Active Attitude Control Research Articles

Development of a Direct Drive Vacuum Arc Thruster Passively Ignited for Nanosatellite

Active attitude control systems require a non-negligible amount of space to be mounted on board satellites. For the nanosatellite case, it becomes even more difficult to accommodate an active attitude control system due to size and mass constraints, and choices of active attitude control system are therefore limited. In this paper, small size and lightweight are realized by direct drive and passive ignition of a thruster. The direct drive is a power supply system without a booster circuit. The passive ignition system is an ignition system using microdischarge generated by interaction with a plasma environment and the propellant surface. Availability of these two systems was verified. As a result, when the thruster was placed into a high-density plasma environment ( $10^{12}~\text{m}^{-3})$ , it was confirmed that the direct drive and passive ignition can operate normally. Moreover, expected performance of this vacuum arc thruster was measured. The results show that the impulse bit was of micronewtons order, and the ion velocity was measured to be approximately 12 km/s. Moreover, it was found that the impulse bit changes with the applied voltage and the capacitance value of the discharge circuit.

Reaction Wheel Control Design Using Linear Quadratic Controller

This paper studies the design of active attitude control system of a nanosatellite in a single axis. In this paper, we consider dc motor based reaction wheel as an actuator, because of its pointing accuracy. However, the power consumption of the dc motor is often relatively large and needed to be optimized. Linear quadratic controller is supposed to have an ability to minimize power consumption and able to enhance the system performance. To show the advantage of this method, simulation result of attitude response, state trajectory, and trajectory of DC motor voltage are presented.

E-st@r-I experience: Valuable knowledge for improving the e-st@r-II design

Many universities all over the world have now established hands-on education programs based on CubeSats. These small and cheap platforms are becoming more and more attractive also for other-than-educational missions, such as technology demonstration, science applications, and Earth observation. This new paradigm requires the development of adequate technology to increase CubeSat performance and mission reliability, because educationally-driven missions have often failed. In 2013 the ESA Education Office launched the Fly Your Satellite! Programme which aims at increasing CubeSat mission reliability through several actions: to improve design implementation, to define best practices for conducting the verification process, and to make the CubeSat community aware of the importance of verification. Within this framework, the CubeSat team at Politecnico di Torino developed the e-st@r-II CubeSat as follow-on of the e-st@r-I satellite, launched in 2012 on the VEGA Maiden Flight. E-st@r-I and e-st@r-II are both 1U satellites with educational and technology demonstration objectives: to give hands-on experience to university students and to test an active attitude determination and control system based on inertial and magnetic measurements with magnetic actuation. This paper describes the know-how gained thanks to the e-st@r-I mission, and how this heritage has been translated into the improvement of the new CubeSat in several areas and lifecycle phases. The CubeSat design has been reviewed to reduce the complexity of the assembly procedure and to deal with possible failures of the on-board computer, for example re-coding the software in the communications subsystem. New procedures have been designed and assessed for the verification campaign accordingly to ECSS rules and with the support of ESA specialists. Different operative modes have been implemented to handle some anomalies observed during the operations of the first satellite. A new version of the on-board software is one of the main modifications. In particular, the activation sequence of the satellite has been modified to have a stepwise switch-on of the satellite. In conclusion, the e-st@r-I experience has provided valuable lessons during its development, verification and on-orbit operations. This know-how has become crucial for the development of the e-st@r-II CubeSat as illustrated in this article.

Fuzzy Active Disturbance Rejection Attitude Control of Spacecraft with Unknown Disturbance and Parametric Uncertainty

Fuzzy Active Disturbance Rejection Attitude Control of Spacecraft with Unknown Disturbance and Parametric Uncertainty

Three-axis active magnetic attitude control asymptotical study

Active magnetic attitude control system providing given inertial attitude is considered. Control algorithm is constructed on the basis of a planar motion model. It decreases attitude discrepancy. Alternative approach is based on the PD-controller design. System behavior is analyzed for specific motion cases and sometimes for specific inertia tensor (axisymmetrical satellite) using averaging technique. Overall satellite angular motion is covered. Necessary attitude is found to be accessible for some control parameters. Stability is proven and optimal algorithm parameters are obtained. Floquet-based analysis is performed to verify and broaden analytical results.

