Hadjitheodosiou, Michael H.Nguyen, Alex T.NASA is interested in using commercial satellites to provide broadband communications support for future space missions. In this paper, we describe a large-scale simulation model that we plan to use for detailed performance studies of critical parameters. We focus on the unique challenges we face and how we plan to use simulations to investigate:<p>ﶴhe feasibility of using proposed commercial constellations to carry various classes of traffic between ground terminals and near-earth spacecraft.<p>ﶴhe performance optimization of such systems.<p>The research and scientific content in this material has been published inthe proceedings from the GLOBECOM2000 Symposium on Satellite Communications for the New Millennium, San Francisco, Nov, 2000.en-USGlobal Communication SystemsTechnical Report