Monday, April 28, 2014

ISRO's bold steps to put India in Top 5 on earth with own GPS Satellite System

Indian Space Research Organisation (ISRO) took another step towards becoming a global force to reckon with in the space sector with the successful launch of its second navigation satellites, the IRNSS 1B, in orbit around earth on Friday, April 04. The satellite was launched from the Satish Dhawan Space Centre at Sriharikota (SDSC SHAR) using India’s workhorse launch vehicle, the Polar Satellite Launch Vehicle (PSLV). The satellite is part of the Indian Regional Navigation Satellite System (IRNSS) programme, which involves launching of seven navigation satellites by mid 2015.

IRNSS 1-B satellite in the clean room at ISRO's Satish Dhawan Space Centre, Sri Harikota;
Image Courtesy: ISRO

Navigation satellites, known to the general public as GPS satellites, after the official name of the system of twenty four US navigation satellites, provide positioning and tracking services for users in a plethora of fields. The IRNSS 1B was initially placed in an intermediate orbit by the PSLV version code named PSLV C-24 from where, 5 orbit raising maneuvers will be performed over next few days to place it in the intended geosynchronous circular orbit (a geosynchronous orbit is one in which a satellite takes 24 hours to revolve around the earth) at a height of 36,000 km.

An ISRO press release stated “After a flight of about 19 minutes, IRNSS-1B Satellite, weighing 1432 kg, was injected to an elliptical orbit of 283 km X 20,630 km, which is very close to the intended orbit. After injection, the solar panels of IRNSS-1B were deployed automatically. ISRO's Master Control Facility (at Hassan, Karnataka) assumed the control of the satellite.”

PSLV C24 rocket takes off from spaceport at Sri Harikota with the IRNSS-1B navigation satellite; Image Courtesy: ISRO

The IRNSS system will be a critical national asset delivering terrestrial, marine and aerial navigation services including disaster management, mapping services, vehicle tracking and visual voice navigation apart from future strategic applications like in guided missile defense systems and other military purposes. 

India already became the fifth nation after the GPS system of US, Russian GLONASS, China’s Beidou and EU’s Galileo to launch an indigenously developed navigation satellite as part of a navigation system when it launched the first in the series, the IRNSS 1A, in July 2013. IRNSS’s primary service area will stretch upto 1500 km beyond the nation’s borders. The design and technology involved has scope for enhancing the coverage area by adding four satellites beyond the seven but ISRO has stated that this would be considered only if future need arises. 

IRNSS-1A, India's first 'GPS' satellite, integrated with PSLV C22 rocket at Satish Dhawan Space Centre, Sri Harikota before launch in July 2013; Image Courtesy: ISRO

The genesis of IRNSS programme occurred ten years ago with the aim of creating a system entirely in control of the Indian government to provide accurate real time positioning, navigation and timing (PNT) services for both civilian and military purposes. It was approved by the Indian government in June 2006 and the project has an estimated cost of Rs.1420 crore with each satellite costing around Rs.125 crore and the ground based infrastructure valued at Rs.300 crore.

A navigation satellite emits microwave signals periodically which contain the exact time when a signal leaves the satellite. Any receiver on the ground, like in a mobile phone, picks up the signal and then based on the time difference between the transmission and reception of the signal, measures the distance of the satellite from the receiver. Thus, as in case of GPS, a receiver gets signals from four satellites and is thereby able to calculate its own precise location.

Thus one critical element in satellite navigation is time measurement upto the smallest possible fraction of a second. Each IRNSS satellite contains 3 rubidium atomic clocks, which keep time upto a few tenths of a trillionth of a second in an hour. Currently, ISRO is importing these clocks but work is on to develop these clocks within the country. Since the accuracy of these clocks gets affected by vibrations, electrical interference and if their temperature goes 1 degree Celsius either way beyond their optimum operating temperature, ISRO designed the satellites accordingly from scratch.

With regards to ground based control and management, the ISRO release added “A number of ground stations responsible for the generation and transmission of navigation parameters, satellite control, satellite ranging and monitoring, etc., have been established in as many as 15 locations across the country”.

The IRNSS is estimated to provide position accuracy within 10 metres on the Indian landmass and position accuracy within 20 metres in the ocean and area within 1500 km of the borders. The position accuracy of US GPS receivers is about 15 metres for civilian purposes. However, civilian use of IRNSS will require separate receivers which the standard GPS receivers cannot meet. ISRO ‘s Space Applications Centre at Ahmedabad is already in advanced stages of development for appropriate IRNSS receivers.
The third and fourth satellites are slated to be launched by the end of this year while the remaining three are targeted for launch in March 2015. The IRNSS 1B launch was the twenty fifth consecutive successful launch of PSLV. The PSLV configuration that was used for this mission is the ‘XL’ version which had been used in the past to launch 5 missions, including India’s maiden moon (Chandrayaan 1) and Mars (Mangalyaan) missions.
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