GPS never finds you. It fixes your clock.

02 · User segment

Four satellites, four unknowns — the fourth unknown is you

The constellation broadcasts proper time. The receiver does not keep it. A cheap quartz oscillator leaves a common clock bias across every measurement, so three ranges are not enough.[1][2]

GNSS uses one-way time-of-arrival pseudoranging. Medium Earth Orbit vehicles broadcast carriers modulated with PRN codes and a navigation message of ephemerides and clock corrections. The receiver solves the four-dimensional state vector [x_r, y_r, z_r, Δt_rx]. The minimum is 4 non-coplanar satellites.[1][3][5]

x_r position y_r position z_r position Δt_rx your clock

Each term in the pseudorange equation is a button. Definitions stay on the page.[1]

= · (t_rx − t_tx,i) = + + + +

ρ_i — measured pseudorange: apparent transit time of the signal, not the true geometric range.

c — speed of light in vacuum. Converts a time offset into metres.

R_i — true geometric range √[(x_i−x_r)²+(y_i−y_r)²+(z_i−z_r)²].

c (Δt_rx − Δt_tx,i) — receiver clock bias is unknown; satellite clock bias is known from the broadcast ephemeris.

I_i — ionospheric path delay.

T_i — tropospheric path delay.

ε_i — multipath, receiver thermal noise, and relativistic residual.

Positioning is what remains after the receiver’s temporal offset is resolved against GPS Time, itself calibrated to UTC via the United States Naval Observatory.[1][14]

03 · Policy error

The 100-metre error was policy, and it was switched off twice

Once the space clocks were made to run right, civil users were still given the wrong time. The Department of Defense inserted Selective Availability on Block II: an intentional clock error, the same control surface as the factory offset, pointed the other way.[1][3][11]

Civil Standard Positioning Service · horizontal, 95%

SA on · δ dither

100 m

Degraded from ~15–20 m. Clock dither (δ) used almost exclusively; ephemeris (ε) distortion was avoided because it broke differential integrity for friendly forces.[1][3]

SA off · 1 May 2000

~15–20 m

Range restored, not a single figure. Clinton’s directive took effect midnight, 0400 UTC 2 May 2000.[1][3][11]

25 Mar 1990SA activated on Block II.[1][3]
Aug 1990 – Jul 1991SA deactivated for Desert Storm. Military P(Y) receivers were short; units navigated the Iraqi desert on commercial C/A boxes.[1][3][11]
1996 · NSTC-6GPS institutionalized as dual-use; intent to terminate SA within a decade. Differential GPS had already cancelled the dither in practice.[1][3][11]
1 May 2000SA set to zero. Second switch-off; this one stayed off.

The civil C/A signal on L1 was already in Block I/II specifications in the 1970s. Reagan’s statement of 16 September 1983, after the shootdown of KAL 007 on 1 September, made that baseline an irrevocable international commitment rather than a fee-or-encrypt option.[1][3][5][11] The dispute over which of those facts is “the origin” of civil GPS is in the ledger below.

04 · Sovereign clocks

Three rivals, three different reasons

A clock you do not control is a clock that can be denied. GLONASS, Galileo, and BeiDou are not copies of GPS. Each follows a distinct political logic.[3][7][10][11]

GLONASS

Strategic parity · ballistic targeting

Authorized in 1976, first launched in 1982, built for Soviet naval, air, and ballistic platforms. Legacy satellites used FDMA — identical PRN codes on channelized frequencies — which removed cross-correlation at the cost of inter-channel hardware bias and SWaP. The constellation is still modernizing toward CDMA on GLONASS-K.[10][11]

2001 operational slots · 6–7 of 24 (range as logged)

Russian MoD declared 24-satellite FOC in September 1995. NORAD / NASA Goddard tracking for 1995–1998 recorded 18–19 satellites consistently broadcasting valid ephemerides after rapid clock and power-bus failures. By 2001 the constellation had dropped to 6–7 operational satellites. Reinvestment restored 24 by late 2011.[3][7][10][11]

64.8° inclination. High-latitude geometry is the point, not an accident.

