Closed Loop Micro-Satellite Attitude Controller

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

Journal of Control Science and Engineering, 2013

We present a satellite attitude control system design using low-cost hardware and software for a 1U CubeSat. The attitude control system architecture is a crucial subsystem for any satellite mission since precise pointing is often required to meet mission objectives. The accuracy and precision requirements are even more challenging for small satellites where limited volume, mass, and power are available for the attitude control system hardware. In this proposed embedded attitude control system design for a 1U CubeSat, pointing is obtained through a two-stage approach involving coarse and fine control modes. Fine control is achieved through the use of three reaction wheels or three magnetorquers and one reaction wheel along the pitch axis. Significant design work has been conducted to realize the proposed architecture. In this paper, we present an overview of the embedded attitude control system design; the verification results from numerical simulation studies to demonstrate the per...

2014

The active magnetic attitude control technique is a recognized attitude control option for small satellites operated in Low Earth Orbit (LEO). The purpose of this thesis is to control a nano-satellite that is operated in LEO so that it always pointing toward the Earth. Two options of control algorithms have been considered for a gravity-gradient satellite. The first control is a passive type, structured for the gravity-gradient satellite (Satellite A). It relies totally on the orbited body's mass distribution and gravitational field. The second control is an active type, structured for the gravity-gradient satellite employing three magnetic torquers onboard (Satellite B). The control is accomplished using a set of magnetic torquers that can generate a mechanical torque thus producing control actions when the torquers interact with the geomagnetic field. The algorithm used in Satellite B is configured for controlling roll, pitch and yaw attitudes using a proportional-derivative (...

2009

Nowadays, most of the designed satellites are dedicated for high performance missions, which require high attitude pointing accuracies. The reaction wheel is the most suitable satellite actuator that can provide high attitude pointing accuracies (0.1°-0.001°). Commonly, three or four reaction wheel configurations are used for a 3-axis satellite attitude control. In fact, higher power is consumed when multiple reaction wheels are employed. Thus, it is rather challenging to adopt multiple reaction wheels for the small satellite missions because of the power constraint. On the other hand, reaction wheels lack of the ability to remove the excess angular momentum and that the wheels have a limited capacity to store momentum. Without a momentum management control, the satellite may be uncontrollable. Therefore, to make the implementation of multiple reaction wheels reliable for a small satellite, it is necessary to find a way to minimize the wheel’s power consumption. Also, it is compulso...

Jurnal Mekanikal, 2004

Different attitude control strategies of a small satellite are presented in this paper as well as their simulation with the MATLAB® software. Firstly, the linear mathematical model of the satellite is derived for the gravity gradient (GG) control method, which represents a passive control design. Simulation results show that the response of the satellite to initial conditions is marginally stable. The second phase of the study focuses on the design of a control algorithm used to damp the satellite oscillations around its equilibrium position with a simple hardware setting added to the satellite. The mathematical model of the new system is developed and simulation about the roll and yaw axis are realized. A consequent amelioration in the satellite response can be observed.

Acta Astronautica, 2012

A miniaturized attitude control system suitable for nanosatellites, developed using only commercial off-the-shelf components, is described in the paper. It is a complete and independent system to be used on board nanosatellites, allowing automated attitude control. To integrate this system into nanosatellites such as Cubesats its size has been reduced down to a cube of side about 5 cm. The result is a low cost attitude control system built with terrestrial components, integrating three micro magnetotorquers, three micro reaction wheels, three magnetometers and redundant control electronics, capable of performing automatics operations on request from the ground. The system can operate as a real time maneuvering system, executing commands sent from the ground or as a standalone attitude control system receiving the solar array status from a hosting satellite and the satellite ephemeris transmitted from the ground station. The main characteristics of the developed system and test results are depicted in this paper.

Acta Astronautica, 2014

This paper presents a novel six degree of freedom, ground-based experimental testbed, designed for testing new guidance, navigation, and control algorithms for the relative motion of nano-satellites. The development of innovative guidance, navigation and control methodologies is a necessary step in the advance of autonomous spacecraft. The testbed allows for testing these algorithms in a one-g laboratory environment. The system stands out among the existing experimental platforms because all degrees of freedom of motion are controlled via real thrusters, as it would occur on orbit, with no use of simulated dynamics and servo actuators. The hardware and software components of the testbed are detailed in the paper, as is the motion tracking system used to perform its navigation. A Lyapunov-based strategy for closed loop control is used in hardware-in-the loop experiments to successfully demonstrate the full six-degree-of-freedom system's capabilities. In particular, the test case shows a two-phase regulation experiment, commanding both position and attitude to reach specified final state vectors.

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 work reproduces an active magnitude attitude control system that has been designed and simulated for a microsatellite onto a 3U CubeSat. The control is accomplished using sets of magnetic torquer that can generate a mechanical torque thus producing control actions when the torquers interact with the geomagnetic field. Algorithm used for the active magnetic attitude control technique is structured for the gravity-gradient satellite employing three magnetic torquers onboard. The algorithm is configured for controlling roll, pitch and yaw attitudes using a proportional-derivative (PD) controller. The satellite is operated in Low Earth Orbit (LEO) and is pointing to Earth. For simulation purpose, a simplified geomagnetic field is first modeled. Then mathematical model of a gravity gradient satellite is established. In orbit external disturbances is also considered. Subsequently attitude control algorithms for a gravity gradient satellite with respect to a simplified geomagnetic field models is developed and modeled using the MATLAB® SIMULINK®. Attitude performance of the 3U CubeSat shows good comparative results with previous work done for microsatellites which can provide us the guidance when designing the magnetic attitude control subsystem for nano-satellites.

Computers & Mathematics with Applications, 2012

This paper presents open-loop and closed-loop attitude control strategies of miniature spacecraft using pseudowheels, which are composed of multiple bimorphs and are mounted on the three principal axes of the spacecraft. Due to the conservation of angular momentum, the vibrations of the bimorph excited by applied voltages can rotate the spacecraft. By applying a sequence of rotations along the three axes, the attitude of the spacecraft can be changed. The modeling of the spacecraft-pseudowheel system includes the inverse piezoelectric effect and the gravity gradient torques. Since one cannot guarantee that a solution will be found for every rotation sequence, this paper proposes an approach to solve this problem. In addition, the voltages applied to the bimorphs are reduced to meet the specifications of the voltage amplifiers. Furthermore, a closed-loop attitude control strategy is presented to reduce the applied voltages and to compensate the attitude error caused by the gravity gradient torques.