Spacecraft Simulator Research Articles

Decentralized formation pose estimation for spacecraft swarms

For spacecraft swarms, the multi-agent localization algorithm must scale well with the number of spacecraft and adapt to time-varying communication and relative sensing networks. In this paper, we present a decentralized, scalable algorithm for swarm localization, called the Decentralized Pose Estimation (DPE) algorithm. The DPE considers both communication and relative sensing graphs and defines an observable local formation. Each spacecraft jointly localizes its local subset of spacecraft using direct and communicated measurements. Since the algorithm is local, the algorithm complexity does not grow with the number of spacecraft in the swarm. As part of the DPE, we present the Swarm Reference Frame Estimation (SRFE) algorithm, a distributed consensus algorithm to co-estimate a common Local-Vertical, Local-Horizontal (LVLH) frame. The DPE combined with the SRFE provides a scalable, fully-decentralized navigation solution that can be used for swarm control and motion planning. Numerical simulations and experiments using Caltech’s robotic spacecraft simulators are presented to validate the effectiveness and scalability of the DPE algorithm.

Ground experiment on rendezvous and docking with a spinning target using multistage control strategy

The spacecraft rendezvous and docking technology has been playing an important role in space missions. This study deals with the planar rendezvous and docking of a chaser spacecraft simulator with a spinning target spacecraft simulator on the air-bearing testbed. On the basis of relative pose information for positions and attitudes, the paper presents the controller formulated in an analytical form, which accounts for the collision avoidance constraint between the two simulators and simultaneously takes the obstacle collision restriction into consideration. The stability analysis ensures that the system state controlled asymptotically converges to the desired state. In addition, to demonstrate the hardware-in-the-loop experiment verification, the paper presents the two floating simulators equipped with electromagnetic docking mechanism, as well as a closed-loop system via the binocular vision-based data acquisition method and the wireless transmission device. The test results show that the multistage control strategy proposed can successfully realize the collision-free docking of the chaser simulator and the spinning target simulator.

Basilisk: A Flexible, Scalable and Modular Astrodynamics Simulation Framework

The Basilisk astrodynamics framework is a spacecraft simulation tool developed with an aim of strict modular separation and decoupling of modeling concerns in regard to coupled spacecraft dynamics, environment interactions, and flight software algorithms. Modules, tasks, and task groups are the three core components that enable Basilisk’s modular architecture. These core components are described and their functionality demonstrated. The Basilisk message-passing system is a critical communications layer that facilitates the routing of input and output data between modules. Furthermore, this paper outlines Basilisk’s data logging and Monte Carlo simulation functionality. The implementation of Basilisk’s Python wrapped C++/C technology stack is described. Finally, a sample spacecraft attitude control simulation demonstrates the modularity and flexibility of the framework.

Analytical Solving the Optimal Control Problem of Spacecraft’s Slew Maneuver with Minimal Energy of Rotation

Dynamic problem of optimal reorientation from an arbitrary initial attitude into the given final angular position with restricted control which minimizes kinetic energy of spacecraft rotation was solved. Termination time of maneuver is known. Quadratic criterion of quality is applied for finding the optimal control program. Use of integral index in special form concerning angular velocity has helped solve the formulated problem by analytical way. Control law was written down in explicit form. Designing the optimal control is based on quaternion variables and models. It is shown that during optimal turn, the controlling moment is parallel to the straight line which is immobile in the inertial space, and direction of spacecraft’s angular momentum in the process of rotation is constant relative to the inertial coordinate system. Special control regime was studied in detail, and conditions of the impossibility of occurrence of this regime are formulated. It is proven that spacecraft rotates by inertia in special control regime if it exists. The formalized equations and computational expressions for determining the optimal rotation program and duration of acceleration and braking were written. A dependence of control variables on phase coordinates is presented also. The proposed control algorithm allows the spacecraft’s reorientation to be carried out within the fixed time period with minimal angular kinetic energy. Analytical expressions for computing the time characteristics of reorientation maneuver are given, and condition for determination of the moment of the beginning of the braking, based on factual kinematic parameters of motion judging by principles of terminal control is formulated, that provides high accuracy of orientation. A comprehensive solution to the control problem is presented for a dynamically symmetric spacecraft: the dependences as explicit functions of time for the control variables are obtained, and relations for calculating the key parameters of the turn maneuver’s control law are given also. A numerical example and the results of mathematical simulation of spacecraft’s motion with optimal control are presented, which demonstrate the practical feasibility of the designed method for controlling the spacecraft attitude. Presence of ready formulas for synthesis of optimal motion program during reorientation maneuver does the executed research as practically significant and suitable for direct use in practice of space flights.

