NASA, Partners Confirm Webb Launch on Dec. 25

NASA, ESA (European Space Agency), and Arianespace confirmed a targeted launch date of Saturday, Dec. 25, for the James Webb Space Telescope. A 32-minute launch window opens at 7:20 a.m. EST in Kourou, French Guiana (9:20 a.m. GFT/12:20 UTC).

An Ariane 5 rocket will lift off from Europe’s Spaceport carrying NASA’s next-generation space observatory.

white mockup of Ariane 5 rocket
A mockup of Arianespace’s Ariane 5 rocket is seen at the entrance to the Guiana Space Center in Kourou, French Guiana, Tuesday, Dec. 21, 2021. The James Webb Space Telescope is a large infrared telescope with a 21.3 foot (6.5 meter) primary mirror. The observatory is scheduled to launch Dec. 25 and 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)

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Ahead of Webb Launch, NASA is Watching the Weather in Space

James Webb Space Telescope Launch Update

Update: 4:30 p.m. EST, Dec. 21, 2021:

NASA and Arianespace successfully completed the Launch Readiness Review for the James Webb Space Telescope on Dec. 21. The team authorized the Ariane 5 rocket carrying Webb to rollout and the start of launch sequencing for the mission.

However, due to adverse weather conditions at Europe’s Spaceport in French Guiana, the flight VA256 to launch Webb – initially scheduled for Dec. 24 – is being postponed.

The new targeted launch date is Dec. 25, as early as possible within the following launch window:

  • Between 7:20 a.m. and 7:52 a.m. Washington
  • Between 9:20 a.m. and 9:52 a.m. Kourou
  • Between 12:20 p.m. and 12:52 p.m. Universal (UTC)
  • Between 1:20 p.m. and 1:52 p.m. Paris
  • Between 9:20 p.m. and 9:52 p.m. Tokyo

Tomorrow evening, another weather forecast will be issued in order to confirm the date of December 25. The Ariane 5 launch vehicle and Webb are in stable and safe conditions in the Final Assembly Building.

Launch Readiness Review Complete

NASA’s James Webb Space Telescope has cleared its launch readiness review, and has been given the formal green light to proceed with final preparations for liftoff planned for Dec. 24.

Additionally, Webb teams recently completed a comprehensive day of launch rehearsal that involved a joint effort between launch site crews in French Guiana, and Webb’s Mission Operations Center (MOC) at the Space Telescope and Science Institute in Baltimore, Maryland. The various teams involved with launching Webb are all standing at the ready, and have practiced each step routinely.

Next, the Ariane 5 rocket — with Webb safely encapsulated on top — is planned to begin the nearly two hour process of rolling out to the launch pad on Dec. 22.

NASA’s Webb Space Telescope Launch Confirmed for Dec. 24

Credit: ©ESA-Manuel Pedoussaut

The James Webb Space Telescope is confirmed for the target launch date of Dec. 24, at 7:20 a.m. EST.

Late yesterday, teams at the launch site successfully completed encapsulation of the observatory inside the Ariane 5 rocket that will launch it to space. Webb’s final launch readiness review will be held on Tuesday Dec. 21 and, if successful, roll-out is planned for Wednesday, Dec. 22.

Details of NASA’s prelaunch, launch, and postlaunch coverage are available on the agency’s website.



Webb Placed on Top of Ariane 5

On Saturday, Dec. 11, NASA’s James Webb Space Telescope was secured on top of the Ariane 5 rocket that will launch it to space from Europe’s Spaceport in French Guiana.

Webb placed on top of Ariane 5
Credit: ESA-M.Pedoussaut

After its arrival in the final assembly building, Webb was slowly hoisted nearly 130 feet and then perfectly aligned on top of the Ariane 5, after which technicians bolted Webb’s launch vehicle adapter down to the rocket.

Webb placed on top of Ariane 5
Credit: ESA-M.Pedoussaut

This whole process was performed under strict safety and cleanliness policies, as it was one of the most delicate operations during the entire launch campaign for Webb. A custom ‘shower curtain,’ already installed between the two platforms where technicians worked to connect Webb to its launch vehicle, served as the walls of a clean room to keep the observatory dirt-free.

Webb placed on top of Ariane 5
Credit: ESA-M.Pedoussaut

The next step ahead is to encapsulate Webb inside the Ariane 5’s specially adapted fairing.

