Flying high

The launch of the IRS-1D with the PSLV-C1 was a significant event despite a minor snag; for the first time an Indian-made launch vehicle has launched an operational satellite, also made in India, from Indian soil.

T.S. SUBRAMANIAN

Even as we go into space, we keep our feet on the ground. - Dr. K. Kasturirangan, Chairman, Indian Space Research Organisation (ISRO).

DESPITE the minor snag in the launch of the 1,200-kg Indian Remote-sensing Satellite (IRS-1D) with the Polar Satellite Launch Vehicle (PSLV-C1) from Sriharikota on September 29, ISRO scientists are confident that the mission's objectives will be achieved. A minor leak of helium gas from one of the components in the fourth stage of the vehicle led to "a little less than the required velocity" being imparted to the satellite which consequently went into a lower orbit. ISRO scientists began quickly to deal with the problem and their efforts to raise the perigee of the spacecraft have begun to take effect.

With the completion of this launch, ISRO is planning to fly higher into space. In about a year, the colossal Geosynchronous Satellite Launch Vehicle (GSLV), about 51 metres tall and weighing 402 tonnes, will lift off from Sriharikota to deploy a 2,500-kg communication satellite into orbit. The GSLV will use cryogenic propellants in its third upper stage. (Liquid hydrogen and liquid oxygen are cryogenic propellants). According to Dr. S. Vasantha, SHAR Director, facilities for storing cryogenic fluids have been built at SHAR and 10 to 15 km of pipelines have been laid to ferry the fluids to the GSLV on its launch pad. The Mobile Service Tower (MST), where the PSLV was integrated vertically, has also been modified to assemble the GSLV.

According to Dr. K. Kasturirangan, there were plans to build a second launching pad, costing Rs. 300 crores, at SHAR to accommodate the more advanced versions of the GSLV. While the initial flights of the GSLV will be powered by a Russian cryogenic engine, subsequent flights will use indigenous cryogenic motors. The first test of the indigenous engine is to take place next year.

The September 29 launch represented total technological self-reliance. This was the first time that an Indian-made launch vehicle launched an operational remote-sensing satellite, also made in India, from Indian soil. The two PSLVs that lifted off from SHAR in October 1994 and March 1996 were developmental flights that launched experimental IRS-P2 and P3 satellites. The IRS-1A, 1B and 1C, built at the ISRO Satellite Centre, Bangalore, were put into orbit by Russian vehicles from the Baikonur cosmodrome. As PSLV-C1 Mission Director S. Ramakrishnan put it, "With this launch, we do not have to depend any more on foreign agencies." He said: "We have our own satellite and we have our own launch vehicles."

While the PSLV put into orbit a 922-kg spacecraft in 1996, the latest satellite weighed 1,200 kg. This was achieved by making improvements in the various stages of the vehicle. Dr. Kasturirangan said, "This is a unique intermediate capability vehicle, unlike Ariane 4 and 5, which are at the higher end of the mass capability." According to him, not many vehicles exist of the intermediate class.

The massive four-stage PSLV-C1, standing 44 metres tall and weighing 294 tonnes, lifted off from the launch pad facing the beach and raced into the sky. The first stage along with four strap-on motors ignited and the remaining two strap-ons burst with life about 25 seconds later. The strap-ons and the first stage separated and fell into the sea. The second stage ignited. The heat-shield, which protects the satellite during the vehicle's ascent through hostile atmosphere, split down its seams and fell away at an altitude of 128 km. The second stage separation and third stage ignition took place simultaneously at 282 seconds after the lift-off. The third stage jettisoned at 501 seconds. Then there was a long coasting phase during which the fourth stage travelled on its own before erupting with life at 602 seconds. The fourth stage fell away at 1,037 seconds and the IRS-1D was injected into orbit.

Prime Minister I.K. Gujral, who watched the launch from the Mission Control Centre, warmly hugged Dr. Kasturirangan and later told presspersons: "It was a great moment for the country." "We have broken new barriers in science and technology," he said and added, "We have done it ourselves in both constructing a rocket and launching a satellite." He congratulated ISRO's scientists on doing "the country proud". He said the success was a manifestation of their team effort. "We have turned every challenge into an opportunity," he said. "Ultimately, what is extremely important in science and technology is self-reliance." Dr. Kasturirangan described the satellite as "one of the best civilian remote-sensing satellites in the world."

R. Aravamudhan, Director, ISRO Satellite Centre, Bangalore, told Frontline that he was "thrilled". According to him, the ignition, performance and separation of the stages "were wonderful". Describing the launch as a "farewell gift" (he is retiring after 37 years in ISRO), he said that he was involved in the building of rockets at the Vikram Sarabhai Space Centre (VSSC); was Director of SHAR from where the satellites are launched; and is now where the satellites are built. "So all our efforts have fructified."

