The 29-hour countdown for the Thursday evening launch of India’s navigation satellite IRNSS-1H using the rocket Polar Satellite Launch Vehicle (PSLV) will begin on Wednesday, ISRO said on Tuesday. According to Indian Space Research Organisation (ISRO), the Mission Readiness Review (MRR) committee and Launch Authorisation Board (LAB) have cleared the 29-hour countdown to begin at 2 p.m. on Wednesday.

India on Thursday will at 7 pm. launch its navigation satellite IRNSS-1H (Indian Regional Navigation Satellite System) weighing 1,425 kg with its PSLV rocket. This eighth IRNSS satellite will be the replacement for IRNSS-1A, as its atomic clocks have failed.

Countdown atomic clocks:

The atomic clocks in the new satellite are modify versions of the original clocks provide by an European supplier under a $4 million euro deal which found deficient. Three similar clocks used in satellites for the European Galileo satellite system also reported similar problems. The PSLV rocket will sling the IRNSS-1H into a Sub-Geosynchronous Transfer Orbit.

earlier this year, ISRO had stated that three Rubidium Atomic Frequency Standard (RAFS) clocks on the IRNSS 1A, the first of the seven IRNSS satellites that launched on July 1, 2013, had malfunctioned, rendering the satellite ineffective. While seven satellites to form the Navigation Indian Constellation or NavIC, two satellites meant to be replacements.

The IRNSS positioning system is intended to provide two services — Standard Positioning Service (SPS) for general users and a Restricted Service (RS), which is an encrypt service provide only for authorised users like the defence forces. NavIC is design to provide accurate position information service to users in India as well as a region extending up to 1500 km from its boundary.

The 1.4-tonne satellite will launched from the state-run Indian Space Research Organisation’s (ISRO) spaceport at the Satish Dhawan Space Centre (SDSC) in Sriharikota in Andhra Pradesh, about 80 km northeast of Chennai. The launch will take place from the second launch pad of Satish Dhawan Space Centre (SDSC) SHAR.