Aditya-L1 : India's Maiden Solar Mission

Indian Space Research Organisation (ISRO) successfully launched Aditya-L1, India's first solar mission, from Satish Dhawan Space Centre in Andhra Pradesh's Sriharikota on September 2, 2023. Aditya-L1 shall be the first space-based Indian observatory to study the Sun. The 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. The successful launch of India's first solar mission came a week after the historic landing of Chandrayaan-3 on the south pole of the lunar surface.

Why study Sun?

The Sun is the nearest star and therefore can be studied in much more detail as compared to other stars. By studying the Sun, the Indian space agency envisages to learn much more about stars in our Milky Way as well as about stars in various other galaxies.

The Sun is a very dynamic star that shows several eruptive phenomena and releases immense amounts of energy in the solar system. ISRO states that if such explosive solar phenomena is directed towards the earth, it could cause various types of disturbances in the near earth space environment.

Various spacecraft and communication systems are prone to such disturbances and therefore an early warning of such events is important for taking corrective measures beforehand. In addition to these, if an astronaut is directly exposed to such explosive phenomena, he/she would be in danger. The various thermal and magnetic phenomena on the Sun are of extreme nature. Thus, the Sun also provides a good natural laboratory to understand those phenomena which cannot be directly studied in the lab.

What are Lagrange points?

Named in honour of Italian-French mathematician Josephy-Louis Lagrange, these points are positions in space where objects sent there tend to stay put. At Lagrange points, the gravitational pull of two large masses, like the Sun and the Earth, precisely equals the centripetal force required for a small object to move with them. These points in space can be used by spacecraft to reduce fuel consumption needed to remain in position.

There are five special points where a small mass can orbit in a constant pattern with two larger masses. The L1 point of the Earth-Sun system affords an uninterrupted view of the Sun and is currently home to the joint NASA-ESA Solar & Heliospheric Observatory mission (SOHO).

Aditya L-1 shall be placed in a halo orbit around the L1 of the Sun-Earth system. A satellite placed in the halo orbit around the L1 point has the major advantage of continuously viewing the Sun without any occultation/eclipses. This will provide a greater advantage of observing the solar activities and its effect on space weather in real time.

Aditya-L1

The Aditya-L1 mission has been launched by ISRO's PSLV rocket. After initially being placed in a low earth orbit, the spacecraft's orbit will subsequently be made more elliptical and later it will be launched towards the Lagrange point L1 by using on-board propulsion. As the spacecraft travels towards L1, it will exit the earths' gravitational Sphere of Influence (SOI). After exit from SOI, the cruise phase will start and subsequently the spacecraft will be injected into a large halo orbit around L1. The total travel time from launch to L1 would take about four months for Aditya-L1.

The Aditya-L1 mission carries a suite of seven scientific payloads to carry out systematic study of the photosphere, chromosphere and the outermost layers of the Sun (the corona) using electromagnetic and particle and magnetic field detectors. The Visible Emission Line Coronagraph (VELC) shall study the solar corona and dynamics of Coronal Mass Ejections. The Solar Ultraviolet Imaging Telescope (SUIT) payload shall image the Solar Photosphere and Chromosphere in near Ultraviolet (UV) and also measure the solar irradiance variations in near UV. The Aditya Solar wind Particle EXperiment (ASPEX) and Plasma Analyser Package for Aditya (PAPA) payloads shall study the solar wind and energetic ions, as well as their energy distribution. The Solar Low Energy X-ray Spectrometer (SoLEXS) and The High Energy L1 Orbiting X-ray Spectrometer (HEL1OS) shall study the X-ray flares from the Sun over a wide X-ray energy range. The Magnetometer payload is capable of measuring interplanetary magnetic fields at the L1 point.

Using the special vantage point L1, four payloads shall directly view the Sun and the remaining three payloads shall carry out in-situ studies of particles and fields at the L1, thus providing important scientific studies of the propagatory effect of solar dynamics in the interplanetary medium.

The suits of Aditya-L1 payloads are expected to provide crucial information to understand the problem of coronal heating, coronal mass ejection, pre-flare and flare activities and their characteristics, dynamics of space weather, propagation of particles and fields, etc.

Objectives of the Mission

·         Study of Solar upper atmospheric (chromosphere and corona) dynamics

·         Study of chromospheric and coronal heating, physics of the partially ionized plasma, initiation of the coronal mass ejections, and flares

·         Observe the in-situ particle and plasma environment providing data for the study of particle dynamics from the Sun

·         Physics of solar corona and its heating mechanism

·         Diagnostics of the coronal and coronal loops plasma: temperature, velocity and density

·         Development, dynamics and origin of CMEs

·         Identify the sequence of processes that occur at multiple layers (chromosphere, base and extended corona) which eventually leads to solar eruptive events

·         Magnetic field topology and magnetic field measurements in the solar corona

·         Drivers for space weather (origin, composition and dynamics of solar wind

How is the Mission unique?

·         First time spatially resolved solar disk in the near UV band

·         CME dynamics close to the solar disk (~ from 1.05 solar radius) and thereby providing information in the acceleration regime of CME which is not observed consistently

·         On-board intelligence to detect CMEs and solar flares for optimised observations and data volume

·         Directional and energy anisotropy of solar wind using multi-direction observations

Compiled by Annesha Banerjee & Anuja Bhardwajan (Young Professionals, Publications Division)

Source: ISRO