The design of the satellite attitude control system (ACS) becomes more complex when the satellite structure has different type of components like, flexible solar panels, antennas, mechanical manipulators, and tanks with fuel. A crucial interaction can occur between the fuel slosh motion and the satellite rigid motion during translational and/or rotational manoeuvre since these interactions can change the satellite centre of mass position damaging the ACS pointing accuracy. Although, a well-designed controller can suppress such disturbances quickly, the controller error pointing may be limited by the minimum time necessary to suppress such disturbances thus affecting the satellite attitude acquisition. As a result, the design of the satellite controller needs to explore the limits between the conflicting requirements of performance and robustness. This paper investigates the effects of the interaction between the liquid motion (slosh) and the satellite dynamics in order to predict what the damage to the controller performance and robustness is. The fuel slosh dynamics is modelled by a pendulum which parameters are identified using the Kalman filter technique. This information is used to design the satellite controller by the linear quadratic regulator (LQR) and linear quadratic Gaussian (LQG) methods to perform a planar manoeuvre assuming thrusters are actuators.

/pdf/satellite-attitude-control-system-design-considering-the-39austm00o.pdf

Satellite Attitude Control System Design considering the Fuel Slosh Dynamics

Design of Satellite Attitude Control System (ACS) that involves plant uncertainties and large angle manoeuvres following a stringent pointing control, may require new non-linear control techniques in order to have adequate stability, good performance and robustness. In that context, experimental validation of new non-linear control techniques through prototypes is the way to increase confidence in the controller designed. The Space Mechanics and Control Division (DMC) of INPE is con- structing a 3-D simulator to supply the conditions for implementing and testing satellite ACS hardware and software. The 3-D simulator can accommodate various satellites components; like sensors, actuators, computers and its respective interface and electronic. Depending on the manoeuvre the 3-D simulator plant can be highly non-linear and if the simulator inertia parameters are not well determined the plant also can present some kind of uncertainty. As a result, controller designed by linear control technique can have its performance and robustness degraded, therefore controllers designed by new non-linear approach must be considered. This paper presents the application of the State-Dependent Riccati Equation (SDRE) method in conjunction with Kalman filter technique to design a controller for the DMC 3-D satellite simulator. The SDRE can be considered as the non-linear counterpart of Linear Quadratic Regulator (LQR) control technique. Initially, a simple comparison between the LQR and SDRE controller is performed. After that, practical applications are presented to address problems like presence of noise in process and measurements and incomplete state information. Kalman filter is considered as state observer to address these issues. The effects of the plant non-linearities and noises (uncertainties) are considered in the performance and robustness of the controller designed by the SDRE and Kalman filter. The 3-D simulator simulink-based model has been developed to perform the simulations ex- amples to investigate the SDRE controller performance using the states estimated by the Kalman filter. Simulations have demonstrated the validity of the proposed approach, once the SDRE controller has presented good stability margin, great per- formance and robustness.

/pdf/application-of-the-state-dependent-riccati-equation-and-4m64wk0ril.pdf

Application of the State-Dependent Riccati Equation and Kalman Filter Techniques to the Design of a Satellite Control System

Real-time implementation of a parameterized Model Predictive Control for Attitude Control Systems of rigid-flexible satellite

Inertia properties of rigid body such as ground, aerial, and space vehicles may be changed by several occasions, and this variation of the properties influences the control accuracy of the rigid body. For this reason, accurate inertia properties need to be obtained for precise control. An estimation process is required for both noisy gyro measurements and the time derivative of the gyro measurements. In this paper, an estimation method is proposed for having reliable estimates of inertia properties. First, the Euler equations of motion are reformulated to obtain a regressor matrix. Next, the extended Kalman filter is adopted to reduce the noise effects in gyro angular velocity measurements. Last, the inertia properties are estimated using linear least squares. To achieve reliable and accurate angular accelerations, a Savitzky-Golay filter based on an even number sampled data is utilized. Numerical examples are presented to demonstrate the performance of the proposed algorithm for the case of a space vehicle. The numerical simulation results show that the proposed algorithm provides accurate inertia property estimates in the presence of noisy measurements.

