James Webb Telescope

Funny comment from one of the team regarding the collimation of the primary. Something like "first light will look like 18 prima donna mirrors each thinking they are the best."
 
Well, I guess all the major deployments went off without a hitch.

What else is left for pessimists to obsess over?
 
I'm not particularly concerned about that part. Should I be?

What about all the tiny little actuators that do the fine adjustments of the mirrors?

Or micrometeorites? Will it be able to cool down to the temperature it needs to?
 
smartcooky said:
Latest cold side temperatures.

Primary Mirror: -164°C (down from -147°C yesterday)
Instrument Radiator: -199°C (down from -197°C yesterday)
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It now says

Primary Mirror: -172°C
Instrument Radiator: -199°C

The primary mirror is 8 degrees colder, but the radiator temperature is unchanged?

https://www.nature.com/articles/d41586-022-00035-4

Next up, Webb will begin tweaking the positions of the primary mirror’s 18 segments to align them to properly focus light that they collect. The telescope also continues to cool down towards its operating temperature of around 40 °C above absolute zero, or –233 °C. It is currently nearly –200 °C on its cold side, behind the sunshield.
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So, looks like there's about 34 degrees C of cooling to go.
 
Puppycow said:
It now says

Primary Mirror: -172°C
Instrument Radiator: -199°C

The primary mirror is 8 degrees colder, but the radiator temperature is unchanged?
Click to expand...

Yes, I would expect that. There are operating instruments in the instrument module that will be generating heat, so I would expect its the temperature to come down very slowly, as opposed to the primary mirror where nothing is operating.

However, it is possible that the mirror temperature might rise slightly when they start operating the drive motors to calibrate and align the segments.
 
Latest cold side temperatures.

Primary Mirror: -178°C (down from -172°C yesterday)
Instrument Radiator: -200°C (down from -199°C yesterday)


Webb is now just over ¾ of its way (just over way ½ time-wise) to its destination as it decelerates under the pull of gravity towards L2.

L2 Halo orbital insertion burn in about 14 days.
 
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So, it's done? Nohting left to do now but wait for the injection burn and hope no random space detritus hits the thing? (Is that even a possibility?)
 
3point14 said:
So, it's done? Nohting left to do now but wait for the injection burn and hope no random space detritus hits the thing? (Is that even a possibility?)
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They are currently going through individual mirror alignment of the 18 primary mirror hexagons. As well as the secondary mirror (which, BTW, has similar actuators but not the center actuator).

NASA addressed the risks of micrometeorite impacts during one of the briefings. Webb is in a pretty benign area of space, and they mentioned the shield at least can take a certain number of punctures/hits.
 
Puppycow said:
They are now saying that there is enough fuel left to keep the telescope operating for about 20 years.
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Looking ahead to that time, just out of interest, presumably the radial instability of the L2 orbit means that JWST will end up departing from it when it runs out of fuel. What's the range of possible trajectories from then on? Will it be necessary to give it a final nudge to send it out of solar orbit altogether?

Dave
 
Dave Rogers said:
Looking ahead to that time, just out of interest, presumably the radial instability of the L2 orbit means that JWST will end up departing from it when it runs out of fuel. What's the range of possible trajectories from then on? Will it be necessary to give it a final nudge to send it out of solar orbit altogether?
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Out of solar orbit? It doesn't have enough fuel to do that now. And it would be ridiculously expensive overkill.

It will just stay in solar orbit and occasionally get diverted by close encounters with Earth. If for some reason it presents an obstacle to something later on there will be a burn to get it reliably away from L2.
 
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Dave Rogers said:
Looking ahead to that time, just out of interest, presumably the radial instability of the L2 orbit means that JWST will end up departing from it when it runs out of fuel. What's the range of possible trajectories from then on? Will it be necessary to give it a final nudge to send it out of solar orbit altogether?

Dave
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L2 is not 100% stable. There is also no telling which direction it will go once it leaves... it could just as easily fall in towards the earth.
 
Chances are it'll get hucked off into deep space, and return a few hundred years hence, radically upgraded by powerful alien intelligences. Upon (re)arrival, it will either want to talk to its original manufacturer, or perform a duet with some whales, with world-ending consequences either way if its childish but godlike demands are not met.

Hopefully Jane Tiberius Bezos-Musk will be on hand to save humanity.
 
Some information about cooling the telescope.

Once the sunshield is deployed, the telescope and scientific instruments begin to cool a little quicker than before, but it will still take several weeks to cool down to the operating temperature and remain stable.

However, the telescopes isn't just allowed to cool down by itself. The cooling is controlled by specially placed electric heating strips. At first, this may seem counter-intuitive - why would you use heating strips to cool down an object. Well, if the telescope cools too fast, then as it shrinks (yes, it will shrink slightly as it cools) water vapour in and on parts of the telescope could freeze and become trapped. The heaters are used to manage the cooling so that everything shrinks carefully and evenly, allowing trapped water to escape as gas into the vacuum of space and not freeze as ice onto mirrors or detectors.
 
theprestige said:
Chances are it'll get hucked off into deep space, and return a few hundred years hence, radically upgraded by powerful alien intelligences. Upon (re)arrival, it will either want to talk to its original manufacturer, or perform a duet with some whales, with world-ending consequences either way if its childish but godlike demands are not met.

Hopefully Jane Tiberius Bezos-Musk will be on hand to save humanity.
Click to expand...

All I can say to that is 'thank Scotty for transparent aluminium'!
 
smartcooky said:
Some information about cooling the telescope.

Once the sunshield is deployed, the telescope and scientific instruments begin to cool a little quicker than before, but it will still take several weeks to cool down to the operating temperature and remain stable.

However, the telescopes isn't just allowed to cool down by itself. The cooling is controlled by specially placed electric heating strips. At first, this may seem counter-intuitive - why would you use heating strips to cool down an object. Well, if the telescope cools too fast, then as it shrinks (yes, it will shrink slightly as it cools) water vapour in and on parts of the telescope could freeze and become trapped. The heaters are used to manage the cooling so that everything shrinks carefully and evenly, allowing trapped water to escape as gas into the vacuum of space and not freeze as ice onto mirrors or detectors.
Click to expand...

Smart Cooky,
I'd like to thank you for your contribution to this thread. Your clear and informative answers make me look like Carl Sagan down the pub!
Cheers mate!
 
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