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James Webb telescope: Sun shield deployment is critical

BBC News

The next few days will be critical in determining whether the new James Webb telescope is able to undertake its thrilling mission to image the first stars to shine in the Universe.

"The space observatory, which launched into orbit on Saturday, is about to attempt to unpack its five-layered sun shield."

NASA reckons that it may be able to stay in operation longer than the scheduled ten years as it has more fuel left than expected https://newatlas.com/space/extra-fuel-james-webb-space-telescope-extend-science-mission/

V8

88V8 wrote:NASA reckons that it may be able to stay in operation longer than the scheduled ten years as it has more fuel left than expected https://newatlas.com/space/extra-fuel-james-webb-space-telescope-extend-science-mission/

V8

I expect that the designers included a convenient re-fueling port. The re-fueling of satellites seems to be becoming a viable option now, albeit quite a long way to travel to re-fuel the JWT. That's assuming that other bits don't fail. The most common failures for that class of satellite are the reaction control wheels that keep it aligned very precisely. Normally there are 3 of them, one for each axis and a fourth redundant one. The Hubble had a couple of fairly early failures but they could be replaced by Space Shuttle crew. The JWT has a docking ring that could be used by an Orion crew, that's if the Orion ever actually gets finished.

RC

ReformedCharacter wrote:I expect that the designers included a convenient re-fueling port. The re-fueling of satellites seems to be becoming a viable option now, albeit quite a long way to travel to re-fuel the JWT. That's assuming that other bits don't fail. The most common failures for that class of satellite are the reaction control wheels that keep it aligned very precisely. Normally there are 3 of them, one for each axis and a fourth redundant one. The Hubble had a couple of fairly early failures but they could be replaced by Space Shuttle crew. The JWT has a docking ring that could be used by an Orion crew, that's if the Orion ever actually gets finished.

That's fascinating, do you know any more about the docking ring, which I have never heard of before?

One thought though, could it have been included only for near Earth emergencies? For instance, for rescue, if its launch had failed to put it into the correct original Earth orbit?

XFool wrote:

ReformedCharacter wrote:I expect that the designers included a convenient re-fueling port. The re-fueling of satellites seems to be becoming a viable option now, albeit quite a long way to travel to re-fuel the JWT. That's assuming that other bits don't fail. The most common failures for that class of satellite are the reaction control wheels that keep it aligned very precisely. Normally there are 3 of them, one for each axis and a fourth redundant one. The Hubble had a couple of fairly early failures but they could be replaced by Space Shuttle crew. The JWT has a docking ring that could be used by an Orion crew, that's if the Orion ever actually gets finished.

That's fascinating, do you know any more about the docking ring, which I have never heard of before?

One thought though, could it have been included only for near Earth emergencies? For instance, for rescue, if its launch had failed to put it into the correct original Earth orbit?

Here's all I know about the docking ring, not much:

https://en.wikipedia.org/wiki/Spacecraft_bus_(James_Webb_Space_Telescope)#Docking_ring

As to whether it may have only been included for near earth emergencies, I doubt it. AFAIK the JWT never went into earth orbit as such, as most but not all manned rockets do for visits to the ISS, and all Apollo missions to the moon did. It made it's biggest correction burn to take it to the L2 point (c. 1m miles away) about 12 hours after launch with most of the tricky deployment still to come, so it will be well on it's way before any likely problems arise. The only possible scenario that I can think of where the docking ring might have been useful close to the earth would be the failure of the rocket thrusters. These are chosen for their simplicity and reliability (used on the Apollo system and many others) and use Hydrazine and nitrogen tetroxide which are hypergolic (ignite when they come into contact) reducing the need for an ignition system and other complexity. They're a very tried and tested technology, so they would be very low on the list of likely problems. Here's a very informative Scott Manley video (13m) on Lagrange points if you are interested:

https://www.youtube.com/watch?v=7PHvDj4TDfM

RC

Sun shield fully deployed: https://www.bbc.co.uk/news/science-environment-59873738
I'm sure there was a massive collective sigh of relief at NASA

Amazing engineering.

--kiloran

kiloran wrote:Sun shield fully deployed: https://www.bbc.co.uk/news/science-environment-59873738
I'm sure there was a massive collective sigh of relief at NASA

Amazing engineering.

--kiloran

And the secondary mirror has now been deployed
https://www.bbc.co.uk/news/science-environment-59885687
Incredible engineering
But the engineers and scientists at NASA must still be on tenterhooks

scotia wrote:

kiloran wrote:Sun shield fully deployed: https://www.bbc.co.uk/news/science-environment-59873738
I'm sure there was a massive collective sigh of relief at NASA

Amazing engineering.

