  Concerted efforts are underway to establish an infrastructure for a global
quantum internet to realise a spectrum of quantum technologies. This will
enable more precise sensors, secure communications, and faster data processing.
Quantum communications are a front-runner with quantum networks already
implemented in several metropolitan areas. A number of recent proposals have
modelled the use of space segments to overcome range limitations of purely
terrestrial networks. Rapid progress in the design of quantum devices have
enabled their deployment in space for in-orbit demonstrations. We review
developments in this emerging area of space-based quantum technologies and
provide a roadmap of key milestones towards a complete, global quantum
networked landscape. Small satellites hold increasing promise to provide a cost
effective coverage required to realised the quantum internet. We review the
state of art in small satellite missions and collate the most current in-field
demonstrations of quantum cryptography. We summarise important challenges in
space quantum technologies that must be overcome and recent efforts to mitigate
their effects. A perspective on future developments that would improve the
performance of space quantum communications is included. We conclude with a
discussion on fundamental physics experiments that could take advantage of a
global, space-based quantum network.
