Sunshield Successfully Deploys on NASA’s Next Flagship Telescope

From NASA


On Jan. 4, 2022, engineers successfully completed the deployment of the James Webb Space Telescope’s sunshield, seen here during its final deployment test on Earth in December 2020 at Northrop Grumman in Redondo Beach, California. The five-layer, tennis court-sized sunshield is essential for protecting the telescope from heat, allowing Webb’s instruments to cool down to the extremely low temperatures necessary to carry out its science goals.Credits: NASA/Chris Gunn

The James Webb Space Telescope team has fully deployed the spacecraft’s 70-foot sunshield, a key milestone in preparing it for science operations.

The sunshield – about the size of a tennis court at full size – was folded to fit inside the payload area of an Arianespace Ariane 5 rocket’s nose cone prior to launch. The Webb team began remotely deploying the sunshield Dec. 28, 2021, three days after launch.

NASA will hold a media teleconference at 12:45 p.m. EST today, Tuesday, Jan. 4, to discuss the completion of this critical step. To participate by telephone, media must RSVP to Laura Betz at: laura.e.betz@nasa.gov. Audio of the teleconference will also stream on the agency’s website

“This is the first time anyone has ever attempted to put a telescope this large into space,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at the agency’s headquarters in Washington. “Webb required not only careful assembly but also careful deployments. The success of its most challenging deployment – the sunshield – is an incredible testament to the human ingenuity and engineering skill that will enable Webb to accomplish its science goals.”

The five-layered sunshield will protect the telescope from the light and heat of the Sun, Earth, and Moon. Each plastic sheet is about as thin as a human hair and coated with reflective metal, providing protection on the order of more than SPF 1 million. Together, the five layers reduce exposure from the Sun from over 200 kilowatts of solar energy to a fraction of a watt.

This protection is crucial to keep Webb’s scientific instruments at temperatures of 40 kelvins, or under minus 380 degrees Fahrenheit – cold enough to see the faint infrared light that Webb seeks to observe.

“Unfolding Webb’s sunshield in space is an incredible milestone, crucial to the success of the mission,” said Gregory L. Robinson, Webb’s program director at NASA Headquarters. “Thousands of parts had to work with precision for this marvel of engineering to fully unfurl. The team has accomplished an audacious feat with the complexity of this deployment – one of the boldest undertakings yet for Webb.”

The unfolding occurred in the following order, over the course of eight days:

  • Two pallet structures – forward and aft – unfolded to bring the observatory to its full 70-foot length
  • The Deployable Tower Assembly deployed to separate the telescope and instruments from the sunshield and the main body of the spacecraft, allowing room for the sunshield to fully deploy
  • The aft momentum flap and membrane covers were released and deployed
  • The mid-booms deployed, expanding perpendicular to the pallet structures and allowing the sunshield to extend to its full width of 47 feet
  • Finally, at approximately 11:59 a.m. EST Tuesday, the sunshield was fully tensioned and secured into position, marking the completion of the sunshield deployment

The unfolding and tensioning of the sunshield involved 139 of Webb’s 178 release mechanisms, 70 hinge assemblies, eight deployment motors, roughly 400 pulleys, and 90 individual cables totaling roughly one quarter of a mile in length. The team also paused deployment operations for a day to work on optimizing Webb’s power systems and tensioning motors, to ensure Webb was in prime condition before beginning the major work of sunshield tensioning.

“The sunshield is remarkable as it will protect the telescope on this historic mission,” said Jim Flynn, sunshield manager at Northrop Grumman, NASA’s primary contractor for Webb. “This milestone represents the pioneering spirit of thousands of engineers, scientists, and technicians who spent significant portions of their careers developing, designing, manufacturing, and testing this first-of-its-kind space technology.”

The world’s largest and most complex space science observatory has another 5 1/2 months of setup still to come, including deployment of the secondary mirror and primary mirror wings, alignment of the telescope optics, and calibration of the science instruments. After that, Webb will deliver its first images.

The telescope’s revolutionary technology will explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe, to everything in between. Webb will reveal new and unexpected discoveries and help humanity understand the origins of the universe and our place in it.

