  Aiming to achieve ubiquitous global connectivity and target detection on the
same platform with improved spectral/energy efficiency and reduced onboard
hardware cost, low Earth orbit (LEO) satellite systems capable of
simultaneously performing communications and radar have attracted significant
attention. Designing such a joint system should address not only the challenges
of integrating two functions but also the unique propagation characteristics of
the satellites. To overcome severe echo signal path loss due to the high
altitude of the satellite, we put forth a bistatic integrated sensing and
communication (ISAC) framework with a radar receiver separated from the
satellite. For robust and effective interference management, we employ
rate-splitting multiple access (RSMA), which splits and encodes users messages
into private and common streams. We optimize the dual-functional precoders to
maximize the minimum rate among all users while satisfying the Cramer-Rao bound
(CRB) constraints. Given the challenge of acquiring instantaneous channel state
information (iCSI) for LEO satellites, we exploit the geometrical and
statistical characteristics of the satellite channel. To develop an efficient
optimization algorithm, semidefinite relaxation (SDR), sequential rank-1
constraint relaxation (SROCR), and successive convex approximation (SCA) are
utilized. Numerical results show that the proposed framework efficiently
performs both communication and radar, demonstrating superior interference
control capabilities. Furthermore, it is validated that the common stream plays
three vital roles: i) beamforming towards the radar target, ii) interference
management between communications and radar, and iii) interference management
among communication users.