Webb will be the largest, most powerful telescope ever launched into space. As part of an international collaboration agreement, the European Space Agency (ESA) is providing the telescope’s launch services using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the procurement of the launch services by Arianespace and for the development and qualification of Ariane 5 adaptations for the Webb mission.

Webb is an international partnership between NASA, ESA, and the Canadian Space Agency.

Find out more about Webb at:

By Thaddeus Cesari, Webb science writer, NASA’s Goddard Space Flight Center, Greenbelt, Md.

Webb’s Mid-Infrared Instrument Is Ready for Launch

Two weeks until launch! Things are moving forward in Kourou, and so we check in with the two leads (one from the U.S., one from the U.K.) of the final instrument in Webb’s suite:

“Webb’s Mid-Infrared Instrument (MIRI) is special – in the wavelengths it covers, the science that enables, its technology challenges, and in the way it was built.

“With the other three instruments, Webb observes wavelengths up to 5 microns. Adding wavelengths out to 28.5 microns with MIRI really increases its range of science. This includes everything from studying protostars and their surrounding protoplanetary disks, the energy balance of exoplanets, mass loss from evolved stars, circumnuclear tori around the central black holes in active galactic nuclei, and a lot more.

“The universe is relatively unexplored at mid-infrared wavelengths. Since anything at room temperature emits mid-infrared light, infrared astronomers working with ground-based telescopes peer through the huge foreground infrared emission of the telescope and atmosphere. With perseverance, some interesting mid-infrared results have been obtained from ground-based telescopes, but the limitations are severe.

“Dramatic results in the mid-infrared have come from telescopes in the vacuum of space, where they are cooled to cryogenic temperatures to eliminate their emission and are clear of Earth’s atmosphere. This brings big technical challenges. To keep the ice off the telescope before it was launched, the first infrared telescopes in space were built into thermos flasks, or Dewars, with thick walls to hold a vacuum. This meant that these telescopes had to be small, around a tenth the diameter of Webb. Despite their small size, these telescopes were very sensitive and have surveyed the entire sky as well as conducted pioneering studies of individual sources.

“Webb is built on a scale approaching the largest telescopes on the ground, and it will be cold enough to provide the full potential for the mid-infrared. The sensitivity gains and the image clarity will both be nearly a factor of 100 better than ever before. This was so exciting that ten European countries plus the United States pooled resources to make MIRI possible. The National Space Agencies of these ten European countries committed additional funding, beyond their ESA membership, specifically to build MIRI and enable its compelling science.

“While Webb provides the kind of capabilities in the mid-infrared that have only been dreamt of since the beginnings of infrared astronomy, we could only fit a single mid-infrared instrument into Webb and the available international resources. So, we designed the MIRI optics to cover almost everything – imaging, low- and medium-resolution spectroscopy, and high-contrast coronagraphy. About a third of the space for MIRI is empty to allow for long, thermally-isolating hexapod legs. MIRI includes a helium-filled closed-cycle cryogenic refrigerator to bring it to an operating temperature 33 degrees colder than the rest of Webb, reaching less than 7 degrees above absolute zero.

“Our multinational, transatlantic team has pulled together for more than two decades, with both exciting additions and painful losses, to provide Webb and the astronomical community with a mid-infrared instrument. Finally, the moment has arrived when the scientific results will reward everyone who has contributed. The instrument is ready, our cooler is full of helium and connected up, and the team is raring to go.”

—George Rieke, professor of astronomy at the University of Arizona, and Gillian Wright, director of the UK Astronomy Centre

By Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center

And Alexandra Lockwood, project scientist for Webb science communications, Space Telescope Science Institute

Webb Moved to Meet its Rocket

On Dec. 7, NASA’s James Webb Space Telescope was transferred to the final assembly building at Europe’s Spaceport in French Guiana to meet its Ariane 5 launch vehicle.

Stowed inside a special transport container and mobile clean room, Webb’s vitals were meticulously monitored throughout the entire process of moving between buildings.

Credit: © ESA-CNES-Arianespace; used with permission

The Ariane 5 rocket Webb will ride to space was moved to the same building on Nov. 29. Here, adjustable platforms allow engineers to access the launch vehicle and its payload.

The next steps ahead are to safely lift Webb to an upper platform which has been prepared so that Webb can be connected to the Ariane 5’s upper stage. After being connected to the rocket, technicians will move forward to encapsulate Webb inside Ariane 5’s specially adapted fairing.

