Garth’s Blog Reports around the December 25 Webb Launch. Distributed as Updates to the Astronomy Community.

Extensive regular updates and coverage and links can be found at:


JWST in L2

After Launch — Day L+30. Monday January 24, 2022. In L2! Secondary and Primary Mirrors also fully-deployed from launch stops to alignment position. Last of the major deployment activities done.

As you have heard, Webb is now home. The 5-minute burn of the on-board thrusters Monday placed Webb into its halo orbit around L2, ready to be fine-tuned over the next few months to make the best images of the universe ever seen. I still cannot quite believe, after 35 years from when we first started discussing the NGST concept at STScI, that Webb is home in L2!

This update is lengthier than usual since it covers getting into L2, as well as the mirror deployments from the last two weeks, and then some future activities.

L2 and the mid-course corrections:

It has been an essentially flawless first month for Webb, with a spectacular launch, and with all the major mechanical deployments being done in just 2 weeks. Then the equally crucial secondary and 18 primary mirror deployments from their launch stops to their operating positions were carried out over the following two weeks (more on this below). Together these two major periods of deployments have turned Webb into a telescope, ready to be fine-tuned in L2 to ensure that it can begin a new era of discovery of the nature of the universe.

The flawless precision of the Christmas-Day launch by Ariane enabled the three burns of the onboard thrusters (mid-course corrections — MCC) to put Webb into L2 using far less of its propellant than planned. The first MCC-1a on launch day was only 65-minute long, much shorter than expected, and it added 45 mph (20 meters/sec) to Webb's speed. The second correction maneuver MCC-1b, two days later, added just 6.3 mph (2.8 meters/sec). The 5-minute MCC-2 burn today (Monday) added a little less than 1.5 m/sec for the insertion maneuver. Every one of these burns, like the initial Ariane final velocity, was chosen to "burn low" to ensure that Webb never overshoots its position relative to L2. Webb cannot be decelerated in the direction to the sun. Short ~1 minute station-keeping burns will be made on ~21 day intervals in its L2 halo orbit, again always set to be a tad less than what would push Webb past L2. The three MCC burns used only about one-third of the pre-launch propellant allocation. JWST now will have a science life in L2, from its propellant load, more like 20 years than the initially hoped-for 10 years. More robust numbers will come from the flight dynamics team, but there will remain some lifetime uncertainty since the on-board thrusters are used to offset the reaction wheel momentum buildup from the pointing changes needed to view targets during science operations. These “momentum dumps" use propellant and are less predictable than the station-keeping burns.

There is an excellent video here showing Webb in its 6-month halo orbit around L2, as the Earth-Moon system moves around the sun, along with further information — https://www.webb.nasa.gov/content/about/orbit.html or on youtube https://www.youtube.com/watch?v=6cUe4oMk69E&list=TLGG8tIphgpDAHkyNDAxMjAyMg&t=2s

An excellent graphic released today is at the bottom.

The primary and secondary mirror "mini-deployments":

Two weeks ago on Saturday January 8 the announcement was made that Webb was "fully deployed". This was a remarkable achievement, accomplished within just two weeks of launch, on schedule and with almost no issues. With the deployment of the starboard Primary Mirror Wing on the 8th, the major mechanical deployments were then behind us. With the completion of that remarkable series of deployments, the Project Manager Bill Ochs emphasized, in response to comments about "that looked easy", that it may have looked easy, but in reality it took a huge team effort over many years to actually accomplish what was seen in the first two weeks. Those nail-biting activities did go incredibly smoothly, due to the stringent test and verification program that JWST underwent. Nonetheless, the lack of challenges was still a surprise to those who had seen just how complex those deployments were — me certainly included.

Yet this was not the end of the deployments. An absolutely crucial series of "mini-deployments" was then started. These were less obvious, but none the less important for Webb to be a success. A key activity, that was carried out during the next 1.5 weeks, was to move the mirrors from their launch positions. The secondary mirror and all 18 primary segments had to move 12.5 mm (half an inch) to their nominal operating position from where they were located with pegs and sockets during the launch — this arrangement held the mirrors in place for launch, ensuring their safety against the huge vibrations from the rocket.

