attitude control

pairs in x and y-direction represents the minimum discrete torque increment that can be generated us- ing a (4 × 4)-array. This already indicates potential challenges for membrane attitude control, in case a limited number of elements across the surface is used. The total torque that can be generated varies significantly, as can be seen in Fig 4.

Abstract—Spacecraft magnetic attitude control has been largely investigated, but the focus has generally been the control of satellites meeting conditions of gravity gradient stability by either inertia parameters or deployed boom. In this study, we consider three axes magnetic control for Turkish earth observation satellite, RASAT. This satellite is significant case study for magnetic control problem since it does not meet gravity gradient stability conditions on pitch axis owing to physical properties such as greater inertia along z axis than x axis. However, near polar orbiting satellites’ pitch axis is controllable under magnetic torques. On the other hand, the controller is supposed to be simple to consider computational efficiency of onboard computer. For this reason, state feedback control methodology is applied. However, the significances of the controller are that the controller gain matrix is constant and its calculation is based on linear quadratic law with averaging method of slowly time varying system. Furthermore, this approach can be extended to control off-nadir attitude.

1.2. Attitude Control 3 globally defined. The unit-quaternion representation is a four-parameters attitude rep- resentation which describes the attitude globally (singularity-free) compared to other three-parameters representations. This has motivated their wide use in many practi- cal applications to represent the rigid-body attitude. For example, quaternion feedback has been used in spacecraft control [Wie et al., 1989, Wie and Barba, 1985], manip- ulators control [Yuan, 1988], robot writs [Salcudean, 1988] and aerial vehicles [Tayebi and McGilvray, 2006]. A comprehensive study of unit quaternion feedback control ap- pears in [Wen and Kreutz-Delgado, 1991] where different quaternion-based control laws have been investigated and compared. The controllers share the common structure of a proportional-derivative feedback plus some feedforward Coriolis torque compensation and/or adaptive compensation. Different robust [Joshi et al., 1995], adaptive [Egeland and Godhavn, 1994], velocity-free [Lizarralde and Wen, 1996, Tayebi, 2008] quaternion feedbacks have been also developed in the past decades. The main drawback of using the unit-quaternion representation is the fact that every attitude can be represented, equivalently, by two different quaternions. This nonuniqueness in representing the atti- tude, if not taken carefully, might result in quaternion-based controllers with undesirable phenomena such as the so-called unwinding phenomenon 1 [Sanjay P. Bhat, 2000]. There have been some attempts to design quaternion-based attitude control systems that do not suffer from the unwinding phenomena by introducing discontinuities, see for instance [Thienel and Sanner, 2003]. However, these discontinuous attitude control systems suffer from non-robustness to arbitrary small measurement disturbances as discussed in [May- hew and Teel, 2011a]. In [Mayhew, 2010, Mayhew et al., 2011], hybrid controllers have been proposed to ensure robust global asymptotic stabilization via quaternion feedback. Also, other hybrid techniques where used in [Mayhew, 2010] to remove the ambiguity in selecting the best quaternion to represent an attitude measurement on SO (3).

Abstract: With the widespread use of automobiles, people's demand for the safety performance of vehicles is also increasing. Nowadays, all kinds of safety technology and equipment are widely used in automobile, such as safety belt, safety seat, air bag and so on. However, the safety performance of a car that falling into the water is rarely considered. Once the car fell into the water and was flooded accidentally, it will be very difficult for passenger to survival which will result in enormous loss of life and property. Aimed at this problem, this paper presents a particular solution. The design on attitude control system can correct the attitude of the car and let it float when the car falling into the water. After being rescued successfully, the car can travel normally after a careful examination and simple maintenance .

The increase of satellite’s dimensions has caused flexibility and formation of uncertainty in their model. This is because of space missions being more complex and using light moving structures in satellites. Satellites are also encountered with various circumferential disturbance torques. This uncertainty in model and disturbance torques will cause undesir- able performance of satellites’ attitude control system. So, for attitude control of these satellites, those methods should be used which are robust to uncertainty of the plant’s model and can reject the effects of disturbances and the measure- ment noise. One of these methods is the robust control design method. But, because of pole’s place of these satellite’s dynamics equations, the designing procedure of robust control will face difficulties. In this paper, by using an internal feedback as a novel idea, the satellite’s dynamics equations are changed in such a way that the poles will be placed in proper locations. Then, for these new equations, by regarding the effects of flexibility as uncertainty and considering the uncertainty in inertia matrix of satellite, an H ∞ controller has been designed and for better performance, a μ -controller has been improved. Afterwards, these two controllers are analyzed and compared for the original dynamic equations, not for the modified ones. Also, for comparison, a classic controller has been also designed for the original plant and eventually all these three controllers are compared with each other.

