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IDSN tracks Japanese lunar mission

Bangalore: The impressive communications infrastructure called the Indian Deep Space Network (IDSN), set up by the Indian Space Research Organisation to transmit and receive signals from Chandrayaan 1, successfully tracked last week the Japanese lunar mission SELENE (Koguya), launched in 2007 and now orbiting the moon.

“We have been able to establish downlink with the spacecraft with the help of JAXA (Japan Aerospace Exploration Agency),” S. K. Shiva Kumar, Director, ISRO Telemetry Tracking and Command (ISTRAC), told The Hindu.

“We have also been able to bring uplink fairly quickly, establish contact with the spacecraft and track the spacecraft successfully. That has given us ample confidence. If you have tracked a similar object closer to the moon and have been able to establish links with it with good margins, to that extent your comfort level is high. You don’t have to worry about our capability to do [it] with Chandrayaan,” he said.

The IDSN has been set up at Byalalu, a village 40 km from Bangalore. It is an important and critical element of Chandrayaan, expected to be launched on October 22, as it is the constant communication link to the lunar satellite from the ground. It will be used for tracking as well as for orbit control and housekeeping operations for the entire duration of the moon mission of about two years.

Doing this for a deep space mission such as the moon mission is a different ball game altogether as compared to the satellite missions that ISRO had undertaken hitherto, which included Low Earth Orbit (LEO) remote sensing IRS system of satellites and geostationary communication INSAT satellites. Missions that go beyond a distance of 1,00,000 km from the earth are usually termed as deep space missions.

The IDSN comprises a 32-metre antenna designed and built indigenously and an 18-metre antenna built by a German agency to ISRO’s specifications. As the launch of Chandrayaan approaches, the natural question is how do we know that DSN-32 will perform as desired, given that ISRO has had no earlier experience in deep space missions? How is DSN-32 calibrated to say with confidence that Chandrayaan will be accurately tracked throughout its lifetime? The IDSN will take over the tracking of Chandrayaan 17 minutes after its launch from the Satish Dhawan Space Launch Centre at Sriharikota, when the satellite would have separated from the launch vehicle.

While, in principle, it would suffice for the IDSN to take over after the lunar satellite reaches the Earth Transfer Orbit (ETO) of 1,00,000-km apogee, being the first deep space mission, the IDSN plans to track in parallel beyond the first ETO apogee of 22,000 km itself, according to Dr. Shiva Kumar.

“When Chandrayaan goes near the moon, we will be there to track it,” Dr. Kumar said. In addition, beginning this week, DSN-32 will be put into calibration and test mode with another deep space probe of the European Space Agency (ESA) called ROSETTA, a probe launched in 2004 with the objective of landing on the Comet 67P/Churyumov-Gerasimenkoin 2014.

When a link with ROSETTA would be established, DSN-32 would have truly proved itself as the real deep space tracking system. In addition, the IDSN is being put to regularly track radio stars. “We have been tracking Cygnus, Cassiopeia (supernova remnant stars) and, of course, sun and moon which are all good radio sources in their own right. We have been able to obtain signals from them and track them,” Dr. Kumar said. “This has also given us ample experience… we now know how to maximise our signals,” he pointed out.

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