ISRO's new heights

Published : Jun 06, 2003 00:00 IST

The perfect deployment of the communications satellite GSAT-2 from the GSLV-D2 once again proves that the Indian Space Research Organisation has mastered the technology to build launch vehicles of its class.

in Sriharikota

INDIA once again displayed its capability to put a satellite in geo-synchronous transfer orbit (GTO) when the gigantic Geo-synchronous Satellite Launch Vehicle (GSLV-D2) rose from the Sriharikota launch pad on May 8 and "hit the bull's eye" 17 minutes later. The trajectory of the vehicle, built by the Indian Space Research Organisation (ISRO), was accurate: GSAT-2 reached a perigee (nearest point to earth) of 180.04 km and an apogee (farthest point to earth) of 36,000 km. There was a deviation of just 40 metres in the perigee. The injection of the satellite into the GTO was precise: an ISRO technologist called it "the best anyone in the world can do". The success showed that ISRO has mastered the technology to build launch vehicles.

Dr. K. Kasturirangan, Chairman, ISRO, called it a remarkable flight in which a host of complex technologies were put to work. "With the successful flight of the GSLV-D2 , we can launch satellites weighing 2,000 kg with the GSLV," he said.

Built by the Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram, the GSLV-D2 is a 49-metre tall, three-stage vehicle, weighing about 414 tonnes at lift-off. GSAT-2, which is essentially a communications satellite, was built by the ISRO Satellite Centre in Bangalore. It is expected to have a lifespan of seven years and more.

This was the GSLV's second developmental flight. During its first developmental flight, on April 18, 2001, the GSLV put GSAT-1 in the GTO. On September 12, 2002, ISRO's Polar Satellite Launch Vehicle (PSLV) proved its versatility when it orbited a meteorological satellite Metsat, now renamed Kalpana, in the GTO. During its previous five flights the PSLV had put satellites in polar orbit.

GSAT-2 was heavier by about 285 kg than GSAT-1, its predecessor, which weighed about 1,540 kg. The GSLV-D2 was able to put this heavier satellite into orbit by using high-performance liquid strap-on booster motors, which developed a better thrust and enabled the vehicle to climb faster. The first stage had 138 tonnes of propellants as compared to 128 tonnes in the previous flight. The payload adapter used better material.

Kasturirangan said: "The satellite reached the GTO at the right height, the right speed and the right direction. It really hit the bull's eye in terms of the accuracy that we achieved in the satellite's orbit. It is a major milestone for ISRO in its capability build-up for launching advanced communication satellites and meteorological spacecraft. We are planning to launch satellites weighing 2,250 kg by GSLV Mark II." He pointed out that the space programme was directed towards meeting the social requirements in communications, remote-sensing, weather forecasting, broadcasting for education, telemedicine, search and rescue missions, and so on.

Dr. K. Sudhakara Rao, Vehicle Director for the previous GSLV flight, called it a great mission. "It was a textbook flight. It proved that the vehicle design is robust, the systems worked consistently and the processes were good," Sudhakara Rao added.

The men who headed the mission were Mission Director R.V. Perumal, Vehicle Director G. Ravindranath and Satellite Director Y.K. Singhal. The vehicle cost Rs.150 crores to build, and another Rs.50 crores was spent to fabricate the satellite.

On May 12, after a series of deft, critical manoeuvres carried out at the Master Control Facility in Hassan, Karnataka, GSAT-2 reached its geostationary orbit and its solar arrays and antenna were deployed.

GSAT-2 is an experimental communications satellite, carrying four C-band and two Ku-band transponders. It carries four piggyback payloads for conducting experiments. One experiment will study the level of radiation around the satellite and another will analyse the unequal build-up of electricity around it, which leads to sparking and other disturbances. The third one will study the origin of X-rays from solar flares, which can harm the satellite and disrupt communications. These experiments will help in developing well-designed satellites. The fourth experiment will analyse the way the ionosphere spreads, moves or oscillates.

ISRO has ambitious programmes ahead. These include developing a powerful GSLV Mark III to launch 4-tonne satellites in the GTO (see interview with R.V. Perumal); using the PSLV to send an unmanned 300 kg spacecraft to orbit around the moon to study its physical and chemical characteristics; using the PSLV again to send 300 kg recoverable capsules into space to perform experiments, after which the capsules will land at sea; sending Radar Imaging Satellites (Risats) that will enable observations even at night and under cloudy conditions; and so on.

