Versatile vehicle

The Polar Satellite Launch Vehicle puts a meteorological satellite in geosynchronous transfer orbit. ISRO thus sets another landmark.

INDIA can put any type of satellite in any orbit using its own launch vehicle. This was the message that rang out when the Indian Space Research Organisation's (ISRO) Polar Satellite Launch Vehicle (PSLV-C4) rose majestically from its launchpad at Sriharikota in Andhra Pradesh on September 12, 2002 and put the 1,060-kg METSAT, a meteorological satellite, in orbit. This is the first time that a PSLV has been used to put a satellite in geosynchronous transfer orbit (GTO) 36,000 km above the earth. This, the sixth successful flight in a row of the PSLV, confirmed India as the sixth country with an assured access to space on its own.

S. Ramakrishnan, Project Director, PSLV-C4, told Frontline after the successful flight: ``We are self-reliant. We can make our own satellites, our own launch vehicles. We can put any type of satellite in any orbit with our own launch vehicle. We have demonstrated this over the last several years.'' All this has been achieved in less than three decades, ISRO having started from scratch in 1969 to launch a `pencil rocket' with a few hundred grams of propellants, from the compound of a church at Thumba, near Thiruvananthapuram.

The PSLV is 44.4 m tall and weighs 295 tonnes. The Vikram Sarabhai Space Centre (VSSC) near Thiruvananthapuram built the PSLV, and the ISRO Satellite Centre in Bangalore fabricated METSAT, in about two years. The PSLV, a unique vehicle, and ISRO's workhorse, can put a satellite weighing about three tonnes in low earth orbit (LEO), at a height of 400 to 600 km. It can deploy satellites weighing up to 1,500 kg in polar sun synchronous orbit 750 km above the earth, as it has done in the case of Indian Remote-Sensing Satellites (IRS). The versatile, flexible vehicle can handle a LEO, a polar orbit and a GTO.

Dr. K. Kasturirangan, Chairman, ISRO, said: ``We can do three broad classes of missions (with the PSLV)''. It can put remote-sensing satellites in polar orbit. It can deploy meteorological/astronomical satellites in GTO. It can do multiple missions as it has demonstrated twice. On May 26, 1999, it orbited three satellites ISRO's IRS-P4, Germany's TUBSAT, and South Korea's KITSAT. On October 22, 2001, it launched the Technology Experiment Satellite (TES) of ISRO, BIRD of Germany and PROBA of Belgium. The PSLV is set to do more complex, multiple missions. It can also launch small communication satellites of 1,250 kg class in GTO.

The GSLV has created a niche market for itself, for there is no other vehicle to put satellites weighing between 1,000 kg to 1,250 kg in GTO. A Russian vehicle called Rockot, which can be a matcher, is yet to become operational. In the coming years, ISRO expects more customers to use the PSLV, which cost Rs.80 crores to build, to launch their spacecraft.

The PSLV is a four-stage vehicle that uses solid and liquid propulsion systems alternately. The first stage, which carries 138 tonnes of propellants, is the third biggest solid propellant booster after the U.S.' space shuttle and Arianespace's Ariane vehicle. Six strap-on motors augment the first-stage thrust. The second stage uses 40 tonnes of liquid propellants. The third and fourth stages are powered by solid and liquid propellants respectively. On top of the fourth stage stays METSAT.

Important changes were made in the vehicle for the GTO mission. The third stage motor was made more powerful compared to the October 2001 flight. The amount of liquid propellants in the fourth stage went up from two tonnes to 2.5 tonnes. Besides, the PSLV-C4 employed a carbon composite payload adopter. All this increased the payload capability of PSLV-C4 by 70 kg.

AN atmosphere of quiet confidence prevailed at the Mission Control Centre at Sriharikota on D-day. The launch campaign for the PSLV-C4 had been under way for a few weeks. It was a hot day. The launch window had been set between 3.39 p.m. and 4.05 p.m. The countdown was smooth. However, at T-minus 16 minutes (that is, 16 minutes before the scheduled launch at 3.39 p.m.), there was a hold as a console did not give the clearance for the go-ahead. After certain navigation parameters were loaded into the computer, the check-back was not satisfactory. After three rounds of checking up, the hold was released and the countdown resumed.

At 3.53 p.m., as the cords connecting the PSLV to the launch tower peeled away, the vehicle rose into the air. Explosions of energy sent sound and vibrations rumbling across the island.

