Fred Y. Hadaegh

A coordination architecture for spacecraft formation control

This paper addresses the problem of coordinating multiple spacecraft to fly in tightly controlled formations. The main contribution of the paper is to introduce a coordination architecture that subsumes leader-following, behavioral, and virtual-structure approaches to the multiagent coordination problem. The architecture is illustrated through a detailed application of the ideas to the problem of synthesizing a multiple spacecraft interferometer in deep space.

Synchronized Formation Rotation and Attitude Control of Multiple Free-Flying Spacecraft

Intheobservationslewingoflongbaselineinterferometersformedbymultiplefree-e yingspacecraftinformation, it is required to rotate the entire formation about a given axis and to synchronize individual spacecraft rotation with formation rotation. Using a particle model for spacecraft formation dynamics and a rigid-body model for spacecraft attitude dynamics, control laws are derived for this mode of operation in the absence of a gravitational e eld and disturbances. A simplie ed control law suitablefor implementation isalso obtained. It is shown thatunder mild conditionstheformation alignmenterrordecaystozeroexponentiallywith time. Computersimulationstudies are made for a free-e ying spacecraft triad in a triangular formation. The results show that the developed control laws are effective in synchronized formation rotation.

A survey of spacecraft formation flying guidance and control (part 1): guidance

This paper provides a comprehensive survey of spacecraft formation flying guidance (FTG). Here by the term guidance we mean both path planning and optimal, open loop control design.

A feedback architecture for formation control

This paper addresses the problem of coordinating multiple spacecraft to fly in tightly controlled formations. The main contribution of the paper is to introduce a coordination architecture that subsumes leader-following, behavioral, and virtual-structure approaches to the multi-vehicle coordination problem. The architecture is illustrated through an application of the ideas to the problem of synthesizing a multiple spacecraft interferometer in deep space.

Control of Deep-Space Formation-Flying Spacecraft; Relative Sensing and Switched Information

Spacecraft formations in deep space can be specified in terms of the relative spacecraft positions and absolute spacecraft orientations. Accurate absolute position measurements are not available, and a formation control design approach, based on relative position information, is presented. This approach exploits the redundancy inherent in ar elative position specification to develop a family of equivalent control topologies for optimal formation control. Switching between topologies provides redundancy and allows combinations of measured relative positions and communicated estimates to be used in the implementation of the optimal formation control. Redundancy can also exist in the actuation specification, and this can be exploited to control the formation centroid, or to implement the minimum fuel control. Information and control switching can be implemented asynchronously without requiring supervisory control. A four-spacecraft, two-dimensional simulation example is used to illustrate the concepts.

Model Predictive Control of Swarms of Spacecraft Using Sequential Convex Programming

DOI: 10.2514/1.G000218 This paper presents a decentralized, model predictive control algorithm for the optimal guidance and reconfiguration of swarms of spacecraft composed of hundreds to thousands of agents with limited capabilities. In previous work, J2-invariantorbitshavebeenfoundtoprovidecollision-freemotionforhundredsoforbitsinalowEarthorbit. This paper develops real-time optimal control algorithms for the swarm reconfiguration that involve transferring from one J2-invariant orbit to another while avoidingcollisions and minimizing fuel. The proposedmodel predictive control-sequential convex programming algorithm uses sequential convex programming to solve a series of approximate path planning problems until the solution converges. By updating the optimal trajectories during the reconfiguration, the model predictive control algorithm results in decentralized computations and communication between neighboring spacecraft only. Additionally, model predictive control reduces the horizon of the convex optimizations, which reduces the run time of the algorithm. Multiple time steps, time-varying collision constraints, and communication requirements are developed to guarantee stability, feasibility, and robustness of the model predictive control-sequential convex programming algorithm.

Adaptive Control of Formation Flying Spacecraft for Interferometry

Abstract This paper presents an adaptive control system for coordination and control of a fleet of micro-spacecraft moving in formation. A fleet of spacecraft are given as a collection of systems which interact with each other in a cooperative manner to achieve a common objective. To provide a desired formation, basic mathematical models for controlled movement of rigid bodies in free space is presented followed by the adaptive control law for formation manipulations and formation keeping. The formation control performance in the presence of constant but unknown disturbances is illustrated by simulations.

Adaptive Kalman filtering, failure detection and identification for spacecraft attitude estimation

Future space missions call for unprecedented levels of autonomy, reliability and precision, thereby increasing the demands on spacecraft failure detection, identification and compensation (FDIC) systems. We address the problems of spacecraft attitude determination (AD) and FDI for sensors and actuators by developing: 1) a nonlinear extended Kalman filter (EKF) which does not require a small angle approximation; 2) a method for online tuning of noise covariances; and 3) a multi-hypothesis extended Kalman filter (MEKF) for detection and identification of sensor (gyro, Star tracker) and actuator (thruster) failures. A nonlinear EKF is designed for AD using angular rates, quaternions and the gyro biases as state variables. It is shown to provide more accurate estimates of the attitude angles and can be used for the detection and removal of bad gyro and Star-tracker measurements. The MEKF approach is used for the detection and identification of gyro, Star-tracker and thruster failures. Gyro failures are the quickest to detect and identify, followed by thruster and star tracker failures.

Phase synchronization control of complex networks of Lagrangian systems on adaptive digraphs

This paper presents a formation control and synchronization method that utilizes adaptive network topologies for a class of complex dynamical networks comprised of a large number of highly-nonlinear Euler-Lagrange (EL) systems. A time-varying and switching network topology, constructed by the adaptive graph Laplacian matrix, relaxes the standard requirement of consensus stability, even permitting exponential synchronization on an unbalanced digraph or a weakly connected digraph that can sporadically lose connectivity. The time-varying graph Laplacian matrix is adapted by an adaptive control scheme based on relative positions and errors of synchronization and tracking. The adaptive graph Laplacian is integrated with a phase synchronization controller that synchronizes the relative motions of EL systems moving in elliptical orbits, thereby yielding a smaller synchronization error than an uncoupled tracking control law in the presence of bounded disturbances and modeling errors. An example of reconfiguring hundreds of spacecraft in Low Earth Orbit shows the effectiveness of the proposed phase synchronization controller for a large number of complex EL systems moving in periodic elliptical orbits.

Control topologies for deep space formation flying spacecraft

A deep space satellite formation can be specified in terms of the relative satellite positions and absolute satellite orientations. Redundancy in the relative position specification generates a family of control topologies with equivalent stability and reference tracking performance. We give a characterization of this equivalence and show that there exists a control topology which achieves a global tracking objective using only local controllers. This local relative topology can be implemented without requiring communication between the formation spacecraft.