1990
Trimble Navigation, the world leader in commercial sales of GPS receivers, founded in 1978, completes its initial public stock offering.

March 25, 1990
DoD, in accordance with the Federal Radionavigation Plan, activates SA—the purposeful degradation in GPS navigation accuracy—for the first time. August 1990 SA is deactivated during the Persian Gulf War. Factors that contributed to the decision to turn SA off include the limited three-dimensional coverage provided by the NAVSTAR constellation in orbit at that time and the small number of Precision (P)-code receivers in the DoD inventory at the time. DoD purchased thousands of civilian GPS receivers shortly thereafter to be used by the Allied forces during the war.

1990–1991
GPS is used for the first time under combat conditions during the Persian Gulf War by Allied forces. The use of GPS for Operation Desert Storm proves to be the first successful tactical use of a space-based
technology within an operational setting.

August 29, 1991
The U.S. government revises export regulations, making a clear delineation between military and civil
GPS receivers. Under the revised regulations, military receivers continue to be treated as “munitions” with strict export restrictions, while civilian receivers are designated “general destination items” available for export without restrictions.

July 1, 1991
SA is reactivated after the Persian Gulf War. September 5, 1991 The United States offers to make GPS standard positioning service (SPS) available beginning in 1993 to the international community on a continuous, worldwide basis with no direct user charges for a minimum of ten years. The offer was announced at the Tenth Air Navigation Conference of the International Civil Aviation Organization (ICAO).

September 1992
The United States extends the 1991 offer at the 29th ICAO Assembly by offering SPS to the world for the foreseeable future and, subject to the availability of funds, to provide a minimum of six years advance notice of termination of GPS operations or elimination of the SPS.

December 8, 1993
The Secretary of Defense formally declares Initial Operational Capability of GPS, signifying that with 24
satellites in orbit, GPS is no longer a developmental system and is capable of sustaining the 100-meter
accuracy and continuous worldwide availability promised SPS users.

February 17, 1994
FAA Administrator David Hinson announces GPS as the first navigation system approved for use as a
stand-alone navigation aid for all phases of flight through nonprecision approach.

June 2, 1994
FAA Administrator David Hinson announces termination of the development of the Microwave
Landing Systems (MLS) for Category II and III landings.

November 1994
Orbital Sciences Corp., a leading maker of rockets and satellites, agrees to purchase Magellan Corp., a
California-based manufacturer of hand-held GPS receivers, in a stock swap worth as much as $60 million, bringing Orbital closer to its goal of becoming a satellite-based two-way communications company.

June 8, 1994
FAA Administrator David Hinson announces implementation of the Wide-Area Augmentation
System (WAAS) for the improvement of GPS integrity and availability for civil users in all phases of flight. Projected cost of program is $400–500 million; it is scheduled to be implemented by 1997.

October 11, 1994
The Department of Transportation Positioning/Navigation Executive Committee is created to provide
a cross-agency forum for making GPS policy.

October 14, 1994
FAA Administrator David Hinson reiterates the United States offer to make GPS-SPS available for the
foreseeable future, on a continuous, worldwide basis and free of direct user fees in a letter to ICAO.

March 16, 1995
President Bill Clinton reaffirms the United States commitment to provide GPS signals to the
international civilian community of users in a letter to ICAO.

April 26, 1980
The first GPS satellite to carry Integrated Operational Nuclear Detonation Detection System (IONDS)
sensors is launched.

1982
A decision to reduce the GPS satellite constellation from 24 to 18 satellites is approved by DoD following a major program restructure brought on by a 1979 decision by the Office of the Secretary of Defense to cut $500 million (approximately 30 percent) from the budget over the period FY81–FY86.

July 14, 1983
The first GPS satellite to carry the newer Nuclear Detonation Detection System (NDS) is launched.

September 16, 1983
Following the Soviet downing of Korean Air flight 007, President Reagan offers to make GPS available for use by civilian aircraft, free of charge, when the system becomes operational. This marks the beginning of the spread of GPS technology from military to civilian aircraft.

April 1985
The first major user equipment contract is awarded by the JPO. The contract includes research and
development as well as production options for 1-, 2-, and 5-channel GPS airborne, shipboard, and
manpack (portable) receivers.

1987
DoD formally requests that the Department of Transportation (DoT) assume responsibility for
establishing and providing an office that will respond to civil user needs for GPS information, data, and
assistance. In February 1989, the Coast Guard assumes responsibility as the lead agency for the Civil
GPS Service.

1984
Surveying becomes the first commercial GPS market to take off. To compensate for the limited number of satellites available to them early in the constellation’s development, surveyors turned to a number of GPS accuracy enhancement techniques including differential GPS and carrier phase tracking.

March 1988
The Secretary of the Air Force announces the expansion of the GPS constellation to 21 satellites plus
3 operational spares.

February 14, 1989
The first of 28 Block II satellites is launched from Cape Canaveral AFS, Florida, on a Delta II booster. The Space Shuttle had been the planned launch vehicle for the Block II satellites built by Rockwell. Following the 1986 Challenger disaster, the JPO reconsidered and has since used the Delta II as the GPS launch vehicle.
Selective availability (SA) and anti-spoofing (AS) become possible for the first time with the Block II
design.