Autonomous in-orbit satellite assembly from a modular heterogeneous swarm

This paper presents a decentralized, distributed guidance and control scheme to combine a heterogeneous swarm of component satellites into a large satellite structure. The component satellites for the heterogeneous swarm are chosen to promote flexibility in final shape inspired by crystal structures and Islamic tile art. After the ideal fundamental building blocks are selected, basic nanosatellite-class satellite designs are made to assist in simulations involving attitude control. The Swarm Orbital Construction Algorithm (SOCA) is a guidance and control algorithm to allow for the limited type heterogeneity and docking ability required for in-orbit assembly. The algorithm consists of two parts, a distributed auction which uses barrier functions to ensure the proper agent selection for each target, and a trajectory generation portion which leverages model predictive control and sequential convex programming to achieve optimal collision-free trajectories to the desired target point even with nonlinear system dynamics. The optimization constraints use a boundary layer to determine whether the collision avoidance or the docking constraints should be applied. The algorithm was tested in a simulated perturbed 6-DOF spacecraft dynamic environment for planar and out-of-plane final structures and on two robotic platforms, including a swarm of frictionless spacecraft simulation robots.

Prospects for the Introduction of the Interactive Electronic Technical Manuals Technology in the Practice of Operation of Manned Spacecraft Simulators

The paper considers an existing information technology to support operation of products namely the technology of interactive electronic technical manuals (IETM) and substantiates the expediency of introducing this technology in the practice of operation of the manned spacecraft simulators.

Optimization Provenance of Whiplash Compensation for Flexible Space Robotics

Automatic controls refer to the application of control theory to regulate systems or processes without human intervention, and the notion is often usefully applied to space applications. A key part of controlling flexible space robotics is the control-structures interaction of a light, flexible structure whose first resonant modes lie within the bandwidth of the controller. In this instance, the designed-control excites the problematic resonances of the highly flexible structure. This manuscript reveals a novel compensator capable of minimum-time performance of an in-plane maneuver with zero residual vibration (ZV) and zero residual vibration-derivative (ZVD) at the end of the maneuver. The novel compensator has a whiplash nature of first commanding maneuver states in the opposite direction of the desired end state. For a flexible spacecraft simulator (FSS) free-floating planar robotic arm, this paper will first derive the model of the flexible system in detail from first principles. Hamilton’s principle is augmented with the adjoint equation to produce the Euler–Lagrange equation which is manipulated to prove equivalence with Newton’s law. Extensive efforts are expended modeling the free–free vibration equations of the flexible system, and this extensive modeling yields an unexpected control profile—a whiplash compensator. Equations of motion are derived using both the Euler–Lagrange method and Newton’s law as validation. Variables are then scaled for efficient computation. Next, general purposed pseudospectral optimization software is used to seek an optimal control, proceeding afterwards to validate optimality via six theoretical optimization necessary conditions: (1) Hamiltonian minimization condition; (2) adjoint equations; (3) terminal transversality condition; (4) Hamiltonian final value condition; (5) Hamiltonian evolution equation; and lastly (6) Bellman’s principle. The results are novel and unique in that they initially command full control in the opposite direction from the desired end state, while no such results are seen using classical control methods including classical methods augmented with structural filters typically employed for controlling highly flexible multi-body systems. The manuscript also opens an interesting question of what to declare when the six optimality necessary conditions are not necessarily in agreement (we choose here not to declare finding the optimal control, instead calling it suboptimal).

Modeling and collision avoidance control for the Disturbance-Free Payload spacecraft

The Disturbance-Free Payload (DFP) spacecraft, which includes the payload module (PM) and the support module (SM) connecting through voice coil motors (VCM), can provide unprecedented control and motion stability for the sensitive payload. The payload module and the support module have a high collision probability because of close proximity formation. In order to perform collision avoidance control on two modules, this paper establishes the dynamics model of the DFP spacecraft and proposes a collision avoidance control strategy based on the model predictive control (MPC). The established model synthesizes the back-Electromotive-Force (back-EMF) of the VCM and the stiffness and damping of the flexible cables. The MPC controller converts the collision avoidance problem into a quadratic programming problem. The control forces are obtained by solving the quadratic programming problem. The collision avoidance control simulation of the DFP spacecraft has performed while the payload module subjects to sudden disturbance. The simulation results verify the effectiveness of the proposed control strategy and show that the proposed MPC controller exhibits better collision avoidance capability than that of the PD controller.

