James Webb Telescope's FINAL Phase of Commissioning
Imagine this - 1000 people from 17 countries working collaboratively together, and it could
fall apart at the last moment.
A tennis court-sized telescope in its prime abruptly ceases to work.
Can you believe despite years of research and the expertise of the top brilliant minds,
the James Webb Space Telescope is a multi-billion dollar gamble?
But seems like it paid off?
Traveling over 1 million miles ( 1.6 million kilometers) through space it has finally reached
its resting orbit.
Tentatively sitting 4 times further from earth than our moon, it has transmitted its first
set of clear photos back to Earth.
Though rigorously tested prior to launch and excelling in the field, the JWST is alone
without the ability to call a repair ship if anything goes wrong.
But, the magnificent telescope has to face its most critical obstacle yet, The Final
Phase of Commissioning.
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Welcome to Factnomenal, and let's examine the eyes of the cosmos as it enters its final
trials.
Meeting the crew
Throughout its journey in space, the James Webb Space Telescope (JWST) has been excelling
every step of the way.
Scientists are ecstatic about the results so far and are currently gearing up for the
final phase of Webb’s commissioning.
They are holding their breath and their nerves are high.
Even though the telescope looks great on paper, scientists don’t know for sure how it will
stand up in reality to the harsh extremes of space.
The final phase of commissioning requires the calibration confirmation and stress testing
of the remaining instruments on board.
First is the Near-Infrared Camera or NIRCam.
It is very aptly named as it is a near-infrared camera but it also plays a vital role in the
calibration of the entire telescope.
This one instrument was used to properly align all 18 segments of the primary mirror that
is the backbone of this observatory.
Utilizing the data transmitted by NIRCam, scientists were able to get the correct angle
of all the mirrors onboard.
This was done by having all cameras take one photo each, resulting in multiple pictures
of the same star set from different angles.
Scientists then overlapped and aligned them all in a process called image stacking.
Bit by bit, like straightening a frame on your wall, eventually all of the images lined
up perfectly with one another.
As a result, there is now 1 giant mirror made up of 18 separate segments all working in
harmony to transmit sparkling clear images back to earth.
Having focused the eyes of Webb clearly on the cosmos, the next instruments to wake up
were the other near-infrared cameras.
They are the Fine Guidance Sensor (FGS) and the Near-Infrared Imager and Slitless Spectrograph
(NIRISS).
Both a mouthful and a handful, this combo is highly anticipated for the work they will
do for Webb.
These two were the logical instruments to calibrate following NIRCam as they were already
very close to their ideal operating temperature.
Very little had to be done to the observatory to accommodate their start-up.
NIRISS is an amazing instrument that captures images as well as spectra.
Both types of imaging work in tandem to allow scientists to gather more data about the stars
and their make-up with each transmission.
Though also a camera, the FGS’s goal is not to take amazing photos but is instead
used for navigation, via pre-selected guide stars.
While taking one photo per second, the FGS keeps the observatory on track and pointing
at the right segments of space.
While doing this the other instruments take photos and measurements, relying heavily on
FGS’s abilities to be accurate with their readings.
This is a very vital and precise job that cannot be overlooked.
The next instrument, the Near-infrared spectrograph (NIRSpec) is a powerhouse of an invention.
It allows scientists to simultaneously collect the spectra of 100 plus objects located in
one 9 square arc-minute field of view.
It does so with its unique micro-shutter array that allows precise aperture control.
With all of this time, energy, and money invested into the project, you would think that it
is important for everything to be working optimally.
But the truth is, this part of the Webb is already broken.
This highly regarded instrument still submitted a flawed photo to NIRCam for the alignment
process of the JWST.
Throughout the entire image, you could see sections that were blacked out and missing
information.
This is because of the 250 thousand micro shutters that are in the NIRSpec,14% of them
are not operational.
What’s even more shocking is that this isn’t a mistake that was overlooked.
The scientists at NASA knew about the faulty 14% but instead of replacing them and risking
damage to other lenses, they sealed off the rows that were not working and continued to
use the camera.
This decision has resulted in the dark streaks you see throughout the NIRSpec photo, but
NASA is ok with that.
Way to go NASA, embracing the flaws!
Lenses being stuck shut isn’t a total issue as it just leaves negative space in the photo.
