Stacked Intelligent Metasurface for Satellite Communication Networks: Architectures, Key Technologies, and Challenges

The seamless integration of satellite communication (SatCom) into future wireless networks necessitates paradigm shifts in physical-layer signal processing and beamforming architectures. This paper investigates stacked intelligent metasurfaces (SIMs) as an enabling technology for multi-satellite networks, offering programmable electromagnetic (EM) wave manipulation through cascaded meta-atom layers. Unlike conventional single-layer reconfigurable intelligent surfaces, SIMs achieve full-dimensional wavefront control via multi-layer amplitude and phase modulation, addressing critical bottlenecks in satellite links including path loss compensation, dynamic beam alignment, and interference management under Doppler effects. We systematically present the working principles, hardware implementations, and deployment strategies of SIMs across different network entities. Three SIM-empowered SatCom architectures, space-air-ground integrated networks (SE-SAGIN), co-orbiting satellites cooperation networks (SE-CSCN), and heterogeneous satellites cooperation networks (SE-HSCN) are proposed for various scenarios. Key enabling mechanisms encompassing wave-domain joint control, time-frequency-spatial synchronization, and collaborative sensing are elaborated alongside practical implementation challenges. The numerical results demonstrate that five-layer SIMs configurations achieve 54.13% throughput improvement over single-layer counterparts, validating the scalability of multi-layer architectures in complex network. Finally, we outline potential future research directions to further enhance the capabilities of SIMs in SatCom applications.