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Robotic Spacecraft (Astronomy, Planetary, Earth, Solar/Heliophysics) => Space Science Coverage => Topic started by: Chris Bergin on 07/10/2021 08:02 pm

Title: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Chris Bergin on 07/10/2021 08:02 pm
Thread 1:
https://forum.nasaspaceflight.com/index.php?topic=10453.0
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 07/11/2021 12:55 pm
First and foremost - my apologies for the wrong choice of words that got the previous thread locked. It is a very sensitive affair. I won't take part in any further discussions of it.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 07/12/2021 01:49 pm
While the final mission analysis review for Ariane has completed, presumably that is still pending on the revised fairing performing as expected later this month?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: FutureSpaceTourist on 07/22/2021 06:06 pm
https://twitter.com/nasawebb/status/1418262128344150017

Quote
This new image fresh from the @northropgrumman cleanroom shows #NASAWebb nearly fully packed up into the same formation it will have for launch. Few tests remain before the team transitions into shipment operations.
 
More on Webb’s recent progress: go.nasa.gov/3BvxLQM
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 07/22/2021 07:39 pm
https://twitter.com/nasawebb/status/1418262128344150017

Quote
This new image fresh from the @northropgrumman cleanroom shows #NASAWebb nearly fully packed up into the same formation it will have for launch. Few tests remain before the team transitions into shipment operations.
 
More on Webb’s recent progress: go.nasa.gov/3BvxLQM
That's odd: just behind the uppermost bronze crossmember (below the cherrypicker basket) a set of components on the underside of the sunshield have been deliberately blurred (not just out of focus, all the shot-noise bas been smoothed out). That areas has been previous picuted unobscured (e.g. here (https://www.flickr.com/photos/nasawebbtelescope/50170359843/) or here (https://www.flickr.com/photos/nasawebbtelescope/46648792405/)), so not sure why NG would go to the trouble now.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: hoku on 07/27/2021 08:19 pm
<snip>
That's odd: just behind the uppermost bronze crossmember (below the cherrypicker basket) a set of components on the underside of the sunshield have been deliberately blurred (not just out of focus, all the shot-noise bas been smoothed out). That areas has been previous picuted unobscured (e.g. here (https://www.flickr.com/photos/nasawebbtelescope/50170359843/) or here (https://www.flickr.com/photos/nasawebbtelescope/46648792405/)), so not sure why NG would go to the trouble now.
Sharp eye spotting the blurred region in the image!

Most likely explanation is that there are some (potentially) ITAR related components. NASA also has a "notech" JWST photo, which seems to be cropped to avoid showing the region with the components:
https://www.nasa.gov/feature/goddard/2021/james-webb-space-telescope-testing-progress-continues (https://www.nasa.gov/feature/goddard/2021/james-webb-space-telescope-testing-progress-continues)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: catdlr on 07/28/2021 08:42 am
<snip>
That's odd: just behind the uppermost bronze crossmember (below the cherrypicker basket) a set of components on the underside of the sunshield have been deliberately blurred (not just out of focus, all the shot-noise bas been smoothed out). That areas has been previous picuted unobscured (e.g. here (https://www.flickr.com/photos/nasawebbtelescope/50170359843/) or here (https://www.flickr.com/photos/nasawebbtelescope/46648792405/)), so not sure why NG would go to the trouble now.
Sharp eye spotting the blurred region in the image!

Most likely explanation is that there are some (potentially) ITAR related components. NASA also has a "notech" JWST photo, which seems to be cropped to avoid showing the region with the components:
https://www.nasa.gov/feature/goddard/2021/james-webb-space-telescope-testing-progress-continues (https://www.nasa.gov/feature/goddard/2021/james-webb-space-telescope-testing-progress-continues)

“Objects in the mirror are closer than they appear"  ;-)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: mmonty on 07/31/2021 12:24 pm
<snip>
That's odd: just behind the uppermost bronze crossmember (below the cherrypicker basket) a set of components on the underside of the sunshield have been deliberately blurred (not just out of focus, all the shot-noise bas been smoothed out). That areas has been previous picuted unobscured (e.g. here (https://www.flickr.com/photos/nasawebbtelescope/50170359843/) or here (https://www.flickr.com/photos/nasawebbtelescope/46648792405/)), so not sure why NG would go to the trouble now.
Sharp eye spotting the blurred region in the image!

Most likely explanation is that there are some (potentially) ITAR related components. NASA also has a "notech" JWST photo, which seems to be cropped to avoid showing the region with the components:
https://www.nasa.gov/feature/goddard/2021/james-webb-space-telescope-testing-progress-continues (https://www.nasa.gov/feature/goddard/2021/james-webb-space-telescope-testing-progress-continues)

When JWST was at Goddard, whenever the OTE was oriented with the back side (the side with all the mechanical linkages to the mirrors and their supports) facing the windows of the viewing gallery, they would close the window shades so on-lookers could not look in due to the proprietary nature of those linkages. Or so I was told.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Scintillant on 08/03/2021 04:08 am
From Dr. Zurbuchen's official blog: Launching the World’s Biggest Space Telescope (https://blogs.nasa.gov/drthomasz/2021/08/02/launching-the-worlds-biggest-space-telescope/)

Quote
For most missions, launch contributes the majority of mission risk – if the spacecraft is in space, most risk is behind us. There are few types of missions that are very much different with most risk coming *after* launch.
...

The second such mission this year is Webb. Like a transformer in the movies, about 50 deployments need to occur after launch to set up the huge system. With nearly 350 so-called single point failures – individual steps that have to work for the mission to be a success – this deployment after launch will keep us on edge for 3 weeks or so. For comparison, this exceeds single point failures for landing on Mars by a factor of 3, and that landing lasted only 7 minutes.

Those who are not worried or even terrified about this are not understanding what we are trying to do.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: zubenelgenubi on 08/03/2021 11:21 pm
So poor it got its own thread:
Arianespace VA254 30 July 2021 launch webcast - discussion
https://forum.nasaspaceflight.com/index.php?topic=54416.0 (https://forum.nasaspaceflight.com/index.php?topic=54416.0)
I split/merged some posts to the above-mentioned thread.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: FutureSpaceTourist on 08/26/2021 03:06 pm
https://twitter.com/sciguyspace/status/1430909077257801731

Quote
The European Space Agency says the James Webb Space Telescope has successfully completed its final tests and is being prepared for shipment to the launch site in French Guiana. https://www.esa.int/Science_Exploration/Space_Science/Webb/Webb_completes_testing_and_prepares_for_trip_to_Europe_s_Spaceport
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Targeteer on 08/27/2021 01:31 am
hthttps://www.nasa.gov/feature/goddard/2021/nasa-s-james-webb-space-telescope-has-completed-testing/

Aug 26, 2021
NASA’s James Webb Space Telescope Has Completed Testing
After successful completion of its final tests, NASA’s James Webb Space Telescope is being prepped for shipment to its launch site.

Engineering teams have completed Webb’s long-spanning comprehensive testing regimen at Northrop Grumman’s facilities. Webb’s many tests and checkpoints were designed to ensure that the world’s most complex space science observatory will operate as designed once in space.

Now that observatory testing has concluded, shipment operations have begun. This includes all the necessary steps to prepare Webb for a safe journey through the Panama Canal to its launch location in Kourou, French Guiana, on the northeastern coast of South America. Since no more large-scale testing is required, Webb’s clean room technicians have shifted their focus from demonstrating it can survive the harsh conditions of launch and work in orbit, to making sure it will safely arrive at the launch pad. Webb’s contamination control technicians, transport engineers, and logistics task forces are all expertly prepared to handle the unique task of getting Webb to the launch site. Shipping preparations will be completed in September.

Webb Will Soon Be on its Way 

“NASA's James Webb Space Telescope has reached a major turning point on its path toward launch with the completion of final observatory integration and testing,” said Gregory L. Robinson, Webb's program director at NASA Headquarters in Washington. “We have a tremendously dedicated workforce who brought us to the finish line, and we are very excited to see that Webb is ready for launch and will soon be on that science journey.”

With integration and testing formally concluded for the James Webb Space Telescope, NASA’s next giant leap into the cosmic unknown will soon be underway.
With integration and testing formally concluded for the James Webb Space Telescope, NASA’s next giant leap into the cosmic unknown will soon be underway.
Credits: NASA/Chris Gunn
While shipment operations are underway, teams located in Webb’s Mission Operations Center (MOC) at the Space Telescope Science Institute (STScI) in Baltimore will continue to check and recheck the complex communications network it will use in space. Recently this network fully demonstrated that it is capable of seamlessly sending commands to the spacecraft. Live launch rehearsals are underway within the MOC with the explicit purpose of preparing for launch day and beyond. There is much to be done before launch, but with integration and testing formally concluded, NASA’s next giant leap into the cosmic unknown will soon be underway.

Once Webb arrives in French Guiana, launch processing teams will configure the observatory for flight. This involves post-shipment checkouts to ensure the observatory hasn’t been damaged during transport, carefully loading the spacecraft’s propellant tanks with hydrazine fuel and nitrogen tetroxide oxidizer it will need to power its rocket thrusters to maintain its orbit, and detaching ‘remove before flight’ red-tag items like protective covers that keep important components safe during assembly, testing, and transport. Then engineering teams will mate the observatory to its launch vehicle, an Ariane 5 rocket provided by ESA (European Space Agency), before it rolls out to the launch pad. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

The James Webb Space Telescope is an amazing feat of human ingenuity, made more impressive by the obstacles Webb personnel overcame to deliver this amazing space science observatory. Earthquakes, a devastating hurricane, snowstorms, blizzards, wildfires, and a global pandemic are only some of what the people behind Webb endured to ensure success. Webb’s story is one of perseverance – a mission with contributions from thousands of scientists, engineers, and other professionals from more than 14 countries and 29 states, in nine different time zones.

“To me, launching Webb will be a significant life event – I’ll be elated of course when this is successful, but it will also be a time of deep personal introspection. Twenty years of my life will all come down to that moment,” said Mark Voyton, Webb observatory integration and test manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We’ve come a long way and worked through so much together to prepare our observatory for flight. The telescope’s journey is only just beginning, but for those of us on the ground who built it, our time will soon come to an end, and we will have our opportunity to rest, knowing we put everything on the line to make sure our observatory works. The bonds we formed with each other along the way will last far into the future.”

Opening NASA’s New Eye on the Cosmos

After launch, Webb will undergo an action-packed six-month commissioning period. Moments after completing a 26-minute ride aboard the Ariane 5 launch vehicle, the spacecraft will separate from the rocket and its solar array will deploy automatically. After that, all subsequent deployments over the next few weeks will be initiated from ground control located at STScI.


Engineering teams have completed the James Webb Space Telescope’s long-spanning comprehensive testing regimen at Northrop Grumman’s facilities. Webb’s many tests and checkpoints were designed to ensure that the world’s most complex space science observatory will operate as designed once in space. Now that observatory testing has concluded, shipment operations have begun. This includes all the necessary steps to prepare Webb for a safe journey through the Panama Canal to its launch location in Kourou, French Guiana, on the northeastern coast of South America.
Credits: NASA's Goddard Space Flight Center Michael P. Menzel (AIMM): Producer, Michael P. Menzel (AIMM): Video Editor, Michael P. Menzel (AIMM): Videographer, Sophia Roberts (AIMM): Videographer
Webb will take one month to fly to its intended orbital location in space nearly one million miles away from Earth, slowly unfolding as it goes. Sunshield deployments will begin a few days after launch, and each step can be controlled expertly from the ground, giving Webb’s launch full control to circumnavigate any unforeseen issues with deployment.

Once the sunshield starts to deploy, the telescope and instruments will enter shade and start to cool over time. Over the ensuing weeks, the mission team will closely monitor the observatory’s cooldown, managing it with heaters to control stresses on instruments and structures. In the meantime, the secondary mirror tripod will unfold, the primary mirror will unfold, Webb’s instruments will slowly power up, and thruster firings will insert the observatory into a prescribed orbit.

Once the observatory has cooled down and stabilized at its frigid operating temperature, several months of alignments to its optics and calibrations of its scientific instruments will occur. Scientific operations are expected to commence approximately six months after launch.

‘Flagship’ missions like Webb are generational projects. Webb was built on both the legacy and the lessons of missions before it, such as the Hubble and Spitzer space telescopes, and it will in turn provide the foundation upon which future large astronomical space observatories may one day be developed.

“After completing the final steps of the James Webb Space Telescope’s testing regimen, I can’t help but see the reflections of the thousands of individuals who have dedicated so much of their lives to Webb, every time I look at that beautiful gold mirror,” said Bill Ochs, Webb project manager for NASA Goddard.

The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.

By Thaddeus Cesari
​NASA's Goddard Space Flight Center, Greenbelt, Md.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jacqmans on 08/27/2021 06:48 am
Webb completes testing
26/08/2021

Fully assembled and fully tested, the NASA/ESA/CSA James Webb Space Telescope has completed its primary testing regimen and is soon preparing for shipment to its launch site at Europe’s Spaceport in French Guiana. On this photo, Webb is folded as it will be for launch.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: FutureSpaceTourist on 09/08/2021 01:10 pm
https://twitter.com/jeff_foust/status/1435590609532764161

Quote
JWST has an official launch date: December 18, 2021. Happy Holidays!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Targeteer on 09/08/2021 10:53 pm
September 08, 2021
RELEASE 21-113
NASA Readies James Webb Space Telescope for December Launch
NASA’s James Webb Space Telescope being prepped for shipment to its launch site.
After successful completion of its final tests, NASA’s James Webb Space Telescope is seen here being prepared for shipment to its launch site.
Credits: NASA/Chris Gunn

NASA plans to launch the James Webb Space Telescope into orbit Dec. 18, 2021, to serve as the premier deep space observatory for the next decade.

The agency set the new target launch date in coordination with Arianespace after Webb recently and successfully completed its rigorous testing regimen – a major turning point for the mission. The new date also follows Arianespace successfully launching an Ariane 5 rocket in late July and scheduling a launch that will precede Webb. The July launch was the first for an Ariane 5 since August 2020.

Webb, an international program led by NASA with its partners ESA (European Space Agency) and the Canadian Space Agency, will launch on an Ariane 5 from Europe's Spaceport in French Guiana on the northeastern coast of South America. ESA is providing the Ariane 5.

The highly complex space telescope is currently resting in its final stow configuration at Northrop Grumman’s facilities in Redondo Beach, California.

“Webb is an exemplary mission that signifies the epitome of perseverance,” said Gregory L. Robinson, Webb’s program director at NASA Headquarters in Washington. “I am inspired by our dedicated team and our global partnerships that have made this incredible endeavor possible. Together, we’ve overcome technical obstacles along the way as well as challenges during the coronavirus pandemic. I also am grateful for the steadfast support of Congress. Now that we have an observatory and a rocket ready for launch, I am looking forward to the big day and the amazing science to come.”

The Webb team is preparing for shipment operations, during which the observatory will undergo final closeout procedures and packing for its journey to the launch site. The major elements of the Ariane 5 rocket that will carry Webb into space have safely arrived in Kourou, French Guiana, from Europe.

The Webb telescope’s revolutionary technology will explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe, and everything in between. Webb will reveal new and unexpected discoveries, and help humankind understand the origins of the universe and our place in it.

For further information about the Webb mission, visit:

www.webb.nasa.gov

For information about the construction and engineering of the Webb telescope, visit:

www.nasa.gov/webb
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: hoku on 09/09/2021 05:07 pm
At some time in the next ~4(?) weeks, JWST inside Super STTARS ("Space Telescope Transporter for Air, Road and Sea") should be passing through the Panama Channel locks. For eager (eagle-eyed) and trained (Texas) tank and crane watchers, here is the link to the locks' webcams
https://multimedia.panama-canal.com/index.html (https://multimedia.panama-canal.com/index.html)

For more info on STTARS, see https://www.nasa.gov/feature/goddard/2018/follow-the-sttars-to-find-nasas-webb-telescope (https://www.nasa.gov/feature/goddard/2018/follow-the-sttars-to-find-nasas-webb-telescope)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: TrevorMonty on 09/09/2021 05:19 pm
Thought they would've flown it to Guiana.
Lets hope the ship doesn't run into any hurricanes.

Sent from my SM-G570Y using Tapatalk

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 09/09/2021 05:40 pm
Thought they would've flown it to Guiana.
Lets hope the ship doesn't run into any hurricanes.


I think it's too big to fit in a plane now.

I'm trying to remember, and maybe somebody has better information, but there's an issue with the road from the airport to the launch site. I think that the road from the port to the launch site is smoother. So even if they could have flown it, they might have chosen sea transport anyway. But I could be in error about this and somebody may have better info.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 09/09/2021 06:04 pm
Thought they would've flown it to Guiana.
Lets hope the ship doesn't run into any hurricanes.


I think it's too big to fit in a plane now.

I'm trying to remember, and maybe somebody has better information, but there's an issue with the road from the airport to the launch site. I think that the road from the port to the launch site is smoother. So even if they could have flown it, they might have chosen sea transport anyway. But I could be in error about this and somebody may have better info.

They increased the size of the container so that it no longer fits in the C-5.

Port is 8 km to processing facility vs 70 from airport
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: catdlr on 09/10/2021 04:31 am
Thought they would've flown it to Guiana.
Lets hope the ship doesn't run into any hurricanes.


I think it's too big to fit in a plane now.

