Country’s first solar mission likely to be launched by June-July

The satellite will be carried by India’s trusted rocket Polar Satellite Launch Vehicle, said ISRO chairperson S Somanath at a ceremony on Thursday where he was given a 3D model of the payload.

He said the complexity of the chronograph and what it was attempting to do was the reason it took 15 years to develop. He said there was a need for a 50-year road map of scientific explorations and missions. Also, Indian scientists need to come up with novel ideas not attempted by other countries – projects that might seem impossible or even never get approval, he said.

“ISRO aims to play an important role in future science experiments in space and an ecosystem needs to be created for this, including a road map,” he said.

The payload handed over on Thursday called ‘Visible Emission Line Coronograph’ (VELC) will be the main payload among seven designed to study various aspects of the sun like its atmosphere, solar wind acceleration and the origin of coronal mass ejection. To get an unobstructed, continuous view of the sun, the satellite will travel to the L1 or Lagrange point between the sun and the earth. Lagrange points — there are five between any two celestial objects — are referred to as parking spots in space because the gravitational pull of the celestial objects equals the force required to keep it in orbit. So, a satellite can stay in Lagrange points between any two celestial objects without expending fuel.

The VELC, which was conceptualised and designed in 15 years, may help is solving one of the main puzzles of solar astrophysics — why the sun’s atmosphere called corona is a million degrees hot even though the surface is just over 5,700 degrees Celsius?

To do this, the scientists have to observe the corona right from its lowermost parts upwards, which is difficult to do owing to the bright light emanating from the sun’s surface.

However, VELC has an ‘internal occulter’, which separates the light from the surface and discards it. The remaining light from the corona is sent for further processing. The VELC weighs 90kg and is 1.7mx1.1mx700mm in dimension.

The VELC can image the solar corona down to 1.05 times the solar radius, which is the closest any such payload has imaged. It can also take these observations roughly 3 times every second, and with a high resolution of 2.5 arcseconds per pixel.

“No other solar coronagraph in space has the ability to image the solar corona as close to the solar disk as VELC can. It can image it as close as 1.05 times the solar radius. It can also do imaging, spectroscopy and polarimetry at the same time, and can take observations at a very high resolution (level of detail) and many times a second,” said Prof Raghavendra, principal investigator of VELC.

It will help in studying the temperature, velocity and density of the corona, understand the processes that result in heating of the corona and acceleration of the solar wind, aid studies on drivers of space weather, measure the magnetic field of corona and study the development and origin of coronal mass ejection.

Not only will it generate high resolution pictures of the corona, it will also maintain a temperature of 22 degrees C by radiating away the enormous heat and light from the solar surface. It is also one of the most precise instruments made in India.

Programme Director of Aditya L1 Nigar Shaji thanked LEOS of ISRO for producing the main mirror as well as 18 different optical assembles for VELC. The main mirror has been polished to an accuracy of about 4 ansgtroms, which is one of the best achieved in the country, she said.

Explaining the logo of the payload, the principal investigator of the VELC payload Prof B Raghavendra Prasad said it is a photo of the solar corona taken 125 years ago by British and Indian astronomers working at the Kodaikanal Solar Observatory.