Civilian GPS error was a setting, not a limit.

02

Position is what falls out when you solve for time

SW-1 altered numbers inside the broadcast navigation message. It moved no satellite. That is possible because the coordinate a receiver reports is not measured — it is solved for, and the quantity actually being solved for is time.¹³⁴

Global navigation satellite systems run on one-way time-of-arrival pseudoranging. Satellites in medium Earth orbit broadcast carrier signals modulated with pseudorandom noise codes and a navigation message carrying precise orbital ephemerides and satellite clock corrections.¹²⁴ The receiver measures the apparent transit time of each signal.

• cSpeed of light in a vacuum.
• R_iTrue geometric range, √((x_i−x_r)² + (y_i−y_r)² + (z_i−z_r)²).
• Δt_rxReceiver clock bias relative to system time — the unknown. The receiver runs an inexpensive quartz crystal oscillator, not an atomic standard, so this bias appears as a common offset across every measurement.¹²
• Δt_tx,iSatellite clock bias relative to system time — known via the broadcast ephemeris.¹
• I_i, T_iIonospheric and tropospheric path delays.¹²
• ε_iMultipath, receiver thermal noise, relativistic residuals.¹

An absolute minimum of four non-coplanar satellites is required to solve the four-dimensional state vector [x_r, y_r, z_r, Δt_rx].¹³⁵ Position is the mathematical consequence of resolving the receiver's temporal offset against the constellation's coordinated time scale — GPS Time, calibrated to UTC via the United States Naval Observatory.¹¹⁴ The system's product is time. Coordinates are the byproduct.

03

The switch that was welded shut

If the product is time, then anything that changes the rate of a clock changes the reported position. Two effects do, continuously, and neither is optional.⁴¹¹

This is SW-2. It is set once, on the ground, per spacecraft. There is no operational state in which it is thrown, no directive that alters it, no user class it discriminates between. Satellite navigation is one of the few engineering disciplines requiring continuous reconciliation of both special and general relativity, and the reconciliation applies identically to every receiver on Earth.⁴¹¹

04

Where the civil signal came from

SW-2 was corrected because it degraded every user equally. Selective Availability degraded one class of user on purpose — which required, first, that a civil class of user exist at all.¹³

1. 1960 – 1973 · PROGENITOR PROGRAMS

   Three competing service programs

   Transit, developed at the Johns Hopkins Applied Physics Laboratory under Frank McClure and Richard Kershner after William Guier and George Weiffenbach's Doppler analysis of Sputnik 1, became operational in 1964 to update the ballistic missile submarine fleet; in low Earth orbit it gave 2D fixes every 90 to 110 minutes and required the user to correct for platform velocity.¹²⁴ TIMATION, at the Naval Research Laboratory under Roger L. Easton (1964–1973), pioneered stable spaceborne crystal and atomic clocks for passive, one-way ranging.¹⁴⁶¹⁵ System 621B, run by the USAF Space and Missile Systems Organization with Aerospace Corporation, demonstrated continuous 3D positioning using pseudorandom noise code modulation at White Sands.¹²⁴

   In April 1973 Deputy Secretary of Defense William P. Clements Jr. mandated consolidation under the Air Force and appointed Col. Bradford W. Parkinson to lead the Joint Program Office. Over Labor Day weekend in September 1973, the "Lonely Halls Meeting" at the Pentagon fused 621B's direct-sequence CDMA spread-spectrum architecture with TIMATION's spaceborne atomic clock passive ranging, formalising NAVSTAR GPS.¹²¹³

   Military only
2. 1974 – 1983 · PROOF OF CONCEPT, THEN A SHOOTDOWN

   The civil access switch is thrown

   NTS-2, launched June 1977 under NRL direction, carried the first space-qualified caesium beam standards and verified the predicted relativistic clock frequency shifts.¹⁴ Navstar 1–4 (1978) validated 3D positioning and demonstrated bombing accuracy at the Yuma Proving Ground.¹² The mission remained strategic: nuclear targeting, submarine positioning, precision weapons guidance.¹³⁷