While the satellite should have reached a circular orbit at a height of 817 km, a leak of helium gas from one of the components in the fourth stage made it an elliptical orbit with an apogee of 817 km and a perigee of 300 km. The fourth stage should inject the satellite into orbit at a velocity of 7.46 km per second - 26,856 km an hour. But the velocity achieved was 7.33 km per second. The shortfall of 130 metres per second made all the difference and the satellite was injected into a lower orbit.

An ISRO scientist explained, "When we fire the fourth stage engine, we have to apply pressure and expel the liquid fuel at a given rate through a swivelling nozzle. To do this, we use helium stored in bottles. The pressure with which the liquid was expelled was not enough. It was burning all right but it produced a lower thrust. So it could not produce enough velocity and the satellite went into lower orbit."

The satellite has on board 85 kg of hydrazine fuel in small rockets called thrusters. The thrusters are fired for orienting the spacecraft properly. The 85 kg of hydrazine is more than is actually needed to take care of the "dispersion" during the injection of the satellite into orbit. Because of the extra fuel, earlier IRS have exceeded their lifespan. Although the projected life-span of each of Indian remote-sensing satellite is three years, the satellites have lasted six to seven years because of the extra fuel they carry on board. The IRS-1A, launched in March 1988, served for more than eight years. The IRS-1B, deployed in August, 1991, is still going strong. The IRS-1C, launched in December 1995, the IRS-P2 and the IRS-P3, are in fine fettle. According to ISRO scientists, the IRS-1D may not last for as long as the most successful of its predecessors did, because the hydrazine fuel is being used up in order to raise the perigee. They are, however, confident that the satellite will last for three years.

ISRO scientists fired the hydrazine thrusters and raised IRS-1D's perigee to 500 km. One of the scientists said, "We have to raise the perigee to 550 km to get into a polar sun synchronous orbit." (Later they achieved this and the satellite started beaming pictures.) He said that the satellite would live for two and a half to three years. "It will be in an elliptical orbit, but it will meet the mission objectives."

What are the mission's objectives? The imagery beamed down by the IRS constellation has been used to keep a watch on the destruction of forests, prospect for minerals, discover deposits of oil and gas, forecast yields of crops, identify potential fishing grounds in the sea, predict crops blights, locate groundwater and so on. The imagery has been used to map different categories of wasteland and assess wasteland that can be reclaimed. All this is done with the help of cameras on board the satellite. The IRS-1D, which is a clone of the IRS-1C, has three cameras.

Locating groundwater was among the early successful applications of the IRS series. The success rate of finding water by means of IRS was 95 per cent compared to the 45 per cent success rate achieved through conventional methods. Remote-sensing imagery has also been used to study coconut wilt disease in Kerala and the health of orange plantations near Nagpur, to re-align a ring road to Bangalore and to detect illegal ganja plantations in Madhya Pradesh.

The PSLV-C1 was able to launch a 1,200-kg satellite into orbit because of the improvements in various stages of the vehicle. The first booster stage had 139 tonnes of solid propellants while the 1996 flight had 128 tonnes of propellants. The second stage had 40 tonnes of liquid propellants compared to 37.5 tonnes in the previous vehicle. This time, four strap-on motors lit up on the ground and two in the air, the reverse of the earlier sequence of two on the ground and four in the air. This gave an additional 60 kg payload capability to the satellite. Besides, according to G.K. Mani, Manager, Liquid Stages Integration, the helium gas in the fourth stage was stored in bottles made of lighter kevlar fibre and not of titanium as in previous missions. This reduced the weight by 24 kg, which translated into 24 kg of extra payload for the satellite. There were also improvements in the avionics bay that forms the "brain" of the vehicle.

The success of the PSLV-C1 flight has opened up large commercial opportunities for ISRO. According to Dr. Kasturirangan, "With two or three more launches in the coming years, we should be able to establish good credentials with respect to international customers." ISRO has already signed a commercial agreement to fly a South Korean 100-kg remote-sensing satellite piggyback on the IRS-P4 satellite in July next year. There have also been inquiries for satellite construction from some countries.

Various countries have expressed an interest in receiving data from the IRS. ISRO had signed an agreement with SSI-EOSAT (Space Systems Imaging-Earth Observation Satellite Corporation of the U.S.) for sharing data from the IRS constellation. Other potential customers include Japan, Australia and South Africa. ISRO has forged a strategic partnership with Hughes Space Communication to supply some components for satellite systems. ISRO also provides tracking and telemetry support and inertial orbit checkout of satellites on a commercial basis for some companies.

ISRO is planning an ambitious series in the coming years - launching five IRS satellites using PSLVs from SHAR. Several GSLV flights using the Russian cryogenic stages and indigenously developed cryogenic motors are also planned. Dr. Vasantha said, "We expect to have two or three launches every year in the coming years." SHAR is all set to become a busy spaceport.