The ignition and jettisoning of the four stages including the six strap-on motors took place smoothly. After the fourth stage ignited about 665 seconds after lift-off, there was a coasting period for about 514 seconds. This was a crucial phase. At 1,211 seconds (about 20 minutes), the fourth stage injected METSAT at a height of 400 km and fell away. The velocity imparted to the satellite as the separation took place was about 10 km a second. With this velocity, it reached 36,000 km above the earth. About six seconds after separation, the solar array, that provides 550 watts of power to the satellite, was deployed.

Dr. Kasturirangan, addressing his ISRO colleagues, said: ``You have done it again. It is a wonderful mission. It is no longer polar orbit but the GTO. This was your idea, resourcefulness, effort and achievement. The spacecraft is in safe, closely intended orbit..."

The successful launch, he said, was ``a humble tribute to that great personality, Prof. Satish Dhawan''. On September 5, Prime Minister A.B. Vajpayee had renamed the SHAR Centre the Satish Dhawan Space Centre, SHAR. Prof. Dhawan, who had made multi-dimensional contributions to ISRO, was its Chairman from 1972 to 1984. He died in January 2002.

PRELIMINARY data indicated that METSAT's apogee was 35,000 km and perigee 215 km, which were within the mission objectives. On September 13 and 14, METSAT's elliptical GTO was circularised into a geosynchronous orbit of 36,000 km by firing the liquid apogee motor on board. This was done by giving commands from the Master Control Facility at Hassan, Karnataka. The satellite is expected to become operational by the end of September.

According to V.K. Kaila, Project Director, METSAT, the satellite will improve meteorological services in the country. This is the first time that ISRO is launching a dedicated weather-monitoring satellite. Till now the meteorological component formed part of the multipurpose INSATs. METSAT has a Very High Resolution Radiometer for imaging the earth in visible, infra-red and water vapour bands. It will give 2 km resolution. Infra-red pictures have a resolution of 8 km. METSAT will give pictures of clouds and warn about approaching cyclones. Its images can help in mapping the water vapour content in the atmosphere. METSAT has a data relay transponder which will collect weather data from various unattended platforms in the country and relay them to a central station in New Delhi.

METSAT was launched in GTO, instead of LEO, because at that height it could give pictures of the same spot on the globe once every 30 minutes. Thus, changes in the movement of clouds and cyclones could be monitored.

S.V. Sharma, Vehicle Director for the PSLV-C4 flight, said: ``Its performance has been pleasing. From 1,060 kg in its maiden flight to GTO, we can improve it to 1,200 kg with minor changes.''

WHAT is behind the six successful flights of the PSLV in a row? The real space career of ISRO began with the launching of the SLV-3 in 1979 from Sriharikota. There were flights in 1980, 1981 and 1983 also. They put in orbit Rohini satellites weighing between 35 kg and 45 kg. The SLVs were followed by the Augmented SLVs, or ASLVs. There were ASLV flights in 1987, 1988, 1992 and 1994. The first two were failures. The third and the fourth orbited Stretched Rohini satellites.

The original aim of the PSLV project was to orbit IRSs in polar sun synchronous orbit. IRS-1A, 1B and 1C were launched by Russian vehicles Vostoks and Molniya. The Russian launch charges, which were reasonable at Rs.60 crores, later shot up.

After being initiated in 1982, it took ten years for the PSLV project to reach fruition. Inputs from the SLV-3 and ASLV missions were useful in designing the PSLV. Thus, the PSLV acquired a robust design. A mock-up was designed. Then structural characterisations were made. Facilities for fabricating the propellants were built. A launch pad to integrate vertically the PSLV was constructed at SHAR.

The first PSLV flight on September 20, 1993 failed because of a software error in the pitch control loop of the on-board guidance and control processor. Ramakrishnan, who has been the Project Director of the three latest PSLV flights, said: ``But the vehicle worked very well. We were happy that the vehicle's design was robust.''

While the SLVs weighed about 17 tonnes, the ASLVs weighed about 40 tonnes. The first PSLV weighed around 240 tonnes at lift-off. The diameter of the vehicle also increased from one metre for the SLV-3 series to 3 metres for the PSLV.

A launch vehicle engineer said that the very first flight of the PSLV carried a satellite that weighed 846 kg. In its present configuration, it could carry a 1,450 kg satellite in polar orbit. From 846 kg to 1,450 kg in seven flights.

After the failure of the first PSLV, the subsequent six flights including the latest were hugely successful because of the maturity of design, detailed engineering, documentation, expertise in hardware realisation and so forth. ISRO has today established itself as a reliable launch vehicle provider.