Satellite Flatness based Fault Tolerant Control

Applying flat systems technique in attitude fault tolerant control of an under-actuated satellite has been investigated in this article. The main purpose of this study is development and implementation of a new idea in order to recovery of satellite stability and its acceptable performance in actuator fault scenarios. Solving the attitude fault tolerant control problem is based on consideration a realistic assumption which can show the ability of FTC system in managing the fault scenarios. Lose of effectiveness of actuators which could be caused in many of fault scenarios, modeled and simulated by multiplicative model. Thanks to provided new idea in this study it will be proven that, a wide range of actuator fault scenarios with different intense of faults could be managed without need to reconfiguring the main controller. Usage of this idea affects in reducing the volume of main controller computations and provides an appropriate base for its robust designing in other to dealing with systematically fault scenarios. Furthermore, the provided active fault tolerant attitude control scheme uses analytical redundancy system which could be considered as analytical observer. The suggested analytical observer by this technique, which belongs to nonlinear observer category, can observe all of the dynamic variables in allowable range of error. Practical implications of this study belong in this fact which analytical redundancy based on new idea in order to maintaining stability could be a perfect option in different fault scenarios such as systematically uncertainties and sensor faults. Hence this idea could be implemented without need to any physical instrument. General Terms Fault tolerant, flatness based control.

Coupled Control of Reflectivity Modulated Solar Sail for GeoSail Formation Flying

The use of the electrochromic device has been proposed for the attitude control of spacecraft for decades because its optical characteristics can be altered by electrical excitation. The technology was recently employed and verified successfully on Interplanetary Kite Craft Accelerated by Radiation of the Sun, the world’s first interplanetary sailcraft. In addition to its ability to control the attitude of a solar sail, the reflectivity control device can also be used directly for the orbit control of the sail. In this study, a new approach for joint active orbit and attitude control of a sail using the reflectivity modulation technology is proposed. The force and torque models of a reflectivity modulated spinning disk sail experienced by solar radiation pressure are discussed, and two reflectivity modulation modes are provided and compared in terms of control performance. One mode, which was used in the Interplanetary Kite Craft Accelerated by Radiation of the Sun mission, is investigated for the active control of solar sails in a GeoSail formation flying application. The coupled attitude and orbit dynamics of the sail in a GeoSail orbit is discussed, and the equation of the relative orbit and attitude motion is given. The control performances of the two modes for GeoSail formation are numerically demonstrated and compared using a typical controller.

Space base laser torque applied on LEO satellites of various geometries at satellite’s closest approach

In light of using laser power in space applications, the motivation of this paper is to use a space based solar pumped laser to produce a torque on LEO satellites of various shapes. It is assumed that there is a space station that fires laser beam toward the satellite so the beam spreading due to diffraction is considered to be the dominant effect on the laser beam propagation. The laser torque is calculated at the point of closest approach between the space station and some sun synchronous low Earth orbit cubesats. The numerical application shows that space based laser torque has a significant contribution on the LEO cubesats. It has a maximum value in the order of 10−8Nm which is comparable with the residual magnetic moment. However, it has a minimum value in the order 10−11Nm which is comparable with the aerodynamic and gravity gradient torque. Consequently, space based laser torque can be used as an active attitude control system.

3-Axis magnetic control: flight results of the TANGO satellite in the PRISMA mission

PRISMA implements guidance, navigation and control strategies for advanced formation flying and rendezvous experiments. The project is funded by the Swedish National Space Board and run by OHB-Sweden in close cooperation with DLR, CNES and the Danish Technical University. The PRISMA test bed consists of a fully manoeuvrable MANGO satellite as well as a 3-axis controlled TANGO satellite without any ΔV capability. PRISMA was launched on the 15th of June 2010 on board DNEPR. The TANGO spacecraft is the reference satellite for the experiments performed by MANGO, either with a “cooperative” or “non-cooperative” behaviour. Small, light and low-cost were the keywords for the TANGO design. The attitude determination is based on Sun sensors and magnetometers, and the active attitude control uses magnetic torque rods only. In order to perform the attitude manoeuvres required to fulfil the mission objectives, using any additional gravity gradient boom to passively stabilize the spacecraft was not allowed. After a two-month commissioning phase, TANGO separated from MANGO on the 11th of August 2010. All operational modes have been successfully tested, and the pointing performance in flight is in accordance with expectations. The robust Sun Acquisition mode reduced the initial tip-off rate and placed TANGO into a safe attitude in <30 min. The Manual Pointing mode was commissioned, and the spacecraft demonstrated the capability to follow or maintain different sets of attitudes. In Sun/Zenith Pointing mode, TANGO points its GPS antenna towards zenith with sufficient accuracy to track as many GPS satellites as MANGO. At the same time, it points its solar panel towards the Sun, and all payload equipments can be switched on without any restriction. This paper gives an overview of the TANGO Attitude Control System design. It then presents the flight results in the different operating modes. Finally, it highlights the key elements at the origin of the successful 3-axis magnetic control strategy on the TANGO satellite.

