James Webb telescope launch info

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Re: James Webb telescope launch info

#61  Postby TopCat » Jan 09, 2022 10:52 pm

Macdoc wrote:The change in technology over the 30 years this was in development was astonishing and I guess at this point perhaps the delays and overruns can be considered worthwhile. :cheers:

Delays and overruns are what happen when a complex project runs into the inevitable unexpected hitches and the management don't cut corners as a result, to save face, and cut and run with a big fat bonus.

The tech is amazing, but what has really impressed me is that the complex project management, with all the bean counters and administrators who must surely be involved, has not managed to scupper the whole damn thing.

I'm sure we've all read and watched Feynman's involvement in the Challenger investigation. And bemoaned the original Hubble debacle.

That history hasn't - so far at least - repeated itself, is quite remarkable to me.
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Re: James Webb telescope launch info

#62  Postby newolder » Jan 16, 2022 9:54 am

The slow and steady un-stowing of the individual mirror segments is underway. Each mirror segment was clamped for launch and about 12.5mm (1/2 inch) of movement is required to move each of them out of their locks. The rate of movement is about 1mm per day and all segments (apart from 2, for some unspecified reason) are about 1/3rd of the way, by post time. This blog post by Alise Fisher gives further info:
Mirror, Mirror…On Its Way!

With major deployments complete, Webb continues its journey to its final halo orbit around L2. In the meantime, there are several smaller deployments in the next couple of weeks, which constitute the beginning of a several-month phase of aligning the telescope’s optics. This week, we have started the process of moving the mirror segments (all primary plus secondary) out of their stowed launch positions. For more details, here is Marshall Perrin from the Space Telescope Science Institute, home of the Webb Mission Operations Center: ...(continues)
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Re: James Webb telescope launch info

#63  Postby Cito di Pense » Jan 16, 2022 9:56 am

newolder wrote:The slow and steady un-stowing of the individual mirror segments is underway. Each mirror segment was clamped for launch and about 12.5mm (1/2 inch) of movement is required to move each of them out of their locks. The rate of movement is about 1mm per day and all segments (apart from 2, for some unspecified reason) are about 1/3rd of the way, by post time. This blog post by Alise Fisher gives more details.
Mirror, Mirror…On Its Way!

With major deployments complete, Webb continues its journey to its final halo orbit around L2. In the meantime, there are several smaller deployments in the next couple of weeks, which constitute the beginning of a several-month phase of aligning the telescope’s optics. This week, we have started the process of moving the mirror segments (all primary plus secondary) out of their stowed launch positions. For more details, here is Marshall Perrin from the Space Telescope Science Institute, home of the Webb Mission Operations Center: ...(continues)


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Re: James Webb telescope launch info

#64  Postby The_Metatron » Jan 16, 2022 11:35 pm

The mirrors in motion are halfway out of launch configuration today, I see. It’s good to see the actuators are all functioning.

Cool trivia, at least for me: My shop service van is a 1997 Grumman Olson step van. It has connections to space. The Apollo Lunar Excursion Modules (LEM) the descent stages of which remain on the moon’s surface to this day, were made by Grumman. The heat shield on the Webb was made by Northrop-Grumman (the companies merged since Apollo). My van has relatives on the moon and on the way to L2!
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Re: James Webb telescope launch info

#65  Postby BlackBart » Jan 17, 2022 8:12 am

And also Flight 19 - avoid driving around the Bermuda Triangle!
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Re: James Webb telescope launch info

#66  Postby newolder » Jan 18, 2022 3:50 pm

All mirror segments bar A3 & A6 now unlocked and ready for fine tweaking. The only additional info. on A3 & A6 I found by a poster at Reddit so, ...
See 2018 SPIE paper by Wolf et al. "JWST mirror and actuator performance at cryo-vacuum" (find it by searching on "JWST A3 and A6 position sensors").

See sec 1.2 and 2.4.2 of the paper.

