Now that NASA’s James Webb Space Telescope has safely arrived at its launch
site in French Guiana, on the northeastern coast of South America, technical
teams have begun making progress on the final checklist of preparations
before liftoff later this year.
These preparations are expected to last 55 days from the observatory’s
arrival by ship to the day of launch.
After Webb arrived at the Arianespace clean room facilities in French
Guiana, contamination control technicians ensured the observatory is clean
and contaminant free following its 5,800 mile journey. Then engineers ran a
final set of electrical and functional tests and checked the stowed
mechanical configuration to ensure delivery went smoothly. A trained crew in
special hazmat suits will soon begin the two-week process of loading the
spacecraft with the hydrazine fuel and nitrogen tetroxide oxidizer it will
need to power its rocket thrusters to maintain its orbit. Next, Webb will
move to the nearby vehicle integration building to be lifted and mounted on
top of the Ariane 5 rocket “stack.” The final few remove-before-flight
“red-tag” items are taken off, and a few remaining add-before-flight “green
tag” items are installed. Then the rocket fairing is lifted and lowered over
top and locked into place, signifying the conclusion of a long journey. At
this point, Webb will be very nearly ready to launch from Europe’s
Spaceport, also known as the Guiana Space Center (CSG).
As a fully integrated launch vehicle with Webb as the payload, the Ariane
rocket will roll out to the launch pad a few days before launch. Engineers
monitor the rocket via electrical connections running from the payload
control room to the pad through an umbilical attachment to the vehicle that
separates at liftoff. A few hours before liftoff, the rocket is loaded with
liquid hydrogen fuel and liquid oxygen oxidizer. About a half hour before
launch, engineers in the payload control room switch the spacecraft from
external electrical power to the spacecraft’s on-board battery.
Webb's launch will be a pivotal moment for NASA and its partners, ESA
(European Space Agency) and the Canadian Space Agency (CSA), but it is only
the beginning. The following 29 days will be an exciting but harrowing time.
Thousands of parts must work correctly, in sequence, to unfold Webb and put
it in its final configuration, all while it flies through the expanse of
space alone, to a destination nearly one million miles away.
A more detailed breakdown of what lies ahead for Webb:
Webb’s 29 days on the edge begin upon liftoff. After 206 seconds of flight,
at an altitude of about 75 miles above the atmosphere, the two halves of the
rocket fairing that shields the observatory during ascent are separated by a
pyrotechnic system with springs that expose the observatory to space. Ground
teams expect to receive communication from Webb shortly after separation.
Webb will then separate from the launch vehicle nearly 28 minutes after
launch, and from this point on the ground team at the Space Telescope
Science Institute in Baltimore will be in full control, to begin the most
complex sequence of deployments ever attempted in a single space
mission.
To unfold the history of the universe, we must first unfold this telescope.
Following launch, over 300 single point failure items and 50 major
deployments must work to ensure optimal science.
Webb’s first deployment, the extension of its solar array, will occur
between 31 to 33 minutes after liftoff, stopping the drain on the
observatory’s internal battery by supplying nearly 2 kilowatts of power to
drive the spacecraft’s electrical systems and avionics. To enable the
highest data rate communication to the ground through NASA’s Deep Space
Network (DSN), the onboard medium and high-gain antenna platform is deployed
at two hours.
At 12 and a half hours after launch, Webb will fire its thrusters,
performing the first of several critical course corrections that send the
observatory towards its final destination in orbit. The observatory will
pass the Moon nearly two and a half days after launch, faster than the time
it took Apollo astronauts to reach lunar orbit.
Webb’s first large deployment, the extension of its sunshield frame known as
a unitized pallet structure, folds down nearly three days after launch,
opening the observatory up to continue expanding. This represents the start
of all major deployments and is scheduled to take approximately five hours
for both front and back pallets to fold down completely.
Four days after launch, a deployable tower will extend to separate the
telescope mirrors and instruments from the spacecraft bus. This separation
effectively isolates the telescope from vibrations and conducted heat coming
from the spacecraft bus. Additionally, this extension allows for the rest of
Webb’s larger deployable components, like its sunshield and primary mirror,
to have enough room to make their own sequence of complex movements
afterwards.
Sunshield membrane deployments formally begin approximately five days after
launch, as special covers that protect the sunshield during ascent will roll
out of the way. Next, a critical juncture in the mission will occur when all
of the 107 sunshield release mechanisms, or special pins that keep the five
sunshield layers locked into place, need to fire on cue and pull themselves
out to free the membranes. After all sunshield pins have been successfully
removed, two wings, known as mid-booms, extend to pull each of the sunshield
layers out into their characteristic diamond formation nearly a day later.
Following full deployment, each of the five layers are tensioned and
separated using special pulleys and motor systems. Sunshield deployments and
tensioning are expected to conclude between eight to nine days after liftoff
but can be slowed down to circumvent any unforeseen issues if they
arise.
Following the conclusion of sunshield tensioning, a special radiator behind
the primary mirror is deployed to help cool down the scientific instruments.
Next, Webb’s optics, and NASA’s new eye on the cosmos, open up. Telescope
deployment begins by unfolding and latching into place the tripod holding
the secondary mirror, and it is expected to conclude two hours into the 10th
day after liftoff. The secondary mirror is one of the most important pieces
of equipment on the telescope, essential to the success of the mission. This
smaller circular mirror plays an important role in collecting light from
Webb’s 18 primary mirrors into a focused beam. Primary mirror deployment is
set to begin on the 12th day, with the mirror’s side panels, each holding
three primary mirror segments, taking nearly three hours to extend out and
latch into place. At 13 days in, Webb’s large-scale deployments are expected
to conclude with the locking in of its primary mirror wings, revealing the
telescope in all its glory.
A 10-day, multi-step process to move all 18 primary mirror segments out of
their launch configuration will begin after the mirror wings are latched in
and conclude on day 25. To begin fine-tuning the mirrors, 126 extremely
precise actuators on the backside of the mirrors will position and subtly
bend or flex each mirror into a specific prescription, a process that will
take months.
On the 29th day, Webb will fire its thrusters once again to insert itself
into its prescribed orbit at the second Lagrange point, or L2, nearly one
million miles away from Earth, formally concluding the most difficult and
complex deployment sequence ever attempted in space.
The James Webb Space Telescope will be the world's premier space science
observatory when it launches in 2021. Webb will solve mysteries in our solar
system, look beyond to distant worlds around other stars, and probe the
mysterious structures and origins of our universe and our place in it. Webb is
an international program led by NASA with its partners, ESA (European Space
Agency), and the Canadian Space Agency
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