GPS signals are by far the single most widely used and most accurate source of navigation, positioning and timing (PNT), and this capability is deeply integrated into every aspect of our society. In particular, the timing service provided by GPS, while virtually unknown to the general public, is essential for a variety of digital operations — from performing financial transactions to operating cell phone networks to running the internet.

Of course, GPS — originally developed to guide nuclear submarines — is now vital to most military missions, and the system’s vulnerabilities are a source of great concern.

GPS has been remarkably reliable over the past quarter century. Solar flares are rare, multipath can be largely mitigated, and obstructed line-of-sight to the satellites is an acute problem only in certain environments, such as urban canyons.

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