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WION has learnt that the twin satellites of the European Space Agency's (ESA) Proba-3 mission arrived at the Satish Dhawan Space Centre (Indian Spaceport) in Sriharikota, Southern India, during the early hours of Wednesday, 6th November.

Over the next four weeks, the spacecraft will undergo final assembly, integration and testing, ahead of its planned December 4th launch on the Indian PSLV rocket.

In its 30 years of operation, the Polar Satellite Launch Vehicle has launched more than 300 foreign origin satellites, raking in millions for the commercial arm of the Indian space agency. 

The Proba-3 satellites were flown to the Chennai airport from Liege, Belgium, following which they were trucked to the spaceport at Sriharikota.

European Space Agency's teams, present at the Indian spaceport, will now prepare the satellite for its planned launch on December 4th.

Originally, the satellites were meant to arrive in India on 21st October and then be readied for a launch by November end.

However, there had been a delay owing to administrative reasons at ESA. "Consequentially the launch date of November 30th will not be met.

The new launch date has not been confirmed but the goal is to launch in December,” an ESA Spokesperson responded to WION's query.

It is learnt that ISRO and ESA are now looking at launching PSLV-C59/Proba-3 on December 4th, if all goes well.

What makes Proba-3 unique
Proba stands for ‘PRoject for OnBoard Autonomy’.

Proba-3 is the world’s first precision formation flying mission.

It consists of two small satellites launched together that will separate apart to fly in tandem, to prepare for future multi-satellite missions flying as one virtual structure. 

As a world first, its two satellites the Coronagraph spacecraft and the Occulter spacecraft will maintain formation to a few millimetres and arc second precision at distances of 144 m or more for six hours at a time. In effect, the pair will be forming a virtual giant satellite.

And this will be achieved autonomously, without relying on guidance from the ground.

The solar corona (the outermost part of the sun's atmosphere) has many mysteries associated with it.

The solar corona is a million degrees warmer than the surface of the sun, and it is the origin of coronal mass ejections (highly charged particles), which can affect the functioning of satellites or communication and power networks back on earth.

There is immense scientific interest in better understanding the solar corona and related phenomena. 

A Coronagraph is a device that can artificially block out the bright light of the sun, thereby enhancing the visibility of the faint corona.

A solar eclipse, when the moon blocks out the sun, is a great natural opportunity to study the solar corona.

But eclipses are rare and occur only for a few minutes.

The two Proba-3 satellites will be precisely aligned so that the Occulter spacecraft casts a shadow across the Coronagraph spacecraft, thereby enabling the visibility of the faint solar corona.

If the two are not perfectly aligned, then the bright disc of the Sun will not be hidden from the instrument, and the corona will be obscured by its bright light.  

India's PSLV-XL launcher was chosen to ferry Proba-3 satellites to space, as the European Space Agency (ESA) does not possess a medium-lift rocket that can launch the 550 kg Proba-3 satellites into the desired orbit.

The mass of the satellites is above the capability of ESA's Vega-C small rocket, while the large Ariane-6 rocket would be too costly for a mission of this kind.

PSLV offers the perfect balance in terms of lift capability and cost.

 ESA will be paying around € 30 million (approx Rs. 271 crore) to avail the launch services from ISRO's commercial arm NewSpace India Limited (NSIL).