The Indian Regional Navigation Satellite System (IRNSS) requires more than just a cluster of satellites. In order to maintain the navigation system’s accuracy, an elaborate ground network is needed to constantly watch over those satellites and the signals they send out, making any corrections that may be needed.

The hub of the whole system is the ISRO Navigation Centre at Byalalu, near Bangalore. Ranging and integrity monitoring stations spread across the country will receive navigation signals transmitted by the satellites and promptly relay them to this Centre. The Centre will also be linked to two-way radio ranging stations as well as laser ranging stations that will help establish the satellites’ orbit parameters with great accuracy.

At the Centre, all the data will be collated and analysed using indigenously developed navigation software. This complex software will then generate the updates that must be beamed to the satellites periodically.

The Centre uses a cluster of hydrogen maser and caesium atomic clocks, which keep time even more accurately than the atomic clocks on the satellites, to maintain a standard reference time, the IRNSS Network Time. The time kept on the satellites must be closely synchronised with this network time. — N.G.R.