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The James Webb Space Telescope

lpetrich

lpetrich

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I have been reluctant to post on the James Webb Space Telescope because it has been so long in coming, being greatly delayed and going far over budget. But it seems like it is ready to launch: NASA’s James Webb Space Telescope Has Completed Testing | NASA

The JWST will be sent to its launch site in Kourou, French Guiana, where it will be launched atop an Ariane 5. After it is launched, it will take one month to reach its destination location, and it will unfold and cool itself down. It will take some 6 months of testing before it is declared ready to go.

From Wiki,
The JWST is oriented toward near-infrared astronomy, but can also see orange and red visible light, as well as the mid-infrared region, depending on the instrument. The design emphasizes the near to mid-infrared for three main reasons:
  • high-redshift objects have their visible emissions shifted into the infrared
  • cold objects such as debris disks and planets emit most strongly in the infrared
  • this band is difficult to study from the ground or by existing space telescopes such as Hubble
Click to expand...
The JWST has a primary mirror with diameter 6.5 meters and a collecting area of 25.4 m^2. It would be too large to send up in one piece in any existing rocket, so it is divided into 18 hexagonal segments and sent up in folded form. Once in space, it then unfolds.

The segments are in two rings with 6 and 12 each, with a center hole. They are gold-plated beryllium.

It has a secondary mirror on a tripod that will also be sent up in a folded state, and also a tertiary mirror a little beyond the primary one relative to the secondary one, making a  Three-mirror anastigmat - "an anastigmat telescope built with three curved mirrors, enabling it to minimize all three main optical aberrations – spherical aberration, coma, and astigmatism. This is primarily used to enable wide fields of view, much larger than possible with telescopes with just one or two curved surfaces."

It will be chilled to 50 K (−223 °C; −370 °F) to enable infrared observations, and to keep it at that temperature, it will have a sunshield. That also will be sent up in a folded state.
 
The JWST will be going out to the Earth-Sun L2 point, about 1.5 million kilometers from the Earth in the opposite direction from the Sun. That is an unstable point, so the JWST will have to adjust its position every now and then.

 List of objects at Lagrange points -  Lagrange point

Three of the five Lagrange points are in line with the two primary bodies:

L3 - (more massive one) - L1 - (less massive one) - L2

The other two points are L4, 60 degrees ahead in the primaries' orbit, and L5, 60 degrees behind.

There are several satellites that are or were at L2, and several others at L1, 1.5 M km toward the Sun, with several planned ones intended to be at L1 or L2.
 
 
lpetrich said:
NASA Webb Telescope on Twitter: "Launch date update! December 18, 2021 is now the target launch date for #NASAWebb! ?????? This date was coordinated between @NASA @ESA, and @Arianespace.

Next: Webb will be packed for its journey to the launch site in Kourou, French Guiana.

Read more: (links)" / Twitter
NASA Readies James Webb Space Telescope for December Launch | NASA

"The highly complex space telescope is currently resting in its final stow configuration at Northrop Grumman’s facilities in Redondo Beach, California"
Click to expand...

How long after it launches before we will be getting quality images from it?

I still can’t believe they named it after a NASA administrator instead of a great American Astronomer. I would have named it after Henrietta Leavitt, or maybe Vera Rubin. That would have inspired people to learn about these remarkable women of Astronomy.
 
SLD said:
lpetrich said:
NASA Webb Telescope on Twitter: "Launch date update! December 18, 2021 is now the target launch date for #NASAWebb! ������ This date was coordinated between @NASA @ESA, and @Arianespace.

Next: Webb will be packed for its journey to the launch site in Kourou, French Guiana.

Read more: (links)" / Twitter
NASA Readies James Webb Space Telescope for December Launch | NASA

"The highly complex space telescope is currently resting in its final stow configuration at Northrop Grumman’s facilities in Redondo Beach, California"
Click to expand...

How long after it launches before we will be getting quality images from it?

I still can’t believe they named it after a NASA administrator instead of a great American Astronomer. I would have named it after Henrietta Leavitt, or maybe Vera Rubin. That would have inspired people to learn about these remarkable women of Astronomy.
Click to expand...