I'm trying to remember, and maybe somebody has better information, but there's an issue with the road from the airport to the launch site. I think that the road from the port to the launch site is smoother. So even if they could have flown it, they might have chosen sea transport anyway. But I could be in error about this and somebody may have better info.

They increased the size of the container so that it no longer fits in the C-5.

Port is 8 km to processing facility vs 70 from airport

One question, I've only seen pictures of the Webb Telescope in an upright position. Will it be OK to transport it on its side as shown by the canister in the photo above?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 09/10/2021 06:27 am
Thought they would've flown it to Guiana.
Lets hope the ship doesn't run into any hurricanes.


I think it's too big to fit in a plane now.

I'm trying to remember, and maybe somebody has better information, but there's an issue with the road from the airport to the launch site. I think that the road from the port to the launch site is smoother. So even if they could have flown it, they might have chosen sea transport anyway. But I could be in error about this and somebody may have better info.

They increased the size of the container so that it no longer fits in the C-5.

Port is 8 km to processing facility vs 70 from airport

From memory: Kourou "airport" is actually Cayenne (which was once France very own Alcatraz  - remember that movie, Butterfly / Papillon) - and it is a long way from Kourou. By contrast the city of Kourou had a port (a bit like Port Canaveral although much smaller !) which is - quite logically - closer than Cayenne.

For the record, back in the day (50 years ago) Europa's Blue Streaks were ferried to Kourou by ship, from Le Havre.
After Europa F11 miserable failure late 1971 the entire program was canned in the spring of 1973 as F12 launch campaign was already started.

Blue Streak F12 had already been shipped from Le Havre and was thus at sea when Europa was cancelled. The Blue Streak nonetheless made it to Kourou only to be stored, then sold to a scrapper which sold the remains to a farmer which turned it into a... chichen coop ! Just like the scrapped N-1s in Tyuratam / Baikonur being turned into the city street furnitures.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: bolun on 09/10/2021 01:42 pm
https://www.bbc.com/news/science-environment-58498676

Quote
JWST must now itself travel by sea from its construction base at Northrop Grumman in California. This involves a trip through the Panama Canal.

Information about the voyage is being kept secret so as not to attract the attention of pirates.

Jack Sparrow?  :o  :-\
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 09/10/2021 01:45 pm

One question, I've only seen pictures of the Webb Telescope in an upright position. Will it be OK to transport it on its side as shown by the canister in the photo above?

It was designed to be transported in that container.  The telescope without spacecraft was transported from GSFC to JSC and then to Redondo Beach in that container.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 09/10/2021 04:16 pm
https://www.bbc.com/news/science-environment-58498676

Quote
JWST must now itself travel by sea from its construction base at Northrop Grumman in California. This involves a trip through the Panama Canal.

Information about the voyage is being kept secret so as not to attract the attention of pirates.

Jack Sparrow?  :o  :-\

Laughed loud. Unfortunately, piracy still exists nowadays. French Guyana has a major issue with illegal gold mining poisoning the rain forrest with mercury.
https://www.rfi.fr/en/france/20210909-mountains-of-gold-rivers-of-mercury-poisoning-of-guiana-and-the-french-amazon
Although I am at lost why would they be interested in JWST.
Then again, with Jack Sparrow very precarious mental state, you never know... peanuts, cuttlefish, mayonnaise, guillotine, and rum...
...
Why... why is the Webb gone ?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 09/10/2021 04:45 pm
https://www.bbc.com/news/science-environment-58498676

Quote
JWST must now itself travel by sea from its construction base at Northrop Grumman in California. This involves a trip through the Panama Canal.

Information about the voyage is being kept secret so as not to attract the attention of pirates.

Jack Sparrow?  :o  :-\

The actual concern is terrorism against a $10 billion piece of American technology.

I was in a meeting back around 2015 where somebody discussed that they were working on the transportation security plan. Even then, they were thinking about how they would keep it secure. You can be sure that when it moves, there will be a US Navy warship shadowing it and security forces on, around, and above the ship.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Robert Thompson on 09/10/2021 07:39 pm
The mirrors are a large concentration of lightweight strong beryllium, coated in IR reflective gold.
18 mirrors * 46 lb Be * $150/oz
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: hoku on 09/10/2021 08:10 pm
Thought they would've flown it to Guiana.
Lets hope the ship doesn't run into any hurricanes.


I think it's too big to fit in a plane now.

I'm trying to remember, and maybe somebody has better information, but there's an issue with the road from the airport to the launch site. I think that the road from the port to the launch site is smoother. So even if they could have flown it, they might have chosen sea transport anyway. But I could be in error about this and somebody may have better info.
Apparently at least one of the bridges between the airport and the launch site isn't designed to support the full weight of STTARS + JWST (which, according to the 2nd post linked below, totals in excess of 80 metric tonnes). I vaguely remember that the bridges were designed to support transports of the Hermes shuttle (launch mass of around 20 t?).

https://forum.nasaspaceflight.com/index.php?topic=10453.msg1228976#msg1228976 (https://forum.nasaspaceflight.com/index.php?topic=10453.msg1228976#msg1228976)
https://forum.nasaspaceflight.com/index.php?topic=10453.msg1758615#msg1758615
 (https://forum.nasaspaceflight.com/index.php?topic=10453.msg1758615#msg1758615)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 09/11/2021 07:16 am
Thought they would've flown it to Guiana.
Lets hope the ship doesn't run into any hurricanes.


I think it's too big to fit in a plane now.

I'm trying to remember, and maybe somebody has better information, but there's an issue with the road from the airport to the launch site. I think that the road from the port to the launch site is smoother. So even if they could have flown it, they might have chosen sea transport anyway. But I could be in error about this and somebody may have better info.
Apparently at least one of the bridges between the airport and the launch site isn't designed to support the full weight of STTARS + JWST (which, according to the 2nd post linked below, totals in excess of 80 metric tonnes). I vaguely remember that the bridges were designed to support transports of the Hermes shuttle (launch mass of around 20 t?).

https://forum.nasaspaceflight.com/index.php?topic=10453.msg1228976#msg1228976 (https://forum.nasaspaceflight.com/index.php?topic=10453.msg1228976#msg1228976)
https://forum.nasaspaceflight.com/index.php?topic=10453.msg1758615#msg1758615
 (https://forum.nasaspaceflight.com/index.php?topic=10453.msg1758615#msg1758615)

Hermès ended at 25 mt, with the disposable module in the back. And weight was still creeping upwards when it was canned in 1992.
And outside the CSG, French Guiana is a rather poor and backward place - shame to the Métropole, which doesn't treats its overseas territories in a great way, as seen once again during the COVID pandemic. Better than Brazil or Surinam, no question about that; but poorer than the Métropole, with badly lacking basic infrastructures. But I'm veering off topic.

In passing, if terrorists try to seize Webb near Kourou, the French foreign legion is there in strength to protect the place. In fact French Guiana harsh jungle is their playground.

"Go ahead, make my day" as would say Shuttle driver Clint Eastwood.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: GWR64 on 09/11/2021 08:50 am
Why was the Ariane 5 chosen as the launcher?
So that ESA is "involved" in JWST?
The Delta IV H would have been possible too, right?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Crispy on 09/11/2021 09:19 am
It's a proper partnership; there are European instruments on there also. In return, European scientists get allocated time on the telescope.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 09/11/2021 10:44 am
Why was the Ariane 5 chosen as the launcher?
So that ESA is "involved" in JWST?
The Delta IV H would have been possible too, right?

At an insane launch cost...
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 09/11/2021 11:26 am
Why was the Ariane 5 chosen as the launcher?
So that ESA is "involved" in JWST?
The Delta IV H would have been possible too, right?

At an insane launch cost...

In hindsight, an extra $165 million in launch costs wouldn't have been all that big of a deal.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: hoku on 09/11/2021 01:00 pm
Why was the Ariane 5 chosen as the launcher?
So that ESA is "involved" in JWST?
The Delta IV H would have been possible too, right?

At an insane launch cost...

In hindsight, an extra $165 million in launch costs wouldn't have been all that big of a deal.
Well, I think ordering a Delta IV Heavy launch sets you back by more than that - NRO was budgeting up to $440 million for a DIVH launch.

Anyway, "word on the street" (in ~2004?) was that the NGST/JWST project was in one of its existential budget crisis, when ESA offered to cover the launch with Ariane V. NASA accepted, and the JWST project lived on to fight another day (and to accumulate further cost overruns ;-)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: GWR64 on 09/11/2021 01:12 pm
Why was the Ariane 5 chosen as the launcher?
So that ESA is "involved" in JWST?
The Delta IV H would have been possible too, right?

At an insane launch cost...

In hindsight, an extra $165 million in launch costs wouldn't have been all that big of a deal.
Well, I think ordering a Delta IV Heavy launch sets you back by more than that - NRO was budgeting up to $440 million for a DIVH launch.

Anyway, "word on the street" (in ~2004?) was that the NGST/JWST project was in one of its existential budget crisis, when ESA offered to cover the launch with Ariane V. NASA accepted, and the JWST project lived on to fight another day (and to accumulate further cost overruns ;-)

Thank you, I understand.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: slobber91 on 09/25/2021 09:09 am
Driving past Space Park in Redondo Beach on my way to the airport this morning, I came across a certain space telescope headed south:
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 09/25/2021 12:10 pm
Anyway, "word on the street" (in ~2004?) was that the NGST/JWST project was in one of its existential budget crisis, when ESA offered to cover the launch with Ariane V. NASA accepted, and the JWST project lived on to fight another day (and to accumulate further cost overruns ;-)

I don't know if the specifics of this account are true, but the generalities are. The ESA launch offer "saved" NASA money. However, I think there were delays in agreeing to the deal, which also resulted in greater costs. I remember hearing somebody say that if NASA had simply gone for a US launcher from the start, it probably would have cost the same or less than the delays over signing up ESA. But I heard that before the JWST cost ballooned again, and then again. Figuring out this budgeting stuff is hard.

However, bringing the Europeans aboard also made it much harder to cancel the program. That's always something that NASA people consider, although they won't say it out loud.




Addendum: I should add a bit more explanation. I'm not exactly sure of the JWST case, but when it comes to science spacecraft, delaying choosing a launch vehicle costs money. The reason is that a launch vehicle represents a specific set of characteristics, and the spacecraft is designed to those characteristics. If you delay picking one, then the designers have to essentially hold two sets of characteristics in their design, and that costs money. So (rough example) if a Falcon is a 5 and an Atlas is a 3, the designers want to design to either a 5 or a 3, but until that decision is made, they have to design for both a 5 and a 3.

This was a problem for New Horizons back in the 2000s--there was a delay in picking the launch vehicle that cost a few tens of millions of dollars. I seem to remember the PI, Alan Stern, saying that NASA "saved" money on the launch vehicle choice, but the delay cost the program about the same money that they saved, so it was a wash (and he was not happy about it). This might be in his book.

I also now have vague memories that when NASA indicated they were going to use Ariane, Boeing (or ULA) protested the decision, resulting in a delay that increased costs to the JWST program. I'm sure that somebody could dig through old copies of Space News and find more information about this.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 09/25/2021 01:10 pm

I don't know if the specifics of this account are true, but the generalities are. The ESA launch offer "saved" NASA money. However, I think there were delays in agreeing to the deal, which also resulted in greater costs. I remember hearing somebody say that if NASA had simply gone for a US launcher from the start, it probably would have cost the same or less than the delays over signing up ESA. But I heard that before the JWST cost ballooned again, and then again. Figuring out this budgeting stuff is hard.


The costs and logistics of traveling outside the US over the years for meetings and for the launch campaign is not cheap.
the extra items they have to bring to Kourou (tankers of purge gas, tools, GSE, comm, etc)
Just the people involved with export control and such.

The US process of encapsulating the spacecraft in the PPF has less contamination risk vs on top of the launch vehicle.  The mitigations have extra costs

A US launcher would have been cheaper in the long run.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: MATTBLAK on 09/25/2021 01:19 pm
Which U.S. launcher do you think could have been used, Jim - Atlas V-551 or Delta IV-Heavy?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 09/25/2021 01:26 pm
Driving past Space Park in Redondo Beach on my way to the airport this morning, I came across a certain space telescope headed south:

Bon voyage en Guyane, Webb. And be careful of COVID - it is flaring up again, there...
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 09/25/2021 01:44 pm
Which U.S. launcher do you think could have been used, Jim - Atlas V-551 or Delta IV-Heavy?

Delta IV Heavy
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 09/25/2021 03:09 pm

I don't know if the specifics of this account are true, but the generalities are. The ESA launch offer "saved" NASA money. However, I think there were delays in agreeing to the deal, which also resulted in greater costs. I remember hearing somebody say that if NASA had simply gone for a US launcher from the start, it probably would have cost the same or less than the delays over signing up ESA. But I heard that before the JWST cost ballooned again, and then again. Figuring out this budgeting stuff is hard.


The costs and logistics of traveling outside the US over the years for meetings and for the launch campaign is not cheap.
the extra items they have to bring to Kourou (tankers of purge gas, tools, GSE, comm, etc)
Just the people involved with export control and such.

The US process of encapsulating the spacecraft in the PPF has less contamination risk vs on top of the launch vehicle.  The mitigations have extra costs

A US launcher would have been cheaper in the long run.

I can believe that. But one problem NASA faces is that international cooperation usually doesn't involve money transfers but barter arrangements. The Europeans wanted a part of the mission, but they were not going to give NASA $400 million in cash. Instead, they provided a launch vehicle. I don't think these kinds of arrangements are ideal, but cost is not the only factor that is taken into consideration, it's one of many.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Josh_from_Canada on 09/27/2021 03:01 am
The Webb Telescope left California on September 26th and is now on its way to the launch site!!!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: su27k on 09/30/2021 04:34 am
https://twitter.com/jeff_foust/status/1443253719211065344

Quote
At the AAAC meeting, NASA’s Eric Smith confirms that JWST is on a boat and in transit to Kourou; on track for Dec. 18 launch.

Quote
Smith also said an investigation into allegations of discriminatory practices by James Webb, linked to a petition calling for the mission’s renaming, “found no evidence at this time that warrants changing the name.” [He referred to a statement I don’t think NASA has made public.]
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ncb1397 on 09/30/2021 02:41 pm
Quote
NASA does not plan to rename its new $10 billion technological marvel, the James Webb Space Telescope, despite concerns that its namesake, former NASA administrator James Webb, went along with government discrimination against gay and lesbian employees in the 1950s and 1960s.

The space agency tells NPR it has investigated the matter and decided to keep the telescope's name as is, ahead of the long-awaited launch in December.

"We have found no evidence at this time that warrants changing the name of the James Webb Space Telescope," says NASA administrator Bill Nelson.
https://www.npr.org/2021/09/30/1041707730/shadowed-by-controversy-nasa-wont-rename-new-space-telescope

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 10/02/2021 12:57 pm
At the AAAC meeting, NASA’s Eric Smith confirms that JWST is on a boat and in transit to Kourou; on track for Dec. 18 launch.


Note that they're being rather low-key about the transit.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 10/02/2021 04:12 pm
At the AAAC meeting, NASA’s Eric Smith confirms that JWST is on a boat and in transit to Kourou; on track for Dec. 18 launch.


Note that they're being rather low-key about the transit.
Hopefully we won't hear another word until it is safely at Kourou.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 10/02/2021 04:57 pm
At the AAAC meeting, NASA’s Eric Smith confirms that JWST is on a boat and in transit to Kourou; on track for Dec. 18 launch.


Note that they're being rather low-key about the transit.
Hopefully we won't hear another word until it is safely at Kourou.

Agreed. But it would be nice if they released some photos later on showing the various aspect of the transport.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Dizzy_RHESSI on 10/04/2021 09:40 am
I did see this unofficial photo on reddit, courtesy of u/MagnificentFloof42. Sadly the image was buried by the thread. It does match the rumors that JWST is onboard MN Colibri, although it's not confirmed.

Quote
Here is the Web being loaded onto a ship for transit to the launch site. My aunt lives next to the port and took this photo from her living room.

https://www.reddit.com/r/space/comments/px6zxk/the_largest_space_telescope_in_history_is_about/heoxxk5/
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: woods170 on 10/04/2021 12:05 pm
I did see this unofficial photo on reddit, courtesy of u/MagnificentFloof42. Sadly the image was buried by the thread. It does match the rumors that JWST is onboard MN Colibri, although it's not confirmed.

Quote
Here is the Web being loaded onto a ship for transit to the launch site. My aunt lives next to the port and took this photo from her living room.

https://www.reddit.com/r/space/comments/px6zxk/the_largest_space_telescope_in_history_is_about/heoxxk5/ (https://www.reddit.com/r/space/comments/px6zxk/the_largest_space_telescope_in_history_is_about/heoxxk5/)

Yes, that is JWST's shipping container (STTARS) allright. And that JWST would be transported on board of one of the two Arianespace MN ships (either MN Colibri or MN Toucan) has been public information since at least December 2017:
https://svs.gsfc.nasa.gov/12785 (https://svs.gsfc.nasa.gov/12785)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: joncz on 10/06/2021 07:45 pm
MN Colibri has departed the Panama Canal on her way to Nantes (h/t MarineTraffic.com)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: russianhalo117 on 10/06/2021 08:53 pm
I did see this unofficial photo on reddit, courtesy of u/MagnificentFloof42. Sadly the image was buried by the thread. It does match the rumors that JWST is onboard MN Colibri, although it's not confirmed.