Credit: © ESA-CNES-Arianespace; used with permission

In preparation for a Dec. 22 launch, ground teams have already successfully completed the delicate operation of loading the spacecraft with the propellant it will use to steer itself while in space.

Webb will be the largest, most powerful telescope ever launched into space. As part of an international collaboration agreement, ESA (the European Space Agency) is providing the telescope’s launch service. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission.

Credit: © ESA-CNES-Arianespace; used with permission

Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).

Find out more about Webb here:

By Thaddeus Cesari, Webb science writer, NASA’s Goddard Space Flight Center, Greenbelt, Md.

NASA’s James Webb Space Telescope Fully Fueled for Launch

Editor’s Note, Dec. 8, 2021: This post has been updated with more accurate fueling figures.

In preparation for launch later this month, ground teams have successfully completed the delicate operation of loading the James Webb Space Telescope with the propellant it will use to steer itself while in space.

The James Webb Space Telescope was fueled inside the payload preparation facility at Europe’s Spaceport in French Guiana on Nov. 26, 2021. Credit: © ESA-CNES-Arianespace/Optique video du CSG – P Piron; used with permission

In order to make critical course corrections shortly after launch, to maintain its prescribed orbit nearly 1 million miles from Earth, and to repoint the observatory and manage its momentum during operations, Webb was built with a total of 12 rocket thrusters. These rocket thrusters use either hydrazine fuel or a special mixture of hydrazine fuel and dinitrogen tetroxide oxidizer.

To safely handle these extremely toxic propellants, Webb was moved to the fueling section of the Ariane payload preparation facility at Europe’s Spaceport in French Guiana. Specialists wore Self-Contained Atmospheric Protective Ensemble, or “SCAPE,” suits while loading the observatory. The nearly 10-day procedure began Nov. 25.

Webb’s spacecraft bus, built by Northrop Grumman, was filled with 369 pounds (168 kilograms) of hydrazine fuel and 292 pounds (133 kilograms) of dinitrogen tetroxide oxidizer. Both fuel and oxidizer will be used together to maximize power for the biggest “burns” by Webb’s Secondary Combustion Augmented Thrusters, which are for mid-course corrections and inserting into L2 orbit, as well as for orbit maintenance around L2 during the mission. However, hydrazine alone will be used for the small “burns” by Webb’s tiny precision Monopropellant Reaction Engine thrusters, which are used for large-angle repointing and for managing spacecraft momentum. The fuel loading system was formally disconnected Dec. 3, followed by inspections and closeouts that concluded over the weekend.

Combined operations between the Arianespace and NASA teams preparing Webb and its Ariane 5 rocket are now set to begin. The next large milestones for the joint teams will be to move Webb to the Bâtiment d’Assemblage Final (BAF), or Final Assembly Building; place it atop its rocket; and encapsulate it inside its protective fairing. With final closeouts complete, the full stack of rocket and payload atop its mobile launch platform will be rolled out of the BAF to the launch pad, two days before its scheduled Dec. 22 launch.

By Thaddeus Cesari, Webb science writer, NASA’s Goddard Space Flight Center, Greenbelt, Md.

Progress for Webb at the Launch Site

On Wednesday, Nov. 17, NASA Headquarters held its final review for the mission prior to launch. A week later, on Nov. 24, a review committee approved Webb’s transition to the next stage in its preparations for launch. This week we’ve asked NASA’s Randy Kimble, Webb’s integration, test, and commissioning project scientist, to tell us how things are going at the launch site:

“The loading of propellants into the Webb observatory is complete at the Arianespace launch facilities in Kourou, French Guiana. This is an important step in the path toward launch.

“The vast majority of the launch energy required to send Webb to its operating orbit around the Sun-Earth Lagrange point L2 will be provided by the massive Ariane 5 rocket. Nevertheless, the observatory carries propellants of its own. After being released from the launcher, Webb will use its own system of small rocket thrusters to fine-tune its approach to its final halo orbit around the L2 point (illustrated below), where the telescope and instruments will cool in the shade of the enormous sunshield, protected from the heat of the Sun, Earth, and Moon. Mid-Course Correction maneuvers for refining the trajectory are planned (nominally) for 12.5 hours and 2.5 days after launch, with a third one month later, to ease Webb into its L2 orbit. Those same thrusters will be used periodically throughout the mission to maintain that orbit, with small maneuvers called ‘station keeping.’

