Explained | ISRO's first solar mission, Aditya L1's 1.5 million km journey

The spacecraft which will travel 1.5 million kilometres from the Earth over the course of four months is set for launch from Sriharikota.

Aditya L1, the first space-based Indian mission to study the Sun is set for launch. The spacecraft developed by the Indian Space Research Organisation (ISRO) will be launched at 11.50 am from Andhra Pradesh’s Sriharikota on September 2, just days after Chandrayaan-3’s success which became the first spacecraft to land on the south pole region of the moon.

About Aditya L1

The spacecraft will travel 1.5 million kilometres from the Earth over the course of four months, and get placed in a halo orbit around the Lagrangian point 1 (L1) of the Sun-Earth system. Aditya L1 will study our nearest star, the Sun, to offer more knowledge about solar activities, and its effect on space weather. 

Key objectives of the mission also include understanding “coronal heating, coronal mass ejection, pre-flare and flare activities and their characteristics, dynamics of space weather, propagation of particles and fields.

“The spacecraft carries seven payloads to observe the photosphere, chromosphere, and the outermost layers of the Sun (the corona) using electromagnetic and particle detectors.  The suit of Aditya L1 payloads is expected to provide 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.,” ISRO said.

Aditya L1 is the first spatially resolved solar disk in the near UV band.

Why study the sun?

The sun is the nearest star and therefore can be studied in much more detail as compared to other stars.

The sun is home to several eruptive phenomena and releases immense amounts of energy in the solar system. If such explosive phenomena are directed towards the Earth, it is crucial to study it, to take corrective measures beforehand.

The Earth's protective shield blocks a number of harmful wavelength radiations including particles and fields. It is tough to study these radiations from the surface of the earth, hence Aditya L1 will provide information about these activities from outside of the earth’s atmosphere. 

Execution of Aditya L1

The spacecraft will first be positioned in a low Earth orbit. The orbit will then be made more elliptical, and utilising onboard propulsion, the spacecraft will then be launched toward the Lagrange point L1.

The spacecraft will leave the gravitational Sphere of Influence (SOI) of the Earth as it moves closer to L1. After leaving SOI, the spacecraft will enter its cruise phase before being sent into a large halo orbit around L1.

Aditya-L1 would require roughly four months to travel from launch to L1. L1 point has the major advantage of continuously viewing the Sun without any occultation/eclipses.

Aditya L1 trajectory.

What are Lagrange points?

Lagrange points are the positions for a two-body gravitational system, in this case, the Earth and the Sun, where a small object tends to stay if put there. These points in space can be used by spacecraft to remain in position with reduced fuel consumption.

Technically at Lagrange point, the gravitational pull of the two large bodies equals the necessary centripetal force required for a small object to move with them. The gravitational force of two celestial bodies creates pockets of gravitational equilibrium. There are a total of five Lagrange points denoted as L1, L2, L3, L4 and L5. 

Lagrange points of the Sun-Earth system

The Lagrange point L1 lies between the Sun-Earth line. NASA’s James Webb Telescope is stationed at L2.  The distance of L1 from Earth is approximately 1% of the total Earth-Sun distance.