The Indian Space Research Organisation (ISRO) Polar Satellite Launch Vehicle (PSLV) conducted its thirtieth flight on Friday evening local time, deploying five British satellites into a Sun-Synchronous orbit. Liftoff occurred at 21:58 local time (16:28 UTC) from the First Launch Pad at the Satish Dhawan Space Centre.



PSLV Launch:

First flown in 1993, the Polar Satellite Launch Vehicle, or PSLV, is by far India’s most-used rocket for orbital missions – accounting for thirty of the country’s 46 launches to date including Friday’s.

The workhorse of India’s space program, the PSLV is on a run of twenty five consecutive successful launches, having achieved twenty seven successes overall. Friday’s launch is being conducted by Antrix Corporation, the commercial branch of the Indian Space Research Organisation (ISRO).

The primary payload for Friday’s mission was a trio of satellites which will join the Disaster Monitoring Constellation (DMC) in orbit.

Forming a new generation of satellites in this series, the three DMC3 spacecraft were manufactured by Surrey Satellite Technology Ltd (SSTL) for DMC International Imaging under a £110 million contract. China’s Twenty First Century Aerospace Technology Company (21AT) will lease all three spacecraft under a seven-year arrangement providing finance for the program.

Based around the SSTL-300 S1 satellite bus, each DMC3 satellite has a mass of 447 kilograms (985 lb). Equipped with a Very High Resolution Imager 100 (VHRI-100) payload the satellite is able to produce panchromatic images of the Earth at a resolution of up to one metre in a spectral band of 450 to 650 nanometres. Alternatively the instrument can produce multispectral images at a resolution of three to four metres.

The Disaster Monitoring Constellation is a British-led international fleet of small Earth imaging satellites which, while being used for commercial imaging, can provide data to assist with monitoring and managing natural and man-made disasters. All of the satellites in the constellation have been manufactured by SSTL.

Deployment of the constellation began in November 2002 with the launch of Algeria’s AlSat-1 atop a Kosmos-3M. Ten months later another Kosmos-3M deployed Britain’s UK-DMC-1, Nigeria’s NigeriaSat-1 and Turkey’s BilSat-1 spacecraft. A third Kosmos-3M deployed China’s first contribution to the program – the upgraded China DMC+4 – in 2005.

An enhanced series of DMC satellites began to launch in 2009, with a Dnepr carrying UK-DMC-2 and Spain’s Deimos-1 into orbit. The most recent launch, also using a Dnepr, occurred in August 2011 with Nigeria’s NigeriaSat-2 and NX spacecraft. All of the spacecraft launched since 2005 remain in operation.

Two technology demonstration satellites joined DMC3 for the journey into orbit. CBNT-1 is a 91-kilogram (201 lb) spacecraft which will be used by SSTL to demonstrate earth observation techniques, while DeorbitSail will investigate the use of a deployable sail to deorbit a satellite.

The DeorbitSail satellite; developed as part of a multinational program led by the University of Surrey; is a seven-kilogram (15 lb) three-unit CubeSat which will deploy a 4-metre (13-foot) square sail once in orbit.

Providing an increased cross-sectional surface area of 16 square metres (172 square feet), the sail will significantly increase the drag generated as the satellite orbits within the thermosphere.

All five satellites were manufactured by SSTL for British operators.

Friday’s launch made use of the PSLV-XL configuration – the heaviest version of the PSLV currently flying. All of the rocket’s configurations share the same core vehicle, with the boosters being configured differently for different payload masses and target orbits.

The standard PSLV uses six PS0M strap-ons, powered by S-9 solid rocket motors; the smaller CA or Core Alone configuration flies without boosters and the heavier PSLV-XL makes use of six PS0M-XL units with S-12 solid motors.

The rocket used for Friday’s launch had the flight number PSLV C28, and flew from the First Launch Pad at the Satish Dhawan Space Centre.

The first stage of the core PSLV is a PS1, powered by a solid-fuelled S-138 motor. Igniting at the zero-second mark in the countdown, the stage was joined 0.42 seconds later by the first pair of boosters.

