Another ISRO milestone: 50th launch from Sriharikota

Sriharikota (Andhra Pradesh), Dec 16: India on Wednesday put into orbit in copy book style six Singaporean satellites that will hover about 550 km above the Earth for up to five years. It was the Indian space agency's 50th launch from here.

The Polar Satellite Launch Vehicle's Core Alone (PSLV-CA) variant -- standing 44.4 metres tall and weighing 227 tonnes -- rose into the evening skies at 6, riding majestically on the tail of fierce orange flames.

The Singapore-built satellites included the city state's first commercial earth observatory TeLEOS-1 weighing 400 kg.

"Today's achievement demonstrates, yet again, India's increasing space capabilities," President Prab Mukherjee said in a message to the Indian Space Research Organisation (ISRO).

ISRO chairman A.S. Kiran Kumar said the agency would keep putting satellites -- both communication and earth observation variants -- into orbit. "We have a lot more to achieve next year."

The expendable rocket carrying six Singaporean satellites -- cumulatively weighing around 620 kg -- as its luggage slung them into their intended orbit just over 21 minutes into flight.

The rocket blasted off from the first launch pad at the Satish Dhawan Space Centre here, around 80 km from Cheni.

For onlookers, the rocket on its way up looked like an inverted flare/torch lighting up the night sky. As it gathered speed, the ISRO team celebrated.

ISRO successfully switched on and off the rocket's fourth stage/engine 46 minutes after it delivered the satellites in space. The test will eble ISRO to develop rockets that can launch orbits at different orbits in one flight.

"The restart test was successful. The engine was fired for nearly five seconds. We will be using this technology sometime next year," Kumar told IANS.

Just over 18 minutes into flight, the rocket ejected the TeLEOS and it was followed by the other five. In just over 21 minutes, all six satellites were put into their intended orbit.

"The restart of the engine happened beautifully. The test was a success," S. Somth, director of the Liquid Propulsions Systems Centre, told IANS.

According to him, the multiple burn fuel stage/engine will be used in PSLV-C35 rocket which will carry two satellites.

One satellite will be launched at an higher orbit and the other one will be at a slightly lower orbit, he said.

The Singapore media said the satellites were built from scratch by teams from defence manufacturer Singapore Technologies Electronics, Singapore-based space technology firm Microspace Rapid, the tiol University of Singapore and nyang Technological University.

The biggest satellite TeLEOS-1 carries a camera that can take pictures at ground resolution of up to a metre and can conduct surveillance missions for maritime and border security.

It is expected to last up to five years. The other smaller satellites -- VELOX-C1 (123 kg), VELOX-II (13 kg), Kent Ridge-1 (78 kg), Galassia (3.4 kg) and Athenoxat-1 -- will last from between six months and three years.

Kumar said the next three satellite launches using PSLV rocket would be vigation satellites. They would be followed by some multiple satellite launches.

Wednesday's mission was the second pure play commercial mission for ISRO in 2015. The first was in July when five British satellites were launched.

The successful launch takes ISRO's total flights of foreign satellites to 57.

Launching of multiple satellites with a single rocket is not new for ISRO. The challenge is to launch several satellites at different orbits with one rocket.

This is what ISRO tested after the PSLV ejected the Singaporean satellites on Wednesday.

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

"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 the space and to restart it at a short gap," an industry expert told IANS.

The engine operating for few seconds went up to an altitude of 524 km before the stage was cut off again.

With Wednesday's success, ISRO has launched 20 satellites -- three Indian and 17 foreign -- from its rocket port in Sriharikota this year.

Last month, India launched its communication satellite GSAT-15 using the Ariane rocket of the European space agency which takes the total number of satellite launches in 2015 to 21 -- 17 foreign, four Indian.