On Wednesday India became the second country in the world after the United States to launch a mission to study climatic and atmospheric changes in tropical regions with the success of Indo-French tropical weather satellite Megha-Tropiques on Wednesday morning from the space launch pad here at the Sastish Dhawan Space Centre.

With the placing in orbit of four satellites, together weighing over 1000 kg, ISRO's tried and tested warhorse PSLV has crossed the half century mark. Since 1993, the various missions of PSLV had launched 48 big and small satellites. PSLV's only failure was in 1993 when the satellite could not reach the orbit.

Within seconds of blasting off from the launch pad of the Satish Dhawan Space Centre here, 80 km from Chennai, the 44 meters high and 230 tonne heavy PSLV-C18 soared with a rumbling sound and vanished into the white and grey clouds as the scientists at the ground control tracked its progress with satisfaction.

Within 25 minutes of its upward journey, the rocket planted Megha Tropiques satellite followed by SRMSAT, VesselSAT and Jugnu in the orbit.

The Indo French satellite Megha Tropiques would study climatic and atmospheric changes in tropical regions. It will look down at the earth from around 800 km low earth orbit and is expected to enable the met authorities predict weather more effectively. With its circular orbit inclined 20 degrees to the equator, it will enable climatic research and help scientists refine prediction models.

"Megha-Tropiques opens up a new era in Indo French cooperation and it would give a lot of information on tropical climate and atmospheric conditions," ISRO chairman K Radhakrishnan said minutes after declaring the PSLV C18 a grand success. "It is a truly global mission," the ISRO chairman said.

He announced two more PSLV missions - one to launch India's remote sensing microwave satellite and another one to launch an Indo-French satellite to study ocean

The French space agency, Centre National d'Etudes Spatiales (CNES), has built three instruments of Megha-Tropiques: SAPHIR, SCARAB and GPS-ROS. The fourth, MADRAS, is a joint effort of ISRO and CNES.

The only other mission to measure tropical rainfall was launched in 1997 which was jointly conducted by NASA and the Japan Aerospace Exploration Agency (JAXA) designed to monitor and study tropical rainfall --was launched Nov 27, 1997.

Apart from Megha-Tropiques, the three small satellites that were ferried by the PSLV-C18 are the 10.9-kg SRMSAT built by the students of SRM University near Chennai; the 3-kg remote sensing satellite Jugnu from the Indian Institute of Technology- Kanpur (IIT-K) and the 28.7-kg VesselSat from LuxSpace of Luxembourg to locate ships on high seas.

On the other hand the Rs 1.1 crore SRMSAT using a grating spectrometer, will monitor greenhouse gases, carbon dioxide and water vapour in the atmosphere.

The Jugnu satellite built by IIT-Kanpur is intended to prove the indigenously developed camera system for imaging the earth in the near infrared region and test image processing algorithms, to evaluate global positioning satellite (GPS) receiver for its use in satellite navigation.

The rocket's fourth payload-VesselSat- is developed and built by LuxSpace of Luxembourg will be used to detect ships at sea automatically from the signals they emit in the regions covered by it. The satellite carries two signal receivers called Automatic Identification System for ships (AIS).

For ISRO, this is the third successful rocket launch this year from India. In April, the agency successfully launched remote sensing satellite Resourcesat-2 and two others. In July, communication satellite GSAT-12 was put in orbit.