Two more boosters lit two tenths of a second later, with the vehicle lifting off from its launch pad at the Satish Dhawan Space Centre. Twenty five seconds after liftoff the final pair of booster rockets ignited.

The first pair of boosters burned out and separate from the rocket 69.9 seconds into the flight, with the second pair of ground-lit solids following two tenths of a second later. The airlit motors continued to burn until the 92-second mark in the mission at which point they too were jettisoned.

Burnout and separation of the first stage occurred one minute and 50.18 seconds after launch, with the vehicle at an altitude of 69 kilometres (43 miles) and travelling downrange at 2.1 kilometres per second (4,700 mph).

Two tenths of a second after stage separation, the PS2 second stage ignited to begin its 150.54-second burn. Powered by a Vikas engine – derived from France’s Viking which powered the Ariane family of rockets between 1979 and 2004 – the liquid-propellant second stage burns UH-25 propellant, a mixture of unsymmetrical dimethylhydrazine and hydrazine hydrate, and dinitrogen tetroxide.

Approximately 1.2 seconds after the conclusion of its burn, the spent second stage was jettisoned and the third stage began its burn. The solid-fuelled third stage consists of an S-7 motor which will fired for about 70 seconds. Following its extinction the third stage remained attached for a brief coast phase, lasting three minutes and five seconds.

Once the third stage separated the coast continued for a further ten seconds before fourth stage ignition marked the resumption of powered flight.

The fourth stage burn – the final powered phase of the mission, lasted eight minutes, 31.88 seconds, with the liquid-propelled stage burning monomethylhydrazine and mixed oxides of nitrogen, mixed in its L-2-5 engine.

The burn left PSLV C28 in the planned deployment orbit for the DMC mission – a circular sun-synchronous orbit at an altitude of 647 kilometres (402 miles, 349 nautical miles) and inclination of 98.06 degrees.

Separation of the DMC3 satellites began at seventeen minutes, 56.58 seconds mission elapsed time; 37.5 seconds after fourth stage cutoff. The three satellites separated at intervals of 22-hundredths of a second. The three DMC spacecraft were mounted on a platform attached to the fourth stage, with the secondary payloads attached below them on the platform’s lower deck.

DeorbitSail was the first of the secondary payloads to separate, 39.06 seconds after the final DMC3 satellite. CNBT was the final payload to leave the PSLV, forty seconds after DeorbitSail.

Friday’s mission marked the thirtieth flight of the PSLV in twenty two years of service. The rocket made its maiden flight of 20 September 1993, attempting to deliver the IRS-1E remote sensing satellite into orbit; however the rocket was destroyed by range safety during its ascent after a malfunction was detected. A second launch, in October 1994, marked the rocket’s first success.

Following another successful test flight in 1996 the rocket was declared operational with its first operational mission to be the deployment of the IRS-1D satellite. This launch resulted in a partial failure, with the rocket reaching a lower-than-planned orbit that impacted upon the IRS-1D spacecraft’s operational lifespan.

The PSLV returned to flight in 1999 with the launch of OceanSat-1, and since then all of its launches have been successful. The PSLV has also formed the basis for the larger – but less reliable – Geosynchronous Satellite Launch Vehicle (GSLV) designed to carry larger satellites into geosynchronous transfer orbit.

Friday’s launch was India’s second orbital attempt of 2015 and the thirty-fifth overall of the year – including the uncatalogued Vega launch which reached orbit following the successful separation of its primary payload and two rockets which failed to achieve orbit.

The failures were the May launch of MEXSAT-1 atop a Proton-M/Briz-M and last month’s attempt by SpaceX to orbit a Dragon mission to the ISS atop a Falcon 9 rocket.

A Russian Soyuz launch – carrying a Progress spacecraft bound for the ISS – also failed due to a problem at third stage separation. However, this had already achieved orbit at the time of the failure.

India’s next launch is scheduled to take place in August, with a GSLV deploying the GSAT-6 military communications satellite. The PSLV will next be in action in September with the AstroSat-1 astronomy spacecraft.

(Images via ISRO and NASA) *Click here for larger images of the satellites*