Journal of Space Science and Technology
Year:2017 | Volume:10 | Issue:3 |Papers Count:6

This study introduces a new computer code termed AZMIN developed by Space Research Laboratory (SRL). This efficient tool which benefits from the Statistical Design Model (SDM) has been developed for the system design of GEO communication satellites. The main advantage of the AZMIN is to determine technical specification parameters of a satellite at both system and subsystem levels, with a high accuracy and time performance. System-level parameters encompass mass, power, dimension and cost; while, subsystem parameters contain mass, power, and solutions for components configurations of each subsystem. Actual computations of this tool are carried out by means of SDM, leading to a dramatic decrease in the conceptual design time and consequently, its cost. The database utilized is composed of records of 462 GEO communication satellites launched from the year 2000 to 2017. The accuracy of the AZMIN code is amply verified through an example and also a statistical method, demonstrating the mean error of approximately 15% in the obtained results.

An optimal explicit guidance law that maximizes terminal velocity is developed for the reentry of a vehicle to a fixed target. The equations of motion are reduced with differential flatness approach and acceleration commands are related to the parameters of trajectory. An optimal trajectory is determined by solving a real-coded genetic algorithm. For online trajectory generation, optimal trajectory is approximated. The approximated trajectory is compared with the pure proportional navigation and genetic algorithm solutions. The near optimal terminal velocity solution compares very well with these solutions. The approach robustness is examined by Monte Carlo simulation. Other advantages such as trajectory representation with minimum parameters, applicability to any reentry vehicle configuration and any control scheme, and Time-to-Go independency make this guidance approach more favorable.

The main objective of this research is to improve the distribution of electrical potential on spacecraft surfaces by changing the surface coatings to reduce the risk of electrostatic discharge in the spacecraft. For this purpose, SPIS software, the EU standard software for modeling and simulating the interaction of space plasma with the spacecraft is used. The spacecraft has 8 nodes, and each node is related to a particular substance. The simulations were compared with the variation in the materials of these nodes in terms of differential electric and floating potential. Investigating materials that differed in the differential electric potential of zero showed that they are conductive materials. In order to choose among several conductive materials, these materials were compared in terms of electric floating potential. Simulations on satellite surfaces showed an average of 11% improvement in the electrical potential on surfaces

The purpose of the present paper is to prove the model-free optimal control theory. This theory is derived from the principles of dynamic programming and it is produced for discrete-time systems. The design of the controller depends merely on the I/O data of the controlled planet; hence, the controller is independent of the model. In this paper, two actions have been performed in order to measure the value of the controller. In the first step, the control method was designed to control the attitude of spacecraft. The purpose of this theory was to create a model-free optimal control for the spatial model and to measure the efficiency of the spacecraft systems. Secondly, designing linear quadratic regulator (LQR) controller for attitude control of spacecraft was carried out. The reason for designing this controller was to compare it with model-free optimal control. If the differences between two controllers was proved to be small, then the theory would be proven. Finally, it has been concluded that controller is valuable and acceptable.

The droplet formation stage of a spray, which enjoys a great diversity in size and droplet velocity, is predictable through a statistical approach. Since the available methods require experimental data such as mean droplet diameter and mean droplet velocity as inputs to estimate the distribution of the droplets, this study attempts to propose a consistent theoretical model based on the energy conservation equation for the estimation of mean droplet diameter to be used in the predictive models of droplet size distribution, such as maximum entropy model. Therefore, those models can be independent of experimental data. The parameters needed in the model, such as atomization efficiency and the Weber number are provided using a CFD model. Then, a parametric study to evaluate the relationship between the atomization efficiency and spray velocity, and mean droplet diameter is carried out. This new proposed model entitled energy-based model (EBM) can provide a very good prediction of mean droplet diameter in comparison with the available experimental data.

The contribution of injured person in creating or worsening the damage caused by space objects is important in determining the international liability for those. This contribution, which is accepted only in respect of damage caused by space objects located in places other than outer space -land orair- will reduce or eliminate the international liability, depending on the extent of the contribution of the injured person. However, in cases where damage is caused by an act contrary to the international laws, this rule will not apply. In order to apply this rule, the contribution of main injured person for the damages to whom the international responsibility will be considered, and the contribution of state which acted the diplomatic protection of its subject or the contribution of member states of the injured International Organization are not considered. In addition, examining the rule of the impact of contribution of injured person, this paper tries to examine the issues related to this rule in the international space law.