After a generation of hard work and anticipation, the James Webb Space Telescope, the largest and most powerful space observatory in history, is poised to reach its final destination on Monday, where it will peer deeper into the universe than ever before, potentially glimpsing the first stars and galaxies.
Since it was launched into space on Christmas Day, Webb has traveled one million miles to Lagrange Point 2 (L2), an area of equilibrium created by the gravitational fields of Earth and the Sun.
The telescope is the product of a decades-long collaboration between NASA, the European Space Agency, and the Canadian Space Agency. With 100 times the sensitivity of the Hubble Space Telescope, Webb is expected to shed light on a host of exciting scientific mysteries, including whether alien life exists on other planets.
The Webb team is gearing up to briefly fire the telescope’s thrusters at around 2pm ET on Monday, a move that should nudge it into orbit around the Sun at L2. NASA plans to hold a press conference at 4pm ET to announce the telescope’s arrival at its new home, where it will offer never-before-seen views of our universe.
“We'll be monitoring the maneuver in real time, and it's only five minutes—it’s a very short maneuver,” said Karen Richon, the James Webb Space Telescope flight dynamics engineer lead at NASA’s Goddard Space Flight Center, in a call. “Soon after that, we'll know in real time whether the spacecraft operated as we expected.”
Lagrange points are weird locations in space where the gravitational pull of two large bodies, such as stars or planets, can strike a balance with the centripetal force of a small object, such as an orbiting spacecraft.
L2 is located behind Earth from the perspective of the Sun, making it an ideal parking spot for an infrared telescope like Webb. This is because, to gaze back into the ancient universe, Webb needs shade from the glare of the Sun. At L2, the observatory’s sunshield will always be positioned toward the inner solar system, creating a permanent dark side that will keep the telescope’s instruments at a chilly -223°C (-370°F). Those frigid temperatures allow Webb to capture infrared light from distant targets without distortion from nearby heat sources.
In the days following its launch, Webb completed two trajectory corrections that placed it on a smooth path toward L2. These initial maneuvers were performed by thrusters designed to propel the telescope in its folded-up form.
“The first two maneuvers were amazingly accurate,” Richon said. “I have worked on many missions, and I've never really had the first time you use a propulsion system be within 1 percent of what you predicted and modeled, so that was wonderful. It was a little more accurate on the second burn because we learned from the first one.”
Over the past several weeks, however, Webb has blossomed into its final form, successfully performing a complex sequence of commands that involved navigating hundreds of potential failure points.
For this reason, Monday’s maneuver will be performed by another set of thrusters matched to the fully unboxed version of the telescope, which has a different center-of-gravity. Despite the fact that these thrusters have not yet been tested in space, Richon said she doesn’t think the maneuver is particularly risky. Even if something goes wrong with the thrusters, there is a redundant set on Webb that could jump into action, she noted.
The thrusters that will fire today will also continue to stabilize Webb’s wide orbit at L2 for the rest of its mission, which is projected to last 20 years or more. The telescope’s path around the point is wider than the Moon’s orbit around Earth, and looks sort of like a “curved potato chip,” Richon noted.
Though Webb is now poised to reach its destination, it will still need about six months to calibrate its instruments before it can begin its science mission. But if all goes to plan, the telescope will be ready to send its observations back to Earth this summer, officially marking a new era in our understanding of the universe.
Update: Webb successfully arrived at L2 on Monday, January 24, according to a NASA media briefing held that day.