نشریه علوم و فناوری فضایی
سال چهاردهم شماره 2 (پیاپی 47، تابستان 1400)

In this paper, the heat transfer and ablation thermal insulators in solid rocket motor are investigated. Therefore, by collecting and solving the thermal ablation equations, a computer program, using MATLAB software, is developed which can predict the thermal response of insulators in different operating conditions and compare the performance of these insulators. The heat and mass transfer equations are considered in two dimensions in a solid body. We used the equations, finite volume method with implicit formulation for time dependency to solve equations. The reaction equation which written in the form of Arrhenius, is solved using Runge-Kutta method, and the density and the flux of the gas produced at each step are obtained. Also we represent a model for the rate of recession.

Awareness of the trend of forest canopy density classification requires an operational exact model for forest crown classification. The preliminary challenge is the separation of the forest crown from other non-warlike vegetation coverings. In the following, previous attempts to improve the performance of the FCD model, in this study, by adding the FCC index and the kernel, improved the average performance of the FCD model. The crown classification of Hyrcanian forests based on images of 1396 Landsat 8 was selected for implementation, evaluation, validation and analysis of the results. Improving the accuracy of the model is entirely sensible and even manual interpretation confirm it. The statistical analysis of the results also indicates a 10% and 24% increase in overall accuracy and kappa coefficient of the improved model compared to the initial model. Specifically, the accuracy of these two classes in the results of the improved model is about 13% and 7%, respectively.

Numerical modeling of space engines aside the experimental test is routine. In the design step of such engines, low-cost softwares are vital. In this paper, small-scale space engine thrust chamber analysis code will be developed. In this code, propellant injection and evaporation distribution will be modelled. 1D Combustion solver calculates the reactions of distributed fuel and oxidizer through the thrust chamber axis by chemical mechanisms. Then the cooling solver computes the heat transfer from hot gases to the film cooling layer and the outer surroundings. Validation shows acceptable errors in the modelling of processes. By this developed code, the performance of the Astrium bi-propellant thruster with MonoMethylHydrazine and NitrogenTetrOxide and distributed chemical reaction has been investigated. Results show that hot gas temperature inside the combustor is not uniform and has a peak. Furthermore, the evaporation of the propellant droplets is continued to the nozzle throat.

This research represents localization of an aerial robot using fisheye cameras on walls in a simulation environment. The virtual testbed in this work is a quadrotor that is simulated in MATLAB Simulink. Subsequently, the simulation outputs as flight records are used in a virtual lab, which is developed in 3DsMAX. Then, the virtual fisheye cameras (here two) are installed in some different points on the walls and the related images from the cameras are received offline. The gathered images will be processed by OpenCV in a C++ environment. For external calibration, each fisheye camera takes an image from a known pattern consist of some lights placed in the virtual lab. We execute Perspective-n-Point method on the images to obtain pierce direction/position of the camera. For more, the aerial robot is localized by computing the nearest point between two lines of sight. In brief, the outcomes exhibit an accuracy of 4cm in the center of the virtual-room room.

Magnetometer is one of the most sensors due to its lightness and low power consumption in satellites. Therefore, the magnitude of the magnetic field at the location of the magnetometer should be less than the magnetic cleanliness characteristics defined for the satellite. One of the best solutions is to properly placement included position and angular position of the equipments in such a way the magnetic field is minimized at the magnetometer location. In this paper, a cost function is defined based on the norm of the magnetic field generated by the equipments at the magnetometer location, and the cost function is minimized by adjusting the angular position of the equipments using the particle swarm optimization (PSO) algorithm. Position adjustment compensates the generated magnetic field and helps to passively achieve the magnetic cleanliness characteristics of a satellite. Finally, by simulating the magnetics of a satellite equipments, the performance of the algorithm in achieving magnetic cleanliness is shown.

In this paper, multi layer radiation shield is designed for electrons and protons space environments to protect in all satellite orbits. The designed shield layer material and thickness is analyzed and optimized by MCNPX linked with Matlab. In Matlab, genetic algorithm is employed for optimization where the cost function is obtained from MCNPX. The designed shield achieves more than 53% TID reduction for proton environment and more 72% TID reduction for electron environment compared with aluminum by similar thickness. This good specifications prove the capability and ability of the deigned multilayer shields to protect the electronic parts in the satellite applications.

Adaptive control technique is taken into consideration because of overcoming the problem of existence of uncertainties in the space missions.In this paper, a novel optimal direct adaptive control technique which is based on Markov parameters is presented. In this technique, the system's performance is expressed based on rotation matrices, and this method doesn't have a singularity problem. The problem of satellite attitude control using this method and nonlinear thruster actuator in existence of uncertainty in moment of inertia is analyzed. The novel adaptive controller using on-off thrusters is robust to inertia changes. In this paper, a mamdani fuzzy logic is used to schedule the gains of PD control method, and the satellite attitude control problem using a fuzzy controller is simulated. With considering the settling and rise times, it's shown that the fuzzy controller is better than the presented adaptive controller. Also, the problem of satellite attitude control using the novel adaptive controller in presence of a constant disturbance is analyzed, and simulation results illustrate that the new adaptive control is robust to a constant disturbance.

Many of the space applications that previously required the use of large, complex and expensive satellites have now been made possible by very small satellites due to the development of technology. The applicable international laws and regulations, which typically govern large satellite operations with sophisticated technology, also govern state's responsibility for regulating and controlling small satellites. However, in recent years, the private sector has increased its commercial use of small satellites without complying with applicable regulations. As a result, the irregular operation of small satellites in space has increased in orbits without states oversight. Therefore, the responsibility of states in the international space community to regulate the operation of small satellites has been challenged. This paper focuses on the responsibility of states and two challenges arise in relation to the responsibility of states in the operation of small satellites; activity of private section and transfer small satellites ownership into orbits. Finally, the author proposes solutions to address these challenges.

In this paper, a new algorithm for determining the density of scattered data at the surface of the sphere is presented and then the proposed algorithm along with Geodesic Weighted K-Means clustering and Deluany triangulation are used to make uniform star catalogs. Comparison of the results with the results of other related articles shows that the proposed algorithm resulted in a significant decrease in the probability of observing a large number of stars in all simulated star sensor fields of view. This improvement is due to the uniformity of the star catalog, especially in the celestial sphere poles due to the proposed density determination algorithm. On the other hand, the use of a proper data density algorithm has increased the likelihood of observing a few stars (such as 3 or 5) in all fields of view used in the Monte Carlo simulation.