دکتر علیرضا احمدی

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.

Very High Resolution Passive Scan Agile Earth Observation Satellites are able to maneuver around all their three body axes and scan the target area in different directions, simultaneously. The most stringent mid-level requirements which dominate their attitude determination and control subsystem performance are applied in detumbling and fine pointing modes. These performance requirements are maneuverability, agility, accuracy and stability. In this research, first, we derive the analytical and statistical relationships between quantitative criteria of mid-level requirements and spatial resolution as a high-level mission requirement, next the design drivers of reaction wheels are extracted consequently. Then the size, mass and consuming power of an operational satellite and the reaction wheels torque authority and momentum capacity is guesstimated based on its imaging payload size and specifications.