Webb Arrives at L2!


“Webb, welcome home!” said NASA Administrator Bill Nelson. “Congratulations to the team for all of their hard work ensuring Webb’s safe arrival at L2 today. We’re one step closer to uncovering the mysteries of the universe. And I can’t wait to see Webb’s first new views of the universe this summer!”

Webb fired its onboard thrusters to complete the final postlaunch course correction to Webb’s trajectory. This mid-course correction (MCC) burn inserted Webb toward its final orbit around the second Sun-Earth Lagrange point (L2), nearly 1.5 million km away from the Earth.

Mathematically, Lagrange points are solutions to what is called the “restricted three-body problem.” Any two massive, gravitationally significant objects in space generate five specific locations – Lagrange points – where their gravitational forces and the centrifugal force of the motion of a small, third body such as a spacecraft are in equilibrium. Lagrange points are labeled L1 through L5 and are preceded by the names of the two gravitational bodies that generate them (the big one first).
While all Lagrange points are gravitational balance points, not all are completely stable. 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.
So why send Webb to orbit Sun-Earth L2? Because it is an ideal location for an infrared observatory. At Sun-Earth L2, the Sun and Earth (and Moon, too) are always on one side of space, allowing Webb to keep its telescope optics and instruments perpetually shaded. This enables them to get cold for infrared sensitivity, yet still access nearly half the sky at any given moment for observations. To view any and every point in the sky over the course of time requires merely waiting a few months to travel farther around the Sun and reveal more of the sky that was previously “behind” the Sun.

Webb’s orbit will allow it a wide view of the cosmos at any given moment, as well as the opportunity for its telescope optics and scientific instruments to get cold enough to function and perform optimal science. Webb has used as little propellant as possible for course corrections while it travels out to the realm of L2, to leave as much remaining propellant as possible for Webb’s ordinary operations over its lifetime: station-keeping (small adjustments to keep Webb in its desired orbit) and momentum unloading (to counteract the effects of solar radiation pressure on the huge sunshield).
Now that Webb’s primary mirror segments and secondary mirror have been deployed from their launch positions, engineers will begin the sophisticated three-month process of aligning the telescope’s optics to nearly nanometer precision.

Watch a special episode of NASA Science Live to learn more about what’s next for the James Webb Space Telescope.