The development of Global Navigation Satellite Systems (abbreviated to GNSS for simplicity) is one of the technological marvels of the modern era. Anyone with a technical background who looks into the design and implementation of GNSS systems is likely to be astonished by what they find. It's easy to become blasé when you are used to the ubiquity and low cost of GNSS receivers (just about every modern pocket phone contains one) but this is nonetheless a triumph of skill and engineering.
Metre-level accuracy in location and almost nanosecond (one billionth of a second) level accuracy in time are both features of these systems, concepts which would have been met with disbelief just a few decades ago if you proposed them even to technically knowledgeable people. Since first made available, the system run by the American military has proved to be highly robust and available everywhere in the world with (almost) no breaks in service at all.
Alternative but broadly compatible systems are provided or are in the process of being provided by Russia, the European Union and China.
The American system has operated with extremely high levels of reliability since its operational launch in 1995 but is of course subject to potential government control, hence the desire for other nations or groupings to have an alternative which is under their own control.
As is evident to any observer, there is now a huge proliferation of in-car and hand-held devices (including practically all smart phones) which take advantage of GNSS to provide precise location information anywhere on the surface of the earth. Many combine that information with knowledge of terrestrial maps to provide driving and other navigational aids to consumers and professionals alike.
In order to provide positioning information the satellites transmit high precision and extremely accurate time signals. The reliability and ubiquity of the satellite signals have led to many systems which have a need for accurate time choosing to use GNSS timing signals as a low-cost source of this information, as will become clear later.
Engineers and others, observing a growing dependency on what could be a single point of failure, started to become concerned about societal dependency on GNSS services. As a result of those concerns the British Royal Academy of Engineering undertook a report investigating what issues might arise if GNSS information were to be lost or degraded.
Subsequent to the Royal Academy report, the UK government undertook a 'Blackett Review' (an independent expert review named after the Nobel Prize winner Patrick Blackett) into the dependencies of 'Critical National Infrastructure Sectors' on GNSS and the impact that loss of the service might have .
The Blackett Review found that dependencies occur in a number of places, both expected and (perhaps) unexpected and often without proper thought being given to backup systems (which may well also be costly or difficult to install). The review points out that GNSS signals are extremely weak by the time they are received on the ground and are subject to various possible forms of disruption amongst which are deliberate jamming, failure of the supporting infrastructure in the countries running the systems, accidental failures, overt hostility and space weather events. Localised jamming is, as the review notes, not merely a theoretical concern but one already routinely observed.
The review introduces a notable term "Systems of Systems" where it states:
Because GNSS applications are so pervasive, they occur in many systems that depend on one another [...]. Consider the electricity system that powers our homes, businesses and practically all modern services. Accurate time from GNSS receivers allows the grid to determine if there is a fault, where it is and where to employ circuit breakers. In turn, the grid powers our communications systems, which themselves use time from GNSS to operate.
Transport weaves another web of dependence. Trains, planes, ferries, buses and lorries use GNSS to determine their position and to navigate, and use telecoms to report their locations to fleet management systems. Intricate logistics are required to operate the just-in-time supply chain that ferries our food from all over the world, on to our roads and into the shops and ultimately our homes; and every stage, from global to local, relies on GNSS for time or position. When one of these systems fails, invariably the engineers sent to repair the fault will use GNSS to find their way to the site of the problem.
Our vulnerability to GNSS failure is increased because of such systems-of-systems interactions. If a problem with GNSS were to cause a major power outage, our ability to coordinate a response could be diminished, our capacity for moving people and goods reduced and our emergency responses hampered.
GNSS is at the heart of diverse systems and networks on which we have become highly reliant. A serious disruption to GNSS would be magnified many times as it forms a common point of failure within such systems of systems, which range from individual radio and computer networks to UK society as a whole.
A further significant study conducted by London Economics  attempts to model the costs to the UK economy of a five-day loss of GNSS services across the region (not merely localised jamming) and states:
The economic impact to GNSS-reliant present-day UK of a loss of GNSS has been estimated at £5.2bn over a five-day period, comprised of £1.7bn in lost GVA [Gross Value Added] and £3.5bn in lost utility benefits. Applications in road, maritime, and emergency and justice services account for 67% of all impacts. This is limited by the resilience that stakeholders have confirmed are in place for a duration of five days, and the difficulty of robustly estimating the costs associated with loss of certain activities. For maritime shipping, for example, the loss of GNSS would severely disrupt all ports and the loading and unloading of containers for the duration of the outage.
The knock-on effects are difficult to estimate in monetary terms, but evidence suggests that factories relying on just-in- time delivery would likely run out of inputs on the first day. Goods imported to the UK by other means would be severely delayed as ports and other transport operations would lose all the efficiencies brought about by GNSS. The telecommunications network, however, would not be affected. The impact on the domestic transport network would be substantial, at £2bn. Congestion would build very quickly, and delivery and minicab drivers would lose their preferred navigation method. This would impact all drivers as the increased congestion would mean that even drivers that know their route would see increases in travel time. Similarly, surveying activity — a critical input in all construction activities — would be expected to shut down for the duration of the outage, costing £345m in lost activity.
There is ample evidence that GNSS dependency pervades modern society, but probably not to the extent that loss of it alone would represent a severe risk to health and wellbeing, even thought the consequences would be irritating and disruptive. It's surprising, perhaps, that port operations appear to be heavily dependent on GNSS for the use of automated cranes moving containers. Food shortages might therefore be a consequence in a prolonged outage, due not only to port operations being hampered but also disruption in road transport, as the London Economics survey predicts.
More importantly, the "Systems of Systems" issue should give pause for thought. Critical National Infrastructures are not independent of one another, but closely interlinked and each depends on the other. This System-of-Systems is not a system that was designed for resiliency in the face of shocks, rather it is one that has simply grown over time and is, indeed, demonstrably non-resilient.