نشریه علوم، فناوری و کاربردهای فضایی
سال دوم شماره 1 (پیاپی 3، بهار و تابستان 1401)

one of the key issues in the operations of on orbit servicing to unmanned satellites is to provide a safe and reliable docking process. This paper investigates the dynamic behavior of a flexible probe in the central docking mechanism of unmanned satellites. This study tries to optimize the docking process by investigation the effect of different connectors between ball and probe, instead of being rigid relative to each other. For simulating the impact phenomenon, a dynamic analysis software has been applied and a three-dimensional model has created based on the assumption of a flexible clamped beam as a shock absorber. additionally, it is possible to consider the parameters such as the type of connection between the beam and the concentrated mass, angular and translational velocity of chaser and target satellites, in order to determine the optimum condition to perform a successful docking operation. The results of this study indicate that the use of a spherical joint for the ball attached to the probe, significantly reduces the maximum value of impact force.

A wideband high-gain microstip patch array antenna for high resolution synthetic aperture radar applications is presented. The antenna operation frequency is in the X-band. The antenna structure is a four-layer configuration consisting of radiating patches, slots, coupling cavities, and a corporate feeding network, which in turn is fed by a coaxial probe. The increased frequency bandwidth of the radiating patch is achieved by employing a square slot, which appears as a cavity for it, and improves the gain and impedance bandwidth of the antenna array by isolating the patch feeding slot and eliminating the mutual coupling effect. The whole antenna structure is fabricated by using a combination of the milling process and printed circuit technology. Measurement results show a relative gain bandwidth of more than 10%, in which the antenna gain is measured above 28.8 dBi over the frequency band of more than 1 GHz. Moreover, the relative impedance bandwidth of the antenna for VSWR>2 is more than 16%.

One of the reasons for the increasing popularity of lithium-ion batteries is the improvement of their rate capability and power density. All components of a battery, including the anode, cathode, electrolyte, and separator, can limit the capability of lithium-ion batteries. While most efforts have focused on the new electrode architecture and electrolyte formulation to improve battery performance, studies on separators have focused mainly on their mechanical and physical properties and little attention has been paid to their effect on the performance of lithium-ion batteries. In this study, a comprehensive study of the physical, thermal and electrochemical properties of disassembled high drain lithium-ion battery separator (HDLIB) with high discharge rate capability and commercial polyethylene separator with a thickness of 16µm (G16) is reported. According to the research, it has been shown that HDLIB separator has 26% less contact angle and better wettability than commercial polyethylene separator. Also, HDLIB separator at 150°C has shrunk by 55.6% less than G16, which may be due to the presence of boehmite ceramic particles in its structure. In addition, it shows that HDLIB separator can play an important role in improving the rate performance and safety of lithium-ion batteries.

The aim of this study is to evaluate the performance of water-jacket cooling system for thermal protection of an exhaust large dimension diffuser at high heat fluxes in a wide range of coolant pressure. For this purpose, a suitable design algorithm has been developed. Using the present method, the parameters of the water-jacket cooling system are determined so that in addition to satisfying the temperature conditions of the metal body, the total pressure drop has remained in the desired range. In the following, the capability of numerical code to design and performance analysis of the cooling system has been evaluated in coolant pressure of 3 to 50 bar and high heat fluxes up to 3.5 MW/m2. The present studies show that the proper selection of coolant pressure is very important in the design of the cooling system with optimal mass flow rate and minimum coolant dimensions, especially at high heat fluxes, so that increasing the coolant pressure from 3 to 10 bar, in addition to significantly reducing the dimensions of the cooling system, reduces the mass flow rate by 75%.

Anodizing is a common method for increasing the adhesion of aluminum surfaces. However, if we heat the manufactured products before adhering due to the hydration of the anodized coating, cracking, and morphological changes, the adhesive capacity will be greatly reduced. As part of the research presented in this study, methods such as non-sealing of the anodize, primer application before heating the coating, sandblasting before and after the anodizing coating, and use of FPL (Forest Products Laboratory) replacement coating have been used to investigate the adhesive behavior of the coating. According to the results, not sealing the anodized coating and priming it before heating will increase the adhesiveness of the coating in all cases. Sandblasting after coating had no significant impact on adhesion. Sandblasting before anodizing improves adhesion by altering the texture of roughness and morphology. FPL can also be used to replace anodized coatings. They were less sensitive to heating and storage.