Attitude control systems, which have ON-OFF actuators, generally converge to a stable limit cycle in their steady state. In the literature, two main reasons are presented for causing this limit cycle. The first reason relates to physical characteristics of ON-OFF actuators. These actuators often have a minimum on-time which means that after the actuator turns ON, there will be no possibility to turn it off in time (thruster valves must stay open over a finite time interval). Therefore, the energy delivered to the system – unlike to the case of using proportional actuators- has a minimum positive value. This cancels the possibility of reaching to the equilibrium state and staying there [2, 5]. The second reason, which causes the limit cycle, is due to the command system. Generally, commanding to the ON-OFF actuator, needs some intermediate systems (such as modulator or bang- bang switches) to change the continuous control command generated by the controller to the ON-OFF command. These intermediate systems generally have a minimum duty cycle or minimum on-time, like the minimum on-time of the actuator, causes a limit cycle. [6]

Abstract:- A Field Oriented control scheme for a BLDC (Brush Less Direct Current) motor is presented. The mo- tor is used for attitude control of 3U sized Pico satellite by exchanging angular momentum with the rigid body. Compared to the conventional control schemes which give performance limitations, with FOC a better dynamic per- formance can be achieved, even the algorithm introduce more complex mathematical transformations in order to decouple the torque generation. The algorithm itself is implemented directly in the hardware and with the math- ematical processing power of modern micro controllers such advanced control algorithms are easily implemented. Computer simulation is presented to verify the control strategy.

Chaos the concept and mathematical precision, seemingly random and complex phenomenon which is inherent deterministic nature. Chaotic dynamics of some features that are important, it is very sensitive to initial conditions (that is, very little difference in the initial conditions that will change future behavior of the rate difference is proportional to Lyapunov exponent) so at first thought that the dynamics are uncontrollable chaos. One of the concepts of chaos control stabilization of chaotic dynamics in unstable equilibrium points. First time in [1] proved that there is a problem of chaos control. They show that a very small control signal can be made to provide conditions for the control chaos dynamics. This is a characteristic of chaos, which is not possible at all nonlinear dynamics model. Then, many methods have been introduced, such as fuzzy control [2], adaptive feedback [3] sliding mode [4], impulsive control [5], backstepping control [6]. So in the past two decades, the problem of controlling chaos dynamics has attracted much interest from researchers. Control chaos, in many applications, including secure communication [7], gyroscopes [8], removal of heart rhythms [9], and many others in [10, 11] has been introduced. In this paper, chaotic satellite attitude control problem with unknown inputs and uncertainties are discussed. The research in [12] was proven to be chaotic attitude motion satellite. Hence, a sliding mode controller design method is proposed for stabilizing the attitude motion chaotic of satellite. Recently, various researches and publications introduced the chaotic dynamics of the satellites. Methods that have been introduced thus far include predictive control [13], impulsive control [14], and neural networks [15]. The second part of the describes the chaotic state of satellite dynamics. Next controller design method is explained. Fourth, the problem attitude control of the satellite with unknown inputs and uncertainties expressed. Finally, part five illustrates the simulation results.

The attitude control of satellites is a significant objective of researchers during past decade of studies. Based on conventional methods modeling of satellite is carried out with various approaches depending on design specification and different uncontrollable external factors. As further investigation in attitude control of satellite this study aim to design a satellite’s attitude control the geosynchronous communication satellite IPSTAR as case study which addressed in (Franklin et al., 2002 ). The proposed satellite is composed of main body as carrier, and the scientific sensor package to capture and transmit the cosmic events. The main aim of this study is to present the appropriate and satisfactory controller strategy in order to meet the best satellite’s attitude in terms of desired dynamic response in the space, especially when the satellite is moving to settle in the new position. Furthermore; the comparative control approach has been intended in this study namely, state-feedback controller and linear quadratic regulator (LQR).