That said, if a shutter is left open then the light can bleed into the photo and greatly
affect image quality.
As a fail-safe, NASA has created the ability for NIRISS to heat up to an intense temperature
in an attempt to un-stick any open shutters.
Though, the reality of doing this is very low because it would result in the entire
observatory requiring recalibration and would set back scientific study greatly.
It is more likely that NASA would also just accept the flaws for the greater good of the
project.
Finally, NASA prepared the last instrument - the Mid-Infrared Instrument (MIRI).
This one was last because it was on the other spectrum of the last 3 instruments and was
nowhere near its ideal operating temperature.
MIRI required both a repositioning of the Webb as well as a boost from a cryocooler
in order to get to its’ ideal chilly resting spot.
This instrument provides imaging, coronagraphy, and important field spectroscopy for wavelengths
that are longer than our eyes can see.
Not one for the sun, it is a great instrument to study in the next and final round of tests
for this powerhouse observatory!
It’s Heating Up!
Right now the JWST is engaging in its thermal stability test.
The goal of this gauntlet is for the telescope to endure the changes and to prove it can
work optimally in spite of conditions.
While being closely monitored it will be exposed to varying degrees of sunlight causing the
observatory to swing through a range of temperatures.
Scientists at NASA will be closely inspecting the observatory’s instruments to measure
their performance, calibration, and overall operations.
These instruments are unique and each was carefully chosen so the stakes are very high.
Dripping with astronomical sweat, the Webb telescope will begin the thermal stability
test by adopting a hot attitude of about 0 degrees pitch for five days.
Heating up and then stabilizing thermally the scientific team at NASA will take the
instruments through a barrage of tests to simulate possible scenarios in the extreme
environments.
After the heat, For another entire week, the telescope will be plunged into freezing temperatures
at plus forty-five degrees pitch from the sun.
After stabilizing there it will rotate to minus five degrees to the sun and heat back
up.
At both attitudes and throughout the transition, the instruments will be closely monitored.
The team will be utilizing the telescope instruments to better understand how they operate at each
extreme, and in between.
The importance of acclimatizing the observatory to all extremes is very apparent because some
of the instruments were made specifically to perform best at certain temperatures.
For example, examining the infrared universe requires that the telescope and instruments
be cold.
Thus, scientists want to know how it operates at higher temperatures to study it in both
optimal and suboptimal conditions.
That sounds like an understatement though as in space the difference is quite extreme
with the observatory experiencing a change of 126 degrees Fahrenheit to negative 384
degrees Fahrenheit from the hot to the cold side.
That fact puts suboptimal conditions into a better perspective.
The Final Gauntlet
In order to complete the commissioning of the James Webb Telescope, all of the instruments
must have a detailed measurement of their performance taken.
This will happen as it oscillates through the spectrum of temperatures as well as afterward,
hopefully maintaining its same image quality and pointing ability throughout.
Let’s explore just a few of the tests that Webb will endure throughout its last 2 months
of preparation.
Firstly the scientists will be measuring the throughput of the instruments.
Throughput is how much of the light entering the telescope actually reaches the detectors
to be recorded.
There is some loss as it bounces through the mirrors and it's impossible for every photon
to be detected.
As it is normal, they want to account for and adjust the sensors appropriately.
NASA will also study Webb’s capabilities to observe moving targets.
For example, they will focus on and follow asteroids of varying speeds to make sure it
is performing up to their high standards.
Next, they will focus on the astrometric calibration of all of the maps that each instrument has.
Astrometric Calibration is the mathematical process of translating the positions of image
pixels to the coordinates of the stars in the sky.
This is important as it will help with the navigation and plotting of the transmitted
data in the future.
NASA will also be measuring the point spread function, or the sharpness, of the images
that are transmitted to the scientists.
They have already calibrated the main mirror to get clear images but each instrument has
sub-abilities.
Some such abilities are filters that collect color information and diffraction grafting
to slice the incoming light into its proper color category.
All of these abilities must be tested so that there is an official baseline of quality.
Even billion-dollar space projects are subject to routine quality checks.
There are only 2 months left before the James Webb Space Telescope is fully functioning
and ready to stare into the heart of the universe, but there are still a lot of tests between
now and then!
How do you think the JWST will perform throughout this gauntlet?!
Let us know your expectations down below!
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Factnomenal.