The James Webb Space Telescope is an international partnership with the ESA (European Space Agency) and the Canadian Space Agency. NASA Headquarters oversees the mission. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages Webb for the agency and oversees work on the mission performed by the Space Telescope Science Institute, Northrop Grumman, and other mission partners. In addition to Goddard, several NASA centers contributed to the project, including the agency’s Johnson Space Center in Houston, Jet Propulsion Laboratory in Southern California, Marshall Space Flight Center in Huntsville, Alabama, Ames Research Center in California’s Silicon Valley, and others.

For more on where Webb is in the commissioning process:

https://webb.nasa.gov/content/webbLaunch/deploymentExplorer.html

-end-

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rah
January 6, 2022 2:34 am

That’s a biggie for sure. Out of the many different components which have to deploy correctly, I have thought all along that sun shield was the weakest link.

Rocketscientist
Reply to  rah
January 6, 2022 8:44 am

Perhaps, but it should be put into perspective. We sit with finger crossed that we didn’t’ screw up somewhere, but this actually is rocket science when the precision needs to be held. Disaster was not left to chance much as one might think. Deployment testing was problematic as we were doing it in 1g with all sorts of overhead cables to off-load the weight. The only concerns were that something may get shifted during transport, which was FAR more taxing than a mere launch. Some minor issues with deployment motors heating, but that must also be put into perspective, as the “heating” involved was very very small, and needs to be dissipated, but is inconsequential.
Alignment is my biggest concern, but that was tested and tested and tested….

beng135
Reply to  Rocketscientist
January 6, 2022 9:30 am

I see the animations & wonder about the reflective surface of the heat shield on the mirror side. Might that reflect starlight & interfere with the light gathered by the mirror? Or is the position of the reflective heat-shield surface not an issue because of the orientation?

Last edited 8 months ago by beng135
Rocketscientist
Reply to  beng135
January 6, 2022 11:59 am

Not so much as the reflective coating is on the underside of the shield and the mirror is, as you observed, at high angles relative to the sunshield. Not much close for the backside of the shield to reflect anyway.

Rocketscientist
Reply to  rah
January 6, 2022 9:36 am

One of the systems I was responsible for assembling aligning and testing was the DTA Deployable Tower Assembly. It is is one of the few parts on the vehicle which actually “telescope”. It is responsible for separating the mirror array apart from the electronics, within .00009 inches true position of exact and less than .00009 radians… all with only 6 degrees of freedom. When it left my facility it was within parameters.

Clinton Muennich
Reply to  Rocketscientist
January 6, 2022 1:13 pm

What did you use to verify the position? I find that level of precision to be fascinating. Also, out of curiosity, how many attempts did it take to get within parameters?

Rocketscientist
Reply to  Clinton Muennich
January 6, 2022 7:02 pm

Lasers mostly, but inclinometers and many other devices.
What’s rather interesting is that much of the equipment was designed for its sole purpose and now is sitting idly unused in an environmentally controlled warehouse not collecting dust. Much of it was as costly as the components they tested.
The large facilities are always in use and many components are reused such as the cryogenic liquid helium cooling panels and vacuum

JBP
Reply to  Rocketscientist
January 6, 2022 5:16 pm

” within .00009 inches true position of exact and less than .00009 radians…”

9 hundred thousandths? Of an inch? Why does the relative positioning of the mirror array and any electronics require that?

Also what other degrees of freedom are there beside 6?

I’m getting old.

Rocketscientist
Reply to  JBP
January 6, 2022 6:55 pm

True, 6 degrees of freedom are all there are, but if you want to be persnickety time is a factor as well as temperature fluctuations matter. I was being facetious. The mechanism had precision elements for each axis. The necessity in precision was for precise alignment and re-alignment between the DTA and the mirror array structure. The alignment holes were very tight and then “potted” in place with pins. The assembly was then separated, once the potting agent had cured inspected and reassembled with specially designed silver plated fasteners.

John Tillman
January 6, 2022 2:40 am

So far so good.