2 Inertial Measurement Unit (IMU). IMU is an electronic device and will provide information about the velocity, orientation, and gravitational forces of rigid body. An IMU system has three types of inertial sensors which are gyroscopes, accelerometer and magnetometer will provide three inertial measurement for three different axis (x, y and z axis). Due to the low cost sensors, may be affected by noise. For example, Micro-electrical mechanical system (MEMS) gyroscopes is used to measure angular rate of rotation along roll, pitch and yaw axis, it usually suffer from measurement noise due to vibration. Besides that, poor implementation process for the linear controllers will also affect the attitude and stability of the UAVs. Hence, this study is going to design and fabricate robust attitude control with low cost hexacopter that propose a stable attitude state feedback linear controller model used for behavior and control algorithm testing under indoor environment which neglect all the disturbance, before implementation on the experimental setup.

However, the spiral mode can correspond to either a slow convergent or a divergent motion.one of the most Important function of any AFCS operating on lateral motion must be therefore to attain a high degree of spiral stability, but it must also improve the others latest flying qualities to that a pilot is not ‘worn out’ whenever he is flying in atmospheric turbulence. By providing the aircraft with good static stability good spiral stability can be achieved. Therefore in order to achieve degree of dynamic stability desired in roll requires the use of the roll attitude control system such a feedback control system maintains the roll attitude in the preserve of disturbances and the responds rapidly and accurately to roll commands from the pilot or a guidance system. For most aircrafts the following assumptions hold: (i) 𝑇 𝑅 ≪ 𝑇 𝑠 , and (ii) the quadratic term in numerator of Eq. 8 cancels the quadratic term in the denominator.

adaptive method is implemented. The spacecraft attitude control subsystem simulator consists of a platform, an air-bearing and a set of four reaction wheels. This set up provides a free real-time three degree of freedom rotation. Spacecraft simulators are applied in upgrading and checking the control algorithms' performance in the real space conditions. The LMI controller is designed, through linearized model. The robust adaptive controller is designed based on nonlinear dynamics in order to overcome a broader range of model uncertainties. The stability of robust adaptive controller is analysed through Lyapunov theorem. Based on these two methods, a series of the laboratory and computer simulation are made. The tests’ results indicate the accuracy and validity of these designed controllers in the experimental tests. It is observed that, these controllers match the computer simulation results. The spacecraft attitude is converged in a limited time. The laboratory test results indicate the controller ability in composed uncertainty conditions (existence of disturbances, uncertainty and sensor noise).

Abstract— After launching, the initial condition of satellite is unknown and tends to be in a tumbling state. At this moment, the satellite needs to reduce the tumbling rate so that the satellite can enter a stable and unruffled state. The satellite also must maintain a certain attitude while orbiting in order to allow precise pointing of the antenna toward the earth. In this study, a hardware-in-loop- simulator was devised for the purpose of improving the design and verifying attitude control concepts for Innovative Satellite (InnoSAT) system. A new software architecture and algorithm was developed based on the controller, InnoSAT plant, actuator and sensor. Firstly, the controller, actuator and sensor was modelled in the MATLAB program together with InnoSAT plant. The actuator and sensor were assumed to be ideal. However, some properties of the actuator and sensor were simulated in the software simulator. If the software simulation performed satisfactorily, the control algorithm will be embedded into Rabbit Micro Controller (RCM4100) using Dynamic C language. This is the part where the hardware simulation is developed which is creating hardware-in- loop-simulation technique for verification of InnoSAT Attitude Control System (ACS) performance. The satellite simulator was tested using simulated data in order to observe the performances of the controller in real time simulation. The results show that the InnoSAT ACS simulator can produce as good result as a MATLAB simulation for the InnoSAT plants. From the results, it is adequate to verify that the developed protocol working satisfyingly and seems to be possible to be implemented on the actual flight.

The Satellite Technology Research Centre (SaTReC) in Korea started research in the field o f micro-satellites in 1989 in collaboration with the United Kingdom. A fter the successful launches and operations o f KITSATs 1 and 2, SaTReC has gained considerable expertise in space technology. Based upon these experiences, the KITSAT- 3 programme w as proposed in 1994 to develop and demonstrate advanced space technology. Compared to its two predecessors, KITSAT-3 has m ore sophisticated requirements, especially in the area o f attitude control and the remote sensing payload. There has been a great leap in technological achievement between these programmes. H igh accuracy three-axis attitude stabilisation is one o f the m ost demanding requirements among them. Figure 1-1 shows the outlines o f the KITSAT series satellites. SaTReC has sponsored a number o f students via international corporations with overseas educational institutes since the start o f its activities in space. A group o f students who studied at University College London played a key role in the KITSAT-3 programme. These scientists and engineers are now actively engaged in the Korean domestic space programme. T he currently booming space industry in K orea will benefit from the results attained during the KITSAT-3 programme.

