|The Indian Space Research Organisation makes history by launching 10 satellites in one flight of the Polar Satellite Launch Vehicle.|
THE Polar Satellite Launch Vehicle, the old faithful of the Indian Space Research Organisation (ISRO), was suddenly the focus of media attention in end-April: It was to launch 10 satellites in a single mission. Until then, it had put multiple satellites in orbit three times and boasted a record of 11 straight successful flights in a total of 12. In June 2006, Russia launched 13 satellites in one mission, but the result was not known. A month later, its attempt to launch 18 satellites in one rocket failed.
Of the 10 satellites ISRO was attempting to put in orbit, only two were Indian and they were the main payloads of PSLV-C9. Launching multiple satellites using a single rocket is technologically challenging because the last stage of the vehicle has to fire the satellites into the required orbits in a precisely timed sequence. The last stage of the vehicle has to be re-oriented each time after it ejects a satellite, to avoid collision of satellites. This is done by firing its onboard thrusters in such a way that the programmed series of ejections take place at the required intervals.
What made the latest mission more daunting was the fact that for the first time ISRO was using the core-alone version of the standard PSLV, without the six strap-down motors, to launch multiple satellites. The core-alone version had been used twice earlier to put single satellites in orbit, one from Italy in April 2007 and the other from Israel in January 2008.
The standard version of the 44-metre-tall, four-stage PSLV weighs 295 tonnes, with six strap-on booster motors surrounding the first stage, while the core-alone version weighs 230 tonnes and is used to put lighter satellites in orbit.
As the 50-hour countdown for the lift-off from Sriharikota at 9.23 a.m. on April 28 was winding down, ISRO ran into an unexpected problem. A trough of low pressure had formed off the Andaman archipelago in the Bay of Bengal, where the spindle-shaped island lies. The Mission Control Centre (MCC) at Sriharikota had begun to weigh its options when, luckily for it, the trough failed to develop and headed off in the north-east direction. At 11 p.m. on April 27, a high-level ISRO team, including members of the Launch Authorisation Board, met and decided to go ahead with the launch the next day.
The launch vehicle sizzled to life on ISRO’s world-class second launch pad at the precise time and sped into the overcast sky with a deep roar. All systems worked to perfection: the stages ignited on time and were jettisoned into the Bay of Bengal when the explosive bolts between the stages sprang into action. After the third stage fell off, the final stage ignited and coasted along for five minutes and 18 seconds.
About 885 seconds (14 minutes and 45 seconds) after lift-off, the fourth stage ejected the main payload, Cartosat-2A, into orbit at a velocity of 7.5 km a second at an altitude of 637 km. Commands went from the MCC for the fourth stage to re-orient itself in order to fire the second satellite, the Indian Mini Satellite (IMS-1), which was put in orbit at an altitude of 637 km about 45 seconds after Cartosat-2A was put in orbit.
Of the eight foreign nano satellites on board, six were in a cluster, collectively called NLS-4, and weighed 50 kg together. Of the six, the first to wing out was CUTE, about 1,031 seconds after lift-off. The remaining five went out at intervals of 20 seconds.
The seventh nano satellite, called NLS-5, also separated 20 seconds after the previous one. The eighth nano satellite, named RUBIN-8, as per plan went into orbit along with the spent fourth stage.
The eight nano satellites went into orbits at an altitude that ranged between 639 km and 641 km. At the end of 19 minutes from lift-off, a voice at the MCC announced “mission completed”, and smiles broke out on the tired faces of the engineers and scientists there.
However, suspense and tension built up for about an hour as the plot boards at the MCC went blank after they showed the separation of Cartosat-2A, IMS-1 and CUTE. No information came about the separation of the remaining satellites.
An ISRO scientist said: “We did send the commands for the separation of the remaining satellites but we did not receive any telemetry signals from them. We are not aware of their separation.” However, another ISRO scientist was of the view that telemetry signals failing to reach the ground on the separations did not mean that the ejections did not take place.
The tension eased when George Koshy, Mission Director, and John P. Zachariah, Deputy Director of the Vikram Sarabhai Space Centre, Thiruvananthapuram, announced that the builders of the nano satellites had informed Sriharikota that their ground stations had received information that the satellites had separated successfully from the fourth stage.
Of the nano satellites, NLS-4, developed by the University of Toronto, Canada, consists of six satellites built by various universities. Two of them, CUTE 1.7 and SEEDS, were built in Japan, while Can-X2, AAUSat-II, COMPASS-1 and Delfi-C3 were built in Canada, Denmark, Germany and the Netherlands respectively. NLS-5 was also built by the University of Toronto. RUBIN-8 belongs to COSMOS International, Germany. The universities built them to learn how to miniaturise satellite technologies and to perform scientific experiments. The launch of the eight nano satellites was done under a commercial contract between Antrix Corporation, COSMOS International and the University of Toronto.
On Cartosat-2A, its project director M. Krishnaswamy said: “We can generate the latest maps with the images from Cartosat-2A. Otherwise, most of the maps available are 100 years old. Many changes have taken place on land in rural and urban areas. We need to have accurate maps of these areas.”