Quote
Here is the Web being loaded onto a ship for transit to the launch site. My aunt lives next to the port and took this photo from her living room.

https://www.reddit.com/r/space/comments/px6zxk/the_largest_space_telescope_in_history_is_about/heoxxk5/ (https://www.reddit.com/r/space/comments/px6zxk/the_largest_space_telescope_in_history_is_about/heoxxk5/)

Yes, that is JWST's shipping container (STTARS) allright. And that JWST would be transported on board of one of the two Arianespace MN ships (either MN Colibri or MN Toucan) has been public information since at least December 2017:
https://svs.gsfc.nasa.gov/12785 (https://svs.gsfc.nasa.gov/12785)
There was an earlier post saying the ship would be escorted by either US Navy or NATO vessels. Some were seen waiting off shore on departure day.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Targeteer on 10/06/2021 11:12 pm
October 06, 2021
MEDIA ADVISORY M21-123


NASA and its mission partners will host a briefing at 9 a.m. EDT on Friday, Oct. 8, for media interested in covering the James Webb Space Telescope launch. Webb, an international partnership with ESA (European Space Agency) and the Canadian Space Agency, is targeted for launch Dec. 18.

The briefing will stream live on NASA’s website.

This informational call will review media coverage opportunities at:

    Europe’s Spaceport in Kourou, French Guiana, Webb’s launch site.
    Space Telescope Science Institute in Baltimore, Webb’s mission operations site.
    ESA’s European Space Research and Technology Centre in Noordwijk, Netherlands, site for a launch day event.
    Canadian Space Agency headquarters in Saint-Hubert, Quebec, Canada, site for a launch day event.

To participate in the call, media must RSVP no later than two hours prior to the start of the briefing by contacting Alise Fisher at: [email protected] NASA’s media accreditation policy for teleconferences and onsite activities is available online.

The discussion will cover logistics, travel requirements, and registration instructions before media accreditation opens for launch. NASA also will preview the schedule of upcoming Webb media events.

NASA’s Webb telescope will serve as the premier space science observatory for the next decade and explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe, and everything in between. Webb will reveal new and unexpected discoveries, and help humanity understand the origins of the universe and our place in it.

For more information about the Webb mission, visit:

https://www.nasa.gov/webb
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Star One on 10/08/2021 06:13 am
If you thought the naming issue was now dead well think again. Interview with Senator Brad Hoylman concerning the matter asking seemingly for the president to intervene.

https://www.inverse.com/science/webb-telescope-name
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: hoku on 10/08/2021 09:59 am
MN Colibri has departed the Panama Canal on her way to Nantes (h/t MarineTraffic.com)
Yep, MN Colibri passed the locks (with its precious cargo?) a few days ago ...
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Zed_Noir on 10/08/2021 12:19 pm
The MN Colibri is under way and have an ETA of October 18 at the port of Nantes according to the Marine Traffic website. So might be off loading JWST about now.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 10/08/2021 12:57 pm
The MN Colibri is under way and have an ETA of October 18 at the port of Nantes according to the Marine Traffic website. So might be off loading JWST about now.

You are correct
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: FutureSpaceTourist on 10/08/2021 12:59 pm
https://youtu.be/6h0vBOEYygo
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: dsmillman on 10/12/2021 03:30 pm
October 12, 2021
RELEASE 21-132
NASA’s Webb Space Telescope Arrives in French Guiana After Sea Voyage
 
After the custom-built shipping container carrying Webb is unloaded from the MN Colibri, Webb will be transported to its launch site, Europe’s Spaceport in Kourou, French Guiana.
Credits: NASA/Chris Gunn
 
The MN Colibri arrived Oct. 12 at Port de Pariacabo on the Kourou River in French Guiana, carrying NASA’s James Webb Space Telescope as cargo.
Credits: NASA/Chris Gunn
NASA’s James Webb Space Telescope successfully arrived in French Guiana Tuesday, after a 16-day journey at sea. The 1,500-mile voyage took Webb from California through the Panama Canal to Port de Pariacabo on the Kourou River in French Guiana, on the northeastern coast of South America.
The world’s largest and most complex space science observatory will now be driven to its launch site, Europe’s Spaceport in Kourou, where it will begin two months of operational preparations before its launch on an Ariane 5 rocket, scheduled for Dec. 18.
Once operational, Webb will reveal insights about all phases of cosmic history – back to just after the big bang – and will help search for signs of potential habitability among the thousands of exoplanets scientists have discovered in recent years. The mission is an international collaboration led by NASA, in partnership with the European and Canadian space agencies.
“The James Webb Space Telescope is a colossal achievement, built to transform our view of the universe and deliver amazing science,” said NASA Administrator Bill Nelson. “Webb will look back over 13 billion years to the light created just after the big bang, with the power to show humanity the farthest reaches of space that we have ever seen. We are now very close to unlocking mysteries of the cosmos, thanks to the skills and expertise of our phenomenal team.”
After completing testing in August at Northrop Grumman's Space Park in Redondo Beach, California, the Webb team spent nearly a month folding, stowing, and preparing the massive observatory for shipment to South America. Webb was shipped in a custom-built, environmentally controlled container.
Late in the evening of Friday, Sept. 24, Webb traveled with a police escort 26 miles through the streets of Los Angeles, from Northrop Grumman's facility in Redondo Beach to Naval Weapons Station Seal Beach. There, it was loaded onto the MN Colibri, a French-flagged cargo ship that has previously transported satellites and spaceflight hardware to Kourou. The MN Colibri departed Seal Beach Sunday, Sept. 26 and entered the Panama Canal Tuesday, Oct. 5 on its way to Kourou.
The ocean journey represented the final leg of Webb's long, earthbound travels over the years. The telescope was assembled at NASA's Goddard Space Flight Center in Greenbelt, Maryland, starting in 2013. In 2017, it was shipped to NASA's Johnson Space Center in Houston for cryogenic testing at the historic “Chamber A” test facility, famous for its use during the Apollo missions. In 2018, Webb shipped to Space Park in California, where for three years it underwent rigorous testing to ensure its readiness for operations in the environment of space.
“A talented team across America, Canada, and Europe worked together to build this highly complex observatory. It’s an incredible challenge – and very much worthwhile. We are going to see things in the universe beyond what we can even imagine today,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington. “Now that Webb has arrived in Kourou, we’re getting it ready for launch in December – and then we will watch in suspense over the next few weeks and months as we launch and ready the largest space telescope ever built.”
After Webb is removed from its shipping container, engineers will run final checks on the observatory’s condition. Webb will then be configured for flight, which includes loading the spacecraft with propellants, before Webb is mounted on top of the rocket and enclosed in the fairing for launch.
"Webb’s arrival at the launch site is a momentous occasion,” said Gregory Robinson, Webb’s program director at NASA Headquarters. “We are very excited to finally send the world’s next great observatory into deep space. Webb has crossed the country and traveled by sea. Now it will take its ultimate journey by rocket one million miles from Earth, to capture stunning images of the first galaxies in the early universe that are certain to transform our understanding of our place in the cosmos.”
For more information about the Webb mission, visit:
https://www.nasa.gov/webb
-end-
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: eeergo on 10/12/2021 03:38 pm
Last few strolls before launch!

https://twitter.com/arianespaceceo/status/1447945335159017479
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 10/12/2021 03:52 pm
https://www.nasa.gov/press-release/nasa-s-webb-space-telescope-arrives-in-french-guiana-after-sea-voyage

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 10/12/2021 05:29 pm
Now some videos showing the movement of the telescope.

https://www.nasa.gov/feature/goddard/2021/how-to-ship-the-world-s-largest-space-telescope-1500-miles-across-the-ocean

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 10/13/2021 01:58 pm
JWST arriving at the payload processing facility.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Star One on 10/13/2021 10:13 pm
Quote
Astronomer Lucianne Walkowicz has resigned from a NASA advisory committee on account of the space agency’s perceived mishandling of a request to rename the upcoming James Webb Space Telescope. Webb was a NASA administrator during the 1960s who aided in the persecution of LGBTQ employees.

Quote
For NASA, this represents a serious loss. As a scientist, Walkowicz has contributed to our understanding of stellar activity and how it impacts the atmospheres of potentially habitable exoplanets and the potential for human activity on Mars. Walkowicz has even had an asteroid named after them.

https://gizmodo.com/nasa-advisor-quits-over-space-telescope-named-for-homop-1847856513
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: deadman1204 on 10/14/2021 08:12 pm
Did the second Ariane5 that was testing the new fairing launch yet?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: hektor on 10/14/2021 09:00 pm
Oct. 22 is the date
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: su27k on 10/17/2021 02:28 am
https://twitter.com/mims/status/1449375672657489921

Quote
🧵 Here’s one to send you for a mental loop:

The telescope so big that it that may allow us to find extraterrestrial life led directly to the manufacture of the display on which you’re probably reading this now.
https://www.wsj.com/articles/how-the-search-for-extraterrestrial-life-helped-make-your-smartphones-screen-possible-11634356804



The 18, 1.32 meter-wide mirrors of the James Webb Space Telescope, to be launched into deep space this December, must all be smooth to within a few angstroms (can’t be off by more than a few atoms in thicknesss).

When NASA stipulated this 20+ years ago, it was impossible.



Tinsley optics, which had already made the corrective lenses for the Hubble Space Telescope, which then brought us decades of stunning images from deep space, bid on polishing these mirrors to a then unheard-of level of perfection.



Fast forward to 2012. Tinsley is winding down production of the James Webb telescope mirrors. But what to do with the purpose-built equipment for polishing these mirrors to unheard-of perfection?



Enter Coherent, the laser company.

Coherent, and a competitor or two, make the schoolbus-size “linebeam” systems that help make near-perfect sheets of silicon, on which OLED and some other displays are made.

They needed giant optics.

Like those on the James Webb.



So! NASA asks the impossible in order to satisfy human curiosity. (Are we alone in the universe?)

And they fund the development of the tech they need. And that leads to economical production of the phone displays we all stare at too many hours a day.



How often does this happen? How much of our modern world do we owe to NASA (and to be fair, DoD) funding “crazy” research to solve problems with no immediate commercial application?

It’s happened thousands of times.

Everything from the DustBuster to the internet are the result.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: dsmillman on 10/19/2021 04:52 pm
There are timelines for the deployment and commissioning of JWST in the following:

https://science.nasa.gov/files/science-pink/s3fs-public/atoms/files/Smith%20Webb-Update%20APAC%20Oct-2021.pdf


Now we just need a single page that defines all the mnemonics.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 10/19/2021 05:21 pm
OSTTAR - Observatory Space Telescope Transportation Air Road and Sea
S5C (not SSC) EPCU - S5 (Ensemble de Préparation Charge Utile) S5 Payload Preparation Facility. C is the nonhazardous portion.
CST -  Combined System Test
RF - Radio Frequency
DSN - Deep Space Network
PA - Payload Adapter
CCU3 - (Conteneur Charge Utile) Payload Transport Container
S5B (not SSC) EPCU - S5 (Ensemble de Préparation Charge Utile) S5 Payload Preparation Facility. B is a hazardous portion.
BAF - (Batiment d'Assemblage Final) Final Assembly Building
HE - (Hall d'Encapsulation) Encapsulation Hall
MU - Mission Unique
MDR - Mission Dress Rehearsal
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Targeteer on 10/20/2021 10:57 pm
October 20, 2021
MEDIA ADVISORY M21-133
NASA Shares Webb Telescope Media Briefing Schedule, Resources

NASA will hold a series of virtual media briefings and events leading up to the launch of the James Webb Space Telescope, the premier space science observatory of the next decade. Webb, an international partnership with the European and Canadian space agencies, is targeted for launch Dec. 18 from Europe's Spaceport in French Guiana, on the northeastern coast of South America.

NASA has also released several new Webb media resources, including a digital press kit, now available online:

    Digital press kit
    Video: “29 Days on the Edge” highlighting the complex series of deployments Webb will complete as it unfolds in space
    An updated suite of materials online, including images and videos, b-roll, and animations
    Media interview request form

The full schedule of media events is as follows (all times eastern):

Tuesday, Nov. 2

11 a.m.: Media briefing on Webb engineering and spacecraft deployments

Thursday, Nov. 18

11 a.m.: Media briefing on Webb science goals

2 p.m.: Media briefing on Webb science instruments

Wednesday, Dec. 15

Time TBD: Prelaunch media briefing

All media briefings will take place virtually and will livestream on NASA TV, the NASA app, and the agency’s website. Registration information for the briefings, as well as the schedule of launch coverage events, is forthcoming.

In addition, NASA invites members of the public to create art – in any form – that depicts what they believe Webb will discover. Participants can share an image or video of themselves with their artwork on social media using the hashtag #UnfoldTheUniverse. The deadline for submissions is Dec. 18. NASA will share submitted art on its website and social media platforms and will feature select participants in Webb’s historic live launch broadcast.

The Webb Space Telescope will explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe – and everything in between. Webb will reveal new and unexpected discoveries, and help humanity understand the origins of the universe and our place in it.

For more information about the Webb mission, visit:

https://webb.nasa.gov
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 10/23/2021 09:42 am
VA255 has been postponed (https://www.arianespace.com/press-release/flight-va255-postponement-of-the-launch/). As this was the second verification flight for the new fairing, this has the potential to move JWST's launch date to the right.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: GWR64 on 10/23/2021 10:42 am
VA255 has been postponed (https://www.arianespace.com/press-release/flight-va255-postponement-of-the-launch/). As this was the second verification flight for the new fairing, this has the potential to move JWST's launch date to the right.

The problem is solved.
It ended up being just a 1-day slip:

https://twitter.com/Arianespace/status/1451786314622308353

https://twitter.com/Arianespace/status/1451786317591941126
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Josh_from_Canada on 10/25/2021 05:56 am
VA255 has successfully launched! The post flight analysis is likely still ongoing. After that's done, Ariane 5 will be cleared to launch JWST.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: su27k on 10/26/2021 05:01 am
How much does the James Webb Space Telescope cost? (https://www.planetary.org/articles/cost-of-the-jwst)

Quote from: Planetary Society
The James Webb Space Telescope (JWST) is expected to cost NASA $9.7 billion over 24 years. Of that amount, $8.8 billion was spent on spacecraft development between 2003 and 2021; $861 million is planned to support five years of operations. Adjusted for inflation to 2020 dollars, the lifetime cost to NASA will be approximately $10.8 billion.

That is only NASA’s portion. The European Space Agency provided the Ariane 5 launch vehicle and two of the four science instruments for an estimated cost of €700 million. The Canadian Space Agency contributed sensors and scientific instrumentation, which cost approximately CA$200 million.

This places the James Webb Space Telescope among the most expensive scientific platforms in history, comparable only to the Hubble Space Telescope and the Large Hadron Collider at CERN.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: AS_501 on 10/26/2021 05:22 am
If "EDL" is used to describe 7 minutes of terror soft landing on Mars, "LLU" (Launch, Lagrange, Unfurling) should be used to describe 3 months of terror until the optics and sunshade are properly unfurled.   ;)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 10/26/2021 11:27 pm
If "EDL" is used to describe 7 minutes of terror soft landing on Mars, "LLU" (Launch, Lagrange, Unfurling) should be used to describe 3 months of terror until the optics and sunshade are properly unfurled. 

Yes and no. The Mars landers had the same kind of months of transit, where everyone involved didn't know if what they'd done would work on arrival at Mars, in addition to the actual EDL "terror".

A big part of the "terror" of Curiosity/Perseverance was not just the complexity of EDL, but also the light-lag. By the time you get the first confirmation of a successful step, or a problem, the whole sequence had already finished or failed a few minutes earlier.

With JWST, other than launch, you always have an opportunity to save the spacecraft. (See Lucy and its solar array.) I expect the people involved are going to be stressed out beyond measure, but it's a fundamentally different kind of terror.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: AS_501 on 10/27/2021 12:24 am
Webb has been tested, retested, back tested, front tested, side tested, top tested and bottom tested so many times, I'm confident all will go well.  Just hope the scope will be working well into the bonus years.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Zed_Noir on 10/27/2021 02:23 am
Webb has been tested, retested, back tested, front tested, side tested, top tested and bottom tested so many times, I'm confident all will go well.  Just hope the scope will be working well into the bonus years.


However JWST could only be tested in orbit with the unfurling in zero-G.  :(


There will likely not many "bonus" years due to propellant usage for station keeping.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: matthewkantar on 10/27/2021 05:30 am
Webb has been tested, retested, back tested, front tested, side tested, top tested and bottom tested so many times, I'm confident all will go well.  Just hope the scope will be working well into the bonus years.

I am not so sanguine. Fingers crossed and knocking on wood.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 10/27/2021 04:59 pm
If "EDL" is used to describe 7 minutes of terror soft landing on Mars, "LLU" (Launch, Lagrange, Unfurling) should be used to describe 3 months of terror until the optics and sunshade are properly unfurled.   ;)

LUL.  The deployments occur during the transit to L2, during the first two weeks.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Targeteer on 10/29/2021 12:06 am
October 28, 2021
MEDIA ADVISORY M21-138
NASA to Host Briefing on Webb Telescope Engineering, Deployments
The James Webb Space Telescope is the premier space science observatory of the next decade.


