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METSAT / Kalpana

METSAT (renamed as Kalpana - 1 on February 5, 2003 after the Indian born American Astronaut Dr. Kalpana Chawla, who died on February 1, 2003 in the US Space Shuttle Columbia disaster) is the first in the series of exclusive meteorological satellites built by ISRO. With the launch of the first Indian weather satellite METSAT from the island space port of Sriharikota in Andhra Pradesh on September 12, the Indian space department has once again demonstrated its confidence to experiment with and diversify its technological prowess.

India’s Polar Satellite Launch Vehicle PSLV-C4 blasted off into space from Sriharikota, carrying a 1060-kg METSAT that will provide weather images and data from the same place every half an hour. This is ISRO’s second success story for the year – earlier on January 24, INSAT-3C was launched by Europe’s Ariane rocket from Kourou in French Guyana.

The launch marks two new features in the Indian Space Research Organisation (ISRO’s) programme. The Polar Satellite Launch Vehicle that shot into air from Sriharokota to lob METSAT into orbit is an improved and stronger version of earlier PSLVs. And for the first time, space scientists have built an indigenous weather satellite.

Weather studies using satellite technology is not new to India. What is new is an exclusive weather satellite. In the past three decades of Indian satellite programme, special cameras to study cloud and air movements, water vapour density and other weather indicators were carried on-board the multipurpose INSAT satellites that were first designed in the 1970s. In addition to imaging cameras, INSAT spacecraft also carried transponders for telecommunications and broadcasting services.

But in recent times, the demand for telecommunication services from INSAT satellites had spiraled, necessitating more telecom transponders on the new-generation INSATs and making them heavier in the process. Neither could space scientists compromise on the crucial weather transponders. Even though the meteorological or weather transponders do not earn revenue like their telecom and broadcasting counterparts, they are none-the-less crucial – as was demonstrated by the devastating super cyclone that hit the Orissa coast in 1999 and whose path was possible to predict with a satellite.

It is for this reason that the Indian space department decided to de-link the various functions of INSAT satellites. ISRO had already designed INSAT satellites exclusively for telecom services and are working on state-of-the-art telecom satellites packed with maximum transponders and with a design life of 15 years.

Simultaneously, ISRO is going in for exclusive weather satellites with advanced sensors. The first in the series is the one-ton METSAT. ISRO scientists are now working on a heavier and advanced two-ton INSAT-3D that will also be dedicated to weather studies and will be launched by the indigenous Geosynchronous Satellite Launch vehicle.

For weather observation studies, METSAT carries a Very High Resolution Radiometer (VHRR) that can image the Earth in the visible, thermal infrared and vapour bands. In addition, it carries a Data Relay Transponder (DRT) to collect data from meteorological platforms spread all over the country and relay to the Meteorological Utilisation Centre in New Delhi.

In its life span of seven years, METSAT will beam pictures of approaching cyclones and moving clouds, and data on water vapour content in the atmosphere. The satellite will give pictures of 2-kms resolution around the globe. In its geostationary transfer orbit, METSAT will give pictures of the same place and the same region once every half an hour, helping in better observation of clouds and cyclones.

METSAT is light weight as it has been built with carbon reinforced plastic fibre instead of aluminium. It has also done away with the solar boom and sail present on INSAT spacecraft for balance, and instead uses magnetic torque to take care of imbalances.

For METSAT launch, ISRO has experimented with a new idea – use a PSLV to put a satellite into a geostationary orbit. The six PSLVs launched so far have put satellites weighing up to one ton into a sun-synchronous polar orbit where the satellite circles from one pole to the other and back. The polar orbit is about 860 kms above the earth. This is the first time PSLV has been designed to put a satellite into a geosynchronous transfer orbit. This orbit is egg-shaped, with its perigee or nearest distance from the earth at 250 kms and apogee or farthest distance from earth at 36,000 kms, and is at an angle of 18 degrees to the Equator.

For the METSAT launch, ISRO scientists upgraded the 44-meter tall PSLV. The PSLV is a four-stage rocket, with each stage separating sequentially after lift-off. The first and third stages have solid fuelled motors, while the second and fourth stages have liquid fuelled motors. The new PSLV-C4 has been fitted with a new high-performance solid-fuelled third stage engine that carries more fuel. In addition, the fourth liquid stage will also have more fuel — 2.5 tons instead of 2 tons.