Isro wants a place in the Sun, sets September 2 date for Aditya-L1

India will soon have a greater advantage of observing solar activities and its effect on space weather in real time, thanks to the launch of Aditya-L1, the first space-based Indian observatory to study the Sun, which is scheduled to be launched on September 2, at 11:50 am from Sriharikota.

Aditya L1 shall be the first space-based Indian mission to study the Sun. Only two other space agencies have had their spacecraft reach L1 or the Lagrange point: USA's National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). The Indian spacecraft shall be placed in a halo orbit around the Lagrange point 1 (L1) of the Sun-Earth system, which is about 1.5 million km from the Earth.

This mission comes on the heels of the successful landing of India's third lunar mission, the Chandrayaan-3 which on Sunday made the first observations of the temperature profile of the lunar south pole.


A satellite placed in the halo orbit around the L1 point has the major advantage of continuously viewing the Sun without any occultation/eclipses. Dipankar Banerjee, Director, Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, told ET, Aditya L1 mission is an observatory class mission.

So far, we've been studying the Sun from India from our ground-based telescopes, which are situated in some of the hill stations like Kodaikanal or ARIES, Nainital, and lakeside observatory like Udaipur Solar Observatory.

"But we did not have such telescopes in the Space," explained Banerjee, adding that from the ground-based telescopes we can only see the visible surface of the Sun but cannot see the atmosphere of the Sun. "We know that the atmosphere of the Sun is different from the planetary atmosphere. For example, the outer atmosphere, which is called the Corona, is very hot. While we have some understanding of why Corona is hot, we do not have a complete understanding," he said.

"But the Corona can only be seen during the total solar eclipse because the moon blocks the solar disc light and the faint light which is one millionth time weaker than the photospheric light, you can only see during the total solar eclipse," he said. "Now the idea is whether we can make an artificial total solar eclipse. We can do that with an instrument called the Coronagraph. Now we have a coronagraph-like telescope which is going to fly aboard the Aditya L-1 mission," Banerjee said.

Banerjee was involved in the conception phase of the coronagraph onboard the Aditya L1 called Visible Emission Line Coronagraph (VELC). Aditya L1 mission formed a science working group and Banerjee has been the co-chair of this group for a decade now. He is also the co-chair of the science outreach committee of Isro, for the Aditya L1 mission. At ARIES, Nainital, is hosting the Aditya L1 support cell, whose objective is to train younger people to work on the science of Aditya L1 mission.

Eminent astrophysicist Prof Somak Raychaudhury, former director of Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, that developed one of the payloads or instruments onboard the Aditya L1 mission told ET India has not sent a spacecraft 1.5 million km away from the earth before.

"It is a 'parking spot', because if we put something in the Lagrange Point, it stays there, as the force of the Sun and the Earth balance out the rotational force. This itself is a novel thing that we can send it there. Because it is between the Earth and the Sun, we can observe the Sun 24 hours, and it is not eclipsed by the Earth," Raychaudhury said.

The instrument to observe the surface of the Sun in an ultraviolet camera was built by IUCAA called the SUIT (Solar Ultraviolet Imaging Telescope). The second instrument is a spectrograph that looks at the corona of the Sun. "Sometimes, magnetic storms on the Sun throw out charged particles and many of them hit the earth. It can cause a lot of disturbance to the earth's atmosphere and affect our satellites, shut down internet and communication services etc. These are called coronal mass ejections (CMEs), one of the objectives of this mission is to study CMEs," Raychaudhury explained.

There are seven different payloads or instruments aboard Aditya that are going to look at different layers of the Sun, optical wavelengths, near UV wavelength, X-ray wavelength, and infrared wavelength. "We are going to study events like solar storms in the solar atmosphere and understand why they happen and its impact," Banerjee explained. "Likewise there are many other studies that we are going to do from this space-based observatory which is also going to be from a unique vantage point called Lagrange 1 Point," he said.

Mission life
The nominal mission life is five years. "With the past experience, it may be longer too. ESA's and NASA's have survived for 20 years," he said. The Solar and Heliospheric Observatory (SOHO) is a joint ESA/NASA spacecraft that was launched on 2 December 1995, to study the Sun. It has also discovered over 4,000 comets.

"Apart from this joint operation from these two space agencies, nobody has reached Lagrange 1 point, so technically, it will be a huge demonstration by India that we are going to be the third nation independently travelling to Lagrange 1 point," Banerjee said.