Figure 4-2 Space Segment Model Organization 4.2. Orbit Geometry The range of system concepts and architectures for space-to-Earth power beaming spans the orbital region from LEO to GEO and encompasses a wide distribution of ground station locations. With the single exception of power transmission from a GEO satellite to ground sites in the field-of-view, the timevarying geometry of the space-to-ground and space-to-space (relay) links is a key determinant of system design requirements, power reception performance, and economic viability of different concepts. Generally, the power beaming satellite does not pass directly over a ground site. The ground link visibility depends on beamline angle constraints and, at best, gives only partial time availability of the link over any given day. Moreover, the geometric characteristics and visibility vary from day to day. A relay link is likewise temporal, constrained by beamline pointing limitations and occultation by Earth. At the outset of this Phase II study, one of the important ground rule concerns was how best to treat the orbital geometry influence in the system model development. If a concept should eventually prove to be viable and is implemented, then a detailed dynamic simulation becomes necessary to completely describe the power reception profile at selected sites. However, this is not a practical method to embed in the SSM spreadsheet model, whose purpose is to quickly investigate parametric trades related to system design, performance, and cost. Instead, we adopted an approach that measured average daily performance of the transmit-receive link for any defined system concept and set of ground site locations. The notion of average in this context accounted for both short and long time scales of the problem by characterizing the effects of varying key geometric parameters such as the orbiter's ascending node and initial position relative to the ground site's latitude and longitude coordinates.
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