JWST Countdown To Terror 😳

[Nicola Fletcher]

24 minutes ago, Laurieast said:

https://www.nasa.gov/nasalive

I'm not aware of any alert, just keep checking the schedule frequently. Or keep it running on another screen just to be sure!

Ok, will do. Thank you!

[gilesco]

Question, can the mirror array tilt and rotate relative to the sunshield, or is the whole apparatus rigid and uses small jets for alignment? Just wondering whether we've got to wait for up to a year to be able to look in particular direction.

[kirkster501]

4 minutes ago, gilesco said:

Question, can the mirror array tilt and rotate relative to the sunshield, or is the whole apparatus rigid and uses small jets for alignment? Just wondering whether we've got to wait for up to a year to be able to look in particular direction.

There is a movable steering mirror inside the black nose thingy that sticks out from the centre of the primary.  That can be "steered" (i.e moved) so the telescope does not have to physically move so much.  Just image how accurately that must have been ground and polished !

Yes, for subjects on the "wrong" side of the sky the JWST has to wait just like we have to for them to become visible in the night sky again.

[Stu]

2 minutes ago, gilesco said:

Question, can the mirror array tilt and rotate relative to the sunshield, or is the whole apparatus rigid and uses small jets for alignment? Just wondering whether we've got to wait for up to a year to be able to look in particular direction.

I believe it is static relative to the shield, but with a small degree of adjustment possible via some other mechanism, not sure what.

Some info here on manoeuvring.

https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-spacecraft-bus/jwst-attitude-control-subsystem
 

I think with the scope movement within the bounds of what is possible whilst remaining protected by the sun shield, a certain amount of sky will be visible but ultimately specific targets will have to wait until in a convenient location on the orbit I guess.

My assumption (which could well be wrong!) is that for the very very deep stuff it is fairly academic which direction they point in. The Hubble Deep and Ultra Deep fields were fairly randomly chosen, just small, clear patches of sky otherwise unoccupied to get a window to the deep stuff.

[gilesco]

1 minute ago, kirkster501 said:

There is a movable steering mirror inside the black nose thingy that sticks out from the centre of the primary.  That can be "steered" (i.e moved) so the telescope does not have to physically move so much.  Just image how accurately that must have been ground and polished !

Yes, for subjects on the "wrong" side of the sky the JWST has to wait just like we have to for them to become visible in the night sky again.

Thankfully without the unknown of whether the weather will be OK!

 

[Stu]

1 minute ago, kirkster501 said:

black nose thingy

Thanks, that was the technical term I was struggling to think of 😉👍

[Laurieast]

Still not finding anything about deployment of the first wing, and the second has moved from Friday to Saturday. 

NASA TV 

FUTURE LIVE EVENTS

(All times Eastern U.S. time. UTC-5)

January 8, Saturday
TBD - Live coverage of the unfolding of the second of the James Webb Space Telescope's primary mirror wings, marking the end of the observatory deployments. The time of the broadcast will be posted here and the James Webb Space Telescope's blog when it is announced. 
TBD - NASA will hold a media briefing as soon as possible after the end of the live broadcast coverage of Webb’s final deployments. The time of the press conference will be posted here and the James Webb Space Telescope's blog when it is announced. 

[AstroKeith]

12 minutes ago, gilesco said:

Question, can the mirror array tilt and rotate relative to the sunshield, or is the whole apparatus rigid and uses small jets for alignment? Just wondering whether we've got to wait for up to a year to be able to look in particular direction.

I believe the whole 'observatory' is steered, but a tertiary mirror is used for fine pointing and stabilisation. So yes, it seems where it can point will vary during the year. This is how Hubble is pointed and so I guess they have learnt a lot, and didnt want to risk a motorised gimbal system that has to operate at near absolute zero.

[tomato]

3 hours ago, andrew s said:

All the selfie cameras in the world would not have shown Hubble's myopia! 

They do, however help keep the paying public engaged. 

Regards Andrew 

I hoping there will be some  real iconic PR images taken by the scope itself, like the 'Pillars of Creation' did for the HST. I'm pretty sure everybody knows what the JWST looks like, I agree with it's gold hex component mirror and sunshield, it is more photogenic than the HST.

[AstroKeith]

38 minutes ago, Laurieast said:

Still not finding anything about deployment of the first wing, and the second has moved from Friday to Saturday. 

NASA TV 

FUTURE LIVE EVENTS

(All times Eastern U.S. time. UTC-5)

January 8, Saturday
TBD - Live coverage of the unfolding of the second of the James Webb Space Telescope's primary mirror wings, marking the end of the observatory deployments. The time of the broadcast will be posted here and the James Webb Space Telescope's blog when it is announced. 
TBD - NASA will hold a media briefing as soon as possible after the end of the live broadcast coverage of Webb’s final deployments. The time of the press conference will be posted here and the James Webb Space Telescope's blog when it is announced. 

The heat radiator has been deployed and the NASA blog states the two sides of the  main mirror are next up...

Webb’s final series of major deployments is planned to start tomorrow, Jan. 7, with the rotation into position of the first of two primary mirror wings. The second primary wing – Webb’s final major spacecraft deployment – is planned for Saturday, Jan. 8.

[Laurieast]

10 minutes ago, AstroKeith said:

The heat radiator has been deployed and the NASA blog states the two sides of the  main mirror are next up...

