Journal of Space Science and Technology
Year:2022 | Volume:15 | Issue:2 (پیاپی 51)|Papers Count:9

This paper presents a study concerning active vibration control of a smart flexible spacecraft during attitude maneuver using thrusters and reaction wheels (RW) in combination and piezoelectric (PZT) sensor/actuator patches. The large-angle maneuver and residual vibration of the spacecraft are controlled using an extended Lyapunov-based design (ELD) and strain rate feedback (SRF) theory for a two-mode mission. The single-axis fully coupled nolinear rigidflexible dynamic of the system is derived applying a Lagrangian approach and Finite Element Method (FEM). The overall stability of the system including energetic terms covering a hub and two flexible appendages, torsional spring, RW, and PZT dynamics, has been proved and the control law has been derived accordingly. A pulse-width pulse-frequency (PWPF) modulation is used to alleviate the excitations of high-frequency flexible modes. However, due to the fast maneuver, there are still residual vibrations in the system. Hence, the SRF algorithm using PZT is applied to prepare further vibration suppression. A great feature of the proposed hybrid actuator system is the switching time of the thrusters and RW, which is based on total systems energy. The numerical results for a flexible spacecraft with large-angle, agile and precise maneuver requirements through a comparative study verify the merits of the proposed approach

In the variable parameter linear method, which is used to express systems with time-varying state-space matrices, the stability and performance of the feedback system are guaranteed, and there is a significant potential for improving efficiency. The dynamics of these systems depend on a variable parameter with time, considered in this research as the angular velocity of the reaction wheel. The values ​​of this parameter are during an unknown period but can be measured by system performance. Using the tabulation gain technique, the stability of the variable parameter system is checked, and the tabulation parameter is selected for estimating practical control factors. The convex algorithm can solve the extracted sufficient conditions converted into linear matrix inequality conditions. By solving these controlling conditions, the tabulated gain is obtained to guarantee the stability and performance of the variable parameter system. Numerical simulation results show the success of the proposed method.

In emergency situations, where there is no possibility of using terrestrial-based or space-based telecommunication platforms or when there is a need for providing telecommunication services in remote, rural or hilly areas which are faced with lacking telecommunication infrastructures, typically using tethered balloon-based telecommunication technology is the best choice. Despite all the advantages of using this technology, small and limited coverage area is the biggest drawback of using tethered balloon platforms. In this paper, using a tethered balloon equipped with antenna pointing mechanism is proposed in order to, extend their small coverage area to a large region, in addition to benefit from inherent tethered balloons technology advantages. In this regard, dynamic and kinematic modeling of the proposed antenna pointing mechanism is discussed. In this research, the kinematic model is validated using RoboAnalyzer software and Robotics MATLAB toolbox. Antenna pointing mechanism provides the rotation ability for the antenna in two Azimuth and Elevation directions which increased the coverage area dramatically.

The interaction of thruster plumes with satellite components can have undesirable effects, such as disturbance force/torque, thermal loading, and species deposition in the surfaces. The purpose of this paper is to use the Direct Simulation Monte Carlo (DSMC) method to analyze the 3D plume impingement flows and investigate its effects. Two impingement problems are computed. The impact of a jet of nitrogen on an inclined flat plate is considered. Good agreement is found between surface quantities calculated by DSMC and experimental data. The plume of a hydrazine control thruster firing in a model satellite configuration is simulated. Surface quantities and net impingement effects are calculated. The effects of partial displacement of the thruster locations on the results have also been investigated. The results show that a 20% displacement of the thruster location can change the disturbance force/torque by up to 15% of the initial values.

Sandwich panels are used in various industries due to their high special strength. It is used in ultra-light aerospace structures. In this paper the protective effect of sandwich structures used in ultralight space structures against gamma rays is investigated. Eight structures of the most widely used structures used in space structures such as telecommunication antennas and satellite bodies are exposed to radioisotopic sources of gamma rays (Amercium barium and cesium) with energies of 60 kV, 80 kV, 382 and 66 kV, have been compared to each other. Surface material (aluminum and carbon), surface thicknesses and honeycomb cell dimensions are the most important evaluation parameters. In this paper, different structures have been compared using the "special protection" parameter and the best structure from a protection perspective has been identified and reported.

Due to the lack of existence of control surfaces in entry capsules, the subject of static and dynamic stability is always important. In this paper, these coefficients are investigated experimentally for the case of forced oscillation at supersonic flow. In this experimental study, the effects of freestream Mach number, mean attack angle and pitch frequency on dynamic stability coefficients were evaluated. According to the results, in Mach 1.8, the geometry starts to be dynamically unstable. One approach to overcome this problem is to change the average attack of angle of the model. This change in the mean attack of angle, similar to the results presented for the five-degree mean angle, will lead to dynamic stability.

Muscle atrophy is one of the problems that astronauts face after returning to earth. Myostatin is a known negative regulator of muscle growth. This study aimed to investigate the effects of simulated microgravity condition on mouse myotube cells (C2C12) growth and the myostatin gene expression. The morphological studies and MTT cytotoxicity assay showed no significant alternation in cells after 48h simulation microgravity, however, after 72h ~40% of cell death accrued (p<0.05). The AO/PI staining and DNA fragmentation analysis confirmed this observation too. Analysis of the gene expression revealed that simulated microgravity reduced myostatin gene expression significantly after 48h (p<0.0001), however, after 72h, increased significantly (P<0.001). So, inhibition of myostatin expression in differentiated myocyte cells of astronauts could be an effective procedure to reduce skeletal muscle atrophy under microgravity condition.

In this article collision probability method is used to satellite collision risk analysis. Among different methods introduced for determining collision probability, Patera's (2005) and Chan methods are chosen to define Noor satellite collision to the other space objects. According to criteria described in the article, Advanced Conjunction Analysis Tools of STK software applied for collision risk analysis. The software, determine position of each object in space using Two Line Elements and appropriate propagation model according to altitude of the orbit. So collision probability calculated by one of the cpllision probability methods. If derived prababilty is larger than 10-3, so its necessary to schdule for suitable maneuver to avoid collision.

The space environment poses many threats to the external components of space structures, and thermal fluctuations are among the most important of these threats. These thermal fluctuations occur due to the position of the system in front of the sun and in the shadow of the earth, and its value depends on the orbit of the spacecraft and the materials of the components. Antennas, which are usually installed on the outer shell of these systems, are therefore always exposed to the thermal fluctuations of the space environment. Thermal fluctuations cause the antenna surfaces to expand, contract and distort and can cause the antenna to malfunction. In this paper, the effects of thermal expansion and contraction due to an LEO orbital mission on the radial characteristics of two X-band reflective antennas, one broadband antenna and the other narrowband, And the resulting radiation characteristics are compared with the characteristics of equivalent sample antennas at ambient temperature. Analyses show that narrowband antennas are very vulnerable to thermal fluctuations and, therefore, it is necessary to choose the material of the antennas from materials whose thermal expansion coefficient is very small. In addition, choosing the appropriate protection method to maintain the optimal performance of the antenna is one of the most essential activities in the construction of space antennas.