   On 1 September 1983 Soviet interceptors destroyed Korean Air Lines Flight 007 after the airliner strayed into prohibited Soviet airspace over the Kamchatka Peninsula and Sakhalin Island through navigational error. On 16 September 1983 President Ronald Reagan issued a formal policy statement ordering that the civil Standard Positioning Service be made available freely to international civil aviation and maritime transport upon operational readiness.¹³¹¹

   Civil access directed
3. 1984 – 1995 · FULL OPERATIONAL CAPABILITY

   Dual use, deliberately degraded

   Selective Availability was implemented on the Block II satellites. Operation Desert Storm (1990–1991) served as the operational trial. GPS reached Initial Operational Capability on 8 December 1993 and Full Operational Capability on 27 April 1995, with 24 operational Block II/IIA satellites in orbit.¹²¹¹

   Dual use · degraded
4. 1996 – 2000 · CIVIL TRANSITION

   The degradation is withdrawn

   Presidential Decision Directive NSTC-6 (1996) institutionalised GPS as a dual-use asset and announced the intent to terminate Selective Availability within a decade. On 1 May 2000 President Bill Clinton directed its cessation.¹³¹¹

   Dual use · undegraded
5. 2000 – PRESENT · MODERNIZATION

   Separate signals rather than one degraded signal

   Block IIR-M, IIF and GPS III integrated dedicated civil signals — L2C, L5, L1C — alongside jam-resistant, cryptographically isolated military signals (M-Code).¹⁷¹¹

   Dual use · separated

The architecture split that made degradation possible

Both services derive from the same satellites and the same clocks.¹³¹¹ The unencrypted C/A code was written into the Block I/II baseline specifications between 1974 and 1980, partly to encourage civil aviation cost-sharing — before the 1983 directive existed.¹²⁵ See dispute 02 in the ledger.

05

Their own troops made them turn it off

The split gave the Department of Defense a signal it could degrade without touching its own. It degraded that signal on 25 March 1990. Five months later its own ground units in Iraq were navigating on it.¹³¹¹

1. 25 MAR 1990 · SA ON

   The Department of Defense activated Selective Availability on the Block II satellites. Two mechanisms were specified: δ-manipulation, phase-dithering the fundamental satellite clock oscillator with a pseudo-random sequence, and ε-manipulation, deliberate truncation and alteration of the orbital ephemeris parameters in the broadcast navigation message.¹³

2. AUG 1990 – JUL 1991 · SA OFF

   The Department faced a severe shortage of military-spec P(Y)-code receivers and deployed thousands of commercial C/A-code receivers to ground units navigating featureless Iraqi desert. To let those units function accurately, Selective Availability was deactivated for the duration of the conflict.¹³¹¹

3. 1991 – 2000 · SA ON, THEN OBSOLETE

   Through the late 1990s, Differential GPS networks developed by the U.S. Coast Guard and aviation authorities eliminated the dither errors of SA, rendering the degradation policy technically obsolete.¹³¹¹ Presidential Decision Directive NSTC-6 (1996) announced the intent to terminate it within a decade.¹³¹¹

4. 0400 UTC · 2 MAY 2000 · SA OFF

   President Bill Clinton's directive of 1 May 2000 took effect at midnight, 0400 UTC on 2 May 2000, immediately improving civil horizontal accuracy from ~100 m to ~15–20 m.¹³¹¹

06

Five places the record disagrees with itself

The dates on the trace above are stamped. Most of this history is not. Where primary sources contend, the analysis records the contest instead of picking a winner: five disputes, each with its contending sources and a stated synthesis.¹²⁴⁶¹³

Dispute 01 · contested

Who invented GPS: Easton, Getting, or Parkinson

Primary and secondary literature contest the origination of GPS across three programs and three men. The dispute is over the priority of intellectual invention versus operational systems engineering.^12461315

Dispute 02 · resolved by synthesisDid KAL 007 create civilian GPS, or only make it permanent? ▾

Reagan White House statement, 16 Sep 1983

Formally announced that GPS would be made available to civil international aviation to prevent navigation disasters.¹³⁵¹¹

