Aditya L1: India’s First Ever Solar Mission

India scripted history with an iconic soft landing on the lunar south pole. A place that was unexplored till now and in Sanatana Dharma parlance, elevating the kundalini shakti dispelling the darkness of the Aghora. Treasuring this landmark achievement, the landing site was aptly named as “Shiva Shakti Point” resonating with the sentiments of the nation. Cherishing India’s relentless pursuit to explore space, the Chandrayaan-2 crash point on the lunar surface is now denominated as “Tiranga Point”. Chandrayaan-3 success invigorated the prospect of the moon being India’s gateway for future interplanetary missions. “This is not the end but the beginning of the end”. The real journey will start now.

Pioneering yet another space mission, ISRO has set the stage for its first-ever study of the Sun, the Aditya L1 mission. The sun-observatory will be hoisted by the PSLV-C59, the 59^th flight of the workhorse PSLV, and the 25^th mission in XL configuration into a low earth orbit. Subsequently, the Aditya L1 spacecraft will undergo orbital maneuvers using Liquid Apogee Motor (LAM) to reach the Sun-Earth Lagrange point L1, halo orbit which is around 1.5 million kilometers from Earth (roughly 1% of the Earth-Sun distance). The rocket will set off from the second launch pad of Sriharikota Range (SHAR) on September 2, 2023.

Solar activities have immense effects on the entire solar system. The Sun is the sole source of energy for the entire solar system including earthlings. It is 150 million kilometers from the Earth. The Sun is an active ball of hydrogen and helium gases.  The centre of the Sun is called the core with temperatures reaching as high as 15 million degrees Celsius. The nuclear fusion reactions occurring in the core powers the Sun. The visible surface or photosphere is relatively cool and has temperatures of 5500⁰C.

The Sun is the nearest star to the Earth and the regular explosive eruptions of the Sun release a lot of energy, which if directed to the Earth can cause disturbances in the Earth’s atmosphere. The thermo-magnetic phenomena on the Sun are accompanied by the release of constant flow of particles and magnetic fields which nearly fill the space. The constant flow of the particles called solar wind is mostly composed of high-energy protons. The solar wind and the Coronal Mass Ejections (CME) change the nature of space and alter the magnetic field of the Earth.

While mild Coronal Mass Ejections (CME) of the Sun’s surface cause Auroras, strong eruptions can potentially disrupt satellite communications and terrestrial grid systems. Hence, it is important to continuously monitor solar activities to better predict the space weather. The core objectives of the Aditya Mission include the study of coronal heating, solar wind acceleration, Coronal Mass Ejections (CME), dynamics of the solar atmosphere, and temperature anisotropy.

Lagrange points are often referred to as the parking places in space which are gravitationally stable. The spacecraft can operate for a long time from these places with very less fuel. These are points of equilibrium where the combined gravitational forces of two large bodies (in this case the Earth and the Sun) are equal to the centrifugal force experienced by a smaller body. These points are named after the Italian Mathematician Joseph Lagrange after his discovery in 1772. In all, there are five Lagrange points. The L1 point which lies between the Earth and the Sun offers an uninterrupted view of the Sun without any “occultations/eclipses”.

For a comprehensive understanding of the space weather and to study the Sun, the European Space Agency (ESA) in partnership with National Aeronautics and Space Administration (NASA) has launched the Solar and Heliospheric Observatory (SOHO) mission in 1996 to be positioned at L1. The mission originally planned for two years continues to operate for over 25 years and is extended till 2025. Even NASA’s Deep Space Climate Observatory is also positioned at L1 because of its vantage position.

Indeed, scientists maintain that L1, L2, (on the opposite side of the Sun), and L3 (behind the Sun) are relatively unstable due to their precarious equilibrium. Spacecrafts destined for these positions must be carefully adjusted to avoid irreversibly falling into the Sun. L2 is considered most ideal for astronomy and previously hosted NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) and the current home of Planck. James Webb Space Telescope is expected to move to this position soon.

L1 and L2 are unstable on a time scale of approximately 23 days. Hence spacecraft orbiting these positions must undergo periodic course correction and altitude correction. L3 is not deemed to be important because of its position relative to the Sun.

The L4 and L5 positions have stable orbits. Due to their stability dust and asteroids accumulate in these regions. The asteroids located around these points are called Trojans in honour of the asteroids Agamemnon, Achilles, and Hector (characters of the Trojan War). These points are relatively closer to the Sun and are highly suitable for asteroid hunting. On the other hand, the SOHO observatory at L1 point has the credit of hunting over 3000 comets till now.

The Aditya L1 spacecraft placed in the Earth’s orbit will be made elliptical and will be pushed towards the L1 position. As it travels towards L1, the spacecraft will move out of the Earth’s Sphere of Influence (SoI). Once the spacecraft exists the SoI, the cruise phase starts and leads to its injection into the large halo orbit around the L1. The entire process from launch to reaching L1 orbit will take four months.

The earth’s atmosphere acts as a protective shield and blocks the entry of numerous harmful radiations, particles, and magnetic fields. Hence our regular instruments on the Earth will not be able to study all these ionised high-energy particles and radiations. To study these particles and phenomena it is important to move away from the sphere of influence of Earth’s magnetic field.

At L1, away from the Earth’s atmosphere, the Aditya probe will deploy all seven instruments on board especially to study solar flares, propagation of particles and fields from the flare, and the Sun’s atmosphere, i.e. Chromosphere and Corona. Aditya L1 has seven instruments on board. Four of them for remote sensing of the Sun and three in-situ instruments for observing the local environment.

The four remote sensing payloads include- Visible Emission Line Coronograph (VELC) for Corona imaging and spectroscopy; Solar Ultraviolet Imaging Telescope (SUIT) for observing the photosphere and Chromosphere; Solar Low Energy X-ray Spectrometer (SoLEXS); High-Energy L1 orbiting X-Ray Spectrometer (HEL1OS).

The in-situ payloads are the Aditya Solar Wind Particle Experiment (ASPEX), Plasma Analyzer Package for Aditya (PAPA); and Advanced Tri-axial Resolution Digital Magnetometers. All these payloads are indigenously developed in different labs of the country in close collaboration with various centres of ISRO. Aditya L1 is only the. Similar to the Chandrayaan series, ISRO can plan missions to stable points like L4 and L5. Built in a budget of Rs 378 crores, Aditya L1 is the most cost-effective solar project in the world.

Coming at the back of the Chandrayaan 3 mission which is making invaluable discoveries, the country is highly hopeful of a breakthrough exploration of the mysteries of the Sun through the Aditya L1 mission.

 

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