Lagrange points

For many spacecraft being put in orbit, being too close to Earth can be disruptive to their mission – even at more distant orbits such as GEO.For example, for space-based observatories and telescopes whose mission is to photograph deep, dark space, being next to Earth is hugely detrimental because Earth naturally emits visible light and infrared radiation that will prevent the telescope from detecting any faint lights like distant galaxies. Photographing dark space with a telescope next to our glowing Earth would be as hopeless as trying to take pictures of stars from Earth in broad daylight.

Lagrange points, or L-points, allow for orbits that are much, much farther away (over a million kilometres) and do not orbit Earth directly. These are specific points far out in space where the gravitational fields of Earth and the Sun combine in such a way that spacecraft that orbit them remain stable and can thus be ‘anchored’ relative to Earth. If a spacecraft was launched to other points in space very distant from Earth, they would naturally fall into an orbit around the Sun, and those spacecraft would soon end up far from Earth, making communication difficult. Instead, spacecraft launched to these special L-points stay fixed, and remain close to Earth with minimal effort without going into a different orbit.

The most used L-points are L1 and L2. These are both four times farther away from Earth than the Moon – 1.5 million km, compared to GEO’s 36 000 km – but that is still only approximately 1% of the distance of Earth from the Sun.