A remote-sensing success

In a remarkable launch, the PSLV-C5 puts in orbit the Resourcesat, the world's most sophisticated remote-sensing spacecraft.

in Sriharikota

IT was a glorious day for the Indian Space Research Organisation (ISRO) when the eighth flight of its Polar Satellite Launch Vehicle (PSLV-C5) put Resourcesat in its precise orbit of 821 kilometres above the earth on October 17. This is the seventh straight success for the PSLV. The PSLV-C5 success was all the more spectacular because the launch took place in Sriharikota in inclement weather when such missions are not normally attempted. Heavy rain, which began a few hours before the launch, persisted past the lift-off time of 10-22 a.m. But that did not affect the launch of the PSLV-C5, because it is a waterproof vehicle, built by the Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram.

While the cost of building the PSLV-C5 was Rs.80 crores, the fabrication of Resourcesat entailed Rs.150 crores. The Resourcesat, weighing 1,360 kg, is the world's most sophisticated remote-sensing spacecraft. It has a combination of the finest earth-observing cameras.

The latest PSLV success confirmed that ISRO could confidently go ahead with its moon mission, called Chandrayan-1, scheduled for 2008. The PSLV will be responsible for putting a satellite, weighing about 525 kg, in orbit about 100 km above the moon. This satellite will have sophisticated cameras on board. Chandrayan-1 will be a dedicated science mission to map in detail the moon's surface including its mineral deposits.

The PSLV's success also signalled that ISRO could go ahead with another challenging job - of building a Geo-Synchronous Satellite Launch Vehicle, called GSLV Mark III. GSLV-Mark I, with a Russian cryogenic engine, had an unalloyed success on May 8 when it put the GSAT-2 in orbit. GSLV-Mark II, with an Indian cryogenic engine, will be launched in 2004.

Seven successes in a row have proved the versatility of the PSLV. It can put satellites of different classes in various orbits - it can deploy satellites in low-earth orbits at a height of 400 km to 600 km above the earth; it can put satellites weighing up to 1,500 kg in a polar orbit at a height of more than 800 km; and it can put satellites in a geo-synchronous transfer orbit at a height of 36,000 km as it did when it deployed the weather satellite METSAT in September 2002. (METSAT was later renamed Kalpana-I in memory of Kalpana Chawla, the India-born astronaut who was killed when the U.S. space shuttle Columbia disintegrated in flight on February 1.) In short, no country has a vehicle that is as rugged, robust and reliable as the PSLV. Only the first flight of the PSLV in September 1993 was a failure; that was on account of an error in software implementation in a computer on board the vehicle.

The PSLV is 44.4 metres tall and weighs 294 tonnes. It has four stages. While its first and third stages are powered by solid propellants, its second and fourth stages use liquid fuel. It has six strap-on booster motors too, clustered around the first stage. Solid propellants fuel the strap-on motors.

RESOURCESAT is the tenth spacecraft of ISRO in the Indian Remote-sensing Satellite (IRS) series. It is the heaviest earth-observation spacecraft launched by ISRO so far. Dr. P.S. Goel, Director, ISRO Satellite Centre, Bangalore, said "the whole world is looking at this satellite" because of the kind of high-resolution imageries it would generate. It has the most sophisticated cameras on board to produce these imageries, which will be helpful in determining the health of crops, locating groundwater availability, surveying whether the spread of lakes and ponds are shrinking, assessing the severity of droughts, real-time monitoring of floods, mapping wasteland, studying the destruction of forests, detecting the death of coral reefs, delineating landslip-prone areas, and so on. "We are confident that we have produced the best satellite," Dr. Goel said.

Resourcesat will provide continuity to IRS-1C and IRS-1D, which are nearing the end of their lives. It will have a life of five years. India has the largest constellation of remote-sensing satellites in space today and they include IRS-1C, IRS-1D, IRS-P3, IRS-P4 (Oceansat) and TES (Technology Experiment Satellite). All these including Resourcesat were built at ISRO Satellite Centre, Bangalore, and their cameras fabricated at Space Applications Centre, Ahmedabad.

There is a great demand from many countries for imageries from the IRS series. Dr. Goel said: "As the market goes up, more than 30 per cent of remote-sensing data will come from IRS spacecraft. It is not the numbers that are important but the fact that we are a force to reckon with (in building remote-sensing spacecraft that produce high-resolution imageries)."

THE weather was threatening the PSLV-C5 launch. The northeast monsoon was setting in over coastal Andhra Pradesh, where the Satish Dhawan Space Centre, Sriharikota, is situated. The launch window was set between 10-22 a.m. and 10-32 a.m. on October 17. The weathermen had predicted that the full-fledged monsoon would set in by the next day. The new ISRO Chairman, G. Madhavan Nair, recalled the difficult situation that ISRO found itself in. He said: "We were virtually driven to a corner. In the last few days, our team here was analysing the pros and cons of meeting the challenge... We were cautiously approaching it." The ISRO Chairman had a word of praise for R.V. Perumal, Associate Director, VSSC. He said, " R.V. Perumal is the champion of building all-weather vehicles and he has guided teams to make the PSLV virtually water-proof."

The vehicle integration team "confirmed and guaranteed that the vehicle was rain-proof". According to VSSC Deputy Director John P. Zachariah, it was made rainproof, by providing rubber-seals to the external cut-outs (grilled windows) of the vehicle, including the umbilical cords. These cords connect the vehicle to the launch tower. They detach themselves in the final moments before lift-off.

As the PSLV-C5 stood on its launch pedestal as it rained, there was quiet confidence in the Mission Control Centre, situated several kilometres away. The countdown progressed smoothly. A sophisticated computer called Automatic Launch Sequence (ALS) scanned thousands of launch sequences in the last 10 minutes leading to the ignition of the vehicle. There was no hold at all. At 10-22 a.m., the vehicle raced majestically into the sky. But thick clouds shrouded the vehicle speeding into the horizon, much to the disappointment of lensmen.

In the Mission Control Centre, the plot boards on the banks of computer consoles showed how the vehicle hugged closely to the predicted trajectory. Its stages ignited and fell off within seconds of the appointed time. The satellite was injected into orbit at the predicted velocity, 1,082 seconds (18 minutes) after lift-off as against the targeted 1,084 seconds. Dr. B.N. Suresh, the new Director of the VSSC, said: "It was a very precise mission. Every stage performed exactly as predicted. All operations, including the ignition of the stages and their cut-off, took place within one or two seconds of the appointed time." Indeed, the second and fourth stages had some more energy left. Soon, the news came that the satellite's solar panels had been deployed.

The success was creditable because the mission was carried out by a new project team that included Mission Director N. Narayana Moorthi, Satellite Director K.S.V. Seshadri and Vehicle Director George Koshy.