NAVIC PROGRAM SUFFERS A BLOW

IRNSS-1A, the first satellite in the IRNSS constellation has become redundant after the failure of all three atomic clocks onboard. The satellite was launched on 1 July, 2013 using PSLV-C22 rocket. 

The satellite was the first one among the series of 7 satellites of the IRNSS constellation to be placed in orbit. The NAVIC(Navigation with Indian Constellation) system, similar to the GPS and GLONASS, provides navigation facilities with an accuracy of 10 meters to public users and 0.1 meters for military usage.

The satellite had 3 rubidium atomic clocks, one primary and two as backups. The first clock failed in July, 2016 and the other two failed some months back. The failure of all three clocks has made the satellite redundant and thus requires a replacement. Reason for the failure is still unknown. The clocks were supplied by Spectratime, a Swiss firm and market leader in manufacturing such instruments. 

Rubidium atomic clocks are most widely used clocks in space applications and are considered to be quite accurate along with being relatively cheaper than hydrogen maser clocks. The principle of navigation by satellite is based on the transmission of signals coming from at least four satellites, to the users. To get very precise location data, these signals must be perfectly synchronized. The extremely precise measurement of time on board each satellite, achieved through atomic clocks, is thus a central condition for the positioning performance of the system. 

The clocks in GLONASS system have also failed which were supplied by the same firm. ISRO had signed a contract worth 4 million Euros with Spectratime in 2004 to supply clocks for 9 satellites of IRNSS program. 7 satellites in orbit and 2 satellites as back-ups. These clocks provide an accurate time measurement of around 10 billionths of a second per day. 

ISRO has decided to launch a replacement for the failed satellite. The replacement satellite IRNSS-1H is expected to be launched in second half of 2017. It is being said that ISRO has replaced the atomic clocks onboard IRNSS-1H with new ones. It has also been heard from ISRO sources that two more clocks on other satellites have developed glitches and hence all the remaining satellites are being run on only one clock and keeping two on off mode to extend the life of satellites. While the initial plan was to run two clocks and keep the remaining one as back up.     

The redundant satellite will continue to function but the data sent by it will be coarse, thus of no use. The mission life of each of the satellite was 10 years. Failure in just 4 years raises some serious concerns regarding the ambitious program. 

Image Credits: ISRO 

IRNSS-1A