Why did ISRO choose Lagrange Point 1 for the Aditya-L1 mission? Explained

ISRO has successfully inserted the Aditya-L1 observatory in an orbit around the Lagrange Point 1 or L1, 126 days after it lifted off from Sriharikota. Aditya-L1 was launched on September 2 as India's first solar mission and it is designed to last at least five years, with possibility of a mission extension.

In order to study the Sun, ISRO has chosen the Lagrange Point for advantages that could only be availed in space, 15 lakh km away from Earth to be precise.

Why did ISRO choose Lagrange Point 1?

There are five different Lagrange Points around the Sun and ISRO chose L1 for several advantages. As shown in the image below, L1 lies between the Sun but closer to Earth as this spot is in equilibrium due to the gravitational pull of both the celestial bodies.

It is worth noting that only two (L1 and L2) of the three Lagrange Points are stable since there isn't a second massive body to balance Sun's gravitational pull at L3, L4 and L5.

But first things first. What is a Lagrange Point? Lagrange Points are location which offer stability to a third object due to gravitational forces to two larger bodies. As a result of the gravitational stability, any spacecraft can remain in a fixed position with minimal fuel consumption. In an official statement, ISRO said, “This specific halo orbit is selected to ensure a mission lifetime of 5 years, minimising station-keeping manoeuvres and thus fuel consumption and ensuring a continuous, unobstructed view of sun.”

Elaborating the advantages, ISRO said that the L1 "provides a smooth Sun-spacecraft velocity change throughout the orbit, appropriate for helioseismology, 
it is outside of the magnetosphere of Earth, thus suitable for the "in situ" sampling of the solar wind and particles and it allows unobstructed, continuous observation of the Sun, and view of earth for enabling continuous communication to ground stations."

This would not have been possible if Aditya was installed in the low-Earth orbit or L2. The L2 is home to the European Space Agency's Gaia telescope and the NASA-ESA James Webb Space Telescope (JWST) which need to face away from the Sun to observe the universe in infrared wavelength of light. 

Now that Aditya-L1 has reached its destination, it will share the space with NASA's Solar and Heliospheric Observatory (SOHO) which was launched on December 2, 1995. 

But, both the "stable" Lagrange points are not entirely so. The stability at L1 and L2 lasts for approximately 23 days after which the spacecraft needs to fire its engines to avoid drifting either toward Sun or away from it - in other words, stay in its spot. During the entire course of mission, ISRO will carry out several engine burns to keep Aditya at L1.  

While Aditya-L1 mission is expected to last five years, the mission can get an extension if the observatory has some fuel left beyond its planned lifespan.