India is expected to launch at least two more navigation satellites this year and one more in 2016 to offer satellite navigation services by the middle of next year, Indian space agency officials said.
Indian Space Research Organisation (ISRO) officials deny any diversion of focus is delaying the operationalisation of navigation satellite system.
The three satellite launches will be in addition to the one that India is expected to put into orbit on March 28 evening.
"We will surely be launching two more navigation satellites this year apart from tomorrow's (March 28) launch. At the end of the year we will have six navigation satellites up in the sky out of the constellation of seven such satellites," senior officials of Indian Space Research Organisation (ISRO) told IANS preferring anonymity.
According to officials, the seventh and the last one of the Indian Regional Navigation Satellite System (IRNSS) in all probability would go up early part of 2016.
The full navigation services are expected to be offered from mid 2016 onwards, according to the officials
They said the countdown for Saturday's rocket launch is progressing at a good pace in a smooth manner and all the activities are geared up for the 5.19 p.m. blast off of the rocket.
The Indian rocket Polar Satellite Launch Vehicle (PSLV-C27) is expected to blast off from Sriharikota rocket port carry the country's fourth navigation satellite IRNSS-1D.
As things stands today, there is already one year delay in the realisation of the satellite navigation system which ISRO officials agree.
And time is also running out fast.
Out of the seven satellites that comprises the IRNSS each having a life span of 10 years, three satellites have already been launched.
The first one-IRNSS-1A is now two years old and has a remaining life span of eight years and the second one is around one year old with a remaining life span of nine years.
And when the whole system comes into play sometime in May 2016, IRNSS-1A will have a remaining life of seven years and IRNSS-1B eight years.
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The first satellite IRNSS-1A was launched in July 2013, the second IRNSS-1B in April 2014 and the third on October 16, 2014.
Curiously all the seven navigation satellites and the rockets used to put them into orbit are also identical.
With two launch pads at its rocket port, ISRO could have focussed on realising its satellite navigation system while putting other futuristic launches for the future date, is one view expressed by officials.
ISRO had earlier said the navigation system would be ready by middle of 2015 with three launches in 2014 and 2015. But that did not happen.
The navigation system was conceptualised in early 1990s and got the sanction in 2006.
Officials at the space agency now say that all the remaining navigation satellites are on different stages of production and would be launched to offer the services middle of next year.
The full system comprises of nine satellites - seven in orbit and two on the ground as stand-by.
Each satellite costs around Rs.150 crore and the PSLV-XL version rocket costs around Rs.130 crore. The seven rockets would involve an outlay of around Rs.910 crore.
"ISRO and its activities have grown and work has to be done simultaneously at several fronts. It is not the question of diversion of focus," an ISRO official said.
However, he agreed that at times priorities change and focus and resources do get diverted.
"That is short term phenomenon and would not delay other projects," he said.
The official said IRNSS-1D could have been launched last year but was postponed due to the experimental launch of Geosynchronous Satellite Launch Vehicle MkIII and the revamping of launch pad infrastructure.
Speaking of IRNSS-1D satellite, an ISRO official said after putting it into the intended orbit, it would be raised to its home slot which would take around eight days.
Following that characterisation of the navigation and ranging payloads would be done and later the satellite will be integrated with the ground stations.
The three satellites launched earlier have all been integrated with the ground stations and are working well.
"From four navigation satellites up in the sky, we will get the signals which would prove the concept on which the whole IRNSS has been designed. While the full range of services may not be available with the constellation of four satellites, a user would be able to locate his position," he said.
Queried about the ground segment infrastructure, he said a good part of that is in place and the balance would be ready soon.
He said the IRNSS system is unique as it consist only seven satellites while other systems have more than 20 satellites.
However, while other systems are global, Indian system is of regional in nature.
Nevertheless, ISRO official claims that India can replace the US GPS with Indian system when full fledged operations begin.
The fully operational system is expected to provide accurate position information service to users across the country and the region, extending up to an area of 1,500 km.