Attitude Control Applications Research Articles

Self-triggered MPC with adaptive prediction horizon for nano-satellite attitude control system

Nano-satellites are essential tools for various applications, including scientific experiments, deep space exploration and astronomical observation. Achieving precise model predictions is crucial for their successful operation. To address the intricate constraints of nano-satellites and enhance control performance, the Model Predictive Control (MPC) algorithm is an effective solution. However, implementing an MPC-based attitude control system in actual engineering scenarios presents significant challenges, primarily due to the substantial computational burden, especially given the limited onboard computing resources of nano-satellites. In this paper, we introduce a modified adaptive self-triggered model predictive control (ST-MPC) algorithm designed to stabilize the attitude of nano-satellites, while simultaneously reducing communication and computational overhead compared to traditional MPC methods. The proposed self-triggered mechanism dynamically determines the next trigger time according to the system state. Moreover, we incorporate considerations for the efficiency of actuators to address the constraints imposed by the magnetic torque characteristics within the modified self-triggered mechanism. Additionally, a strategy for adaptive prediction horizon is proposed to balance computation load and control accuracy. The results of our simulations demonstrate the effectiveness of the modified ST-MPC algorithm in comparison to both traditional MPC and standard ST-MPC approaches. This algorithm may have the potential to significantly impact attitude control applications for nano-satellites.

A Nonlinear Observer-Based Approach to Robust Cooperative Tracking for Heterogeneous Spacecraft Attitude Control and Formation Applications

This article proposes a nonlinear observer-based approach to address the robust cooperative tracking problem and application for heterogeneous spacecraft systems. By introducing appropriate assumptions, a weight average estimation is proposed to construct a class of distributed nonlinear observers for heterogeneous spacecraft systems with a target whose dynamics are available only to a few chasers. By synthesizing the observer dynamics among the neighbors, a novel cooperative tracking controller is developed to address nonidentical parameters both in model uncertainties and nonlinear dynamics. Then, the robust consensus tracking problem can be solved if the cooperative behaviors between the chasers and their observers can be achieved synchronically. A special case of the identical model uncertainty and nonlinear dynamics scenario is also discussed. As applications of the proposed nonlinear observer-based approaches, the controller and observer designs of heterogeneous spacecraft attitude control and formation flying systems are revisited. Numerical simulations with a nonlinear dynamic model of spacecraft attitude control and formation flying systems demonstrate the effectiveness of the proposed approaches.

DESIGN AND PERFORMANCE OF A 110 N ATTITUDE CONTROL THRUSTER FOR LUNAR MISSIONS

The design and development of an attitude control thruster, designated A110, developed for broad attitude control applications, including lunar landers, is described. The A110 thruster produces 110 N (25 lbf) of nominal thrust and in-excess of 305.5 s of specific impulse (I<sub>sp</sub>) while operating on a fuel blend of 20% monomethylhydrazine-80% hydrazine (M20) with mixed oxides of nitrogen containing 3% nitric oxide (MON3) as the oxidizer. The injector and combustion chamber are additively manufactured with cobalt-chrome and niobium C103, respectively, to enable the rapid development required of the industry. The thruster is capable of response times of under 10 ms and currently produces a minimum impulse bit (MIB) of 0.436 N.s and has demonstrated operation in pulse-mode with a variety of duty cycles during development testing. These capabilities allow for the generation of precise pulses for accurate control of a lander. The testing of this thruster is used to evaluate steady-state and pulse-mode specific impulse, impulse repeatability, and combustion stability. The measured performance (i.e., specific impulse and characteristic velocity (C*), are compared with theoretical values. The capabilities demonstrated by the A110 thruster are applicable to a wide range of lunar lander missions and can be qualified for minor changes in thruster requirements for additional missions without the need for major design changes. This article is published with the permission of the authors granted to 3AF - Association Aéronautique et Astronautique de France (www.3AF.fr) organizer of the Space Propulsion International Conference.

Prescribed Time Attitude Tracking Control of Spacecraft With Arbitrary Disturbance

The problem of developing a controller for spacecraft to accomplish attitude maneuvers within a prescribed time, independently of the initial states, is addressed. A fixed-time disturbance observer-based control is established and proved to drive the error state to zero, in a prescribed time, in the presence of modeling and external uncertainties. The key advantages of the proposed control are that the gains are explicitly determined by the prescribed maneuvering time only and that it is also robust to instantaneous disturbances. The control approach enables an efficient design process for attitude control applications with time constraints. Simulation results are presented for the attitude control of a rigid spacecraft to verify the benefits of this control scheme.

