NavIC satellite loses its atomic clock

The Indian Space Research Organisation has announced that the last atomic clock aboard the IRNSS-1F satellite has failed, further weakening India’s indigenous satellite navigation system, popularly known as Navigation with Indian Constellation (NavIC).

The IRNSS-1F satellite, launched in March 2016, completed its 10-year design mission life on March 10, 2026. Atomic clocks are crucial for satellites because they enable precise positional, navigational, and timing (PNT) services by maintaining extremely accurate time signals.

Status of the NavIC Constellation

• Since 2013, nine IRNSS satellites have been launched.
• Eight satellites successfully reached their intended orbit.
• The last satellite of the constellation, IRNSS-1I, was launched in 2018.
• Publicly available information indicates that only about three of the 11 NavIC satellites are currently performing their core navigation role.

The Indian Regional Navigation Satellite System (IRNSS) — operationally called NavIC — was originally designed as a seven-satellite constellation to provide regional positioning services over India and up to 1,500 km beyond its borders. When fully operational, the system is capable of location accuracy of about 10 metres over the Indian landmass and surrounding region.

Importance of Atomic Clocks

An atomic clock is the most precise timekeeping device, measuring time using the stable resonant frequency of atoms such as cesium or rubidium. These clocks can lose or gain less than one second over hundreds of millions of years.

Precise timing is essential for satellite navigation because:

• To determine spacecraft position within a metre-level accuracy, clocks must measure time intervals in billionths of a second.
• Even the best quartz crystal oscillators—used in most modern clocks—can drift by about a nanosecond after an hour, which is insufficient for space navigation.
• Atomic clocks combine quartz oscillators with atomic transitions, providing the extreme stability required for navigation satellites.

Global Navigation Systems

Only four satellite constellations provide global navigation services:

• Global Positioning System (GPS) (USA)
• GLONASS (Russia)
• Galileo (Europe)
• BeiDou Navigation Satellite System (China)

Additionally, Quasi-Zenith Satellite System (QZSS) is a regional four-satellite system that augments GPS signals over Japan.