]n recent years, extensive research has been focused on the key materials of vanadium redox flow batteries (VRFBs) to improve the power and energy density. In a VRFB system, the ion-exchange membrane is an important component, because it is used to separate the positive and negative electrolytes and to allow the transfer of ions. Nafion membrane is now widely used in VRFBs due to their high proton conductivity and remarkable chemical stability. In the present study, the Nafion 117 membrane was subjected to an acid-heat pretreatment for utilizing in VRFBs. Three-cell stacks of VRFB were assembled using bare and pretreated membranes, and their performances were evaluated during charge/discharge cycles. The results indicate that acid and heat pretreatment on the Nafion 117 membrane improves the VRFB energy density by 30%. In addition, the average discharge voltage, which is one of the key parameters in the VRFB performance, is increased from 3.57 V (for the bare membrane) to 3.9 V (for the pretreated membrane). This helps to reduce the weight of the VRFB stack as well as the cost of the battery manufacturing. On the other hand, the acid and heat pretreatment of membrane improves the energy and voltage efficiencies of VRFB from 66.9% and 76.8% to 73% and 87%, respectively.

In this paper, the computational fluid dynamics simulation of a tactical aerostat is conducted and the longitudinal static coefficients of the aerostat is evaluated. The simulation is conducted using the Fluent software and the Spalart-Allmaras turbulent model is used. First, in order to validate the numerical method and the applied turbulent model, a famous airship hull is simulated and the drag coefficient at zero angle of attack is compared with the references and the CD0 is in very good agreement with references. Then, the designed aerostat is simulated and the pressure and Y+ contours and the streamlines around the aerostat are presented in angle of attack -10≤AoA≤30. Furthermore, the aerodynamic longitudinal coefficients are calculated for 5 and 20 m/s. The results show that the aerodynamic coefficients do not vary significantly with the change of velocity and the pitch moment coefficient about the nose of the designed aerostat has a negative slope. Comparing the pitch moment coefficient of the designed aerostat with two American a Korean aerostats depict that the designed aerostat has more static stability.

In this paper, a satellite attitude control system (SACS) based on tube-based robust model predictive control (TMPC) methodology is designed which is robust to disturbances. All Euler angles and their derivatives are ensured not to deviate more than a determined limit under those disturbances with known bounds. It is conducted based on the concept of the minimal robust positive invariant (mRPI) set. Actuators and Euler variables constraints could be considered in the SACS. The dynamics are guaranteed to be robustly stable. Given that the satellite dynamics consists of a great number of states, it is not possible to implement A TMPC scheme on the SACS in real-time. The number of satellite system states in this article is 6. Which has practically increased the volume of calculations. Makes it impossible to use TMPC theory. A theory will be presented based on reduced calculations to demonstrate a practical TMPC scheme that results in a real-time SACS.

In this paper, the effects of different weight percentage of iridium (Ir) nanoparticles loadings on performance parameters of hydrazine catalyst and monopropellant thruster have been studied. Nanoparticles of iridium with different contents of 10 wt%, 20 wt%, and 30 wt% has been coated on gamma-alumina of 1 to 2 mm size for decomposition of hydrazine during some various steps of calcination. These catalysts then have been tested in a 1 N thruster. The tests were conducted with a scenario of different stages of steady and pulsating fires of different times and duty cycles. Test results showed that catalyst loss was minimum with 30 wt% of iridium nanoparticles loading. Despite of this, there were no meaningful difference between other parameters such as pressure roughness, thrust, specific impulse, and catalyst crushing. The results showed a good value of characteristic velocity. All parameter values of three type of catalysts were within desired range.