Research and Application of Attitude Control and Stability Adjustment Technology for Underwater Robot Platform

This research is mainly aimed at the difficulty in maintaining the stability of the position and posture of underwater visual equipment, and it is unable to provide reliable images for underwater search and salvage rescue operations. Investigating the existing mature technology and scheme, combined with the characteristics of the underwater operation of the visual equipment and based on the comprehensive analysis, a set of motion attitude stability analysis theory suitable for the underwater platform is proposed. Combined with various control theories, the motion control equations of underwater robots are established, and the optimal control method is designed. The control method is verified by computer simulation.The research results of the project can provide a reliable technical support and decision-making means for underwater search and salvage work, improve the automation level of underwater operations, reduce the difficulty of underwater operations, and improve the comprehensive response capability and technical level of deepwater search and rescue salvage levels.

Unmanned Aerial Vehicle Pitch Control Using Deep Reinforcement Learning with Discrete Actions in Wind Tunnel Test

Deep reinforcement learning is a promising method for training a nonlinear attitude controller for fixed-wing unmanned aerial vehicles. Until now, proof-of-concept studies have demonstrated successful attitude control in simulation. However, detailed experimental investigations have not yet been conducted. This study applied deep reinforcement learning for one-degree-of-freedom pitch control in wind tunnel tests with the aim of gaining practical understandings of attitude control application. Three controllers with different discrete action choices, that is, elevator angles, were designed. The controllers with larger action rates exhibited better performance in terms of following angle-of-attack commands. The root mean square errors for tracking angle-of-attack commands decreased from 3.42° to 1.99° as the maximum action rate increased from 10°/s to 50°/s. The comparison between experimental and simulation results showed that the controller with a smaller action rate experienced the friction effect, and the controllers with larger action rates experienced fluctuating behaviors in elevator maneuvers owing to delay. The investigation of the effect of friction and delay on pitch control highlighted the importance of conducting experiments to understand actual control performances, specifically when the controllers were trained with a low-fidelity model.

Usability evaluation of attitude control for a robotic wheelchair for tip mitigation in outdoor environments

Tips and falls are the most prominent causes of wheelchair accidents that occur when driving on uneven terrains and less accessible environments. The Mobility Enhancement Robotic Wheelchair (MEBot) was designed to improve the stability of Electric Powered Wheelchairs (EPW) when driving over these environments. MEBot offers six independently height-adjustable wheels to control attitude of its seat over uneven and angled terrains. Its attitude control application uses an inertial measurement unit to detect seat angles changes to adjust each wheel-height accordingly. MEBot was compared to commercial EPWs in terms of EPW performance (seat angle changes and response time) and participant perception (satisfaction and task-load demand) towards each device. Ten participants drove their own EPW and MEBot for five trials each through driving tasks that replicated outdoor environments. Results showed less change in the pitch angle when driving up and down a 10° slope using MEBot (5.6 ± 1.6°, 6.6 ± 0.5°) compared to the participants’ own EPW (14.6 ± 2.6°, 12.1 ± 2.6°). However, MEBot required 7.8 ± 3.0 s to self-adjust to the minimum angle when driving over the tasks. Participants reported no difference in satisfaction and task load demand between EPWs due to similarities in comfort and ease-of-use. Improving the speed and efficiency of MEBot's attitude control application will be addressed in future work based upon participants’ feedback.

Nonlinear guaranteed cost attitude control via dynamic gain design

This paper investigates the guaranteed cost attitude control problem of a rigid-body subject to parameter uncertainty problem. The traditional LQR and guaranteed cost control (GCC) methods rest on linear systems and then entail model linearization in the application of attitude control by assuming small-angle rotations, since rigid-body attitude systems are highly nonlinear. In contrast, the proposed method effectively accounts for the nonlinearities inherent in the attitude dynamics of the rigid-body and ensures the attitude system with asymptotic stability and a guaranteed cost index. A linear state-feedback controller of the classical proportional/derivative (PD) structure is provided, which is off-line designed by some linear matrix inequality (LMI) conditions. Moreover, by virtue of the dynamic gain technology, the conditions are of simple structure, which thereby are easy to solve and eligible to turn into some optimization problems for optimizing the cost index and/or controller gains. The optimization problems are tractable to handle computationally and thus the optimal solution can be ensured. The developed theoretical results are illustrated by simulations.