Novel Non-Model-Based Fault Detection and Isolation of Satellite Reaction Wheels Based on a Mixed-Learning Fusion Framework

Abstract This paper suggests a model-free framework for Fault Detection and Isolation (FDI) of satellite reaction wheels for the first time. The proposed FDI method is based on multi-classifier fusion with diverse learning algorithms and configured in a parallel form where a unique module simultaneously performs both detection and isolation tasks. In other words, a multi-classifier-based arrangement is presented on the basis of Mixed Learning strategy where four classic and well-practised classification schemes including Random Forest, Support Vector Machine, Partial Least Square, and Naive Bayes are incorporated into FDI module in order to make a decision on the occurrence of a fault and its location. Extensive simulation results with a high-fidelity nonlinear spacecraft simulator considering gyroscopic effects, measurement noise, and exogenous aerodynamic disturbance signals show that the proposed FDI scheme can cope with faults affecting reaction wheel torques and obtain promising FDI performances in most of the designed scenarios.

Attitude control of spacecraft simulator without angular velocity measurement

In this paper the attitude control of a spacecraft simulator using Reaction Wheels (RW) as the actuators is investigated. The main goal of the current study is to bring the RWs to the rest at the end of the maneuver without angular velocity measurement. A modified feedback linearization controller is applied by considering the Euler angles of the simulator as the output and the RWs angular momentums as the internal state variables. The stability of the proposed controller and the internal dynamics is analyzed using Lyapunov theory. Two modified sliding mode observers are designed to estimate the angular velocities of the spacecraft attitude control subsystem simulator. The proposed observers do not use the control input and the detailed knowledge of the model and thus it can be implemented easily. The global stability of the system is proved. The proposed controller and observers are finally evaluated numerically and experimentally on an attitude spacecraft simulator.

Modular Software Architecture for Fully Coupled Spacecraft Simulations

Computer simulations of spacecraft dynamics are widely used in industry and academia to predict how spacecraft will behave during proposed mission concepts. Current technology and performance requirements have placed pressure on simulations to be increasingly more representative of the environment and the physics that spacecraft will encounter. This results in increasingly complex computer simulations. Designing the software architecture in a modular way is a crucial step to allow for ease of testing, maintaining, and scaling of the software code base. However, for complex spacecraft modeling including flexible or multibody dynamics, modularizing the software is not a trivial task because the resulting equations of motion are fully coupled nonlinear equations. In this paper, a software architecture is presented for creating complex fully coupled spacecraft simulations with a modular framework. The architecture provides a solution to these common issues seen in dynamics modeling. The modularization of the fully coupled equations of motion is completed by solving the complex equations analytically such that the spacecraft rigid-body translational and rotational accelerations are solved for first and the other second-order state derivatives are found later. This architecture is implemented in the Basilisk astrodynamics software package and is a fully tested example of the proposed software architecture.

A suboptimal excitation torque for parameter estimation of a 5-DOF spacecraft simulator

Five degrees of freedom spacecraft simulators are designed to verify spacecraft control strategies, rendezvous and docking techniques. The accurate knowledge of simulator inertia parameters which can be calculated by parameter estimation is of vital importance in these experiments. However, the rotation limits of the simulator must be considered during estimation process. This paper presents an approach to determine a suboptimal excitation torque for the system identification of the inertia parameters. The continuous optimization problem is transcribed into a discrete nonlinear programming problem by integral gauss pseudospectral method. To reduce the effect of noise, the states and inertia parameters are estimated simultaneously by joint filter within Extended Kalman Filter (EKF) or Unscented Kalman Filter (UKF). The proposed method is validated by simulations and the results indicate that this method not only satisfies the constraints of simulator rotation angles, but also improves the efficiency of parameter estimation.

PID 컨트롤러를 이용한 우주선 시뮬레이터의 자동 밸런싱 시스템

PID 컨트롤러를 이용한 우주선 시뮬레이터의 자동 밸런싱 시스템

Tube-based robust model predictive control for spacecraft proximity operations in the presence of persistent disturbance

Rendezvous and Proximity Operations (RPOs) of two autonomous spacecraft have been extensively studied in the past years, taking into account both the strict requirements in terms of spacecraft dynamics variations and the limitations due to the actuation system. In this paper, two different Model Predictive Control (MPC) schemes have been considered to control the spacecraft during the final phase of the rendezvous maneuver in order to ensure mission constraints satisfaction for any modeled disturbance affecting the system. Classical MPC suitably balances stability and computational effort required for online implementation whereas Tube-based Robust MPC represents an appealing strategy to handle disturbances while ensuring robustness. For the robust scheme, the computational effort reduction is ensured adopting a time-varying control law where the feedback gain matrix is evaluated offline, applying a Linear Matrix Inequality approach to the state feedback stabilization criterion. An extensive verification campaign for the performance evaluation and comparison in terms of constraint satisfaction, fuel consumption and computational cost, i.e. CPU time, has been carried out on both a three degrees-of-freedom (DoF) orbital simulator and an experimental testbed composed by two Floating Spacecraft Simulators reproducing a quasi-frictionless motion. Main conclusions are drawn with respect to the mission expectations.

