نشریه علوم و فناوری فضایی
سال چهاردهم شماره 1 (پیاپی 46، بهار 1400)

In this paper, the dumbbell model is used for gravity field of asteroid 216 Kleopatra. Utilizing the model results in governing equations of motion of a spacecraft around an asteroid similar to those of motion of a spacecraft in the restricted circular three-body problem. The equilibrium points and Jacobi regions are calculated and symmetric periodic orbits are computed utilizing grid search and shooting methods. The xz-plane is considered as the symmetry plane. Stability of the periodic orbits is evaluated by Floquet theory that shows all the computed orbits are unstable. By adding the solar radiation pressure term to the governing equations of motion, the symmetric periodic orbits are recomputed and index of stability are examined. The results show that the solar radiation pressure, though change the values of the index of stability, does not affect the stability of computed periodic orbits. Therefore, stabilizing a spacecraft on the unstable periodic orbits requires controlling spacecraft.

LED light spectrums are the proper light source for plant research in the International Space Station and the life support system. In the present study, effects of different light spectrums on some growth parameters, and antioxidant activity were investigated in Anthemis gilanica. Seedlings irrigated with 1/2 Hougland solution under different light spectrums including white, red-blue and deep red. Seedlings were harvested for physiological and biochemical analyzes after 4 weeks. Results showed the fresh and dry weight, relative water content and root length increased under the red-blue light spectrum comparing to other spectrums. Hydrogen peroxide level didn't significantly change under different light spectrums. Seedlings treated with white spectrum showed the highest DPPH scavenging activity. Also, seedlings treated with deep red spectrum showed the maximum shoot length. It seems that decrease of growth under white spectrum is related to transfer carbon and energy sources for antioxidant compound biosynthesis.

n GEO communicational satellites, thrusts are being used for many missions such as station keeping, longitude change maneuver and actuators desaturation. These types of actuators need fuel and its estimation requires many complicated calculations. In this paper, a novel method based on availed data for previous satellites is proposed for estimation of satellite fuel mass and it does not need mathematical modeling of satellite dynamics. Two methods, least square method and artificial intelligence, are used to this aim and two mathematical model are proposed for satellite fuel mass estimation. By applying the models to several previous satellites, it is shown that the models have lower than 5% average error. The proposed method in this paper is quick and accurate and can be utilized for GEO satellites feasibility study and conceptual design

In this paper, a shielding box is designed for a Ku-band VSAT transmitter power amplifier based on an electromagnetic band gap structure. The proposed structure, is a bed of nails on the inner surface of the top wall of the box. It suppresses cavity resonances in the Ku-band uplink frequency range of 14-14.5 GHz. The amplifier which is composed of two cascaded modules (a pre-amplifier and a 50 W power amplifier) is first imported to a full wave simulation software. Full wave simulation of the printed circuit board (PCB) which includes the small signal scattering parameters of the power amplifier modules, proves the optimum performance of the proposed design.

In this research, a new and effective approach to managing change control is presented in the design process of complex engineering products. This approach involves the use of design constraints in a combination of two structures of DSM matrices and a system process for controlling changes. The system process involves the use of a systemic code for evaluating of changes, how to create a transfer model, and a management change assessment request. The process presented in this article, in addition to using similar activities in this field, has provided a systematic approach to using the knowledge of designers of a project to guide the control of changes to major engineering projects, including decision-making on controlling changes and how to identify the best The path to the change control process.

This paper presents a modification to a type of Pulse-width Pulse-Frequency (PWPF) Modulator utilized an integrator block. In this modulator that called here as "Integral Pulse-Width Pulse-Frequency (IPWPF)," an integrator is used instead of the first-order low-pass filter. To improve the performance of the control system, the modulator is modified by using a logical circuit in order to reset the output of the integrator. In this logical circuit, if the error signal becomes less than a specified small value, the integrator will be reset, that is, "Small Error-Reset Integrator (SE-RI)." The modification is applied to the stabilization and pointing modes. In stabilization mode, the control gain is obtained analytically such that the angular rate of the satellite becomes zero or less than a specific percentage of its initial value by a single pulse. Simulation results show that the performance of the modified IPWPF is comparable with that of PWPF in pointing mode.

In this research, to investigate the effects of uncertainties on the natural frequency of satellite system attributed to the variation of layout components, the optimal layout of the satellite is performed utilizing particle swarm optimization (PSO) algorithm, considering stability and geometrical constraints. In order to produce random samples, enough number of results will be extracted, which are mass center of components, and based on the outputs, the finite element modeling of different samples by considering mass point is carried out. After modal analysis, mass and stiffness matrices are extracted, the simulation of Monte - Carlo runs based on Wishart random matrix theory and the eigenvalues of the matrix, i.e. natural frequencies, are obtained. Probabilistic distribution of natural frequencies is shown that in the proposed layout, the distribution of samples is very low and the variation of natural frequency is robust to the proposed optimal location.

The problem of jointly controlling relative attitude and position of spacecraft in the presence of actuator fault is investigated in this paper. Following a description about drawbacks and limitations of the existing models and the control approaches based on them, a new formulation of the spacecraft relative motion is provided. Subsequently, the subspace predictive control framework, which is a powerful model-free approach, is extended in several dimensions, that is, adaptive nonlinear control, tolerance against abrupt faults and control allocation. Based on this generalized framework, three distinct data-driven fault-tolerant controllers for coupled, nonlinear and time-variant plants are developed. From the viewpoint of fault diagnosis, the only requirement of the control structure is to detect the occurrence time of faults. Furthermore, an internal data-driven fault diagnosis capability is introduced, which makes the control structure completely self-sufficient. The three controllers are then designed to solve the aforementioned problem, and their efficiency are verified via a multidimensional simulation scenario.