Characterization of a High Thrust, Pressure-Fed Electrospray Thruster for Precision Attitude Control Applications

Nonlinear guaranteed cost attitude control via dynamic gain design

When naval vessels moving on the sea, the carrier air wake disturbance will arise. The carrier air wake makes the landing environment of carrier aircraft fair adverse, which puts forward a high demand for the high precise attitude control of carrier based aircrafts. In this paper, high precise robust attitude control problems for carrier based aircrafts with the carrier air wake disturbance are investigated. Firstly, the small disturbance linearization method is introduced to transform the nonlinear system into a linear one, which is a necessary procedure for aircraft system analysis and controller design. Secondly, the model of the carrier air wake disturbance is established and its effects on the aerodynamic parameters are analyzed in detail. Then the effects are transformed into the augmented disturbance in the system. Thirdly, a nonlinear extended state observer is utilized to estimate the disturbance. Besides, a robust adaptive attitude controller with integral term is proposed to achieve high precision attitude tracking. The stability of the closed-loop system is prove based on Lyapunov theory. Finally, a numerical example is provided to demonstrate the effectiveness of the obtained results.

Spacecraft attitude control systems rely on reaction wheels as the primary means of precise three-axis attitude control. Faults in these reaction wheels might lead to system instability and, in severe cases, mission failure. This paper presents advanced machine learning-based techniques for the detection, isolation, and identification of reaction wheel faults in spacecraft.The proposed approach leverages advanced data analytics and machine learning algorithms to analyze sensor data from the reaction wheels, enabling early detection of faults and effective isolation of the faulty component and identify the types of faults detected, specifically, voltage, current and temperature faults.Three-axis controlled satellite high-fidelity models are simulated to generate data for both nominal and faulty states of RW. The simulated data is employed with the FDII approach. The generated data is passed into five different machine learning classifiers, the isolation and identification results are verified via cross-validation. The proposed techniques is tested on three defined datasets using the three-orthogonal RW configuration to verify its robustness. The results show that the system has higher isolation and identification accuracy when compared to other studies that used various methodologies.

Visual servoing for coordinated precise attitude control in the TOM small satellite formation

Permanent magnet brushless direct current motor (BDCM) used in attitude control and energy storage flywheel system features large air gap and large radius-to-length ratio. The air gap flux density of this kind of BDCM along circumference orientation and axis one is analyzed. Equivalent flux leakage coefficient and equivalent flux density calculating coefficient are brought about and calculated in order to design the motor conveniently. The presented results are verified by prototype experiment.

This paper proposes an adaptive predefined-time accurate anti-unwinding attitude controller for a spacecraft with uncertain inertia. The novelty of the proposed algorithm lies in that the spacecraft attitude error is regulated to exact zero after a predefined settling time, which is an explicit parameter in the control algorithm. A time mapping function containing the predefined settling time is introduced, thus transforming the time scale of the original attitude control system. Then a composite barrier Lyapunov function is constructed to avoid the unwinding phenomenon in the attitude control process, and an adaptive backstepping attitude controller is designed based on the attitude system in the new time scale. The stability analysis of the attitude system is carried out based on LaSalle-Yoshizawa theorem, and it is proved that the attitude quaternion and angular rate can converge to zero accurately within the desired predefined time without using the spacecraft inertia information. Numerical simulation results show the effectiveness and superiority of the proposed controller.

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.

Multifrequency flexible vibration generated from solar arrays and deployable antennas has become the dominant disturbance source for communication spacecrafts with high precision, high stability, and fast-response attitude control requirements. Thereby, focusing on the accurate and rapid rejection of flexible vibration disturbance, a deep-coupled sliding mode disturbance observer (DO)-based composite attitude control scheme is proposed in this article for flexible communication spacecrafts. First, the dynamic of flexible vibration disturbance has been fully excavated and described by a recessive model, overcoming the conservativeness of derivative-bounded assumption in traditional methods. Second, a novel deep-coupled sliding mode DO with finite-time convergence and adaptive parameter estimation capabilities is proposed to estimate the flexible vibration disturbance, where the disturbance model has been fully utilized. Then, based on the output of deep-coupled sliding mode DO, a composite attitude control law is proposed by combining a finite-time backstepping control. Unified stability analysis has been conducted by combining the observer dynamic and attitude control dynamic. Finally, numerical simulation and experiment verification are respectively carried out to show the performances of the proposed method.

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.

