'One Nation, One Time': Why Isro is sending atomic clocks into space

NVS-03 is the third satellite in India’s next-generation navigation series. ISRO is sending it into orbit to support NavIC, India’s regional navigation system, and strengthen the country’s independent navigation and timing capabilities. Its coverage will include India and an area extending 1,500 kilometres beyond the country’s geopolitical boundary.

The satellite carries multiple atomic clocks. One is an indigenously developed rubidium atomic clock, while others were procured. These clocks provide extremely precise and stable timing. Navigation satellites need synchronized clocks because receivers calculate position from the travel time of radio signals sent by several satellites.

NVS-03 is scheduled to launch on the GSLV-F18 rocket at 11.51 pm from Sriharikota. It is the third NVS satellite, following NVS-01 and NVS-02. The series replaces and extends older IRNSS satellites, while adding the civilian L1 signal used by many consumer devices and smartphones.

An atomic clock is one of the most accurate timekeeping devices. It measures time by monitoring the natural vibrational frequency of atoms, most commonly cesium-133. These atomic vibrations provide a highly stable reference, making the clock far more precise than ordinary timekeeping systems.

An ordinary clock may rely on a pendulum or a vibrating quartz crystal to keep time. An atomic clock instead uses the predictable behavior of atoms. In satellite navigation, that difference is crucial. Satellites and receivers must compare signal timing with extraordinary accuracy to calculate position.

Atomic clocks are placed in space mainly to provide precise timekeeping and frequency references. A timing error of only one nanosecond can produce an error of about 300 meters on the ground. India’s NVS-03 carries an indigenous rubidium atomic clock as part of efforts to control its navigation timing infrastructure.

NavIC is designed to provide accurate position information across India and a region extending up to 1,500 kilometres beyond the country’s boundary. It is a regional system, rather than a navigation network intended to cover the entire world. The system was developed as India’s indigenous alternative for dependable navigation services.

The original IRNSS programme used seven satellites. They were launched between 2013 and 2016. Together, they formed the first-generation regional constellation that provided the foundation for India’s navigation services. NavIC is the current name for the Indian Regional Navigation Satellite System.

The newer NVS satellites are intended to replace and extend the older IRNSS satellites. NVS-03 will support continuity and strengthening of services. The series also adds the civilian L1 signal alongside existing L5 and S signals, helping support consumer devices and smartphones that commonly use L1 for GPS.

A satellite clock wrong by one nanosecond can create a positional error of about 300 meters on the ground. That is a surprisingly large effect from an interval lasting only one-billionth of a second. Navigation systems depend on timing so precise that tiny errors become meaningful distance errors.

The mechanism is simple. Radio waves and light travel at roughly 300,000 kilometres per second. A receiver estimates its position by measuring how long signals take to arrive from multiple satellites. If a satellite’s clock reports the wrong time, the receiver misjudges the signal’s travel distance.

That error can distort the calculated position and reduce navigation accuracy. Accurate atomic clocks keep the satellite constellation synchronized and support reliable position information. This is why NVS-03 carries multiple atomic clocks, including an indigenous rubidium clock, as India strengthens NavIC and its control over critical timing infrastructure.

India decided to build its own navigation system after the 1999 Kargil conflict. The article states that India reportedly could not obtain GPS data from the United States for the region during that conflict. That experience highlighted the risks of relying on another country’s system.

Navigation information can support military and other critical operations. If access to a foreign service can be restricted or unavailable, users may lose dependable positioning information when it matters most. India therefore began developing the Indian Regional Navigation Satellite System, now known as NavIC, as an indigenous regional system.

The first seven IRNSS satellites launched between 2013 and 2016. New NVS satellites are intended to replace and extend them. The programme now also focuses on timing independence. Indigenous atomic clocks can help India maintain its own navigation infrastructure and reduce reliance on imported timing technology whose failures previously degraded parts of the constellation.

NavIC determines a user’s position by sending radio signals from multiple satellites to a receiver on Earth. Each signal carries timing information from its satellite. The receiver measures how long each signal took to travel and uses those measurements to work out where it is.

The key mechanism is precise synchronization. Radio signals travel at roughly 300,000 kilometres per second, so travel time reveals distance. Comparing distances from several satellites lets the receiver identify the user’s position. Atomic clocks provide the stable timing reference needed for this calculation. Even a one-nanosecond error can create about 300 meters of positional error.

NavIC’s satellites therefore need accurate, synchronized clocks. NVS-03 carries multiple atomic clocks, including an indigenous rubidium clock. Its addition is intended to support service continuity, strengthen the next-generation constellation, and improve India’s ability to maintain its own navigation infrastructure.

The article names GPS, Glonass, Galileo, and BeiDou as foreign navigation systems India could use instead of NavIC. NavIC gives India an indigenous regional system designed for accurate positioning across the country and up to 1,500 kilometres beyond its boundary.

Control matters because navigation depends on synchronized timing, not just satellites. Atomic clocks provide the precise time and frequency references that receivers need to calculate position. India’s first-generation NavIC satellites used imported rubidium clocks, and several failed from around 2016–17. Those failures degraded the constellation and encouraged ISRO to develop indigenous clocks.

The strategic benefit extends beyond navigation. The article links reliable timing to telecommunications, financial transactions, digital payments, power grids, transportation, data centres, and government information systems. NVS-03 and its indigenous clock support India’s wider effort to control critical timing and navigation infrastructure, alongside the “One Nation, One Time” vision for Indian Standard Time.