--kiloran

And the secondary mirror has now been deployed
https://www.bbc.co.uk/news/science-environment-59885687
Incredible engineering
But the engineers and scientists at NASA must still be on tenterhooks

Unfolding now completed.

https://www.theguardian.com/science/2022/jan/08/nasa-engineers-complete-the-unfolding-of-the-james-webb-space-telescope

Nasa engineers yesterday completed the final unfolding of the huge primary mirror of the agency’s James Webb space telescope. The manoeuvre was the final step of the $10bn observatory’s two-week deployment phase that began with its launch on Christmas Day.
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And this was followed up yesterday when engineers released the final, second segment of mirrors which slotted into the mirror’s central core, thus completing the telescope’s vast 6.5 metre diameter mirror. Last night engineers were completing the final latching manoeuvres that will hold this last segment in place.

But it will still be a while before it is finally in position and calibrated so that it is able to start work

The James Webb, named after a former Nasa administrator, still has to travel 400,000 miles to its destination and will then need five more months for its instruments to be carefully calibrated.

So far, so good.

Now how long before they discover that the mirror has been ground to the wrong shape?

--kiloran

kiloran wrote:So far, so good.

Now how long before they discover that the mirror has been ground to the wrong shape?

--kiloran

They have a cunning plan, or at least a cunning design - the curvature is adjustable:

https://webb.nasa.gov/content/observatory/ote/mirrors/index.html

RC

ReformedCharacter wrote:

kiloran wrote:So far, so good.

Now how long before they discover that the mirror has been ground to the wrong shape?

--kiloran

They have a cunning plan, or at least a cunning design - the curvature is adjustable:

https://webb.nasa.gov/content/observatory/ote/mirrors/index.html

RC

Ah, but have they planned for the adjustment to be in imperial or metric units? Or a mixture?
It's a $10B project, there just has to be a schoolboy error somewhere

--kiloran

ReformedCharacter wrote:

kiloran wrote:So far, so good.

Now how long before they discover that the mirror has been ground to the wrong shape?

--kiloran

They have a cunning plan, or at least a cunning design - the curvature is adjustable:

https://webb.nasa.gov/content/observatory/ote/mirrors/index.html

RC

The alignment process of which, according to the final video at that link, will take "several months to complete"!

And it has now reached its final position. From the BBC site:-
https://www.bbc.co.uk/news/science-environment-60116475

scotia wrote:And it has now reached its final position. From the BBC site:-
https://www.bbc.co.uk/news/science-environment-60116475

This short clip gives quite a good animation of how it moves then around that point.

https://www.youtube.com/watch?v=IyyQqaF4tNY

Note it's field of view will constantly be changing as it orbits the sun, AIUI it has some clever gyroscopes and tracking kit on board to hold onto it's target.

kiloran wrote:Ah, but have they planned for the adjustment to be in imperial or metric units? Or a mixture?
It's a $10B project, there just has to be a schoolboy error somewhere

--kiloran

We can be sure it's not imperial. Americans don't use, and have never used, "imperial units". Imperial units weren't defined until 1824 (well after 1776). They may use "customary units", some of which differ from imperial by various degrees.

moorfield wrote:

scotia wrote:And it has now reached its final position. From the BBC site:-
https://www.bbc.co.uk/news/science-environment-60116475

This short clip gives quite a good animation of how it moves then around that point.

https://www.youtube.com/watch?v=IyyQqaF4tNY

Note it's field of view will constantly be changing as it orbits the sun, AIUI it has some clever gyroscopes and tracking kit on board to hold onto it's target.

Yes, the Youtube video shows the pattern, but what I don't understand is exactly 'how' it can orbit about that point. I've been fascinated by space exploration since I was about 7 and follow all the Mars rovers. But this telescope has arrived at the L2 point which is empty. Yes, I know there are gravitational forces, maybe stronger due to the line-up of the earth-sun, but I find it incredible that the telescope can actually orbit around this point.

If it is so clear, why didn't NASA or ESA ever do the same to examine the moon's far side. i.e. send an orbiting probe to orbit the point that is in balance between the moon and earth? Actually, wouldn't that be another good place for a telescope?

Steve

PS Just realised that it wouldn't be a good place for a telescope due to changing exposure to sun.

stevensfo wrote:
Yes, the Youtube video shows the pattern, but what I don't understand is exactly 'how' it can orbit about that point.

How James Webb orbits Nothing

The explanation starts at about 7:00 if you get bored by the rest of the excellent video.

9873210 wrote:

stevensfo wrote:
Yes, the Youtube video shows the pattern, but what I don't understand is exactly 'how' it can orbit about that point.

How James Webb orbits Nothing

The explanation starts at about 7:00 if you get bored by the rest of the excellent video.

If I could give you more than one rec, I would!

Fascinating!

Steve