A defense requirement
The origins of satellite positioning lie in a simple military problem: forces need to know where they are, and where a target is, with accuracy and without relying on a system an enemy can disable. By the late 1950s and 1960s, the United States had missile submarines, long-range bombers and fast-moving ships, and each had navigation needs that existing tools met imperfectly. Celestial navigation required clear skies, and radio systems such as LORAN covered limited regions. Inertial systems drift over time and need periodic correction.
The first answer was the Navy’s Transit satellite system, introduced in our article on the first GPS system. The later GPS program grew from a recognition that Transit was too slow and too limited for aircraft and for the accuracy that planners hoped for. This article concentrates on the program and policy side. The equipment story is in our look at GPS receivers.
One program from several
In the early 1970s, the Navy, Air Force and Army all had satellite navigation ideas, and each service was reluctant to give up its own approach. Pentagon officials wanted a single system to avoid duplicate costs. The joint program office created in 1973 was led by Air Force Colonel Bradford Parkinson and staffed by officers from several services. The design is usually described as a compromise that drew on Navy work on satellite clocks and on Air Force work on signal structure. Over time the program became known as Navstar GPS.
The military wanted several things from the system:
- Worldwide coverage in any weather, day and night.
- Passive use: receivers only listen, so they do not reveal their position by transmitting.
- Resistance to jamming, achieved partly by a wide-bandwidth signal.
- Common use by all services, so aircraft, ships and ground troops could share one reference.
- Support for weapons guidance, for which accurate position and time are useful.
Some of these requirements are the reason for the design of the signals. The precise military code was encrypted and is available only to authorized users, while a simpler code was built for easier signal acquisition, which in time became the basis for civilian use. Our article on civilian GPS access describes how that open signal came to be left available.
Funding and doubts
The program went through the usual pressures of defense budgets. Concerns about cost, and about how many satellites were needed, were raised in Congress and within the Pentagon. The loss of the Challenger shuttle in 1986 delayed launches, since the plan had assumed use of the shuttle. Eventually the program moved to expendable rockets. Public sources give varying cost figures, so none are quoted here.
It is also worth noting that the early view of civilian use was modest. Planners generally expected a small civil community and were more concerned about military value. That view changed as the number of potential users, and the economic benefits, became clear.
The proof in battle
The Gulf War of 1991 is often described as the first conflict where GPS mattered widely. The desert gave few landmarks, and troops and vehicles used GPS to navigate and to maintain positions. Because there were not enough military receivers, many units bought commercial ones. The system was not yet complete, though coverage was good enough in the region for much of the day. The use of GPS in the war gave the system a high profile and helped build support for completing it.
Later operations saw satellite positioning used with precision weapons, in which guidance packages combine satellite and inertial data. This is a military application and carries ethical and legal debate that is outside this article’s scope.
Opening the system
Over the following years, decisions were made that opened the system to everyone. After the 1983 airliner tragedy, the president promised civilian availability. The military limited the quality of the open signal for years through selective availability, before it was turned off in 2000 as part of a broader policy to support civil use. The details are in our article on the policy path. In 1996, a presidential directive described GPS as a dual-use system, with the Defense Department continuing to operate it and civil agencies taking part in management. Today, the system is operated by the U.S. Space Force on behalf of the nation, and the signals are free to use without charge.
Dual use
The history of GPS is a good example of a technology that began in defense and became a general utility. The military remains a major user and keeps protected signals, while civil users take advantage of open ones. Other countries observed the dependence on a U.S.-controlled service and built their own, including Russia’s GLONASS, the European Union’s Galileo and China’s BeiDou. The civilian benefits of satellite positioning are large, but the origin of the system is a reminder that its design reflects defense priorities, including the ability to restrict signals in a crisis. For this reason, users of critical services are often encouraged to maintain backups rather than assume the signal will always be available.