JPO requirements & baseline specs, 1974–1980

Block I/II design specifications had already established a bifurcated signal structure — unencrypted C/A on L1, encrypted P(Y) on L1/L2 — partly to encourage civil aviation cost-sharing.¹²³⁵

Synthesis

The dual-use civil signal was architecturally incorporated in the 1970s, but its operational status remained vulnerable to military user fees or encryption. Reagan's 1983 directive converted an unstable technical baseline into an irrevocable international political commitment.¹³⁵¹¹

Dispute 03 · resolved by synthesisSelective Availability: dates, mechanism, and the degradation actually applied ▾

DoD policy & Federal Radionavigation Plans

SPS horizontal accuracy stated as throttled to 100 m (95% confidence) via clock dither (δ) and ephemeris manipulation (ε).¹³¹¹¹⁴

Empirical tracking logs, 1990–1991

SA activated on Block II on 25 March 1990; monitoring networks documented deactivation from August 1990 to July 1991 because allied units relied heavily on commercial C/A-code receivers.¹³¹¹

Synthesis

SA was deactivated during the Gulf War owing to receiver shortages. The degradation relied almost exclusively on clock dither (δ); ephemeris distortion was avoided because it degraded the differential integrity networks used by friendly forces.¹³

Dispute 04 · numbers do not agreeWas GLONASS fully operational in 1995? ▾

Russian Ministry of Defence notices, 1995

Declared 24 operational satellites in orbit in September 1995, claiming full operational parity with GPS.¹⁰¹¹

NORAD / NASA Goddard orbital tracking, 1995–1998

24 spacecraft occupied orbital slots in late 1995, but early satellites suffered rapid onboard atomic clock and power bus failures within months of launch, leaving only 18–19 consistently broadcasting valid ephemerides.³¹⁰¹¹

Synthesis

GLONASS achieved nominal numerical constellation size in late 1995. Spacecraft longevity deficiencies reduced functional coverage to sub-FOC levels until the 2011 restoration program.³⁷¹⁰¹¹

Dispute 05 · resolved by synthesisBeiDou-1's dual-GEO architecture: indigenous, or borrowed? ▾

Chinese state records

Attribute the system to academician Chen Fangyun's 1983 "Twin-Satellite Positioning System" model using two geostationary satellites and ground digital elevation models.¹⁰

Geostar / Locstar filings, 1983–1991

Western systems engineering files document Gerard K. O'Neill's active two-way satellite ranging architecture, licensed to the French Locstar consortium; Locstar's technical data was marketed internationally after its 1991 insolvency.³

Synthesis

Chen Fangyun independently formulated the mathematics of dual-GEO ranging in 1983. The practical engineering realization and transponder topologies of BeiDou-1 reflected system configurations demonstrated during the Western commercial Geostar/Locstar initiatives.³¹⁰

07

Four constellations, four strategic logics

The United States could throw SW-1 because it owned the switch. Three other powers built constellations of their own rather than remain on the far side of it.³⁷¹⁰¹¹

08

How this was built

The brief was "the evolution and history of GPS." Answering it required two kinds of expertise at once, and required refusing three tidier accounts.

Three readings ruled out

1. RULED OUT · SINGLE-INVENTOR ORIGIN STORY

   Easton, Getting and Parkinson are each credited as "the inventor of GPS" by different primary sources, and two different national awards split the difference. Naming one would have contradicted the record; credit is reported as structurally distributed.⁶¹³¹⁵

2. RULED OUT · A CLEAN GLONASS 1995 NUMBER

   Russian Ministry of Defence notices and Western orbital tracking give different constellation counts for the same months. Reporting either alone would have been false precision; both are shown.³¹⁰¹¹

3. RULED OUT · ONE SELECTIVE AVAILABILITY MECHANISM

   Policy documents specify clock dither and ephemeris manipulation; empirical audits indicate dither almost exclusively. The page states the specification and the observed practice separately.¹³¹⁴

09

Sources

Fifteen sources, grouped as the deliverable groups them. Every inline [n] above links to its entry here.