In cellular and satellite networks, the resource capacity is shared among handoffs and new calls. Forced termination has a significant impact on the quality of service perceived by users. The guard channel scheme is an access priority that has been proposed in order to reduce the handoff failure probability. The effectiveness of this mechanism has been emphasized in terrestrial cellular networks. In this paper, we propose a dynamic reservation scheme for satellite networks which adapts the number of reserved channels according to the current number of ongoing calls and on the localization of users. The efficiency ofthe proposed mechanism has been investigated for Low-Earth Orbit (LEO) satellite systems based on a satellite-fixed cell concept.