Lagrange points: Parking spots in space

Attributed to Joseph-Louis Lagrange who published an essay discussing three gravity locked bodies, in 1772, Lagrange points are spots where a smaller object (such as a satellite or space platform) can maintain a stable position, in relation to two larger bodies. Lagrange points could be ideal for space platforms, from where the solar system could be explored.

Let’s look at the space bodies most of us are familiar with, the Earth and the Moon. The two are orbit locked. There are five Lagrange points where gravitational force, centripetal force and Coriolis acceleration act in tandem. Lagrange points are measured from the center of the two large space bodies.Earth-Moon system

Earth-Moon system

In the Earth-Moon system, the L1 point is positioned between the Earth and the Moon at 326,400 kilometres from Earth’s center. This is 15.1% in front of the Moon, when measuring between Earth’s center, and the Moon’s.

The L2 point lies behind the Moon (when visualised from Earth) at 448,900 kilometres from Earth’s center. Its 16.8% behind the moon (where the distance between Earth’s centre and the Moon’s, is 100%).

L3 is located close to the moon’s orbit, behind the Earth (when facing the Moon). It’s at 381,700 kilometres or 99.3% of the distance between Earth’s centre and the Moon’s.

The L4 and L5 points form and equilateral triangle, measured from the center of the two large bodies, Earth and Moon. For these points to provide a safe and stable parking point, the primary body (Earth) needs to have a mass that’s at least 25 times more than the secondary body (Moon). Fortunately, the Earth mass is 81 times more than the Moon’s.

Solar system parking spots

The solar system contains numerous known Lagrange points. Most of these lie on Sun-planet systems and others on planet-moon systems. For immediate space exploration purposes, the Earth-Moon, Sun-Earth, Sun-Mars and Sun-Venus Lagrange points become important. They could be used as staging points and in-system transportation hubs.

What other uses do you think the Lagrange points could have?