12.5 mm does not sound like much, but the very same actuators that will have to move the mirrors around to get diffraction-limited images from Webb in infinitesimal 8 nm steps, 1/10,000 the size of a human hair, now had to move the mirrors a distance that was over one million times greater. And each of the mirrors had 6 actuators so the secondary plus 18 segments had 114 actuators, plus the 18 radius of curvature actuators — 132 actuators in all — had to move. Fortunately these remarkable actuators have a coarse mode and can also move in 58 nm steps for the deployment. Even so, it was a huge bunch of moves. These actuators required some incredible engineering. See here: https://jwst.nasa.gov/content/observatory/ote/mirrors/index.html#1c and for much more detail here https://esmats.eu/amspapers/pastpapers/pdfs/2006/warden.pdf

Moving the mirrors thus took time! Lots of it! In fact, watching the mirror positions change was like watching grass grow! Every actuator move is done one at a time under human oversight from the MOC. The moves also required short periods of operation to keep the actuator motor from heating the mirror segment. In effect, this meant that to move all the segments approximately 1 mm, actuator-by-actuator and segment-by-segment, took about a day. Hence the "watching grass grow" comment. The NASA team put an excellent day-by-day summary of the mirror positions during this activity that was shown on the deployment explorer web page. https://jwst.nasa.gov/content/webbLaunch/deploymentExplorer.html A typical mirror status figure is shown below, with the final one as well. Seeing the final graphic, with every mirror segment and the secondary at 0.0, definitely called for a celebration!

All these moves were completed late last week, again going remarkably smoothly. While this did not have the visibility of the initial major deployments, having all the mirrors move to their operational position was absolutely essential for JWST to produce its needed exquisite images! Webb is now a full telescope, ready for all the hard, time-consuming work to get aligned images (~3 months of effort), and then to get all the instruments ready for science operations (another ~2 months). There is a lot left to do, but with all the deployments behind us now comes the long hard slow slog of commissioning.

The JWST System Engineer Mike Menzel put this phase of the deployments and commissioning activities in context by noting that, after the major deployments, JWST was entering the precision phase of its commissioning activities.

Current status and future activities:

It is fascinating to see that the primary mirror segments are already down to a brisk ~70K above absolute zero (-202C or -330F), with a range of temperatures (60-80K) as expected, while the secondary is nearer to 35K (lower, again as expected). The spacecraft on the warm side is at about 13C or 55F. So the sunshield is really doing its job, dropping the layer one temperature of 54C down dramatically, allowing the telescope to get nicely cool.

All the initial deployments that were listed on the one-page deployments commissioning timeline that I distributed on December 28 for the first month of activities have now been completed. This also includes a crucial high-gain Ka band antenna deployment late last week that is essential for the high data-rate transfer for science operations of the science instruments. The high-speed data transfer of the Ka band link through Webb's communication network is now being checked out.

The transition to the very long, slow commissioning process has already begun. Within roughly a week or so it is expected that NIRCam will be cold enough (~100K) to be operated to begin mirror alignment/phasing (for science operations NIRCam will be quite a bit colder — more like 50-60K). NIRCam has a dual role as a science instrument and as an alignment/phasing tool. The phasing will be to about 1/5000 of a human hair, or a few actuator fine steps (8 nm step size). But don't expect instant results. This is expected to take months!

As anyone who has worked on a brand new astronomical instrument, or been involved in telescope commissioning, can tell you, there is a large number of items, hardware and software, that have to be checked out, their “real-world” operation understood, and then corrected, as necessary. This entails a huge number of activities to initiate, to verify that they work as planned, and to fine-tune all the elements to make everything work smoothly together. Making everything work together and tuning everything up is really where the rubber hits the road. Until this is done we don’t have a functional Observatory.

The grass-growing analogy will be used often in the coming months, I suspect. But the outcome will be an incredibly powerful Observatory!


JWST in L2
(Credit: Steve Sabia/NASA Goddard)

Intermediate 18 primary mirror segment positions, plus the secondary mirror position, as of 01/14/2022 — all were at -12.5 mm initially. Secondary (SM) shown in the central mirror "hole".

Final 18 primary mirror segment positions, plus the secondary mirror position, as of 01/19/2022 — after all 12.5 mm of movement was done. Secondary (SM) shown in the central mirror "hole”. This was definitely a moment for celebration!

