The James Webb Space Telescope is soon arriving at its destination. As it nears the end of its journey, it loses speed. How to explain it?
The James Webb Observatory (JWST) is very close to its objective. The NASA telescope arrives this Monday, January 24, 2022 to its final destination, 1.5 million kilometers from Earth. From there, James Webb will evolve in his orbit around the Sun, taking advantage of the cold to easily observe the first galaxies of the Universe, in the infrared range.
After a month-long journey (the telescope took off on December 25, 2021), the JWST must perform a braking maneuver to fit into orbit around the Lagrange point L2 — a point of equilibrium in the alignment of the Sun and the Earth. If you follow the position of James Webb in real time from time to time, you may have noticed that when approaching the L2 point, the telescope tends to slow down (this January 24 around 6 p.m., it displays a speed of about 200 meters per second (by comparison, on December 28 it was moving at more than one kilometer per second). How to explain such a phenomenon ?
James Webb is like a ball thrown in the air
Why is the observatory going slower? After all, when the JWST took off, it only took 3 days to get away from the Moon’s orbit (a quarter of its journey). NASA opts for a comparison to help us understand: that of a ball thrown in the air, which begins its course very quickly, then slows down little by little under the effect of gravity.
” Just like the bullet, Webb slows down and would eventually fall back to Earth if we let him. “, explains the space agency on Twitter. The Ariane 5 rocket that launched it into space gave it enough energy to take it on a very long journey, but not enough to escape Earth’s gravity.
” Webb’s rocket gave him just enough energy to put him in orbit “, continues NASA (with some adjustments during the trip, to correct the trajectory a little). And ” engines aboard Webb will use propulsion every 3 weeks or so to keep it in a loop around L2 “.
On this site devoted to the particular orbit of James Webb, NASA uses another comparison: ” Bringing Webb into its orbit around L2 is like reaching the top of a hill pedaling vigorously on a bicycle only at the very beginning of the climb, generating enough energy and speed to get you most of the way. to climb the hill, and in such a way as to slow down until you stop and arrive almost at the top. »