Simulated World The simulated world is constructed specifically for UAV attitude control in mind. The technique we developed allows attitude control to be accomplished independently of guidance and/or navigation control. This is achieved by fixing the center of mass of the aircraft to a ball joint in the world, allowing it to rotate freely in any direction, which would be impractical if not impossible to achieved in the real world due to gimbal lock and friction of such an apparatus. In this work the aircraft to be controlled in the environment is modeled off of the Iris quadcopter [9] with a weight of 1.5 Kg, and 550 mm motor-to-motor distance. An illustration of the quadcopter in the environment is displayed in Figure 3. Note during training Gazebo runs in headless mode without this user interface to increase simulation speed. This architecture however can be used with any multicopter as long as a digital twin can be constructed. Helicopters and multicopters represent excellent candidates for our setup because they can achieve a full range of rotations along all the three axes. This is typically not the case with fixed-wing aircraft. Our design can however be expanded to support fixed-wing by simulating airflow over the control surfaces for attitude control. Gazebo already integrates a set of tools to perform airflow simulation. Interface The digital twin layer provides two command interfaces to the communication layer: simulation reset and motor update. Simulation reset commands are supported by Gazebo’s API and are not part of our implementation. Motor updates are provided by a UDP server. We hereby discuss our approach to developing this interface.

This project intends to look into passive and active ACS based on gravity gradient control and magnetic attitude control respectively. Firstly mathematical models of a gravity gradient satellite will be determined. Subsequently this model will be equipped with electromagnetic based device called magnetic torques for active control. Performance of both designs will be tested and simulated in the presence of a simplified geomagnetic field model as well as disturbance torques model using MATLAB/SIMULINK.

Utilizing magnetic torque for spacecraft attitude control is a common way since the actuator is light, non- expensive and relatively easy to use. The contribution of this paper is to simulate the earth’s magnetic field precisely and to study the accuracy of some common approximate models as well. In addition, utilizing the earth’s magnetic field as a way for spacecraft attitude control and its considerations, such as using different transformations, are investigated. In order to apply this torque, the earth’s magnetic field has to be modeled accurately. In this study, the 11 th generation of IGRF

To gather information rapidly in disaster sites, a lot of search/rescue robots have been developed. It is difficult to correspond to the complicated environment composed of fields requiring various locomotion strategies, because most of these robots have only one type of locomotion device. To increase the available search routes under such conditions with the aim of gathering information more efficiently, we have previously proposed a legged aerial vehicle. The vehicle has tandem rotors to fly in the air and four legs to walk on the ground. The particular feature of this robot is that it has fewer actuators than the sum of those required for controlling a quadrupedal robot and a tandem-rotor helicopter individually. This paper presents modeling of the robot and development of an attitude control system that uses the leg motions. The behavior of the vehicle with the proposed attitude control is simulated using Multibody Dynamics (MBD) simulation software.

In [15], a non-adaptive robust control scheme based on the quaternion feedback for attitude control of aprojectile which employs thrust vector controlis proposed. The control law consists of two parts: the nominal feedback part and an additional term to guarantee the robustness against the plantuncertainties. Quaternion attitude control of a projectile model, which is nonlinear inaerodynamics with atmospheric moment and inertia coefficients uncertainties together with bounded disturbances, is presented in [16]. In this work, a free chattering adaptive sliding mode controlleris designed based on back stepping technique to stabilize the state variables of the closed loop system to a small region of there ference states.

It is important to understand the range of limitations of these SMC methods before further improvements can be made. Hence, the main novelty of this paper is to design and investigate the SMC control law with a focus on the switching function (SFD) characteristics and capability at two different points (critical gains and proper gains) for a spacecraft’s attitude control. A notable part of the proposed approach is that some of the gains can be tuned using trial and error while satisfying some mild conditions to ensure the existence of a sliding mode. Characteristics such as chattering in the control inputs and transient response in the outputs are observed. Consequently, the switching function with most advantages is chosen as a basis for proposed improvements. On the other hand, ideally, the discontinuous control law must produce chattering due to a fast switching mechanism and discontinuous control across the sliding surface [8]. In this paper, approaches for chattering attenuation are not discussed and elimination techniques are proposed for future work.