ISRO will soon launch a PSLV that will deploy Resourcesat to study the resources of the country. Starting with that, there will be as many as eight PSLV flights by the end of 2007 that will deploy Cartosat-1 and 2 for mapping applications, Astrosat (to conduct experiments in astronomy), an Oceansat, Risat and Indian Remote-Sensing satellites.

There will be four more flights of the GSLV in the next four years. To meet this hectic schedule, a second launch pad is being built at the Satish Dhawan Space Centre at Sriharikota. The huge mobile service tower at the second launch pad is designed so that the different stages of future vehicles such as the massive GSLV-Mark III will be put together there.

ISRO is also developing the indigenous cryogenic engine, which powers the third and final stage of the GSLV. This and the previous flight had Russian cryogenic engines that use liquid hydrogen and liquid oxygen as propellants. The next GSLV flight will also use a Russian cryogenic engine. But the fourth GSLV flight in 2005 will be powered by an indigenous cryogenic engine built at Mahendragiri in Tamil Nadu.

N. Vedachalam, Director, Liquid Propulsion Systems Centre, Mahendragiri, said that the development of the indigenous cryogenic engine has been completed. Full duration tests, with the engine burning for 1,000 seconds, have been done. "We are now concentrating on the second phase of integrating the engine with the stage," he said. For it is the stage with the engine that goes into the rocket. Conversion of the engine into a stage is a technologically demanding task that requires integration of electronics, guidance, control systems and so on. This work is under way and will be completed in two years. The qualification of the stage will lead to its being used in the fourth GSLV flight in 2005.

In the first GSLV flight in 2001 there was a slight underperformance in the Russian cryogenic stage. This led to GSAT-1 going into a lower orbit than targeted. A good quantity of liquid propellant on board was used to manoeuvre the satellite into its intended orbit. But a shortage of 10 kg of liquid propellant led to the satellite going into the "drift orbit" rather than the final geo-synchronous orbit.

G. Madhavan Nair, Director, VSSC, explained: "Last time we had a problem in the total management of the cryogenic fluid in the upper stage. Some anomaly was observed in terms of fuel consumption and management." The problem was analysed thoroughly by means of a series of tests in Russia and ISRO's laboratories here. "Based on these, we fine-tuned the performance of the upper (cryogenic) stage," he added.

The launch of the GSLV-D2 took place with aplomb. The 56-hour countdown was flawless. The atmosphere in the Mission Control Centre was relaxed. Ten minutes before the lift-off, the automatic launch sequence (ALS) computer took over. At the appointed time of 4-58 p.m, the vehicle rose from its launch-pad facing the Bay of Bengal.

Earlier, 4.8 seconds before lift-off, the four liquid strap-on booster stages, carrying 42 tonnes of propellants, lit up. The on-board computer checked whether the four motors had developed the needed thrust before the core solid first stage ignited. This is done because once the core stage is ignited, it is a no-retractable condition. If the four stages had not developed the necessary thrust, the computer would have aborted the flight as it did one second before lift-off on March 28, 2001. That first flight ultimately took place on April 18.

This time, all the four liquid engines developed the necessary pressure at the right time. The core first stage, powered by 138 tonnes of solid propellant, erupted 4.8 seconds after the strap-on motors were ignited.

After lift-off, the first stage burnt for 105 seconds and the strap-ons for 148 seconds, taking the vehicle to an altitude of 69 km. The second stage, with 39.3 tonnes of liquid propellants, ignited 1.6 seconds before the burnout of the last of the four strap-on stages. The second stage fired for another 140 seconds, taking the vehicle to 131 km, and its velocity increased to 5.4 km a second.

When the vehicle was at a height of 115 km and had cleared the dense atmosphere, the "payload fairing" split down its sutures and it was jettisoned into the sea. The heat shield, which goes by the new name of payload fairing, protects the satellite from getting overheated during the ascent. After the separation of the second stage 292 seconds after lift-off, the third cryogenic stage ignited.

This cryogenic stage, which carries liquid oxygen and liquid hydrogen together weighing 12 tonnes fired for 704 seconds, taking the satellite and the equipment bay (which is the "brain" of the vehicle with its electronics) to an altitude of 206 km. Then the stage injected GSAT-2 into a perfect GTO of 180 km by 36,000 km at a velocity of 10.24 km a second. All through its flight, the vehicle was guided by the inertial navigation and guidance system developed by ISRO.

Although the cryogenic stage was procured from Russia, it was an ISRO team that built the control systems, electronics and guidance for the stage. This process was as complex as building the engine.

ISRO scientists now look forward to the next PSLV launch from Sriharikota.

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