Mathematical Description of the OMNIS Satellite Orbit Generation Program (OrbGen)

This document discusses the mathematical procedures used in the OMNIS orbit generation program. It provides a detailed description of the top-level procedures used for the numerical integration, references all of the force models employed and discusses those force models that have a substantial impact on the integration technique chosen. The document attempts to discuss the mathematics of the orbit integration but does not discuss the details of the implementation into code. A primary use of the program has been for Global Positioning System (GPS) satellites; however, it is used for low altitude satellites as well. Force models follow the World Geodetic System 1984 (WGS 84) constants and models, the International Earth Rotation Service (lERS) conventions when models are not covered by WGS 84, and specialized models when required, e.g., specialized radiation pressure forces for various GPS satellite vehicle types, as well as atmospheric density models for use in the atmospheric drag modeling of low altitude satellites. The program can segment drag forces, during the integration span, in order to accommodate inaccurate drag modeling. The program can accommodate several thrusts of arbitrary duration and magnitude. The inertial system used is J2OOO and the conversion to the Earth-fixed International Terrestrial Reference Frame (ITRF) is based on the 1980 revision of the 1976 International Astronomical Union (IAU) precession and 1980 mutation theory, using the Earth Orientation Parameters published by the lERS. The program is completely coded in FORTRAN 77. It is coded in double precision and executes on a UNIX operating system.Naval Surface Warfare Center Dahlgren Div VA is the author of 'Mathematical Description of the OMNIS Satellite Orbit Generation Program (OrbGen)', published 2004 under ISBN 9781423519294 and ISBN 1423519299.