Design and development of prototype carpal wrist cold gas propulsion system for attitude control applications

In recent years, the Philippine space program has launched several small-scale satellites, and lately has commissioned its own space program. Research on improving the subsystems of these satellites would be beneficial to future space programs in the Philippines. This paper will detail the process of designing, validating, fabricating, and testing a prototype Carpal Wrist Cold Gas Propulsion System (CW-CGPS). By making use of a carpal wrist’s (CW) hemispherical movement capabilities, the sixteen thrusters could theoretically be replaced by four mounted on opposite ends. Optimization of the propulsion system is based on finding the nozzle design with the most adequate values for thrust, Mach number, and specific impulse while the CW design is validated when it can be calibrated to move as the program dictates. This study uses multiple programs to simulate and verify the design. The conditions of the testing environment are established by resources from international space organizations. Assembly and feasibility are assessed based on the results of the research. It was found that the final optimized system had a model torque of 0.247 N-m, more than enough to overcome the maximum combined influence of the gravity gradient torque of 2.34E-06 N-m and aerodynamic torque of 1.57E-25 N-m. The design, development, and test campaign for the thruster system is presented.

Design of a low-cost mini quadrotor and altitude control using a micro laser sensor

Purpose The purpose of this paper is to introduce a low-cost quadrotor that can be used for educational purposes and investigate the applicability of a low-cost MEMS laser sensor for accurate altitude control. Design/methodology/approach A single printed circuit board is designed to form the structure of the quadrotor. A low-cost MEMS motion sensor, a microcontroller and four small motors are mounted on the board. A separate laser sensor module measures the altitude. A remote controller is designed to control the quadrotor’s motion. The remote controller communicates with the quadrotor via wireless connection. Roll and pitch attitude stabilization is achieved using the proportional and derivative control algorithm. The applicability of an MEMS laser sensor for altitude control is also studied. Findings The low-cost quadrotor works well even though its body structure is made using a printed circuit board. Low pass and Kalman filters work well for attitude estimation and control application. The laser sensor is very accurate and good for altitude feedback; however, it has a relatively short measurement range and its sampling rate is relatively slow, which limits its applications. The vertical velocity obtained by differentiating the laser altitude has delay and inhibits suitable damping. Using the vertical velocity obtained by integrating the vertical accelerometer’s output, the damping performance is improved. Originality/value Developing a low-cost quadrotor that can be used for educational purposes and successfully implementing altitude control using a laser sensor and accelerometer.

A Multi-Model Combined Filter with Dual Uncertainties for Data Fusion of MEMS Gyro Array.

The gyro array is a useful technique in improving the accuracy of a micro-electro-mechanical system (MEMS) gyroscope, but the traditional estimate algorithm that plays an important role in this technique has two problems restricting its performance: The limitation of the stochastic assumption and the influence of the dynamic condition. To resolve these problems, a multi-model combined filter with dual uncertainties is proposed to integrate the outputs from numerous gyroscopes. First, to avoid the limitations of the stochastic and set-membership approaches and to better utilize the potentials of both concepts, a dual-noise acceleration model was proposed to describe the angular rate. On this basis, a dual uncertainties model of gyro array was established. Then the multiple model theory was used to improve dynamic performance, and a multi-model combined filter with dual uncertainties was designed. This algorithm could simultaneously deal with stochastic uncertainties and set-membership uncertainties by calculating the Minkowski sum of multiple ellipsoidal sets. The experimental results proved the effectiveness of the proposed filter in improving gyroscope accuracy and adaptability to different kinds of uncertainties and different dynamic characteristics. Most of all, the method gave the boundary surrounding the true value, which is of great significance in attitude control and guidance applications.

Kinematics and Stability Analysis of a Novel Power Wheelchair When Traversing Architectural Barriers.