Webb orbit
Credit: NASA

“A second set of smaller thrusters on the observatory compensate for momentum buildup caused by the pressure of solar radiation onto the large area of the sunshield. Although Webb is designed to keep that pressure well balanced, angular momentum builds up as the telescope points at different targets, so occasional, small momentum-unloading maneuvers are required to keep the observatory’s reaction wheels within their proper operating ranges. Reaction wheels are flywheels in the Webb spacecraft that help keep the payload’s orientation stable.

“Propellant loading was the final major operation for the observatory itself, before it moves to the Final Assembly Building (BAF is the French acronym) for integration with the Ariane 5 launch vehicle.

“One special aspect of processing the Webb observatory at the launch site is the need to keep it clean. Unlike Hubble, whose telescope is enclosed in a protective tube, Webb can operate successfully with just the shade of the sunshield to protect it in space. While it is subject to the air on Earth, the environment around the telescope must be kept as clean as possible. This ensures that Webb’s mirrors and sunshield are not contaminated with small particulates or molecular films, both of which could reduce the observatory’s sensitivity. The NASA, ESA (European Space Agency), Arianespace, and French space agency (Centre National d’Etudes Spatiales) teams have cooperated very closely to custom-clean the launch facilities to Webb’s demanding requirements. NASA’s Goddard Space Flight Center has also provided portable HEPA filter walls to augment the contamination control of the airflow near the payload. Goddard contamination engineers Eve Wooldridge and Alan Abeel have reported excellent results from the joint contamination control efforts for the roughly seven weeks Webb has been in Kourou so far. They note that continued vigilance is required for the remainder of the ground processing flow, as the most challenging facilities are still ahead.

“From Eve and Alan, ‘Our NASA contamination control engineers and technicians have transformed facilities that are not designed for scientific spacecraft into well-controlled clean rooms not just with HEPA filters, but by covering, cleaning, removing, bagging, and sealing over items incompatible with Webb’s stringent cleanliness requirements, and then cleaning every surface daily.’ The launch site facilities that Webb has encountered so far have all performed well, thanks to these efforts. The next challenge is to transform the facilities in the BAF (which opens huge doors for the rockets and spacecraft), where Webb will be integrated with the rocket and then encapsulated. This can be done because of the excellent team Eve and Alan are so fortunate to work with. ‘We maintain that this is not just the largest contamination control team in the world doing this type of work; it is the best and most hard-working. They have cheerfully worked long days, six days a week, and have proven to be a strong morale-booster for the entire launch campaign team. While we all look forward to launching Webb and getting home to our families, we know we will miss each other and this amazing time in Kourou very much.’

Webb in the clean room at Europe's Spaceport. Credit: NASA/Chris Gunn.
Webb in the clean room at Europe’s Spaceport. Credit: NASA/Chris Gunn

“As Webb prepares to move to the final steps of ground integration, there are no more planned major ground tests of the payload – only minimal electrical checks. The Comprehensive Systems Test that was performed in late October to confirm the observatory’s health after arriving at the launch site represented the culmination of many years of testing. The successful completion of that major ground test put members of the Webb team who had traveled to Kourou in a reflective mood:

“Macarena Garcia Marin, ESA’s instrument and calibration scientist for Webb’s Mid-Infrared Instrument (MIRI), noted with pride the ‘can-do’ attitude and the wonderful feeling of camaraderie among the team that was required to get through years of often-grueling test campaigns. She was also thrilled by the opportunity to see a ‘sneak preview’ of the Webb launch, having viewed the most recent Ariane 5 launch (VA255, on October 23) from a distance of three miles away – ‘Breathtaking!’

“Scott Lambros, Webb instrument systems manager at Goddard, reported mixed feelings as ground testing of the observatory drew to a close: ‘Strangely enough, it’s sad to see the observatory going away – we’ve been working with it so long now, it’s like saying goodbye to a friend. It’s also sad that many of the wonderful people I’ve been working with in the last 19 years soon will be going in different directions. On the other hand, I am extremely excited to see Webb ready for launch and prepared to fulfill its scientific purpose out at L2.’

“As are we all.”

—Randy Kimble, Webb integration, test, and commissioning project scientist, Goddard

By Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center

And Alexandra Lockwood, project scientist for Webb science communications, Space Telescope Science Institute