India has continued deployment of its IRNSS navigation system Saturday, with the launch of the fourth satellite atop a Polar Satellite Launch Vehicle from the Satish Dhawan Space Centre at Sriharikota. Launched on schedule at 17:19 local time (11:49 UTC), the IRNSS-1D mission marks India’s first orbital launch of the year.



Indian Launch:

The IRNSS-1D satellite will join three others already in orbit, the fourth in a planned seven-satellite constellation which will provide India and its surrounding region with an independent satellite navigation system.

Operating in geosynchronous orbit, the Indian Regional Navigation Satellite System (IRNSS) has been under development by the Indian Space Research Organisation (ISRO) since 2006, with the first satellite reaching orbit in mid-2013.

The IRNSS constellation calls for three geostationary satellites and four more in inclined geosynchronous orbits. The geostationary slots, located at 34, 83 and 132 degrees East will each be occupied by a single satellite, while the two inclined stations, at 55 and 111.75 degrees East will each be home to a pair of spacecraft.

IRNSS-1D will be the first satellite to be located at the 111.75-degree East station in the inclined orbit, joining the IRNSS-1A and 1B satellites operational in the 55-degree slot. IRNSS-1C, which launched last year, is in the 83-degree geostationary position.

The IRNSS spacecraft are built around ISRO’s I-1K satellite bus, with a mass of 603 kilograms (1,330 lb). Loaded with 822 kilograms (1,812 lb) of propellant for orbit-raising and manoeuvring, its mass at launch will be around 1,425 kilograms (3,142 lb).

The spacecraft are powered by a pair of solar arrays, capable of generating 1.6 kilowatts of power, used to broadcast L5 and S band navigation signals. Each satellite also carries C-band transponders and retroreflectors, which can be used for range calibration to determine precisely the spacecraft’s position in space.

The propulsion and control system of each IRNSS satellite consists of a liquid-fuelled apogee motor which produces up to 440 newtons (99 pounds-force) of thrust to raise the satellite into its operational orbit, and twelve reaction control thrusters for three-axis attitude control.

Reaction wheels and magnetorquers are also fitted to help control the spacecraft’s attitude. Like the three satellites already in orbit, IRNSS-1D is expected to have an operational lifespan of ten years.

The twenty-ninth Polar Satellite Launch Vehicle to fly, PSLV-C27 was the rocket that deployed IRNSS-1D. Flying in the PSLV-XL configuration, the four stage rocket delivered its payload into a transfer orbit from which the satellite will manoeuvre to its final destination.

The PSLV is part of India’s second generation of expendable launch systems, replacing the replacing the smaller Augmented Satellite Launch Vehicle which had been derived from the earlier Satellite Launch Vehicle.

The workhorse of India’s space programme, the PSLV has made more launches than all of India’s other orbit-capable rockets combined.

To date all but two PSLV launches have been successful; the failures occurring during the vehicle’s 1993 maiden flight which was destroyed by range safety, and the first operational flight four years later which reached a lower than planned orbit.

The PSLV is capable of launching from both of the active launch pads at India’s Satish Dhawan Space Centre – either the older First Launch Pad (FLP) which was built at the beginning of the PSLV programme or the newer Second Launch Pad which was added in the mid-2000s. Saturday’s launch used the Second Launch Pad.

The first stage of the PSLV, the PS1, is powered by an S-138 solid rocket motor which ignited when the countdown reached zero.

For the first minute and a half of flight, six PS0M-XL solid rocket motors augmented the PS1’s thrust; the four ground-lit motors ignited in pairs 0.42 and 0.62 seconds after the first stage, with the remaining two motors air-lit twenty five seconds into the mission.

The solids were powered by S-12 solid rocket motors, with the use of the PS0M-XL in place of the smaller and less powerful PS0M motors being the principal difference between the PSLV’s standard and XL configurations.

Around seventy seconds after launch the ground-lit solids burnt out and separated from the PSLV; the first pair falling away at the 69.9 second mark in the mission and the second pair following two tenths of a second later. The air-lit motors separated 92 seconds after liftoff.

The first stage burned for 110.8 seconds, propelling the rocket to an altitude of 56 kilometres (35 miles, 30 nautical miles) and a velocity of 2.39 kilometres per second (1.49 miles per second) before burning out and separating.

Igniting two tenths of a second later, the second stage, or PS2, fired its Vikas engine to continue PSLV-C27’s ascent into orbit. The Vikas, derived from the French Viking engine which powered the Ariane series of rockets from 1979 to 2004, is a liquid-fuelled engine burning UH25 propellant and dinitrogen tetroxide.

Second stage flight lasted approximately two minutes and 21.8 seconds, with separation of the payload fairing taking place midway through; about 92.8 seconds after ignition.

The spent second stage was jettisoned 1.2 seconds after burnout, with the third stage, or PS3, igniting to begin its own 70-second burn. Another solid-fuelled component, the third stage is powered by an S-7 motor. It remained attached after burnout, with the rocket coasting for four minutes and 53.9 seconds before separation.

A further 10.3 seconds after the third stage is jettisoned, the fourth stage ignited to begin the final phase of powered flight. The fourth stage, known as the PS4 or L-2-5, is powered by two engines which burn monomethylhydrazine oxidised by mixed oxides of nitrogen (MON-3).

Firing for eight minutes and 39 seconds, the fourth stage completed the insertion of IRNSS-1D into its initial transfer orbit. The target orbital parameters for Saturday’s mission are a perigee of 284 kilometres (176 statute miles, 153 nautical miles), an apogee of 20,650 kilometres (12,830 miles, 11,150 nautical miles) and an inclination of 19.2 degrees.

The deployment orbit is lower than a standard geosynchronous transfer orbit, a typical feature of geosynchronous missions that use the PSLV as the orbit is a trade-off between the mass the rocket can carry and the velocity that it can impart upon the payload.

The PSLV was not originally designed for geosynchronous launches and even in its most powerful configuration – the PSLV-XL – the payload it can carry is more limited than the larger rockets used by other countries to reach these orbits.

India’s own Geosynchronous Satellite Launch Vehicle is more suited to launching geosynchronous satellites, however its poor reliability has seen ISRO unwilling to risk important payloads until its performance improves.

Spacecraft separation occurred 37 seconds after fourth stage cutoff, at 19 minutes and 25 seconds mission elapsed time.

Saturday’s mission was the first of four or five launches that India plans to conduct in 2015. The next PSLV launch is currently scheduled for June, carrying three British satellites for the Disaster Monitoring Constellation (DMC).

In August a Geosynchronous Satellite Launch Vehicle is scheduled to carry the GSAT-6 satellite into orbit for the Indian military and then towards the end of the year two further PSLV launches are planned; one carrying the AstroSat-1 astronomy payload and the other with the next IRNSS mission, IRNSS-1E.

The nineteenth orbital launch of 2015 – including February’s Vega launch which was not catalogued despite the upper stage achieving orbit after a suborbital primary mission – Saturday’s IRNSS launch is the sixth to occur worldwide in the space of three days.

On Wednesday evening (UTC) a Delta IV deployed a Global Positioning System spacecraft in a mission from Cape Canaveral, with Russia’s Dnepr orbiting South Korea’s Ariarang-3A Earth resources satellite from the Dombarovsky missile base a few hours later and Japan’s H-IIA lifting off from Tanegashima with a reconnaissance satellite in the early morning of Thursday.

Friday saw two launches of Soyuz rockets, two hours apart, the first from Baikonur with the manned Soyuz TMA-16M mission bound for the International Space Station and the second from Kourou, French Guiana with a pair of Galileo navigation satellites.

(Images via ISRO)