After a successful launch of NASA’s James Webb Space Telescope Dec. 25, and completion of two mid-course correction maneuvers, the Webb team has analyzed its initial trajectory and determined the observatory should have enough propellant to allow support of science operations in orbit for significantly more than a 10-year science lifetime. (The minimum baseline for the mission is five years.)
The analysis shows that less propellant than originally planned for is needed to correct Webb’s trajectory toward its final orbit around the second Lagrange point known as L2, a point of gravitational balance on the far side of Earth away from the Sun. Consequently, Webb will have much more than the baseline estimate of propellant – though many factors could ultimately affect Webb’s duration of operation.
Webb has rocket propellant onboard not only for midcourse correction and insertion into orbit around L2, but also for necessary functions during the life of the mission, including “station keeping” maneuvers – small thruster burns to adjust Webb’s orbit — as well as what’s known as momentum management, which maintains Webb’s orientation in space.
Arianespace’s Ariane 5 rocket launches with NASA’s James Webb Space Telescope onboard, Saturday, Dec. 25, 2021, from the ELA-3 Launch Zone of Europe’s Spaceport at the Guiana Space Centre in Kourou, French Guiana. The James Webb Space Telescope (sometimes called JWST or Webb) is a large infrared telescope with a 21.3 foot (6.5 meter) primary mirror. The observatory will study every phase of cosmic history—from within our solar system to the most distant observable galaxies in the early universe. Photo Credit: (NASA/Bill Ingalls)
The extra propellant is largely due to the precision of the Arianespace Ariane 5 launch, which exceeded the requirements needed to put Webb on the right path, as well as the precision of the first mid-course correction maneuver – a relatively small, 65-minute burn after launch that added approximately 45 mph (20 meters/sec) to the observatory’s speed. A second correction maneuver occurred on Dec. 27, adding around 6.3 mph (2.8 meters/sec) to the speed.
The accuracy of the launch trajectory had another result: the timing of the solar array deployment. That deployment was executed automatically after separation from the Ariane 5 based on a stored command to deploy either when Webb reached a certain attitude toward the Sun ideal for capturing sunlight to power the observatory – or automatically at 33 minutes after launch. Because Webb was already in the correct attitude after separation from the Ariane 5 second stage, the solar array was able to deploy about a minute and a half after separation, approximately 29 minutes after launch.
From here on, all deployments are human-controlled so deployment timing – or even their order — may change. Explore what’s planned here.
Webb is beginning to resemble the form it will take when it is fully deployed – now that the mission operations team has successfully deployed and latched into place the observatory’s forward and aft Unitized Pallet Structures.
The team began working through the deployment of the forward pallet this morning, concluding at approximately 1:21 p.m. EST. The team then moved on to the aft pallet deployment, completing the process at approximately 7:27 p.m. EST. While the actual motion to lower the forward pallet from its stowed to its deployed position took only 20 minutes, and the lowering of the aft pallet took only 18 minutes, the overall process took several hours for each because of the dozens of additional steps required. These include closely monitoring structural temperatures, maneuvering the observatory with respect to the sun to provide optimal temperatures, turning on heaters to warm key components, activating release mechanisms, configuring electronics and software, and ultimately latching the pallets into place.
The unfolding of the pallets marks the beginning of Webb’s major structural deployments and also the beginning of the sunshield deployment phase – which will continue through at least this Sunday, Jan. 2.
The planned timeline of these deployments is laid out here but could change as the operations team gets deeper into the schedule.
Early this afternoon the Webb mission operations team concluded the deployment of the first of two structures that hold within them Webb’s most unpredictable and in many ways complicated component: the sunshield.
The structures – called the Forward and Aft Unitized Pallet Structures – contain the five carefully folded sunshield membranes, plus the cables, pulleys, and release mechanisms that make up Webb’s sunshield. The team completed the deployment of the forward pallet at approximately 1:21 p.m. EST, after beginning the entire process about four hours earlier. The team will now move on to the aft pallet deployment.
Engineers at Northrop Grumman Space Park in Redondo Beach, California, oversee Webb’s final mirror fold test in April 2021. The forward pallet structure is seen here in the foreground, in its unfolded state. Credit: Northrop Grumman
The deployment of the forward pallet required several hours of the mission operations team carefully walking through dozens of steps – only one of which was the actual motor-driven deployment to move the pallet from its stowed position to its deployed state. The lowering of the forward pallet also marks the first time that structure has conducted that movement since it underwent its final unfolding and deployment test in December 2020 at Northrop Grumman Space Park in Redondo Beach, California.
