Sen—India’s fourth navigation satellite was successfully launched from the Satish Dhawan Space Centre at 11.49 a.m. UTC (5.19 p.m. IST) on Saturday March 28 by the advanced version of the four-stage 44.4 metre tall Polar Satellite Launch Vehicle, PSLV-XL.

With a ten year mission span, the navigation satellite, designated IRNSS-ID (Indian Regional Navigation Satellite System) is the fourth out of an eventual constellation of seven satellites which will augment satellite-based navigation and also provide tracking and mapping services. The cost of the satellite is approximately USD $24 million.

The launch was originally scheduled for March 9, but had been postponed due to a technical problem.

The first of the eventual seven satellites was launched in July 2013 and the second and third in April and October 2014 respectively. According to the Indian Space Research Organisation (ISRO) the complete constellation is expected to become operational by the end of 2016.

The mission is important because India wants to have an independent satellite-based navigation system. 

It was the 29th flight of the PSLV on Saturday and the eighth one using the XL configuration. The XL version is deployed when heavier satellites have to be launched. It was used for India’s maiden mission to the moon, Chandrayaan-1 in October 2008, and for the Mars Orbiter Mission in November 2013.

The IRNSS-ID flight was the first mission for the new ISRO chairman A.S. Kiran Kumar. IRNSS-ID project director, Dr Nageshwar Rao, speaking with the ISRO fraternity after the launch, dubbed Saturday 'navigation day' because a few hours earlier a Soyuz rocket had launched two Galileo satellites for Europe’s own global positioning system.

The mood among the scientists and engineers in the mission operations control room at the space centre was one of nervous apprehension as the IRNSS-ID lift off was nearing. As minutes ticked by, they were glued to their work stations monitoring the constant flow of data from the rocket and satellite.

About twenty minutes before the launch all the stations reported that they were ready for go. Thirteen minutes prior to the much-awaited lift off mission director Kunhi Krishnan, gave the final go for launch and activated the launch authorisation key. Four minutes before the take off ISRO finally confirmed that the weather was 'green' for the mission.

The countdown then moved rapidly and then at 5.19 p.m. local time (11.49 a.m. UTC) the mighty rocket roared into life, lifted off and triggering a huge round applause among the ISRO team and a large number of spectators who had gathered in the terraces and balconies in the buildings in and around the vast space complex.

As the rocket soared higher and higher, travelling in a plume of yellowish flame with an ear-deafening roar which reverberated throughout the centre, it pierced the clear evening sky over the space centre. The sound gradually faded away as the rocket disappeared into the clouds and finally was out of sight.

ISRO stated in commentary that the rocket performed flawlessly with all the stages separating precisely. Nineteen minutes and 25 seconds into the mission, the satellite separated at an altitude of 506.83 km when the velocity of the rocket was 9598.98 metres per second. The mission was a success, once again setting of a round of applause and an exchange of congratulatory handshakes and embraces among the ISRO team.

The spacecraft will be initially placed in a geostationary transfer orbit with a perigee of 284 km and an apogee of 20,650 km.

The two solar panels immediately deployed. They are equipped with what are known as ultra triple junction solar cells which will generate about 1660 watts of electrical power. The spacecraft is equipped with star sensors and gyroscopes which will help in orienting it, and so also the attitude and orbit control systems. The propulsion system consists of 440 Newton liquid apogee motor and twelve 22 Newton thrusters.

It is has a navigation and ranging payload and the main ground segment is at the ISRO Navigation Centre at Byalalu off the Bengalaru-Mysuru highway.  

After a few tests, the spacecraft will become operational next month.

Post launch Mr Kunhi Krishnan said that in June the PSLV will be launching a satellite for the United Kingdom. Mr Chandra Dathan, director of the Vikram Sarabhai Space Centre, announced that there will be five launches this year, consisting of three PSLVs, one GSLV (Geo Synchronous Satellite Launch Vehicle) and the reusable launch vehicle.