusions will focus the comparison between results obtained using different attitude control system, and the possibility to use such system for small satellite.

Journal of Physics: Conference Series, 2013

The objective of this paper is to analyze the stability of the rotational motion of a symmetrical spacecraft, in a circular orbit. The equilibrium points and regions of stability are established when components of the gravity gradient torque acting on the spacecraft are included in the equations of rotational motion, which are described by the Andoyer's variables. The nonlinear stability of the equilibrium points of the rotational motion is analysed here by the Kovalev-Savchenko theorem. With the application of the Kovalev-Savchenko theorem, it is possible to verify if they remain stable under the influence of the terms of higher order of the normal Hamiltonian. In this paper, numerical simulations are made for a small hypothetical artificial satellite. Several stable equilibrium points were determined and regions around these points have been established by variations in the orbital inclination and in the spacecraft principal moment of inertia. The present analysis can directly contribute in the maintenance of the spacecraft's attitude.

2009

In this paper, we modify and apply a robust almost global attitude tracking control scheme to the model of a small satellite. The control scheme, which has been reported in prior literature, is modified to take into account the actuator constraints and actuator configuration of this satellite, which are based on a small satellite currently being developed at the University of Hawaii. The actuators consist of three magnetic torquers and one small reaction wheel. The mass and inertia properties correspond to the known values for this satellite. The satellite is in circular low earth orbit of altitude 600 km and its dynamics model includes gravity, atmospheric and geomagnetic effects. The control strategy used here achieves almost global asymptotically stable attitude trajectory tracking, which implies that the desired attitude trajectory is tracked from all initial conditions on the state except for those that lie on a zero-volume subset within the state space. The continuous feedback control law is also globally defined. Feedback control gains are continuously varied based on known actuator constraints and tracking errors. The almost global asymptotic tracking property can be shown using a generalized Lyapunov analysis on the nonlinear state space of the attitude dynamics. The control torque obtained from this almost-globally-stabilizing feedback control law is partitioned so that each actuator generates a part of this control torque that is within its saturation limits. The control law for the reaction wheel has a singularity when the reaction wheel axis is perpendicular to the local geomagnetic field. To avoid actuator saturation, the control inputs to the actuators are kept constant whenever any actuator reaches a certain fraction of its saturation value. Numerical simulation results for two de-tumbling maneuvers, one where the control law singularity does not appear and one where it does, confirm that the desired attitude trajectory is tracked almost globally.

This article describes a simulator of small satellite attitude environment and dynamics, complete with a set of realistic sensors and the most commonly used actuator in this class of satellites. The simulator described is useful in attitude estimation and control algorithm development. Some results of the simulation of the PoSAT-1 satellite are presented.

2010

As well as other subsystems, Attitude Determination and Control System (ADCS) development is a challenging process for small satellites because of design limitations, such as size, weight and the power consumption. Besides, if they are thought in a concept with military missions, then the requirement for a high attitude pointing accuracy is something certain. Works on the effective attitude determination and control methods for small satellites can be accepted as a part of this struggle. In this paper, problems that are met during ADCS development phase for future small satellites are stated and possible solutions are suggested.

Kufasat is a student satellite program and the goal of this program is to design and launch a cube satellite .The purpose of this study is to design and to develop an efficient Attitude Determination and Control System- ADCS for the satellite. The satellite is intended to fly in a low earth orbit at 600km altitude and its mission is to perform scientific measurements. The satellite is to be cubic with 10 cm on all sides and have a total mass of approximately 1kg and be three -axis gravity gradient stabilized. The satellite consists of (1.5) m long gravity gradient boom. The gravity gradient boom has a tip mass of (40) g to improve the gravity gradient stabilization .A gravity gradient stabilized satellite has a limited stability and a pointing capabilities, and a magnetic coils are added to improve both the three axis stabilization and the pointing properties. Magnetic coils around the satellite's XYZ axes can be fed with a constant current-switched in two directions-to generate a magnetic dipole moment which will interact with the geomagnetic field to generate a satellite torque, which is used to control the rotation of the satellite. A problem is that both the direction and the strength of the geomagnetic field change and magnetic control become non-linear and time dependent .The magnetic coils are controlled by using a fuzzy logic controller, based on a combination of membership functions and rules. The controller consists actually of 3 MISO fuzzy control laws, one for each magneto torquer (MX, MY and MZ coils). Each control law embodies a fuzzy rule base to decide on the control desirability and output level when using the corresponding torquer. Magnetic coils allow cheaper satellite, and are an attractive solution to small, inexpensive satellite in low earth orbit. The satellite will be during separation from the launch vehicle is exposed to forces from the release mechanism and tumbling may occur. A detumbling mode is activated in order to calm down the movement .The gravitation boom will be deployed first when the movement of the satellite is sufficient small. This study deals with attitude control after the detumbling mode has successfully been completed and the boom is fully deployed.

The 2nd International Conference on Control, Instrumentation and Automation, 2011