The deployment of the pallet structures begins what will be at least five more days of necessary steps to deploy the sunshield – a process that will ultimately determine the mission’s ability to succeed. If the sunshield isn’t in place to keep Webb’s telescope and instruments extremely cold, Webb would be unable to observe the universe in the way it was designed.
The steps involved – outlined here – will continue after today with the extension of the Deployable Tower Assembly, followed by the release of the sunshield covers, the extension of the mid-booms, and finally the tensioning of the five Kapton layers of the sunshield itself.
As the deployment of the sunshield will be one of the most challenging spacecraft deployments NASA has ever attempted, the mission operations team built flexibility into the planned timeline, so that the schedule and even sequence of the next steps could change in the coming days.
While the team continues to work on unfolding Webb, we take a moment to learn more about the launch from two European Space Agency (ESA) representatives, Daniel de Chambure, Acting Head Ariane 5 Adaptation & Future Missions for ESA and Maurice Te Plate, JWST NIRSpec Systems and AIV Engineer for ESA. They provide details about the launch trajectory, which is the first phase of Webb’s journey before additional planned course corrections:
Europe’s Ariane 5 delivered Webb, with a launch mass of about 13,700 lbs (6200 kg), into the first phase of its planned trajectory toward its final position orbiting the L2 Lagrange point. As we all held our collective breath, lift-off was on December 25, 2021 at 7:20 am EST from Europe’s Spaceport in Kourou, French Guiana, for a flight lasting about 27 minutes before spacecraft separation.
About seven seconds after start of the ignition of the main stage cryogenic engine, the two solid propellant boosters were ignited, enabling liftoff. The launcher first climbed vertically for about 13 seconds, and then rotated towards the East. The solid boosters were jettisoned 2 mins and 14 sec after liftoff.
The fairing that protected Webb from the acoustic, thermal and aerodynamic stresses during the ascent, was jettisoned 3 minutes and 19 sec after liftoff. In order to protect the delicate thermal sunshield blankets of Webb, the fairing had been modified to minimize the shock of depressurization at separation. Updated venting ports allowed the pressure inside the fairing to properly equalize prior to opening. The recorded residual pressure was successfully below the required allowed maximum.
Artist’s impression of the James Webb Space Telescope, folded in the Ariane 5 rocket during launch from Europe’s Spaceport in French Guiana. Webb is the next great space science observatory, designed to answer outstanding questions about the Universe and to make breakthrough discoveries in all fields of astronomy. Webb will see farther into our origins – from the formation of stars and planets, to the birth of the first galaxies in the early Universe. Webb is an international partnership between NASA, ESA and CSA. Credit: ESA / D. Ducros
Once the atmospheric part of the flight was completed, Ariane’s onboard computers optimized the trajectory in real time, and brought the launcher to the intermediate orbit targeted at the end of the main stage propulsion phase, at 8 minutes and 35 seconds after launch. Ten seconds later, the HM7B engine of the cryogenic upper stage, with Webb still on top, was ignited and operated for a duration of 16 minutes. After engine shut-down, the upper stage underwent a number of positioning maneuvers with its attitude control system in order to separate Webb at the required attitude.
After separation, the upper stage underwent a delicate series of contamination and collision avoidance maneuvers, making sure that its thruster plumes did not impinge on Webb and its precious optics.
Finally, an end-of-life maneuver was performed to avoid potential long term collision risks with Webb.
Webb had started its journey to explore the Universe. Webb is on its way!
-Daniel de Chambure, Acting Head Ariane 5 Adaptation & Future Missions, ESA -Maurice Te Plate, JWST NIRSpec Systems and AIV Engineer, ESA
On Dec. 25, the Webb team successfully executed the first of three planned orbit corrections to get Webb into its halo orbit around the second Lagrange point, L2. To hear more about these important maneuvers, here is Randy Kimble, the Webb Integration, Test, and Commissioning Project Scientist, at NASA Goddard:
In sending the Webb Observatory into its orbit around the Sun-Earth L2 point, the vast majority of the energy required was provided by the Ariane 5 rocket. After release of the observatory from the rocket, several small tweaks to the trajectory are planned, to ease the observatory into its operating orbit about one month after launch.
