Index

Low Earth Orbit Numerical Analysis & Research Tools

This module enables the configuration of satellite constellations, stations and mobile users zones. It simulates satellite ephemeris, generate visibility data between the satellites of the constellation and users or stations. Time statistics about visibility are computed and displayed in the form of reports, curves, images and maps.

The CAT Configurator proposes an interface to set up constellation of satellites, ground stations and mobile user zones.

The configuration of a constellation means to give the six orbital elements of each satellite at a reference date. This can be done satellite by satellite, or the constellation generator can be used. It provides entries for inclined constellations of the Walker type, or optimized polar Beste constellations with a reduced set of parameters. The orbital elements of each satellite are generated automatically. Any type of orbit type can be generated: LEO, MEO, HEO and of course GEO.

The ground stations configuration consists in defining its name, location (longitude and latitude), and minimum elevation angle under which radio links are no more possible.

The mobile user zone configuration consists in giving for each user its location and minimum elevation angle. A user mesh generator is provided to define large zones with a great number of users.

The CAT Simulator provides an interface to initialize simulation parameters and to run the simulation programs, that are totally independent of the interface. The main simulations that are provided are the following:

• Orbital simulations

After the selection of a constellation file, it computes the satellites position in time, i.e. the ephemeris.

• Visibility simulations

The visibility simulations are made after the selection of a constellation ephemeris file, a ground station file and a user zone file. Visibility data of the satellites by the ground stations and by the users can be computed. The mutual visibility, which means the simultaneous visibility of a satellite by a user and a station, can also be computed.

• Elevation angles simulations

The elevation angles with which a satellite is seen by a station or the users of the service zone are computed at each time simulation step. They are then used by the CAT Analyzer or the FAT for fade margins computations.

The CAT Analyzer provides powerful tools to process the simulation data of CAT and to display them in friendly formats.

• Visibility simulation data analysis

The first step in analyzing visibility simulation data is the generation of a time statistical report. For each station or mobile user, 15 statistical parameters are computed and stored into a data file. Typical statistical parameters of interest are the mean time ratio of visibility of at least 1 satellite, the mean time ratio of visibility of n satellites simultaneously, the minimum, mean, maximum time of no-visibility,...

This statistical report can then be edited in text format for a given user or ground station. A selected statistical parameter can be displayed for each mobile user of t he service zone on a map with color levels , or as curve of the evolution of the parameters value as a function of latitude or longitude.

Time visibility curves can also be obtained, showing the evolution of the number of satellites in visibility as a function of time for a given user or ground station.

• Elevation simulation data analysis

The elevation simulation provides the elevation angle with which each satellite of the constellation is seen by each user or station as a function of time. The analysis enables the computation of an elevation time statistics report. This report can be edited as text for a given user or station. For a mobile user zone, a selected elevation statistical parameter can be displayed as a colored map or longitude/latitude curve.

Elevation distributions can also be computed for ground stations as curves or images (double visibility case). The evolution of the elevation of the best elevation satellite as a function of time can also be displayed on a curve for a given station or user.

The elevation distribution data can then be used as input parameters for the Fade Analysis Tools, FAT , in order to compute fade margins and availability.

Some additional visual analysis of data is provided by LEONART :

• Satellites ground tracks display on a map.
• Satellites footprints on a map.
• Ground stations visibility circles on a map.