James Webb Space Telescope

[Alberon]

It's just being slow and sure, making sure each section works before moving on to the next bit.

And also, if a deployment fails but the rest goes ahead you might destroy the equipment. If the mirror turns towards the sun it's game over.

[Mr_Simnock]

When you say 'fixable' I take it you mean a manned space walk to repair it? We can't really do that now the shuttle has gone. Or do you mean fix itself somehow? Some problems can be fixed by itself via commands from earth but if, say, the sun shield was torn then that would be basically a no go to sort by any means, same goes for any serious issues with the main mirror segments too. It just takes this long so as to give each stage as much chance as possible of completing successfully. You couldn't have an unfurling sequence via orbiting the moon before moving out to the L2 point, that would take too much extra fuel onboard, in fact that would require a substantially larger satellite to carry that fuel.

[Alberon]

There are several fixes that can be applied from the ground. Using the thrusters to shake the craft if the shield didn't deploy fully, for instance.

Maybe SpaceX could get out to L2 in five years or so, but it would be a very risky mission.

[TrenterPercenter]

If it orbited somewhere close then surely it could be fixed manually and refuelled at the same time.  That is if it needed to.  If something goes wrong with the unfolding and can't be fixed remotely then it is game over being so far away so I was just thinking unfolding first in space then it moving to L2 would be less risky (thought two rockets might be needed).

[NoSleep]

It is in space, and moving towards its destination. So why not use the time on its journey to get ready? Where did you think it was?

[Mr_Simnock]

If it orbited somewhere close then surely it could be fixed manually and refuelled at the same time.  That is if it needed to.  If something goes wrong with the unfolding and can't be fixed remotely then it is game over being so far away so I was just thinking unfolding first in space then it moving to L2 would be less risky (thought two rockets might be needed).

The overall mission cost for that would be far too high unfortunately. It would only have to orbit about 400km up to be fixed manually and refueled, and with current space tech (without the shuttle) I'm not sure how anyone would do that.

[Alberon]

It has to be further out as even Earthlight would damage the optics.

At L2 the sunshade can block light from the Earth as well as the sun.

[TrenterPercenter]

It has to be further out as even Earthlight would damage the optics.

At L2 the sunshade can block light from the Earth as well as the sun.

Ah yes this makes sense.  Nice one!

[TrenterPercenter]

It is in space, and moving towards its destination. So why not use the time on its journey to get ready? Where did you think it was?

I know where it is I'm watching it everyday on the where's Webb page.  I'm just talking about how it is doing its setup further and further away when it mistake could be potentially fixed if closer and what the rationale was for not doing that.

[touchingcloth]

"Refuel in space and then blast off for the journey proper" would also be unprecedented in the history of spaceflight, I think, and probably won't get seriously considered until all other options for getting a craft to where it needs to go to have been exhausted. They'd probably need to double their budget or halve what they spent on instruments to make that viable (maybe not exactly, but fuel costs make up a substantial portion of the cost of a mission, and the vast majority of a rocket's launch weight, so sending a rocket up with nothing but fuel on board would take a lot of convincing to get approved for funding), so I can see why they'd avoid doing that when not absolutely necessary. They'll be gutted if the telescope doesn't successfully deploy in the place it needs to deploy, but the odds of that not happening are a small percentage rather than the 100% odds of enormous costs just for a precautionary few loops around the earth. It's almost better to assume you'll get funding for a do-over if catastrophe strikes, which is definitely the case with Mars missions as the litany of failures haven't stopped us sending stuff there.

[JesusAndYourBush]

I just thought of something. Rocket fuel is made from liquid oxygen and liquid hydrogen.  When a rocket launches into Earth orbit that oxygen and hydrogen is getting blasted back down to Earth, but when a rocket goes further away that hydrogen and oxygen is just getting pissed away into space.  Can we, as a planet, afford to lose it?

[touchingcloth]

I just thought of something. Rocket fuel is made from liquid oxygen and liquid hydrogen.  When a rocket launches into Earth orbit that oxygen and hydrogen is getting blasted back down to Earth, but when a rocket goes further away that hydrogen and oxygen is just getting pissed away into space.  Can we, as a planet, afford to lose it?