NASA will hold a virtual media briefing 11 a.m. EDT Tuesday, Nov. 2, to discuss the engineering of the James Webb Space Telescope, the world’s largest and most powerful space science telescope. Participants will discuss how the observatory’s science goals drove its design and preview the complex series of deployments Webb will complete as it unfolds in space.

The briefing will livestream on NASA TV, the NASA app, and the agency’s website.

The briefing participants are:

    Bill Ochs, Webb project manager, NASA’s Goddard Space Flight Center, Greenbelt, Maryland
    Alphonso Stewart, Webb deployment systems lead, Goddard
    Begoña Vila, Webb instrument systems engineer, Goddard
    Krystal Puga, Webb spacecraft systems engineer, Northrop Grumman, Redondo Beach, California
    Mike Menzel, Webb lead mission systems engineer, Goddard

To participate by telephone, media must RSVP no later than two hours before the start of the briefing to Laura Betz at: [email protected] and Alise Fisher at: [email protected] Media and members of the public may also ask questions on social media using #NASAWebb.

NASA’s media accreditation policy for virtual and onsite activities is available online.

The James Webb Space Telescope, an international partnership with the European and Canadian space agencies, is targeted for launch Dec. 18. It will explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe, and everything in between. Webb will reveal new and unexpected discoveries, and help humanity understand the origins of the universe and our place in it.

For more information about the Webb mission, visit:

https://webb.nasa.gov
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 10/29/2021 01:09 am
Webb has been tested, retested, back tested, front tested, side tested, top tested and bottom tested so many times, I'm confident all will go well.  Just hope the scope will be working well into the bonus years.
There will likely not many "bonus" years due to propellant usage for station keeping.
There are folks seriously considering re-fueling comsats.  Given Webb's cost, refueling would make a lot of sense, if it's working well otherwise.

Was this considered at all in the design for Webb?   It would not have had to have been much - perhaps some optical fiducials, a docking plate, and an exposed refueling port.  Even if these do not match the eventual standards for comsat refueling, they could make the job of custom re-fueler much easier.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: deadman1204 on 10/29/2021 03:02 am
Webb has been tested, retested, back tested, front tested, side tested, top tested and bottom tested so many times, I'm confident all will go well.  Just hope the scope will be working well into the bonus years.
There will likely not many "bonus" years due to propellant usage for station keeping.
There are folks seriously considering re-fueling comsats.  Given Webb's cost, refueling would make a lot of sense, if it's working well otherwise.

Was this considered at all in the design for Webb?   It would not have had to have been much - perhaps some optical fiducials, a docking plate, and an exposed refueling port.  Even if these do not match the eventual standards for comsat refueling, they could make the job of custom re-fueler much easier.

Ignoring the fact that webb won't be in earth orbit, it's unrefuelable. The maneuvering thrusters of an approaching craft would destroy the sunshield.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 10/29/2021 04:25 am
It would not have had to have been much


I love it when I read stuff like this on the internet.

You guys have no idea what goes into designing a spacecraft.
I've discovered over the years that most people have no clue about the details and challenges in any industry they have never been directly involved in.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 10/29/2021 04:46 am
It would not have had to have been much
I love it when I read stuff like this on the internet.

You guys have no idea what goes into designing a spacecraft.
With all due respect, I stand by my statement.

Would adding a port potentially capable of refueling be trivial?  Of course not - nothing about designing a spacecraft is trivial.  But compared to the challenges of folding beryllium cryogenic mirrors, or microshutter IR detectors, it's comparatively simple.

Comsats are already adding these ports.  Comsats are typically worth a few hundred million dollars at the beginning of their life (or at least that's what they are insured for).  Refueling would only be used to extend their life, at which point they would already be a decade or so old.  So assuming the comsat designers are not idiots, the cost to add the port, including all the engineering required, must be less than the value of a depreciated comsat.  The Webb is worth roughly 100 times as much, and a lot harder to replace, so the effort to add a potential refueling port cannot be a major addition to the engineering required.

Looking at this another way, the Webb is roughly a $10 billion dollar project.  How much might you reasonably spend on a change that could double the life of the observatory?  Perhaps 1% of the total?  For Webb, that's $100 million.  And if was that expensive, the comsat folks would not be considering it.

Finally, from an engineering viewpoint, adding a potential refueling port is not conceptually difficult.  It's a replacement for the fill/drain valve, which must already exist.  From a technical maturity point of view, refueling valves already exist and are space-qualified.  From a programmatic point of view, Northrop Grumman  is an investor in a satellite refueling company (https://phys.org/news/2021-09-gas-station-space.html), so the access to the details of the technology is there.

Overall, I still don't think adding potential for servicing (as did Hubble when they added a capture ring) would have been a major effort.  I can also understand the opposing view, that given all the challenges and brand new technology of Webb, there was no interest in anything that was not absolutely required.  But if in 10 years, Webb's working well but running out of gas, that decision is going to look pretty short-sighted.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: armchairfan on 10/29/2021 07:40 am

Was [refueling] considered at all in the design for Webb?   It would not have had to have been much - perhaps some optical fiducials, a docking plate, and an exposed refueling port.  Even if these do not match the eventual standards for comsat refueling, they could make the job of custom re-fueler much easier.

Ignoring the fact that webb won't be in earth orbit, it's unrefuelable. The maneuvering thrusters of an approaching craft would destroy the sunshield.

A reasonable question from a senior member with (at the very least!) a demonstrated history of understanding basic engineering followed by a respectful, reasonable albeit negative reply. I happen to agree with Lou but I can understand arguments to the contrary -- especially given prevailing opinions when JWST was designed.

I love it when I read stuff like this on the internet.

You guys have no idea what goes into designing a spacecraft.

While I acknowledge that you're a space industry professional whose opinions I often find insightful, this post was unhelpful and arrogant. Please take it down a notch.

(rant)
While I'm not directly involved in the space industry, I have an engineering background and my company did various consulting gigs before we developed our own products. One of my take aways from consulting was as you get closer to "how the sausage is made" some things impress you while others don't. There were numerous reasons for the latter but a frequent one was complacency: "we've always done it that way and it's good enough". The problem was that good enough then had become not good enough now given the new competitive environment.

Certainly I can sympathize with your frustration over apparently clueless questions or suggestions from industry outsiders. Perhaps you can sympathize with others that are sometimes frustrated by what they consider overly conservative thinking or approaches in an industry that they perceive is (or should be) undergoing rapid innovation.
(/rant)

With all due respect, I stand by my statement.
Good for you!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 10/29/2021 01:00 pm
Ignoring the fact that webb won't be in earth orbit, it's unrefuelable. The maneuvering thrusters of an approaching craft would destroy the sunshield.
These are real problems, but not insurmountable. 

Refueling is already designed to work in GEO.  L2 is close enough that it is not considered deep space, so the same radio system can be used, though uplink power may need to be increased, and downlink will be slower.  Likewise it's close enough to Earth orbit so the solar arrays, sun sensor, and so on should be OK.  Overall, operating a GEO refueler at L2 should not be a huge task.

The subshield is indeed delicate.  But at L2, the gravity gradients are very low, and the refueler can approach very slowly.  Then the final alignment and deceleration could be done with ion thrusters or other very low force devices.  The  sun facing sunshade layer is about 50 microns thick (https://www.jwst.nasa.gov/content/observatory/sunshield.html) and  hence will mass about 50 grams per square meter.  The film itself can hold up under earth gravity (about 500 millinewtons per square meter) and so should be OK with the ion thruster forces, typically 100 millinewton or so.  The supporting structure for the sunshield is strong enough to survive when the station-keeping thrusters are used (about 35 newtons) and should also be OK with milli-newton forces.  Using noble gas ion thrusters should also reduce worries about contamination (although Webb itself uses chemical thrusters on the sunward side of the sunshade, so this may not be a limitation).

So approaching Webb from the sunshield side seems possible without damaging it.


Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 10/29/2021 01:34 pm
it's comparatively simple.

Back around 2009 or so there was a proposal to add a grapple fixture to JWST--the kind of thing that they used for payloads to be gripped with the shuttle's arm. I sat in on a meeting where this was discussed. Adding something like that late in the design would have rippled throughout the entire spacecraft. It affected the structural loads, the thermal loads, the control and guidance programming, everything, for adding something about the size of a doorknob to the spacecraft.
I completely agree that adding anything after the detailed design is complete is not practical.  That's why, when a science instrument is not ready, it is replaced by an inert block of the same mass, drawing the same amount of power.

On the other hand, designing it in from the start is not hard, as shown by the adaptation by the comsat community.

So the answer to the original question seems pretty clear.  Refueling was NOT considered in any way during the design of the Webb.  It WAS considered later (at the meeting you sat in on), but at that point it would have required so much redesign that it was rejected.

This answers my original question.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 10/29/2021 01:45 pm

The subshield is indeed delicate.  But at L2, the gravity gradients are very low, and the refueler can approach very slowly.  Then the final alignment and deceleration could be done with ion thrusters or other very low force devices.  The  sun facing sunshade layer is about 50 microns thick (https://www.jwst.nasa.gov/content/observatory/sunshield.html) and  hence will mass about 50 grams per square meter.  The film itself can hold up under earth gravity (about 500 millinewtons per square meter) and so should be OK with the ion thruster forces, typically 100 millinewton or so.  The supporting structure for the sunshield is strong enough to survive when the station-keeping thrusters are used (about 35 newtons) and should also be OK with milli-newton forces.  Using noble gas ion thrusters should also reduce worries about contamination (although Webb itself uses chemical thrusters on the sunward side of the sunshade, so this may not be a limitation).

So approaching Webb from the sunshield side seems possible without damaging it.


No, throwing ions at the spacecraft is not a good idea.   
And ions thrusters are going to be insufficient for translation control and even attitude control of the approaching vehicle.  They can't react fast enough considering the mass of the servicing spacecraft.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 10/29/2021 02:53 pm
No, throwing ions at the spacecraft is not a good idea.   
And ions thrusters are going to be insufficient for translation control and even attitude control of the approaching vehicle.  They can't react fast enough considering the mass of the servicing spacecraft.
Attitude control is not a problem.  The combination of reaction wheels and ion thrusters (to keep the wheels unloaded) works well.  This has been proven on all-electric comsats (https://arc.aiaa.org/doi/pdf/10.2514/6.2018-2601).

Translation in the two axes perpendicular to approach can use normal chemical thrusters - Webb itself does this. This leaves slowing down as you approach the Webb as the main problem.  The Shuttle docked at about 3 cm/sec.  A 100 milli-newton thruster, acting on a 1000 kg spacecraft, can add or subtract this much velocity in about 300 seconds (5 minutes).  During this time the spacecraft will travel about 5 meters.  So a slow approach, especially given the low gravity gradient of L2, seems feasible.

As as far as the impact of the ions on the sunshade, this clearly needs to be looked at.  The sunshade is covered with a layer of silicon, and the ion thrusters are generating inert gas, so it's likely not a problem.  Here is a video of an ion thruster acting on aluminum foil at close range (https://youtube.com/watch?v=hTlcYbIrgmQ).  No damage is apparent, but obviously a more formal study would be needed.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 10/29/2021 04:00 pm

1.  Attitude control is not a problem.  The combination of reaction wheels and ion thrusters (to keep the wheels unloaded) works well.  This has been proven on all-electric comsats (https://arc.aiaa.org/doi/pdf/10.2514/6.2018-2601).

2.  Translation in the two axes perpendicular to approach can use normal chemical thrusters - Webb itself does this. This leaves slowing down as you approach the Webb as the main problem.  The Shuttle docked at about 3 cm/sec.  A 100 milli-newton thruster, acting on a 1000 kg spacecraft, can add or subtract this much velocity in about 300 seconds (5 minutes).  During this time the spacecraft will travel about 5 meters.  So a slow approach, especially given the low gravity gradient of L2, seems feasible.

3. As as far as the impact of the ions on the sunshade, this clearly needs to be looked at.  The sunshade is covered with a layer of silicon, and the ion thrusters are generating inert gas, so it's likely not a problem.  Here is a video of an ion thruster acting on aluminum foil at close range (https://youtube.com/watch?v=hTlcYbIrgmQ).  No damage is apparent, but obviously a more formal study would be needed.

1.  It is a problem.  This is not a stationary comsat, but spacecraft doing prox ops.  It has to be able to rotate and react quicker.  Reaction wheels are not used, thrusters are.
3

2.  No, the plumes from the other two axis will still affect the sunshield. 
The spacecraft is going to weight much more than 1000kg. 
 cm/sec was final velocity and not approach.  The shuttle was braking.
Again, too slow to react.  JWST isn't stationary.  It is orbiting L2 and reacting to solar pressure

3.  The issue I was raising was charge and not pressure.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: rsnellenberger on 10/29/2021 04:10 pm

Translation in the two axes perpendicular to approach can use normal chemical thrusters - Webb itself does this. This leaves slowing down as you approach the Webb as the main problem.  The Shuttle docked at about 3 cm/sec.  A 100 milli-newton thruster, acting on a 1000 kg spacecraft, can add or subtract this much velocity in about 300 seconds (5 minutes).  During this time the spacecraft will travel about 5 meters.  So a slow approach, especially given the low gravity gradient of L2, seems feasible.

As as far as the impact of the ions on the sunshade, this clearly needs to be looked at.  The sunshade is covered with a layer of silicon, and the ion thrusters are generating inert gas, so it's likely not a problem.  Here is a video of an ion thruster acting on aluminum foil at close range (https://youtube.com/watch?v=hTlcYbIrgmQ).  No damage is apparent, but obviously a more formal study would be needed.
Even assuming that a tanker can approach and dock on the shade-side without physically damaging it — how do you propose to protect that great, gaudy mirror and the just-as-important secondary mirror? Hubble had a cover to protect its optical components, but Webb’s mirrors are exposed even in the launch configuration - and the tanker brings along a cloud of propulsion byproducts (hypergol, argon/krypton ions, or a combination) when it arrives regardless of its approach trajectory or strategy.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 10/29/2021 04:44 pm
Translation in the two axes perpendicular to approach can use normal chemical thrusters - Webb itself does this. This leaves slowing down as you approach the Webb as the main problem.  The Shuttle docked at about 3 cm/sec.  A 100 milli-newton thruster, acting on a 1000 kg spacecraft, can add or subtract this much velocity in about 300 seconds (5 minutes).  During this time the spacecraft will travel about 5 meters.  So a slow approach, especially given the low gravity gradient of L2, seems feasible.
Even assuming that a tanker can approach and dock on the shade-side without physically damaging it — how do you propose to protect that great, gaudy mirror and the just-as-important secondary mirror? Hubble had a cover to protect its optical components, but Webb’s mirrors are exposed even in the launch configuration - and the tanker brings along a cloud of propulsion byproducts (hypergol, argon/krypton ions, or a combination) when it arrives regardless of its approach trajectory or strategy.
Well, the center of the sun-shield on the sun side is where the Webb's own hypergol and monoprop thrusters are, and it uses them even after the mirror is deployed.  Since L2 has a good vacuum, reaction products will travel in straight lines. So if you approach from the direction of the sun, the mirror should be protected from reaction products for the same reason it's protected from sunlight.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: DaveS on 10/29/2021 06:13 pm
- and the tanker brings along a cloud of propulsion byproducts (hypergol, argon/krypton ions, or a combination) when it arrives regardless of its approach trajectory or strategy.
Exactly. After each service mission HST needed several months for the new components to offgas and all the crud from the shuttle to dissipate before any serious observation campaigns could begin. And that was with the HST Aperture Door (AD) closed the entire time.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 10/30/2021 07:39 am
Refuelling is the alternative to end-of-mission. Even a diminished performance at some wavelengths due to vented gases depositing on the mirror is better than zero performance. Hand-wringing over possible damage is pointless.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 10/30/2021 03:35 pm
1.  Attitude control is not a problem.  The combination of reaction wheels and ion thrusters (to keep the wheels unloaded) works well.  This has been proven on all-electric comsats (https://arc.aiaa.org/doi/pdf/10.2514/6.2018-2601).

2.  Translation in the two axes perpendicular to approach can use normal chemical thrusters - Webb itself does this. This leaves slowing down as you approach the Webb as the main problem.  The Shuttle docked at about 3 cm/sec.  A 100 milli-newton thruster, acting on a 1000 kg spacecraft, can add or subtract this much velocity in about 300 seconds (5 minutes).  During this time the spacecraft will travel about 5 meters.  So a slow approach, especially given the low gravity gradient of L2, seems feasible.

3. As as far as the impact of the ions on the sunshade, this clearly needs to be looked at.  The sunshade is covered with a layer of silicon, and the ion thrusters are generating inert gas, so it's likely not a problem.  Here is a video of an ion thruster acting on aluminum foil at close range (https://youtube.com/watch?v=hTlcYbIrgmQ).  No damage is apparent, but obviously a more formal study would be needed.
[Answers re-ordered to put like problems together]
1.  It is a problem.  This is not a stationary comsat, but spacecraft doing prox ops.  It has to be able to rotate and react quicker.  Reaction wheels are not used, thrusters are.  The spacecraft is going to weight much more than 1000kg.  3 cm/sec was final velocity and not approach.  The shuttle was braking.

