Two more such satellites will be launched in the next two months to fully ready India's regional navigation system by later this year.

The four satellites launched earlier are already operational. While four satellites are sufficient to start operations of the IRNSS system, the remaining three are needed to make the signal available 24x7 with both accuracy and precision, scientists said.

In a series of tweets, PM Narendra Modi congratulated the ISRO scientists for the successful launch of PSLV C31.

The navigation system, which will cost about Rs 1,400 crores, helps provide locational specificity. The satellites continuously beam down data that can be read by hand-held instruments or smart phones. India is the fourth country after USA, Russia and China to have a satellite-based navigation system. Once the full system is launched it will be at par with the US' GPS, scientists said.

ISRO says the system will have an error margin of no more than 20 metres. It is designed to cover a region of about 1,500 km from India's borders in the region from which the country experiences a threat perception. The restricted user signal which will be encrypted will be very useful for the military, especially to target missiles.

The IRNSS-1E was launched today on board the PSLV-C31 rocket from Sriharikota in Andhra Pradesh.

It was ISRO's 33rd PSLV launch and the first this year, the Workhorse Rocket's 33 consecutively successful launches are an enviable record.

A 48-hour countdown for the launch had begun on Monday at the spaceport in Sriharikota, which is about 100 km from Chennai.

The IRNSS-1E carries two types of payloads - navigation and ranging payload. It weighs 1,425 kg and has an expected life span of over a decade.