Spin-stabilized satellite magnetic attitude control scheme without initial detumbling

The angular motion of an axisymmetrical satellite equipped with an active magnetic attitude control system is considered. The dynamics of the satellite are analytically studied on the whole control loop. The control loop is as follows: preliminary reorientation along with nutation damping, spinning about the axis of symmetry, then precise reorientation of the axis of symmetry in inertial space. Reorientation starts right after separation from the launch vehicle. Active magnetic attitude control system time-response with respect to its parameters is analyzed. It is proven that low-inclined orbit forces low control system time-response. Comparison with the common control scheme shows the time-response gain. Numerical analysis of the disturbances effect is carried out and good pointing accuracy is proved.

Ground Base Laser Torque Applied on LEO Satellites of Various Geometries

This paper is devoted to investigate the feasibility of using a medium power ground-based laser to produce a torque on LEO satellites of various shapes. The laser intensity delivered to a satellite is calculated using a simple model of laser propagation in which a standard atmospheric condition and linear atmospheric interaction mechanism is assumed. The laser force is formulated using a geocentric equatorial system in which the Earth is an oblate spheroid. The torque is formulated for a cylindrical satellite, spherical satellites and for satellites of complex shape. The torque algorithm is implemented for some sun synchronous low Earth orbit cubesats. Based on satellites perigee height, the results demonstrate that laser torque affecting on a cubesat has a maximum value in the order of 10 -9 which is comparable with that of solar radiation. However, it has a minimum value in the order of 10 -10 which is comparable with that of gravity gradient. Moreover, the results clarify the dependency of the laser torque on the orbital eccentricity. As the orbit becomes more circular it will experience less torque. So, we can conclude that the ground based laser torque has a significant contribution on the low Earth orbit cubesats. It can be adjusted to obtain the required control torque and it can be used as an active attitude control system for cubesats.

Plastic Cubesat: An innovative and low-cost way to perform applied space research and hands-on education

This paper describes the design and the manufacturing of a Cubesat platform based on a plastic structure.The Cubesat structure has been realized in plastic material (ABS) using a “rapid prototyping” technique. The “rapid prototyping” technique has several advantages including fast implementation, accuracy in manufacturing small parts and low cost. Moreover, concerning the construction of a small satellite, this technique is very useful thanks to the accuracy achievable in details, which are sometimes difficult and expensive to realize with the use of tools machine. The structure must be able to withstand the launch loads. For this reason, several simulations using an FEM simulation and an intensive vibration test campaign have been performed in the system development and test phase. To demonstrate that this structure is suitable for hosting a complete satellite system, offering innovative integrated solutions, other subsystems have been developed and assembled.Despite its small size, this single unit (1U) Cubesat has a system for active attitude control, a redundant telecommunication system, a payload camera and a photovoltaic system based on high efficiency solar cells.The developed communication subsystem has small dimensions, low power consumption and low cost. An example of the innovations introduced is the antenna system, which has been manufactured inside the ABS structure. The communication protocol which has been implemented, the AX.25 protocol, is mainly used by radio amateurs. The communication system has the capability to transmit both telemetry and data from the payload, in this case a microcamera.The attitude control subsystem is based on an active magnetic system with magnetorquers for detumbling and momentum dumping and three reaction wheels for fine control. It has a total dimension of about 50×50×50mm. A microcontroller implements the detumbling control law autonomously taking data from integrated magnetometers and executes pointing maneuvers on the basis of commands received in real time from ground.The subsystems developed for this Cubesat have also been designed to be scaled up for larger satellites such as 2U or 3U Cubesats. The additional volume can be used for more complex payloads. Thus the satellite can be used as a low cost platform for companies, institutions or universities to test components in space.

Study of a bunch of three algorithms for magnetic control of attitude and spin rate of a spin-stabilized satellite

We consider the angular motion of an axi-symmetrical satellite equipped with an active magnetic attitude control system. Dynamics of the satellite is studied on the entire control loop, consisting of a bunch of three successively used algorithms. The control cycle includes the stages of nutation damping, spinning up the satellite about its symmetry axis, and reorienting the symmetry axis into a preset direction in the inertial space. The results are confirmed by numerical simulations.

Asymptotic study of a complete magnetic attitude control cycle providing a single-axis orientation

The angular motion of an axisymmetrical satellite equipped with the active magnetic attitude control system is examined. Attitude control system has to ensure necessary orientation of the axis of symmetry in the inertial space. It implements the following strategy: coarse reorientation of the axis of symmetry with nutation damping or “-Bdot” without initial detumbling; spinning-up about the axis of symmetry to achieve the property of a gyro; fine reorientation of the axis in the inertial space. Dynamics of the satellite is analytically studied using averaging technique on the complete control loop consisting of five algorithms. Solutions of the equations of motion are obtained in terms of quadratures for most cases or even in closed-form. The latter allowed to study the dependence of motion parameters including time-response with respect to the orbit inclination and other parameters for all algorithms.

