India’s PSLV successfully launches the IRNSS-1B spacecraft

by William Graham

India’s ISRO launched its second navigation satellite on Friday, with a Polar Satellite Launch Vehicle orbiting the IRNSS-1B spacecraft in a mission originating from the Satish Dhawan Space Centre. Liftoff was on schedule at 11:44 UTC.¬†IRNSS-1B, is the second of seven which comprise the first-generation Indian Regional Navigation Satellite System (IRNSS).

ISRO Mission:

The IRNSS system will consist of three geostationary satellites and two pairs of spacecraft in inclined geosynchronous orbits.

Bound for an inclined orbit, IRNSS-1B will join IRNSS-1A at a longitude of 55 degrees east, completing the first pair of satellites. Future launches will deploy a second pair at 111 degrees East, with the geostationary satellites taking up positions at 34, 83 and 132 degrees.

Each IRNSS satellite uses a rubidium-based atomic clock to keep time, transmitting signals on L and S-band frequencies at 1,176.45 and 2492.028 megahertz respectively. A C-band transponder and an array of retroreflectors will be used to determine ranging data for calibration.

Z5Based on ISRO’s I-1K bus, IRNSS-1B is designed to operate for ten years. Fully-fuelled it has a mass of 1,432 kilograms (3157 pounds), or 614 kg (1,354 lb) without fuel. The satellite measures 1.58 by 1.5 by 1.5 metres (5.18 by 4.9 by 4.9 feet) excluding the twin solar panels extended from its sides to generate 1.66 kilowatts of power.

IRNSS-1B is three-axis stabilised by means of gyroscopes, magnetorquers and reaction wheels, as well as twelve manoeuvring thrusters. Each of these is capable of generating 22 newtons of thrust, while the satellite’s main apogee motor can provide 440 Newtons.

Z8Friday’s launch was designated PSLV C24, and represented the twenty-sixth flight of the Polar Satellite Launch Vehicle.

C24 was the sixth vehicle to fly in the PSLV-XL configuration, using larger and more powerful strap-on boosters to augment the thrust of the first stage.

The first stage, or PS1, consists of an S-138 solid rocket motor. Attached to it are six PS0M-XL boosters, each containing an S-12 motor.

An L-40 second stage, also designated the PS2, sits atop the first stage.

This is powered by a liquid-fuelled Vikas engine which burns UH25 propellant and dinitrogen tetroxide.

Z19The Vikas is a license-produced derivative of France’s Viking engine which flew many times as part of Ariane rockets between 1979 and 2004.

The third stage of the PSLV-XL is a PS3, with an S-7 solid rocket motor. This is topped with the PS4, or L-2-5, fourth stage with a pair of liquid engines.

India last used the PSLV-XL to deploy its Mars Orbiter Mission spacecraft in November 2013. Before that it was used to orbit the previous IRNSS satellite, IRNSS-1A.

Earlier missions saw the Chandrayaan-1 mission to the Moon, the GSAT-12 communications satellite and the RISAT-1 radar imaging spacecraft placed into orbit.

In addition to the XL variant, two more PSLV configurations are available.

The standard PSLV has a similar configuration to the XL model, however with PS0M solids powered by S-9 motors instead of the PS0M-XLs. The PSLV-CA, or Core Alone configuration, omits the boosters altogether reducing the cost and complexity of the vehicle for orbiting smaller payloads.

The PSLV has become the most-used and most reliable rocket in India’s fleet. Despite its first launch ending in failure, and its first operational flight four years later achieving a lower-than-planned orbit, the PSLV has gone on to post twenty one consecutive successful launches.

PSLV C24 departed from the First Launch Pad at the Satish Dhawan Space Centre. Built in the early 1990s, the First Launch Pad is primarily used by the PSLV, although several GSLV launches have occurred from it in the past. Friday’s launch is the twenty-second to make use of the facility, which was first used for the PSLV’s maiden flight in September 1993.

Z77There are two active orbital launch complexes at the Satish Dhawan Space Centre – the other being the Second Launch Pad which continues to be used by both the PSLV and GSLV.

A third launch complex is planned to accommodate the GSLV Mk.III, however this rocket can also launch from the Second pad.

The Satish Dhawan Space Centre is named after Satish Dhawan, who was the chairman of the Indian Space Research Organisation from 1972 to 1984. The site, which was previously named the Sriharikota High Altitude Range (SHAR) was renamed in 2002 shortly after Dhawan’s death.


For the IRNSS-1B mission, ignition of the first stage occurred when the countdown reached zero. Two of the solid rocket motors ignited half a second later, with two more lighting 0.2 seconds afterwards. These were the four ground-lit motors; the remaining two were air-lit, igniting twenty five seconds into the flight.

Seventy seconds after liftoff, the first pair of ground-lit solids burned out and separated from PSLV C23, followed a tenth of a second later by the second pair. The air-lit motors continued to burn until the 92-second mark at which point they were also jettisoned.

First stage flight concluded one minute and 51.5 seconds after ignition, with the spent stage falling away from the vehicle.

Z76Ignition of the second stage engines took place two tenths of a second after staging, with the second stage conducting a 151.8-second burn. Fifty nine seconds from the end of this burn, the payload fairing separated from the nose of the PSLV, at an altitude of 112.8 kilometres (70.1 miles, 60.9 nmi).

The third stage ignited 1.2 seconds after the separation of the second stage. After completing its 110-second burn this stage coasted for about 234 seconds, finally separating at ten minutes and 8.7 seconds mission elapsed time. Fourth stage ignition, ten seconds later, began the final phase of powered flight.

The fourth stage’s burn lasted eight minutes and 30.1 seconds, carrying IRNSS-1B into its initial transfer orbit. The payload was released forty seconds after fourth stage cutoff, with the mission plan calling for an orbit with a perigee of 284 kilometres, an apogee of 20,650 km (176.5 x 12,831 mi or 153.3 x 11,150 nmi) and inclination of 19.2 degrees.

Significantly lower than a typical geosynchronous transfer orbit, this trajectory allows India to use a PSLV to deploy the satellite rather than having to rely upon the larger but far less reliable Geosynchronous Satellite Launch Vehicle (GSLV).

Z69After separation, the satellite will make a series of five manoeuvres using its main propulsion system in order to achieve geosynchronous orbit. The first burn will occur at perigee during the fifth revolution, with another on the eighth revolution to raise the orbit’s apogee.

Three apogee burns during the ninth, eleventh and twelfth orbits will circularise the orbit and increase inclination to put the spacecraft into its operational position.

Friday’s launch marked India’s second of 2014, following the year-opening flight of GSLV D5 which successfully deployed the GSAT-14 communications satellite and ended a run of four consecutive GSLV failures.

India plans two more PSLV launches before the end of the 2014; the next is expected to carry France’s SPOT-7 imaging spacecraft and three or four secondary payloads, with another IRNSS mission scheduled later on in the year. ISRO also intends to conduct a suborbital test flight of the GSLV Mk.III, carrying a prototype capsule for a proposed manned spacecraft, towards the end of the year.

(Images via ISRO).

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