On January 24, 2021, the NASA/ESA/CSA James Webb Space Telescope fired its thrusters for 297 seconds to complete the final post launch course correction to its trajectory; this burn inserted the telescope toward its ‘halo’ orbit around the second Lagrange point of the Sun-Earth system (approximately 1.5 million km, or 0.93 million miles, from Earth).
An artist’s impression of the James Webb Space Telescope. Image credit: ESA.
“Webb, welcome home! Congratulations to the team for all of their hard work ensuring Webb’s safe arrival at L2 today,” said NASA Administrator Bill Nelson.
“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!”
The second Lagrange point, L2, is an ideal location for an infrared observatory.
At 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.
Moreover, at L2, Earth is far enough away that the roughly room-temperature heat radiating from it won’t warm up Webb.
And because L2 is a location of gravitational equilibrium, it is easy for Webb to maintain an orbit there.
Note that it is simpler, easier, and more efficient to orbit around L2 than to dwell precisely at L2.
Furthermore, by orbiting rather than being exactly at L2, Webb will never have the Sun eclipsed by Earth, which is necessary for Webb’s thermal stability and for power generation.
In fact, Webb’s orbit around L2 is larger in size than the Moon’s orbit around Earth!
L2 is also convenient for always maintaining contact with the Mission Operations Center on Earth through the Deep Space Network. Other space-based observatories including WMAP, Herschel, and Planck orbit L2 for the same reasons.
This diagram shows a conceptual view of Webb’s trajectory and halo orbit. Image credit: Steve Sabia / NASA’s Goddard Space Flight Center.
The January 24 burn added only about 1.6 m/sec to Webb’s speed, which was all that was needed to send it to its preferred ‘halo’ orbit around the L2 point.
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.
“During the past month, Webb has achieved amazing success and is a tribute to all the folks who spent many years and even decades to ensure mission success,” said Webb project manager Dr. Bill Ochs, a researcher at NASA’s Goddard Space Flight Center.
“We are now on the verge of aligning the mirrors, instrument activation and commissioning, and the start of wondrous and astonishing discoveries.”
Source link: https://www.sci.news/astronomy/webb-second-lagrange-point-10489.html
