Hadjitheodosiou, Michael H.Nguyen, Alex T.NASA is interested in using commercial satellites to provide broadband communications support for the International Space Station and other space missions. We describe a large-scale simulation model that we plan to use for detailed performance studies of critical parameters such as QoS guarantees for specific services, traffic routing schemes, transport protocol support, dynamic bandwidth allocation methods, queuing disciplines, and handoff strategies. In this paper we focus on the unique challenges we face and how we plan to use simulations to investigate:ﶴhe feasibility of using proposed commercial constellations to carry mission telemetry, command and control, and tele-science traffic between ground terminals and near-earth spacecraft.ﶴhe end-to-end performance optimization of such systems.<p>The research and scientific content in this material has been published in the proceedings from the 18th AIAA International Conference on Satellite Systems & Communications, Oakland, CA, April 2000.en-USGlobal Communication SystemsTechnical Report