On April 26, 2012 India's Radar Imaging Satellite (RISAT-1) will be launched from the spaceport at Sriharikota. The 4-stages of the PSLV-XL (Polar Satellite Launch Vehicle – Extra Large) have been piled up.
- Essentially a remote-sensing satellite.
- ISRO’s first radar-imaging satellite.
- Weighs 1858 kg
- ISRO’s heaviest remote-sensing satellite.
- Heaviest satellite to be put in orbit by the PSLV.
- RISATs uses Synthetic Aperture Radar (SAR) and the big benefit of RISATs is that it can take pictures of the earth at all times, through rain, sun, clouds, fog and cyclones.
- A powerful PSLV-XL is being used to put RISAT-1 in polar orbit at an altitude of 480 km. The satellite's propulsion system will then be used to take it to the final orbit at an altitude of 536 km.
- Life-span is 5years.
RISAT-1 (1858 kg) is the heaviest satellite to be put in orbit by the PSLV. The rocket is called PSLV-XL (XL stands for “extra-large”) because it uses 6 more powerful strap-on motors than those used in the standard PSLV version. If the normal PSLV version's six strap-on motors each use nine tonnes of solid propellants, each of them in the PSLV-XL use 12 tonnes of propellants.
This is the third time the ISRO is using a PSLV-XL version with the first one used in October 2008 to put Chandrayaan-1 in orbit and second one used in July 2011 during the GSAT-12 launch.
What will be the applications of RISAT-1?
Pictures from RISAT-1 would be used to estimate the crop yield - especially to monitor paddy crop, assess its acreage and predict its health during the kharif season, when the sky is covered with clouds. The satellite's images can be used for disaster management during cyclones and floods, to assess how much area has been inundated and so on.
Why SAR is used and what are the benefits of SAR?
Contrasting the normal, optical remote-sensing satellites, the RISATs use Synthetic Aperture Radar (SAR). This radar emits waves in a special way and collects part of the reflected radiation. From this reflected radiation, images of the earth can be built and these images have excellent clarity. Since it is difficult to carry a radar/antenna with a big aperture on a satellite, an SAR is used because it can synthesise (artificially create) a larger aperture electronically. Therefore it is called SAR.
Active Microwave Remote Sensing provided for cloud penetration and day-night imaging capability. These unique characteristics of C-band (5.35 GHz) SAR enables applications in agriculture, particularly paddy monitoring in kharif season and Management of natural disasters like flood and cyclone. Thus, SAR helps taking pictures of the earth at all times, through rain, sun, clouds, fog and cyclones.
Is this the first time ISRO is launching a RISAT?
NO. Although this is the first time the ISRO is launching its own RISAT, it has twice launched Israel's RISATs in orbit using the PSLVs from Sriharikota.
- In January 2008, the ISRO first put Israel's RISAT, “Tecsar”, in orbit.
- In April 2009, ISRO deployed Israel's ‘RISAT-2’ in orbit.
Both Tecsar and RISAT-2 are reconnaissance/surveillance satellites. Whilst Israel utilizes the images from ‘Tecsar’, India uses the images from ‘RISAT-2’ for surveillance.