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IRNSS-1I navigation satellite launched by Indian PSLV rocket

PSLV launch c34 photo credit Indian Space Research Organisation - Copy

Archive Photo of PSLV launch. Photo Credit: Indian Space Research Organisation

Some two weeks after mysteriously losing contact with the GSAT-6A satellite, the Indian Space Research Organisation (ISRO) launched its next spacecraft into orbit, IRNSS-1I, which was launched to support the country’s regional navigation satellite system.

IRNSS-1l is short for Indian Regional Navigation Satellite System, and is the eighth satellite successfully orbited as part of the IRNSS constellation. The mission, dubbed PSLV-C41, was launched at 6:34 p.m. EDT (22:34 GMT) on April 11, 2018, atop a Polar Satellite Launch Vehicle (PSLV) in the “XL” configuration.

IRNSS-1I undergoes a vibration test. The satellite will be a replacement for the IRNSS-1A spacecraft launched in 2013. Photo Credit: ISRO

IRNSS-1I undergoes a vibration test. The satellite will be a replacement for the IRNSS-1A spacecraft launched in 2013. Photo Credit: ISRO

IRNSS-1I had a liftoff weight of some 3,142 pounds (1,425 kilograms). According to the ISRO, the spacecraft has an L5 and S-band navigation payload with rubidium atomic clocks, and a C-band ranging payload. 

The cube-shaped spacecraft’s overall size is about 5 feet (1.5 meters) on all sides before its antennas and solar panels are deployed. Once they are, the two panels should produce an estimated 1,670 watts of power.

The IRNSS constellation only needs seven satellites (six primary and one redundant spacecraft which serves as a spare). However, in 2017 the ISRO reported that the three rubidium clocks on the first satellite launched, IRNSS-1A, had failed. This prompted the need to send up one of the four ground-spares. The first spare, called IRNSS-1H, was launched in August 2017. However, due to a failure of the PSLV rocket launching it, the satellite was lost.

An issue with the separation mechanism on that flight’s payload fairing prevented the protective nose cone from jettisoning. The fairing is supposed to fall away after shielding its precious cargo through Earth’s turbulent atmosphere after the first several minutes of flight so as to save weight as it is no longer needed. As a result, the added mass being pushed into orbit caused the spacecraft to be inserted into a lower-than-planned orbit—while still encapsulated.

For this flight, however, everything appears to have gone by the book. The 144-foot (44-meter) tall PSLV launched on time from the Satish Dhawan Space Centre.

The PSLV is a four-stage expendable rocket. Its first stage consists of a 66-foot (20-meter) long, 9.2-foot (2.8-meter) wide solid rocket motor that has six 39-foot (12-meter) long, 3.3-foot (1-meter) wide strap-on solid rocket motors attached—four of which are ground-lit, while the other two ignite 25 seconds into the flight—to increase the vehicle’s thrust. Combined, the liftoff thrust of the vehicle measured more than 1.7 million pounds (7,600 kilonewtons).

Once the strap-on boosters burned out, they separated from the PSLV. The first four dropped away 1 minute, 10 seconds into the flight, while the two air-lit boosters jettisoned at approximately 1 minute, 32 seconds into the flight. Less than 20 seconds later, the first stage, having burned all of its propellant, also separated with the second stage igniting an instant later to continue powering the payload toward orbit.

At 42 feet (12.8 meters) long, the second stage was powered by a single Vikas rocket engine that consumes a nitrogen tetroxide/Unsymmetrical dimethylhydrazine mix to produce up to 179,000 pounds (799 kilonewtons) of thrust. This stage burned for about 2.5 minutes before also dropping away.

During the second stage’s powered flight, the payload fairing separated successfully around the 3 minute 23 second mark.

The 12-foot (3.6-meter) long third stage began the powered phase of its flight some 4 minutes, 24 seconds after leaving India. Burning solid fuel with a maximum thrust of 54,000 pounds (240 kilonewtons), it continued pushing the stack toward space. Its burn lasted for about 83 seconds.

After a several minute long coast phase, the third stage separated and the fourth, and final, stage ignited some 10 minutes, 8 seconds into flight. It was 9.8 feet (3 meters) long and was powered by two PS-4 engines that consume monomethylhydrazine and a nitric oxide mix. This final injection burn lasted for some 8.5 minutes to place the IRNSS-1I satellite into a sub-geosynchronous transfer orbit of 176 miles (284 kilometers) by 12,800 miles (20,650 kilometers) with an inclination of 19.2 degrees relative to Earth’s equator.

The IRNSS-1I satellite separated less than a minute later, some 19 minutes, 20 seconds after it had left the launch pad in India. Using on board propellant, the spacecraft will gradually raise its own orbit to 22,400 miles (36,000 kilometers), inclined 22 degrees. It’s final location will be 55 degrees East.

This was the 43rd flight of a PSLV launch vehicle and the 20th in its “XL” configuration. Additionally, this was the 32nd launch from the space center’s First Launch Pad and the ISRO’s third mission conducted in 2018.




Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a website about human spaceflight called Orbital Velocity. You can find him on twitter @TheSpaceWriter.

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