A wholly Indian-built spy/surveillance satellite - Radar Imaging Satellite (Risat-1) - that can see through clouds and fog and has very high- resolution imaging is slated for launch in April, a senior official of the Indian space agency has said.

An official of the Indian Space Research Organisation (ISRO) said thorough tests were being done on the Risat-1. "The Risat-1 is put to thermal vacuum test (a test to check the satellite's functioning in space environment). It is a complex microwave satellite being built for the first time in India. The satellite is expected to be launched in April," the senior official told IANS, not wishing to be named because of the organisational rules.

In earlier satellites, one major component, the synthetic aperture radar (SAR) was imported, but in Risat-1 that has also been developed in India.

He said Risat-1 is the first such satellite being built by India and is a bit complex compared to other remote sensing/earth observation satellites built and sent up earlier.

According to ISRO officials, Risat-1 at 1,850 kg is the heaviest microwave satellite to be built by India.

The satellite would be used for disaster prediction and agriculture forestry, and the high resolution pictures and microwave imaging could also be used for defence purposes.

Risat-1 will have all weather, day and night imaging capability.

The satellite's synthetic aperture radar can acquire data at C-band.

ISRO Chairman K. Radhakrishnan had said last October that the space agency would launch two more satellites - Risat-1 and SARAL - before 2011-end. But that did not happen. He also said two more satellites - AstroSat and Aditya - will be launched in 2012-13.

Remote sensing satellites send back pictures and other data for use. India has the largest constellation of remote sensing satellites in the world providing imagery in a variety of spatial resolutions, from more than a metre ranging up to 500 metres, and is a major player in vending such data in the global market.

In 2009, ISRO had launched 300 kg Risat-2 with an Israeli built SAR enabling earth observation on all weather, day and night conditions. The satellite can look through clouds and fog.

With 11 remote sensing/earth observation satellites orbiting in the space, India is a world leader in the remote sensing data market. The 11 satellites are TES, Resourcesat 1, Cartosat 1, 2, 2A and 2B, IMS 1, Risat-2, Oceansat 2, Resourcesat-2, Megha-Tropiques.

According to ISRO officials, the rocket that would sling Risat-1 will be the Polar Satellite Launch Vehicle's (PSLV) upgraded variant called PSLV-XL.

The rocket would weigh around 320 tonnes at lift-off and will be the third such expendable rocket to be sent up by ISRO, and first time to launch a remote sensing satellite.

ISRO had used the PSLV-XL variant (rocket with extended strap-on motors than what the base model has) for its moon mission (Chandrayaan-1) in 2008 and for launching its communication satellite GSAT-12 in 2011.

The PSLV is a four-stage (engine) rocket powered by solid and liquid propellants alternatively. The first and third stages are fired by solid propellant and the second and fourth stages are fired by liquid propellant.

ISRO has developed three PSLV variants. The first is the standard variant weighing around 290 tonnes with six strap-on motors measuring 11.3 metres with a fuel capacity of nine tonnes.

The other two rocket variants are the PSLV Core Alone without the six strap-on motors and PSLV-XL with longer strap-on motors measuring 13.5 metres having a fuel capacity of 12 tonnes of solid fuel.

Source: Indo-Asia News Service