At least Vera Rubin got a telescope, the formerly named LSST.
 
lpetrich said:
Shadowy Man said:
At least Vera Rubin got a telescope, the formerly named LSST.
Click to expand...
I had to look it up:  Vera C. Rubin Observatory - the Large Synoptic Survey Telescope (LSST)
Click to expand...

Sad that it has to be looked up. Generations of school kids learned who Edwin Hubble was because of the space telescope. Such a great opportunity to learn about and inspire girls to study science was lost by naming the space scope after an administrator. He should have had the headquarters of NASA named after him. Not such an important scientific instrument. Sad.
 
SLD said:
lpetrich said:
Shadowy Man said:
At least Vera Rubin got a telescope, the formerly named LSST.
Click to expand...
I had to look it up:  Vera C. Rubin Observatory - the Large Synoptic Survey Telescope (LSST)
Click to expand...

Sad that it has to be looked up. Generations of school kids learned who Edwin Hubble was because of the space telescope. Such a great opportunity to learn about and inspire girls to study science was lost by naming the space scope after an administrator. He should have had the headquarters of NASA named after him. Not such an important scientific instrument. Sad.
Click to expand...

The naming was sorta a nuanced jab at the glory that goes to astronauts which hurt the hard sciences that the bureaucrats like Webb wanted to get back to. Regardless, I agree, let's inspire girls to do more science. Let's build more satellites. Let's explore more!
 
I saw that the telescope would have the precision to detect a bumble bee on the surface of the Moon. This scope has so much potential.
 
Jimmy Higgins said:
I saw that the telescope would have the precision to detect a bumble bee on the surface of the Moon. This scope has so much potential.
Click to expand...
If that is true then the context is the thermal emission from the bee. It can’t angularly resolve a bee at that distance and make an image.

We would refer to this kind of capability as “sensitivity”, in that there is a threshold for detection limit based on the amount of light it can gather relative to sources of noise.
 
Jimmy Higgins said:
I saw that the telescope would have the precision to detect a bumble bee on the surface of the Moon. This scope has so much potential.
Click to expand...

I'd say the scope of the LSST is equally if not more impressive. The sheer amount of observational data is overwhelming. It's basically taking a comprehensive, high resolution "snapshot" of the entire observable sky every few days. Glad they named it after Rubin, too.
 
Ford said:
Jimmy Higgins said:
I saw that the telescope would have the precision to detect a bumble bee on the surface of the Moon. This scope has so much potential.
Click to expand...

I'd say the scope of the LSST is equally if not more impressive. The sheer amount of observational data is overwhelming. It's basically taking a comprehensive, high resolution "snapshot" of the entire observable sky every few days. Glad they named it after Rubin, too.
Click to expand...

That is why young astronomers are getting into machine learning. There will be so much data it couldn't possibly be looked at individually by a human.
 
It's a Vox article that goes into pretty good overview detail of the Webb telescope, it's potential, complexity, infrared capability, construction and deployment.
 
NASA on Twitter: "✅ Closer to launch! Our @NASAWebb Space Telescope has arrived in French Guiana for its scheduled Dec. 18 liftoff.

From California, through the Panama Canal, to South America – get the details on Webb's ~5,800-mile (~9,300 kilometer) voyage: (links)" / Twitter

NASA on Twitter: "@YJiden @NASAWebb 🚀 The rocket and launch services are part of @ESA's contribution to the mission, so liftoff will be from Europe's Spaceport in French Guiana! This launch site is also near the equator, which is beneficial because the spin of the Earth can help give an additional push." / Twitter

NASA’s Webb Space Telescope Arrives in French Guiana After Sea Voyage | NASA
NASA’s James Webb Space Telescope successfully arrived in French Guiana Tuesday, after a 16-day journey at sea. The 5,800-mile voyage took Webb from California through the Panama Canal to Port de Pariacabo on the Kourou River in French Guiana, on the northeastern coast of South America.

