India has launch its third navigation satellite Thursday morning local time, with a Polar Satellite Launch Vehicle (PSLV) successfully carrying the IRNSS-1C satellite on the first leg of its journey towards geostationary orbit. Liftoff was on schedule at 01:32 local time (20:02 Wednesday) from the Satish Dhawan Space Centre.

Indian Launch:

IRNSS-1C forms part of the Indian Regional Navigation Satellite System (IRNSS), a constellation of geosynchronous satellites which the Indian Space Research Organisation (ISRO) has been deploying to provide navigation data to India and the surrounding region.

The first satellite, IRNSS-1A, was launched last July with the seven-satellite constellation scheduled for completion by the end of 2015.

Based on ISRO’s I-1K satellite bus, each IRNSS satellite has a mass at launch of 1,425 kilograms (3,142 lb). Unfuelled, the spacecraft has a mass of only 600 kilograms (1,323 lb), with the remaining 825 kilograms (1,819 lb) being taken up by propellant for their apogee motors and manoeuvring engines.

The spacecraft are designed for ten years’ operational service. Generating 1.6 kilowatts of power through twin solar arrays, the satellites broadcast L5 and S band navigation signals. C-band transponders and retroreflectors are used for range calibration.

Each satellite is fitted with a single liquid apogee motor producing 440 newtons (99 pounds-force) of thrust. Three-axis control is provided by reaction wheels, magnetorquers and twelve reaction control thrusters.

The apogee motor is tasked with propelling the satellite from its initial deployment orbit into the final geostationary orbit, while the remaining thrusters will be used to manoeuvre and orient the spacecraft once it is in orbit.

IRNSS-1C is the first geostationary satellite in the IRNSS system. Planned for operation at a longitude of 83 degrees East, it will operate at the middle station of the constellation.

Two more geostationary satellites will be added; at longitudes of 34 and 132 degrees, while the remaining four spacecraft will operate in inclined geosynchronous orbits to increase the angle of separation between signals.

Two of the inclined satellites are already in orbit; IRNSS-1A and 1B operate at a longitude of 55 degrees East. A second pair will be located at 111 degrees East next year.

The two satellites already in orbit were deployed in July 2013 and April 2014, both riding PSLV rockets to orbit from the Satish Dhawan Space Centre. The PSLV, or Polar Satellite Launch Vehicle, is the same rocket which will be used to launch IRNSS-1C.

Thursday’s launch was the twenty-eighth for the PSLV, with the flight number for the IRNSS-1C launch being C26.

The four-stage rocket uses a mixture of solid and liquid-fuelled stages, standing 44.4 metres (146 feet) tall with a mass at liftoff of 320 tonnes (315 Imperial tons, 350 US tons).

The PSLV was introduced in September 1993, replacing the smaller Augmented Satellite Launch Vehicle, and has become the workhorse of India’s space program.

In its twenty-seven flights to date the rocket has experienced two failures; the maiden flight had to be destroyed by range safety after the vehicle went off course, and the fourth flight – which marked the rocket’s first operational mission – delivered the IRS-1D satellite into an unusable orbit.

The first stage of the PSLV, the PS1, is powered by an S-138 solid rocket motor. Depending on the configuration the rocket is flying in, this may or may not be augmented by six strap-on solid rocket motors.

Thursday’s launch used the PSLV-XL configuration – the most powerful version of the PSLV currently flying – which makes use of six PS0M-XL boosters containing S-12 solid rocket motors.

Four of these motors were lit when the rocket leaves its launch pad, with the remaining two lit during the early stages of its ascent.

Thursday’s flight plan called for liftoff at 01:32 local time (20:02 UTC), with first stage ignition occurring when the countdown reached zero.

The four ground-lit solid rocket motors ignited shortly afterwards; the first pair 0.42 seconds after the first stage and the second pair two tenths of a second later, giving the rocket sufficient thrust to lift off. The air-lit motors ignited twenty five seconds after launch.

Around 69.9 seconds into flight the first pair of ground lit solids burned out and separated, with the second pair separating a fraction of a second later. Separation of the air-lit strapons came around the 92 second mark in the flight.

First stage flight lasted 109.62 seconds, with the spent stage separating at an altitude of 56 kilometres (35 miles, 30 nautical miles). The second stage lit 0.2 seconds later, beginning a two minute, 21.84-second burn. The payload fairing separated from the nose of the rocket around 89.5 seconds into this burn.

The second stage of the PSLV, known as the L-40 or the PS2, is liquid fuelled and powered by a Vikas engine burning UH25 propellant oxidised by dinitrogen tetroxide. Produced under license from France, the Vikas is a derivative of the Viking engine which powered Ariane rockets until the Ariane 4 was retired from service in 2004.

Following second stage burnout by approximately 1.2 seconds, the PS3 third stage ignited its S-7 solid rocket motor for a 110-second burn. After burnout, the third stage remained attached for around four minutes and fifty seconds as the flight enters a coast phase, finally separating ten seconds before fourth stage ignition.

The PS4, or L-2-5, fourth stage ignited eleven minutes and 12.7 seconds after launch to begin its burn. The liquid-fuelled stage is powered by two engines burning monomethylhydrazine and mixed oxides of nitrogen (MON-3). These engines fired for eight minutes and 28.98 seconds, propelling IRNSS-1C into its initial deployment orbit.

The expected parameters for spacecraft separation, which took place 37 seconds after fourth stage cutoff, are a perigee of 284 kilometres, an apogee of 20,650 kilometres (176 x 12,830 statute miles, 153 x 11,150 nautical miles) and 17.86 degrees of inclination. The acceptable margins of error in these parameters are a deviation of 5 km (3.1 mi, 2.7 nmi) in perigee altitude, 625 km (389 mi, 337 nmi) in apogee and 0.2 degrees in inclination.

Lower in apogee than a traditional geostationary transfer orbit, the deployment orbit is constrained by the limited performance of the PSLV, which was not designed to carry satellites bound for geosynchronous orbits.

The more powerful Geosynchronous Satellite Launch Vehicle (GSLV) which was designed for this purpose has endured a troubled development with a high rate of failure in early flights. As such the PSLV has been drafted in to launch smaller geostationary satellites. The PSLV was also used to launch India’s Chandrayaan 1 and Mars Orbiter Mission spacecraft to the Moon and Mars.

Thursday’s launch occurred from the First Launch Pad at the Satish Dhawan Space Centre, on the island of Sriharikota.

One of two pads used for PSLV launches, the First Launch Pad (FLP) entered service in 1993 with the maiden flight of the PSLV. It was not the first pad to be built at Sriharikota – older complexes to the South were used for early orbital flights with the SLV and ASLV rockets and several older sounding rocket pads exist at the site – however it is the oldest pad at the site still used for orbital missions.

The nearby Second Launch Pad was introduced in 2005 and is used for both PSLV and GSLV launches. It is currently being readied for a suborbital test flight of the GSLV Mk.III rocket, which will carry a prototype for ISRO’s proposed manned spacecraft. This mission, which will mark the maiden flight of the GSLV Mk.III – the largest rocket India has developed to date – could occur in late November although it may be delayed until 2015.

Following the launches of GSAT-14 by a GSLV in January, IRNSS-1B by a PSLV in April and SPOT-7 by a PSLV in June, Thursday’s launch marked the first time that India has conducted four orbital launches in one calendar year. A fifth launch is tentatively scheduled for December, with another PSLV-XL deploying the fourth IRNSS satellite, IRNSS-1D.