An atomic clock is a highly sophisticated timekeeping device that relies on the resonant frequency of atomic transitions in elements such as rubidium, cesium, or hydrogen.

Unlike conventional quartz-based clocks, which can drift by a second in just a few days, atomic clocks are so precise that they gain or lose only one second in about 100 million years.

This extraordinary accuracy makes them indispensable for navigation satellites, where even a nanosecond’s error can translate into a positional deviation of around 30 centimetres on Earth. Given the speed and distance at which satellites orbit, such precision is non-negotiable for reliable navigation services.

The Indian Regional Navigation Satellite System (IRNSS), also known as NavIC, has relied on atomic clocks since its inception. The IRNSS-1F satellite, launched in March 2016, carried an imported Swiss-made rubidium atomic clock.

After completing its design mission life of ten years, the clock ceased functioning in March 2026. While the satellite will continue to provide limited services such as one-way broadcast messaging, the failure of its atomic clock means it can no longer contribute to accurate navigation. This underlines the critical role atomic clocks play in sustaining the integrity of satellite-based positioning systems.

Earlier generations of ISRO’s navigation satellites used Swiss Rubidium Atomic Frequency Standards (RAFS) supplied by SpectraTime. Each satellite carried three clocks for redundancy, but several of these failed prematurely, not only in Indian satellites but also in Europe’s Galileo constellation. 

Investigations by the European Space Agency in 2017 suggested that short circuits, possibly triggered during ground testing, were responsible for these failures. This created significant challenges for both ISRO and ESA, as navigation systems cannot function without precise timing signals.

Recognising the risks of dependence on imported technology, India embarked on developing its own indigenous atomic clocks. The Indian Rubidium Atomic Frequency Standard (iRAFS) project began in the mid-2010s, and by 2022–23, the clocks had achieved full qualification.

These were first deployed on the NVS-01 satellite, launched in May 2023, and have since performed flawlessly. All subsequent satellites in the NVS series now carry iRAFS units, ensuring that India no longer relies on foreign suppliers for this critical technology. The indigenous clocks are compact, radiation-hardened, and designed to withstand the harsh conditions of space, with a lifespan of 10–15 years.

India’s efforts in atomic clock development are not limited to satellites. The Council for Scientific and Industrial Research’s National Physical Laboratory (CSIR-NPL) developed India’s first indigenous atomic clocks between 2008 and 2011, including cesium fountain and rubidium clocks.

These are used to maintain Indian Standard Time (IST) with an accuracy of 2.8 nanoseconds, enabling India to independently uphold its national timekeeping standard. This achievement reflects the country’s growing self-reliance in advanced scientific instrumentation.

The story of IRNSS-1F’s clock failure highlights both the vulnerability of imported technology and the importance of indigenous innovation.

Atomic clocks are the backbone of satellite navigation systems, and their reliability directly determines the accuracy of positioning services. India’s successful transition to home-grown atomic clocks marks a significant milestone in its space programme, ensuring continuity of navigation services and strengthening national technological sovereignty.

Agencies