Spaceflight Insider

India launches its final IRNSS navigation satellite


Archive photo of IRNSS-1D launching in March 2015. Photo Credit: IRSO

The Indian Space Research Organisation (ISRO) has successfully launched the last spacecraft of its homegrown navigation satellite system. The satellite, designated IRNSS-1G, lifted off atop a Polar Satellite Launch Vehicle (PSLV) on Thursday, April 28, at 3:20 a.m. EDT (07:20 GMT) from the Satish Dhawan Space Centre in Sriharikota.

PSLV is a 144-foot (44-meter) tall launcher. On Thursday, this vehicle was used in the so-called “XL” configuration – an upgraded variant of the rocket. The “XL” option features increased thrust by more powerful, stretched strap-on boosters.

Side view of the fully integrated PLSV-C33 awaiting launch.

Side view of the fully integrated PLSV-C33 awaiting launch. Photo Credit: ISRO

The flight, designated PSLV-C33, was given the green light Monday, April 25, when the Mission Readiness Review was performed. On the next day, a 51.5-hour countdown started during which final preparations and propellant filling operations were carried out.

The rocket’s first stage was ignited at 3:20 a.m. EDT (07:20 GMT), beginning its 20-minute ascent to deploy the IRNSS-1G satellite.

Almost immediately after liftoff, four out of six strap-on boosters began firing to provide a powerful thrust in the initial phase of the flight. The last pair of boosters were ignited 25 seconds after the launch, when the rocket was at an altitude of about 1.68 miles (2.7 km).

When the launch vehicle was approximately 14.7 miles (23.7 kilometers) above Earth’s surface, the four boosters were jettisoned at one minute and 10 seconds into the flight. The remaining two boosters separated from the rocket about 22 seconds later.

Separation of the first stage occurred at about one minute and 50 seconds after launch. Then, the rocket’s second stage fired its Vikas engine to take control over the mission. One and a half minutes later, the payload fairing detached from the launch vehicle at an altitude of 70 miles (112.6 kilometers), exposing the IRNSS-1G satellite. The second stage continued powering the stack for about one minute until its separation.

The third stage was ignited at about four minutes and 23 seconds after launch, assuming control over the mission for nearly seven minutes. At about 11 minutes and 3 seconds into the flight, the third stage separated from the stack, leaving the payload powered by the fourth stage alone, which carried on with the mission for slightly more than nine minutes. The satellite was deployed approximately 20 minutes and 19 seconds after liftoff at an altitude of 310 miles (498 kilometers).

Shortly after the injection into this preliminary orbit, the spacecraft deployed its solar panels and ISRO’s Master Control Facility (MCF) assumed control over the spacecraft. The MCF will perform a series of orbit raising maneuvers to put the craft into the targeted 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.

IRNSS-1G is the seventh satellite in the IRNSS series. It 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.

IRNSS-1G faring

IRNSS-1G is encapsulated in the launch fairing. Photo Credit: ISRO

Approved in 2006, IRNSS, short for the Indian Regional Navigation Satellite System, 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. The 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.

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.

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 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 was India’s third mission this year and the 35th launch of the PSLV booster overall.

Video courtesy of ISRO


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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