  In this paper, we consider a multi-antenna dual-functional
radar-communication (DFRC) satellite system, where the satellite has a dual
capability to simultaneously communicate with downlink satellite users (SUs)
and probe detection signals to a moving target. To design an appropriate DFRC
waveform, we investigate the rate-splitting multiple access (RSMA)-assisted
DFRC beamfoming, and employ the Cramer-Rao bound (CRB) as a radar performance
metric, which represents a lower bound on the variance of unbiased estimators.
The beamforming is optimized to minimize the CRB subject to quality of service
(QoS) constraints of SUs and a per-feed transmit power budget. Satellite
communication and detecting ground/ sea objects in a bistatic mode are
accomplished simultaneously using the DFRC waveform we designed. Simulation
results demonstrate that the proposed RSMA-assisted DFRC beamforming
outperforms the conventional space-division multiple access (SDMA) strategy in
terms of the communication-sensing trade-off and target estimation performance
in a multibeam satellite system.
