نشریه علوم و فناوری فضایی
سال چهارم شماره 3 (پیاپی 9، پاییز و زمستان 1390)

New algorithm is presented in this paper for attitude determination of LEO nanosatellite with 2 accuracy in attitude determination independent of time. The most important limitation in nanosatellites is about subsystems’s masses so, reduction of subsystems’s masses is always considered. ADS plays the important role in the successful orbital maneuver missions. ADS accuracy is connected with increasing of sensors and complex processors which lead to increase the ADS mass. The presented algorithm uses one magnetometer sensor and one horizon sensor and position data receiving by GPS sensor as minimum required sensors. The selected configuration is resulted to minimum ADS mass and mission cost. Finally, error analysis at two most important orbit zones is done and the performance of the presented algorithm is confirmed.

To design a manned spacecraft carrying one to two crews to the low Earth orbits, design phases should be completed in various levels. It also needs to gather manned spacecrafts technical data which is developed in the same category. In the system design algorithm presented in this paper, the conceptual design sequences of a manned spacecraft named Dousti is accomplished systematically. First of all, in accordance with a target group of manned spacecrafts’ mission, Dousti’s mission profile is defined and system level requirements are recognized. User’s requirements are also considered in the mission profile and subsequently in system level requirements. General characteristics of Dousti spacecraft as well as its mass and dimensional features are derived in the next step. Statistics and parametric models are systematically applied in design sequence. Then, final characteristics of the spacecraft’s main subsystems designed through engineering methods and applying parametric models are introduced. Afterwards, resulting characteristics of the spacecraft are traded off to reform and then validated by statistics and parametric models to present the final plan.

The purpose of this paper is introducing the concept of nondeterministic optimal design or optimal design in the presence of uncertainty based on researches done in the past two decades. Therefore, after an introduction about uncertainty, the uncertainty and uncertainty modeling techniques are described. After that, the traditional method of dealing with uncertainty in the design is described. The importance of paying attention to the uncertainty and its benefits for different projects and companies is described. The third section is dedicated to introducing the methods of interval analysis, fuzzy logic and probability analysis, which are used in the analysis of uncertainty. The two general categories of nondeterministic design problems, the robust optimal design and reliabilitybased optimal design are reviewed. The next section introduces the application of nondeterministic design methods in the different disciplines and recent researches in the world on this topic. Finally, future aspects and challenges of the nondeterministic design are addressed.

In this paper the apparent velocity regulation system has been studied and simulated. The objective of this system is to adjust the missile’s fight velocity with the predetermined value, in specified time steps. In fact the apparent velocity regulation system calculates and changes the thrust of the engine (pressure of the combustion chamber) in order to accomplish the desired fight velocity. For this purpose, a dynamic simulation for the propulsion system and also the missile’s flight has been developed. After analyzing the results, it is revealed that using the apparent velocity regulation system; the flight’s range accuracy will be improved dramatically. Comparing two similar missiles, with a same disturbance; one equipped with the apparent velocity regulation system and the other not, revealed that using such a controlling system will keep the accuracy of the target hitting within 200 meters while in the absence of it, the error would be more than 1.5 kilometers.

During Persian Gulf war (1990), space assets played a valuable role and their usefulness was revealed for the first time. Space technology creates an infrastructure that helps military strategies. It helped a lot in some battles such a Afghanistan, Siberia and Cosovo war. In this article we are going to explain the existing rules on international humanitarian law and other rules and have some recommendations to protect outer space from military threats.

Automatic Modulation Recognition is an important task for intelligent receivers in modern communication systems, in which several modulation types are used. In order to improve the performance of modulation classification systems, the idea of multi-receiver recognition has been developed recently. In this paper multiple receivers’ collaboration at different information levels is investigated for classification of signals used in DVB-S2 standard.Three methods are proposed for receivers’ cooperation at each one of signal, feature and decision levels. The proposed methods use cumulants and MLP neural network as signal features and classifier respectively. These methods are evaluated and compared through performance, complexity and equipment. The results show that receivers’ cooperation at signal level offers more accurate classification compared to feature and decision levels, in addition to less computational complexity.

In this research, an approximate solution of the required velocity with final velocity constraint is derived using linear gravity assumption along the path of current position to the final position vectors. Moreover, an approximate solution for sensitivity matrix of the required velocity with respect to the position vector is obtained. The presented solutions are given for a predetermined final time. In this case, for the free final position, the analytical solution is rather more difficult than its fixed final position counterpart. Therefore, three approaches are utilized for approximation of the final position vector. Finally, the obtained solutions are compared to exact numerical one for the spherical- Earth model.

A current method by which star trackers identify stars is to match the angles between stars within its field of view to angles stored in a catalog. If an angle can be matched to one pair of stars, the attitude of the star tracker can be determined. However, the measurement of the angle will include error, and so the true angle can only be known to lie within a certain measured range. The result is, after comparing the measured angle to the catalog of angles, more than one pair of stars can be the correct solution. A method for narrowing down to one solution involves employing many angles within the field of view in a certain order, called “pivoting,” which can be time consuming and does not always yield a solution. another method presented here matches planar triangles made from sets of three stars within the field of view to planar triangles stored within a catalog. By using both the area and polar moment properties of the planar triangle, the range of possible solutions is very quickly narrowed, fewer pivots to other planar triangles are required, and the method is more likely to yield the correct solution than the angle method. New method presented here use these two methods simultaneously, first, by angle method candidate some stars to identification. In this level reduces stars in FOV. Second, by triangle method in fewer time identification completed, because FOV is smaller. So this new method is faster than triangle and more accurate than angle method and we do not pivoting the same as each method. In addition, Simulation results show the performance of the new method as well as its robustness with respect to including false stars.