Isro's NavIC is down: What is an atomic clock that has put India's desi GPS in danger

Atomic clocks are the heart of any satellite navigation system, providing the ultra-precise timing required to determine location on Earth.

In Short

• Atomic clocks are the heart of any satellite navigation system
• It provides the ultra-precise timing required to determine location
• Without accurate time signals, navigation satellites cannot calculate positions

India’s indigenous satellite navigation system, Navigation with Indian Constellation (NavIC), is facing scrutiny after reports that an atomic clock onboard one of its satellites has stopped functioning, raising concerns about the reliability of the country’s homegrown positioning network.

"IRNSS-1F satellite, launched in March 2016, has completed its design mission life of 10 years on March 10, 2026. On March 13 2026, the onboard Atomic clock stopped functioning. However, the satellite will continue to function in orbit for various societal applications to provide one-way broadcast messaging services," Isro said in a statement.

Atomic clocks are the heart of any satellite navigation system, providing the ultra-precise timing required to determine location on Earth.

Without accurate time signals, navigation satellites cannot calculate positions correctly, potentially affecting services used in aviation, maritime navigation, disaster management and everyday mapping.

WHAT IS AN ATOMIC CLOCK?

An atomic clock is a device that measures time based on the vibration frequency of atoms, usually caesium or rubidium.

These vibrations occur at extremely stable and predictable rates. In navigation satellites, the clocks generate signals with precision measured in billionths of a second, allowing receivers on Earth to determine distance from the satellite by calculating how long a signal takes to travel.

Satellite navigation works on a simple but precise principle: a receiver determines its location by measuring its distance from multiple satellites.

Each satellite continuously broadcasts its position and the exact time the signal was transmitted. Even a tiny error in timing, just a few nanoseconds, can translate into several meters of error in positioning.

WHAT IS NAVIC?

India’s NavIC system was developed by the Indian Space Research Organisation (Isro) to provide independent positioning, navigation and timing services for the country and surrounding regions.

Earlier known as the Indian Regional Navigation Satellite System, NavIC consists of seven satellites supported by a network of ground stations operating around the clock.

Three satellites are placed in geostationary orbit, while four others operate in inclined geosynchronous orbits with an inclination of about 29 degrees. Together, the constellation provides coverage over India and an area extending roughly 1,500 kilometres beyond its borders.

NavIC offers two types of services: the Standard Positioning Service (SPS) for civilian users and the Restricted Service (RS) meant for strategic and defence applications.

Signals are transmitted at both L5 and S-band frequencies, allowing receivers to determine positions with better than 20 meters of accuracy and timing precision of around 50 nanoseconds.

The system is also designed to be interoperable with global navigation systems such as the Global Positioning System, GLONASS, Galileo and BeiDou.

Experts say that the failure of an atomic clock does not immediately cripple a satellite because backup clocks and ground corrections can compensate for it temporarily. However, repeated clock failures could reduce system redundancy and accuracy over time.

For India, which increasingly relies on NavIC for civil aviation navigation, strategic operations and emerging positioning-based technologies, maintaining the health of these precision clocks remains critical to safeguarding the reliability of its independent navigation infrastructure.

- Ends