Galileo

Strategic autonomy · civil independence

Conceived in the late 1990s by the European Union and ESA as civil-controlled infrastructure, not a military system. The aim was to avoid unilateral GPS denial or degradation.[3][7][10]

The U.S. Department of Defense objected to the proposed Public Regulated Service overlapping U.S. M-Code near L1/E1, which would have complicated selective theater jamming. The 2004 EU–US Agreement on GPS-Galileo Cooperation standardized Binary Offset Carrier modulation MBOC(6,1,1/11).[7][10][11][12]

Passive Hydrogen Maser clocks beside rubidium. High Accuracy Service at decimeter level; PRS authentication.

BeiDou

Anti-access sovereignty · global PNT

Development accelerated after U.S. naval operations in the 1995–1996 Third Taiwan Strait Crisis and the 1993 Yinhe incident.[10]

BeiDou-1 (2000–2003) — active two-way ranging (RDSS) on GEO. User terminals transmitted uplink pings and therefore an emission signature.[10]
BeiDou-2 (2007–2012) — passive one-way TOA (RNSS), hybrid GEO+IGSO+MEO, Asia-Pacific.
BeiDou-3 (2015–2020) — completed June 2020. Ka-band inter-satellite links for autonomous orbit determination without overseas ground stations, plus short-message communication.[10]

Chen Fangyun independently formulated dual-GEO ranging mathematics in 1983. The physical implementation reflected topologies already demonstrated by Geostar/Locstar. Both claims stand in the ledger; they are not collapsed into one origin story.[3][10]

05 · The rest of the record

The documents do not agree

Five places in this history still have primary sources pointing at different facts. The analysis does not average them. Each card states the synthesis; open it for the contending files.[1][6][13]

Conflict 1 · Attribution Easton invented time-synchronized passive ranging. Getting led early advocacy and PRN. Parkinson synthesized NAVSTAR and kept it alive.

The 2003 Charles Stark Draper Prize went jointly to Ivan A. Getting and Bradford W. Parkinson, omitting Roger L. Easton. In 2006 Easton received the National Medal of Technology for space-based tracking and timing. Credit is structurally distributed, not awarded to one man.[6][13][15]

Easton / NRL: U.S. Patent 3,789,409 (filed 1970, issued 1974) documents synchronized spaceborne clocks and passive one-way ranging. Easton argued GPS took TIMATION’s baseline and that USAF 621B was a transponder-repeater.[1][2][6]

Getting / Aerospace: 3D hyperbolic advocacy from 1960; 621B’s PRN CDMA as the breakthrough for passive multi-user navigation on one frequency.[1][2][4]

Parkinson / JPO: Labor Day weekend, September 1973, “Lonely Halls Meeting” at the Pentagon. Direct-sequence CDMA from 621B fused with TIMATION’s clocks. Program defense through cancellation attempts.[1][2][13]

Conflict 2 · Civil access Civil C/A was architecturally in the 1970s. KAL 007 made dual-use politically irrevocable.

Reagan’s 16 September 1983 statement did not invent the civil signal. It converted an unstable technical baseline into an international political commitment.[1][3][5][11]

White House narrative: GPS would be made available to civil international aviation to prevent navigation disasters.

JPO / SAMSO records, 1974–1980: dual-frequency, bifurcated SPS/PPS already specified — unencrypted C/A on L1, encrypted P(Y) on L1/L2 — partly to encourage civil aviation cost-sharing.[1][2][5]

Conflict 3 · Selective Availability Policy named two mechanisms. Telemetry shows almost only clock dither. SA was off for the Gulf War.

SPS was stated at 100 metres (95%) via δ dither and ε ephemeris manipulation. Empirical audits: DoD almost exclusively used δ. SA on, 25 March 1990; off, August 1990 to July 1991; zeroed 1 May 2000.[1][3][11][14]

DoD Federal Radionavigation Plans describe both δ and ε. Tracking logs (JPL, UNB) and Gulf War receiver shortages explain the outage. ε was avoided because it degraded differential networks used by friendly forces.

Conflict 4 · GLONASS 1995 FOC Nominal 24 in late 1995. Functional coverage was 18–19 within months, then 6–7 by 2001.

FOC was nominally achieved. Spacecraft longevity did not match the announcement. Full 24 returned in 2011.[3][7][10][11]

Russian Ministry of Defence, 1995: 24 operational satellites, parity with GPS.

NORAD / NASA Goddard, 1995–1998: 24 slots occupied; early Block IIv clocks and power buses failed; 18–19 broadcasting valid ephemerides.

