Aditya-L1: What is Lagrange Point and why is it important for ISRO's solar mission?

Produced by: Tarun Mishra
Designed by: Manoj Kumar

After the successful Chandrayaan-3 mission, the Indian Space Research Organisation (ISRO) is now preparing to embark on another ambitious journey on September 2: the Aditya-L1 mission. The spacecraft's trajectory will position it within a halo orbit encircling the L1 Lagrange point, stationed at a distance of about 1.5 million kilometres from Earth. But one question arises: What is a Lagrange Point?

Travelling to Lagrange
Point

Imagine the cosmos as a grand stage where celestial bodies engage in an intricate dance. Among the performers are the Lagrange Points – cosmic positions shaped by the gravitational interplay between two massive actors, like the Sun and Earth. These points give rise to amplified regions of attraction and repulsion, setting the stage for spacecraft to choreograph their manoeuvres.

Enhanced forces in space

These celestial orchestrations owe their name to the ingenious Italian-French mathematician, Joseph-Louis Lagrange. Five such special points mark the choreographic masterpieces in space – places where a small mass can gracefully orbit in sync with two larger masses.

Who is Lagrange Point
named after?

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The Lagrange Points are celestial equilibrium zones, where the combined gravitational pull of two massive bodies equals the centripetal force that keeps a smaller object in rhythmic motion. This intricate mathematical conundrum, known as the "General Three-Body Problem," captivated Lagrange's mind.

Balancing act of forces

Among these points, three teeter on the edge of instability - L1, L2, and L3 - aligned along the Sun-Earth axis. In contrast, the remaining two, L4 and L5, portray celestial stability as they crown the vertices of equilateral triangles formed by the massive actors. L4 leads Earth's orbit while L5 follows.

Three's a crowd, five's a performance

Nestled at L1, the Solar and Heliospheric Observatory Satellite (SOHO) enjoys an uninterrupted view of our fiery star, enabling critical solar observations

Front-row seat to the Sun

L2, the cosmic sweet spot, housed the WMAP spacecraft and currently accommodates Planck. It is also reserved for the upcoming James Webb Space Telescope. This position offers optimal conditions for astronomy – close communication with Earth, shielding from Sun-Earth-Moon, and a clear view of deep space.

Cosmic Observatories

L4 and L5 are home to stable orbits when the mass ratio of the large bodies surpasses 24.96. These points have earned their name "Trojans," inspired by Homer's epic. Hundreds of Trojan Asteroids orbit Jupiter and Mars, and even Saturn's moons engage in this cosmic dance.

Trojan asteroid hideout

Imagine understanding Lagrange points as reading a weather map – the lines on the map show how different forces work together. Points where the lines are close mean strong celestial forces, and points where they're far apart mean everything is in cosmic balance.

Eureka moment

Just as dancers move gracefully, these Lagrange Points epitomise the delicate celestial choreography scripted by gravity's symphony. In this cosmic theatre, Lagrange Points are the stages where space missions unfold their tales of exploration, unlocking the mysteries of our universe.

Cosmic choreography

Ahead of the launch of India's solar mission, Aditya-L1, ISRO on Wednesday announced that the launch rehearsal has been completed along with the vehicle internal checks.

ISRO completes launch
rehearsal