Low Earth Orbit (LEO) satellite systems undergo a period of rapid development
driven by the ever-increasing user demands, reduced costs, and technological
progress. Since there is a paucity of literature on the security issues of LEO
Satellite Communication Systems (SCSs), we aim for filling this knowledge gap.
Specifically, we critically appraise the inherent characteristics of LEO SCSs
and summarize their unique security vulnerabilities. In light of this, we
further discuss their security vulnerabilities, including the issues of passive
and active eavesdropping attacks, interference scenarios, single event upsets,
and space debris. Subsequently, we discuss the corresponding active and passive
security countermeasures, followed by unveiling a range of trade-offs, security
vulnerabilities and their countermeasures. Furthermore, we shed light on
several promising future research directions for enhancing the security of LEO
SCSs, such as secure quantum communications, three-dimensional virtual arrays,
artificial intelligence-based security measures, space-based blockchain, and
intelligent reflecting surface enabled secure transmission. Finally, the
take-away messages of this paper are crystallized in our concluding design
guidelines