Fully-deployed Telescope

After Launch; Day L+14. Saturday, January 8, 2022. Fully-deployed and latched Primary Mirror wings.

Webb now is a full telescope, with its Primary Mirror complete. All major mechanical deployments done. Mirror segment moves from launch stops next.

Science and space engineering are getting a great deal of positive visibility through Webb’s deployment successes. The media attention has been spectacular. It is great to have Webb now looking like our simulated images, even if unseen. And this all happened in just 2 weeks from its folded compact configuration at launch. It is remarkable that all the major deployments were done so quickly — with no serious issues or challenges. Given the complexity of JWST, this is a stunning accomplishment. All that careful testing, re-testing and cross-checking by the Webb NASA and Northrop Teams really paid off.

A bit of added info beyond what you may have seen. The NASA Live from this morning’s final primary wing deployment is here: https://www.youtube.com/watch?v=tlGTem8vkB0 The mirror wing move runs for ~4 min from ~53:20 min to when the wing reaches its hard stop. Then several hours later the latching is completed around 3h 45 min. The image below is from the NASALive video feed. It shows the real-time updated Webb simulation displayed in the MOC, and also the Webb MOC team members cheering and clapping when the second wing moved into position to make Webb’s primary mirror whole.

The press briefing that came after the completion of latching is here: https://www.youtube.com/watch?v=hET2MS1tIjA

The last 4 of the 178 non-explosive actuators (NEAs) were fired today. Having all 178 fire without any issues is a tremendous relief. At this point only 49 single point failure (SPF) items remain out of the 344 — about 85% are retired — but some would impact “only” one of the instruments, so not all 49 are SPFs that impact the full mission. 15 SPFs are in instruments. Many SPFs will also not be retired until the end of the full mission life... When it comes to SPFs we have now entered a more “normal” mission complement.

Two weeks from now Webb will be commanded to execute a small propellant burn to put itself into its halo orbit around L2 — its home until the propellant runs out, way into the future, which is now significantly over the 10 year lifetime goal.

The last few weeks have been an incredible, and exhausting time! But on refection, looking back on over 3 decades of effort by so many, it is remarkable what dedicated and committed people can do when taking an ambitious concept and carrying it through to completion, against hugely challenging technical, managerial and political odds.

Starting in less than 6 months from now, the science and discoveries from Webb, our Hubble on steroids, will be dramatic and paradigm shattering...


A Telescope is Born

After Launch Day L+11. January 6, 2022. Secondary Deployment.

A telescope is born. As the Project Manager said: "we actually have a telescope".

Today was a truly momentous day. A telescope was born. The JWST Project Manager Bill Ochs proclaimed, when the secondary latched into place, "we are 600,000 miles from Earth and we actually have a telescope”. Bill was in the Mission Operations Control room conveying his congratulations to the whole JWST team. That was right on. We don’t have a completely-aligned, fully-operational telescope and instruments by any means. That is ~5 months away. But for sure, light can, in principle, now go through JWST from objects in the universe and into Webb's instruments — albeit as 18 very fuzzy blobs, at best, until it is all tuned up!

With the secondary deployed, the remaining major deployments later this week are the release, rotation and latching of the two primary mirror backplane assembly wings (the PMBA-V2 and PMBA+V2). So at this point I am not counting all the chickens until they are latched.

The secondary deployment has been widely reported in the media and on social media, etc., but I wanted to convey a little more on that crucial deployment. And also mention two other key activities that get us closer to having a fully deployed telescope. See also https://blogs.nasa.gov/webb/ and the replay of the NASA TV Live of the secondary mirror deployment with the excellent discussion and footage https://www.youtube.com/watch?v=-EnlaXnFcGs

First — opening a cover for the mid-infrared instrument MIRI: Overnight a key step was performed on MIRI to power up the instrument control electronics (ICE) and to unlock and open a contamination cover (CCC). This successful demonstration of the ICE to power up was followed by a successful opening of the CCC. These steps were part of the early deployment sequence in the overall timeline I sent around last week, and are a key first activity of many for eventual MIRI functionality in 4-5 months after it has cooled to 7 degrees above absolute zero!

