فهرست مطالب a. kosari

At the present time, the industry of space systems design, manufacture and launch has fallen out of favor with governments and numerous private sector representatives around the world are competing with each other for a greater share of this thriving business. The tendency from large single-satellites, high life-cycles in high-altitude orbits to high numbered constellations consisting of small satellites with low life-cycles and in low-altitude orbits is one consequence of this change. Space industries are increasingly keen to deploy small and low-cost satellites which demand for low-cost design. Technological advances in the design and manufacture of each satellite subsystem have accelerated this process and it has made the new generation of satellites superior not only in size but also in terms of performance. Minimizing multiple cycles in the design process and replacing cyclic optimization methods with straightforward ones can help improve this process. Rapid sizing techniques are well-known in aircraft industries as they allow designers to quickly prepare a ball-park design for their intended aircraft. In this research, we propose a similar approach, for Very High Resolution Passive Scan Agile Earth Observation Satellites that allows designers to become aware of the design different boundaries. The key is to prepare a 2/D space which describes any specific mission-leg with respect to the key configuration parameters. Such a design tool exhibits critical mission phases and their relationship to the key technological factors. In this approach, a designer can quickly decide upon technological barriers that might influence the Research, Development, Test and Evaluation (RDT&E) phases of the design and/or negotiate with stakeholders on any changes to the satellite mission. As total life-cycle cost is normally influenced by decisions made during RDT&E phase, it is expected that this method play an essential role to keep the overall cost down. Such rapid-sizing technique allows designers to do more trade-studies. This research has been concentrated on three main issues: (1) Existence of a design space for RS-satellites (2) The parametric characteristics and influential parameters that form such space. One suitable case-study have been discussed to support the proposed methodology. The maximum mass of VHR-PS-AEOS is largely influenced by its overall configuration, and its minimum mass is also influenced by the altitude reduction rate during the satellite's operational lifetime. The dimensions of the payload and its placement inside the structure to provide the required agility are critical requirements for determining the overall dimensions of the satellite and as a result its surface and volume. This research has been concentrated on three main issues: (1) Existence of a design space for RS-satellites (2) The parametric characteristics and influential parameters that form such space. One suitable case-study have been discussed to support the proposed methodology. The maximum mass of VHR-PS-AEOS is largely influenced by its overall configuration, and its minimum mass is also influenced by the altitude reduction rate during the satellite's operational lifetime. The dimensions of the payload and its placement inside the structure to provide the required agility are critical requirements for determining the overall dimensions of the satellite and as a result its surface and volume.

This article proposes a new approach for centralized path planning of multiple aircraft in presence of the obstacle-laden environment under low flying rules. The problem considers as a unified nonlinear constraint optimization problem. The minimum time and control investigate as the cost functions and the maximum velocity and power consider as the constraints. The pseudospectral method applies as a popular and fast direct method to solve the constrained path planning problem. The three-degree-of-freedom nonlinear point mass equations of motion with realistic operational aircraft constraints consider through the simplified mathematical model. The fixed obstacle considers as a combination of spheres with different radius. Also, the moving obstacles consider as a sphere with a known radius and fly at a constant speed. The effectiveness of the proposed concept will be demonstrated by presenting four case studies with a different number of aircraft along with the static and moving obstacles in various scenarios to ensure safe and effective flights.

In this paper, a novel method for designing the flight paths of an aircraft is presented based on the concept of conformal mapping. Here, a low-altitude route-planning problem has been considered. In this problem, maintaining the control effort to reduce aircraft's altitude and increasing the speed with the limitations of Terrain Following (TF) and Terrain Avoidance (TA) issues, is the main strategy of this performance maneuver. In the proposed approach, attempts are made to convert the real space including terrains and obstacles, in which their data are provided using a digital elevation map, into a pseudo obstacle-free virtual space with no barriers and altitude constraints. In this regard, the concept of conformal mapping has been used as a facilitating mathematical tool for this problem-solving space transformation. The transformation of the problem-solving spaces under the mapping leads to solving the problem of dynamic reflection, the performance criterion, and the real altitude constraints in the virtual space. It is noteworthy that in designing a path in a newly converted space, the effect of barriers on the formation of flight routes is somehow included in the equations expressed in the virtual space. The results of multiple case studies and numerical optimizations performed for 2D geometrical terrains and obstacles show that the proposed approach is more consistent with the basic flight concepts as well as real-world applications.