Journal of Space Science and Technology
Year:2014 | Volume:7 | Issue:3 |Papers Count:10

This paper presents a method for calculation the non observable states in alignment and calibration process in gimballed inertial navigation system, using estimation method in static linear system and heuristic optimization algorithms. The non observable constant states in alignment process are horizontal accelerometers biases and azimuth gyroscope drift. In order to use the estimation method in static system, the observations are recorded in necessary time duration to convert the dynamic alignment process to static process. Simulation results show appropriate accuracy of purposed method for calculation the non observable states. Although the case study is the alignment process for gimballed inertial navigation system, the purposed method can be used for calibration and alignment of any inertial navigation systems. In purposed method the genetic heuristic optimization algorithm is used.

Designing space propulsion systems as one of the important subsystems of the spacecrafts and upper stage space launch systems needs to bypass different and complicated steps. In this article the comprehensive process of designing liquid fuel low-thrust space propulsion systems was illustrated. In the presented pattern, first of all according to the requirements and mission constraints, the main characteristics of the system were determined and then other characteristics were extracted. Finally, for the evaluation of the presented pattern, a low- thrust space propulsion system was designed based on a special mission and the results were compared with a real model. Comparison between the designed space propulsion system and the real one showed an appropriate accuracy of the presented pattern.

In this research, second order level set method for simulation of grain burn-back analysis is presented and compared with the first order level set according to discretisation technique, accuracy, and CPU time. In this manner and at the first step, we describe total necessities of level set method that are grid generation, minimum distance function calculation, relative condition estimation, ballistic characteristics calculation, and obtaining results. Then, at the second step, we improve forth necessity of level set method by second order model. For validation of presented model, we consider many type of simple and complex grains and evaluate grain burn- back analysis. The obtained results indicate that second order model is more accurate than the first order model for simulation of complex grains. But, at the simple grains with more CPU time related to second order model, accuracy of two models are similar. A compromise between accuracy and CPU time suggest that one can use second order model for simulation of complex grains and first order model for simulation of simple grains.

When space vehicles did not take off horizontally (like airplanes), they had to cross airspace of states other than the launcher state. This phenomenon exists still now for the states who intend to launch space objects, especially when launch pads are located near borders of adjacent states. What has been the attitude of the international law toward the issue of passage of space object through a foreign territory during its launch and re-entry into the atmosphere? Are the states allowed to use territory of other states, while launching their space objects? Do the international instruments or customary international law provide precise answers for this issue? In this paper, the researcher investigates sovereignty of states over their territorial air-space and discusses different legal viewpoints on passage of space objects through territory of other states. It clear that states cannot launch space objects without first obtaining permission of the concerned state. It is asserted that up to now no international law instrument have been linked to that effect, i.e. regarding innocent passage of space objects without consent of the concerned state (s).

In this paper, a new approach for orbital position prediction of satellites, is introduced. As traditional methods are based on keplerian equations of motion, orbital disturbances are uasualy neglected for simplicity. This paper, suggests artificial intelligent time series peridiction methods for orbital position prediction of satellites. The advantage of this method is based on usage of actual data, so all disturbances are taken into account. For this reason use of TLE as the most reachable actual data is considered. Compariosion of output of this method with actual data, proofs the accuracy of proposed method.

The Agile Satellite Attitude Control System Simulator (ASACSS) is a laboratory system designed for the purpose of developing and testing attitude control algorithms in a low- risk, low- cost environment. In this paper, the design and development of the ASACSS is described, including hardware and software. There are many papers that present a new mathematical technique or prove a new theory, but this study presents the design and development of a new experimental system. This simulator consists of four main components: 1) power supply system 2) on-board control system 3) supporting equipments and 4) monitoring computer. On-board control system includes a industrial computer, four single gimbal control moment gyros and a sensor for attitude determination. Supporting equipments include a platform for installing simulator subsystems, a semi-spherical air bearing and a pedestal. A high-speed wireless LAN connection enables remote command initiation, monitoring and data collection for post- experimental analysis. In this paper, The design and construction process of the simulator are described. More over some experimental results presented from the application of a simple PID attitude controller on the spacecraft simulator. Finally, experimental results are compared with those obtained from simulation.

Land is a limited and vulnerable resource with many permanent and renewable benefits if it is used appropriately. By considering the limited lands and the need for updated data and information for land planning, necessity and importance of land use studies is clear. In fact remote sensing data with geographic information systems are strong tools in change detection of land use pattern. They are much cost and time effective. In this study, satellite image has been used for extraction of update land use map of Tehran metropolitan. Three different methods (unsupervised classification, supervised classification and visual interpretation) have been utilized for preparation of land use map.

In this paper, a fuzzy logic guidance algorithm is presented for the ascending phase of satellite launch vehicles in the presence of wind effects. In this algorithm, the midcourse constraints including maximum allowable angle of attack at the maximum dynamic pressure and the product of the dynamic pressure and angle of attack, as well as constraints on the final altitude and flight-path angle are considered. The algorithm uses a Mamdani- type fuzzy controller with centroid defuzzification. Maximizing and minimizing set methods to reduce wind effect, while satisfying the midcourse and final constraints. Simulation results show that the presented algorithm improves the performance of the satellite launch vehicle, satisfying the constraints within the maximum allowable estimation error on wind speed.