Background: Electric-powered wheelchairs (EPWs) are essential devices for people with disabilities for mobility and quality of life. However, the design of common EPWs makes it challenging for users to overcome architectural barriers, such as curbs and steep ramps. Current EPWs lack stability, which may lead to tipping the EPW causing injury to the user. An alternative Mobility Enhancement Robotic Wheelchair (MEBot), designed at the Human Engineering Research Laboratories (HERL), was designed to improve the mobility of, and accessibility for, EPW users in a wide variety of indoor and outdoor environments. Seat height and seat inclination can be adjusted using pneumatic actuators connected to MEBot's 6 wheels. Method: This article discusses the design and development of MEBot, including its kinematics, stability margin, and calculation of the center of mass location when performing its mobility applications of curb climbing/descending and attitude control. Motion capture cameras recorded the seat angle and joint motion of the 6 wheel arms during the curb climbing/descending process. The center of mass location was recorded over a force plate for different footprint configurations. Results: Results showed that the area of the footprint changed with the location of the wheels during the curb climbing/descending and attitude control applications. The location of the center of mass moved ±30 mm when the user leaned sideways, and the seat roll and pitch angle were 0° and ±4.0°, respectively, during curb climbing and descending. Conclusion: Despite the user movement and seat angle change, MEBot maintained its stability as the center of mass remained over the wheelchair footprint when performing its mobility applications.

Minimum switching control for systems of coupled double integrators

This paper studies the minimum switching control problem for a system of coupled double integrators with on–off input signals, in the presence of a constant disturbance term. This type of problem is relevant to a variety of applications in which the number of transitions of on–off actuators must be minimized, in order to prevent actuator wear. Two solutions are presented in terms of steady state limit cycles. The first one provides an analytic upper bound to the maximum number of transitions per input signal. The second solution exploits the relative phases of the trajectories of the state variables, thus providing a less conservative upper bound. Additionally, a control law is presented, which steers the system in finite time to the previously derived limit cycles. The proposed techniques are demonstrated on a spacecraft attitude control application.

UAV Flight Control System Based on an Intelligent BEL Algorithm

A novel intelligent control strategy based on a brain emotional learning (BEL) algorithm is investigated in the application of the attitude control of a small unmanned aerial vehicle (UAV) in this study. The BEL model imitates the emotional learning process in the amygdala- orbitofrontal (A-O) system of mammalian brains. Here it is used to develop the flight control system of the UAV. The control laws of elevator, aileron and rudder manipulators adopt the forms of traditional flight control laws, and three BEL models are used in above three control loops, to on- line regulate the control gains of each controller. Obviously, a BEL intelligent control system is self-learning and self-adaptive, which is important for UAVs when flight conditions change, while traditional flight control systems remain unchanged after design. In simulation, the UAV is on a flat flight and suddenly a wind disturbs it making it depart from the equilibrium state. In order to make the UAV recover to the original equilibrium state, the BEL intelligent control system is adopted. The simulation results illustrate that the BEL-based intelligent flight control system has characteristics of better adaptability and stronger robustness, when compared with the traditional flight control system.

Design, calibration and error analysis of a piezoelectric thrust dynamometer for small thrust liquid pulsed rocket engines

Small thrust liquid pulsed rocket engines operating in pulsed mode have gained a good reputation in attitude control applications for their potential reliability and efficiency. However, the pulsed characteristic creates a difficult measurement problem. In this paper, a novel thrust dynamometer with high natural frequency is developed for accurately measuring the pulsed thrust. It consists of two shear mode piezoelectric quartz crystal sensors and an integral shell. The sensors are inserted into unique double-elastic-half-ring grooves with an interference fit. Stiffness equations of the shell which are used to estimate the amount of interference are derived. The thrust dynamometer is calibrated both statically and dynamically. Static calibration uncertainty is evaluated. A trapezoidal impulse force is used to simulate the pulsed thrust for further characterizing the dynamic measurement performance of the thrust dynamometer. An evaluation algorithm of dynamic error is presented and used to evaluate the results of the dynamic simulation. The results show the thrust dynamometer has high sensitivity and natural frequency, good linearity and repeatability, and excellent dynamic performance. It can accurately trace trapezoidal thrust signal of 50 Hz without waveform distortion.

