1. Introduction

This paper presents a brief review of the main characteristics of the Earth's trapped radiation belts and of the engineering models that are used to evaluate mission fluences and doses. More detailed descriptions of the Earth's radiation environment and the related physical processes can be found in references (1-3).

The Belgian Institute for Space Aeronomy (Belgisch Instituut voor Ruimte-Aëronomie - Institut d'Aéronomie Spatiale de Belgique) has developed for the European Space Agency (ESA) a World-Wide Web interface to models of the space environment and its effects on spacecraft and systems. The SPace ENVironment Information System (SPENVIS) can be accessed at http://www.spenvis.oma.be/spenvis/. The figures in this paper, except those with a reference number, were produced with the SPENVIS plotting facilities.