Torque and Speed Control Loops of a Reaction Wheel (original) (raw)
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A study of reaction wheel configurations for a 3-axis satellite attitude control
Advances in Space Research, 2010
The satellite reaction wheel's configuration plays also an important role in providing the attitude control torques. Several configurations based on three or four reaction wheels are investigated in order to identify the most suitable orientation that consumes a minimum power. Such information in a coherent form is not summarized in any publication; and therefore, an extensive literature search is required to obtain these results. In addition, most of the available results are from different test conditions; hence, making them difficult for comparison purposes. In this work, the standard reaction wheel control and angular momentum unloading schemes are adopted for all the reaction wheel configurations. The schemes will be presented together with their governing equations, making them fully amenable to numerical treatments. Numerical simulations are then performed for all the possible reaction wheel configurations with respect to an identical reference mission. All the configurations are analyzed in terms of their torques, momentums and attitude control performances. Based on the simulations, the reaction wheel configuration that has a minimum total control torque level is identified, which also corresponds to the configuration with minimum power consumption.
2011
Within the motto smaller, cheaper and better, several nations can have now easy access to space, both buying or developing their own satellites. In fact, the number of small companies and even universities that make business selling space platforms weighting less than 100 kg, including payload, increases each day. If in the past small satellites mean also low power, low pointing accuracy, low price and therefore low reliability, today it is no longer valid. Some low cost satellites have 3 axis attitude control systems with high degree of pointing accuracy, like FedSat, CHIPSat and MOST. The pointing requirements for MOST (Canada's space telescope) are 25 arc-seconds in the telescope focal plane. The once expensive 3 axis attitude control system, based on gyros, star tracker and reactions wheels is now affordable for micro-satellites, giving both reliability and pointing accuracy for scientific and technological satellites. The attitude and control subsystem (ACS) acts on the reaction wheels in response to attitude errors provided by star tracker and gyros. Reactions wheels are simple brushless DC motor, coupled to a high inertia wheel. They provide torques over wide magnitude range, from micro Newton-meter up to hundreds of mili-Newtonmeter. Normally they are operated in "speed control mode" in which an internal closed loop control adjusts the motor current in order to achieve a commanded angular rate. Although reaction wheels can also operate in "current mode", the non-linear bearing friction, mainly in low speed rates, causes attitude deviation whenever the wheel changes its rotation sense. By the other hand, speed control mode introduces some time lack due to the internal control loop. This work aims to model the non-linear friction of the wheel, and to compensate it in the attitude control loop based in current mode. The reaction wheel and gyro are assembled in a one-axis air-bearing table, which provides micro friction similar to those encountered in space. Furthermore, both control modes, speed and current, shall be compared. The results proved to be helpful in deciding which strategy shall be used in future micro-satellite missions.
THE 3RD INTERNATIONAL CONFERENCE ON PHYSICAL INSTRUMENTATION AND ADVANCED MATERIALS (ICPIAM) 2021
The attitude control system of a satellite allows the satellite's attitude possible to be maintained or reoriented such that its mission is achieved. A popular actuator used in the attitude control system is the reaction wheel, i.e., a flywheel attached to a brushless direct current motor with an electronics board to control its commutation. This actuator works according to the angular momentum conservation. Due to a limited power supply to the motor as well as its specifications, the control torque capability provided by the reaction wheel is also limited. This nonlinear property would imply undesired behavior called windup since inconsistency between the control system states and the control torque. This paper addresses a simulation study of the application of some anti-windup compensators to overcome this undesired behavior. The conducted simulation is a single-axis attitude control of a model of an air bearing, i.e., a platform usually used for the satellite's attitude control design at the ground. The resulted control system performances are compared. The simulations run show the designed anti-windup compensators are promising to satisfy the stability guarantee as well as practical implementation.
Attitude control simulation of small satellites with reaction wheels
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...
2017 Fifth International Conference on Aerospace Science & Engineering (ICASE), 2017
Reaction Wheels (RWs) provide precise pointing accuracies in attitude control of satellites. They are frequently used in satellite due to their high reliability, less power consumption and wide range of torque capability. This paper presents the detail design analysis of nitrogen purged hermetically sealed reaction wheel. The RWs are major source of vibrations in the satellite. Therefore, the methodology for the attenuation of static and dynamic imbalances of the current reaction wheel is adapted as per ISO standard 1940/1 and is discussed in detail. Transient and steady state thermal analyses of the reaction wheel are carried out to ensure the proper heat transfer from the RW to the satellite body and are presented in detail in this paper. The reaction wheel assembly (RWA) is hermetically sealed by nitrogen gas and extensive testing on ground has been performed for the determination of gas leakage. A smooth decay curve is obtained which shows good agreement with the theoretically s...