Second — the final step in the deployment of the aft deployable instrument radiator (ADIR): This deployment is planned for Thursday. The ADIR is a crucial structure on the cold telescope/instrument side that helps radiate heat away from Webb's instruments and mirrors. Eagle-eyed readers of the earlier timeline page I sent around will have noticed that ADIR deployment is listed as Part 1 and Part 2. Part 1 was an initial release of three of the non-explosive actuators that held the ADIR during launch. These first three actuators were released just after launch to prevent any strain from dimensional change in the ADIR as the telescope and ADIR cooled considerably after sunshield deployment. Part 2, the final step in the sequence, is planned for Thursday morning when the last actuator is fired and the panel does its full release, with springs driving the ADIR into its final deployed position.

Third — and most dramatically, the secondary deployment and latching: The last time the secondary was deployed and latched into position was 2.5 years ago at Northrop before the optical telescope and the instruments (OTIS) were attached to the sunshield and spacecraft (SCE). The images below give a good view of the secondary tripod and its key components as it is deployed, under its own motor power, while the primary mirror is lying on its side (since the tripod had to be on its side to allow proper gravity off-loading — note the cables). And show how large the structures are. This deployment was realistic in that the actual motors and command control was done as though Webb was in space, as well as the firing of the launch restraint mechanism. A complete secondary deployment could not be performed on the ground for the next ~2 years once OTIS and SCE were combined into the full observatory when the optical telescope system was upright in the clean room atop the sunshield. So there was a long time between secondary deployments!

There was discussion today on the NASA Live media about the drive motor and latching. These images from mid-2019 showed just how this crucial deployment and latching was carried out — to a precision of ~1.5 mm or so for the ~7 m long tripod. The discussion, the views of the MOC, and of the Webb status screen, in the replay of the NASA Live video of the secondary mirror deployment, are a good way to see what was going on: https://www.youtube.com/watch?v=-EnlaXnFcGs

With this step we are getting very close to having all the major deployments done. That is truly remarkable, given that we are less than two weeks from launch.


Sunshield Fully Tensioned

After Launch Day L+10. January 4, 2022. Sunshield Fully Tensioned.

Incredible accomplishment for Webb with the sunshield fully deployed.

This is an amazing moment, now that the sunshield is fully deployed and tensioned. And it was done quickly and smoothy. It was great to see the well-justified excitement in the Mission Operations Center (MOC). The MOC was on NASA Live this morning. Great comments at the end from the Project Manager thanking the team. It is here now: https://www.youtube.com/watch?v=IBPNi7uGgWM

Incredible accomplishment. All that thorough development and testing really paid off!

Getting closer to a full observatory, with a number of very important releases coming up, including the next major steps of the secondary deployment and the primary mirror wings, but this was an incredible accomplishment for Webb and the Webb Teams.


This is what JWST looks like now — minus all the support equipment underneath. This was taken in the Northrop M8 clean room when the sunshield was deployed last year (for the final time).

Sunshield Partially Tensioned

After Launch — Day L+9. Monday January 3, 2022. Sunshield Deployed. Partially Tensioned.

Good progress on JWST. Mid-booms and sunshield in position. Sunshield tensioning next.

Quick update after initial message below. Really great progress today. The three lowest (warmest) sunshield layers are all tensioned. Remaining two on Tuesday.

Happy New Year. The first year of many of great JWST science!

A status update (1), followed by some comments (2) on the major deployments to date, as well as the spectacular cleaned-up ESA video (3) showing separation and early solar array deployment from the Ariane VIKI camera.

(1). An update as a crucial (and one of our more complex) steps is now beginning — sunshield layer separation and tensioning. The Observatory is now taking shape with the sunshield out, but not separated and tensioned. Given this, it was decided after the mid-boom deployments Friday to pause operations for a couple of days and fully assess the new information from power systems and temperature sensors for the “real” observatory in space, in contrast to what was understood would be seen from testing and modeling JWST in the hugely-different ground environment.