Again, too slow to react.  JWST isn't stationary.  It is orbiting L2 and reacting to solar pressure

2.  No, the plumes from the other two axis will still affect the sunshield.

3.  The issue I was raising was charge and not pressure.

1:  JWST will be essentially stationary.  It orbits L2 with an orbit that takes 6 months and is larger than the moon's orbit (https://www.jwst.nasa.gov/content/about/orbit.html).  Complications from orbital dynamics show up when the final sequence takes more than a fraction of an orbit.  Since Webb's orbit is almost 3000 times longer than the Shuttle's, a refueler could approach much more slowly, up to about 3000 times more slowly if needed.  Reaction wheels and ion thrusters, even acting on a mass of 2-3 thousand kg (the mass of existing servicing satellites MEV-1 and MEV-2), are more than fast enough at this scale.

Solar pressure is not enough to cause a problem here.  The Webb sunshade is about 200 m^2.  The solar power incident upon it is about 3x10^5 watts, resulting in a force of about 2 milli-newtons (assuming it's perfectly reflective).  An ion thruster is about 100 milli-newtons, and so can easily compensate for any JWST motion caused by solar pressure.

2:  The Webb thrusters do exactly this, so the sunshade must already withstand it.

3:  In an ion engine, the outgoing ions are neutralized, otherwise any spacecraft with ion thrusters would accumulate an enormous charge.  And in any event, the Webb's sun-facing shield is coated with a conductive layer of doped silicon, precisely to prevent any charge from accumulating on the membrane.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: deadman1204 on 10/31/2021 03:43 pm
I think we should stop this conversation. Its obvious that some people are considering most likely scenarios vs pie in the sky idealism. We're just talking past him.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: lrk on 10/31/2021 05:52 pm

3:  In an ion engine, the outgoing ions are neutralized, otherwise any spacecraft with ion thrusters would accumulate an enormous charge.  And in any event, the Webb's sun-facing shield is coated with a conductive layer of doped silicon, precisely to prevent any charge from accumulating on the membrane.

That's not how an ion thruster works, there is a separate electron gun to dissipate the accumulated negative charge, but that doesn't thoroughly neutralize all the outgoing ions. 

I agree that this is pretty off topic - mods, could this discussion on refueling Webb be moved to a seperate thread? 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 11/01/2021 09:11 am
Earlier there was some speculation on an earlier launch, but I presume the date of December 18th still scheduled as is even with the prior Ariane 5 launch going off early?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 11/02/2021 07:02 pm

1: Reaction wheels and ion thrusters, even acting on a mass of 2-3 thousand kg (the mass of existing servicing satellites MEV-1 and MEV-2), are more than fast enough at this scale.

2:  The Webb thrusters do exactly this, so the sunshade must already withstand it.

3:  In an ion engine, the outgoing ions are neutralized, otherwise any spacecraft with ion thrusters would accumulate an enormous charge.  And in any event, the Webb's sun-facing shield is coated with a conductive layer of doped silicon, precisely to prevent any charge from accumulating on the membrane.

1.  no, not true. JWST IS orbiting L2 and is not stationary. 

2.  Wrong.  Webb's thrusters are not pointed at the sunshield.

3.  No, the exhaust is not completely neutralized.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 11/02/2021 07:03 pm
Earlier there was some speculation on an earlier launch, but I presume the date of December 18th still scheduled as is even with the prior Ariane 5 launch going off early?

That has no bearing on the spacecraft schedule once on site.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Zed_Noir on 11/02/2021 07:16 pm
Out of curiosity. How much will it cost to build a similar version of the JWST? Presuming the infrastructure exists to make new parts.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 11/02/2021 07:57 pm
Last post on a hypothetical Webb refueling mission:

It's certainly true that such a mission is entirely hypothetical, Webb was not designed for refueling, and it's not even launched and we don't know how well it will work. or what it might find.

But in about 10 years, assuming it's working well but running out of fuel, the exact same question will come up.  After all, it's a hugely expensive asset, and the question will be refuel or let it die and plan for a replacement. This is exactly what happened with the Hubble, when crewed servicing looked impossible for safety reasons.  A robot maintenance mission was seriously considered (https://www.space.com/579-study-hubble-robotic-repair-mission-costly.html), as was letting it die, but in the end a crewed mission was used. 

Assuming Webb works as designed, it should have as spectacular a scientific career as the Hubble, and the pressure to keep it going will be high.  So let's revisit this in about 10 years.  The issues will be exactly those we are discussing now.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: AS_501 on 11/02/2021 08:51 pm
Out of curiosity. How much will it cost to build a similar version of the JWST? Presuming the infrastructure exists to make new parts.

Good question.  Taking Ariane 5 out of the equation, it might be cheaper to build a performance-equivalent telescope with a much simpler (thus less costly) 6m monolithic mirror.  Perhaps the wider payload fairings on FH or SLS* would permit this?

*This a purely technical question, not meant to stir up anyone's wrath on SLS costs, etc.  :)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: AS_501 on 11/02/2021 09:00 pm
Two additional points:

-  Since JWST will have a 5 to 10 year lifespan, it won't turn out the shear volume of observations generated by HST.  Many interesting objects and phenomena will have to be ignored for the sake of time.

-  Since JWST is not astronaut-serviceable, it won't benefit from new-technology upgrades as was possible with HST.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: niwax on 11/02/2021 09:35 pm
Out of curiosity. How much will it cost to build a similar version of the JWST? Presuming the infrastructure exists to make new parts.

Good question.  Taking Ariane 5 out of the equation, it might be cheaper to build a performance-equivalent telescope with a much simpler (thus less costly) 6m monolithic mirror.  Perhaps the wider payload fairings on FH or SLS* would permit this?

*This a purely technical question, not meant to stir up anyone's wrath on SLS costs, etc.  :)

Same problem as reusing Shuttle hardware now, the project has been so long and convoluted that there isn't a warehouse full of assembly jigs and a trained workforce that could just knock another few out. Ideally, we'd set up a small production run anytime these complex projects are attempted, possibly even with a staggered launch so faults can be fixed. But that's not possible using a government budget, a big reason JWST and other programs run off course is the yearly budgeting.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ttle2 on 11/02/2021 09:42 pm
Out of curiosity. How much will it cost to build a similar version of the JWST? Presuming the infrastructure exists to make new parts.

Good question.  Taking Ariane 5 out of the equation, it might be cheaper to build a performance-equivalent telescope with a much simpler (thus less costly) 6m monolithic mirror.  Perhaps the wider payload fairings on FH or SLS* would permit this?

*This a purely technical question, not meant to stir up anyone's wrath on SLS costs, etc.  :)

I'm not at all sure a monolithic mirror would be that much (if at all) simpler and cheaper to build. No one has built a 6 m monolithic mirror operating at cryogenic temperatures. Herschel is the largest at 3.5 m, but because it operated at longer wavelengths, its surface accuracy requirements etc. are much lower.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 11/02/2021 09:55 pm

Good question.  Taking Ariane 5 out of the equation, it might be cheaper to build a performance-equivalent telescope with a much simpler (thus less costly) 6m monolithic mirror.  Perhaps the wider payload fairings on FH or SLS* would permit this?


Not true. 
a. A monolithic mirror would be too heavy.  And it would be more complex to fly.
b.  Even large follow ons to JWST are planned to be segmented.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 11/02/2021 09:57 pm
Ideally, we'd set up a small production run anytime these complex projects are attempted, possibly even with a staggered launch so faults can be fixed. But that's not possible using a government budget, a big reason JWST and other programs run off course is the yearly budgeting.


not true.  It has nothing to do with gov't budgets.  Just no need for many of them.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: AS_501 on 11/02/2021 10:23 pm

Good question.  Taking Ariane 5 out of the equation, it might be cheaper to build a performance-equivalent telescope with a much simpler (thus less costly) 6m monolithic mirror.  Perhaps the wider payload fairings on FH or SLS* would permit this?


Not true. 
a. A monolithic mirror would be too heavy.  And it would be more complex to fly.
b.  Even large follow ons to JWST are planned to be segmented.

"Monolithic" is obviously the wrong term.  Perhaps a segmented-mirror telescope that does not have to be unfurled?  Like Keck, albeit smaller.  You eliminate all those complex unfurling steps involving each segment.  I guess my fear is based on Galileo's high gain antenna, Lucy's solar array, etc.

PS:  I read somewhere that one of the designs of a JWST follow-on would have much larger aperture (segmented of course) and be robotically serviceable.

Thanks for the clarifications.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 11/02/2021 11:06 pm
  I guess my fear is based on Galileo's high gain antenna, Lucy's solar array, etc.

Not remotely related.  Especially Galileo's antenna.  See MGS solar array.

So counter your irrational fear, I give you MER A & B, MSL, M2020, Inspiration, TDRS A-G, TDRS H-M, Phoenix, Insight, O-Rex, HEXAGON, GAMBIT, CORONA, (and supposably RHYOLITE/MAGNUM/ORION, CANYON/VORTEX, LACROS/ONYX).  Spacecraft with very complex mechanisms and deployments.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 11/03/2021 08:24 am
A pretty apt name; it is quite logical to perform LUL during the.. lull between launch and arrival to SEL-2. (runs for cover).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: deadman1204 on 11/03/2021 03:14 pm

Good question.  Taking Ariane 5 out of the equation, it might be cheaper to build a performance-equivalent telescope with a much simpler (thus less costly) 6m monolithic mirror.  Perhaps the wider payload fairings on FH or SLS* would permit this?


Not true. 
a. A monolithic mirror would be too heavy.  And it would be more complex to fly.
b.  Even large follow ons to JWST are planned to be segmented.

"Monolithic" is obviously the wrong term.  Perhaps a segmented-mirror telescope that does not have to be unfurled?  Like Keck, albeit smaller.  You eliminate all those complex unfurling steps involving each segment.  I guess my fear is based on Galileo's high gain antenna, Lucy's solar array, etc.


JWST must be folded so that it can fit on the rocket. That is the real limiting factor. Anything beyond what can fit inside the rocket faring must be folded up.

I also think you're confusing/combining two different things. The mirror must be expanded, but so must the sunshield. They are 2 different systems, though both must be folded up to fit on the rocket. JWST has the big folded up heat shield so that it can be passively cooled. Otherwise it would only have a few years of coolant, and then be unable to work at those temperatures.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: AS_501 on 11/04/2021 01:13 am
  I guess my fear is based on Galileo's high gain antenna, Lucy's solar array, etc.

Not remotely related.  Especially Galileo's antenna.  See MGS solar array.

So counter your irrational fear, I give you MER A & B, MSL, M2020, Inspiration, TDRS A-G, TDRS H-M, Phoenix, Insight, O-Rex, HEXAGON, GAMBIT, CORONA, (and supposably RHYOLITE/MAGNUM/ORION, CANYON/VORTEX, LACROS/ONYX).  Spacecraft with very complex mechanisms and deployments.

Per Jim's point, you can add Gaia, the galaxy imaging probe.  It also had a complex sunshade deployment (successful).

PS:  Imagine being the Lead Design, Assembly and Test Engineers when a spacecraft of probe suffers a critical deployment failure.  "Did I miss something?"  "Did a do something wrong during a procedure?"  Occupational hazard, I guess.


Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: bolun on 11/13/2021 01:19 pm
https://twitter.com/daily_hopper/status/1455253490360590336
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 11/13/2021 04:00 pm
PS:  Imagine being the Lead Design, Assembly and Test Engineers when a spacecraft of probe suffers a critical deployment failure.  "Did I miss something?"  "Did a do something wrong during a procedure?"  Occupational hazard, I guess.


Back around 2007 or so I was in a briefing where we saw some proposals from Northrop Grumman (builder of the JWST) for much bigger optical telescope designs. They had even more unfolding parts. Many deployments. They had some video animations of these (which might be on the internet somewhere). I think this was before the Advanced Technology Large-Aperture Space Telescope (ATLAST) which then led to LUVOIR. Anyway, the NG people were asked some questions about the deployments and they were rather dismissive about it. Yeah, they know what they're doing, they've done lots of deployments before, etc., hinting that they've done this kind of stuff with classified spacecraft and it's not a big deal, don't worry about it.

I don't think this went over well with our experts. There's a kind of game that some of these contractors play where they imply that they've solved all the problems doing classified stuff, so you don't have to worry about it when they get hired to build a civilian system like Webb--ignoring the fact that the civilian system might be much more complicated and challenging in some ways than the classified system.* They use their classified experience as a tool to shut down discussion and to reassure. Don't worry your pretty little head...

It wasn't much later after that than Webb ran into technical and cost and schedule problems. I'm sure that the Northrop Grumman people would insist that none of that was their fault. But I can still remember the arrogance of those engineers.

By the way, ATLAST is here, and if anybody finds those videos for even larger telescope deployments, you should post them:

https://asd.gsfc.nasa.gov/ATLAST/






*Examples: Hubble had much higher pointing requirements than any NRO satellite. And JWST has much higher cryo requirements than any other spacecraft.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: baldusi on 11/15/2021 07:34 pm
PS:  Imagine being the Lead Design, Assembly and Test Engineers when a spacecraft of probe suffers a critical deployment failure.  "Did I miss something?"  "Did a do something wrong during a procedure?"  Occupational hazard, I guess.


Back around 2007 or so I was in a briefing where we saw some proposals from Northrop Grumman (builder of the JWST) for much bigger optical telescope designs. They had even more unfolding parts. Many deployments. They had some video animations of these (which might be on the internet somewhere). I think this was before the Advanced Technology Large-Aperture Space Telescope (ATLAST) which then led to LUVOIR. Anyway, the NG people were asked some questions about the deployments and they were rather dismissive about it. Yeah, they know what they're doing, they've done lots of deployments before, etc., hinting that they've done this kind of stuff with classified spacecraft and it's not a big deal, don't worry about it.

I don't think this went over well with our experts. There's a kind of game that some of these contractors play where they imply that they've solved all the problems doing classified stuff, so you don't have to worry about it when they get hired to build a civilian system like Webb--ignoring the fact that the civilian system might be much more complicated and challenging in some ways than the classified system.* They use their classified experience as a tool to shut down discussion and to reassure. Don't worry your pretty little head...

It wasn't much later after that than Webb ran into technical and cost and schedule problems. I'm sure that the Northrop Grumman people would insist that none of that was their fault. But I can still remember the arrogance of those engineers.

By the way, ATLAST is here, and if anybody finds those videos for even larger telescope deployments, you should post them:

https://asd.gsfc.nasa.gov/ATLAST/






*Examples: Hubble had much higher pointing requirements than any NRO satellite. And JWST has much higher cryo requirements than any other spacecraft.

NG failed to differentiate "will" from "shall" in the JWST specifications, they justified because "younger engineers are not aware of the difference" and then "there's not enough budget to correct it". Which if you ask me, is so ridiculous that I wouldn't have dared to write that on a comedy.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Targeteer on 11/17/2021 03:06 am
November 16, 2021
MEDIA ADVISORY M21-156
NASA Invites Media to Webb Telescope Science Briefings

NASA will hold two virtual media briefings Thursday, Nov. 18, on the science goals and capabilities of the James Webb Space Telescope.

Participants will preview how the world’s largest and most powerful space science telescope will build on the discoveries of other missions to answer fundamental questions about the universe and its origins. Participants will also discuss Webb’s four scientific instruments, designed to study a wide range of objects in space, from planets and stars to galaxies and dark energy.

The briefings will livestream on NASA TV, the NASA app, and the agency’s website. All times are provided in Eastern.

11 a.m. – Briefing on Webb’s science goals with the following participants:

    Greg Robinson, Webb program director, NASA Headquarters in Washington
    John Mather, Webb senior project scientist, NASA’s Goddard Space Flight Center in Greenbelt, Maryland
    Antonella Nota, Webb project scientist and head of the ESA (European Space Agency) office at the Space Telescope Science Institute
    Sarah Gallagher, science advisor to the president, Canadian Space Agency
    Klaus Pontoppidan, Webb project scientist, Space Telescope Science Institute
    Amber Straughn, Webb deputy project scientist for communications, Goddard

2 p.m. – Briefing on Webb’s science instruments with the following participants:

    Eric Smith, Webb program scientist, NASA Headquarters
    Lee Feinberg, Webb optical telescope element manager, Goddard
    Marcia Rieke, principal investigator for Webb’s Near-Infrared Camera, University of Arizona
    Pierre Ferruit, principal investigator for Webb’s Near-Infrared Spectrograph, ESA
    Gillian Wright, European principal investigator for Webb’s Mid-Infrared Instrument, U.K. Astronomy Technology Centre
    René Doyon, principal investigator for Webb’s Near-Infrared Imager and Slitless Spectrograph and Fine Guidance Sensor, University of Montreal

To participate by telephone, media must RSVP no later than two hours before the start of each briefing to Alise Fisher at: [email protected] Media and members of the public may also ask questions on social media using #NASAWebb.

NASA’s media accreditation policy for virtual and onsite activities is available online.

NASA’s Curious Universe podcast also will debut a special Webb mini-series Tuesday, Nov. 23, exploring the mission’s science, engineering, people, and launch. NASA will release episodes every Tuesday leading up to Webb’s Dec. 18 launch. The trailer is available online.

The Webb telescope, an international partnership with the European and Canadian space agencies, will explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe, and everything in between. Webb will reveal new and unexpected discoveries, and help humanity understand the origins of the universe and our place in it.

For more information about the Webb mission, visit:

https://nasa.gov/webb
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: SPKirsch on 11/22/2021 01:54 am
https://twitter.com/haygenwarren/status/1462527773302575111
Quote
After separating from an Ariane 5 rocket this December, the complex six-month-long commissioning process for the James Webb Space Telescope will begin.

