A Short History of the Navstar Global Positioning System (GPS)
Pre-GPS History
GPS was developed by the US Department of Defense. It’s roots can be traced back to the early 1960s when the DoD became interested in an accurate positioning and navigation system that could be used globally, under any weather conditions, and that would be continuously available. Around this time, the US Navy and Air Force began studying the idea of using radio signals broadcasted from satellites for navigation and positioning.
There were several predecessors to GPS developed by the US Navy. One was called Transit and was the first satellite-based navigational system in the world. It was deployed in the early 1960s. It was designed to locate submarines and other military vessels on the ocean. It was made available for civilian use in 1967 and turned out to be so popular that it is still in use today.
Another GPS predecessor developed by the US Navy was called Timation. Like Transit, Timation was also satellite-based. It was started in 1964, with the first satellite launch taking place in 1967. The Timation system eventually came to use atomic clocks just like GPS satellites of today. The last two Timation satellites were actually used as prototype GPS satellites.
Separately, the US Air Force was developing another navigational design called System 621B. It used a technology called pseudorandom noise (PRN) which made the radio signals more resistant to enemy jamming attempts. In 1972, the US Air Force began to make plans to deploy 16 satellites in geosynchronous orbits to implement this system.
Early GPS Development
In 1973, the Deputy Secretary of Defense designated the US Air Force as the lead agency to consolidate the various space-based navigational systems being developed by different groups into a single system which would be shared by the entire DoD. It would be known as the Defense Navigation Satellite System (DNSS). In late 1973, a new system was being developed which combined the best features of earlier Navy and Air Force systems. It would eventually be known as the NAVSTAR Global Positioning System.
Between 1974 and 1979, the GPS system entered a validation phase during which it would demonstrate its potential for supporting military navigational and positioning needs. The original budget was for $100 million which was to cover four satellites, launch vehicles, a satellite control facility, three types of end-user equipment, and a testing program.
The first NAVSTAR satellites were originally Timation satellites. They carried the first atomic clocks ever launched into space. These early satellites only functioned for brief periods of time after launch, but they lasted long enough to prove the validity of several key technologies used by GPS – namely spread spectrum radio signals and precise timing derived from orbiting atomic clocks.
The first developmental GPS satellites were launched and tested beginning in 1978 and were known as Block Is. Between 1978 and 1985, a total of eleven Block I satellites were deployed. Originally designed to last three years, many of these early GPS satellites continued to operate well beyond their design lifetimes.
One little known detail about GPS satellites is that they have multiple roles. In addition to carrying a global positioning payload, they also contain nuclear detonation sensors designed to detect nuclear weapon explosions. Although the US Air Force and Atomic Energy Commission developed a series of satellites known as Vela to detect nuclear explosions in the 1960s, the DoD felt that having additional sensors would significantly improve detection capability.
Testing of GPS user equipment started with ground-based transmitters in 1977. By the time the first of the Block I satellites were in orbit in 1978, the DoD was testing several types of user equipment carried on aircraft, ships, ground vehicles, and soldiers wearing 25-pound backpacks.
GPS Gets the Green Light
In 1979, the DoD gave the go-ahead to proceed with full-scale development of GPS. Later that year, the Office of the Secretary of Defense cut $500 million from the original budget of about $1.65 billion which forced the GPS program to be restructured with a reduced scope. The final number of satellites was reduced from 24 to 18. Block II development satellites were scrapped, and the design was scaled down by eliminating hardening against nuclear and laser-based attacks.
Another setback to the GPS system occurred in 1986 when the Space Shuttle Challenger exploded. The shuttle was the only launch vehicle for GPS satellites at that time and its loss caused a 2-year delay in the launch of the second generation of GPS satellites – the Block IIs.
In 1989, the first Block II GPS satellite was launched aboard a Delta II rocket and became fully operational several months later. Since then, there have been 23 more Block II satellite launches. The Block II satellites incorporate several design differences affecting security and integrity. They have radiation-hardened electronics, anti-spoofing capabilities, and additional fault detection logic.
During the 1990-1991 Persian Gulf War, the GPS system was first tested combat. After the war, it was recognized as a key piece of technology that led to the rapid and successful conclusion of the war. The GPS satellites enabled coalition forces to navigate and direct munitions with unprecedented accuracy in the open desert nearly 24 hours a day, despite difficult operating conditions. GPS receivers were in such short supply during this time that 10,000 commercial units were ordered by the military to enable more coalition forces to benefit.
Since the Persian Gulf War, the US military has employed GPS in every significant operation from Somalia in 1993 through the current conflicts in Iraq and Afghanistan.
In 1994, the 24th Block II satellite was launched, completing the GPS constellation. Presently, the NAVSTAR system consists of 25 satellites, including one Block I satellite. The DoD announced Initial Operational Capability in December of 1993, and the US Air Force formally declare the GPS met the requirements for Full Operational Capability in 1995.
Recent Developments
During the 1990s, additional satellites were developed by Lockheed Martin and later Boeing as replacements for the previous Block II and Block IIA satellites. These are known as Block IIR satellites (Lockheed Martin) and Block IIF satellites (Boeing). They provide enhanced performance over the earlier generation of satellites. Among the more interesting enhancements is the capability to autonomously navigate and generate their own navigational message data.
In 1983, following the downing of Korean Airlines Flight 007 after it strayed into Soviet Union airspace, President Ronald Reagan announced that the GPS system would be made available for international civil use when it became operational. Then in 1987, the DoD requested the Department of Transportation to establish an office to act as a liason between civil GPS users and the DoD. In 1989, the US Coast Guard became the lead agency for this project.
In 1991, the US offered to make available a degraded accuracy version of the GPS to civilian users worldwide. At the International Civil Aviation Organization’s Tenth Air Navigation Conference. Known as the time as the Standard Positioning Service but since called Selective Availability (SA), it would provide accuracy to approximately 330 feet. Later that year, FAA administrator James Busey promised that GPS would be available free of charge to the international community beginning in 1993. In 1994, the US promised to provide GPS-SA service to the world indefinitely and promised to provide at least six years notice prior to termination of GPS operations or elimination of the service to civilians.
In the mid-1990s, the FAA began pressuring the DoD to switch off SA, thus granting to civilian users the same accuracy that DoD users enjoyed. In 1996, President Bill Clinton signed an Executive Order requiring Selectiva Availability to be turned off no later than 2006. Selective Availability was subsequently turned off at midnight on May 1st, 2000, following the development of a new DoD system that provides the capability to deny use of GPS to hostile forces in a specific area of the world without affecting other areas or allied GPS systems.
In 2004, the US Government signed an agreement with the European Community establishing cooperation between GPS and Europe’s planned Galileo system. The Galileo system is another satellite-based navigation system being developed by the EU and scheduled to become operational in 2013. It will provide significant improvements on accuracy over the GPS system. Another similar system is the Russian GLONASS system which began operation in 1995, although rapidly fell into a state of disrepair. It is currently being restored by the Russians and is planned to be in full operation again by 2009.
The most recent GPS launch was on March 15th, 2008. The oldest GPS satellite still in operation was launched on July 4th, 1991.