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View File - University of Engineering and Technology, Taxila

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2.5.3 Swath WidthThe width <strong>of</strong> the viewed section along the orbit ground trace is called theswath width. Following the previous assumption <strong>of</strong> a spherical earth, it can bedemonstrated that the swath width may be written asw s ¼ R e90 90 y BW2cos 1h 0 R vR esin y BW2ð2:25Þwhere y BW is the antenna beamwidth in degrees. Other symbols are as definedpreviously. The above expression can be used to determine the coverage at anylatitude during a particular operation. For practical explanation, when a polarorbit is used, the percentage coverage at the equator is taken as the ratio <strong>of</strong>swath width to the total distance between consecutive passes. To the contrary,at latitudes beside the equator, the percentage coverage in a given day is theequatorial coverage divided by the cosine <strong>of</strong> the latitude.2.6 SYSTEMS ENGINEERING: DESIGN PROCEDUREThe constraints imposed by the satellite on size, shape, cost, <strong>and</strong> weight areimportant factors in design consideration [7]. A satellite design block diagramis shown in Fig. 2.9; it shows the flow-down <strong>of</strong> requirements to systemdevelopment. Several factors dictate the satellite system design process, butsome generalizations are possible.The overriding concern is the cost for developing the system. It isimperative that system cost-effectiveness analysis be performed, as it supportsthe development <strong>of</strong> the lifecycle <strong>of</strong> products, processes, <strong>and</strong> risk managementactivities.2.6.1 Mission RequirementsIn general, mission requirements are intended to indicate, as definitively aspractical, the objectives <strong>of</strong> the mission: what is to be achieved <strong>and</strong> how tomeasure performance. In some cases, the requirements are not clear-cut. It isthe system engineer’s responsibility to (1) ensure that both the customer <strong>and</strong>the developer underst<strong>and</strong> the mission objectives <strong>and</strong> (2) clearly definepractically attainable <strong>and</strong> practically verifiable results.Copyright © 2002 by Marcel Dekker, Inc. All Rights Reserved.

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