Bengaluru, Aug 10 ( IANS India will launch its eighth navigation satellite this month-end as a spare or back-up for its constellation in the geo-orbit, a top space agency official said on Thursday."We are preparing to launch the eighth Indian Regional Navigation Satellite System (IRNSS-1H) at the end of this month as a standby for the Navigation Indian Constellation (NavIC), which is operational for services," ISRO Satellite Centre Director M. Annadurai told IANS here.The 1.4-tonne satellite will be launched from the state-run Indian Space Research Organisation 's (ISRO) spaceport at Sriharikota off the Bay of Bengal in Andhra Pradesh , about 80 km northeast of Chennai "The satellite is ready to move from our centre to Sriharikota on August 12 on a special vehicle for integration with the rocket at the space centre," said Annadurai on the margins of a technology event.The launch authorization board will decide on the date and time after all the checks were completed during the window for the launch schedule.The space agency, however, will use a medium Polar Satellite Launch Vehicle ( PSLV C39) with four strap-on motors to deploy the satellite first in the geo-transfer orbit and later in the geo-stationary orbit, about 36,000 km above the earth , where the NavIC is orbiting over the last four years."The spare or standby satellite will also make up for the non-functioning of the three rubidium atomic clocks on board the first one (IRNSS-1A) and one each in the other two NavIC satellites," ISRO's Vikram Sarabhai Space Centre Director K. Sivan told IANS from Thiruvananthapuram.Clarifying that the spare satellite (IRNSS-1H) would augment the NavIC's operations, Sivan said IRNSS-1A would continue to orbit and provide the services it is programmed for the intended users as part of the system."We are not going to abandon the first one (IA) as it working well with all its functions except the atomic clocks being normal. In the other satellites, we are using only one clock, as other two are for redundancy," said Sivan.The clocks provide precise locational data for the users.The first one was launched in July 2013 and the seventh one (IRNSS-1G) in April 2016.The multi-purpose satellite-based positioning system, akin to the American GPS, Glonass of Russia , Galileo of Europe and China's Beidou , supports vehicle tracking, fleet management, disaster management and mapping services besides terrestrial, marine and aerial navigation in the sub-continent.The space agency plans to launch an additional space navigation satellite later this year to augment the services of the Rs 1,420 crore NavIC."The two spare navigation satellites will make up for any shortfall in the operations and service provided by NavIC to the users round-the-clock over the next 10 years," added Sivan.NavIC provides two types of services -- standard positioning service and restricted service. The former is for all users while the latter is an encrypted service for only authorised users.--IANSfb/him/mr