Somewhere above you right now, a GPS satellite is broadcasting the time — accurate to within about a microsecond by the time it reaches the ground. That number sounds like trivia until you learn who’s listening: the relays that keep the power grid in phase, the exchanges that timestamp your retirement fund’s trades, the systems that line aircraft up with runways in bad weather. None of them carry a clock good enough to do this alone. They all set their watches by the same satellites.
A quick note on names: GPS is the American satellite-navigation system. Europe runs Galileo, Russia GLONASS, and China BeiDou — collectively these are called GNSS, Global Navigation Satellite Systems. When you see “GNSS” below, it means all of them; the dependency and the vulnerability are the same whichever constellation a receiver listens to.
That arrangement is cheap, precise, and astonishingly easy to break. This brief explains the dependency in plain terms, what has changed in the last three years, and the questions worth asking if continuity, resilience, or oversight is your job.
The dependency, in one paragraph
Electric grids use GPS-disciplined clocks to synchronize measurements across thousands of miles — devices called phasor measurement units need time agreement on the order of a microsecond to tell operators the grid is stable. Financial regulators in the U.S. and Europe require trading systems to keep tightly synchronized, auditable timestamps; the cheapest trusted source is GPS. Aviation leans on GPS for navigation and increasingly for approaches. Cell networks, broadcast, and water systems sit in the same line. In 2019, a study sponsored by the National Institute of Standards and Technology modeled a hypothetical 30-day nationwide GPS outage at roughly $1 billion per day on average — and the authors themselves called that figure a likely underestimate, since it covered only selected private-sector industries.
What changed
Interference used to be an anecdote. It is now a statistic. OPSGROUP, a network of flight-operations professionals, estimated from ADS-B data that GPS spoofing affecting civil aviation grew from roughly 300 flights a day in January 2024 to roughly 1,500 by August, concentrated near conflict zones but bleeding outward along major corridors — and their report cautions the true number is likely higher. In April 2024, Finnair suspended its Tartu, Estonia route for a month after interference forced two flights to abandon approaches; the airport’s only instrument approach at the time required GPS. The United States has had its own tastes of the problem with no adversary involved: a transmitter inadvertently broadcasting in the GPS band disrupted the Denver area for about 33 hours in January 2022, and an unexplained event made a runway unusable around Dallas–Fort Worth for more than a day in October 2022. The source of that one was never publicly identified.
Policy has been moving, though slower than the threat. Executive Order 13905 (2020) told federal agencies to map their PNT dependencies and stop treating GPS as a given. The National Timing Resilience and Security Act (2018) ordered a land-based backup timing system — subject to appropriations that never came, so it remains unbuilt. The Department of Transportation has put real money — $7.2 million across nine vendors in 2024, nearly $5 million more in 2025 — into demonstrating complementary timing and navigation technologies. The FCC opened a formal inquiry in March 2025 (WT Docket 25-110) on promoting alternatives, and in June 2026 a House Energy & Commerce subcommittee held a hearing on exactly this dependency. The machinery is turning. What it hasn’t produced yet is a funded, operating backup.
Why this is a diplomacy story
Interference rarely respects borders, and attribution is genuinely hard — a receiver can’t easily tell a hostile spoofer from a misconfigured repeater. The rules for what states owe each other about the radio spectrum and the satellites behind it are written in slow rooms: the ITU, ICAO, UN committees. That contest over rules — who gets blamed, who must harden, who pays — is the diplomacy of space and aerospace arriving at street level. GPS timing is simply where it reaches your constituents first.
If this is your desk, ask these
- Which of our systems take time from GPS, and what do they do when the signal degrades — hold steady, alarm, or quietly drift?
- How long can each critical system “coast” on its internal clock before something operational breaks? Hours and days are very different answers.
- Have we adopted the DHS resilient-PNT guidance (released February 2025) for procurement — and do our vendor contracts mention holdover or interference at all?
- Who in our organization would even know an interference event was happening, versus debugging it as a mysterious IT fault?
- What did we tell the FCC docket, or the DOT demonstrations — and if nothing, who should have?
The honest caveats
The $1B/day figure is a model, not a measurement — it averages a hypothetical 30-day nationwide outage, which has never happened, and the modeled range runs $16–35 billion in total. The spoofing counts are algorithmic estimates from flight-broadcast data, which the authors say likely undercount. And solid mitigations exist: holdover clocks, multi-GNSS receivers, terrestrial timing over fiber. The gap isn’t technology. It’s that nobody’s budget line says “the time.”
Sources
- RTI International for NIST, “Economic Benefits of the Global Positioning System” (2019) — the ~$1B/day outage model.
- OPSGROUP, “Report of the 2024 GPS Spoofing Workgroup” (Sept. 2024) — spoofing estimates from ADS-B data.
- Executive Order 13905, “Strengthening National Resilience Through Responsible Use of PNT Services,” Federal Register, Feb. 2020.
- National Timing Resilience and Security Act, Public Law 115-282 §514 (2018).
- U.S. DOT / Volpe Center, Complementary PNT Demonstration Report to Congress (Jan. 2021).
- U.S. DOT complementary-PNT award announcements, July 2024 and October 2025.
- DHS, Resilient PNT best-practices guidance for critical infrastructure (document dated Sept. 2024, released Feb. 2025).
- FCC, Notice of Inquiry, WT Docket No. 25-110 (March 2025).
- House Energy & Commerce, Subcommittee on Communications & Technology, “Where Are We?: Examining Positioning, Navigation, and Timing Capabilities in the United States,” June 4, 2026.
- FAA advisories, CISA Insights on the Denver event (Jan. 2022), and reporting on the Dallas–Fort Worth event (Oct. 2022).
- Finnair and Estonian authorities on the Tartu route suspension, April–May 2024.
Boundary note: this brief uses public sources only and describes no exploitation technique beyond what those sources publish. Corrections: howdy [at] diplospace · org.
Want the math and the full figures? The underlying papers are free: Field Note 01 — When GPS Lies (PDF) and Field Note 02 — The Grid Has a Heartbeat (PDF).