51.30-hour countdown for ISRO's final navigation satellite IRNSS-IG begins

The 51.30-hour countdown for the 28 April launch of the country's seventh and final navigation satellite, IRNSS-1G, on board Polar Satellite Launch Vehicle- C33 from the spaceport of Sriharikota, began today.

The Mission Readiness Review Committee and the Launch Authorisation Board gave their approval on Monday for the countdown that began at 9.20 AM today for the launch scheduled on Thursday at 12.50 PM from the first launch pad at the spaceport of Sriharikota, ISRO said.

IRNSS-1G on board PSLV-C33 in its 35th flight is the last in the series of the Regional Navigation Satellite System (IRNSS), comprising seven satellites that would give a fillip to the Indian space agency's attempt to set up its own independent regional navigation system on par with the US-based Global Positioning System.

While four satellites would be sufficient to start operations of the IRNSS system, the remaining three would make it more "accurate and efficient".

ISRO had launched the sixth navigation satellite IRNSS-1F on 10 March, the other five being IRNSS-1A on 1 July 2013, IRNSS-1B (4 April 2014), IRNSS-1C (16 October 2014), IRNSS-1D (28 March 2015) and IRNSS-1E (20 January 2016).

ISRO scientists are using the same XL variant, used in previous launches of IRNSS satellites, for the launch of IRNSS-1G, given its capacity to carry load.

Rockets with XL configuration were used during the launch of Chandrayaan-1, Mars Orbiter Mission, ASTROSAT besides the six IRNSS satellites.

The 44.4 metre tall IRNSS-1G has a lift-off mass of 1.425 kg and would be launched in sub-Geosynchronous Transfer Orbit (sub GTO). It has a 12-year mission life.

With the operationalisation of six satellites, India has demonstrated the system's targeted position accuracy which is much better than 20 metres over 24 hours of the day.

With the launch and operationalisation of IRNSS-1G, the seventh in the constellation, the completion of IRNSS constellation will be achieved, ISRO said.