NASA’s space telescope record is mixed. Hubble’s orbit is low enough that astronauts were able to correct the vision of its near-sighted optics. But the agency could effect no repairs to Earth-trailing Kepler when two of its four reaction wheels failed. Three were needed to point it accurately in its mission to search for exoplanets.

Webb will orbit the Sun at a distance four times farther away than the Moon, beyond hope of repair.

Joseph Zorzin
Reply to  John Tillman
January 6, 2022 3:08 am

“Webb will orbit the Sun at a distance four times farther away than the Moon, beyond hope of repair.”

Unless we contract with aliens for that service. :-}

Tom Abbott
Reply to  Joseph Zorzin
January 6, 2022 10:09 am

All we need is an orbital transfer vehicle and Webb is within reach.

Rocketscientist
Reply to  Tom Abbott
January 6, 2022 1:15 pm

“Nothing is impossible for the man who does not have to do the job.”
I sort of cringe when somebody says “All you need to do is…”

But, making an orbital transfer vehicle and readily being able to transfer fuel is not impossible, it just hasn’t ben done yet. Simply transferring fuel in 0g is problematic as there is no density gradient and the fuels liquid/gaseous mixture will float about. That is why just prior to main engine burn, spacecraft will do a “settling burn” with maneuvering thrusters just to get the fuel into the end of the tanks where the sump pick-ups are. Not sure how we plan on transferring fuel without some sort of kinetic maneuvers to keep the liquid fuel separated from gaseous.

Tom Abbott
Reply to  Rocketscientist
January 6, 2022 1:57 pm

Musk and several others have plans to transfer fuel in space. A refueling vehicle will be launched in the near future that is supposed to be able to travel to GEO and refuel satellites there.

mcswell
Reply to  Rocketscientist
January 6, 2022 3:34 pm

I’m sure people have thought of these ideas before, but two possibilities occur to me: 1) a piston the same size as the inside of the tank, or 2) carry the fuel inside a mylar (or etc.) bag inside the tank, and use air or other gas between the bag and the tank to compress the bag, forcing the liquid in the bag out. (Or I suppose the liquid could be in the tank outside the bag, and when the mylar bag was inflated it would the liquid out of the tank.)

Rocketscientist
Reply to  mcswell
January 6, 2022 7:10 pm

Bladders are problematic. A simple spin-up might work.

Ruleo
Reply to  Tom Abbott
January 6, 2022 7:52 pm

All we need is an orbital transfer vehicle and Webb is within reach.

Gonna have to be unmanned. Humans cannot cross the van Allen Belt.

Tom Abbott
Reply to  Ruleo
January 7, 2022 2:10 am

How did humans survive the trip to the Moon then?

Rocketscientist
Reply to  Ruleo
January 7, 2022 11:15 am

Perhaps you mean that humans risk dangerous exposure to high frequency radiation and gamma rays, which is true. We have evolved on a planet that has a spinning magnetic core and therefore creates a deflector shield worthy of the envy of Star Trek. Current radiation shielding for safe exposure outside of our deflector shields is very difficult to incorporate. You need dense absorbing material to soak up gamma rays. So far LEO exposure isn’t such an issue as we are within the shields. During Apollo NASA watched the sun very closely during expected lunar launch windows and chose benign periods of solar activity.
We need about 6″ of lead (Pb), or 18″ of water, or 24″ of compacted regolith (lunar gravel) to provide adequate shielding. That is why most deep space manned vehicle designs incorporate the water storage tanks around the outsides and lunar station (outpost) propose burying the habitats. The over coating provides protection from radiation and meteorites, as well as thermal mass for better thermal control.

Adrian Mann
Reply to  Ruleo
January 8, 2022 5:32 pm

This has already happened. You were wrong in 1969!

Gordon A. Dressler
Reply to  John Tillman
January 6, 2022 8:02 am

John, you posted: “Webb will orbit the Sun at a distance four times farther away than the Moon, beyond hope of repair.”

