Shu-Fan Wu

On-line free-flight path optimization based on improved genetic algorithms

Free flight (FF) is the ideal strategy of current investigations on air traffic management systems, where an on-line flight path optimization algorithm is of top importance. This paper proposes an innovative algorithm with potential real-time properties for FF path optimization, by using an improved genetic algorithm (GA). Two kinds of mathematical models for the on-line flight path optimization problem are proposed to cover the near and far future applications. Several improvements are introduced to the GA to speed up its convergence as well as to improve performance. Simulation results show that the new algorithm is effective and has potential to solve the on-line FF path optimization problem in real time.

Fuzzy logic based full-envelope autonomous flight control for an atmospheric re-entry spacecraft

An intelligent and autonomous flight control system for an atmospheric re-entry vehicle is investigated, based on fuzzy logic control and aerodynamic inversion computation. A common PD-Mamdani fuzzy logic controller is designed for all the five re-entry flight regions characterized by different actuator configurations. A linear transformation to the controller inputs is applied to tune the controller performance for different flight regions while using the same fuzzy rule base and inference engine. An autonomous actuator allocation algorithm is developed, based on the aerodynamic inversion computation, to cover all the five actuator configurations with the same fuzzy logic controller. Simulation results of tracking both a bench mark trajectory and a given nominal re-entry trajectory are presented to evaluate the control performance.

Fuzzy logic based attitude control of the spacecraft X-38 along a nominal re-entry trajectory ☆

Abstract Fuzzy logic control techniques are investigated for applications in the intelligent re-entry flight control of the ESA–NASA crew return vehicle. Three PD-Mamdani fuzzy controllers are constructed to control the inner-loop attitude dynamics, simulated by a fully nonlinear 3 degree-of-freedom simulator of the CRV. Each controller uses an angle tracking error and its derivative to calculate a commanded control surface deflection of the simulator. The input-domains are partitioned with 5 membership functions, resulting in 25 fuzzy rules for each rule-base. The output-domains are partitioned with 9 membership functions. The Mamdani controllers use a standard max–min inference process and a fast center of area method to calculate the crisp control signals. Simulation results show the ability to track a reference trajectory with acceptable performance, though the real strength of a nonlinear fuzzy logic controller is yet to be proven with more demanding benchmark trajectories.

QFT-based robust/fault-tolerant flight control design for a remote pilotless vehicle

The following topics were dealt with: mobile multimedia applications guaranteed service resource allocation; Web search for general and scientific information access; Internet online databases and infocash concept; scalable open-architecture media server; ATM to IP European trials; programmable router IP services creation; Russian academic and research networks remote collaboration services; SMARTS-information support for Russian SMES in information society technologies; advanced packet switching network arrival processes characteristics estimation; ATM networks path delay reduction, multicasting performance evaluation; reliable multicast using IP/CMP protocol; multiservice networks threshold based admission control; speech processing and IP-telephony human perception statistical model; scientific library; library catalogues Internet representation; mobile IP and security; wireless Internet over LMDS; Russian Internet information search; YANDEX.RU search and research engine

Optimum Flight Trajectory Guidance Based on Total Energy Control of Aircraft

The guidance technique for optimal vertical flight trajectory with a total energy control system (TECS) is discussed. The flight profile is optimized based on the point-mass energy state approximation model of aircraft with direct operating cost as its index function. The guidance law is developed with the total energy control concept used in TECS. To improve the guidance precision, several methods are adopted in the optimization and tracking process, and two preprocessing algorithms, the lead-compensation algorithm and the smooth filtering algorithm, are developed for the ideal optimal trajectory. Satisfactory digital simulation results for a Boeing-707 transport model are finally obtained.

