NVS-02's — carrying an indigenously developed atomic clock — liftoff will not only be the 100th launch but also a significant step towards developing a strong Indigenous space-based positioning and navigation system.

ISRO's Baahubali Geosynchronous Satellite Launch Vehicle (GSLV)-F15 is scheduled to launch the second of five next-generation 'Navigation with Indian Constellation (NavIC)' satellites, NVS-2, carrying an indigenously developed atomic clock, into Geosynchronous Transfer Orbit. The launch will occur at 06:23 (IST) on January 29, 2025, from the Satish Dhawan Space Centre (SDSC)'s Second Launch...

ISRO's Baahubali Geosynchronous Satellite Launch Vehicle (GSLV)-F15 is scheduled to launch the second of five next-generation 'Navigation with Indian Constellation (NavIC)' satellites, NVS-2, carrying an indigenously developed atomic clock, into Geosynchronous Transfer Orbit. The launch will occur at 06:23 (IST) on January 29, 2025, from the Satish Dhawan Space Centre (SDSC)'s Second Launch Pad in Sriharikota. This will be the 100th important launch from the Sriharikota Space Centre.

Launching this satellite would bolster India’s satellite-based regional positioning navigation systems capabilities. The satellite-based positioning and navigational system is critical to national security and various civilian applications. The Indian positioning system, for example, is utilised in Aadhar registration to ensure that the registration facility is located within the country and to prevent its fraudulent use. An indigenous positioning system is critical for many e-governance platforms.

How does the satellite-based positioning work?

Imagine you are lost in a jungle with no clue where you are. You call three friends for help. Each friend tells you how far you are from their house, but not the exact direction. You draw circles on the map in your hand around each friend's location, with the radius equal to the distance they gave. The point where all three circles intersect is your location. Similarly, your smartphone measures its distance from at least four satellites. It calculates its position using this method called triangulation (or, more accurately, trilateration).

The key to determining distance is time. Positioning System (PS) satellites constantly broadcast signals with precise timestamps. The receiver on smartphones and aeroplanes calculates how long the signal took to arrive, and using the speed of light, it converts this into the distance to find their exact location with remarkable precision. Even a tiny error in time measurement, for example, one-millionth of a second, could cause errors of hundreds of meters.

To avoid this, PS satellites carry atomic clocks, which are incredibly precise, losing only about one second in millions of years. Without atomic clocks, minor timing errors would make PS unreliable for applications like navigation, mapping, and emergency response.

Why the Indian positioning system

We are all familiar with the Global Positioning System (GPS) on our mobile phones, and we use it regularly for navigation on Google Maps. However, it was not mere vanity that drove ISRO to develop, build, and manage India's own satellite-based positioning and navigation system.

GPS was created and is controlled by the United States military. The United States withheld India's GPS data during the 1999 Kargil conflict. This motivated ISRO, and the plan to construct India’s autonomous regional navigation satellite system, 'Navigation with Indian Constellation' (NavIC), was approved in May 2006. Previously, it was known as the Indian Regional Navigation Satellite System (IRNSS).

Various nations and regional organisations are building satellite-based navigational systems similar to the American GPS (Global Positioning System). Global Navigation Satellite System (GLONASS) of Russia, China's satellite navigation system BeiDou, and the European Union's satellite navigation system Galileo are the most significant initiatives.

The first generation of the NavIC began with the launch of its first satellite, IRNSS-1A, on July 1, 2013. A network of 21 ranging stations around the country was constructed.

How many satellites are needed?

Just as three friends were required to properly establish your position on Earth's surface, at least four satellite signals are needed to determine your location from orbit. This means that the satellite-based navigation system requires more than four satellites in line of sight. That is why the NavIC is a constellation of satellites.

Initially, ISRO suggested a constellation of seven to eight satellites with minimal coverage of the Indian subcontinent and a 1500-kilometer radius around it. However, the imported atomic clocks in some of these satellites failed, compelling ISRO to launch nine satellites: IRNSS-1A, IRNSS-1B, IRNSS-1C, IRNSS-1D, IRNSS-1E, IRNSS-1F, IRNSS-1G, IRNSS-1H, and IRNSS-1I, to maintain the services.

