The Hindu : The PSLV-Metsat launch

Online edition of India's National Newspaper
Monday, Sep 02, 2002

Opinion

Opinion - Leader Page Articles

The PSLV-Metsat launch

By N. Gopal Raj

It is only now that a separate meteorological satellite has become a viable option... This will also be the very first time that the PSLV is sued to take a satelite to geostationry tranfer orbit.

FOR NEARLY a decade, success has been the norm for satellite launches carried out from Sriharikota and it is easy to become blase about "yet another launch". But the upcoming launch of the Polar Satellite Launch Vehicle (PSLV), which is likely to happen some time in the second week of September, is particularly significant.

The PSLV will be carrying aloft the Metsat, India's first dedicated meteorological satellite. Other nations have long had such satellites. But in the 1970s when the Indian Space Research Organisations set out to convince sceptical user agencies of the advantages of satellite-based services, it became necessary to include the weather cameras as part of the Insat communication satellites. It is only now that a separate meteorological satellite has become viable.

The PSLV was designed to put remote sensing satellites into polar orbit, a path which sends the satellites in a loop close to the Earth's north and south poles. But the Metsat has to be stationed in geostationary orbit, some 36,000 km above the equator. In this orbit, the satellite matches the Earth's rotation and therefore appears stationary from the ground. A meteorological camera on such a satellite can keep constant watch over a developing weather system, such as a cyclone. The unavailability of a suitable weather camera in geostationary orbit was given as one of the reasons why the path of the `super cyclone' which struck Orissa in 1999 was not predicted accurately.

This will be the very first time that the PSLV is used to take a satellite to geostationary transfer orbit (GTO), an oval-shaped intermediate path from which the satellite will subsequently be moved to the final geostationary orbit using its own small rocket engines. Putting a satellite into GTO requires more effort from the launch vehicle. The rocket needs to impart almost 40 per cent more velocity to the satellite to put it into GTO as compared to putting it into an 800-km polar orbit. For the GTO orbit, the PSLV will be launched eastwards, taking advantage of the Earth's rotation to get an extra push.

The PSLV has been upgraded to carry the 1,050 kg Metsat. The most significant of the enhancements to this PSLV, the seventh to be launched, is the improved third stage. The new high performance stage has less inert weight and accommodates more solid propellant, making it a truly world class upper stage solid motor. If used for a polar launch, this PSLV could carry a satellite of about 1,500 kg.

But more than brute force is required. A GTO launch from Sriharikota is quite an obstacle course. Once the Bay of Bengal is crossed, there are islands and landmasses speckled all over the place. When the spent stages of the PSLV are separated and abandoned, they have to fall into empty ocean. As India would be liable for any damage caused, it cannot afford to have the spent stages fall on land or in territorial waters. It is a measure of the confidence of ISRO's launch vehicle teams that they believe that the PSLV will be able to precisely fly the chosen trajectory.

When the Insat-1 satellites were configured in the mid-1970s, ISRO made sure that user groups, such as the Department of Telecommunications, the Ministry of Information and Broadcasting and the India Meteorological Department were fully involved. At that time, when the utility of satellite services was still to be proven in India, it was difficult enough for ISRO to persuade these departments that satellites were needed at all.

In the end, the user departments agreed to jointly fund the Insat-1 satellites which became multi-purpose, with a meteorological camera included along with the conventional communications payload. The Insat-1 series were both built and launched abroad. These satellites cost about Rs. 100 crores each then.

The multipurpose configuration was retained for the Insat-2 series which were built by ISRO but launched abroad. At the time, three major options were considered, including one with separate communication and meteorological satellites. The multipurpose configuration still turned out to be technically and financially the most attractive.

Since meteorological payloads are not revenue earning and in the nature of a societal service, it would have been difficult to make out a case for a separate meteorological satellite, according to a source who was closely involved in those studies and inter-departmental negotiations. The Insat-2 satellites were one and a half times heavier than the Insat-1 satellites and had more communications capacity too. An Insat-2 satellite could cost about Rs. 130 crores to build and a further Rs. 200 crores for its launch on Europe's Ariane rocket.

The present PSLV-Metsat mission was conceived with the long-term objective of separating the meteorological segment from the existing multipurpose Insat satellite, says the ISRO Chairman, K. Kasturirangan. The considerations which led to the multipurpose configuration in the late 1970s were less applicable in today's context of increasing demand for telecommunications and broadcasting capacity. Now it was possible to think in terms of exclusive communication satellites, packed with the maximum number of transponders and designed for an operational life of 15 years, thereby providing services at competitive prices, he told The Hindu.

The meteorological segments too stands to evolve in the coming years, points out Dr. Kasturirangan. The addition of improved and more advanced sensors, which were being contemplated, would demand increased satellite resources. From that point of view also "it appears pragmatic at this point of time to go for stand-alone meteorological satellites", he added.

Other factors too appear to have contributed to ISRO's decision to separate the meteorological payload. One is the availability of India's own launch vehicles. The first Geosynchronous Satellite Launch Vehicle (GSLV), intended to put Insat satellites into GTO, was successfully launched in April 2001. The two tonne Insat-3D, a dedicated meteorological satellite with advanced sensors for climate and weather studies, is expected to be launched by the GSLV in two years' time. Now, with the PSLV, ISRO has an even cheaper option for GTO launches of one tonne class satellites. Each PSLV probably costs in the neighbourhood of Rs. 75 crores while a GSLV could cost twice as much.

The three indigenous Very High Resolution Radiometers (VHRRs), providing weather images from space, flown on Insat satellites have given trouble. Even though these meteorological cameras may not earn revenue, the 1999 Orissa cyclone showed the importance of always having an operational VHRR in space. In recent times, the Meteorological Department has been using VHRR data from Europe's Meteosat-5 satellite. The conflicting demands of increasing Insat's communications capacity in space rapidly enough and of replacing the VHRR played an important part in ISRO's decision to build the Metsat.

A Metsat can be built relatively quickly and cheaply. The present Metsat was sanctioned with a project cost of Rs. 75 crores. Unlike with communication satellites, which require complicated international coordination to avoid interference with the radio signals from other satellites, the Metsat can be placed more easily in an advantageous position in the geostationary orbit. Moreover, as the Insat satellites grow in size and carry more radio transponders which generate a good deal of heat, it is better that the VHRR, which needs to be kept cool, is carried on another satellite. The basic structure of the Metsat satellite can be used to create a small 1,000 kg class communication satellite carrying four to six transponders, observes P.S. Goel, Director of the ISRO Satellite Centre in Bangalore. Such a satellite, combined with the low cost of a PSLV launch, could provide an attractive option which ISRO could offer on the international market.

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