Well, my crystal ball is not that clear regarding the future of tele-robotics, but it is quite obvious—isn’t it?— that we currently have the capability to send large spacecraft to the L2 point in space.

No, the future does offer hope.

Rocketscientist
Reply to  Gordon A. Dressler
January 6, 2022 8:53 am

Yes, there are already design underway for refueling craft to replenish the station keeping thruster system.
L2 is an unstable la grange point, and items parked there will not stay without outside control. Much the same as an inverted pendulum minor perturbations away from the balance point will only increase forces causing further drift. Spacecraft “parked” at these points need station keeping thrusters albeit very small (think mouse farts). In orbital reality these spacecraft are parked in a “halo orbit about these points”, which I have described in earlier posts on JWST. Eventually JWST will run out of fuel for station keeping, but we have more than 10 years.
…But currently propellant transfer in 0g is very problematic.

Mark D
Reply to  Rocketscientist
January 6, 2022 6:01 pm

While not connected to the topic would you care to comment as to how much light pressure or solar wind impacts an object that size and how is it dealt with?

Rocketscientist
Reply to  Mark D
January 8, 2022 8:18 am

It is not my field, and I have pondered about such. The Solar shields are huge by current standards (22m x 14m) they are small. A side issue might be if the sails were too big how might one tension them and stop them from wiggling? (https://webb.nasa.gov/content/observatory/sunshield.html

I suspect an actual solar sail would have to be measured in hectares before it became more of an issue than the thruster control system can handle.

Mark D
Reply to  Rocketscientist
January 8, 2022 9:46 am

Thank you.

Rocketscientist
Reply to  Gordon A. Dressler
January 6, 2022 9:23 am

Gordon,
After reading your replies to my earlier posts please forgive my remedial comments as they are not meant for you. I’m sure you are more familiar with the propulsion system details on JWST than I.
And why we absolutely still need hypergolics.

mcswell
Reply to  Rocketscientist
January 6, 2022 3:35 pm

Ion engines?

Johanus
January 6, 2022 3:28 am

This protection is crucial to keep Webb’s scientific instruments at temperatures of 40 kelvins, or under minus 380 degrees Fahrenheit – cold enough to see the faint infrared light that Webb seeks to observe

The sunshield will extend the telescope’s IR range from 0.6 to 28 microns. These wavelengths would include Earth’s “earthshine”, the blackbody radiation emitted by the Earth, centered at around 10 microns.

Not clear to me if the telescope will ever see the Earth, since the sunshield will ostensibly block the view. But certainly the telescope will be able to see the other planets, including many yet to be discovered exoplanets revolving around distant stars.

There is a lot to be seen in the infrared universe which is invisible to our eyes.

Alastair Brickell
Reply to  Johanus
January 6, 2022 5:02 am

My understanding is that it will never look towards the Earth or Moon. It will however, be able to study Jupiter and Saturn’s moons which could be interesting.

MarkW
Reply to  Alastair Brickell
January 6, 2022 7:15 am

From L2, looking back at the Earth or Moon would involve looking towards the sun.
That will never happen.

Rocketscientist
Reply to  MarkW
January 6, 2022 8:55 am

Not more than once!

beng135
Reply to  Rocketscientist
January 6, 2022 9:38 am

Will it look at objects at right angles to the plane of the solar system? That would mean the sun shield would be at a lesser angle to the sun/earth/moon instead of ~90 deg….

Last edited 8 months ago by beng135
menace
Reply to  Johanus
January 6, 2022 8:36 am

Not sure if it can directly image exoplanets but it is expected to be able to tell more about atmospheric composition and in many cases it can detect them when earth bound telescopes may not.

https://www.space.com/james-webb-space-telescope-science-overview

January 6, 2022 7:08 am

The center of the Milky Way should be interesting with the Webb, no? It should reveal much more than the Hubble. On an unrelated subject, Sean Carroll mentioned in a video that one photon of visible light ON AVERAGE reaches earth during the day and 20 infrared photons return that energy ON AVERAGE during the night….each infrared being 5% of the visible photon…and thus the entropy of the energy is increased.

