NavIC explained: Why India's own navigation system needs four satellites

NavIC can no longer provide standalone navigation services after the number of operational satellites fell below the minimum required. Here's what happened and why it matters

India can no longer rely on its homegrown NavIC system for standalone navigation after the number of operational satellites dropped below the minimum required, the government said on Wednesday.

 

In a written reply to Parliament, Union Minister of State for Space Jitendra Singh said only three NavIC satellites — IRNSS-1B, IRNSS-1I and NVS-01 — are currently capable of providing Position, Navigation and Timing (PNT) services.

 

That is one short of the minimum four satellites needed for the system to accurately determine a user’s location. The shortfall arose after the atomic clock aboard IRNSS-1F failed in March this year.

 

The development has raised fresh concerns over the resilience of India’s indigenous navigation network, which was built to reduce dependence on foreign systems such as the US Global Positioning System (GPS) for civilian and strategic applications.

 

For most smartphone users, however, there will be no immediate disruption because devices typically rely on multiple global navigation systems, including GPS.

 

What is NavIC?

 

NavIC stands for Navigation with Indian Constellation. It is India’s own satellite-based system for determining location, speed and time — the same basic function performed by the US’ GPS, Russia’s GLONASS, Europe’s Galileo and China’s BeiDou. It was earlier officially known as IRNSS, or the Indian Regional Navigation Satellite System, and was built by Isro.

 

Like GPS, NavIC helps users determine their location, track movement and synchronise time. It supports applications ranging from vehicle navigation and disaster management to fleet tracking, railway operations, fisheries, surveying and emergency response. It also offers an encrypted service for authorised users, including the armed forces.

 

How many satellites does NavIC have?

 

NavIC was originally designed as a constellation of seven satellites — three placed in geostationary orbit and four in inclined geosynchronous orbit — to ensure continuous coverage over India and nearby regions. Isro has launched 11 satellites under the programme over the years, including replacements.

 

However, several satellites have either completed their design life, suffered failures of their onboard atomic clocks or failed to reach their intended orbit. Consequently, only three satellites are currently capable of providing PNT services, while some others are being used only for one-way messaging services.

 

Why does NavIC need at least four satellites?

 

A satellite navigation system determines a receiver’s position by calculating how long signals from multiple satellites take to reach it.

 

To accurately calculate a user’s location on Earth, the receiver must simultaneously receive signals from at least four satellites. Three satellites can estimate a position, but a fourth is needed to correct timing errors in the receiver’s clock and produce a reliable three-dimensional location — latitude, longitude and altitude. Without four operational satellites, the system cannot consistently deliver accurate standalone navigation.

 

This is why the government said NavIC’s standalone navigation capability has been affected after the constellation dropped to just three operational navigation satellites.

 

Why is NavIC important for India?

 

NavIC was developed to give India an independent navigation capability rather than relying entirely on foreign systems such as the US’ GPS, Russia’s GLONASS, Europe’s Galileo or China’s BeiDou.

 

The need for an indigenous system became evident after the 1999 Kargil conflict, when access to GPS data in the region was restricted, highlighting the strategic risks of depending on foreign navigation services.

 

NavIC is designed to support a wide range of civilian applications, including vehicle tracking, road, rail and maritime navigation, disaster management, surveying, mapping, location-based services and precise timing.

 

The system also offers an encrypted Restricted Service (RS) for authorised users, including defence and strategic agencies, enabling secure navigation and timing without relying entirely on foreign satellite systems.

 

What happens next?

 

Isro is gradually rebuilding the constellation through its second-generation NVS satellites, which are equipped with improved payloads, a longer design life and indigenous atomic clocks. These satellites are intended to replace ageing spacecraft and restore the minimum number of operational satellites required for reliable navigation services.