ISRO's IRNSS-1F Satellite Atomic Clock Malfunctions Post-Mission Life
The Indian Space Research Organisation (ISRO) has reported that the onboard imported atomic clock on the IRNSS-1F satellite stopped functioning on March 13, 2026. This occurred just after the satellite completed its design mission life of 10 years on March 10, 2026. Launched aboard the PSLV-C32 rocket on March 10, 2016, and placed into geosynchronous orbit, IRNSS-1F was the sixth satellite in the Indian Regional Navigation Satellite System (IRNSS) series. Despite the clock failure, ISRO stated that the satellite will continue to operate in orbit for various societal applications, providing one-way broadcast messaging services.
The Indispensable Role of Atomic Clocks in Navigation
Atomic clocks are ultra-precise, space-hardened devices that measure time by monitoring the resonant frequency of atomic transitions in elements like cesium, rubidium, or hydrogen. Invented in the 1950s, they are the most accurate timekeeping instruments ever developed, losing or gaining only one second every 100 million years, compared to conventional quartz clocks that may deviate by a second in a few days. For space-based navigation systems, this extreme precision is crucial due to factors such as distance from Earth, orbiting speed, and relative motion. A minuscule error of just one nanosecond can result in a GPS position inaccuracy of 30 centimeters on Earth, equivalent to 300,000 kilometers per second.
These clocks are designed to withstand the harsh conditions of space, including launch vibrations, radiation, extreme temperature fluctuations, and vacuum. Typically, they have a lifespan of 10 to 15 years, aligning with the average operational life of a satellite. Physically, they resemble sealed metal boxes, about the size of a small microwave oven and weighing 3-5 kilograms, containing complex circuitry and processors. Unlike standard clocks, they do not display time but send critical inputs to the spacecraft's onboard control systems.
Challenges with Imported Swiss Clocks
Earlier ISRO navigation satellites, launched between 2013 and 2018, utilized Rubidium Atomic Frequency Standards (RAFS) manufactured by SpectraTime, a Swiss company. Each satellite carried three imported clocks for redundancy. In 2008, ISRO signed a contract worth 4 million euros with SpectraTime for these devices, which were the only foreign atomic clocks used by the agency. However, a significant number of these clocks failed prematurely, affecting not only Indian satellites but also the European Space Agency's Galileo navigation system, which relies on 28 satellites.
In 2017, after nine atomic clocks failed on Galileo satellites, ESA investigations suggested that probable short circuits, possibly triggered by specific ground-testing procedures before launch, were the cause. The same RAFS model was installed on ISRO's satellites, where issues began emerging in 2016-2017.
India's Shift to Indigenous Atomic Clocks
In response to the problems with Swiss equipment, India developed its own indigenous atomic clocks, known as the Indian Rubidium Atomic Frequency Standard (iRAFS). The project commenced in the mid-2010s, with full qualification achieved by 2022-2023. These indigenous clocks were first deployed onboard the NVS-01, also referred to as IRNSS-1J, launched in May 2023 by the GSLV-F12 rocket. According to ISRO, the iRAFS clocks have been operating flawlessly since July 2023.
All subsequent NVS-series satellites now use iRAFS as standard, eliminating ISRO's dependence on imported clocks. The iRAFS is integrated into the satellite's navigation payload as a compact, radiation-hardened metal pack, similar in size to the Swiss RAFS. Additionally, the Council for Scientific and Industrial Research's National Physical Laboratory (CSIR-NPL) developed India's first indigenous atomic clocks, including Cesium fountain clocks and Rubidium clocks, between 2008 and 2011. These clocks maintain the Indian Standard Time (IST) with high precision, achieving an accuracy within 2.8 nanoseconds, allowing India to uphold its own timekeeping standard independently.
The failure of the IRNSS-1F atomic clock underscores the critical importance of reliable timekeeping in navigation satellites and highlights India's successful transition to self-reliant technology in space exploration.