Satellite attitude control using three reaction wheels
2008 American Control Conference, 2008
This work addresses the attitude control of a satellite by applying MIMO quantitative feedback approach. The objective is to design a set of proper controllers in presence of unknown disturbances and parametric uncertainties for a nonlinear MIMO system. The physical model of satellite utilizes three reaction wheels as actuators. The controller goal is to change the rotational speed of reaction wheels to adjust the satellite in desired course. First, the mathematical model of satellite and its actuators using angular kinematics and kinetic equations is developed. Quantitative feedback theory is then applied to synthesize a set of linear controllers that deals with both nonlinearities in the equations and unknown parameters or disturbance sources. By using basically non-interacting desired outputs and extracting sets of linear time invariant equivalent (LTIE) plants, the controllers set is designed for nine SISO systems. Simulation of closed loop system shows that all desired specifications of closed loop (tracking, stability, disturbance rejection) are robustly satisfied.
Revista Interdisciplinar de Pesquisa em Engenharia - RIPE, 2017
The success of a space mission where the satellite must perform rapid attitude maneuvers with great angles is extremely dependent of a careful investigation of the nonlinear dynamics of the satellite. Since these big maneuvers imply in the dynamic coupling between the satellites angular motion and the actuators such as reaction wheels and/or gas jets. As a result, this coupling must be taking into account in the Attitude Control System (ACS) design. This paper presents the nonlinear model derivation of a rigid satellite and the performance comparison of two controllers designed by Lyapunov and LQR methods. The dynamics of the satellite is initially derived in the non-linear Euler equations form and the kinematics is based on the quaternion parametrization which represent the rotation and attitude motion, respectively. In the sequel, the linear model is obtained where linearization is about an operating point of the arbitrary angular velocity and the reaction wheel angular momentum. From this model, several simulations are performed in order to investigate the influence of the nonlinear dynamics in the in the SCA performance which is designed by trial and error and by the Linear Quadratic Regulator approaches. The ACS performance is evaluated considering the capacity of the reaction wheels to maintain the stability and to control the angular velocity and the attitude of the satellite. The stability is investigated comparing the location of the poles and zeros of the open and closed loops. The ACS performance is evaluated comparing the amount of energy spend by each control law. .
Journal Européen des Systèmes Automatisés, 2019
In many space applications, the spacecraft (SC) must have good agility performance, which depends heavily on the capability of attitude control system. This paper aims to maximize the onboard capability of SC attitude control system by optimizing the use of reaction wheels (RWs). The authors firstly investigated the optimal configuration of the rotation axes relative to cluster design frame, and the cluster arrangement relative to the SC body frame. Then, the octahedron pyramid configuration was selected as the RWs configuration. For this configuration, the cluster of two shifted assemblies (four wheels each) has a 20.7 % larger envelope volume, and a 10 % longer inscribed sphere radius than the cluster of coinciding assemblies. Using the optimal agility performance criterion, the cluster of shifted assemblies can maximize the system capability by increasing the SC acceleration by 9.85 % along the worst direction. Subsequently, the controller saturation limits were updated depending based on the number and arrangement of the RWs. In case of one RW off, the SC acceleration in roll or pitch channel could be enhanced by 26.23 %. Overall, our RWs configuration could enhance the SC agility by 38.51 %. The research findings make it possible to optimize the agility of the SC and rationalize the selection and sizing of the RWs.
GyroWheel™ - An Innovative New Actuator/Sensor for 3-axis Spacecraft Attitude Control
1999
The Bristol GyroWheel is an innovative attitude control system device that provides both an angular momentum bias and control torques about three axes while at the same time measuring the spacecraft angular rates about two axes. The principles of operation of this device are explained and the flight model design is described that is targeted at small satellite applications which is currently under development. A fully functional prototype of the GyroWheel has been developed that has demonstrated the actuator and rate sensing capabilities and some of the test results are given. One of the key advantages of the GyroWheel is that, for earth pointing applications, it can be used with a single 2-axis earth sensor to provide fine pointing control in all three axes. This allows for reducing the mass, power above all cost of this class of ACS system. A GyroWheel based ACS design is developed for an example case consisting of a small earth pointing microsat mission. Performance simulations are given that show that the pointing control can be maintained within 0.1 degrees in all axes. The GyroWheel promises to fulfill the need for low cost, low mass, high reliability and high accuracy attitude control systems for applications such as communications, remote sensing, and space science.
Inertia-Free Spacecraft Attitude Control Using Reaction Wheels
Journal of Guidance, Control, and Dynamics, 2013
This paper extends the continuous inertia-free control law for spacecraft attitude tracking derived in prior work to the case of three axisymmetric reaction wheels. The wheels are assumed to be mounted in a known and linearly independent, but not necessarily orthogonal, configuration with an arbitrary and unknown orientation relative to the unknown spacecraft principal axes. Simulation results for slew and spin maneuvers are presented with torque and momentum saturation.