The James Webb Space Telescope has been traveling through space since its launch on December 25, 2021, and will soon face the next crucial step in its mission, performing an orbital burn to insert itself into an orbit around the sun.
Webb is set to arrive at its new home on Monday: A location almost 1 million miles away called L2, or the second Sun-Earth Lagrange point. These points are places where the gravities of the sun and the Earth interact so that a small body like a spacecraft will stay in place as it moves with them. There are five of these Lagrange points, called L1 through L5, in different locations relative to the sun and the Earth. But not all of them are suitable to use as orbit.
“While all Lagrange points are gravitational balance points, not all are completely stable,” NASA representative Alise Fisher writes in an update. “L1, L2, and L3 are ‘meta-stable’ locations with saddle-shaped gravity gradients, like a point on the middle of a ridgeline between two slightly higher peaks wherein it is the low, stable point between the two peaks, but it is still a high, unstable point relative to the valleys on either side of the ridge. L4 and L5 are stable in that each location is like a shallow depression or bowl atop the middle of a long, tall ridge or hill.”
The advantage of using the L2 location is in the way it allows the observatory to stay in the shade. The light and the heat from direct sun would cause many problems for the delicate instruments on board Webb, so the best solution is to keep them in the shade. By positioning Webb at the L2 orbit, it ensures that one side of it always faces the sun, with its giant sunshield to protect it, while the other side faces out into the cool of space. And because the observatory is moving around the sun, it can capture every piece of the sky as it travels.
The gravitational properties of L2 also make it easier for a craft to maintain an orbit, plus it has advantages for communications using NASA’s Deep Space Network. Other observatories use the L2 orbit for the same reasons, including NASA’s Wilkinson Microwave Anisotropy Probe and the European Space Agency’s Herschel Space Observatory and Planck satellite.