The new maps would help the government earn more revenue because they would provide information on how many people had land holdings. Besides, the images would provide information on soil types, the kinds of crops grown and their health and yield and so on, said Krishnaswamy.
The images would also help in planning rural and urban infrastructure, laying ring roads and so on. The camera on board Cartosat-2A can be used to obtain scene-specific images of the earth with a resolution of one metre.
Cartosat-2A images would be used for defence applications as well.
The images from IMS-1 would be used to monitor the health of crops, forest coverage and the rate of deforestation, and to map wasteland, coastal features, coral reefs and landslips. While D.V.A. Raghavamurthy was project director for IMS-1, vehicle director of PSLV-C9 was C. Venugopal.
The mission sent out two emphatic signals. First, it demonstrated India’s leadership position in the world in the area of putting multiple satellites in orbit using a single rocket. Secondly, although Antrix Corporation, ISRO’s marketing agency, earned $0.6 million for putting the eight nano satellites in orbit, what was more important was that the mission proved ISRO’s capability in the launch business and helped instil confidence in the international community to be partners with ISRO.
ISRO Chairman G. Madhavan Nair said: “It is a memorable occasion for ISRO and India. We have set a record for launching 10 satellites into orbit. Very few countries have done it. Russia launched 13 satellites at a time. We do not know the result. We have shown to the world today that we can do multiple launches in a precise manner…. The PSLV has performed excellently well.” Indeed, the PSLV has been a flawless performer, be it the standardised version or the core-alone one. Except for the first one that failed, all the other flights of the PSLV up to the latest one have been successes and the last three have been core-alone missions.
PSLV-C9 being wheeled to the launch tower of the second launch pad at Sriharikota on April 26.
On May 26, 1999, PSLV-C2 launched three satellites, the first time an Indian launch vehicle had demonstrated that capability. The satellites included India’s Indian Remote-sensing Satellite (IRS-P4), Tubsat of Germany and KITSAT of the Republic of Korea.
On October 22, 2001, PSLV-C3 put in orbit three satellites: Technology Experiment Satellite (TES) of India, which was used for defence purposes, BIRD of Germany and Proba of Belgium.
On January 10, 2007, PSLV-C7 put in orbit four satellites: Cartosat-2 and the Space Capsule Recovery Experiment (SRE) of India, Lapan-Tubsat of Indonesia and Pehuensat-1 of Argentina. The PSLV in these three missions were the standard versions.
In its maiden core-alone flight on April 23, 2007, the PSLV ejected into a tricky orbit Italy’s Agile satellite, which was meant for astronomical purposes. ISRO termed this its first dedicated commercial launch because Agile was the only satellite in that launch and Antrix charged the Italian Space Agency almost double the prevailing international rates. Antrix received Rs.50 crore for the launch, which put Agile into a demanding, specific orbit. For the three multiple launches Antrix had received only nominal rates.
On January 21, 2008, the core-alone again did its job by putting Tescar, an Israeli remote-sensing satellite, in orbit.
After the third core-alone PSLV flight billeted 10 satellites into orbit, K.R. Sridhara Murthi, managing director of Antrix Corporation, said: “The PSLV has got good brand value. It has flexibility. It is versatile. It can put any satellite, whether mini, small, or big, into orbit. It can launch satellites into any type of orbit that the customer wants. Besides, we launch [foreign satellites] on time. All these attract customers…. All the eight nano satellites are doing well. The universities which built them are quite happy.”
Antrix Corporation, which was set up in 1992, has found its feet despite stiff competition from advanced countries, which would not like their monopoly in the launch-service business to come under threat. Antrix today makes its money from four areas: selling remote-sensing images from the IRS to several countries; leasing communication transponders on board its INSATs to companies; using the PSLV to put foreign satellites in orbit; and supply of satellite components and ground systems.
According to Sridhara Murthi, Antrix earned a revenue of Rs.664 crore in financial 2006-07. Provisional accounts showed that Antrix might make Rs.900 crore in 2007-08.
Antrix has leased 11 transponders on board ISRO’s INSATs for use for banking and stock exchange transactions and for direct-to-home telecasts. “Our major activity [in leasing these transponders] is with the Indian customers although we have a few customers in Sri Lanka, Bhutan and Russia,” Sridhara Murthi said.
Antrix has teamed up with EADS-Astrium, Paris, and won contracts to build two satellites. This follows an agreement between the two to build jointly communication satellites for the international market. The satellites – one for Eutelsat and another for Avanti Screenmedia Group in the United Kingdom – are being built by the ISRO Satellite Centre, Bangalore.
Discussions are under way with various countries on using ISRO’s powerful Geosynchronous Satellite Launch Vehicle (GSLV) with an indigenous cryogenic engine to put satellites weighing 2,000 kg to 3,000 kg in orbit, Sridhara Murthi said.
Launching of satellites in that weight-class has been the exclusive territory of the U.S., Russia, China and Arianespace so far.
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