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India to complete homegrown navigational satellite system with launch of IRNSS-1G

IRNSS-1G being prepared for a pre-launch test

IRNSS-1G being prepared for a pre-launch test. Photo & Caption Credit: ISRO

The Indian Space Research Organisation (ISRO) is about to launch its last navigational satellite for the indigenous IRNSS system, completing the series. The spacecraft, designated IRNSS-1G, will be launched Thursday, April 28, atop the country’s flagship PSLV rocket from the Satish Dhawan Space Centre in Sriharikota. Liftoff is currently scheduled for 3:20 a.m. EDT (07:20 GMT).

IRNSS, short for the Indian Regional Navigation Satellite System, will consist of seven satellites in orbit. The network is used to provide accurate real-time positioning and timing services over India and a region extending to 930 miles (1,500 km) around the country.

IRNSS-1F spacecraft integrated with PSLV-C32

Archive photo of IRNSS-1F spacecraft integrated with PSLV-C32. (Click to enlarge) Photo Credit: ISRO

IRNSS-1G, the seventh satellite in the series, will be put into a sub-geosynchronous transfer orbit (sub-GTO), with a 176-mile (284-kilometer) perigee and a 12,836-mile (20,657-kilometer) apogee, inclined 17.86 degrees with respect to the equatorial plane.

The mission that will launch the final IRNSS satellite will employ India’s Polar Satellite Launch Vehicle (PSLV) in the ‘XL’ configuration. The flight is designated PSLV-C33 and will be the 35th launch of the booster.

The flight will last for about 20 minutes and 19 seconds, ending in the spacecraft’s separation at an altitude of approximately 309 miles (498 kilometers). After the injection into this preliminary orbit, the satellite will deploy its solar panels and ISRO’s Master Control Facility (MCF) will assume control over the spacecraft. The MCF will perform a series of orbit raising maneuvers to put the craft into the targeted orbit.

IRNSS-1G weighs about 1.5 tons (1.4 metric tons) and has dimensions of 5.18 by 4.92 by 4.92 feet (1.58 by 1.5 by 1.5 meters). It is based on ISRO’s I-1K (I-1000) bus and features two deployable solar arrays and one lithium-ion battery capable of generating 1,660 watts of power. The satellite is designed to be operational for up to 12 years.

The satellite has two payloads: a navigation payload and a CDMA ranging payload. The navigation payload will transmit navigation service signals to users of the system. It will be operating in L5-band and S-band. A highly accurate rubidium atomic clock is part of the navigation payload of the satellite. The ranging payload consists of a C-band transponder, which facilitates accurate determination of the range of the spacecraft. The design of the payloads makes the IRNSS system interoperable and compatible with both the U.S. GPS and European Galileo systems.

The configuration of IRNSS-1G is the same as its predecessors: IRNSS-1A, 1B, 1C, 1D, 1E, and 1F. The first IRNSS satellite (IRNSS-1A) was launched by a PSLV rocket July 1, 2013, from the Satish Dhawan Space Centre. The most recent satellite in the series, IRNSS-1F, was sent into orbit March 10, 2016, also by a PSLV booster.

The newest IRNSS satellite should provide accurate position information services to users in India as well as the surrounding region. It will deliver Standard Positioning Service (SPS) – responsible for navigation parameter generation and transmission – satellite control, ranging, and integrity monitoring, as well as timekeeping services.

IRNSS, approved in 2006, is a satellite-based positioning system for critical national applications. Its primary objective is to provide reliable position, navigation, and timing services over India and its neighborhood. It is expected to grant accuracy of better than 66 feet (20 meters) in the primary service area.

Once complete, the constellation should provide their services in a fixed orbit above the Indian region. While four satellites would be sufficient to start operations of the IRNSS system, seven would make it more accurate and efficient. All the satellites of the constellation are configured identically.

The four-stage PSLV booster is India’s most reliable launch vehicle. The rocket has been used to delivered more than 40 satellites into space for some 19 countries. PSLV is capable of lofting up to 3.58 tons (3.25 metric tons) to low-Earth orbit and about 1.57 tons (1.42 metric tons) to a geosynchronous transfer orbit (GTO).

The rocket uses an Earth-storable, liquid-fueled rocket engine for its second stage, known as the Vikas engine. It was developed by the Liquid Propulsion Systems Centre. The third stage of the PSLV is powered by a solid rocket motor that provides the upper stage’s high thrust after the atmospheric phase of the mission. The fourth stage is composed of two Earth-storable liquid-fueled engines.

The 144-foot (44-meter) tall XL version of the PSLV, which will be used for Thursday’s mission, is the upgraded variant of the rocket in its standard configuration. Its thrust is increased by more powerful, stretched strap-on boosters.

The vehicle has a mass of 353 tons (320 metric tons) at liftoff and uses the larger strap-on motors (PSOM-XL) that provide the capability of hoisting heavier payloads into orbit. PSOM-XL uses the larger, 3.2-foot (1-meter) diameter, 44-foot (13.5-meter) length motors.

This version of the rocket carries 13.2 tons (12 metric tons) of solid propellants instead of the 9.9 tons (9 metric tons) that were used in an earlier configuration of the booster.

The PSLV rocket in its XL configuration was launched for the first time on Oct. 22, 2008, when it sent India’s Chandrayaan-1 lunar probe toward the Moon.

The launch of IRNSS-1G will be India’s third mission this year.


Tomasz Nowakowski is the owner of Astro Watch, one of the premier astronomy and science-related blogs on the internet. Nowakowski reached out to SpaceFlight Insider in an effort to have the two space-related websites collaborate. Nowakowski's generous offer was gratefully received with the two organizations now working to better relay important developments as they pertain to space exploration.

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