MarkW
Reply to  Anti-griff
January 6, 2022 7:18 am

Any object that is above absolute zero will radiate photons, and they will do it all the time.
It doesn’t matter whether they are receiving energy at the time.
The Earth radiates in the infra-red 24 hours a day.

Reply to  MarkW
January 6, 2022 7:45 am

Sean was lecturing on another subject but mentioned the energy balance – energy in during the day – energy out at night so temp does not increase overall. I would like Sean to lecture on the global warming thing but, alas, he is not into the subject at least publicly. He was working on a mathematical proof why entropy always increases. The process is of course going on simultaneously – the lit side of earth receiving net enrgy while the dark side is emitting net energy. It is not a singular photon in question…it is ON AVERAGE that one visible photon results in 20 infrared photons.

Last edited 8 months ago by Anti-griff
DMacKenzie
Reply to  MarkW
January 6, 2022 11:16 am

Technically not quite correct, Mark. Atoms/molecules only emit photons when an electron drops an “orbital”. It only seems to our human eyes that they do it “all the time” because we are looking at huge numbers of atoms, a few of which end up emitting photons because they were excited by some outside phenomenon. Nitrogen and oxygen at Earth-like temperatures don’t emit squat for example, whereas H2O and CO2 do. Mostly from water vapour at low altitude where 15000ppm Water/ 400 ppm CO2 greatly favours H2O emissions…..while at altitudes of say 10 km, 10ppm Water/400ppm CO2 favours CO2 emissions. Which is why increasing CO2 from 280 ppm to 400 ppm over the last 150 years has had relatively little effect on ground level temperatures.

AndyHce
Reply to  DMacKenzie
January 6, 2022 12:15 pm

Nitrogen and oxygen at Earth-like temperatures don’t emit squat

While they may not emit IR, they do emit electromagnetic radiation. The measurement of microwave length radiation from oxygen is where the satellite atmospheric temperature numbers come from.

menace
Reply to  Anti-griff
January 6, 2022 8:44 am

That statement makes no sense to me on any level. Gazillions of the sun’s photons strike the earth during on the day side. If you are talking about light from the Milky Way, if only one photon per day reaches the earth the Milky Way simply would not be visible as your eye or any camera cannot resolve single photons. If you are talking about distant celestial objects or galaxies, then what does day or night on Earth have to do with how many photons reach the earth?

Reply to  menace
January 6, 2022 10:02 am

Well, I dunno, Meanace…maybe try reading again…the subject of Sean Carroll and earth’s energy balance is separate from the Webb telescope…OK? The Webb should see through the dust clouds obscuring the Milky War center…much better than the Hubble.

Last edited 8 months ago by Anti-griff
Gordon A. Dressler
Reply to  Anti-griff
January 6, 2022 10:31 am

Anti-griff,

If you meant to state that, for every photon that is intercepted by Earth having a frequency in the visible range of the EM spectrum, there are (on average) twenty photons in the infrared range of the EM spectrum that return that equivalent amount of energy, THAT statement says absolutely nothing about the “entropy of the energy”.  

The entropy involved with Earth “converting” visible spectrum energy received from the SUN to IR spectrum energy that it radiates depends greatly on the physical processes involved in such conversion (e.g., simple absorption of a visible light photon by a green leaf does NOT immediately or automatically lead to direct emission, on average, of twenty IR photos from that same leaf).

Then too, about 30% of all solar photons “reaching Earth” (the energy of which is mostly in the spectrum of visible light) are simply reflected from Earth’s atmospheric clouds, land surfaces and water surfaces without ever being “converted” to IR photons.

Last edited 8 months ago by Gordon A. Dressler
Reply to  Gordon A. Dressler
January 6, 2022 2:07 pm

I meant what I stated…which are Sean Carroll’s words – not mine. I agree with Sean that the entropy of the energy is increased. There may be some photon that comes in and is reflected off the ocean surface and then goes up and hits an ice crystal and then returns and is reflected off a bald man’s head, etc……but who cares? Overall, ON AVERAGE, the near balance of energy in and out of the earth system is why the temp is relatively moderate allowing life to exist. Regardless of all complications, the basic process is one visible light photon in…and 20 IR photons out.

