Countdown for PSLV rocket's longest mission begins

Chennai: The countdown for the launch of an Indian rocket with a weather and seven other satellites began on Saturday at rocket port Sriharikota in Andhra Pradesh, the Indian space agency said.

According to the Indian Space Research Organisation (ISRO), the countdown for the launch of the Polar Satellite Launch Vehicle (PSLV) began at 8.42 a.m.

This will be ISRO's longest PSLV satellite launch mission spread over two hours and fifteen minutes.

The 320 tonne PSLV rocket carrying eight satellites - three Indian and five foreign - will blast off from the first launch pad at Sriharikota on September 26 at 9.12 a.m.

The rocket's main cargo will be the 371 kg SCATSAT-1 for ocean and weather related studies which will be placed into a 730 km polar sun synchronous orbit around 17 minutes into the flight.

According to ISRO, SCATSAT-1 is a continuity mission for Oceansat-2 scatterometer to provide wind vector data products for weather forecasting, cyclone detection and tracking services to the users.

The satellite carries Ku-band scatterometer similar to the one flown onboard Oceansat-2.

The mission life of the satellite is five years.

The five foreign satellites are: three from Algeria (Alsat-1B 103kg, Alsat-2B 117kg, Alsat-1N 7kg); and one each from Canada (NLS-19, 8kg) and the US (Pathfinder-44kg).

The two other Indian satellites are: Pratham (10kg) built by Indian Institute of Technology - Bombay and Pisat (5.25 kg) from PES University, Bengaluru and its consortium.

The seven satellites will be placed in a 689 km polar orbit.

This is the first mission of PSLV in which it will be launching its payloads into two different orbits.

According to ISRO after putting into orbit SCATSAT-1, the rocket's fourth stage or the engine will be shut down.

The fourth stage will be restarted and cut off one hour 22 minutes after the blast off twice.

Two hours and 11 minutes into the flight the fourth stage will be restarted. Four minutes later all the seven satellites would be put into their intended orbit. 

The switching off and switching on of the rocket's fourth stage is called multiple burn technology which was first tested by ISRO while flying its PSLV rocket on December 16, 2015

Launching of multiple satellites with a single rocket is nothing new for ISRO and it has been doing that for several years. The challenge, however, is to launch several satellites at different orbits with one rocket, but the ISRO already did so successfully when the PSLV ejected six Singaporean satellites on December 16, 2015.

The PSLV rocket is a four stage/engine rocket powered by solid and liquid fuel alternatively.

"Restarting a rocket engine soon after it is shut off is a critical technology that has to be mastered. Once a rocket engine is activated, then the heat generated is very high. The trick is to cool it down in space and to restart it at a short gap," an industry expert told IANS.

"This is entirely different from switching on and off the communication satellite's engines in space. The interval between two restarts of a communication satellite engine will be in days. But in the case of restarting a rocket engine, the time gap will be in hours," the expert added.

"By that time the rocket's engine has to be cooled down. This part of the experiment is very critical," he explained.