It turns out that the mirror segments at A3 and A6 have "faulty"linear variable differential transformers (LVDT) (position sensors). Each LVDT is suppose to have two coils to cancel out differential thermal effects. In each of A3 and A6, one of the two coils is faulty.The engineers had to work out a way of getting accurate readouts using only one coil in each LVDT. So they developed a different readout procedure that could use only the one good coil in each LVDT.

I would guess that they wanted to use a uniform readout procedure (the nominal procedure). to get the 16 segments with good sensors in place, before switching to the modified procedure for A3 and A6. Otherwise, switching back and forth between readout procedures could increase the risk of using the "wrong" procedure. I do not know why it was impossible to replace the faulty LVDTs before launch. It probably had to do with the extensive test time required to re-certify the the whole primary mirror if two new LVDTs were installed.


ETA
Jan 19
All segments deployed. Woohoo! Now on to L2 insertion in the coming week and a few months of mirror tweaks and instrument calibrations thereafter. And then... First light!
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Re: James Webb telescope launch info

#67  Postby newolder » Jan 20, 2022 10:06 pm

Jan 20, 2022
MEDIA ADVISORY M22-011

NASA to Discuss Webb’s Arrival at Final Destination, Next Steps

Scientists and engineers operating NASA’s James Webb Space Telescope will answer questions about the mission’s latest milestones in a NASA Science Live broadcast at 3 p.m. EST Monday, Jan. 24, followed by a media teleconference at 4 p.m.

The broadcast will air live online on the NASA Science Live website, as well as YouTube, Facebook, and Twitter. Audio of the teleconference will stream live on the agency’s website.

Ground teams plan to fire Webb’s thrusters at 2 p.m. Monday, Jan. 24 to insert the space telescope into orbit around the Sun at the second Lagrange point, or L2, its intended destination, nearly 1 million miles from Earth...(continues at link)

NASA link
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Re: James Webb telescope launch info

#69  Postby TopCat » Jan 21, 2022 12:35 pm

So the L2 insertion burn is scheduled for next Monday, 24th Jan.

It's nearly a million miles away. How do they measure its position and velocity accurately enough to get the burn - duration and direction - exactly right?

I can think of a variety of ways, including integrating telemetry data from onboard accelerometers (once for the velocity, again for the distance), but I have no feel for whether that could be precise or accurate enough.

Anyone with actual knowledge? I mean it can't be rocket science, surely ... ah wait :ask:
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Re: James Webb telescope launch info

#70  Postby hackenslash » Jan 21, 2022 1:07 pm

Doppler shift in reception throughout the flight would be the obvious check for ensuring accuracy, I'd venture, though it's mostly a matter of extremely careful planning of the entire flight from selection of launch window to orbital insertion all carefully timed, a.k.a., the brilliance of Katherine Johnson.

Now ask yourself the same question about Cassini-Huygens which, after four slingshots and a distance of 15x1011 kilometres, executed an insertion burn to go from a hyperbolic to an elliptical orbit (this was Johnson's truly spectacular genius again) within 20 metres of its targeted orbit using math from a guy who was wrong (albeit only wrong by that minuscule margin).

Boggles the mind
Last edited by hackenslash on Jan 21, 2022 3:09 pm, edited 1 time in total.
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Re: James Webb telescope launch info

#71  Postby The_Piper » Jan 21, 2022 2:57 pm

I can't believe some don't realize how technologically advanced humans are. We invented cows 10,000 years ago and never looked back. :mrgreen:
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Re: James Webb telescope launch info

#72  Postby BlackBart » Jan 21, 2022 3:16 pm

The_Piper wrote:We invented cows 10,000 years ago and never looked back. :mrgreen:


Named after their inventor, Sir Reginald Cow. True fact.
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Re: James Webb telescope launch info

#73  Postby TopCat » Jan 21, 2022 3:29 pm

hackenslash wrote:Doppler shift in reception throughout the flight

Ok, I'd buy that, to get the velocity in real time. I guess you could integrate that to get the distance, or perhaps time the return trip for a signal would be simpler.