For example, as mentioned on the deployment update media telecon today, some motor temperatures were a bit higher than was wanted for the start of tensioning, and the observatory has been reoriented to bring those temperatures down. Some power system adjustments and usage changes were performed also. Generally though it was noted that the observatory has been operating quite close to what was expected. Tweaks needed. Nothing dramatic. The plan from Saturday is now being followed — that is, once the "as-is Webb in space" was further characterized and adjustments made, the sunshield tensioning would begin. As noted in the telecon, the first steps towards the layer one (the lowest hottest layer) tensioning activities have started; see later blog updates on progress (https://blogs.nasa.gov/webb/)

(2). Meanwhile it is interesting to note just how far Webb has come. While essentially every deployment has the potential for being challenging (as in "very challenging" if the releases don’t work, etc), there are some deployment steps which I had mentally flagged (deployable tower; sunshield mid-booms; sunshield separation and tensioning). The complex DTA (Deployable Tower Assembly) deployment was definitely on my list. That deployment moved the whole telescope/instrument structure up about 4 ft (1.2 m) from the spacecraft, with, obviously, a whole lot of crucial power, communications and cryocooler connections. It took about 6 hrs on Wednesday to complete the move and it was a great success. This was an essential precursor to the sunshield deployment too, of course, since room was needed for the sunshield layers to be separated.

Reaching the final sunshield configuration involves several major steps. The first of these was the release of the sunshield covers on Thursday, followed the next day (Friday) by the sunshield Mid-Boom deployments. Together this ensemble of activities required firing a very large number (107) of membrane release mechanisms and long motor drives. All worked. With these done, the majority of the non-explosive actuators have now been successfully fired. The cover release appeared to go well, though, as reported, some switches did not indicate full roll-around. Some time was spent evaluating the indirect indications from temperature sensors and gyroscopic units. The data suggested that the covers had rolled out and so the motor-driven mid-boom deployment on the first side (+J2 left) was carried out (very slowly ,taking about 3 hrs to pull the five layers of sunshield out to about 7 m each side) late on Friday afternoon. It was then decided to do the second (-J2 right) mid-boom deployment Friday evening since the observatory was in a less-than-optimal asymmetric configuration with just one side out. That -J2 deployment was also very successful, with “nominal” motor power draw profiles (consistent with expected from ground tests, which is very impressive!).

With the the mid-boom deployments done, the sunshield now has its iconic 21m by 14 m footprint. Webb is starting to look like the real thing! And the majority of the non-explosive actuators have already been deployed. So Webb is well on the way to retiring a large fraction of its over 300 single point failures (as noted on the telecon, some 2/3 -3/4 of the SPFs should be retired by the end of sunshield tensioning).

Webb is now at step “3” and starting the work to carry through step “4”.

(3). Going back to launch day, ESA has released a spectacular cleaned-up video from the Ariane 5 VIKI camera on the upper stage. This shows our incredible separation, and the early deployment of the solar array — early because the attitude of Webb was spot-on after the precise Ariane 5 upper stage maneuvers and then the smooth decoupling with the spring separation of Webb. As a result, the small Monopropellant Reaction Engine thrusters (MRE) on Webb had minimal attitude corrections to make, and so the autonomous system governing array deployment gave the “Open” command. This was earlier than expected, but quite as designed, given the launch vehicle’s excellent performance. As I have said before, Ariane really nailed this launch and trajectory, and did an incredible job from the pad to separation! The drift-away VIKI video is fabulous.

The cleaned up video is on twitter https://twitter.com/esa/status/1476584214434914308 and also can be seen and downloaded from https://www.esa.int/ESA_Multimedia/Videos/2021/12/Webb_separation_from_Ariane_5

There is an extract from the ESA VIKI video here — with this magnificent image of JW just 15 seconds after its release from the upper stage — as well as an extract from the launch day video feed showing the simulated release of Webb, at the point where the Flight Manager got actual confirmation of the release, and called out “GO Webb” with his arm raised!

Deployment Timeline

After Launch Day L+3. Tuesday December 28, 2021. Fully-deployed and latched Primary Mirror wings.

Webb passed the moon today on its way to L2! And the first sunshield support arms are extended.

Following a spectacularly successful mid-course correction MCC-1a burn, due in no small part to Ariane getting our trajectory “spot-on” (Ariane “nailed-it”, one colleague noted), the second small course-correction burn MCC-1b was executed successfully. The high-data-rate, high-gain antenna had been successfully deployed earlier (on Sunday). The big recent events today were the lowering of, first, the Forward Unitized Pallet Structure (UPS), and then of the Aft UPS. These large very long structures carry the sunshield and it's cover and mechanisms. These are a crucial first step towards getting our sunshield in place over the next few days. The Deployable Tower Assembly (DTA) release planned for Wednesday will be the next major event, allowing the telescope (OTE) to separate from the spacecraft (SC), so that the sunshield membranes can fully deploy.

