Lagrange Points
Lagrange points are positions in space where objects sent there tend to stay put. At Lagrange points, the gravitational pull of two large masses 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. Lagrange Points are positions in space where the gravitational forces of a two- body system like the Sun and the Earth produce enhanced regions of attraction and repulsion. These can be used by spacecraft to reduce fuel consumption needed to remain in position.
These are five special points where a small mass can orbit in a constant pattern with two larger masses.
Of the five Lagrange points, three are unstable and two are stable. The unstable Lagrange points - labelled L1, L2 and L3 - lie along the line connecting the two large masses. The stable Lagrange points - labelled L4 and L5 - form the apex of two equilateral triangles that have the large masses at their vertices. L4 leads the orbit of earth and L5 follows. The L1 point of the Earth-Sun system affords an uninterrupted view of the sun and is currently home to the Solar and Heliospheric Observatory Satellite SOHO.
The L2 point of the Earth-Sun system was the home to the WMAP spacecraft, current home of Planck and the James Webb Space Telescope. L2 is ideal for astronomy because a spacecraft is close enough to readily communicate with Earth, can keep Sun, Earth and Moon behind the spacecraft for solar power and (with appropriate shielding) provides a clear view of deep space for our telescopes. The L1 and L2 points are unstable on a time scale of approximately 23 days, which requires satellites orbiting these positions to undergo regular course and attitude corrections.
Facts to remember:
There are 5 Lagrange points in outer space
Here, the orbit, gravity of sun and the gravity of earth are in balance
If spacecraft is placed on such points, it will remain in a HALO orbit and Earth and the spacecraft together will go round the sun
L1, L2, and L3 points are in unstable equilibrium whereas L4 and L5 points are in stable equilibrium
L4 and L5 are extremely vulnerable to asteroids
Therefore, even though they have stable equilibrium, L5 is preferred