10 eyes in the sky give India space edge

With the successful launch of Cartosat-2B on Monday, India has reached a `critical constellation' of 10 active remote sensing satellites in space, which gives it a clear edge in the region for monitoring borders and movements across them.

While mapping and infrastructure development are seen as primary applications of a remote sensing satellite, its use in spying is often underplayed. A combination of four Cartosats (1,2,2A and 2B) hovering 630 km above earth allows India to keep areas under close and prolonged surveillance. Multiple satellites ensure that a particular geographical area can be `revisited' every 48 hours.

Three of the cartosats now in orbit have a spatial resolution of less than one metre (0.8 m for Cartosat-2B), which means that they can observe and photograph objects smaller than a car. Cartosat-2B's steerability of 26 degrees allows it to stay focused on the object for a longer duration while on the move as compared to the other remote sensing satellites, which have a range of applications.

"The latest addition enhances our revisit capability and ensures continuity of services. The revisit capability of one such satellite is about 10 days, but with four such satellites, we can revisit an area almost every other day. With Cartosat-1 (launched in 2005) likely to complete its mission in another year, Cartosat-2B ensures there is no break in services,'' Isro spokesperson S Satish told TOI.

China has launched nine remote sensing satellites in the `Yaogan' series since 2006 using its Long March range of rockets. With the addition of Cartosat-2B to the constellation, India has matched if not outdone China in remote sensing. Pakistan, meanwhile, is still working on its first remote sensing satellite PRSSS, which it plans to launch next year with China's help.

Asked specifically about Cartosat-2B's applications in surveillance, Isro chairman K Radhakrishnan said: "Depending on the user's imagination, it can be used for surveillance and intelligence (gathering).''

India was working on its indigenous radar imaging satellite Risat-1, an all-weather satellite which uses a synthetic aperture radar (SAR) and multiple antennas to see through clouds and darkness, when the 2008 Mumbai attacks happened. This prompted the nation to speed up and launch the Israeli Risat-2 satellite with SAR on April 20, 2009. Risat-1 is scheduled for launch late this year.

Cartosats use panchromatic cameras to take black and white pictures of earth. While cartosat-1 weighed 1560 kg and had a spatial resolution of 2.5 metres and a swathe of 30 km, the later versions had a finer spatial resolution of less than a metre and a swathe of 9.6 km.

Going around in a 630-km high polar sun synchronous orbit, Cartosat-2B carries a 64GB solid state recorder which stores images which can be later transmitted to the ground station when the satellite comes within the visibility range. The Spacecraft Control Centre, Bangalore will be continuously monitoring the satellite's health with the help of the ISTRAC network of ground stations at Bangalore, Lucknow, Mauritius, Biak in Indonesia, Svalbard in Norway and Troll in Antarctica.