Tuesday, April 21, 2009

The Radar Imaging Satellite : RISAT

The PSLV-C12, carrying 300-kg Radar Imaging Satellite (RISAT-2) and 40-kg Micro Satellite ANUSAT lifted off from ISRO’s Satish Dhawan space Centre from Sriharikota on Monday 20 April 2009 .

At the end of the 48-hour countdown, the 44-meter tall four-stage PSLV-C12 blasted off from the second launch pad with the ignition of the core first stage.

The Polar Satellite Launch Vehicle, weighing 230 tonnes at the time of launch, soared into a clear sky at 6.45am(local time) from the spaceport here, about 90 km north of Chennai.

This is the 15th flight of ISRO’s workhorse PSLV, which had launched 30 satellites (14 for India and 16 for foreign countries) into a variety of orbits since 1993.

The launch vehicle carries two payloads - RISAT-2 (with all weather capability to take images of Earth) and ANUSAT (the first satellite built by an Indian University to demonstrate the technologies related to message store and forward operations).

The rocket would place both the satellites in their orbits around the earth shortly.

What’s RISAT?

RISAT is the first satellite imaging mission of ISRO (Indian Space Research Organization) using an active radar sensor system, namely a C-band SAR (Synthetic Aperture Radar) imager, an important microwave complement to its optical IRS series observations missions. The overall objective of the RISAT mission is to use the all-weather as well as the day-and-night SAR observation capability in applications such as agriculture, forestry, soil moisture, geology, sea ice, coastal monitoring, object identification, and flood monitoring.

RISAT is a newly developed agile spacecraft, featuring a multi-mode and multi-polarization SAR system in C-band, providing spatial resolutions in the range of 3-50 m on swath widths ranging from of 30-240 km.


The spacecraft bus consists of a prism shape build around a central cylinder. Most of the spacecraft subsystems and the complete payload are integrated in the prism structure and the central cylinder. The spacecraft is 3-axis stabilized, developed, manufactured and integrated by ISRO/ISAC, Bangalore, India. The solar panels and some subsystems are mounted on the cuboid portion of the spacecraft. Two solar panels with high efficiency multijunction solar cells provide the S/C power; they are charging two sets of NiH2 batteries, each with a capacity of 40 Ah. Both energy sources deliver 3.5 kW of sustained DC power at 70 V regulated voltage to the payload for 10 minutes duration in each orbit. The on-orbit total spacecraft mass is about 1750 kg with about 950 kg of SAR payload mass.

Designed by the Israeli Aerospace Industries, RISAT can take images through the thickest cloud cover, rain, snow or fog conditions during night and day.

While the RISAT will be used extensively for purposes like mapping, managing natural disasters and surveying the seas, it can also see through camouflage like cloth or foliage used to conceal camps or vehicles.

RISAT will enable India to keep a watch on terror camps, military installations across boundaries, missile sites and suchlike.
However, RISAT is not India’s first spy satellite. The Technology Experiment Satellite has been used for photo-reconnaissance since 2001.

But unlike previous remote sensing satellites, RISAT is the first with a synthetic aperture radar, which gives it a day-night, all-weather snooping capability.

It should also help keep track of ships at sea that could pose a threat.
The RISAT will reduce India’s dependence on foreign suppliers like Ikonos for satellite imagery. But many more gaps need to be plugged. Despite the desperate need, India is still awaiting a dedicated military satellite