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The Aditya-L1 spacecraft before its launch last September. (credit: ISRO)

India’s mission for understanding the dynamics of the Sun

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On January 6, the Indian Space Research Organisation (ISRO) successfully completed halo-orbit insertion of its solar observatory spacecraft, Aditya-L1. (In Sanskrit, Aditya means Sun.) It took 127 days for this craft to reach its final destination, the Lagrangian point 1 (L1) of the Sun-Earth system, around 1.5 million kilometers from the Earth. That is now where this spacecraft will operate for around five years, with an uninterrupted view of the Sun.

History is replete with examples of the impact of space weather on satellite systems operational in space and on the ground.

Aditya-L1's journey commenced with its launch aboard the PSLV-C57 on September 2, 2023. This spacecraft was successfully injected into an elliptical orbit of 235 by 19,500 kilometers around the Earth. Aditya-L1 then performed four Earth-bound orbital maneuvers between September 3 and 18. After the fourth maneuver, the spacecraft had achieved a new orbit of 256 by 121,973 kilometers. The journey towards the Sun-Earth L1 point started on September 19 and, with this, began the process of data collection. Much before reaching its final halo orbit, the spacecraft collected some interesting information and images.

This spacecraft has seven scientific payloads, which have been developed by various ISRO centers and scientific institutes. Out of seven, three sensors are for in-situ measurements of the solar wind and magnetic field and for plasma analysis. The remaining four sensors include soft and hard X-ray spectrometers, solar ultraviolet imaging, sensors used for spectropolarimetry and spectroscopy, and for assessment of the characteristics of the Sun’s corona. Broadly, this spacecraft will investigate the dynamics of the Sun’s outer layers. The idea is to understand the chromospheric and coronal dynamics of the Sun.

Space weather refers to distinctions in the space environment due to the Sun and Earth. To understand the vagaries of space weather, it is extremely important to continuously monitor the behavior of the Sun. History is replete with examples of the impact of space weather on satellite systems operational in space and on the ground. The largest geomagnetic storm in recorded history was on September 2, 1859, famously known as “Carrington event”. This storm is known to have created major problems with telegraph communications. In February 2022, SpaceX lost around 40 recently launched Starlink satellites after they were hit by a geomagnetic storm that increased atmospheric drag. Today, prediction of space weather is becoming increasingly important since significant increase in space activities is getting witnessed.

The sunspot cycle, solar wind, solar flares, and coronal mass ejections (CME) erupting from the Sun’s surface require continuous monitoring and India’s Aditya-L1 would be exactly doing that job. Magnetic fields, radiation, particles, and matter ejected from the Sun can interact with the Earth’s magnetic field and upper atmosphere and can produce a variety of effects, and their monitoring is essential. Hence missions like Aditya-L1 are important.

Since 1995, the Solar and Heliospheric Observatory (SOHO) has been operating at L1. SOHO is the longest-lived Sun-watching satellite thus far and is a joint project of ESA and NASA. This craft was expected to work for two years, but is still operating after more than 25 years and is expected to remain operational through the end of 2025. Owing to the longevity of this mission, SOHO was able to observe two 11-year solar cycles associated with sunspots.

Space weather prediction has been happening for decades. At present, space weather forecasts are issued at regular intervals by the Space Weather Prediction Center (SWPC) at NOAA. Also, there are agencies in a few other countries that are issuing such forecasts. Any fresh inputs about the conditions on the Sun would definitely add to the accuracy of such predictions. ISRO has already made it clear that the data collected by Aditya-L1 would be shared with the rest of the world.

It has been observed that on various occasions that the adverse space weather induced by solar events does not impact systems in space and on the ground that much. However, in some specific cases the impact is so significant that various space systems become totally inoperable. This leads to major financial losses as well as major inconveniences for society. Indian investments towards understanding more about the Sun should be viewed against this backdrop.

Today, with the launch of Aditya-L1 satellite, ISRO has started its mission to understand the secrets of the Sun. However, ISRO needs to plan its next mission now so that there is no interruption in such data.

Space science research has been an important part of India’s space program. The policy directions in this field are given to ISRO by its Advisory Committee for Space Sciences (ADCOS). The mission to study the Sun was conceptualized in January 2008 by ADCOS. Initially, the proposal was to launch a small satellite weighing around 400 kilograms into a low Earth orbit (800 kilometers) with a coronagraph to study the solar corona. But subsequently it was decided that ISRO should plan for a comprehensive solar and space environment observatory to be placed at Sun-Earth L1.

India has always believed in sharing the data received from its scientific satellites. India’s first mission to Moon, Chandrayaan-1 in 2008, was instrumental in discovering water on the Moon. The Moon Mineralogy Mapper, a NASA instrument, was carried by Chandrayaan-1. ISRO had its indigenous sensor, called Moon Impact Probe (MIP), on Chandrayaan-1 as well. This was programmed to separate from the craft at a height of 100 kilometers and to strike the lunar south pole, collecting data during its descent. Scientists from both ISRO and NASA used the data to measure the availability of the water on the Moon.

In 2015, ISRO launched a satellite called AstroSat. This is India’s first dedicated astronomy mission aimed at studying celestial sources in X-ray, optical, and ultraviolet spectral bands simultaneously. Over the years, this satellite is known to have picked up various observations and many scientists all over the world are known to be using these observations in the conduct of their research.

Today, with the launch of Aditya-L1 satellite, ISRO has started its mission to understand the secrets of the Sun. This mission is expected to last for five years, but could remain operational even for longer depending on the spacecraft’s fuel reserves. However, ISRO needs to plan its next mission now so that there is no interruption in such data.

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