QFT based robust/fault tolerant flight control design for a remote pilotless vehicle

Quantitative feedback theory (QFT) was applied successfully to enhance the robust stability and tracking performance of the pitch flight control system for a remote pilotless vehicle within its full flight envelope. The influence of control surface loss or damage to the dynamic derivatives of the aircraft model can be treated as an extension of the model uncertainty robustness problem. QFT is applied to the analysis and design of the fault tolerant flight control system allowing for possible control surface damages.

Optimization of Spacecraft Thruster Management Function

Some new mathematical algorithms related to spacecraft thruster selection problems have been designed, implemented, and tested. The proposed approach is based on the concept of precomputing a set of optimal combinations of thrusters and storing the according data in the onboard computer (OBC) memory. During the nominal flight of a spacecraft, only a look-up procedure will be required to select, in the real-time mode, the right combination of not more than six thrusters (for a six-dimensional task) and their firing times. For off-nominal situations, when the spacecraft propulsion subsystem has to often operate at the edge of its capability and provide maximum linear and/or angular control accelerations, an additional algorithm has been proposed based on a modification of the parametric simplex method, Real-time software implementing the proposed algorithms requires from 0.05 ms to 0.21 ms to be executed on a SUN workstation with a 550-MHz UltraSparc processor. Regarding the size of OBC memory required for storing real-time computation data, only 52 KB are needed for a spacecraft with 20 thrusters. The user is provided with the flexibility to select the option, which better meets specific criteria and constraints such as execution time and accuracy of the optimal solution (at the expense of execution time or memory). In addition to C-code implementation, the software module (intended for real time) could be implemented as a standard SIMULINK library block and can be integrated with different simulators for test purposes. The software implemented in the project demonstrated effectiveness and robustness of the designed algorithms both in open-and closed-loop tests including various spacecraft maneuvers.

Modelling and in-orbit calibration practice of a miniature 2-axis analogue sun sensor

Abstract The modelling relations and calibration techniques of the miniature analogue sun sensors, developed at Surrey Satellite Technology Limited (SSTL), are discussed in this paper. Two model equations, an algebraic model based on a multi-variable polynomial algebraic curve-fitting procedure and a physical model based on analytical geometry relations, were developed. Parameter sensitivity analyses were conducted for the physical model, and an in-orbit calibration approach is proposed and was implemented with the sun sensors on-board UoSAT-12 and Tsinghua-1. A sequential batch filter algorithm was developed, based on the principle of the least-square estimation for regression models, to handle the large amount of in-orbit data in a sequential way. Satisfactory performance improvements have been achieved through the in-orbit calibration analyses for both satellites.

PATH GUIDANCE AND CONTROL OF A GUIDED WHEELED MOBILE ROBOT

Abstract A practical mobile-robot-based automatic transport service system is presented and discussed in this paper. A wheeled mobile robot, capable of two-directional movement, is developed to transport and feed materials to an industrial production line. For path guidance, an electromagnetic approach is investigated in detail. A conductor line laid on or under the ground defines the path, through which runs a square-wave current signal of a certain frequency, to produce an alternating magnetic field. Specific sensors are designed to measure this field and provide a path guidance signal for the robot. For path control, the proportional plus derivative (PD) algorithm is adopted to control the robots movement along the path line. Multi-mode control strategies are developed to cover different path cases. The active turn control scheme is used for turning path modes. Finally, some practical testing results are presented.

Closed Loop Performance and Limitations of the LISA Pathfinder Drag-Free Control System

LISA Pathfinder is a technology satellite project that is currently in full implementation phase, with a launch date scheduled for 2010. One of the key technologies to be tested is the drag-free control system. It consists of two cubic test masses with measurement and actuation provisions along all degrees of freedom. In total, 15 degrees of freedom must be controlled such that the differential free-fall requirement between the two test masses is met. In this paper the control design approach is revisited and the control requirements breakdown is discussed, based on the differential measurement equation. Then emphasis is put on the expected control performance of the drag-free control system with comprehensive numerical results. Performance limitations are addressed together with its driving parameters, and further possibilities for performance improvements are discussed, including test mass DC alignment aspects.