...
Late in the evening of Friday, Sept. 24, Webb traveled with a police escort 26 miles through the streets of Los Angeles, from Northrop Grumman's facility in Redondo Beach to Naval Weapons Station Seal Beach. There, it was loaded onto the MN Colibri, a French-flagged cargo ship that has previously transported satellites and spaceflight hardware to Kourou. The MN Colibri departed Seal Beach Sunday, Sept. 26 and entered the Panama Canal Tuesday, Oct. 5 on its way to Kourou.

The ocean journey represented the final leg of Webb's long, earthbound travels over the years. The telescope was assembled at NASA's Goddard Space Flight Center in Greenbelt, Maryland, starting in 2013. In 2017, it was shipped to NASA's Johnson Space Center in Houston for cryogenic testing at the historic “Chamber A” test facility, famous for its use during the Apollo missions. In 2018, Webb shipped to Space Park in California, where for three years it underwent rigorous testing to ensure its readiness for operations in the environment of space.

...
After Webb is removed from its shipping container, engineers will run final checks on the observatory’s condition. Webb will then be configured for flight, which includes loading the spacecraft with propellants, before Webb is mounted on top of the rocket and enclosed in the fairing for launch.
Click to expand...
Seal Beach is just east of Long Beach, in turn, south of downtown Los Angeles. Redondo Beach is also on the coast, southwest of downtown LA.

Port de Pariacabo is about 5 km / 3 mi upriver from the Atlantic Ocean, and the Guiana Space Center is 3 km / 2 mi by road from Pariacabo.

So it won't be much longer before the telescope arrives in the spaceport to be checked out.
 
The launch was on time, 4:20 AM PDT, and I watched it on NASA TV.

The JWST is now in a transfer orbit for its destination, Lagrange point L2. It is about 1.5 million km / 0.93 million mi / 3.9 * the distance to the Moon / 0.01 AU from the Earth in the direction away from the Sun. It will will reach that point in 30 days.

Where Is Webb? NASA/Webb

Deployment Explorer Webb/NASA - all the steps in getting the telescope into place and into service.

The launch was was an uninterrupted sequence, without going into a parking orbit on the way. The telescope was released with a spring-loaded mechanism that pushed it away. A few minutes later, it extended its solar array -- only one.

The booster rocket's upper stage caught some video of the departing telescope, the last good view of it that we will ever have in a long time. It then turned to fire its engines to get into an escape orbit that will put it into a heliocentric orbit.

Coming up:
  • +12.5 h -- midcourse correction 1a
  • +1d -- gimbaled antenna array
  • +2d -- midcourse correction 1b
  • +3d -- forward unitized pallet structure, contains sunshield membranes
  • +3d -- aft unitized pallet structure, contains sunshield membranes
  • +4d -- deployable tower assembly, moves the telescope proper away from its spacecraft body
  • +5d -- aft momentum flap, for aiming the telescope with solar radiation pressure
  • +5d -- sunshield covers release
  • +6d -- left/port sunshield boom deployment, stretching the sunshield in its direction
  • +6d -- right/starboard sunshield boom deployment, stretching the sunshield in its direction
  • +7d -- sunshield layer tensioning, for all 5 layers
  • +8d -- sunshield layer tensioning should be complete. Temperature: Sun side: 383 K, telescope side: 36 K
  • +10d -- secondary mirror deployment
  • +10d -- secondary mirror deployment should be complete
  • +11d -- aft deployed instrument radiator
  • +12d -- port primary wing deployment
  • +12d -- port primary wing deployment should be complete
  • +13d -- starboard primary wing deployment
  • +13d -- starboard primary wing deployment should be complete
  • +13d -- JWST should be fully deployed
  • +15-24d -- primary mirror movements
  • +29d -- midcourse correction 2 - L2 insertion burn
  • +29.5d -- JWST is now orbiting L2
  • next 5 months -- aligning the optics and calibrating the instruments
Setting up for this gruesomely complicated procedure is likely a major contributor to JWST's cost and schedule overruns.
 
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