ResourceGuy
January 6, 2022 7:22 am

Does this mean NASA and its contractors have now solved the problems of differing measurement of metric vs. Imperial? We only aborted one Apollo mission and one mars orbiter with those problems.

mcswell
Reply to  ResourceGuy
January 6, 2022 3:38 pm

Which Apollo mission? (and to be pedantic, no mars orbiter was aborted for this problem–one mars lander crashed, though)

Felix
January 6, 2022 7:38 am

XKCD tells us the truth, again: https://xkcd.com/2564

Gordon A. Dressler
January 6, 2022 7:56 am

Wow . . . great accomplishment! Plus, the secondary mirror (and its tower support structure) and the Aft Deployed Instrument Radiator (ADIR) have been successfully deployed following completion of the sun shield deployment.

Both the secondary mirror and ADIR were deployed on the cold (shadowed) side of JWST after the large sun shield was fully deployed and tensioned. Therefore, the mechanical joints/linkages/bearings required for their deployment had to function without galling or differential-CTE-induced jamming at temperatures around minus 250 °F, not that far away from the normal boiling point of liquid oxygen (-297 °F).

Rocketscientist
Reply to  Gordon A. Dressler
January 6, 2022 9:08 am

Proving out and testing the ADIR deployment system was one of the systems of which I was directly responsible. The deployment hinges are pretty robust in that they can take twice the full load of the panel in while under 1g. They are largish to reduce deployment loads. The biggest PIA was designing and developing the cryo-vacuum chamber set up to get this this beastie cold enough for real functional testing. It took many days to evacuate the air and chill the chamber with liquid helium pumped cold plates. It radiated just as desired. It swiveled just fine.
But, I sat with fingers and toes crossed anyways.

Tom Abbott
Reply to  Rocketscientist
January 6, 2022 2:04 pm

It looks like you did a pretty good job. 🙂

Rocketscientist
Reply to  Tom Abbott
January 6, 2022 7:10 pm

thanks

Tom Abbott
Reply to  Rocketscientist
January 7, 2022 12:32 pm

Thank you!

Your efforts have the Webb telescope well on the way to success, and just think of the discoveries your efforts will make possible. I can’t hardly wait!

You and all the people who made this possible deserve much more than just a thank you.

Last edited 8 months ago by Tom Abbott
Rocketscientist
Reply to  Tom Abbott
January 8, 2022 8:20 am

The pay is good.

Alan Robertson
Reply to  Gordon A. Dressler
January 6, 2022 9:12 am

This telescope’s deployment was truly a gift to mankind, as stated here in a previous article.
Many people are frequently checking on the mission’s progress,
Who knows what phenomena we may observe, which has not yet been conceived by the minds of men.

There’s conjecture that those galaxies “furthest out” have already accelerated to the point that light emitted from them will never be visible to us and that we may watch as some of Webb’s newly observable galaxies cross that threshold and go dark, for us.

beng135
Reply to  Gordon A. Dressler
January 6, 2022 9:50 am

Therefore, the mechanical joints/linkages/bearings required for their deployment had to function without galling or differential-CTE-induced jamming at temperatures around minus250 °F, not that far away from the normal boiling point of liquid oxygen (-297 °F).

Yeah, I wonder about that too. Materials become extremely brittle at those temps.

Rocketscientist
Reply to  beng135
January 6, 2022 12:07 pm

Not just material embrittlement due to cold and radiation, but very weird other happenings as well. No zinc on the vehicle right down to the fastener coatings and circuit boards. Bizarrely zinc has a tendency to reconfigure and grow metallic whiskers as it recrystallizes. These whiskers are very conductive and can short out electrical connections and jam mechanisms.

Rocketscientist
Reply to  Rocketscientist
January 6, 2022 12:11 pm

BTW because we cant use zinc plating or solder we use pure silver.
Yep, JWST is silver plated, literally.

pochas94
January 6, 2022 11:05 am

Apparently these Academics feel that in view of the obvious incompetence of democratically elected leaders, a Tyrant is a better choice. That depends.