/pdf/rigid-body-inertia-estimation-using-extended-kalman-and-2u5up6admp.pdf

Rigid Body Inertia Estimation Using Extended Kalman and Savitzky-Golay Filters

The satellite attitude control system (ACS) design becomes more complex when the satellite structure has components like, flexible solar panels, antennas and mechanical manipulators. These flexible structures can interact with the satellite rigid parts during translational and/or rotational manoeuvre damaging the ACS pointing accuracy. Although, a well-designed controller can suppress such disturbances quickly, the controller error pointing may be limited by the minimum time necessary to suppress such disturbances thus affecting the satellite attitude acquisition. This paper deals with the rigid-flexible satellite ACS design using the H infinity method. The rigid-flexible satellite is represented by a beam connected to a central rigid hub at one end and free at the other one. The equations of motions are obtained considering small flexible deformations and the Euler-Bernoulli hypothesis. The results of the simulations have shown that the H-infinity controller was able to control the rigid motion and suppress the vibrations.

https://iopscience.iop.org/article/10.1088/1742-6596/641/1/012030/pdf

H infinity controller design to a rigid-flexible satellite with two vibration modes

Future space missions will involve satellites with great autonomy and stringent pointing precision, requiring of the Attitude Control Systems (ACS) with better performance than before, which is function of the control algorithms implemented on board computers. The difficulties for developing experimental ACS test is to obtain zero gravity and torque free conditions similar to the SCA operate in space. However, prototypes for control algorithms experimental verification are fundamental for space mission success. This paper presents the parameters estimation such as inertia matrix and position of mass centre of a Satellite Attitude Control System Simulator (SACSS), using algorithms based on least square regression and least square recursive methods. Simulations have shown that both methods have estimated the system parameters with small error. However, the least square recursive methods have performance more adequate for the SACSS objectives. The SACSS platform model will be used to do experimental verification of fundamental aspects of the satellite attitude dynamics and design of different attitude control algorithm.

/pdf/satellite-attitude-control-system-simulator-2m8iqq6dkl.pdf

Satellite attitude control system simulator

The assessment of human and diagnostic resources is a prerequisite to improving the management of emergency neurology.To provide a landscape on the organization of the Lombardy Region hospitals for emergency neurological care management.We designed an anonymized questionnaire including 6 sections with 21 questions on facilities, human and diagnostic resources, and intra- and between-hospital connections. The time needed to fill the questionnaire was estimated not to exceed 6 min.The questionnaire was returned by 33/41 (80.5%) hospitals, 22 classified as level 1 (spoke), and 11 as level 2 (hub). Five of 33 (15%) did not have a neurology unit. The mean annual rate of neurological consultations accounted for 5-6% of all admissions (range 2-8%) and did not differ between levels 1 and 2 hospitals. Neurologists were 24-h available in 21/33 (64%) hospitals, 12-h and on call at night in 6 (18%), less than 12 h without nocturnal availability in 5 (15%), and neither present nor available in 1 (3%). Brain CT and CSF examinations were 24-h universally available, whereas EEG and neurosonology were not in most hospitals. Despite angio-CT was 24-h available in more than 75% of the hospitals, only 45% of them had 24-h availability of diffusion/perfusion imaging, and 43% were not available at any time. Only 12% of the hospitals had 24-h availability of neuroradiologists and 6% of interventional neuroradiologists.Our data, while emphasizing current critical issues, offer clues for identifying priorities and improving the management of emergency and time-dependent neurological diseases. 

/pdf/a-snapshot-of-emergency-neurology-management-in-the-lombardy-29rja3wi.pdf

G.T. Conti

Papers

Satellite attitude control system simulator

A snapshot of emergency neurology management in the Lombardy Region, Italy