SCHRIEVER AIR FORCE BASE, Colorado, July 8 — The constellation of satellites that guides everything from jeepney routes in Manila to fishing boats in the Visayan Sea is a marvel of precision engineering, and its inner workings are more fascinating than most people realise. GPS, or the Global Positioning System, relies on a network of satellites that continuously broadcast radio signals containing their exact location and the precise time the signal was transmitted.
This is not a simple clock; each satellite carries multiple atomic clocks, including cesium and rubidium clocks, that are accurate to within one second in 100,000 years. For communities across Asia, the system has become so embedded in daily life that its complexity is easy to overlook.
A GPS receiver calculates its distance from a satellite by measuring the time delay between when the signal was sent and when it was received, then multiplying that by the speed of light, which is approximately 299,792 kilometres per second. To determine a three-dimensional position — latitude, longitude, and altitude — the receiver needs signals from at least four satellites. The method used is trilateration, not triangulation; distances are measured, not angles.
Each satellite broadcasts on two primary frequencies. The L1 frequency, at 1575.42 MHz, is used for civilian purposes.
The L2 frequency, at 1227.60 MHz, is reserved for military use. There is also a modernised frequency, L5 at 1176.45 MHz, which was first broadcast in 2010 and is designed specifically for safety-of-life applications — think aircraft landing systems or maritime navigation in busy straits. The satellites themselves orbit at an altitude of approximately 20,200 kilometres.
They are arranged in six orbital planes, each inclined at 55 degrees to the equator, and complete an orbit in about 11 hours and 58 minutes. This geometry ensures that users anywhere on Earth, including across the sprawling archipelago of the Philippines, can typically see enough satellites for a reliable fix.
Relativity and the daily correction
One of the most remarkable aspects of the system is how it accounts for Einstein’s theories of relativity. Because of both special and general relativity, the clocks aboard the satellites gain about 38 microseconds per day relative to clocks on Earth. That may sound tiny, but without correction, the accumulated error would throw off positioning by kilometres within a single day.
The system corrects for this effect, ensuring that a farmer in Nueva Ecija checking field boundaries or a delivery rider in Bangkok navigating traffic gets accurate coordinates. The control segment that keeps everything running includes a master control station here at Schriever Air Force Base, an alternate master control station at Vandenberg Space Force Base, and monitoring stations positioned around the world.
The U.S. Space Force operates the system and is responsible for ensuring its accuracy and availability. For families across the region who rely on GPS for transport, logistics, and even agricultural planning, that continuous oversight matters. Closer to home, the implications of this technology are vast.
Fishing communities in the Philippines use GPS to navigate safely and to return to productive grounds. Farmers use it for precision agriculture.
Urban commuters depend on it for ride-hailing and navigation apps. The system is so deeply woven into modern life that its failure would be felt immediately, yet its daily operation is largely invisible. Looking ahead, the continued modernisation of the GPS constellation, including the expansion of the L5 frequency for safety-critical uses, points to an even more integrated future.
For the communities that depend on this technology across Asia, the quiet work of satellites 20,200 kilometres overhead remains a steady, reliable presence.
