Our Sun is the nearest star and the largest celestial body in the solar system. The estimated age of the Sun is about 4.5 billion years. It is a hot glowing ball of hydrogen and helium gases. The distance to the Sun from the Earth is about 150 million kilometres, and is the source of energy for our solar system. The gravity of the Sun holds all the objects of the solar system together. At the central region of the Sun, known as 'core', the temperature can reach as high as 15 million degree Celsius. At this temperature, a process called nuclear fusion takes place in the core which powers the Sun. The Sun constantly influences the Earth with radiation, heat and constant flow of particles and magnetic fields. The constant flow of particles from the Sun is known as solar wind and are mostly composed of high energy protons.
Aditya L1 is the first space based observatory class Indian solar mission to study the Sun. Its primary material is High Strength Alloy Steel. With a hefty launch weight of 3,252 lb (1,475 kg) and carrying a payload of 538 lb (244 kg), its destination is a halo orbit around the L1 point, roughly 1.5 million km from our home planet. A satellite placed in the halo orbit around the L1 point has the major advantage of continuously viewing the Sun without any occultation/ eclipse. Thus this will provide a greater advantage of observing the solar activities continuously. For a two-body gravitational system, the Lagrange Points are the positions in space where the gravitational pull of the two large bodies equals the necessary centripetal force required for a small object to move with them. For two-body gravitational systems, there are a total five Lagrange points, denoted as L1, L2, L3, L4, and L5. The Lagrange point L1 lies between the Sun-Earth line. The distance of L1 from Earth is approximately 1% of the Earth-Sun distance.
The spacecraft carries seven payloads to observe the visible surface of the Sun, the photosphere, chromosphere, and the outermost layers of the Sun, the corona using electromagnetic and particle detectors.
i. VELC (Visible Emission Line Coronagraph) is the prime payload onboard Aditya-L1, designed as a reflective coronagraph with a multi-slit spectrograph.
ii. SUIT (Solar Ultra-violet Imaging Telescope) to image the Solar Photosphere and Chromosphere in near Ultra-violet (UV) and, to measure the solar irradiance variations in near UV.
iii. SoLEXS (Solar Low Energy X-ray Spectrometer) is a soft X-ray spectrometer onboard Aditya-L1. The payload is designed to measure the solar soft X-ray flux to study solar flares.
iv. HEL1OS (High Energy L1 Orbiting X-ray Spectrometer) is a hard X-ray spectrometer designed to study solar flares in the high energy X-rays.
v. The ASPEX (Aditya Solar wind Particle Experiment) payload comprises 2 subsystems: SWIS and STEPS.
· SWIS (Solar Wind Ion Spectrometer) is a low-energy spectrometer that is designed to measure the proton and alpha particles of the solar wind.
· STEPS (Suprathermal and Energetic Particle Spectrometer) is a high-energy spectrometer that is designed to measure high-energy ions of the solar wind.
vi. PAPA (Plasma Analyser Package for Aditya) is designed to understand solar winds and its composition and do mass analysis of solar wind ions.
vii. Magnetometer (MAG) is meant to measure the low intensity interplanetary magnetic field in space. It has two sets of Magnetic Sensors: one at the tip of a 6 meter deployable boom, and the other in the middle of the boom, 3 meters away from the spacecraft.
Thus the suit of Aditya L1 payloads are expected to provide most crucial information to understand the problems of coronal heating, Coronal Mass Ejection, pre-flare and flare activities, and their characteristics, dynamics of space weather, study of the propagation of particles, and fields in the interplanetary medium etc. For India, Aditya L1 is more than a spacecraft; it's a beacon of the nation's aspirations in space science. The inaugural craft dedicated to solar exploration, its insights will deepen our grasp of the Sun's interactions with Earth.