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Dish antenna being readied to track Chandrayaan

T.S. Subramanian

Photo: K. Murali Kumar

Various payloads of Chandrayaan-I being tested at the ISRO Satellite Centre in Bangalore. —

CHENNAI: As a tall crane lifts a steel plank called “counter-weight,” workers standing on the rampart of the “mount” on top of a pedestal building shout instructions on walkie-talkie to the crane operator where to lodge the counterweight on the mount. On the ground below are the “petals” which will soon be assembled into a massive dish with a diameter of 32 metres on the mount. A petal has already been hoisted on top. There is activity everywhere, with contraptions arriving and several buildings under construction. In a couple of weeks, this dish antenna will be the centrepiece of the Deep Space Network (DSN) that is fast coming up at Byalalu village, about 40 km from Bangalore.

The dish antenna will track the Indian Space Research Organisation’s Chandrayaan-I and II spacecraft to the moon, which is 3.84 lakh km away, send commands to them and receive telemetry signals including science data. The antenna will also keep a tab on the ISRO’s proposed spacecraft to Mars, six crore km away from the earth. The entire technology for the dish antenna has been indigenously developed. All mechanical systems have been designed and developed in India.

“We are on the verge of completing the installation of the 32-metre antenna,” said S.K. Shivakumar, Director, ISRO Telemetry, Tracking and Command Network (ISTRAC), Bangalore. ISTRAC is responsible for establishing the DSN at Byalalu. “We have reached the limit in the state-of-the-art technology available in 2007 for an antenna of this class. It is meant not only for one mission but for many missions into deep space that we plan in the future.” The dish alone weighs 60 tonnes. It can rotate horizontally and vertically.

A few hundred metres away is another dish antenna with an 18-metre diameter, built to ISRO specifications by Vertex RSI, a German company.

National effort

The development of the 32-metre dish antenna was a massive national effort with key contributions from the Electronics Corporation of India Limited (ECIL), Hyderabad; the Bhabha Atomic Research Centre (BARC), Trombay; ISTRAC; ISAC; and several industries.

Mr. Shivakumar said: “We chose the ECIL as the prime contractor for the development of the system. The total reflector (the 32-metre dish) was designed and developed by the ECIL. We completed the trial assembly of the dish at Hyderabad and made a good amount of measurements. After ascertaining that everything was all right, we brought it to Byalalu, re-assembled it on the ground and the final installation is going on now.”

First step

Cut back to Bangalore. In a huge ultra-clean facility with high-purity environment at the ISRO Satellite Centre (ISAC), “disassembled mode of testing” is under way on Chandrayaan-I. Spacecraft Engineers are busy scanning its payloads. In an adjacent room, women engineers are monitoring their computer consoles for results. “Chandrayaan-I is the first step for India in planetary science … Although ISRO’s earlier satellites formed its bread-and-butter missions, Chandrayaan-1 has fired us with enthusiasm because the unknown is always exciting,” said M. Annadurai, Project Director. “We are having a tight schedule. We are working overtime. Everything is on course,” he said.

Chandrayaan-I will carry 11 instruments — five from India and six from abroad. They will look for chemicals, minerals and water on the moon. Besides, the spacecraft will map the entire surface as it circles the moon at an altitude of 100 km during its two years of life.

Four of the 11 instruments have already been integrated into the spacecraft — Moon Mineralogy Mapper and Miniature Imaging Radar Instrument, both from the United States, Radiation Dose Monitor from Bulgaria and Infra-red Spectrometer from Germany. The next phase of assembly, integration and testing of instruments will begin on November 15.

Moon Impact Probe

On board Chandrayaan-I will be a Moon Impact Probe (MIP), a 20-kg instrument. Mr. Annadurai said, “On reaching the lunar orbit, we will reorient Chandrayaan-I and we will eject the MIP, which has a motor. It will fire for two seconds to reduce the MIP’s velocity to 75 km a second.” As the MIP speeds towards the moon, its video-camera will take pictures of the lunar surface. The MIPs’ altimeter will measure its instantaneous altitude from the moon’s surface. A third instrument, a mass spectrometer, will “sniff” the tenuous atmosphere above the moon to find out what it is made of. All these data will be sent to Chandrayaan-I until the MIP crashes on the moon’s surface.

If things progress as per plan, a galvanised Polar Satellite Launch Vehicle will lift off from Sriharikota on April 9, 2008 and put Chandrayaan-I into orbit.

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