The NASA Webb blog and the twitter feed (@NASAWebb) are really good places to get updates. They are being kept very much up to date. Particularly the blog.



A great place to see the deployment sequence is here, with information and videos. The folks who set this up did a really nice job. This is the place to look for deeper insights.


However, I have had requests for a summary chart of the deployments, activities and the overall timeline. Here are two. These are “planned activities”. While the actual deployments and activities could follow this schedule and sequence, clearly changes may occur as the deployments proceed. What is here is just a high-level overview (but one that I really find good as reference charts).

Note: some acronyms relevant to these charts are below (JWST has many duplicate acronyms so context can be important!). *** For more info on each deploy go to ***


Webb is doing great. But a there are a few weeks yet of nail-biting deployments before we enter our L2 halo orbit at about day 30 with the MCC-2 burn at L+29d, and then 5 months more of of OTE and instrument commissioning before science begins. And all in L2 after the first month, where Webb will live until the on-board propellant runs out well into the future.

Happy New Year and best wishes for a Webb-science-filled 2022.


Some acronyms (sort of in order in most cases). For more info go to the specific items on https://webb.nasa.gov/content/webbLaunch/deploymentExplorer.html

MCC Mid Course Correction 1a and 1b are done. MCC-2 is a small, but crucial burn, to inject JWST into its halo orbit about L2.
MRI, NIRSpec NIRISS, NIRCam — our science instruments.
FGS. Fine Guidance System FPE. Focal Plane Electronics. ICE. Instrument Control Electronics. MSA. Micro-Shutter Array. CCC. Contamination Control Cover.
Deployments: SA. Solar Array (done). ADIR. Aft Deployable ISIM Radiator. GAA. Gimbaled Antenna Assembly (done). SS Sunshield. UPS. Unitized Pallet Structure (out — FWD and AFT)
SC. Spacecraft. OTE. Optical Telescope Element. LRM. Launch Restraint Mechanism. ( 3/4inch — the large NEAs holding the OTE to the SC). DTA. Deployable Tower Assembly. (big deal deploy — separates OTE from SS/SC). IEC Instrument Electronics Compartment.
CJAA Cryocooler Jitter Attenuator Assembly. CCA. Cooler Compressor Assembly. DRSA-H. Horizontal Deployable Radiator Shade Assembly. DRSA-V. Vertical Deployable Radiator Shade Assembly
SMSS. Secondary Mirror Support Structure. PMBA Primary Mirror Backplane Assembly.
CCE. Cryocooler Control Electronics. ADU. Actuator Drive Unit. FSM. Fine Steering Mirror. ACS. Attitude Control Subsystem. IRSU. ISIM Remote Services Unit. MSC. Multi-Spacewire Concentrator.
STA. Star Tracker Assembly. FSS. Fine Sun Sensor. IRU. Inertial Reference Unit.
DITCE. Differential Impedance Transducer Control Electronics.
PMSA. Primary Mirror Segment Assembly SMA. Secondary Mirror Assembly.
HGA. High Gain Antenna.

JWST Launch

L+1. December 26. Spectacular launch. Ariane 5 delivered Webb to its trajectory towards L2 (with remarkable precision). Solar array deployed early. First course correction burn was short and left much propellant for a >10 yr life for Webb.

As you have seen, we had a flawless launch, with a spectacular liftoff (image below). The Ariane 5 flight VA256 Range Operations Manager at Kourou kept saying “nominal” (same in French!), which was music to everybody’s ears, since it meant everything was going exactly to plan. And now we have had, successfully, the two key deployments that are really the only ones for which timing was really important: solar array deployment and the mid-course correction burn MCC-1a (more on that below — and on the truly remarkable performance of the Ariane 5 for Webb’s launch).

Solar Array Deployment: When Webb was released from the upper stage, the new, VIKI video camera (Independent HD Video Telemetry Kit) on board the upper stage not only showed the release of Webb, but also, quite astonishingly, the beautiful deployment of the solar array. In fact, in some ways, the two most delightful words of the day were “power positive” when that fully-deployed array, crucially, took over powering JWST from the batteries. That was an absolute make-or-break moment for JWST.