I sat down with Keith Parrish, Observatory Manager, to discuss JWST's commissioning process ⬇️

https://www.nasaspaceflight.com/2021/11/commissioning-jwst-1/
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: zubenelgenubi on 11/23/2021 04:09 am
Moderator reminder:
Launch campaign content and discussion in the launch thread (https://forum.nasaspaceflight.com/index.php?topic=49417.0), in the European launch sub-forum.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: faramund on 11/23/2021 07:42 pm
I'm a frequent reader of the Economist, and while I think its very good, it does still make mistakes. I was reading their article of JWST (https://www.economist.com/science-and-technology/2021/11/23/a-new-eye-on-the-heavens (https://www.economist.com/science-and-technology/2021/11/23/a-new-eye-on-the-heavens) (but paywall)) and it had the following text:

The cloud of delay, meanwhile, has had silver linings. ...
There is also a chance that the wait will permit the telescope’s lifetime to be extended. It will probably use up the thruster fuel needed to keep it on station within a decade. In the past, that would have been that. In light of advances in space technology, however, NASA has installed an arrangement which would let a service vessel dock and offer a top-up.

I'd be very surprised if the Economist, just made this up, but maybe they misinterpreted something they'd been told, but what that was, I have no idea.

Although I found (https://space.stackexchange.com/questions/38389/is-it-possible-to-refuel-the-james-webb-space-telescope (https://space.stackexchange.com/questions/38389/is-it-possible-to-refuel-the-james-webb-space-telescope)) which states that the German wikipedia for JWST has an unsourced statement saying this. Maybe that's the source. Although that still leads to the question of what's that sources source.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 11/23/2021 08:17 pm
I'm a frequent reader of the Economist, and while I think its very good, it does still make mistakes. I was reading their article of JWST (https://www.economist.com/science-and-technology/2021/11/23/a-new-eye-on-the-heavens (https://www.economist.com/science-and-technology/2021/11/23/a-new-eye-on-the-heavens) (but paywall)) and it had the following text:

The cloud of delay, meanwhile, has had silver linings. ...
There is also a chance that the wait will permit the telescope’s lifetime to be extended. It will probably use up the thruster fuel needed to keep it on station within a decade. In the past, that would have been that. In light of advances in space technology, however, NASA has installed an arrangement which would let a service vessel dock and offer a top-up.


They only were going add a docking adapter.  There is no ability to refuel.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: whitelancer64 on 11/23/2021 08:42 pm

Good question.  Taking Ariane 5 out of the equation, it might be cheaper to build a performance-equivalent telescope with a much simpler (thus less costly) 6m monolithic mirror.  Perhaps the wider payload fairings on FH or SLS* would permit this?


Not true. 
a. A monolithic mirror would be too heavy.  And it would be more complex to fly.
b.  Even large follow ons to JWST are planned to be segmented.

"Monolithic" is obviously the wrong term.  Perhaps a segmented-mirror telescope that does not have to be unfurled?  Like Keck, albeit smaller.  You eliminate all those complex unfurling steps involving each segment.  I guess my fear is based on Galileo's high gain antenna, Lucy's solar array, etc.

PS:  I read somewhere that one of the designs of a JWST follow-on would have much larger aperture (segmented of course) and be robotically serviceable.

Thanks for the clarifications.

The mirror is not the issue. The two "wings" on the JWST primary mirror fold out on two hinges. The secondary mirror folds out on five.

The complexity is virtually entirely in the sunshade, which has nearly 600 moving parts.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 11/23/2021 09:01 pm
The complexity is virtually entirely in the sunshade, which has nearly 600 moving parts.

At the risk of being pedantic, I think it is useful to discuss what kind of complexity. I think you're primarily referring to mechanical complexity.

When I visited JWST at NG back around November 2019, we discussed with the program manager what was the most difficult part of the telescope to design. I forget most of the details, but he said that it was the connection points to the back of the mirrors. The thermal (cryo) requirements for that were extreme, so that was the most complex part of the telescope development.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: kessdawg on 11/23/2021 09:02 pm
I'm a frequent reader of the Economist, and while I think its very good, it does still make mistakes. I was reading their article of JWST (https://www.economist.com/science-and-technology/2021/11/23/a-new-eye-on-the-heavens (https://www.economist.com/science-and-technology/2021/11/23/a-new-eye-on-the-heavens) (but paywall)) and it had the following text:

The cloud of delay, meanwhile, has had silver linings. ...
There is also a chance that the wait will permit the telescope’s lifetime to be extended. It will probably use up the thruster fuel needed to keep it on station within a decade. In the past, that would have been that. In light of advances in space technology, however, NASA has installed an arrangement which would let a service vessel dock and offer a top-up.


They only were going add a docking adapter.  There is no ability to refuel.

Would anything prevent something like the Northrop Grumman Mission Extension Vehicle being used? That adds a thruster pack I think.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: whitelancer64 on 11/23/2021 09:20 pm
The complexity is virtually entirely in the sunshade, which has nearly 600 moving parts.

I think you're primarily referring to mechanical complexity.

As is AS_501, who I was replying to. Context is key.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: whitelancer64 on 11/23/2021 09:25 pm
The complexity is virtually entirely in the sunshade, which has nearly 600 moving parts.

At the risk of being pedantic, I think it is useful to discuss what kind of complexity. I think you're primarily referring to mechanical complexity.

When I visited JWST at NG back around November 2019, we discussed with the program manager what was the most difficult part of the telescope to design. I forget most of the details, but he said that it was the connection points to the back of the mirrors. The thermal (cryo) requirements for that were extreme, so that was the most complex part of the telescope development.

Note also: You said you asked what was most difficult to design, not what the most complex part of JWST is. Some things can be relatively simple, but fiddly to design.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbenton on 11/24/2021 05:05 am
I'm a frequent reader of the Economist, and while I think its very good, it does still make mistakes. I was reading their article of JWST (https://www.economist.com/science-and-technology/2021/11/23/a-new-eye-on-the-heavens (https://www.economist.com/science-and-technology/2021/11/23/a-new-eye-on-the-heavens) (but paywall)) and it had the following text:

The cloud of delay, meanwhile, has had silver linings. ...
There is also a chance that the wait will permit the telescope’s lifetime to be extended. It will probably use up the thruster fuel needed to keep it on station within a decade. In the past, that would have been that. In light of advances in space technology, however, NASA has installed an arrangement which would let a service vessel dock and offer a top-up.


They only were going add a docking adapter.  There is no ability to refuel.

Would anything prevent something like the Northrop Grumman Mission Extension Vehicle being used? That adds a thruster pack I think.

Someone asked this awhile back on the Hubble thread. The extreme pointing requirements of large space telescopes might preclude this approach:

When Hubble finally dies - and I hope that wont be for awhile - that's it; it's over. Money spent to refurbish Hubble would be better spent on  either new technology, more capable space telescopes or new technology, ground-based telescopes.

What about an MEV-style robotic service module to take over attitude control and allow for orbit raising?  The optics/instruments on Hubble are likely to outlast the reaction wheels and control systems by a fair margin. 

No.  Hubble's pointing accuracy needs to be sub milli-arcsecond which would be hard without the scope.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 11/24/2021 08:40 am
Would anything prevent something like the Northrop Grumman Mission Extension Vehicle being used? That adds a thruster pack I think.
Someone asked this awhile back on the Hubble thread. The extreme pointing requirements of large space telescopes might preclude this approach

He's suggesting the MEV to take over the thruster role. JWST doesn't achieve high level pointing with thrusters, just station-keeping and reaction-wheel de-saturation burns.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: kessdawg on 11/24/2021 03:28 pm
Right. I understand that Jim has mentioned issues with docking damaging the telescope, but from a layman's perspective potentially a degraded telescope would still be worth it? I'm not a scientist (rocket or otherwise) and I'm sure the professionals are considering this. Just asking for my own understanding.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbenton on 11/24/2021 04:21 pm
Would anything prevent something like the Northrop Grumman Mission Extension Vehicle being used? That adds a thruster pack I think.
Someone asked this awhile back on the Hubble thread. The extreme pointing requirements of large space telescopes might preclude this approach

He's suggesting the MEV to take over the thruster role. JWST doesn't achieve high level pointing with thrusters, just station-keeping and reaction-wheel de-saturation burns.

That's right, and neither does Hubble:
https://www.nasa.gov/content/goddard/hubble-space-telescope-pointing-control-system

I realized as I was typing that last night that pointing control didn't seem to me to fully answer the question, but I figured that maybe I was missing something obvious

Perhaps Lee Jay was suggesting that the added mass in a new place would be too much of a challenge for the onboard pointing system? As a complete layman myself, I'd assume that this could just require software upgrade (albeit, a complicated one) but I'm probably missing something.

There's also the issue of running out of helium coolant. WISE has had a fairly successful warm mission doing less demanding tasks (as did Spitzer). I have no idea if that's possible for JWST's instruments.
EDIT: I forgot that JWST's cooling systems don't work the way that the other telescopes I mentioned work. "Running out of coolant" might not be a concern at all.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: kdhilliard on 11/24/2021 05:51 pm
... There's also the issue of running out of helium coolant. ...

JWST's MIRI cryocooler doesn't actively consume helium, does it?
Is the concern leakage?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 11/24/2021 05:58 pm
Would anything prevent something like the Northrop Grumman Mission Extension Vehicle being used? That adds a thruster pack I think.
Someone asked this awhile back on the Hubble thread. The extreme pointing requirements of large space telescopes might preclude this approach

He's suggesting the MEV to take over the thruster role. JWST doesn't achieve high level pointing with thrusters, just station-keeping and reaction-wheel de-saturation burns.

That's right, and neither does Hubble:
https://www.nasa.gov/content/goddard/hubble-space-telescope-pointing-control-system

I realized as I was typing that last night that pointing control didn't seem to me to fully answer the question, but I figured that maybe I was missing something obvious

Perhaps Lee Jay was suggesting that the added mass in a new place would be too much of a challenge for the onboard pointing system? As a complete layman myself, I'd assume that this could just require software upgrade (albeit, a complicated one) but I'm probably missing something.

There's also the issue of running out of helium coolant. WISE has had a fairly successful warm mission doing less demanding tasks (as did Spitzer). I have no idea if that's possible for JWST's instruments.

Look at the question I was answering:

When Hubble finally dies - and I hope that wont be for awhile - that's it; it's over. Money spent to refurbish Hubble would be better spent on  either new technology, more capable space telescopes or new technology, ground-based telescopes.

What about an MEV-style robotic service module to take over attitude control and allow for orbit raising?  The optics/instruments on Hubble are likely to outlast the reaction wheels and control systems by a fair margin. 

Notice the "take over attitude control" part.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: deadman1204 on 11/24/2021 08:53 pm

Would anything prevent something like the Northrop Grumman Mission Extension Vehicle being used? That adds a thruster pack I think.
The thrusters used to approach, move away,  and maneuver would shred the sunshield. At that point the telescope would be worthless.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Redclaws on 11/24/2021 08:55 pm

Would anything prevent something like the Northrop Grumman Mission Extension Vehicle being used? That adds a thruster pack I think.
The thrusters used to approach, move away,  and maneuver would shred the sunshield. At that point the telescope would be worthless.

Really?  The sunshield can't handle the thruster firings required to approach?  Even if they're as small as possible?  It would be shredded?  Like so much confetti, no doubt.

Sorry, no.  Thruster firings can be incredibly small and gentle and largely pointed away from the shield.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 11/25/2021 12:04 am
This again? Just go read the rest of the thread before you start designing your own spacecraft.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: catdlr on 11/25/2021 06:57 am
Just background info....

James Webb Telescope Delayed Due to "Incident"

Quote
NASA announced that the James Webb Space Telescope's launch was postponed to no earlier than December 22nd due to an incident that occurred during launch prep. The anomaly was due to a clamp band that shook the telescope unexpectedly. NASA is verifying that JWST is safe to fly before proceeding.

00:00 Clamp band anomaly
01:37 Prior shaking events
02:29 Anomaly review and testing
03:29 Delay
04:00 Next Steps

https://youtu.be/IfLoayApkk4
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 11/26/2021 04:04 pm
[Edit: That said, potential repair missions on that scale seem off-topic for this thread. Even discussing a MEV life-extension seems to be pushing the edges too far. Creating a new topic for "JWST life-extension and repair mission concepts and speculation" is just a matter of clicking a button.]
OK, new thread created.  If mods could move over the existing life-extension posts, that would be great.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: daveglo on 11/29/2021 02:14 am
Webb telescope confirmed undamaged during clamp band release incident by Arianespace:

https://www.arianespace.com/corporate-news/testing-confirms-webb-telescope-on-track-arianespace-launch/

Key bit: "On Wednesday, Nov. 24, engineering teams completed these tests, and a NASA-led anomaly review board concluded no observatory components were damaged in the incident. A “consent to fuel” review was held, and NASA gave approval to begin fueling the observatory. Fueling operations will begin Thursday, Nov. 25, and will take about 10 days."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: SPKirsch on 11/30/2021 09:00 pm
https://twitter.com/ChrisG_NSF/status/1465735852982685702
Quote
With #JamesWebb's MIRI instrument, scientists will observe the universe in the mid-infrared. But MIRI requires a very cold temperature, just 6K. How will it get this cold & why is MIRI so important?

@haygenwarren & I talked with the NASA MIRI lead

https://www.nasaspaceflight.com/2021/11/jwst-miri-instrument/
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: bolun on 12/06/2021 05:35 pm
Webb fuelled for launch

https://www.esa.int/ESA_Multimedia/Images/2021/12/Webb_fuelled_for_launch

Quote
Webb’s propellant tanks were filled separately with 79.5 l of dinitrogen tetroxide oxidiser and 159 l hydrazine. Oxidiser improves the burn efficiency of the hydrazine fuel.

These propellants are extremely toxic so only a few specialists wearing Self-Contained Atmospheric Protective Ensemble, or ‘scape’ suits, remained in the dedicated fuelling hall for fuelling which took 10 days and ended on 3 December.

Quote
The next steps will start soon for ‘combined operations’. This is when specialists working separately to prepare Webb and Ariane 5 will come together as one team. They will place Webb atop its Ariane 5 launch vehicle and encapsulate it inside Ariane 5’s fairing.

Then, no longer visible, Webb, joined with its Ariane 5 launch vehicle will be transferred to the Final Assembly building for the final preparations before launch.

Image credit: ESA/CNES/Arianespace
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Star One on 12/06/2021 08:08 pm
Webb moved for fuelling #shorts - ESA:

https://youtu.be/ni-JnSucxXY
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: catdlr on 12/07/2021 02:18 am
Webb Journey to Space Part 5: Spacecraft Fueling

https://youtu.be/kQO7kY-xv8c
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/09/2021 08:59 pm
Just watched a presentation on Hubble to JWST. He had a bunch of slides, but I grabbed a few that are most relevant.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: bolun on 12/10/2021 09:34 am
Webb moved to meet Ariane 5 (https://www.esa.int/ESA_Multimedia/Images/2021/12/Webb_moved_to_meet_Ariane_5)

Quote
The James Webb Space Telescope was transferred to the final assembly building at Europe’s Spaceport in French Guiana on 7 December 2021, to meet its Ariane 5 launch vehicle.

Stowed inside a special 23-tonne transport container, Webb was protected and monitored throughout the transfer.

Ariane 5 was already moved to the same building on 29 November. Here, adjustable platforms allow engineers to access the launch vehicle and its payload.

The next steps are to hoist Webb to the upper platform which has been prepared so that Webb can be integrated on Ariane 5’s upper stage and then encapsulated inside Ariane 5’s specially adapted fairing.

Image credit: ESA/CNES/Arianespace
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 12/14/2021 09:14 pm
The BBC has an article with pictures of the Webb being lifted and placed on the rocket:

https://www.bbc.com/news/science-environment-59632757 (https://www.bbc.com/news/science-environment-59632757)

Edit - They didn't drop it.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: litton4 on 12/15/2021 09:10 am
In that article there is a comment that JWST launch has been pushed to NET 24th December due to an issue with interfacing the telescope to the launcher....

Confirmed?

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: eeergo on 12/15/2021 09:24 am
In that article there is a comment that JWST launch has been pushed to NET 24th December due to an issue with interfacing the telescope to the launcher....

Confirmed?

Yes: https://mobile.twitter.com/NASA/status/1470906003168411657
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: woods170 on 12/15/2021 09:24 am
In that article there is a comment that JWST launch has been pushed to NET 24th December due to an issue with interfacing the telescope to the launcher....

Confirmed?

Yes: https://spaceflightnow.com/2021/12/14/nasa-delays-launch-of-webb-telescope-to-no-earlier-than-dec-24/
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/15/2021 12:47 pm
IXPE had a similar problem.   This occasionally happens.  It usually is masked by the how soon the EGSE racks are allowed on the launch pad/launch platform and  timeframe to work the issue.  Also how good the spacecraft simulator is plays into it.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/15/2021 12:52 pm
https://forum.nasaspaceflight.com/index.php?topic=34584.msg1190422#msg1190422

The issue is between the rocket and the comm rack is the pad room
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 12/15/2021 05:12 pm
What an awesome Christmas present, it would be.

Incidentally... https://en.wikipedia.org/wiki/Ariane_1#Maiden_flight
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/15/2021 07:12 pm
What an awesome Christmas present, it would be.

