This contribution focuses on securing end-to-end unicast communications in heterogeneous wireless sensor networks comprising satellite links, while maintaining effective network performance. The proposed protocol extends the LOCKSAT key management procedure, and is able to guarantee a frequent key renewal while overcoming limitations of each subnetwork (e.g., sensor and satellite). The effectiveness of the proposed solution is assessed through the design of the system supporting the algorithm even through a frame format definition and a test bed including satellite link delays.