After Chandrayaan-2, it is back to business for the Indian Space Research Organization. On Wednesday, ISRO will launch Cartosat-3, and 13 other foreign satellites, aboard a PSLV (Polar Satellite Launch Vehicle). This will be ISRO’s fifth launch this year and the first since the July 22 launch of the Chandrayaan-2 Moon mission.
The main purpose of the mission is to place the 1,625-kg Cartosat-3 satellite, the third generation of Earth-observation remote sensing satellites that ISRO has been launching and using 1988. These satellites provide high-resolution imagery of the Earth that are used for applications like 3-D mapping, disaster management, agriculture and water management, recording of changes in land use, and urban and rural infrastructure planning, and even border surveillance.
The PSLV-C47 rocket is also carrying 13 commercial nano-satellites from the US. Twelve of them are Flock-4P satellites, also Earth-observation satellites, from the private company Planet, which has sent several such satellites on PSLV rockets earlier. In fact, it was an earlier version of these same Flock satellites that, in February 2017, had helped ISRO launch a world record 104 satellites at one go. Of the 104 satellites on board PSLV-C37, 88 were Flocks. Those Flocks were called doves, and the current bunch is known as super-doves.
The main payload in Wednesday’s launch would be the next-generation Cartosat satellite. The Cartosat satellites, used mainly for large-scale mapping of the Earth through high-resolution cameras, are part of the large range of earth observation satellites deployed by ISRO, starting with the Indian Remote Sensing series of satellites. The Earth-observation satellites also include the Resourcesat and RISAT series, the Oceansat series and many more. These satellites now focus on generating theme-based user-friendly data that are in great demand. The Resourcesat and RISAT series of satellites, for example, provide imageries and data that are needed for land and water resources applications. The Oceansat series and the SARAL satellite, meanwhile, produce data on the oceans, while satellites like INSAT 3D, INSAT-VRR or Megha Tropiques study the atmosphere.
Data from Earth-observation satellites are in great demand, both from government agencies, which need it for planning and infrastructure development, as well as private companies looking to execute infrastructure and other projects.
Cartosat, then and now
Cartosat-3 has been developed as an improvement over the Cartosat-1 and Cartosat-2 series satellites, though ISRO has not yet revealed the full specifications of this satellite.
Cartosat-1, launched in May 2005, was the first Indian remote sensing satellite capable of taking three-dimensional images. With a resolution of 2.5 metres, which meant it could identify a car on the ground from space, Cartosat-1 helped in creating new digital maps of over 150 towns and cities in the country at a scale of 1:10,000. Earlier maps were of a scale of 1:50,000 or even lower. Data from this satellite were also used to a do an inundation vulnerability assessment of the Indian coastline in the event of a tsunami or a major cyclone, and even for estimating the status of irrigation potential created by the large number of projects under the Accelerated Irrigation Benefit Programme.
The first of the Cartosat-2 series was launched in 2007 and these have been substantially advanced versions of Cartosat-1. Seven of them are in orbit, each with the capability of taking images of resolution better than 1 metre. The last three Cartosat-2 series satellites are also placed in a lower orbit — 505 km from the Earth’s surface compared to the 640 km earlier — thereby increasing their resolution further.
ISRO has not revealed the quality of the camera on Cartosat-3 or the resolution of the images it would be able to take. But it is likely to have the capability to take images with resolution better than 0.25 metres.
“There is great demand for reliable high resolution data because these are needed for a very wide range of applications. It is needed by the government, private companies, and also academics who are studying earth, ocean or atmosphere systems. We need to know how the forest or vegetation cover is changing for example, or how urbanisation is spreading. Cartosat satellites come back to the same place after every few months, so that they are able to capture the change that is happening on the ground. And this is valuable for a number of user agencies. ISRO is therefore only catering to the increased demand by deploying more such satellites,” said a retired space scientist.
Wednesday’s mission will fly on a four-stage PSLV rocket that has been the most consistent of ISRO’s launch vehicles. This would be the PSLV’s 49th flight. All but two of them have been successful. Apart from Chandrayaan-2, which flew on a GSLV rocket, the other three launches this year have all used PSLV variants.
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