19 July 1977

The world’s first Global Positioning System (GPS) signal was transmitted from Navigation Technology Satellite 2 (NTS-2) and received at Rockwell Collins in Cedar Rapids, Iowa, at 12:41 a.m. Eastern time (ET).

The Global Positioning System (GPS) is a satellite-based navigation system that provides location and time information to users anywhere on or near the Earth’s surface. It was developed and is operated by the United States Department of Defense (USDOD). GPS was primarily designed for military use but has since become a crucial tool for civilian applications, ranging from navigation and mapping to scientific research and everyday consumer devices.

Satellites: The GPS system consists of a constellation of at least 24 satellites orbiting the Earth at about 20,200 kilometers (12,550 miles) above the surface. These satellites are spread across six orbital planes to ensure global coverage.

Ground Control Stations: On the Earth’s surface, there are several ground control stations that monitor and maintain the GPS satellite constellation. These stations keep track of the satellites’ positions and health, and they make adjustments to the satellites’ orbits when necessary.

User Receivers: GPS receivers are devices that the general public, as well as various industries and sectors, use to access and utilize GPS signals. These receivers process signals from multiple satellites to calculate the receiver’s precise location, speed, and time.

Triangulation: GPS receivers determine their position by triangulating their distance from at least four satellites in the GPS constellation. By measuring the time it takes for signals from multiple satellites to reach the receiver, the device can calculate its distance from each satellite and pinpoint its position accurately.

Accuracy: The accuracy of GPS varies depending on the number of satellites in view and the quality of the GPS receiver. Most consumer-grade GPS receivers can provide a location accuracy within a few meters, while advanced military and scientific-grade receivers can achieve centimeter-level accuracy.

Selective Availability (SA): Historically, the military introduced SA to intentionally degrade the accuracy of civilian GPS signals for security reasons. However, in 2000, the U.S. government discontinued SA, resulting in a significant improvement in the accuracy of GPS for civilian use.

GPS has become an integral part of modern life, with applications in various sectors, including:

Navigation: GPS is widely used for personal navigation in smartphones, car navigation systems, aviation, marine navigation, and more.
Mapping and Surveying: GPS enables accurate mapping, surveying, and geographical information systems (GIS) applications.
Emergency Services: GPS helps emergency services locate and respond to distress calls more effectively.
Timing and Synchronization: Many critical systems, such as financial transactions, telecommunications, and power distribution, rely on GPS for precise timing and synchronization.
Agriculture: GPS is used in precision agriculture for optimized planting, irrigation, and harvesting.
Geocaching and Outdoor Activities: GPS is used by geocachers and outdoor enthusiasts for treasure hunting and location-based gaming.