This paper presents the design and architecture of a network emulator whose links' parameters (such as delay and bandwidth) vary at different time instances. The emulator is used as a digital twin for satellite communication systems, in order to test and evaluate novel solutions before their final deployment. To achieve such a goal, different existing technologies are carefully combined to emulate link dynamicity, automatic traffic generation, and overall topology emulation. Since emulating asymmetric dynamic links (as required in satellite communications) is far from trivial, we provide a detailed design architecture for solving such task. Experimental results show the precision of our dynamic assignments and the overall flexibility of the proposed solution.