A lot of the people involved were hoping to launch it and then go home to their families for Christmas. So I doubt they think this is awesome.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: etudiant on 12/15/2021 07:49 pm
What an awesome Christmas present, it would be.

A lot of the people involved were hoping to launch it and then go home to their families for Christmas. So I doubt they think this is awesome.

Guess I'd feel a lot better if the whole thing was put off a couple of weeks.
Let the staff enjoy the holidays and then come back refreshed to do a great job. After a 10 year delay, it is not that the schedule really matters.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/15/2021 08:09 pm
What an awesome Christmas present, it would be.

A lot of the people involved were hoping to launch it and then go home to their families for Christmas. So I doubt they think this is awesome.

Guess I'd feel a lot better if the whole thing was put off a couple of weeks.
Let the staff enjoy the holidays and then come back refreshed to do a great job. After a 10 year delay, it is not that the schedule really matters.

The logistics is too great
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: webdan on 12/15/2021 08:51 pm
https://forum.nasaspaceflight.com/index.php?topic=34584.msg1190422#msg1190422

The issue is between the rocket and the comm rack is the pad room

What a great thread to read. Thanks Jim!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Hobbes-22 on 12/16/2021 06:58 am
https://forum.nasaspaceflight.com/index.php?topic=34584.msg1190422#msg1190422

The issue is between the rocket and the comm rack is the pad room

For Ariane 5, the pad room is inside the launch table.

I've attached an old version of the Ariane 5 user guide that has this info - it's been removed from newer versions. The UG also has lots of detail on the interfaces we're talking about, between the spacecraft and the comm rack.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/16/2021 03:51 pm
A very funny and irreverent movie from some of the scientists working on JWST:

https://youtu.be/lrY04VPDg8I

Great outreach, in my opinion.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: etudiant on 12/16/2021 07:07 pm
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/16/2021 07:31 pm
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.nce.

That is wrong.  Also, most spacecraft don't have backups anyways.


frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.

Not going to change this type of mission
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 12/16/2021 07:34 pm
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
Most of the costs on the Webb had little to do with launch constraints.  Most of the costs were associated with building a telescope that has to be so precisely built and maintain its shape with the thermal environment it is operating in.  The cost of developing the cameras to operate in this environment has also been a major challenge.  Starship would not have changed that.  A telescope of that size and capability would have been incredibly expensive even if it didn't have to unfold on the way to its operational location.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: etudiant on 12/16/2021 07:48 pm
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
Most of the costs on the Webb had little to do with launch constraints.  Most of the costs were associated with building a telescope that has to be so precisely built and maintain its shape with the thermal environment it is operating in.  The cost of developing the cameras to operate in this environment has also been a major challenge.  Starship would not have changed that.  A telescope of that size and capability would have been incredibly expensive even if it didn't have to unfold on the way to its operational location.
Vehemently disagree with you. 
The vast bulk of the cost is paying for the marching army of non contributors that are part of the effort.
They need to get paid whether the project gets done or not.
The cost escalation of both Hubble and the JWST (or Sofia) are because of that.
Move fast and break things is good advice, even in science.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: deadman1204 on 12/16/2021 07:58 pm
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
What does spaceX have to do with any of this? NASA isn't even paying for the launch., so cost is irrelevant. Also, name basically ANY mission in the last 30 years that did have backups? There aren't any.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 12/16/2021 08:28 pm
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
Most of the costs on the Webb had little to do with launch constraints.  Most of the costs were associated with building a telescope that has to be so precisely built and maintain its shape with the thermal environment it is operating in.  The cost of developing the cameras to operate in this environment has also been a major challenge.  Starship would not have changed that.  A telescope of that size and capability would have been incredibly expensive even if it didn't have to unfold on the way to its operational location.
Vehemently disagree with you. 
The vast bulk of the cost is paying for the marching army of non contributors that are part of the effort.
They need to get paid whether the project gets done or not.
The cost escalation of both Hubble and the JWST (or Sofia) are because of that.
Move fast and break things is good advice, even in science.
Even if you are right on paying for an army of non-contributors, how would Starship have changed that on the Webb telescope?  They were still only going to build one.  The launch vehicle has had very little to do with the cost of it.

Before you disparage the people who worked on Webb, who exactly are the army of non-contributors?  Are the in NASA, Northrup Grumman?  And what were they twittering away their time on?  I'd like to hear about an example?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/16/2021 08:34 pm
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
Most of the costs on the Webb had little to do with launch constraints.  Most of the costs were associated with building a telescope that has to be so precisely built and maintain its shape with the thermal environment it is operating in.  The cost of developing the cameras to operate in this environment has also been a major challenge.  Starship would not have changed that.  A telescope of that size and capability would have been incredibly expensive even if it didn't have to unfold on the way to its operational location.
Vehemently disagree with you. 
The vast bulk of the cost is paying for the marching army of non contributors that are part of the effort.
They need to get paid whether the project gets done or not.
The cost escalation of both Hubble and the JWST (or Sofia) are because of that.
Move fast and break things is good advice, even in science.
Even if you are right on paying for an army of non-contributors, how would Starship have changed that on the Webb telescope?  They were still only going to build one.  The launch vehicle has had very little to do with the cost of it.

Before you disparage the people who worked on Webb, who exactly are the army of non-contributors?  Are the in NASA, Northrup Grumman?  And what were they twittering away their time on?  I'd like to hear about an example?

I've learned over time that it's not necessary to respond to certain posts.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/16/2021 08:51 pm

Vehemently disagree with you. 
The vast bulk of the cost is paying for the marching army of non contributors that are part of the effort.
They need to get paid whether the project gets done or not.
The cost escalation of both Hubble and the JWST (or Sofia) are because of that.
Move fast and break things is good advice, even in science.

Completely clueless
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/16/2021 11:04 pm
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

The sunshield on JWST is 220m^2.  We’ve successfully deployed similar thin-membranes in space at that scale, like the NanoSail-D2 solar sail at 110m^2.

JWST’s primary mirror only folds into three sections.  And each of those three sections has independently actuated mirror subassemblies to correct inaccuracies and distortions.

The secondary mirror and solar panel deployments are old hat.

Quote
frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.

The diameter of SS is 9m.  Even the shorter length of JWST’s sunshield is 10m.  It just won’t fit without folding.

JWST costs ~$10 billion (with a “b”).  The Ariane V that JWST is launching on goes for about $200 million (with an “m”), and ESA is providing the launch in-kind.  Even if SS launches were available at $2 million per and NASA was paying $200 million for that Ariane V, moving to SS would only save $198 million, or less than 2% of JWST’s cost.  While lower cost and better launch is important to a lot of space missions and applications, SS won’t change the economics of a mission like JWST.

Vehemently disagree with you. 
The vast bulk of the cost is paying for the marching army of non contributors that are part of the effort.
They need to get paid whether the project gets done or not.
The cost escalation of both Hubble and the JWST (or Sofia) are because of that.

HST and JWST suffered from poor cost estimates.  HST further suffered from bad optics that were later corrected.  SOFIA suffered from poor engineering and management from concept thru operation.  None suffered from “non-contributors”.  There is no doubt a lot of underutilized workforce at NASA, but the Space Science Enterprise/Directorate has not had that problem since the late 90s/early 00s when its budget was nearly doubled.  In some places these days, there’s too much work.

Quote
Move fast and break things is good advice, even in science.

There are places to move faster, try new things, and even break instruments in NASA space science.  But they’re done in labs, suborbitally, or on smaller space missions, not flagship-scale missions.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/17/2021 06:07 am
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
Most of the costs on the Webb had little to do with launch constraints.  Most of the costs were associated with building a telescope that has to be so precisely built and maintain its shape with the thermal environment it is operating in.  The cost of developing the cameras to operate in this environment has also been a major challenge.  Starship would not have changed that.  A telescope of that size and capability would have been incredibly expensive even if it didn't have to unfold on the way to its operational location.

But a fixed main mirror and a fixed sunshield, had the fairing been sufficiently roomy, would reduce the risk factor considerably. Maybe the telescope would have cost only 1/3 less but its chance of success would be much bigger, and that surely counts for a lot.

A fixed sunshield could probably be built with smaller dimensions and SpaceX could probably also design a bigger fairing for an expendable Starship. That way there would be perhaps one or two major deployments instead of the many complex ones we see now. 

Crossing fingers and eating peanuts. (Too much) Excitement guaranteed. It will be unbearable if it doesn't work out. Not just for the loss of science but also because it will harden the resistance to big science. Many elected representatives will be swayed from funding future missions if this one fails. 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 12/17/2021 06:31 am
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
Most of the costs on the Webb had little to do with launch constraints.  Most of the costs were associated with building a telescope that has to be so precisely built and maintain its shape with the thermal environment it is operating in.  The cost of developing the cameras to operate in this environment has also been a major challenge.  Starship would not have changed that.  A telescope of that size and capability would have been incredibly expensive even if it didn't have to unfold on the way to its operational location.

But a fixed main mirror and a fixed sunshield, had the fairing been sufficiently roomy, would reduce the risk factor considerably. Maybe the telescope would have cost only 1/3 less but its chance of success would be much bigger, and that surely counts for a lot.

A fixed sunshield could probably be built with smaller dimensions and SpaceX could probably also design a bigger fairing for an expendable Starship. That way there would be perhaps one or two major deployments instead of the many complex ones we see now. 

Crossing fingers and eating peanuts. (Too much) Excitement guaranteed. It will be unbearable if it doesn't work out. Not just for the loss of science but also because it will harden the resistance to big science. Many elected representatives will be swayed from funding future missions if this one fails.
A fixed sunshade would not have been any smaller.  It is sized for just how big it needs to be to keep the telescope cold enough.  And fully deployed with layers separated it might not survive the launch forces stretched out.  It is very fragile.  Packed up protects the thin film and support structure better during the high vibration and acceleration of launch.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: woods170 on 12/17/2021 07:05 am

The secondary mirror and solar panel deployments are old hat.


Emphasis mine.

I'll be very blunt here: I don't ever want to hear you say that again.
Solar array deployment failures and boom-type deployment failures constitute ~70 percent of all deployment failures on spacecraft.

Also, there is quite a few engineers at Airbus D&S that will vehemently disagree with your statement. And the recent little mishap with Lucy guarantees that NG now also has engineers disagreeing with your statement.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/17/2021 08:44 am

The secondary mirror and solar panel deployments are old hat.


Emphasis mine.

I'll be very blunt here: I don't ever want to hear you say that again.
Solar array deployment failures and boom-type deployment failures constitute ~70 percent of all deployment failures on spacecraft.

Also, there is quite a few engineers at Airbus D&S that will vehemently disagree with your statement. And the recent little mishap with Lucy guarantees that NG now also has engineers disagreeing with your statement.

Now that you mention it, I'd rather like to live in the world where these things aren't nerve wracking moments for the mission engineers. It'd be great if there was a good way to go about that.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/17/2021 02:57 pm
Emphasis mine.

I'll be very blunt here: I don't ever want to hear you say that again.
Solar array deployment failures and boom-type deployment failures constitute ~70 percent of all deployment failures on spacecraft.

Around the world, literally hundreds of solar arrays and booms deploy successfully every year.  JWST’s solar array and secondary mirror are old hat from that perspective.  They’re also old hat compared to, say, JWST’s thermal blankets, where we have only a handful-ish of prior thin-membrane deployments.

That doesn’t take away from your points.  Engineers are human.  Once in a while we screw up.  And some systems are more prone to failures than others by the nature of the physics involved.  And so there needs to be effective checks and balances to minimize those human errors and doublecheck those error-prone systems.  We should never say, “Well, we don’t need to test the solar array deployment because that’s been done before.”

But to be clear, that’s not what I was saying or implying.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/17/2021 03:47 pm
What an awesome Christmas present, it would be.

A lot of the people involved were hoping to launch it and then go home to their families for Christmas. So I doubt they think this is awesome.

Guess I'd feel a lot better if the whole thing was put off a couple of weeks.
Let the staff enjoy the holidays and then come back refreshed to do a great job. After a 10 year delay, it is not that the schedule really matters.

The logistics is too great



https://spacenews.com/communications-problem-delays-jwst-launch/

"He added that more than 150 people from NASA are in Kourou to support the launch. “We have given to NASA to maximum visibility into our launcher.”

So that's 150 people who are being supported at the location. Flying them all home, then back again, would be difficult.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: etudiant on 12/17/2021 04:43 pm
Emphasis mine.

I'll be very blunt here: I don't ever want to hear you say that again.
Solar array deployment failures and boom-type deployment failures constitute ~70 percent of all deployment failures on spacecraft.

Around the world, literally hundreds of solar arrays and booms deploy successfully every year.  JWST’s solar array and secondary mirror are old hat from that perspective.  They’re also old hat compared to, say, JWST’s thermal blankets, where we have only a handful-ish of prior thin-membrane deployments.

That doesn’t take away from your points.  Engineers are human.  Once in a while we screw up.  And some systems are more prone to failures than others by the nature of the physics involved.  And so there needs to be effective checks and balances to minimize those human errors and doublecheck those error-prone systems.  We should never say, “Well, we don’t need to test the solar array deployment because that’s been done before.”

But to be clear, that’s not what I was saying or implying.

Apologize if what I said about the 'marching army of non contributors' is deemed offensive, but it remains true that the bulk of aerospace costs are government mandated administrative overheads. That is equally true for NASA as well as for military programs and helps understand why privately administered SpaceX was able to underprice ULA's Atlas by more than half.
Those administrative costs are annually recurring, add zip to the technology effort, just balloon the cost of any long term development effort such as the JWST. Any protracted development gets dragged down by this burden, so there is an inherent conflict between NASA's innovation mandate and their budget constraints. The miracle of the JWST is that it has survived despite this, but it sure would not have cost much extra to build two instead of just one.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/17/2021 04:45 pm
, but it remains true that the bulk of aerospace costs are government mandated administrative overheads. That is equally true for NASA as well as for military programs and helps understand why privately administered SpaceX was able to underprice ULA's Atlas by more than half.


That is wrong on many levels
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/17/2021 05:05 pm
Apologize if what I said about the 'marching army of non contributors' is deemed offensive, but it remains true that the bulk of aerospace costs are government mandated administrative overheads.  That is equally true for NASA as well as for military programs and helps understand why privately administered SpaceX was able to underprice ULA's Atlas by more than half.

It’s not that what you’re saying is offensive.  It’s that what you’re saying is not true and has nothing to do with JWST.

It is true that SX is largely vertically integrated, which means they don’t have a lot of external suppliers and subcontractors that need to show a profit margin.  It is true that this gives SX a pricing advantage vice horizontally integrated launch providers like ULA who have to feed the profit margins at many external suppliers and subcontractors.  It is _not_ true that this is due to “government mandated administrative overheads” (otherwise SX would suffer the same as a NASA and DOD contractor).  And it is _not_ true that this represents the “bulk of aerospace costs”.  And most importantly, the profit structure of launch providers like SX and ULA has _nothing to do_ with the costs of science spacecraft like JWST, which are built by neither.

Quote
it sure would not have cost much extra to build two instead of just one.

The production learning curve is nowhere near that steep.  A second copy of JWST would have cost billions of dollars.  It would easily have eaten the budget for the Roman space telescope that is to follow JWST.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: freddo411 on 12/17/2021 07:20 pm

it sure would not have cost much extra to build two instead of just one.

The production learning curve is nowhere near that steep.  A second copy of JWST would have cost billions of dollars.  It would easily have eaten the budget for the Roman space telescope that is to follow JWST.


I don’t believe the assertion that a copy would cost billions more.    Did the spirit and opportunity mission cost billions more than a single copy?  Compare the cost with the persy program.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/17/2021 07:24 pm
The production learning curve is nowhere near that steep.  A second copy of JWST would have cost billions of dollars.  It would easily have eaten the budget for the Roman space telescope that is to follow JWST.

Isn't Roman fundamentally, and considerably less capable than JWST?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/17/2021 07:29 pm
I don’t believe the assertion that a copy would cost billions more.    Did the spirit and opportunity mission cost billions more than a single copy?  Compare the cost with the persy program.

The two rovers cost about twice as much as a single rover. But comparing MER to JWST is a lousy comparison. JWST is a considerably more complex mission.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 12/17/2021 07:32 pm
Solar array deployment failures and boom-type deployment failures constitute ~70 percent of all deployment failures on spacecraft.
Around the world, literally hundreds of solar arrays and booms deploy successfully every year. 
Both of these statements are true.  Every year there are hundreds of deployments, and only a few fail.  But of those that fail, most are solar arrays or booms.

However, my worry level is much closer to Woods170.   The reason most deployments succeed is that the bugs have been worked out.  New deployment designs, even those very similar to existing designs, are much more likely fail (ask Lucy, or Galileo, or ...).  Webb has lots of one-off deployment mechanisms.  Sure, they are based on existing designs that are known to work.   But that's only mildly comforting - most designs that fail were also based on designs that worked.   And Webb adds designs without even this heritage, such as the quite complex sunshield deployment.  I guessing at least something will not deploy according to plan, and hope it's recoverable.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/17/2021 07:47 pm

it sure would not have cost much extra to build two instead of just one.

The production learning curve is nowhere near that steep.  A second copy of JWST would have cost billions of dollars.  It would easily have eaten the budget for the Roman space telescope that is to follow JWST.


