ISRO's indigenous atomic clock which are integrated in the NavIC constellation of satellites

India’s ambitious plan to modernise and expand its indigenous navigation system, NavIC (Navigation with Indian Constellation), has encountered significant hurdles owing to delays in the development and deployment of high-precision indigenous atomic clocks.

These atomic clocks, vital for the accurate functioning of navigation satellites, are essential to provide precise timing signals that enable location-based services. According to senior officials from the Indian Space Research Organisation (ISRO), the new generation of rubidium-based atomic clocks, which have been designed indigenously, are facing technological and procurement challenges that are slowing down their integration into the fleet of replacement satellites.

Though the design is fully developed in India, critical components still need to be imported, and bottlenecks in their procurement are creating delays in commissioning the satellites. ISRO has outlined plans to deploy at least three new satellites before the end of 2026 to compensate for the ageing and partially defunct IRNSS fleet, but these plans are dependent on the timely availability of the clocks.

The NavIC system, formally known as the Indian Regional Navigation Satellite System (IRNSS), was conceived to provide India with a reliable, independent satellite navigation service similar to other global positioning systems such as the U.S. GPS, Russia’s GLONASS, China’s BeiDou, and Europe’s Galileo. Unlike these global constellations, NavIC primarily serves India and a 1,500-kilometer radius around it, with its services tailored to both civilian and military requirements.

The civilian services provide relatively good accuracy, but the restricted, encrypted signals for the armed forces offer a higher level of precision and reliability, ensuring that national security and strategic communication needs are insulated from potential global conflicts that could restrict access to foreign navigation constellations. However, the effectiveness of NavIC has been hindered by the malfunctioning of its critical atomic clocks.

Of the nine satellites launched since 2013 to form the original NavIC constellation, only eight successfully reached their intended orbits, with the final one, IRNSS-1I, added in 2018. Over time, multiple failures have occurred within the system, mainly due to issues with imported atomic clocks supplied by the Swiss company SpectraTime. Based on data disclosed under a Right to Information (RTI) query, five NavIC satellites are now completely defunct because all three of their onboard atomic clocks have failed.

In addition, three more satellites are partially functional, with two of their three installed clocks having failed, leaving only two satellites in the original constellation operating with fully functional clocks. This has led to a sharp reduction in NavIC’s effectiveness and reinforced the urgency of developing replacements.

ISRO has already launched two new satellites—NVS-01 in May 2023, which is currently working in the designated orbit, and NVS-02 in January 2025, which unfortunately failed to achieve the specific orbit required for navigation purposes. This leaves the constellation in a precarious state, heavily dependent on the successful commissioning of the planned upcoming satellites.

To improve reliability and extend operational lifespans, ISRO has decided to equip the new generation satellites with five rubidium atomic clocks each, compared to the earlier design that featured only three per satellite.

This redundancy aims to reduce the risk of complete satellite failure due to clock malfunctions, a recurring issue with the earlier fleet. The rubidium clock program represents a major step in India’s self-reliance strategy, as dependence on imported atomic clocks has proven unsustainable.

However, while ISRO scientists have successfully designed the rubidium clocks indigenously, supply chain restrictions and limitations in domestic production capacity mean that several critical subcomponents, particularly specialised electronics and high-stability oscillators, still need to be sourced internationally.

These constraints have directly contributed to delays in preparing the upcoming NavIC satellites for launch. Officials acknowledge that overcoming these bottlenecks is pivotal to ensuring India’s uninterrupted navigation services.

Beyond NavIC, India has ambitious long-term space goals. ISRO has announced its vision to launch at least 100 satellites by 2040 to provide capabilities ranging from earth observation and imaging to communication support for both government and private sector applications.

These plans align with India’s rising space capabilities and aim to create robust space infrastructure to support sectors such as defence, agriculture, transportation, telecommunications, and disaster management.

Within this broader framework, the NavIC project remains a cornerstone of India’s strategic and technological sovereignty. However, unless the development of indigenous atomic clock technology can be fully stabilised and scaled, India risks continued delays in modernising its navigation fleet.

In conclusion, the future of NavIC hinges on ISRO’s ability to overcome the technological and procurement challenges tied to indigenous rubidium atomic clocks. With a large portion of the fleet defunct and only a narrow window to deploy three replacement satellites before 2026, the pressure on ISRO is immense.

The program underscores both India’s scientific progress and the challenges inherent in building critical strategic infrastructure domestically, especially amid geopolitical uncertainties and supply chain vulnerabilities. Successfully indigenising such core technologies will not only strengthen India’s autonomy in navigation services but also bolster its status as a leading space power in the coming decades.

Based On The Hindu Report