Back in the day, people have developed ways to navigate by reading what is around them. The stars, for example. This would be why we have devised names such as the North Star (Polaris) that would always lead you northwards. In our new era, we still have constellations to guide us by, but not they would not be composed of stars in the sky. These are what we call satellite constellations, and believe it or not, we have been quite acquainted with them.
The Global Positioning System (GPS) would trace its developments to the beginning of the Space Race in the 1950s, when the beeping transmissions of artificial satellite Sputnik 1 was tracked to determine where it was in orbit. Prevailing phenomena, such as the gravitation and magnetic fields of the Earth, provided space for errors in orbital positioning systems developed in the following decade.
This led the United States to work on the direct predecessor of the GPS, which was then called Navstar. Eventually, the system expanded from its initial military purposes to civil, commercial, and scientific applications. It would be reason why we also have GPS in our everyday devices like phones and vehicles.
The space segment of this system would be a nominal constellation composed of 24 satellites operating 95 percent of the time. More satellites have been in actual use for the purpose, with 31 being operational as of June 2022. The ephemeris (tabular statement of trajectory) is updated every 2 hours.
The Global Navigation Satellite System (GLONASS) would also have a similar history as the GPS, inspired by the prospects of radio-astronomy technologies for navigation. Starting with the Soviet “Cicada” constellation composed of four satellites in 1979, the GLONASS system would be formally declared operational by 1993. Also like the GPS, it currently has a nominal constellation constituted by 24 satellites, but there would also be differences to note. For one, the ephemeris update for GLONASS would be more frequent at every half hour.
No, this is not based on a Genshin Impact character, although they may still have something in common. The BeiDou Navigation Satellite System (BDS) was named after the Chinese term for the Big Dipper (Plough), the seven bright stars of the Ursa Major. Developed by the People’s Republic of China in the late 20th century to have a system “suitable for its national conditions,” the first BeiDou constellation made up of three satellites was completed in the period 2000-2003. The system has since grown to operate 35 satellites for its space segment. Heralding the swift global progress of BeiDou was the Chinese government, which claims that their system is comparable with the GPS.
Perhaps unlike the previous three systems, which supposedly had military applications in their respective historical developments, Galileo was said to have been created by the European Union mainly for civilian purposes. As of 2021, the space segment of Galileo has a constellation composed of at least 24 satellites. Operating at heights beyond those usually utilized by GPS, GLONASS, and BeiDou, the intention of Galileo would be to provide better positioning accuracy for civilian users. The ephemeris update for Galileo, meanwhile, would be every three hours.
How they work
When in orbit, satellites are expected to circle the planet quite constantly owing to the law of inertia. That is, the balance between the satellite velocity and the gravitational pull keeps them from getting incinerated by the Earth’s atmosphere, or from “bouncing off” to the vast expanse of outer space. It would also be a similar principle concerning the relationship between the Earth and the Moon. Meanwhile, the method used by these satellites to pinpoint your location would be called trilateration. Each satellite would emit signals within their circles as it attempts to determine your distance from them, and more satellites would help the calculation become more accurate.
Since the satellites would also have internal clocks in them, tracking your location at real-time is made possible. The receivers of these signals could be our devices, such as phones, vehicles, or even fitness trackers. Some receivers are said to be able to establish a location within 1 centimeter, although accuracy may vary depending on various factors, including prevailing conditions in any one geographical area. At this juncture, the significance of having more than one system available in your receivers shows, allowing the opportunity to obtain even more precise mapping results.
Besides the aforementioned systems, there would also be regional constellations that cover more specific areas on the planet. But of course, this may be better left for another discussion.