They also need to know where on the spherical sector X million meters away from the transmitter it is?

though it's mostly a matter of extremely careful planning of the entire flight from selection of launch window to orbital insertion all carefully timed, a.k.a., the brilliance of Katherine Johnson.

Not disputing the brilliance, or the extremely careful planning, but I'm not sure I buy that as a method of ensuring the required precision.

For instance, the duration of the MCC-1a burn wasn't scheduled until they knew how precisely how much was needed.

I guess the three ground stations, with an accurate distance from each, would give the location on that spherical sector.

Boggles the mind

It really does :cheers:
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Re: James Webb telescope launch info

#74  Postby The_Metatron » Jan 21, 2022 4:19 pm

It’s mind bottling.
[Reveal] Spoiler: full explanation
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Re: James Webb telescope launch info

#75  Postby newolder » Jan 21, 2022 4:43 pm

TopCat wrote:So the L2 insertion burn is scheduled for next Monday, 24th Jan.

It's nearly a million miles away. How do they measure its position and velocity accurately enough to get the burn - duration and direction - exactly right?

I can think of a variety of ways, including integrating telemetry data from onboard accelerometers (once for the velocity, again for the distance), but I have no feel for whether that could be precise or accurate enough.

Anyone with actual knowledge? I mean it can't be rocket science, surely ... ah wait :ask:


One may follow the telescope at the eyes.nasa.gov pages. Go to Solar system and a search on JWST brings up James Webb Space Telescope that can be clicked... The image it returns has the telescope still stowed so it's going to be some time before it gets updated, I guess. :dunno:

The calculations in that tool in general are truly gobsmacking... :thumbup:

Anyhoo here's a link to the view I've just returned from: https://eyes.nasa.gov/apps/orrery/#/sc_ ... .856+00:00
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Re: James Webb telescope launch info

#76  Postby The_Piper » Jan 21, 2022 5:31 pm

BlackBart wrote:
The_Piper wrote:We invented cows 10,000 years ago and never looked back. :mrgreen:


Named after their inventor, Sir Reginald Cow. True fact.

That's still disputed. I've seen it claimed that Isaac L. Dung had a hand in it. :dopey:
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Re: James Webb telescope launch info

#77  Postby BlackBart » Jan 21, 2022 5:55 pm

The_Piper wrote:
BlackBart wrote:
The_Piper wrote:We invented cows 10,000 years ago and never looked back. :mrgreen:


Named after their inventor, Sir Reginald Cow. True fact.

That's still disputed. I've seen it claimed that Isaac L. Dung had a hand in it. :dopey:

I think that's a MOOt point.
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Re: James Webb telescope launch info

#78  Postby hackenslash » Jan 21, 2022 6:06 pm

The_Piper wrote:
BlackBart wrote:
The_Piper wrote:We invented cows 10,000 years ago and never looked back. :mrgreen:


Named after their inventor, Sir Reginald Cow. True fact.

That's still disputed. I've seen it claimed that Isaac L. Dung had a hand in it. :dopey:


Pretty sure that's an urban myth stemming from the fact that he was founding editor of the International Journal of Bovine Coprolitics. His own field of study was, as you're no doubt aware, ballistic scatography, though he also made important contributions to political science, predicting the rise of a world-class bullshitter in politics manty decades prior to the elevation of Boris Johnson. Further, some suggest that his elucidation of the relationship between ballistic scatology and bioorganic methane production was the inspiration for Werner von Braun, meaning that the current mission relates directly back to him.

He also laid the foundations for bovine orbital mechanics, and his theoretical work underpins all the iterations of the gedanken involving spherical cows in a vacuum.

In fact, in a little-known letter published in Phil. Trans. B and subsequently lost (some suggest Hooke destroyed it to piss off Newton), he acknowledged that all his early work was derivative, though he neither denied nor confirmed whether Cow was the originator.
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Re: James Webb telescope launch info

#79  Postby The_Metatron » Jan 21, 2022 6:15 pm

Ballistic scatography. Now there’s a job.
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