I. INTRODUCTION  
II. MOTIVATION  
A. New Constellation Types  
B. On-board Capabilities  
C. Non Terrestrial Networks  
D. New Space  
III. APPLICATIONS & USE CASES  
A. 5G Non Terrestrial Network  
B. VLEO and SatCom-assisted Aerial Networks  
C. Aeronautical and Maritime Tracking and Communication  
D. Earth Observation Data Collection  
E. Space Communications  
IV. SYSTEM ASPECTS  
A. Constellation types  
B. Communication architecture  
C. Interface with other systems  
D. Spectrum  
E. Standardization  
V. AIR INTERFACE: ENABLERS & TOPICS  
A. Channel Modelling  
B. Antennas  
C. Ultra High Throughput Satellites (UHTS)  
D. Data Collection  
E. Others  
VI. MEDIUM ACCESS CONTROL: ENABLERS & TOPICS  
A. MAC Protocols for UHTS  
B. MAC protocols for Satellite IoT  
C. System Coexistence  
VII. NETWORKING: ENABLERS & UPPER-LAYER INTEGRATION  
A. Software Defined Networking and Network Function Virtualization  
B. Caching over Satellite  
VIII. TESTBEDS & PROTOTYPING  
A. PHY & MAC: SDR Based  
B. Network Testbeds  
IX. FUTURE & OPEN TOPICS  
A. Digital twins for satellite systems  
B. Cooperative satellite swarms and clusters enabled by intersatellite links  
C. Hierarchical Aerial Networks  
D. Internet of Space Things/ Planetary Communications  
E. Onboard regeneration / Flying Base Stations  
F. Aggressive frequency reuse and dynamic spectrum management for both GSO and NGSO  
G. Satellite Network Automation  
H. Advanced Satellite Resource Orchestration  
I. Quantum Key Distribution through Optical Satcom  
J. Machine Learning Applications  
X. CONCLUSION