Platinum nanoparticles are widely used in the oil and gas industries, electronics, space tools, pharmaceutical industries, biomaterials and etc.Platinum catalysts are more active and selective than the other catalysts. In this regard, the preparation of a suitable alumina catalyst base and more effective coating of platinum particles are presenting an important role in increasing the quality and efficiency of the catalyst. The purpose of this research is to prepare a high Specific surface area alumina base via aluminum anodizing and coating them with platinum particles. As a result, two steps of the work have been carried out, which are as follows: anodizing aluminum in an oxalic acid solution and optimizing its parameters to reach alumina nanotubes with controlled diameter, thickness and height. Subsequently, the research is resumed using scanning electron microscopy and data related to the special surface.In the next step, different amounts of platinum coatings using a suitable metal salt and solvent is deposited via an optimized electrochemical method.Finally, nanotubes with a diameter, thickness, height of about 60 nm, 20 nm, 15 μm, respectively were produced as the catalyst base.The optimized parameters include: applied voltage of 40 v DC and temperature range of 0-4 °C and the duration of anodizing for 7 h.The platinum coat array is masked on the substrate lithographically. The Samples are prepared using H2PtCl6.6H2O under an electrochemical 12V AC of 200 Hz with a sinusoidal waveform in a solution at a concentration of 8 mM in 150 seconds.The specific surface area was 3.16 m2/g and the absorbed gas volume was 0.728 cm3/g, absorption and desorption isotherm had a hysteresis suitable for catalytic activity.This knowledge was acquired in order to optimize the synthesis and coating conditions of the substrate with a suitable coating for catalytic applications and thermal knives.

In this paper, a passive fault tolerant control method is proposed for the satellite attitude tracking in the presence of external disturbances, the inertia matrix uncertainties, and reaction wheel faults. To achieve this goal, a modified fast terminal sliding model approach is used due to its robustness against the un-modeled uncertainties and being suitable for the nonlinear system model. The sliding surface variable is chosen to avoid singularity, converge to zero in a finite time, and also reduce the Chatting phenomenon. The stability and finite time convergence of the attitude variables are also demonstrated by the extended Lyapunov condition. In order to increase the accuracy of the controller, the dynamic model of the mentioned actuators is considered. Finally, the simulation is performed on a satellite with four reaction wheels under the mentioned conditions to evaluate the performance of the proposed method. The results show that the proposed method could maintain the stability of the system under actuator faults, and it makes the state variables converge to the desired trajectories in a finite time and also produce chattering-free control signals.

Forest biomass is one of the most important parameters in the ecosystem changes assessment and global carbon cycle modelling. In the other hand, the forest height is an effective parameter in the allometric equations which are used for biomass estimation. In this research the effect of two physical factors, forest height and forest density, will be evaluated in the applicability of the four common inversion algorithms for forest height estimation based on the Polarimetric Interferometry SAR (PolInSAR) technique. The applicability of the digital elevation model (DEM) differencing, volume coherence amplitude, hybrid and three-stage methods is studied for different forest height and forest density by using simulated polarimetric interferometric SAR data in L-band. The experimental results of the forest height estimation in simulated data with a density of 100 to 900 trees per hectare and a height of 10 to 18 meters show that the results of the hybrid method show high sensivity to changes in both height and density. The root mean square of error was 5.8, 5.6, 3.2 and 4 m for data with variable height and 11.6, 6.7, 5.8 and 5.3 m for data with different densities, respectively.

One of the key subsystems in satellites is the attitude determination and the sun sensor is one of the most common sensors in this field. Today, due to the increasing development of satellites, the need to increase the accuracy of satellite subsystems seems very necessary. In this paper, the design of a sun sensor made with an optimized slit in the entire field of view are examined. In this sensor, two orthogonal linear detectors are used, on top of each of the detectors, an optimal gap perpendicular to the detectors is required at an optimal distance according to the field of view. Due to the light passing through the optimized slits and its effect on the detectors and the slit, a peak can be seen in the output of the detectors, which according to the location of the peak, the angle of the incoming light can be calculated with high accuracy. The sun sensor made in Shiraz Mechanics Research Institute has an absolute error (2 sigma) of 0.14 in the 50 degrees of field of view.