In this paper, we have provided hands-on experience in systematic design, implementation and flight test of an atmospheric data acquisition flying vehicle as a standard CanSat telemetry mission. This system is designed for launching from a rocket at a separation altitude about 1000-meter. During its flight, the reusable flying vehicle collects environmental data and transmits it directly to the ground station. The ground station, which is implemented at a predefined radio frequency band receives data and plots the respective graphs. The design performs based on a systematic approach, in which the first step is set aside to mission and objectives definition. In the next step, the system requirements are identified and the required main subsystems and elements with their technical requirements will be extracted. The structure analyses were also performed by ABAQUS software to obtain the natural frequency and the mode shape. The wireless communications, onboard microcontroller programming, sensor interfacing and analog to digital conversion describe the basic technologies employed in the system implementation. This flying vehicle in comparison with the other similar ones is more lightweight, has few interface circuits and high precision sensors. According to the flight test outputs, low power consumption, high transmit line up to 2Km despite of limitation in TX power and up to 10g normal acceleration withstanding are important specific characteristics of the implemented flying system.
The main objective of this paper is to enhance the robustness of an on-off attitude control under uncertainties while limiting the probability of failure in attitude control. To do this, the concept of system optimization is utilized for detailed engineering of spacecraft control using reliability-based robust design optimization (RBRDO). The probability of failure of the attitude control is chosen by the system designer as the input of the RBRDO algorithm. The single-axis spacecraft attitude is controlled using a combination of the observer-based anti-windup modified PI-D with pulse-width pulse-frequency modulator in the presence of external disturbance. The on-off thruster is modeled with a delay followed by a second-order transfer function. The input frequency of the thruster is limited to 50 Hz. The uncertain parameters are given as the spacecraft moment of inertia, thrust level, and thruster delay. The controller gains are determined by using traditional, robust, and reliability-based robust design optimizations under uncertainties and disturbance. The simulations are carried out using quasi-normalized equations, along with reducing problem variables and computational burden, to obtain more applicable results for a preliminary design. The traditional optimization gives the highest pointing accuracy without uncertainty, whereas the robust optimization obtains an approximately flat behavior for the mean of absolute pointing error under uncertainties. Under this situation, RBRDO could satisfy the prescribed reliability with a small loss in accuracy for the on-off attitude control of spacecraft, but under system limitations.
In this paper, the performance of the spacecraft attitude control system is enhanced using model-based disturbance feedback control (DFC) strategy in the presence of disturbance. This control strategy is applied to a single-axis spacecraft attitude control with thruster, reaction wheel, and magnetic torqrod actuators, separately. An anti-windup observer-based modified PI-D is utilized for each actuation system as a main controller. The controller gains are tuned using genetic algorithm when the time average of absolute value of pointing error is chosen as an objective function. The performance of DFC with the modified PI-D controller is investigated under disturbance and model uncertainties. The numerical simulation shows that the DFC strategy can reject disturbance effect and improve the pointing error for the three mentioned actuators; however, for a very large value of external disturbance, a critical value for uncertainty is observed for the thruster lag at which the pointing error is suddenly increased. For this critical value, the control system cannot tolerate any longer lag uncertainty in comparison with the two other actuation systems. Increasing the value of disturbance decreases the tolerable value of uncertainty in the thruster lag.
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