Investigation of the effectiveness of an algorithm of active magnetic damping

We consider the rapid rotation of a satellite equipped with an active magnetic attitude control system with the -Bdot algorithm designed to damp the initial angular velocity. The time-response of the algorithm is analytically studied as a function of orbit inclination.

Fuzzy Adaptive Variable Structure Active Attitude Control of Flexible Spacecraft

This paper presents a novel control system design method for the three-axis-rotational tracking and vibration stabilization of a spacecraft with flexible appendages. Based on the sliding control theory, a robust attitude control law is derived to control the attitude motion of spacecraft. For actively suppressing the induced vibration, both fuzzy methods and strain rate feedback (SRF) control methods are presented. Numerical simulations are performed to show the feasibility and effeteness of the proposed methods.

Design of template to fabricate magnetic torquer coils for nano and picosatellite missions

PurposeRecent advances in nano and picosatellite missions and future such missions require three axis attitude control system hardware for attitude control purposes. A simple, cost effective, yet an efficient devise that is used for active attitude control is magnetic torquer coil. The purpose of this paper is to describe the design and fabrication of a template to manufacture magnetic torquer coils of varying sizes and shapes.Design/methodology/approachDetails about the development of the template design, analysis, and fabrication are discussed. The development status of the system is outlined and the working prototype of the device is described and some preliminary test results are given.FindingsA fully functional prototype of the template has been developed and testing has been conducted that demonstrated the effectiveness of the device. Magnetic torquer coils of varying sizes were fabricated and tested. A finite element analysis was performed by modeling the characteristics of the fabricated coils to determine thermally induced stresses and deformations during its space operations.Practical implicationsThe paper illustrates and demonstrates an effective application of torquer coil template in the satellite fabrication industry. The benefits from the approach are generally applicable to any future university and industry missions using picosatellite technology.Originality/valueThe designed template satisfied all the constraints and requirements. Furthermore, its advantages include scalability, modularity, and its capability to fabricate magnetic torquer coils of varying sizes and shapes.

Attitude stabilization of a pico-satellite by momentum wheel and magnetic coils

The three-axis active attitude control method with a momentum wheel and magnetic coils for a pico-satellite is considered. The designed satellite is a 2.5 kg class satellite stabilized to nadir pointing. The momentum wheel performs a pitch-axis momentum bias, nominally spinning at a particular rate. Three magnetic coils are mounted perpendicularly along the body axis for precise attitude control through the switch control mechanism. Momentum wheel start up control, damping control and attitude acquisition control are considered. Simulation results show that the proposed combined control laws for the pico-satellite is reliable and has an appropriate accuracy under different separation conditions. The proposed strategy to start up the wheel after separation from the launch vehicle shows that its pitch momentum wheel can start up successfully to its nominal speed from rest, and the attitude convergence can be completed within several orbits, depending on separation conditions.

Attitude manoeuvre and vibration control of flexible spacecraft using computed feed-forward input commands and proportional-derivative feedback

The current paper presents an investigation into development of feed-forward and feedback control strategies for active vibration and attitude control of a flexible spacecraft. In this approach, the feed-forward loop consists of a computed-torque scheme and a command shaping technique based on component synthesis vibration suppression (CSVS) method for shaping the input signal. For relaxing the requirement of dynamic linearity in traditional CSVS, a new approach is developed for designing the input component command by utilizing a structure, in which the modal forces of flexible modes vibration are shaped according to a predefined trajectory, to achieve the vibration suppression for the non-linear attitude dynamics. In addition, to follow the predefined trajectory identically or at least as closely as possible, a model-independent feedback control loop is employed, which can accomplish further reduction of the residual vibration of flexible appendages. This proposed control strategy is practical as it does not require direct measurement of mode vibration, and also has a simple structure with low online computational load. Numerical simulations demonstrate the effectiveness of the control strategy.

Active Vibration and Attitude Control of a Vibration Isolation Table with Pneumatic Actuators (A Modeling Method for the Redundant System of Actuators and Sensors)

Active control of a vibration isolation table using pneumatic actuators is studied in this paper. The vibration isolation table is supported by four pneumatic actuators at corners of the square rigid table. A 3DOF physical model of the vibration isolation table is constructed with taking account of redundancy of the actuators and sensors. We introduce a method to determine the air pressure of each actuator to minimize the error between the average pressure of the actuators and the air pressure of each actuator. The regulator for the pneumatic actuator is driven by a stepping motor. Characteristics of the transfer function from input pulse for the stepping motor to the air pressure of the actuator are investigated experimentally and the mathematical model of the actuator is constructed as a second order delay system. Type I digital servo system is applied to control the vibration and position of the vibration isolation table. Control performance of the system is verified experimentally and the results are shown in figures.