This image is a grab from the VIKI video and shows Webb drifting away just before its early solar array deployment, along with a couple of screen grabs from the video of the panel deployment. The reflected sunlight saturated the camera, but there is a partial deployment image and a full deployment image.

The VIKI video showing the solar array deployment can be seen here https://www.youtube.com/watch?v=8PxT4iFKdZg

MCC-1a: What did not come across, particularly with the low key “nominal” was just how remarkable the performance of the Ariane 5 was. Ariane really delivered at 150% for Webb and for Webb’s science. It had to deliver JWST at its release with a velocity that was not too much (otherwise JW would overshoot L2), but also not too little boost. Too little boost and we would need to use a lot of JWST’s on-board propellant to actually get JWST to L2. That propellant is critically required for JWST to perform science at L2 (momentum off-loading and station keeping). The MCC-1a burn usage is thus crucial for JWST science since using a lot of propellant limits JWST’s science life. Too much and we may not have been able to even do 10 years. This is fine-tuning at its best and Ariane did the boost job for Webb incredibly well. The MCC-1a burn was carried out at its nominal 12.5 hrs after launch and was only 65 minutes long (https://blogs.nasa.gov/webb/2021/12/25/the-first-mid-course-correction-burn/). While the lifetime estimates remain to be completed, both the timing and duration of MCC-1a point to a very positive outcome for a very long life for Webb from a fuel availability perspective.

We all owe Ariane a great deal for their remarkable “on-the-money” launch.


JWST Pre-launch

L-1. December 24. JWST in Ariane 5 on the launch pad. Checkout underway. Looking good for launch Christmas Day at 0720 EST.

Couple of nice photos below showing the Ariane 5 flight VA256, with Webb nestled inside, ready for departure. There are also a few images showing launch timing and trajectory. Plus an image showing the Ariane 5 and its JWST cargo, to give a sense of the scale of what is being launched by Ariane from Kourou.

Once Webb separates from the upper stage at L+27 min we have the two time-critical deployments in the first day of the deployment sequence. One starts near L+31 min, and that is the deployment of the solar array over a number of minutes. The solar array then provides power for Webb for its whole lifetime. The second is an on-board thruster “burn” for the mid course correction (MCC-1a). This burn, planned for L+12.5 hrs, is a crucial supplemental burn to the thrust from our Ariane 5 to put JWST accurately on a trajectory for a later insertion into L2. These two activities constitute the two most important activities of Day 1.

Getting close!


JWST Pre-launch

L-2. December 23, 2021. JWST fully encapsulated. JWST rolled out and moved to the launch pad.

Getting close. Ariane 5 VA256 with JWST nestled inside rolled out today and is on the launch pad. Checkout tomorrow and if all good, and no more weather issues (looking good at this point), then the “GO” button gets pushed early Sat morning.

Rollout image...


JWST Pre-launch

L-5/L-3 December 20/22, 2021. JWST on-board propellant fueling completed. JWST moved to theFinal Assembly Building and attached to the Ariane 5 rocket.

Just confirmed that weather is projected to be good and launch is set for Dec 25. Same place, time, duration. Roll-out to launch pad Thursday.

7.20 am EST (9.20 am Kourou; 4.20 am PST) on Dec 25 will be the start of the 32-min window for the Ariane 5 launch that will send JWST to its ultimate destination 1.5 million km away in a halo orbit around L2. The launch will be from the Europe Space Centre, French Guiana (Centre Spatial Guyanais CSG).

Two key events occurred over the last month. A little over a week ago JWST was mated successfully with the Ariane 5 rocket after being fueled with about 300 kg total (5% of the mass of JWST!) of its propellants, hydrazine fuel and the dinitrogen tetroxide oxidizer. Both fueling and mating operations required a delicate touch, with a lot of care, and considerable precision in both activities. They both went very well.

Between these operations JWST had to be moved in a large sealed container to the Bâtiment d’Assemblage Final (BAF), or Final Assembly Building, from its original Kourou "home" in the Satellite preparation building S5. For nearly 2 months JWST had been in the Satellite preparation building S5 after its arrival October 10 by ship from 3 years of a very comprehensive I&T (integration and test) effort at Northrop Grumman Space Park in Redondo Beach, California.

