Lagrange Points

1. They are points in space between celestial bodies where a spacecraft stays more or less stationary.
2. Lagrange points are found along the plane of two objects in orbit around their common centre of gravity, where their gravitational forces cancel each other, so that a third body of negligible mass will remain at rest between them.
3. Advantages:
   1. Best ‘parking spots’ in space for satellites
   2. Ideal for controllers on the ground to communicate with spacecraft stationed at these points.
   3. Spacecraft will need very little fuel to remain in orbit or to launch to another planet,
4. Lagrange points exist throughout the Solar System due to this gravitational interaction between the sun and the planets and their moons.
5. Of the five Lagrange points L1, L2, L3, L4, and L5,
   1. Lagrange points – L1, L2, and L3 are unstable positions which lies along an imaginary straight line connecting the two larger bodies. These unstable positions can easily de-orbited objects by even weak forces, and then drift off into space.
   2. Points L4 and L5 are stable locations that form the apexes of two imaginary equilateral triangles with the two large celestial bodies at the vertices of each triangle. But they also tend to accumulate interstellar dust and asteroids called Trojans.
6. The recently launched Aditya-L1 by ISRO is designated to a parking slot at L1 in the sun-earth system.
7. Robotic explorers placed in L1:
   1. NASA’s Solar and Heliospheric Observatory Satellite
   2. Deep Space Climate Observatory
   3. Advanced Composition Explorer
   4. The Global Geospace Science Wind satellite. 
8. Upcoming missions to park objects at L1:
   1. Three U.S. probes – Interstellar Mapping and Acceleration Probe, Near Earth Object Surveyor, Space Weather Follow.
   2. The European Vigil mission.