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You may never have believed it would actually happen, but the James Webb Space Telescope
has launched, and it no, its rocket didn’t explode in a fireball on the way up.
But that doesn’t mean we are all good to go just yet, the telescope has some risky
months ahead of it.
Why is that?
Well, James Webb has to make it to the Earth’s L2 Lagrange point, all the while performing
the delicate operation of unfolding itself before it can unfold our understanding of
the universe.
I’m Alex McColgan, and you’re watching Astrum, and in this video I want to go through
the deployment process of the James Webb Space telescope, and go into the details of how
James Webb goes from being in the rocket all the way until its final science ready state.
I hope by the end of this video I’ve earned your like and subscription.
The Ariane 5 rocket is what engineers planned the James Webb Space telescope around, the
rocket being one of the European Space agency’s big contributions to the mission.
The Ariane 5 launches by first igniting the liquid fuel main stage and then the supplementary
solid fuel boosters.
Ariane 5 has two of these boosters, weighing 277t each, and those combined with the liquid
fuel main stage can take the rocket to the edge of space by themselves.
Solid fuel is often used initially as while it can’t be controlled so easily, it is
a cheaper fuel type and good for that brute force initial lift-off.
Once the boosters are expended at about 75km up, they are jettisoned from the main stage,
leaving just the liquid fuel engine burning.
Liquid fuel is useful because it can be throttled if needs be.
About a minute later, the rocket is beyond the Karman line of 100km, and the fairing
surrounding James Webb can be safely jettisoned.
At this altitude there is virtually no atmosphere anymore, so the telescope no longer needs
the fairing’s protection.
After about 8 and a half minutes after lift-off, the main liquid fuel stage is finally expended,
and it too separates from the upper stage.
The main stage, like the fairings and the boosters before it, will all end up in the
ocean.
With all that weight gone, the upper stage ignites and gives Webb the boost it needs
to get to the Earth’s L2 point.
Initially, the altitude doesn’t increase, in fact it even dips, as this part of the
process is about building speed, and gravity helps with that a bit.
However, this is already a potentially risky phase of the trip, as the Sun’s rays are
directly interacting with the telescope here.
Although it is folded up, the sunshield is not deployed, and sunlight can reach Webb’s
delicate instruments here, warming them up.
Until the sunshield fully deploys, it’s not totally protected.
In order to distribute heat as evenly as possible, and to keep the really delicate parts in shadow,
this upper stage rotates back and forth by 30°, like a baby in a cradle.
Once in position, the flight trajectory takes it up into space.
Its speed still increases even as it combats Earth’s gravity due in part to the fact
that the rocket is getting lighter with every passing second as the fuel is burning.
At 25 minutes in, the upper stage cuts off, and there is a 2-minute coasting phase.
Here, the rocket rotates around in order to perform a collision avoidance manoeuvre.
Webb then separates from the upper stage, and from then it is all by itself.
It is very interesting to me that this view of it leaving the upper stage is the last
view we will ever have of the telescope itself, and seeing as this has already happened, here’s
a beautiful shot of the very first thing Webb did, which is its thrusters firing, and then
its solar panels deploying, which was actually performed slightly earlier than expected.
During separation, usually some rotation is introduced on the payload, but this time there
was hardly any rotation at all, and the thrusters had to do very little to keep James Webb from
rotating too much, meaning it was safe to deploy the solar panels almost immediately.
From here, James Webb provides its own thrust.
The cradling manoeuvre continues using these thrusters, regulating the telescope’s temperature.
To protect the mirrors as much as possible, these thrusters are only located on the sun-facing
side of the spacecraft.
A day and a half after launch, the high gain antenna is deployed, and James Webb passes
the moon’s orbit.
At this point, James Webb has already slowed considerably, as it’s basically going directly
against the gravity of Earth.
Just short of three days into the mission, the sunshield palettes begin to deploy.
This is a very slow process to ensure nothing breaks, and so Webb doesn’t start spinning
around uncontrollably from the palette’s movement.
Almost 5 days into the mission, the tower separating the telescope and the sunshield
extends.
Next is the aft momentum flap.
This is a pretty clever fuel saving idea, this flap will offset the tiny amount of solar
pressure pushing on the sunshield’s membrane, meaning Webb won’t need to use as much fuel
to combat this pressure and stay aligned.
Still on day 5, the sunshield protectors will unroll and open.
Now for the really delicate operation.
The centre booms will extend, and with them they will gently pull the sunshield membrane
open.
If you recall, this was one of the tests that failed back in 2018, as the membrane ripped
in deployment.
These membranes are thinner than a human hair, and once fully extended, are the size of a
tennis court.
When stretched, these membranes will be tensioned, finally fully protecting James Webb from the
Sun’s harsh rays.
The sun facing side of the telescope will get very hot, almost to a boiling temperature,
whereas the side with all the instruments will be kept to a cool -230°C thanks to this
sunshield.
10 days after launch, the instruments are cooling down by passively radiating their
heat into space.
From here, the secondary mirror deploys, locking in place.
Next is the aft radiator, a passive cooling system that will radiate the instruments own
heat into space.
This is crucial to maintain cool temperatures.
On day 12, the side mirror wings will rotate and latch into place.
15 days in, the telescope is fully deployed, and its simply a matter of waiting for the
telescope to reach the L2 point, and cool into its final cryogenic temperature state.
The last operation to complete before James Webb will be operational is the alignment
of the primary mirror segments.
Each can be adjusted to within nanometre precision, allowing the light collected by Webb to be
turned into crystal clear images.
After 29 days, there is one final correction using the onboard thrusters to put Webb into
its halo orbit around the Earth’s L2 point.
From this orbital point, the bright Sun, Earth and Moon will always be behind the sunshield,
meaning the brightest thing in Webb’s view will only ever be Jupiter.
Roughly 160 days after launch, the instruments will have cooled down enough to be operational,
and any adjustments that need to have been made will have already been completed.
From here on out, the James Webb Space Telescope will be collecting science and unfolding the
universe.
If you like space telescopes, there’s a lot more than just Hubble and James Webb out
there.
We’ve had telescopes in space for decades, from Kepler, to Spitzer, to Gaia, and more.
If you want to know more about some of these other ones, there’s an interesting documentary
on MagellanTV called “Eyes to the Heavens” where they explain more about some of these
missions.
Gaia in particular is fascinating to me, as it’s a sky survey mission, and it has catalogued
billions of stars and their motion in the sky over the years.
MagellanTV has a special offer on right now, where you can buy a years’ worth of membership
and get another annual membership for free, potentially a good gift for someone you know
that enjoys science and history documentaries.
If you want to check out Eyes to the Heavens and MagellanTV’s offer, check my link in
the description below, I highly recommend it.
Thanks for watching.
Check out my other James Webb video here if you want to know about what the mission hopes
to accomplish.
A big thanks to my Patrons and members for supporting the channel, if you want to support
too, check the links in the description below.
All the best, and see you next time.