Conflict 5 · BeiDou-1 heritage Independent mathematics, 1983. Engineering topologies already shown by Geostar/Locstar.

Chen Fangyun independently derived dual-GEO ranging. The practical transponder layout reflected Western commercial RDSS configurations marketed after Locstar’s 1991 insolvency.[3][10]

Chinese state records: Chen Fangyun’s 1983 “Twin-Satellite Positioning System,” two GEO plus ground digital elevation models.

Geostar / Locstar filings, 1983–1991: Gerard K. O’Neill’s active two-way architecture; Locstar technical data circulated internationally after insolvency.

Comparison matrix · four constellations

Parameter	NAVSTAR GPS (USA)	GLONASS (RF)	Galileo (EU)	BeiDou BDS-3 (PRC)
Authority	U.S. Space Force (DoD)	Roscosmos / Aerospace Forces	European Commission / EUSPA	China Satellite Navigation Office (PLA)
Logic	Force enhancement & global utility	Strategic parity; ballistic targeting	Strategic autonomy; civil independence	Anti-access sovereignty; global PNT
Topology	24+ SVs (nominal 31); 6 planes @ 55°	24 satellites; 3 planes @ 64.8°	24 nominal + spares; 3 planes @ 56°	24 MEO + 3 IGSO + 3 GEO
Altitude / period	20,180 km / 11 h 58 m	19,100 km / 11 h 15 m	23,222 km / 14 h 04 m	MEO 21,528 km / 12 h 53 m; GEO/IGSO 35,786 km
Access	CDMA (direct-sequence)	FDMA (legacy); CDMA modernizing	CDMA (direct-sequence)	CDMA (direct-sequence)
Bands	L1 1575.42 / L2 1227.60 / L5 1176.45 MHz	G1 ~1602 / G2 ~1246 / G3 CDMA 1202.025 MHz	E1 1575.42 / E5a/b 1176.45 & 1207.14 / E6 1278.75 MHz	B1I/B1C 1575.42 / B2a/b 1176.45 & 1207.14 / B3I 1268.52 MHz
Ground-track repeat	1 sidereal day (2 orbits)	8 sidereal days (17 orbits)	10 sidereal days (17 orbits)	7 sidereal days (13 orbits, MEO)
Distinct	M-Code spot-beams; NDS nuclear detonation detection	High-latitude geometry @ 64.8°	HAS (PPP); PRS authentication	Short Message Communication; Ka-band ISL

Figures as stated in the comparison matrix.[1][7][10][11]

Chronology · 1957–2020

4 Oct 1957Sputnik 1. Guier and Weiffenbach at APL recover the orbit from Doppler; the reverse — observer from satellite — follows.[4]
1964–1973Transit operational (USN, 1964): LEO, 2D fixes every 90 to 110 minutes, user must correct for platform velocity. TIMATION (NRL, Easton) puts stable clocks in orbit for passive one-way ranging. System 621B (USAF/Aerospace) demonstrates PRN CDMA 3D positioning at White Sands.[1][2][4]
Sep 1973DepSecDef Clements mandates consolidation under the Air Force. Col. Bradford W. Parkinson, JPO. Lonely Halls Meeting, Pentagon, Labor Day weekend: NAVSTAR GPS.[1][2][13]
Jun 1977NTS-2 carries the first space-qualified cesium beam standards and verifies the predicted relativistic frequency shifts.[1][4]
Sep 1983KAL 007, 1 September. Reagan civil-access policy, 16 September.
1993–1995IOC 8 December 1993. FOC 27 April 1995, 24 operational Block II/IIA.[1][2][11]
1 May 2000Selective Availability set to zero. Civil horizontal accuracy from ~100 m to ~15–20 m.
2000–2020BeiDou-1 through BeiDou-3 (complete June 2020). GPS Block IIR-M, IIF, GPS III: L2C, L5, L1C, M-Code. GLONASS restored 2011. Galileo PHM and HAS.

GPS never finds you. It fixes your clock.

Four satellites, four unknowns — the fourth unknown is you

The 100-metre error was policy, and it was switched off twice

Three rivals, three different reasons

GLONASS

Galileo

BeiDou

The documents do not agree

A clocks-first historian, not a map explainer

Receipts

Cited

Further research consulted