Countdown starts for launch of Isro's IRNSS-1I navigation satellite

The Indian Space Research Organisation (Isro) will launch navigation satellite IRNSS-1I, a backup satellite to replace NavIC navigation satellite constellation's IRNSS-1A, from the Sriharikota spaceport.

The launch will be Isro's second attempt at sending a replacement satellite. The previous mission of a PSLV carrying IRNSS-1H in August last year failed after the heat shield covering the satellite failed to separate.
India's Polar Satellite Launch Vehicle, in its forty-third flight (PSLV-C41) in XL configuration will launch IRNSS-1I satellite from first launch pad (FLP) of Satish Dhavan Space Centre (SDSC) SHAR, Sriharikota.
The 'XL' configuration of PSLV is used for the twentieth time. The IRNSS-1I is the eighth satellite to join the NavIC navigation satellite constellation.
PSLV-C41/IRNSS-1I Mission is scheduled to be launched on Thursday, 12 April 2018 at 04:04 hrs (IST).
IRNSS-1I is the eighth navigation satellite to join the IRNSS space segment. Its predecessors, IRNSS-1A, 1B, 1C, 1D, 1E, 1F and 1G were launched by PSLV-C22, PSLV-C24, PSLV-C26, PSLV-C27, PSLV-C31, PSLV-C32 and PSLV-C33 in July 2013, April 2014, October 2014, March 2015, January 2016, March 2016 and April 2016 respectively. Like all other IRNSS satellites, IRNSS-1I also has a lift-off mass of 1,425 kg. The configuration of IRNSS-1I is similar to IRNSS-1A, 1B, 1C, 1D, 1E, 1F and 1G.
Payloads: Like its other IRNSS predecessors, IRNSS-1I also carries two types of payloads – navigation payload and ranging payload. 
The navigation payload of IRNSS-1I transmits signals for the determination of position, velocity and time. This payload is operating in L5-band and S-band. Rubidium atomic clocks are part of the navigation payload of the satellite. 
The ranging payload of IRNSS-1I consists of a C-band transponder, which facilitates accurate determination of the range of the satellite. It also carries Corner Cube Retro Reflectors for LASER Ranging.
IRNSS-1I, the backup navigation satellite with a new atomic clock, has been built by a consortium of mid- and smallsized firms led by Bengaluru-based aerospace firm Alpha Design Technologies, under the watchful eye of Isro.
It is also the first satellite to be built at a special Isro facility for private firms.
The space agency plans to install signal receivers on the ground, which will give weather alerts to fishermen in the sea and will also help them in positioning.
The launch will be Isro's second attempt at sending a replacement satellite. The previous mission of a PSLV carrying IRNSS-1H in August last year failed after the heat shield covering the satellite failed to separate.
Weighing 321 tonnes, the PSLV-C41 will put the IRNSS-1I into orbit 19 minutes and 19 seconds after lift-off. The IRNSS-1I weighs 1,425 kg at lift-off and is the ninth satellite in the IRNSS satellite constellation. It will be placed in a sub-geosynchronous transfer orbit and at its closest point will be 284 km above the Earth and at its farthest will be 20,650 km above the Earth.
The IRNSS-1I mission comes two weeks after the space agency launched GSAT-6A on board GSLV Mk-II. The satellite, however, drifted off during its orbit raising operations.
Isro now says it has precisely located communication satellite GSAT-6A with which the signal link got snapped soon after its second orbit  raising operations on 30 March  (See: Isro loses contact with GSAT-6A after second orbit raising). 
The space agency is waiting for the right orientation for the satellite to capture the signal from the ground station and restore communication.
“Currently, GSAT-6A is moving in the geo transfer orbit at perigee of around 26,000km and apogee of about 33,000km,” Isro director Dr Sivan was quoted as saying.