The James Webb Space Telescope (JWST) is the next of NASAs Great Observatories; following in the line of the Hubble Space Telescope, the Compton Gamma-ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope. At Sun-Earth L2, the Sun and Earth (and Moon, too) are constantly on one side of space, enabling Webb to keep its telescope optics and instruments constantly shaded. By orbiting rather than being precisely at L2, Webb will never have actually the Sun eclipsed by Earth, which is required for Webbs thermal stability and for power generation. Webbs orbit around L2 is bigger in size than the Moons orbit around Earth!” So, why did the Ariane not offer Webb more energy and why did Webb need course correction?
Why send out Webb to orbit Sun-Earth L2? At Sun-Earth L2, the Sun and Earth (and Moon, too) are constantly on one side of area, enabling Webb to keep its telescope optics and instruments constantly shaded. To see any and every point in the sky over the course of time needs simply waiting a few months to travel further around the Sun and expose more of the sky that was previously “behind” the Sun.
At L2, Earth is far enough away that the approximately room-temperature heat radiating from it wont warm up Webb. And since L2 is a place of gravitational stability, it is simple for Webb to maintain an orbit there. Note that it is simpler, much easier, and more effective to orbit around L2 than to dwell exactly at L2. By orbiting rather than being precisely at L2, Webb will never have the Sun eclipsed by Earth, which is essential for Webbs thermal stability and for power generation. Webbs orbit around L2 is bigger in size than the Moons orbit around Earth! L2 is likewise practical for always preserving contact with the Mission Operations Center on Earth through the Deep Space Network. Other space-based observatories including WMAP, Herschel, and Planck orbit Sun-Earth L2 for the exact same reasons.
Generally speaking, getting a spacecraft to Sun-Earth L2 is fairly uncomplicated, but Webbs architecture included a wrinkle. Karen Richon, Webbs Flight Dynamics lead engineer, explains getting Webb to L2 and keeping it there:
” Think about throwing a ball directly up in the air, as difficult as you can; it starts out really fast, however slows down as gravity pulls it back towards Earth, ultimately stopping at its peak and after that going back to the ground. Comparable to your arm offering the ball energy to increase a few meters from the Earths surface, the Ariane 5 rocket gave Webb energy to go the excellent distance of 1.1 million kilometers, but not quite enough energy to get away Earths gravity. Similar to the ball, Webb is decreasing, and, if we permitted it, would ultimately stop and fall back towards Earth. Unlike the ball, Webb would not return to the Earths surface area, but would be in a very elliptical orbit, with a perigee elevation of 300 kilometers and an apogee altitude of 1,300,000 kilometers. Utilizing thrust every 3 weeks or so from small rocket engines aboard Webb will keep it orbiting L2, looping around it in a halo orbit when every 6 months.
” So, why did the Ariane not provide Webb more energy and why did Webb need course correction? If the Ariane had offered Webb even a little bit too much energy than required to get it to L2, it would be going too quickly when it got there and would overshoot its wanted science orbit.
” Therefore, Webb requested just sufficient energy from the Ariane rocket to make sure that we would never ever have to do a retro burn, however would constantly require a burn from the observatory to precisely make up the distinction and place it in the preferred orbit. The Ariane 5 targeted Webb so accurately that our first and most vital burn was smaller sized than we needed to create and prepare for, leaving more fuel for a prolonged mission!”
— Karen Richon, Webb Flight Dynamics lead engineer, NASAs Goddard Space Flight Center
A detailed breakdown of Webbs orbit can be found here.
The James Webb Space Telescope (JWST) is the next of NASAs Great Observatories; following in the line of the Hubble Space Telescope, the Compton Gamma-ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope. JWST combines qualities of two of its predecessors, observing in infrared light, like Spitzer, with great resolution, like Hubble. Credit: NASA, SkyWorks Digital, Northrop Grumman, STScI
On Monday, January 24, engineers plan to advise NASAs James Webb Space Telescope to complete a last correction burn that will position it into its wanted orbit, almost 1 million miles away from the Earth at what is called the second Sun-Earth Lagrange point, or “L2” for short.
Mathematically, Lagrange points are options to what is called the “restricted three-body issue.” Any 2 huge, gravitationally significant objects in space generate five particular places– Lagrange points– where their gravitational forces and the centrifugal force of the motion of a little, third body such as a spacecraft remain in equilibrium. Lagrange points are identified L1 through L5 and are preceded by the names of the 2 gravitational bodies that produce them (the huge one first).
The Lagrange points associated with the Sun-Earth system. Lagrange Points are positions in area where the gravitational forces of a two-body system like the Sun and the Earth balance out, allowing a spacecraft to remain in position with lowered fuel consumption. The image consists of a small icon representing NASAs WMAP spacecraft orbiting around L2, which is about 1.5 million km from Earth. Credit: NASA/WMAP Science Team
While all Lagrange points are gravitational balance points, not all are entirely stable. L3, l1, and l2 are “meta-stable areas with saddle-shaped gravity gradients, like a point on the middle of a ridgeline between two slightly greater peaks in which it is the low, steady point between the two peaks, but it is still a high, unsteady point relative to the valleys on either side of the ridge. L4 and L5 are steady because each area resembles a shallow depression or bowl atop the middle of a long, tall ridge or hill.