Just googled and found that

The total mass of Oxygen on and in the Earth is about 12.9 quintillion metric tons.

[JesusAndYourBush]

Ah, that is quite a lot!

[Blumf]

Can we, as a planet, afford to lose [oxygen/hydrogen]?

https://phys.org/news/2016-07-curious-case-earth-leaking-atmosphere.html

Earth's atmosphere is leaking. Every day, around 90 tonnes of material escapes from our planet's upper atmosphere and streams out into space.

But, on the other hand:

https://briankoberlein.com/blog/is-earth-gaining-mass/

Earth gains mass through dust and meteorites that are captured by its gravity. If you watched the recent meteor shower you know this can occur on a regular basis. In fact from satellite observations of meteor trails it's estimated that about 100 – 300 metric tons (tonnes) of material strikes Earth every day. That adds up to about 30,000 to 100,000 tonnes per year. That might seem like a lot, but over a million years that would only amount to less than a billionth of a percent of Earth's total mass.

[mothman]

Live video of the tensioning:

https://spaceflightnow.com/2022/01/04/jwst-deployments-mission-status-center/

or

https://youtu.be/21X5lGlDOfg

[touchingcloth]

I wonder how long it will be before PC component manufacturers start producing JWST heatsinks.

[Replies From View]

Has there ever been a space telescope before that had acute phimosis

[touchingcloth]

Has there ever been a space telescope before that had acute phimosis

https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Flawed_mirror

[MojoJojo]

I know where it is I'm watching it everyday on the where's Webb page.  I'm just talking about how it is doing its setup further and further away when it mistake could be potentially fixed if closer and what the rationale was for not doing that.

Stopping in orbit, deploying everything, then accelerating off to the L2 point would have used loads of fuel - and it would be satellite fuel rather than the launch rockets fuel.

Also, I doubt there are many things that could be fixed if something did go wrong. Hubble was unusual in that regard.

[Replies From View]

https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Flawed_mirror

Not specific enough to the tensioning theme.

[Replies From View]

Stopping in orbit, deploying everything, then accelerating off to the L2 point would have used loads of fuel - and it would be satellite fuel rather than the launch rockets fuel.

Also, I doubt there are many things that could be fixed if something did go wrong. Hubble was unusual in that regard.

They use weird screw heads like iPhones

[mothman]

Worse than that - like in McDonalds Happy Meal toys.

[touchingcloth]

Worse than that - like in McDonalds Happy Meal toys.

That's because they store notorious sex pests like Epstein inside the toys, and they want to avoid children accidentally managing to unleash peodos into their homes with a simple Phillips head, pardon. A spokesperson provided an evasive answer when asked why the Happy Meal toys were filled with nonce in the first place.

[Replies From View]

Worse than that - like in McDonalds Happy Meal toys.

Never had one, but I understand they are quite bad when the screwdriver is only floating towards them and then bouncing off to infinity.

[Alberon]

All five layers of the sunshield have been fully tensioned.

[TrenterPercenter]

All five layers of the sunshield have been fully tensioned.

Is it weird that I have been aroused by this sentence?

[mothman]

In space, no-one can hear them twang.

[Alberon]

The secondary mirror has been successfully deployed.



This was another absolutely critical step as it will reflect images from the main mirror to the sensing devices inside the telescope.

From space.com

Over the next few days, Webb will deploy its aft radiator, followed by folding out the two side segments, or wings, of its main mirror. Those steps will mark the final major deployment stages of the telescope.

Engineers will still have to move each of the 18 primary mirror segments out of their launch configuration so that they can be calibrated for observations. Once that is complete (slated for 15 days after launch), the next major step will be Webb's arrival into orbit around its L2 point.

[Replies From View]

Stupid idiot going all the way over there with a radiator. 

[Cuellar]

Let us be the judges of that, pls.  Photo.

Sorry been trying to find a good pic, here's one from a couple of christmases ago