June 21, 1989
Martin Marietta (after buying out the General Electric Astro Space division in 1992) is awarded a contract to build 20 additional “replenishment” satellites (Block IIR). The first Block IIR satellite will be ready for launch as needed at the end of 1996.

1920s
Origins of radionavigation Early WW II LORAN, the first navigation system to employ timedifference-of-arrival of radio signals, is developed by the MIT Radiation Laboratory. LORAN was also the first true all-weather position-finding system, but is only two-dimensional (latitude and longitude).

1959
TRANSIT, the first operational satellite-based navigation system, is developed by the Johns Hopkins Applied Physics Laboratory (APL) under Dr. Richard Kirschner. Although Transit was originally intended to support the U.S. Navy’s submarine fleet, the technologies developed for it proved useful to the Global Positioning System (GPS). The first Transit satellite is launched in 1959.

1960
The first three-dimensional (longitude, latitude, altitude) time-difference-of-arrival navigation system is suggested by Raytheon Corporation in response to an Air Force requirement for a guidance system to be used with a proposed ICBM that would achieve mobility by traveling on a railroad system. The
navigation system presented is called MOSAIC (Mobile System for Accurate ICBM Control). The idea
is dropped when the Mobile Minuteman program is canceled in 1961.

1963
The Aerospace Corporation launches a study on using a space system as the basis for a navigation system for vehicles moving rapidly in three dimensions; this led directly to the concept of GPS. The concept involves measuring the times of arrival of radio signals transmitted from satellites whose positions are precisely known. This gives the distances to the known satellite positions—which, in turn, establishes the user’s position.

1963
The Air Force begins its support of the Aerospace study, designating it System 621B. By 1972, the
program has already demonstrated operation of a new type of satellite-ranging signal based on pseudorandom noise (PRN).

1964
Timation, a Navy satellite system, is developed under Roger Easton at the Naval Research Lab (NRL) for
advancing the development of high-stability clocks, time-transfer capability, and 3-D navigation.
Timation’s work on space-qualified time standards provided an important foundation for GPS. The first
Timation satellite is launched in May 1967.

1968
DoD establishes a tri-service steering committee called NAVSEG (Navigation Satellite Executive Committee) to coordinate the efforts of the various satellite navigation groups (Navy’s Transit and Timation programs, the Army’s SECOR or Sequential Correlation of Range system). NAVSEG contracted a number of studies to fine-tune the basic satellite navigation concept. The studies dealt with some of the major issues surrounding the concept, including the choice of carrier frequency (L-Band versus CBand), the design of the signal structure, and the selection of the satellite orbital configuration (a 24- hour figure 8s constellation versus “Rotating Y” and “Rotating X” constellation).

1969–1972
NAVSEG manages concept debates between the various satellite navigation groups. The Navy APL
supported an expanded Transit while the Navy NRL pushed for an expanded Timation and the Air Force
pushed for an expanded synchronous constellation “System 621B.”

1971
L2 frequency is added to the 621B concept to accommodate corrections for ionospheric changes.

1971–1972
User equipment for the Air Force 621B is tested at White Sands Proving Ground in New Mexico. Ground
and balloon-carried transmitters simulating satellites were used, and accuracies of a hundredth of a mile
demonstrated.

April 1973
The Deputy Secretary of Defense determines that a joint tri-service program be established to consolidate the various proposed positioning/navigation concepts into a single comprehensive DoD system known as the Defense Navigation Satellite System (DNSS). The Air Force is designated the program manager. The new system is to be developed by a joint program office (JPO), with participation by all military services. Colonel Brad Parkinson is named program director of the JPO and is put in charge of jointly developing the initial concept for a space-based navigation system.

August 1973
The first system presented to the Defense System Acquisition and Review Council (DSARC) is denied
approval. The system presented to DSARC was packaged as the Air Force’s 621B system and therefore
not representative of a joint program. Although there is support for the idea of a new satellite-based
navigation system, the JPO is urged to broaden the concept to include the views and requirements of all the services.

December 17, 1973
A new concept is presented to DSARC and approval to proceed with what is now known as the NAVSTAR GPS is granted, marking the start of concept validation (Phase I of the GPS program). The new concept was really a compromise system negotiated by Col. Parkinson that incorporated the best of all available satellite navigation system concepts and technology. The approved system configuration consists of 24 satellites placed in 12-hour inclined orbits.

June 1974
Rockwell International is chosen as the satellite contractor for GPS.

July 14, 1974
The very first NAVSTAR satellite is launched. Designated as Navigation Technology Satellite (NTS)
number 1, it is basically a refurbished Timation satellite built by the NRL. The second (and last) of the
NTS series was launched in 1977. These satellites were used for concept validation purposes and carried the first atomic clocks ever launched into space.

1977
Testing of user equipment is carried out at Yuma, Arizona.

February 22, 1978
The first Block I satellite is launched. A total of 11 Block I satellites were launched between 1978 and
1985 on the Atlas-Centaur. Built by Rockwell International as developmental prototypes, the Block Is were used for system testing purposes. One satellite was lost as a result of a launch failure.