Isro launches third radar imaging satellite Risat-2B

Chennai: A decade after Indian Space Research Organisation (Isro) placed the first Risat into orbit, the space agency started expansion of radar imaging satellites’ fleet in space with the textbook launch of Risat-2B, third in the series, onboard a PSLV early on Wednesday. With the capability to identify and capture images of objects on the ground on a centimetre scale precision in all-weather conditions through day and night, Wednesday’s launch of the radar imaging earth observation satellite comes as a shot in the arm for reconnaissance both on the land and at sea and for disaster management.
At 5.30am, PSLV-C46 lifted off with the 615kg Risat-2B from the first launch pad at Satish Dhawan Space Centre, Sriharikota.It was PSLV’s 48th flight and 14th with ‘core-alone’ configuration. “We achieved a precise orbit of 555km and an inclination of 37 degrees,” said Isro chairman K Sivan, in his post-launch address from the mission control centre at Sriharikota. “With this launch, PSLV has lofted 50 tonnes into space by placing 354 satellites into orbit, including national, foreign and student satellites.”
The rocket also carried a microelectrocmechanical systems (MEMS)-based inertial navigation system and an indigenous Vikram processor, which, Vikram Sarabhai Space Centre (VSSC) director S Somanath said, will be used in all future missions.
The satellite carried an indigenous 3.6m radial rib unfurlable and deployable antenna developed in a record time of 13 months, instead of an imported antenna that would have taken about 3-4 years, a release from Isro said. The antenna was folded and stowed during the launch and was unfurled and deployed in orbit in 7 mins and 20 seconds. “Development of light weight structure, hinge mechanism, design of newer mesh, actuators, etc. was one of the challenges involved in the realization of this antenna. They require very high level of expertise han-dling space-based antenna sy-stem, excellent workmanship and building redundancy, apa-rt from managing its in-orbit deployment,” the release said.
With its X-band synthetic aperture radar (SAR), experts said Risat-2B, however, has lower penetration through cloud cover and cannot penetrate through the ground. Radar satellites illuminate the ground with own microwave radiation and identify, differentiate and capture images during night – a capability that is not present in optical imaging satellites or regular remote sensing satellites.
“Airport radars use L and S-Band, which have higher penetration through cloud and fog, but need much larger antenna than X-band. X-band radar has all day/night imaging on ground and an all-wea-ther capability except in very heavy cloud and fog. It can be used for civil and military purposes of planning and tracking,” said Prof Uday K Khankhoje, department of electrical engineering, Indian Institute of Technology, Madras.
With plans to launch at least four more in the Risat series in the next one year, the constellation will be a boost for border and inland surveillance, agriculture, forestry and disaster management.
Risat-2 was the first to be launched (on April 20, 2009) after Isro prioritized its launch post-2008 Mumbai terror attack. The radar carried an Israeli-made X-band SAR sensor. Subsequently, Risat-1 launched on April 26, 2012, carried an indigenously developed radar. Both the satellites had a five-year mission life.