Passivity-Based Iterative Learning Control for Spacecraft Attitude Tracking on SO(3)

The FORMOSAT-5 (FS-5), the fifth space program initiated in 2008, is currently developed by National Space Organization (NSPO) of the National Applied Research Laboratories (NARL) in Taiwan, Republic of China (ROC). The satellite will be deployed into a sun-synchronous orbit with 720-km altitude and 98.28o inclination angle. It is a threeaxis attitude stabilized spacecraft providing high precision attitude determination and control for a high resolution Remote Sensing Instrument (RSI). To meet the 0.012 deg, 3sigma, per axis, absolute bus attitude knowledge requirement flown-down from RSI for meeting its geo-location accuracy, the micro-Advanced Stellar Compass (ASC) consisting of three Camera Head Units (CHUs) along with four single-axis fiber-optics gyros is mounted on a stable optical bench common to the RSI structure. The ASC is a highly advanced and fully autonomous star tracker produced by the Measurement & Instrument System (MIS) Section of the Orsted Department of the Technical University of Denmark (DTU). The gyroscopes considered in this mission are the fiber-optics rate sensors, -FORS6U, manufactured by Litef, a Northrop Grumman branch in Germany. The -FORS6U was originally designed to meet the requirements of a wide range of air, land, and sea applications, and was later certified by NSPO for space applications after a series of environmental tests. The primary spacecraft attitude and rate determination for the spacecraft Attitude and Orbit Control System (AOCS) will be provided by a gyro-stellar attitude determination system, which utilizes attitude data provided by three CHUs and rate data provided by the four single-axis fiber-optics gyros. To account for the possibility of more than one gyro failures due to lack of space-flight heritage, a gyro-less attitude and rate determination algorithm is developed as a back-up for the AOCS design. This paper describes the detailed development of a gyro-less attitude and rate determination algorithm which uses the computed gyro data (numerical gyro data) instead of physical gyro data as in a typical gyro-stellar attitude determination system. The numerical gyro data are computed using the assumed spacecraft dynamics (or Euler equations of motion). By perturbing the spacecraft kinematic equations, the linearized attitude error equations are obtained. Similarly, by perturbing the spacecraft dynamic equations, the linearized rate error equations are obtained. With the obtained linearized attitude error equations and the linearized rate error equations, a reduced-order (6-state) Extended Kalman Filter (EKF) providing spacecraft attitude and rate estimates is then implemented in the algorithm. The developed gyro-less attitude and rate determination algorithm was incorporated and tested in a 6-DoF nonlinear, high-fidelity simulation model developed for the FS-5 program to assess its performance. Its performance estimates and sensitivities to spacecraft inertia tensor uncertainties, reaction wheel momentum uncertainties, and torque uncertainties produced by torque-rods during normal operations will be presented in the paper.

Nonlinear adaptive control of an underwater towed vehicle

In response to the non-linear and underactuated characteristics of quadrotor UAV suspension transportation system, this paper proposes a novel control strategy aimed at achieving precise position control, attitude control, and anti-swing capabilities. Firstly, a dynamical model required for controller design is established through the Newton-Euler method. In the controller design process, the paper employs the energy method and barrier Lyapunov function to design a double-closed-loop nonlinear controller. This controller is capable of not only accurately controlling the position and attitude angles of the quadrotor UAV suspension transportation system but also effectively suppressing the swing of the payload. Building on this, considering the elastic deformation of the lifting cable, and by analyzing the forces in the Newton-Euler equations, this paper proposes an adaptive control design for the case where the length of the cable connecting the UAV and the payload is unknown. To validate the effectiveness of the proposed control scheme, comparative experiments were conducted in the MATLAB simulation environment, and the results indicate that the method proposed in this paper exhibits superior control performance compared to traditional controllers.

Over the next decade the gravitational physics community will benefit from dramatic improvements in many technologies critical to the tests of gravity and gravitational-wave detection. The highly accurate deep space navigation, interplanetary laser ranging and communication, interferometry and metrology, high precision frequency standards, precise pointing and attitude control, together with the drag-free technologies will revolutionize the field of the experimental gravitational physics. Deep-space laser ranging will be ideal for gravitational-wave detection, and testing relativity and measuring solar-system parameter to an unprecedented accuracy. ASTROD I is such a mission with single spacecraft; it is the first step of ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) with 3 spacecraft. In this paper, we will present the progress of ASTROD and ASTROD I with emphases on the acceleration noises, mission requirement, charging simulation, drag-free control and low-frequency gravitational-wave sensitivity.

The Engineering Systems Design Lab (ESDL) at the University of Illinois introduced Strain-Actuated Solar Arrays (SASAs) as a solution for precise satellite Attitude Control System (ACSs). SASA is designed to provide active mechanical vibration (jitter) cancellation, as well as small slew maneuver capabilities to hold a pose for short time periods. Current SASA implementations utilize piezoelectric distributed actuators to strain deployable structures, and the resulting momentum transfer rotates the spacecraft bus. A core disadvantage, however, is small strain and slew capability. Initial SASA systems could help improve pointing accuracy, but must be coupled with another ACS technology to produce large reorientations. A novel extension of the original SASA system is presented here that overcomes the small-displacement limitation, enabling use of SASA as a sole ACS for some missions, or in conjunction with other ACSs. This extension, known as Multifunctional Structures for Attitude Control (MSAC), can produce arbitrarily-large rotations, and has the potential to scale to large spacecraft. The system utilizes existing flexible deployable structures (such as solar arrays or radiators) as multifunctional devices. This multi-role use of solar panels extends their utility at a low mass penalty, while increasing reliability of the spacecraft ACS.