What is GNSS

Feature by Shreya Agarwal

GNSS stands for Global Navigation Satellite System. 

Before we get any further into the topic, we should try and understand the ideas of navigation that evolved over the years, and their cons, that led to the development of this technology. 

The history of navigation

In the olden times, to reach different places, people used specific landmarks, and even celestial bodies to find their path.

The problem with this is, obviously, that these will not always be fixed and there will be some or the issues with it. For instance, what if it’s raining? One cannot use celestial bodies to find their path in such a case. Or what if the landmark is removed by someone or gets destroyed by nature? Also, these work for only a certain area, and definitely cannot be considered globally. 

The world now needed a navigation system that was constant, globally accessible, user-friendly, and reliable.

In the 1880s, Heinrich Hertz proved the existence of radio waves. This was an important discovery for the building of navigational technologies. Radio waves could travel several miles and transfer signals and data. In This led to the coming up of the first ever global navigation system, OMEGA, developed by the United States with some partner nations in 1971.

This enabled ships and aircrafts to determine their position by receiving very low frequency radio signals, transmitted by eight radio transmitters (OMEGA stations) located throughout the world.

US also developed the LORAN navigation system in which the receiver catches the radio signals sent by radio stations which are usually hundreds of miles far away. These radio stations were also placed hundreds of miles apart. These navigation systems were not easy to work with, and weren’t cost effective. The first ever navigation system, which wasn’t wholly based on radio waves, but also satellites, was US-based Transit.

Rolled out in 1964, it was first used by the US Navy to find the location of the marine surface ships and other equipment, but it was soon released for commercial use as well. It was also known as NAVSAT or NNSS (Navy Navigation Satellite System).

Inaccuracies in these systems is what led to the ideas of NAVSTAR or what we know as GPS or Global Positioning System today.

GPS – Global Positioning System

GPS is a type of a GNSS. Now we can define what a GNSS is. A GNSS is a group of satellites that orbit the earth and use radio signals and other technology to determine the position, time, etc. of an object. 

GPS was a project started by the U.S. Department of Defense in 1973. It was originally called the Navstar and was meant for the military to use. The first satellite was put in space in 1978. The system was fully operational with 24 satellites in space by 1993.

How does GNSS work?

A GNSS has typically three elements:

The Space Element: A GNSS contains groups of satellites or constellations that orbit the earth. These satellites know the parameters of their orbit and time very well. They are thousands of kilometers above the earth’s surface. For ex: the GPS consists of 31 satellites, 20,000kms above the earth’s surface.

The Control Element: Consist of master ground control stations, monitor systems, that control the satellites, manage their parameters etc. For ex: correct errors like fixing the satellite back in its actual position if it deviates. They also facilitate satellite repair. 

The User Element/ Reciever Element: It consists of recievers and devices that transform the satellite information and process it into the information that we need. For ex: smartphones, GPS recievers in airplanes etc. 

A GNSS uses a method called trilateration to find our position. To simply put it, to determine the position of point on earth, we need the distance of at least 3 satellites from the point itself. The distances from these three satellites actually work as imaginary radii and when these form imaginary spheres (with the satellite at the centre) the point where all the spheres coincide is the actual point of the user. Please note that a GNSS can also find the position of a point in space, not just on land. 

How does GNSS show time?

The clocks we use at our homes are mechanical clocks. They use certain physical parts and tools. Errors can occur in these watches since there can some manual defects or they can even degrade after some time. But what GNSS satellites use to give extremely accurate time are something known as atomic clocks.

These clocks use atoms to determine the timing. Most clocks determine time on the basis of how many times something moves back and forth. Atomic clocks measure time on the basis of how many times does an atom (the smallest unit of matter) move forward and backward. To give an idea of its accuracy, atomic clocks might make an error of a second in 100 million years. Mostly, atoms of an element called caesium are used in the clock.

Today GNSS is used in a variety of spheres like space stations, aviation, maritime, agriculture, scientific research, mining, telecommunications, etc. 

Functional GNSS

Some GNSS systems currently in use around the world are:

GPS of USA,

GLONASS (Globalnoya  Navigatsionnaya Sputnikovaya Sistema) of Russia,

SAGAR SAMPARK of India 

BeiDou (China),

Galileo (Europe). 

GNSS only in a specific region:

1. IRNSS (Indian Regional Navigation Satellite System) / NavIC (Navigation Indian Constellation)

2. Quasi Zenith Satellite System (QZSS)- Japan.