Pune institute close to finishing lab model of solar ultraviolet imaging telescope

An image of the SUIT — Solar Ultraviolet Imaging Telescope — one of the most important payloads of Aditya-L1 mission. 

The discovery of gravitational waves in 2015, for which three scientists received the Nobel Prize in physics this year, gave the city-based Inter-University Centre for Astronomy and Astrophysics (IUCAA) plenty of reasons to cheer, as many of its scientists had actively collaborated in the global effort to detect gravitational waves. Now, another team of scientists is all set to bring more glory to the IUCAA, as they give finishing touches to the laboratory model of one of the most important payloads that will be put on Aditya L-1 mission, the Indian Space Research Organisation’s (ISRO’s) first attempt to study the sun.

The Aditya-L1 mission is scheduled to to be launched some time in 2019 or 2020. Initially meant to observe only the corona, the outermost part of the sun, the mission has been expanded and now aims to look much deeper into the sun than has ever been done before. Accordingly, several additional instruments are to be put on a much bigger satellite than was earlier planned.

One of the most important ones, called Solar Ultraviolet Imaging Telescope, or SUIT, is being developed at IUCAA. This telescope is going to measure the radiations coming from one of the middle layers of the sun, the photosphere. Not a part of the original mission plan, SUIT is now the second biggest instrument to go on the satellite. The biggest one, known as the Visible Emission Line Coronagraph, or VELC, is being developed at the Bengaluru-based Indian Institute of Astrophysics. Meant to study the corona, the VELC was supposed to be the only payload in the original plan for Aditya mission.

SUIT is IUCAA’s biggest collaboration with ISRO so far. Designed to measure ultraviolet radiation from the sun in the 200 to 400 nanometre range, this telescope will take the first full disk images of the sun within this range. Durgesh Tripathi, who is part of the development team at IUCAA, said this wavelength range was important because it allowed scientists a glimpse into the behaviour of the solar atmosphere, besides procuring data on the variations in ultraviolet radiations.

Exposure to the radiation between 310 and 400 nm, which reaches earth’s upper atmosphere, can lead to skin cancer, said Tripathi, adding that the SUIT payload will also study the variation of this part of radiation from the sun. Studying the solar radiation at these wavelengths was important to understand the relationship between the sun and the climate system over earth, he said.

“Since the telescope will be looking at the sun all the time, a special thermal filter has also been designed to protect the instrument from heat as well as ultraviolet radiation,” said Tripathi. The photosphere, the subject of observation by SUIT, has a temperature of about 6,000 Kelvin — approximately 5,720 degree celsius. The corona, the outermost layer of the sun, which is thousands of kilometres away from the core, has temperatures of over one million Kelvin. The reason for this seeming discrepancy is not properly understood, and something the VELC aims to explore.

SUIT is being built in collaboration with several agencies of the ISRO, and data collected by the telescope as well as other payloads on board Aditya-L1 will be used by solar astronomers in several institutes in India and abroad. While some parts of the instrument, like the camera, have been imported, most others, including the thermal filter, have been designed by the IUCAA scientists. The filter, to be placed at the front end of SUIT, is meant to reflect over 90 per cent of the light arriving from the sun. Only about 0.1% of the incoming solar radiation is allowed to enter the telescope and other components of the SUIT instrument, said Tripathi.

“The lab model is being assembled at IUCAA and being given the final touches. A review committee from ISRO will assess the model, after which we can take it for designing in the flight mode,” he said.