Current Issue : April - June Volume : 2016 Issue Number : 2 Articles : 6 Articles
Tracking control system based on linear quadratic (LQ) tracker is designed for a ducted-fan unmanned aerial vehicle (UAV) under\nfull flight envelope including hover, transition, and cruise modes. To design the LQ tracker, a system matrix is augmented with a\ntracking error term. Then the control input can be calculated to solve a single Riccati equation, but the steady-state errors might\nstill remain in this control system. In order to reduce the steady-state errors, a linear quadratic tracker with integrator (LQTI) is\ndesigned to add an integral term of tracking state in the state vector. Then the performance of the proposed controller is verified\nthrough waypoint navigation simulation under wind disturbance....
The scope of the present work was to design, build and fly test a solar UAV, Sun Falcon 2 for long endurance day and night flight operations. A software program was written to design the UAV with appropriate aerodynamic attributes, power requirements and other flight mission constraints to keep the vehicle airborne for multi day and night operations. More specifically the design called for an least 12 hours of endurance during the day with solar panels deployed to absorb sufficient daylight energy to top up the on board batteries for the complete subsequent night flight mission. With Sun radiation levels averaging at about 6003 W/m2 during the Saudi day it was not too difficult to conform to multi day and night design requirements. The prototype Sun Falcon 2 has already been built and flight tested with satisfactory performance records satisfying the design criteria....
This paper presents the error dynamic model of motorized momentum exchange tether (MMET) based on the momentum exchange\nprinciple of space tether.The error dynamics are caused by the structural bias of the differences in tethers� length and the difference\nin payloads� mass. After that, the coupling analysis between orbit and attitude is presented. It is shown that, with increasing the\ndifferences in tethers� length and payloads� mass, the COM deviation of the MMET increases linearly.The numerical simulations\nof the MMET by considering the structural asymmetries are presented; the results show that the asymmetries have tiny influences\non the orbit of the chief satellite by decreasing the apogee, which will change the instantaneous velocity at the apogee and affect\nthe payload injection precision. What is more, the structural asymmetries have effects on the attitude elements (including the\npitch angle and yaw angle); however, the effects could be weakened by the external torque.The structural asymmetries and gravity\ngradient torque have composite effects on the angular velocity of the propulsion tether....
With radar and surface-to-air missiles posing an increasing threat to on-orbit spacecraft, low-observable satellites play an important\nrole in low-thrust transfers. This paper presents the design for a low-thrust geostationary earth orbit (GEO) transfer control strategy\nwhich takes into consideration the low-observable constraint and discusses Earth shadow and perturbation. A control parameter\noptimization addresses the orbit transfer problem, and five thrust modes are used. Simulation results show that the method outlined\nin this paper is simple and feasible and results in reduced transfer time with a small amount of calculation. The method therefore\noffers a useful reference for low-thrust GEO transfer design...
Guidance with traditional trajectory correction scheme usually starts from the trajectory apex time to reduce drag penalties early\nin flight; however, this method cannot get the max trajectory correction capability of canards according to our analysis. This paper\npresents an optimized trajectory correction scheme by taking different control phases of canards in ballistic ascending segment and\nballistic descending segment. Simulation indicates that the optimized trajectory correction can improve the trajectory correction\ncapability greatly. The result of an example trajectory and Monte Carlo simulations with the predictive guidance law and the\ntrajectory tracking guidance law testifies the effectiveness of the optimized trajectory correction scheme....
An autopilot inner loop that combines backstepping control with adaptive function approximation is developed for airdrop\noperations. The complex nonlinear uncertainty of the aircraft-cargo model is factorized into a known matrix and an uncertainty\nfunction, and a projection-based adaptive approach is proposed to estimate this function. Using projection in the adaptation law\nbounds the estimated function and guarantees the robustness of the controller against time-varying external disturbances and\nuncertainties. The convergence properties and robustness of the control method are proved via Lyapunov theory. Simulations are\nconducted under the condition that one transport aircraft performs a maximum load airdrop task at a height of 82 ft, using single\nrow single platform mode. The results show good performance and robust operation of the controller, and the airdrop mission\nperformance indexes are satisfied, even in the presence of �±15% uncertainty in the aerodynamic coefficients, �±0.01 rad/s pitch rate\ndisturbance, and 20% actuators faults....
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