An adaptive control allocator for autonomous vehicles with parameter uncertainty

In this article, an adaptive control allocation scheme for a class of nonlinear vehicles is proposed. The parameter uncertainty of the effectors is considered in the design of the control allocation algorithm. A reference model is integrated in the framework to overcome the negative effects brought by the parameter uncertainty. The optimum of the solution is discussed for a class of objectives. Stability proof is given. Compared to most existing methods, the conditions to guarantee the stability of the system are relaxed, which is addressed in the theoretical analysis and the experiment. Finally, a digital simulation and an experiment based on a spacecraft simulator are implemented. The results of the simulation and the experiment validate the effectiveness and advantages of the proposed adaptive control allocator.

Robust Control of Spacecraft: Application to an Actuated Simulator

In this article, a hardware-in-the-loop implementation of two robust controllers based on high-order sliding mode and μ-synthesis method are performed and compared in terms of performance and functionality. The spacecraft simulator consists of a free-floating platform hinged on a spherical air-bearing support. The proposed scheme makes full use of adaptive super twisting algorithm to alleviate the chattering effects without increasing the control effort; both controllers are adapted to deal with the saturation of reaction wheels with respect to momentum and its rate of change. The ab-initio simulations compared well with the simulator responses, implying that involved instruments including actuators and sensors have been properly emulated. This also proved that the external disturbances were modeled in a reliable manner. The robustness and effectiveness of the proposed scheme have been validated experimentally under extreme circumstances and uncertainties.

Методическое обеспечение разработки и создания тренажеров пилотируемой космонавтики для отработки управленческих решений в нештатных ситуациях

Методическое обеспечение разработки и создания тренажеров пилотируемой космонавтики для отработки управленческих решений в нештатных ситуациях

Active Vibration Suppression of Flexible Spacecraft During Attitude Maneuver With Actuator Dynamics

A novel active vibration suppression approach based on a flywheel actuator for flexible spacecraft during attitude maneuvering is proposed in this paper. The flywheel is regarded as the only actuator. The rotation of the flywheel, the motion of the rigid body, and the vibration of the modes are coupled in this paper. The system model is obtained using the Euler-Lagrange methodology and the Assumed-mode Method, in which the dynamics of the flywheel is considered. The stability of the flywheel transfer function from input voltage to output torque is analyzed using the Lyapunov method. Effects on system caused by flywheel are analyzed. Based on component synthesis vibration suppression theory, a typical vibration suppress law during attitude maneuver is derived. The input voltage of the flywheel actuator is designed according to this law. The presented novel approach is easily applied and practical without changing the spacecraft’s structure properties. The simulation results and experiments on an air bearing spacecraft simulator are presented to verify the efficacy of the proposed approach.

Hybrid Control for Autonomous Spacecraft Rendezvous Proximity Operations and Docking

A hybrid control methodology is presented for autonomous rendezvous, proximity operations and docking of a pair of spacecraft. For the theoretical development of the control algorithms, the dynamics of the spacecraft are modeled using the Clohessy-Wiltshire-Hill equations, which result in a linear system of relative motion equations. Only in-plane motion is considered, resulting in a two-dimensional system, and the control input is the acceleration vector of the active spacecraft, constrained by a maximum thrust value. Individual controllers are designed for different phases of the of approach and transitions are governed by a hybrid supervising algorithm. The hybrid control algorithm is implemented both in MATLAB, using a simplified dynamic model, as well as in actual spacecraft flight code and tested in a high-fidelity spacecraft simulation test environment.

Inertia and Center of Mass Estimation of a 3 DoF Air Bearing Platform

Rigorous ground testing of spacecraft dynamics will significantly reduce various risks to a mission. A spherical-air-bearing-based testing platform provides nearly frictionless rotations about the three axes and can be used to simulate spacecraft attitude dynamics on Earth. However, gravity-induced unbalance torque causes undesirable disturbances on the platform during testing. This paper explores two techniques for estimating the inertia properties and center of mass offset values of a spacecraft simulator with three rotational degrees of freedom. Numerical simulation results of these two estimation techniques: a batch method using linear least squares, and an online method using recursive least squares, are reported. These techniques are then compared in terms of accuracy of the estimated parameters, noise sensitivity, and computational load.