Walter Sobchak
January 6, 2022 12:08 pm

The secondary mirror has been deployed, as has the Aft Deployed Instrument Radiator (ADIR).

https://webb.nasa.gov/content/webbLaunch/deploymentExplorer.html

Next the folded wings of the main mirror beginning with the port mirror wing tomorrow Friday Jan 7.

It has completed about 3/4ths of its journey to its orbit around L2.

NASA’s Webb site (pun intended) is a great resource.

https://webb.nasa.gov/content/webbLaunch/whereIsWebb.html

January 6, 2022 2:32 pm

Was it in earth orbit during this deployment?

mcswell
Reply to  Jeff in Calgary
January 6, 2022 3:47 pm

I guess it depends on what you mean by “earth orbit”. IIUC, it’s sort of in solar and earth orbit at the same time. (Well, *I* am in solar orbit, in the sense that I’m going around the Sun each year just like the rest of you.) At any rate, it is not in Low Earth Orbit.

Actually, the NASA webbsite (https://jwst.nasa.gov/content/about/orbit.html) says that at the L2 point, JWST will not be in Earth orbit. I think that depends on what you mean by “Earth orbit”, though–since it’s further away from the Sun than the Earth is, its orbit should be longer than Earth’s; but because it is pulled along by the Earth’s gravitational attraction, it keeps up with the Earth (has a 365 1/4 earth-day orbital period). To me that sort of means it’s in Earth orbit, but it’s a question of definition.

Gordon A. Dressler
Reply to  mcswell
January 7, 2022 11:37 am

It is correct to say being in a halo orbit around the L2 point is not being in an “orbit around Earth”.

The L2 point is defined by being a gravitational point of “balance” defined by the masses of Earth and Sun, with the Moon’s orbit around Earth tending creating periodic variations in distance of the L2 point with respect to the framework of the the Earth, but these gravitational variations are not sufficient to overcome the L2 point being a region of general 2-D gravitational stability* (sometimes referred to as a “gravitational well”) that is located permanently on the side of Earth directly opposite the Sun, and that revolves around the Sun with the same period as Earth. Being in a “halo orbit” around the L2 point smoothes out (i.e., minimizes the effects of) gravitational perturbations at L2, thus further reducing the amount of propellant required over the long term to maintain the design orbit.

And, BTW, there are four other Lagrangian points defined by the Earth-Sun system (L1, L3, L4, and L5). L2 is the one that is always farthest away from the Sun and that has Earth partially shielding light coming direcly from the Sun, a distinct advantage to the passive cooling employed by JWST for its mission.

*However, “A small object at L1, L2, or L3 will hold its relative position until deflected slightly radially, after which it will diverge from its original position.”—see: https://en.wikipedia.org/wiki/Lagrange_point
JWST has small on-board monopropellant thrusters that will be used occasionally to insure there are no radial (with respect to Earth or Sun) deflections in its halo orbit that would lead to orbital divergence..

WXcycles
January 7, 2022 12:46 am

So hoping this mission succeeds in all ways from here.

beng135
January 8, 2022 7:33 am

Mirror fully deployed 1/8/22 10:30 am EST.

Gordon A. Dressler
January 8, 2022 12:27 pm

As of January 8, 2022, the James Webb Space Telescope has completed all of its spacecraft deployments. This involved performing over 100 single-point failure operations.

JWST is now coasting to it’s planned insertion into a halo orbit around the L2 (Lagrangian) stability point on the far side of the Sun-Earth alignment axis.

The propulsion system needed for L2 halo orbit insertion has already been primed and used for a mid-course trajectory correction maneuver. Thus, the only remaining significant risk items involve (a) precise alignment of each of the deployed hexagonal mirror segments, and (b) successful activation of each of the four major scientific observing instrument packages.

Kudos, at the level of 10^42 intergalactic credits, to all of the parties (indeed, a large segment of humanity) that made this mission possible “for all mankind”!

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