Although the role of the environment in generating spacecraft potential variations at geosynchronous orbit is well documented, variations in the ambient environment itself have not been well-defined. Similarly, no studies of the environment have attempted an analytic formulation of the various parameters needed to model the spacecraft charging phenomenon. This paper describes the parameters needed to formulate such a model and outlines a systematic procedure for constructing a simple analytic model that includes the effects of local time and geomagnetic activity. Observational data from the ATS- 5 satellite are analyzed using this procedure to give a preliminary analytic description of the geosynchronous environment in the form of a FORTRAN program.