Webb’s orbit is around L2—a point of gravitational balance on the other side of Earth from the Sun—but it does not reside exactly at the L2 point. Right at that point, Earth’s shadowing of the Sun would be large enough to greatly reduce the amount of power available for Webb’s solar arrays, without greatly simplifying the cooling challenges. In addition, when Webb’s communication antennas point at Earth to receive commands, they would be blinded by the huge radio emission of the Sun in the same direction. Instead, as the diagram indicates, Webb operates in a very loose orbit (many hundreds of thousands of km in diameter) around L2, in constant sunlight and with clean communications with the ground stations. Credit: NASA
The largest and most important mid-course correction (MCC), designated MCC-1a, has already been successfully executed as planned, beginning 12.5 hours after launch. This time was chosen because the earlier the course correction is made, the less propellant it requires. This leaves as much remaining fuel 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).
The burn wasn’t scheduled immediately after launch to give time for the flight dynamics team to receive tracking data from three ground stations, widely separated over the surface of the Earth, thus providing high accuracy for their determination of Webb’s position and velocity, necessary to determine the precise parameters for the correction burn. Ground stations in Malindi Kenya, Canberra Australia, and Madrid Spain provided the necessary ranging data. There was also time to do a test firing of the required thruster before executing the actual burn. We are currently doing the analysis to determine just how much more correction of Webb’s trajectory will be needed, and how much fuel will be left, but we already know that the Ariane 5’s placement of Webb was better than requirements.
One interesting aspect of the Webb launch and the Mid-Course Corrections is that we always “aim a little bit low.” The L2 point and Webb’s loose orbit around it are only semi-stable. In the radial direction (along the Sun-Earth line), there is an equilibrium point where in principle it would take no thrust to remain in position; however, that point is not stable. If Webb drifted a little bit toward Earth, it would continue (in the absence of corrective thrust) to drift ever closer; if it drifted a little bit away from Earth, it would continue to drift farther away. Webb has thrusters only on the warm, Sun-facing side of the observatory. We would not want the hot thrusters to contaminate the cold side of the observatory with unwanted heat or with rocket exhaust that could condense on the cold optics. This means the thrusters can only push Webb away from the Sun, not back toward the Sun (and Earth). We thus design the launch insertion and the MCCs to always keep us on the uphill side of the gravitational potential, we never want to go over the crest – and drift away downhill on the other side, with no ability to come back.
Therefore, the Ariane 5 launch insertion was intentionally designed to leave some velocity in the anti-Sun direction to be provided by the payload. MCC-1a similarly was executed to take out most, but not all, of the total required correction (to be sure that this burn also would not overshoot). In the same way, MCC-1b, scheduled for 2.5 days after launch, and MCC-2, scheduled for about 29 days after launch (but neither time-critical), and the station-keeping burns throughout the mission lifetime will always thrust just enough to leave us a little bit shy of the crest. We want Sisyphus to keep rolling this rock up the gentle slope near the top of the hill – we never want it to roll over the crest and get away from him. The Webb team’s job, guided by the Flight Dynamics Facility at NASA Goddard, is to make sure it doesn’t.
-Randy Kimble, JWST Integration, Test, and Commissioning Project Scientist, NASA Goddard Space Flight Center
Shortly after 10 am EST on Dec. 26, the Webb team began the process of releasing the gimbaled antenna assembly, or GAA, which includes Webb’s high-data-rate dish antenna. This antenna will be used to send at least 28.6 Gbytes of science data down from the observatory, twice a day. The team has now released and tested the motion of the antenna assembly — the entire process took about one hour.
Separately, overnight, the temperature sensors and strain gauges on the telescope were activated for the first time. Temperature and strain data are now available to engineers monitoring Webb’s thermal and structural systems.
At 7:50 pm EST, on Dec. 25, 2021, the James Webb Space Telescope initiated its first course correction burn to adjust its trajectory toward its final orbit. Credit: NASA Goddard Space Flight Center
At 7:50 pm EST, Webb’s first mid-course correction burn began. It lasted 65 minutes and is now complete. This burn is one of two milestones that are time critical — the first was the solar array deployment, which happened shortly after launch.
