This chapter addresses typical applications in SGINs, including tracking and data-relay service; tracking, telemetry, and control (TT&C) service; and wide-area time-sensitive connectivity. We explore the optimization of their performance metrics, including service coverage, mission completion ratio, and end-to-end delay. The model in Chap. 2 is used to assist in modeling the performance optimization problem, and sources of optimization gains are mined through the performance analysis of the SGIN capacity and delay in Chap. 3 . Tracking and data-relay service applications aim to cover the wide-area broadband access scenario that requires a wide frequency band and high data rate. TT&C service applications aim to cover the wide-area high-precision positioning scenario that is characterized as requiring a narrow frequency band and low data rate. Wide-area time-sensitive connectivity applications aim to cover a scenario requiring a wide frequency and sensitive delay. These three applications cover most typical applications in SGINs. The design of optimization methods and simulation experiments are used to provide theoretical references for SGIN performance optimization, so as to provide the theoretical insight needed to solve similar performance optimization problems in SGINs.