The NavIC constellation currently provides Position, Velocity, and Timing (PVT) services with an accuracy of better than 20 meters and timing accuracy of better than 40 nanoseconds in the primary service area for civilian Standard Positioning Service users and an undisclosed accuracy for Restricted Service users. When the five second-generation satellites join the constellation, the precision is expected to climb to ten meters.

Made-in-India atomic clocks

Disheartened by the failures and breakdowns of imported atomic clocks, ISRO's Space Application Centre (SAC) Ahmedabad launched an initiative to produce an indigenous atomic clock. At record speed, it created Indian Rubidium Atomic Frequency Standard (IRAFS) atomic clocks. The clocks are so precise that the error in 2 hours is just +72 nanoseconds. A nanosecond is one billionth of a second.

Incorporating these Indian-made atomic clocks, ISRO replaced the ageing and failing IRNSS-1 satellites with NavIC second-generation navigational satellites. Since precise clocks are at the heart of navigational satellites, they typically carry several clocks. To offer redundancy, ISRO has included four atomic clocks in its NVS class spacecraft, one of which is an Indian Rubidium Atomic Frequency standard atomic clock built and developed in India.

L1 frequency

Cellphones and other consumer devices acquire GPS signals using the L1 frequency; however, the previous IRNSS operated in the L5 and S bands. To allow smartphones and other devices used by the civilian population to run on this frequency, the Indian government directed mobile and chipset makers to alter their chipsets to work in the L5 band.

ISRO has, however, provided the L1 band for civilian users in the second-generation NVS constellation, beginning with NVS-01. ISRO and the Indian Institute of Science (IISc) in Bengaluru collaborated to create these codes. This means that all smartphones and gadgets might be connected, increasing civilian use of the NavIC system.

Expanding the reach

Initially, these second-generation satellites were intended to augment the existing NaVIC constellation, boosting coverage. However, the malfunctions of the imported atomic clocks have resulted in the NVS series only functioning as a replacement for the existing fleet.

Before NVS-01, only four of seven IRNSS-1 satellites were operational for positioning, navigation, and timing (PNT) services. Remember, four is the bare minimum for accessing PNT services. The NVS-01 replaced the IRNSS-1G, while the NVS-02 will replace the IRNSS-1E satellite in the 111.75ºE orbital location to maintain services.

Going global

NVS-03, 04, and 05 will replace the other ageing satellites, including those with defective atomic clocks. Once all five are in place, a constellation of eleven satellites will constitute the backbone of second-generation NavIC. When this happens, the service area will expand from 1500 to 3000 km outside Indian territory. This is the first step towards NavIC's worldwide reach.

ISRO intends to deploy 24 to 30 satellite constellations, including around twelve in Medium-Earth Orbit, to achieve a worldwide reach comparable to that of the United States, Russia, China, and Europe. Some propose a radical new way for acquiring precise PNT services: a train of tiny nanosatellites in low-earth orbit.

ISRO’s century

Satish Dhawan Space Centre (SDSC), formerly known as Sriharikota Range (SHAR), was founded in 1969 on the Sriharikota island, some 80 kilometres north of Chennai, and the maiden launch occurred on October 9, 1971. RH-125, an indigenously manufactured Rohini class-sounding rocket, can send a measly 7-kilogramme payload to a height of just 19 miles. Since then, ISRO has expanded its launch vehicle capabilities, introducing the Polar Satellite Launch Vehicle (PSLV) and GSLV (also known as LVM3) to deploy satellites in orbit and launch spacecraft to the Moon and Mars.

The launch of GSLV-F15 will be the 100th significant launch, which has placed a satellite in orbit, sent spacecraft to the Moon, Mars, and into orbit around the Sun, and carried out key technology demonstrations such as the Crew Module Atmospheric Re-entry Experiment (CARE) Pad Abort Test for Gaganyaan. This count excludes the launch of sounding rockets and military launches.

It is the 17th launch of the GSLV class launch vehicles, including two demonstration launches, and the 11th to use indigenous cryogenic fourth-stage engines.

Next Story