Now, where was that hiding!  😉

Edit: Oh ok I see the light now 

 

Edited January 6, 2022 by Laurieast

[AstroKeith]

50 minutes ago, tomato said:

I hoping there will be some  real iconic PR images taken by the scope itself, like the 'Pillars of Creation' did for the HST. I'm pretty sure everybody knows what the JWST looks like, I agree with it's gold hex component mirror and sunshield, it is more photogenic than the HST.

I guess now it shielded from the Sun, the photogenic mirrors will be as dark as the background sky and hence effectively invisible. I believe this is just one reason why no selfie cameras were added.

[Laurieast]

NASA TV 

Talking about it now, overview only.

Edited January 6, 2022 by Laurieast

[kirkster501]

Webb’s Specialized Heat Radiator Deployed Successfully – James Webb Space Telescope (nasa.gov)

Radiator opened successfully.  "Just" the mirror flaps now.

[Laurieast]

12 minutes ago, kirkster501 said:

Radiator opened successfully.  "Just" the mirror flaps now.

Maxim Brailovsky: Piece of pie.
(Movie 2010) 

[discardedastro]

6 hours ago, kirkster501 said:

"Just" the mirror flaps now.

The radiator was the last really critical physical thing - if they couldn't get the two side mirror segments in they'd have less aperture to use but with the adaptive optics could still do great science. But fingers crossed for the last two bits - feeling good about it though given everything else!

Then still a lot of cooling and cryo to be done, along with all the mirror segment alignment, but home stretch...

[Gfamily]

12 hours ago, Alien 13 said:

 

Agreed to some extent but a camera is a wonderful diagnostic tool, like the old saying "a picture is worth a thousand lines of code" if a problem needs fixing.

Alan

I believe there was a discussion in today's Nasa TV transmission about this. 

As @AstroKeith mentioned, with the sunshield deployed, it's dark - there's no source of illumination on the 'business' side of the telescope brighter than Sirius, so there's no point in having a camera without the addition of an light source, and if it's to be of any diagnostic use it'll need to be steerable and zoomable and ... etc etc. Simply not worth it. 

On the Sunshield side, where would you put it? For it to be any use, it'll need some 'stand off' or otherwise you're stuck with a single field of view - simply not worth the weight, and the risk of it causing a problem in itself.

  

[Gfamily]

8 hours ago, AstroKeith said:

I believe the whole 'observatory' is steered, but a tertiary mirror is used for fine pointing and stabilisation. So yes, it seems where it can point will vary during the year. This is how Hubble is pointed and so I guess they have learnt a lot, and didnt want to risk a motorised gimbal system that has to operate at near absolute zero.

One critical difference between HST and JWST is that JWST always has to be oriented within much narrower range of angles relative to the Sun, so that the sunshield remains effective. 

This means that at any time the Scope can only observe a band between 85 and 135 degrees from the Sun - but it can be rotated to see anything within this band.  I assume that the use of the tertiary mirror allows fine guidance while reducing the need to use reaction wheels or propellant.

Over the year, this band will cover the complete celestial sphere.  

You may recall that one of the first deployments was the Aft Momentum Flap - this is a 'hard fix' that was implemented to try and negate some of the torque that is imparted by the pressure of sunlight on the SunShield. Because the centre of impulse of the sunlight isn't coincident with the centre of mass of the JWST, there would always be a turning motion caused by sun pressure, and the Aft Momentum Flap is designed to reduce this by a fixed amount - however, the negating effect depends on the exact angle of the Sun - so my expectation is that the science team will try and keep observations to a much narrower range than the 85 to 135 degrees as, ultimately, the torque has to be dissipated by using the limited store of propellant.  

 

[Rusted]

Two three four thoughts:

Crookes Radiometer and a worm wheel reduction, Goto drive.

and, I'll never believe another science fiction film which shows the craft bathed in light while traveling between the stars.

Do rockets roar in the silence of a space vacuum?

Now what was the question again?

[Stu]

This latest blog post explains the decision not to fit cameras. Pretty much as suspected.

https://blogs.nasa.gov/webb/2022/01/06/why-doesnt-webb-have-deployment-cameras/

[Laurieast]

https://blogs.nasa.gov/webb/2022/01/07/primary-mirror-deployment-has-begun/

Primary Mirror (Port wing) Deployment Has Begun.

NASA Live

NEXT LIVE EVENTS

(All times Eastern U.S. time, which equates to UTC-5.) 

January 8, Saturday
No earlier than 9 a.m. - Live coverage of the unfolding of the second of the James Webb Space Telescope's primary mirror wings, marking the end of the observatory deployments.
No earlier than 1:30 p.m. - NASA will hold a media briefing as soon as possible after the end of the live broadcast coverage of Webb’s final deployments.

Edited January 7, 2022 by Laurieast

[SuburbanMak]

12 minutes ago, Laurieast said:

https://blogs.nasa.gov/webb/2022/01/07/primary-mirror-deployment-has-begun/

Primary Mirror Deployment Has Begun

Gulp!

[Zermelo]

56 minutes ago, Laurieast said:

https://blogs.nasa.gov/webb/2022/01/07/primary-mirror-deployment-has-begun/

Primary Mirror Deployment Has Begun

not on the live stream?

[Laurieast]

1 minute ago, Zermelo said:

not on the live stream?

No, and can't see explanation of why anywhere. 

[AstroKeith]

Looks like the live stream was a 'special'

Anyway - mirror deployed and locked! Phew.

https://webb.nasa.gov/content/webbLaunch/deploymentExplorer.html#21

Edited January 7, 2022 by AstroKeith