れいめい（INDEX）衛星における統合化衛星制御

REIMEI/INDEX (INnovative-technology Demonstration EXperiment) is a 70kg class small satellite which the Institute of Space and Astronautical Science, Japan Exploration Agency, ISAS/JAXA, has developed for observation of auroral small-scale dynamics as well as demonstration of advanced satellite technologies. An important engineering mission of REIMEI is integrated satellite control using commercial RISC CPUs with a triple voting system in order to ensure fault-tolerance against radiation hazards. Software modules concerning every satellite function, such as attitude control, data handling, and mission applications, work cooperatively so that highly sophisticated satellite control can be performed. In this paper, after a concept of the integrated satellite control is introduced, the Integrated Controller Unit (ICU) is described in detail. Also unique topics in developing the integrated control system are shown.

Combined attitude control application of an underactuated helicopter experimental system

In this paper, combined attitude control of an underactuated helicopter experimental system is considered. The controlled helicopter experimental system has two inputs and three outputs, namely, this system is underactuated. The combined attitude controller includes a non-linear MIMO controller based on adaptive sliding mode control and non-adaptive non-linear controllers. Control system stability is guaranteed by Lyapunov function-based proof. Experimental results show the effectiveness of the proposed method.

Attitude control system design and application on a helicopter experimental system

In this paper, an experimental study which takes account of variation of weight of a helicopter system is discussed. The weight changes of the helicopter system are modelled as unstructured uncertainties and the uncertainties are compensated by the proposed combined controller. That is, we divide uncertainties of the system into structured uncertainties and unstructured uncertainties. When the weight of the helicopter varies, an upper bound value of the unstructured uncertainties is evaluated and considered to control inputs. Comparing experiments between a former design method and the proposed design method show the effectiveness of the proposed method.

CMC 20N thruster for hermes attitude control

Ceramic Matrix Composite materials (CMC) have been developped by SEP Solid Propulsion an Composite Materials Division in Le Haillan since the seventies for solid propulsion applications. In the race to create a new generation of small high performance bipropellant engines, SEP has opted for Ceramic Matrix Composite (CMC) such as SEPCARBINOX (R) or CERASEP (R), as combustion chamber and nozzle material. The main advantage of these composites is enabling increase of maximum combustion temperature to 1600°C without requiring anti-oxydation coatings, and with improved resistance to thermal cycles. SEP's Defense and Space group started preliminary work on choosing the composite materials best adapted to liquid bipropellant engines in 1983. Based on some 30 5N thrust combustion chambers, about 20 different materials were evaluated during firing tests. Next, using different combustion chambers sizes, SEP implemented a program designed to demonstrate the endurance of this material, and initiated a study on producing larger size parts including large area ratio nozzles. This program comprised the production and testing of combustion chambers rated at 200N and 6000N, associated with injectors derived from other applications. Finaly, in order to simulate the operating conditions experienced by certain motors on HERMES spaceplane, tests of the 200N motor were also carried out with an external thermal protection system. As of end 1987, designers had set the thrust level required for the HERMES attitude control system at between 10 and 30N. SEP therefore decided to focus further work on 20N-thrust engines, a choice which took into consideration the potential applications of this thrust level for satellite attitude control systems. Starting in mid-1988 and continuing until fall 1990, this program is designed to validate before going into final qualification all technologies required for the two planned applications: • - the HERMES spaceplane, which has several thrusters integrated in the nose, • - satellites, where the motor is free to radiate heat into space. Manufacturing procedures for the composite parts apply to the production of both thrust chambers and nozzles common to both applications. HERMES specific parts are also in production; these basically involve exhaust elements connected to a highly-scarfed nozzle, which enables the integration of the motor and its insulation in the spaceplane nose. Injection studies comprise the design, production and testing of injectors of two different types: • - a high performance version, for satellite thrusters, with a specific impulse goal of 300 s. • - another, designed for HERMES, which will limit wall temperature when the motor is insulated, with a specific impulse of about 287 s. The SEP 20N thrusters are presented with specific topics for HERMES attitude control application.

Stability of discrete-time attitude control systems

Attitude control systems are normally treated as continuous-time systems even though, in reality, control will be implemented in discrete time. In a similar vein, realistic attitude sensors are sampled-data in nature. Motivated by satellite attitude control applications, this paper treats the fundamental problem of proportional plus rate plus integral (PDI) feedback control of a rigid non-spinning spacecraft using sampled-data attitude and attitude-rate sensors. Using ℒ-transforms, the characteristic equation is derived and literal stability criteria are extracted and illustrated through stability diagrams. The stability criteria have also been confirmed through simulation, a typical case of which is included.