This burn adjusts Webb’s trajectory toward the second Lagrange point, commonly known as L2. After launch, Webb needs to make its own mid-course thrust correction maneuvers to get to its orbit. This is by design: Webb received an intentional slight under-burn from the Ariane-5 that launched it into space, because it’s not possible to correct for overthrust. If Webb gets too much thrust, it can’t turn around to move back toward Earth because that would directly expose its telescope optics and structure to the Sun, overheating them and aborting the science mission before it can even begin.
Therefore, we ease up to the correct velocity in three stages, being careful never to deliver too much thrust — there will be three mid-course correction maneuvers in total.
After this burn, no key milestones are time critical, so the order, location, timing, and duration of deployments may change.
You can track where Webb is in the process and read about upcoming deployments. NASA has a detailed plan to deploy the Webb Space Telescope over a roughly two-week period.The deployment process is not an automatic hands-off sequence; it is human-controlled. The team monitors Webb in real-time and may pause the nominal deployment at any time. This means that the deployments may not occur exactly in the order or at the times originally planned.
The James Webb Space Telescope is on its way! The mission launched on an Ariane 5 rocket at 7:20 a.m. EST on Saturday, Dec. 25.
Jane Rigby, the operations project scientist for Webb at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, told us what it was like to be supporting the launch from the Mission Operations Center at the Space Telescope Science Institute in Baltimore:
Launch day. It’s 7:00am, and I’m at the Mission Operations Center, “the MOC” — mission control to regular folks, for the launch of JWST. I’m wearing a mission patch polo and a headset. We launch in twenty minutes. The mood here is nervous, excited, and ready. I hear laughter in the hallways and see grim eyes over KN95 masks. We know that the future of NASA science is at stake. We know how audaciously hard the task will be. We know how many times we rehearsed. Now we do it for real.
Here was my Thanksgiving script:
Family: “Where will you be for launch?”
Me: “Baltimore!”
Friends: “It’s launching from Baltimore?”
Me: “No, we’re launching from French Guiana. Mission Control is in Baltimore.”
Jane Rigby, the operations project scientist for Webb at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, is seen sitting in the Mission Operations Center at the Space Telescope Science Institute in Baltimore during the launch of the James Webb Space Telescope.
So much must go right the first day. JWST must deploy its solar array to get power. No solar array, no mission.
LAUNCH. I can hear some shrieking from the VIPs downstairs, but it’s quiet here. We’re waiting to take control of JWST when it separates from the rocket about 30 minutes after launch.
The second stage shuts down and the launch vehicle separates. The call comes out that the attitude control system is working. The solar array should be deploying automatically…. There’s a tense wait… and then the call “Sun is on the array, current is on the array!” Suddenly it’s DEAFENINGLY loud on the voice loops, with clapping and shouts of happiness echoing through the MOC. I look up to see the video feed from the launch vehicle and THERE IT IS, our beautiful observatory with its solar panel all the way out, shining in the sun.
Things keep getting better. We acquire our first ground station, Malindi in Kenya, and the MOC sends our first command to JWST, accompanied by shouts and cheering. The reaction wheels are powered up and take over. We hear “Wheel Sun!” and I write it in all caps in my log. The call comes over the voice loop: “JWST is flying on its own.”
I glance down at the photos I brought for luck: my wife and my kid in front of JWST under construction; and my hero Frank Kameny in his youth, peering through a telescope. I close my eyes and give silent thanks for the entire team. Every piece of this huge, gorgeous observatory was ingeniously designed, custom made, mostly by hand, and torture-chamber tested and re-tested. So many hands cradled this bird. So many brains dreamed up science observations. So many worked so hard — now we see if it works.
—Jane Rigby, operations project scientist for Webb at NASA’s Goddard Space Flight Center
The James Webb Space Telescope is safely in space, powered on and communicating with ground controllers.
Webb continues in coast phase, and is now oriented correctly with respect to the Sun. The six reaction wheels of the spacecraft’s attitude control system have been powered on, and they are now responsible for keeping the spacecraft pointing in the right direction – so that its massive sunshield, which is the size of a tennis court and which will deploy over the course of the next week – will be able to keep the telescope protected from solar radiation and heat.
Webb is on its way to L2. Our next big milestone is this evening, when we conduct the first Mid-Course Correction burn.
