FIRST INDIAN WEATHER SATELLITE GOES INTO THE SKY

T V Padma *

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The Indian space department has witnessed a string of successes in the last three years. With METSAT, ISRO toasts its second success in 2002, a year that began on a good note for the space department when it launched its third-generation INSAT-3C satellite from Kourou in French Guyana. The previous year, 2001 too was marked by launches that are major landmarks in the space department’s history. On April 18, ISRO successfully launched the first developmental Geosynchronous Satellite Launch Vehicle (GSLV-D1) that carried a 1.5-ton G-SAT on board and demonstrated ISRO’s capability to make indigenous rockets that can carry INSAT-class satellites into space. Later, on October 22, ISRO had a successful three-in-one launch with its PSLV-C3 that carried three satellites into space. These were the Technology Experiment Satellite (TES) of India, BIRD of Germany and PROBA of Belgium. In 2000, ISRO launched INSAT-3B, the first satellite in the INSAT-3 series, aboard Ariane rocket from Korou in French Guyana on March 22. And now is the turn of the first Indian weather satellite METSAT to prove the country’s excellence in the field.

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.

Improved Weather Studies

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 has 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.

Improved PSLV

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-metre 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.

Background

Indian space scientists have traveled a long way since the beginning of their space trek that began four decades ago. The country’s space programme has been well orchestrated since its inception. ISRO made a modest beginning in 1963 when it launched a small sounding rocket from Thumba near Thiruvananthapuram. It then went through an experimental and demonstration phase in the 70s when India conducted large-scale experiments like Satellite Instructional Television Experiment (SITE) and Satellite Telecommunication Experiments Project (STEP). Simultaneously it built experimental rockets like Aryabhatta, and Bhaskara.

These small Indian satellites and rockets were the forerunners of the more powerful, sophisticated and complex satellites and satellite launch vehicles or rockets that were commissioned in the 80s and today form part of the ambitious Indian space programme.

The IRS series of satellites are considered the world’s best civilian remote sensing satellites. Remote sensing data from these satellites is being used for estimating agricultural crop acreage and yields, ground water location, forest cover survey, wasteland mapping for possible reclamation, snow melt run-off estimates, mineral prospecting, identification of potential fishing zones, urban planning and environment monitoring. Four IRS spacecraft – IRS1C and IRS1D as well as two experimental ones IRS-P3 and IRS-P4 – now find the pride of place in the sky.

India’s capability to build and operate world-class remote sensing world-class satellites has brought in commercial benefits for it. Data from IRS satellites is now being sold to several countries, including US, European nations, Japan, Korea, Thailand and Middle East countries.

The INSAT system is one of the largest domestic communications satellite systems in the world. The country has had three generations of INSAT satellites, of which two – INSAT2E and INSAT3B – are now in operation. Since it was first commissioned in 1983, the INSAT system has vastly improved telecommunications, television broadcasting, radio networking, meteorology and disaster management services.

INSAT satellites have also helped harness space technology for grass root level applications – for example, the Jhabua Development Communication Project (JDCP) that started in November 1996, the extensive Training and Development Communication Channel (TDCC) of INSAT, and the Vidya Vahini programme for education and training in remote rural areas with INSAT3B.

India matched its strides in satellite technology with similar advances in satellite launch vehicle technology. The sounding rocket from Thumba helped ISRO scientists design the Satellite Launch Vehicle (SLV) to place small 40-kg satellites in orbit. This was followed by the Augmented Satellite Launch Vehicle (ASLV) to launch 150-kg satellites into space. ASLV paved the way for the four-stage Polar Satellite Launch Vehicle (PSLV) to launch 1000-kg IRS satellites, and the latest GSLV to launch 2000-kg INSAT class satellites.