The post-shipping checkout in S5 and the launch payload adapter attachment (and clamp band, with its incident) was carried out in S5C, taking somewhat over a month. The clamp-band incident required additional careful testing and checkout that put the launch 4 days behind its initial Dec 18 date to Dec 22. Once that testing was successfully completed, indicating no damage from the shock event, a move, internal to S5, was made of JWST to the fueling facility in S5B. The potentially-hazardous fueling operation in S5B went smoothly and took a little under two weeks.

The move to the Final Assembly Building (BAF), where JWST and the Ariane rocket were to be joined for their flight, also went smoothly. A few images below are of these respective activities, showing the fueling operation, and then JWST being moved, hoisted over a hundred feet and being attached to the Ariane 5 upper stage. During these operations a lot of attention was paid to minimizing contamination. Special plastic shrouding was used to provide a tent-like clean environment for JWST as it was being attached to the rocket, and subsequently tested.

The challenge following attachment to Ariane that led to the recent 2-day launch slip resulted from connectivity issues in the external cable from JWST that enables communication to ground support and verification equipment. This cabling is essential for battery charging and for verification of "aliveness", both before and after "encapsulation" (the lowering of the fairing that covers JWST during launch). Resolving the communication issues resulted in the additional 2-day delay from the 22nd to the 24th. Following a successful aliveness test, the fairing was lowered, with great care since the clearances are not large(!), over JWST, "encapsulating" it from a last view by earthlings. Launch was then set for Dec 24.

At this point JWST is now part of its Ariane 5 for launch, designated as VA-256, and it is in the Arianespace flow typical of Ariane 5 launches. Recent Ariane 5 launches have gone very smoothly, typically launching at their designated lift-off time. Webb’s final launch readiness review was held on Tuesday Dec 21 and approved the roll-out to the launch pad for the Ariane 5 with JWST. Concerns about predicted high-altitude winds on the 24th then led to a delay for the roll-out. Launch is now set for the 25th, with roll-out to the pad on the 23rd.

Looking forward to a smooth, on-time departure early Saturday morning Dec 25 Christmas Day (fingers-crossed....)!

Thinking very positive thoughts....

Garth Illingworth

PS - The links below give the latest information and also how to get launch-day updates and viewing.



JWST Pre-launch

November 28, 2021. At the launch site in Kourou. Preparatory work to set up JWST a month before launch. Clamp band issue resolved. Preparations for on-board propellant fueling.

Last week I sent a message around (below) about the inadvertent release of the clamp band holding JWST at its base on the spacecraft to its launch adapter ring. That incident put launch preparations on hold while cross-checks were done to ensue that no damage was done to the Observatory from the vibration/shock event.

The tests were completed during the week and the NASA review board concluded that no observatory components were damaged by the event. Work is now continuing on the normal launch preparation activities. The next major step in that preparation sequence is fueling the propellant tanks on JWST for the thrusters that will be used for a course correction during the transfer flight to L2, to put JWST into its orbit around L2, and then to offload momentum buildup in the reaction wheels during normal science operations over the life of JWST. A “consent to fuel” review was held, and NASA gave approval to begin fueling the observatory. Fueling activities will occupy about another week. And then JWST will be moved, slowly and carefully, as with all such moves, as part of a series of activities leading to its integration onto the Ariane launcher and into its fairing.

Launch is now scheduled for Dec 22 at 7.20 am EST. Early on the west coast!


JWST Pre-launch

November 22, 2021. At the launch site in Kourou. Preparatory work a month before launch. Checking JWST post-clamp band incident.

Quick update. The JWST launch date has slipped to Dec 22 (at this point the date is given as “Not Earlier Than” Dec 22 in the usual NASA way when evaluations are still underway by review boards).

A series of cross-checks are being done because JWST was subjected to an unexpected sharp vibration event when a large metal band that attaches JWST to the launch adapter, that itself then attaches to the rocket upper stage, suddenly released inadvertently as it was being tightened. That sudden release of the band resulted in a shock event that carried into JWST. JWST itself was safely supported. To be prudent and sure that nothing was compromised on JWST a series of cross-checks are being done this week to further verify that JWST’s hardware components are OK.


There will be further updates later this week.