Global Positioning System (GPS)

GPS uses satellites to compute positioning in 3D space, allowing automatic mapping and advanced navigation.

The Soviet Union launched the Sputnik satellite on October 4, 1957. Sputnik did nothing but send out radio pings audible on radio receivers on earth. Conveniently, they launched the satellite to fly over then arch-enemy the United States.

As scientists listened to the pings from Sputnik they realized it was possible to compute the satellite’s approximate location by computing the time between pings. Specifically, the doppler effect allowed an accurate computation of latitude, longitude, and altitude.

Subsequently, scientists also realized the opposite is possible. Fixed satellites, orbiting the same speed as the earth turned, could track one’s position on the ground.

Consequently, work began immediately. However, it was decades before the technology matured. Satellites needed to orbit exactly the same speed as the earth, known as geostationary orbit. An ongoing power source was required to deliver the pings. Finally, they needed to encrypt the system, hiding it from hostile adversaries.

The very first system, Transit, launched in 1960 for use by the US Navy. There were just five satellites.

The first Global Positioning System consisted of 24 satellites. The Navigation System with Timing and Ranging (NAVSTAR) launched between 1973-1978. It was not fully functional, globally, until 1995.

In the early 1980s, civilians came online. However, a partially distorted lowered accuracy for national security reasons. Subsequently, in 2000, the US government removed that restriction making the system about 10x more accurate.

As of 2019, there are six GPS systems. Four are global: GPS (US), GLONASS (Russia), Galileo (EU), and BeiDou (China). Two are regional, QZSS (Japan) and IRNSS/NavIC (India).

GPS receivers are tiny, inexpensive, and ubiquitous.