Security in Outer Space: Planning for Compromised Positioning, Navigation and Timing

More than a hundred different Global Navigation Satellites orbit the Earth providing Positioning, Navigation and Timing (PNT) services, with the latter capability being the least appreciated or understood.
PNT does more than guide motorists, aviators, sailors and hikers. Many industries such as construction, mining, surveying, package delivery, logistical supply chain management, farming, fixed and wireless communications networks, banking systems, defence, security and emergency services, financial markets, water utilities and power grids depend on the accuracy and availability of PNT.
How robust is this ‘invisible utility’, what are the consequences of compromised PNT on critical national infrastructure and what contingencies exist to protect it?
Most of the terrestrial-based PNT systems have been or are being progressively decommissioned leaving satellite-based PNT as a vulnerable single point of failure for many users…