I don’t believe the assertion that a copy would cost billions more.    Did the spirit and opportunity mission cost billions more than a single copy?  Compare the cost with the persy program.



MSL ans M2020
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/17/2021 08:16 pm

it sure would not have cost much extra to build two instead of just one.

The production learning curve is nowhere near that steep.  A second copy of JWST would have cost billions of dollars.  It would easily have eaten the budget for the Roman space telescope that is to follow JWST.


I don’t believe the assertion that a copy would cost billions more.   

It would have, just not quite as many billions.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/17/2021 08:17 pm
The production learning curve is nowhere near that steep.  A second copy of JWST would have cost billions of dollars.  It would easily have eaten the budget for the Roman space telescope that is to follow JWST.

Isn't Roman fundamentally, and considerably less capable than JWST?

No. Just very, very different. JWST is an IR scope. Roman is a wide field version of Hubble.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: deadman1204 on 12/17/2021 08:18 pm
I don’t believe the assertion that a copy would cost billions more.    Did the spirit and opportunity mission cost billions more than a single copy?  Compare the cost with the persy program.
There literally are not the facilities to build 2 JWST's at the same time. There also aren't the people. In fact, part of the delay for WFIRST (Nancy Grace), is that it needs the facilities and people that JWST has been using.

The comparison to spirit/opportunity is a bad one, because those were no where near as intricate. They also didn't cost over $11 billion for 1 of them. Consider JWST, it needs to be able to see something 13 billion light years away. We've NEVER built anything that exquisitely sensitive before. You cannot simply slap something together to do that. It needs to work, and you need to be able to prove that its working correctly.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/17/2021 09:58 pm
The production learning curve is nowhere near that steep.  A second copy of JWST would have cost billions of dollars.  It would easily have eaten the budget for the Roman space telescope that is to follow JWST.

I don’t believe the assertion that a copy would cost billions more.

You’ll save the design costs, but they’re only a small fraction of JWST’s total cost.  JWST development was $8.8B and another $0.9B is budgeted for operations.  That only leaves a few hundred million in design cost savings out of JWST’s ~$10B total cost.

The standard production learning curve is an 80% curve, which means that the cost of a copy comes down by 20% for every doubling of production.  80% of $8.8B is a little over $7B.  And we have to pay another $0.9B for the operations for that spacecraft.  And we have to pay for its launch on a second $200 million Ariane V that ESA is no longer providing in-kind.  So we’re looking at ~$8.1B (or thereabouts) for JWST II.  Even if the standard production learning curve is off by a factor of five or more (and it won’t be), we’re still looking at a multi-billion dollar (more than $2B) total cost for JWST II.

Using the standard production learning curve, we don’t get down below $1B for a JWST copy until we’ve produced over 2,000 of them at a cost north of $2.5 trillion (with a “t”).  Obviously, that’s not in the cards for multiple reasons.

Big constellations of thousands of satellites can reap the benefits of serial production because: 1) they’re building thousands of satellites, not one or a few, and 2) they’re starting from an initial build cost measured in the millions, not billions, of dollars.  That’s just not the case with one-off, flagship-scale science missions.

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Did the spirit and opportunity mission cost billions more than a single copy?

No, it’s a totally different scale of mission.  The total development cost of the two MERS rovers together was sub-billion ($744 million total).

Obviously, building JWST II will not magically make JWST I development cost less than the $8.8 billion that’s already been spent on it.

Isn't Roman fundamentally, and considerably less capable than JWST?

Yes and no.  Roman does not have JWST’s resolution and sensitivity, but JWST does not have Roman’s field of view for surveying large numbers of objects and events.  JWST will tell us what the very early universe looked like by staring really hard at small areas of the sky.  Roman will tell us what the habitable planetary population of our galaxy currently looks like by surveying millions of microlensing events and what the heck is going on with the runaway acceleration of the universe/dark energy by surveying oodles of supernovae standard candles in faraway galaxies.  They’re different tools for different jobs.

Roman is a ~$4B mission.  It would easily get eaten by an ~$8B JWST II.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/17/2021 10:01 pm
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
Most of the costs on the Webb had little to do with launch constraints.  Most of the costs were associated with building a telescope that has to be so precisely built and maintain its shape with the thermal environment it is operating in.  The cost of developing the cameras to operate in this environment has also been a major challenge.  Starship would not have changed that.  A telescope of that size and capability would have been incredibly expensive even if it didn't have to unfold on the way to its operational location.

But a fixed main mirror and a fixed sunshield, had the fairing been sufficiently roomy, would reduce the risk factor considerably. Maybe the telescope would have cost only 1/3 less but its chance of success would be much bigger, and that surely counts for a lot.

A fixed sunshield could probably be built with smaller dimensions and SpaceX could probably also design a bigger fairing for an expendable Starship. That way there would be perhaps one or two major deployments instead of the many complex ones we see now. 

Crossing fingers and eating peanuts. (Too much) Excitement guaranteed. It will be unbearable if it doesn't work out. Not just for the loss of science but also because it will harden the resistance to big science. Many elected representatives will be swayed from funding future missions if this one fails.
A fixed sunshade would not have been any smaller.  It is sized for just how big it needs to be to keep the telescope cold enough.  And fully deployed with layers separated it might not survive the launch forces stretched out.  It is very fragile.  Packed up protects the thin film and support structure better during the high vibration and acceleration of launch.

The thin film sunshade, I think, is bigger than a fixed one would be because it has the extraction booms beyond the area of the actual sunshade.

If it were a fixed sunshade it obviously would not be made out of fragile thin film layers. I imagine that it would rather be a sturdy, multi-layered honeycomb structure, with several pretty well thermically isolated layers. Maybe heavier but also much simpler than the contraption we have now, which makes me very nervous.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 12/18/2021 12:21 am
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
Most of the costs on the Webb had little to do with launch constraints.  Most of the costs were associated with building a telescope that has to be so precisely built and maintain its shape with the thermal environment it is operating in.  The cost of developing the cameras to operate in this environment has also been a major challenge.  Starship would not have changed that.  A telescope of that size and capability would have been incredibly expensive even if it didn't have to unfold on the way to its operational location.

But a fixed main mirror and a fixed sunshield, had the fairing been sufficiently roomy, would reduce the risk factor considerably. Maybe the telescope would have cost only 1/3 less but its chance of success would be much bigger, and that surely counts for a lot.

A fixed sunshield could probably be built with smaller dimensions and SpaceX could probably also design a bigger fairing for an expendable Starship. That way there would be perhaps one or two major deployments instead of the many complex ones we see now. 

Crossing fingers and eating peanuts. (Too much) Excitement guaranteed. It will be unbearable if it doesn't work out. Not just for the loss of science but also because it will harden the resistance to big science. Many elected representatives will be swayed from funding future missions if this one fails.
A fixed sunshade would not have been any smaller.  It is sized for just how big it needs to be to keep the telescope cold enough.  And fully deployed with layers separated it might not survive the launch forces stretched out.  It is very fragile.  Packed up protects the thin film and support structure better during the high vibration and acceleration of launch.

The thin film sunshade, I think, is bigger than a fixed one would be because it has the extraction booms beyond the area of the actual sunshade.

If it were a fixed sunshade it obviously would not be made out of fragile thin film layers. I imagine that it would rather be a sturdy, multi-layered honeycomb structure, with several pretty well thermically isolated layers. Maybe heavier but also much simpler than the contraption we have now, which makes me very nervous.
See the linked NASA page with a picture of the sun shield during a test deployment.  Very little extends beyond the actual shield.  So no a fixed shield would not be any smaller.

https://jwst.nasa.gov/content/observatory/sunshield.html (https://jwst.nasa.gov/content/observatory/sunshield.html)


Look at the cross section diagram of the shield and you will also see why the layers need to be thin for the rejection of heat out the side.  The very thin film is used because it is a design that can do the job by minimizing the heat storage capacity of each layer.  You want as much of the energy provided by solar radiation dumped out the side as fast as possible.  Any thicker layers would absorb more heat over time and make it harder to quickly reject heat out of the side of the shield.  The layers would get warmer and radiate more energy to the next layer complicating the problem.  You have to remember the cooling requirements are far beyond any spacecraft of this size ever built before.  This is a significantly different thermodynamic problem than reentry heat shields.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: freddo411 on 12/18/2021 01:24 am
The production learning curve is nowhere near that steep.  A second copy of JWST would have cost billions of dollars.  It would easily have eaten the budget for the Roman space telescope that is to follow JWST.

I don’t believe the assertion that a copy would cost billions more.

You’ll save the design costs, but they’re only a small fraction of JWST’s total cost.  JWST development was $8.8B and another $0.9B is budgeted for operations.  That only leaves a few hundred million in design cost savings out of JWST’s ~$10B total cost.

The standard production learning curve is an 80% curve, which means that the cost of a copy comes down by 20% for every doubling of production.  80% of $8.8B is a little over $7B.  And we have to pay another $0.9B for the operations for that spacecraft.  And we have to pay for its launch on a second $200 million Ariane V that ESA is no longer providing in-kind.  So we’re looking at ~$8.1B (or thereabouts) for JWST II.  Even if the standard production learning curve is off by a factor of five or more (and it won’t be), we’re still looking at a multi-billion dollar (more than $2B) total cost for JWST II.

Using the standard production learning curve, we don’t get down below $1B for a JWST copy until we’ve produced over 2,000 of them at a cost north of $2.5 trillion (with a “t”).  Obviously, that’s not in the cards for multiple reasons.

Big constellations of thousands of satellites can reap the benefits of serial production because: 1) they’re building thousands of satellites, not one or a few, and 2) they’re starting from an initial build cost measured in the millions, not billions, of dollars.  That’s just not the case with one-off, flagship-scale science missions.

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Did the spirit and opportunity mission cost billions more than a single copy?

No, it’s a totally different scale of mission.  The total development cost of the two MERS rovers together was sub-billion ($744 million total).

Obviously, building JWST II will not magically make JWST I development cost less than the $8.8 billion that’s already been spent on it.


Lumping all costs together into development is confusing the issue.   Clearly, it’s very expensive to figure out how to build JWST, this has zero to do with the production cost of the second copy.

The scale of MERS  and/or JWST has virtually nothing to do with the cost of making a second copy.  Why would it?

I don’t give much weight to your production learning curve heuristic in the JWST case.  It’s not really production ... it’s actually a bespoke one off.

No one in this thread has credibly argued that two copies of MERS cost anything like 2x the price of 1 MER.  It is plausible the simultaneously making 2 copies of JWST would have cost marginally more than making one.

Question to the thread:   Was there a ground based copy of JWST made?


Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/18/2021 05:17 am
Lumping all costs together into development is confusing the issue.

No one did that.  Spacecraft or mission costs are always divided into design, development, launch, and operations.  I separated those out upthread.  My figures come from the Planetary Society:

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The James Webb Space Telescope (JWST) is expected to cost NASA $9.7 billion over 24 years. Of that amount, $8.8 billion was spent on spacecraft development between 2003 and 2021; $861 million is planned to support five years of operations. Adjusted for inflation to 2020 dollars, the lifetime cost to NASA will be approximately $10.8 billion.

That is only NASA’s portion. The European Space Agency provided the Ariane 5 launch vehicle and two of the four science instruments for an estimated cost of €700 million. The Canadian Space Agency contributed sensors and scientific instrumentation, which cost approximately CA$200 million.

https://www.planetary.org/articles/cost-of-the-jwst

Design is really the only area where a second JWST build would incur zero costs, and it’s only measured in a few hundred million dollars.  After design, building the first copy of JWST cost NASA $8.8B plus ESA and CSA instrument and sensor contributions (that I forgot upthread), or around $9.5B total.  A second copy of JWST should cost less to build but it will still incur a significant fraction of that $9.5B cost.  More on that below.  And a second JWST will still pay the full freight of another $0.2B for an A5 launch and $0.9B in operations.

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Clearly, it’s very expensive to figure out how to build JWST, this has zero to do with the production cost of the second copy...

The cost of figuring out how to build the first copy of something is logarithmically related to with the cost of figuring out how to build the second copy (and additional copies) of the same thing.  This phenomenon — called the learning curve — has been noted, measured, characterized, and understood by engineers, economists, businessmen, and psychologists across multiple and varied industries since 1925, i.e., for almost a century.  It was instigated by observations about aircraft manufacturing.  Per the classic 1964 Harvard Business Review article:

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While the learning curve is a universal phenomenon, it has many variations in form; for example, there are great variations in the level at which a curve starts (i.e., the cost of the first unit). This is simply because of the different ranges of complexity of items. Nevertheless, the slope of the curve is common to a wide variety of experience. In fact, it was the regular finding of the common slope of about 80% for fighter, bomber, and transport planes that started speculation about a general theory of learning curves.  Further investigation showed that, although operations having essentially the same proportions of labor content have fairly common slopes, other operations differ in characteristics and corresponding slopes of curve.

Thus, operations paced by people have steeper slopes than those paced by machines. For example:

— In airframe manufacture three-fourths of the direct labor input is assembly; the balance is represented by men engaged in machine work. In such a largely man-paced operation, an 80% curve is commonly found.

— But when the proportion of assembly work is lower, the downward slope of the curve is not so steep. If the ratio of assembly to machine work is 50/50, the slope is about 85%. If the ratio is one-fourth assembly and three-fourths machine work, the operation is largely machine-paced, and the slope is around 90%.

These results might be expected since learning is related to people—the fewer the people, the less the capacity for learning.

https://hbr.org/1964/01/profit-from-the-learning-curve

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I don’t give much weight to your production learning curve heuristic in the JWST case.  It’s not really production ... it’s actually a bespoke one off.

As the HBR article describes, different industries have faster or slower learning curves based on the amount of labor involved in assembly versus machining.  The more assembly involved, the greater the opportunity for learning.  Big assemblies like aircraft have an ~80% learning curve.  JWST is certainly a big assembly.  Applying that 80% to the ~$9.5B cost to build JWST I yields a cost of $7.6B to build JWST II.

Getting more specific, according to this DOD-sponsored study from 2013 (see slide 23), satellite manufacturing has an learning curve of 87% to 91%.

http://www.iceaaonline.com/ready/wp-content/uploads/2017/09/M1-3_Presentation_LearningCurveAnalysisOfSmallDataSetsSpacecraftBusCostImprovementAnalysis_Welsh.pdf

Call it 89%.  Applying that to the ~$9.5B cost to build JWST I yields a cost of $8.5B to build JWST II.

Even the fastest learning manufacturing industry only has a 55% learning curve.  See Figure 2 in the classic Argote and Epple paper from 1990. 

https://abis-files.yildiz.edu.tr/avesis/f2a2efe0-365f-4805-9713-c8c8f4938c04?AWSAccessKeyId=6D327F5837HU474MD1QL&Expires=1639803263&Signature=ni0mxKaaGLlZojY5PxQfklE4DDU%3D

Applying that 55% to the ~$9.5B cost to build JWST I yields a cost of $5.2B to build JWST II.

Regardless of what real-world learning curve we apply, there’s nothing out there will drop the cost of a second build below $1B, as you posited upthread, starting from a multi-billion dollar first build cost like JWST.  Even if the build cost of JWST I was magically $2B and even if we could apply the fastest observed learning curve of 55%, it would still yield of cost of $1.1B for JWST II.  And to be clear, both those figures are pure fantasy and bear no relation to JWST’s actual build cost or the learning curve observed in aerospace or satellite manufacturing.

And we still have to add another $1.1B in launch and operations costs to any of these figures for the JWST II build.  So even our fantasy JWST II mission will still cost $2.2B total.

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The scale of MERS  and/or JWST has virtually nothing to do with the cost of making a second copy.  Why would it?

As explained above, the starting point for the cost of building the second copy of anything is the cost of building the first copy of that thing.

However, I don’t think learning curves apply much to MERS as the rovers were built in parallel, not serially.

A more relevant example might by the Mars Insight lander mission, which reused the design of the Mars Phoenix lander.  Phoenix cost $420M total, while Mars Insight was coming in at $675M total before its two-year launch delay.  So there were no huge savings from reusing the lander design, certainly not enough to offset the costs of the other differences between the two missions.

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No one in this thread has credibly argued that two copies of MERS cost anything like 2x the price of 1 MER.

MERS was budgeted and managed as one mission, so aside from Opportunity’s many mission extensions over Spirit, you won’t find separate costs for each rover.

I covered NASA Space Science at OMB at the time the decision was made to fund two MERS rovers.  The decision to fund two MERS rovers was driven by the desire to insure against unknown unknowns in the wake of the failure of the Mars Climate Orbiter and Mars Polar Lander missions.  It had nothing to do with cost savings.  We did not expect any.

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It is plausible the simultaneously making 2 copies of JWST would have cost marginally more than making one.

If by “plausible” you mean that the cost of building JWST II would be less than $1 billion (as you posited upthread), no, it’s not plausible.  Even using a fantasy cost for building JWST I and using a fantasy learning curve from outside the aerospace sector, a serially built, second JWST II would still be multiple billions of dollars.

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Question to the thread:   Was there a ground based copy of JWST made?

Nope.  As shown by Roman development, NRO has built multiple copies of HST-class observatories to look at the Earth.  But that’s all black budget, so there’s no way to access or share those figures.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: KaarlisK on 12/18/2021 06:50 am
If I may ask (and I'm not sure if this is at all on topic), how did launching two MERs at the same time insure against unknown unknowns?
I can see it helping against known unknowns (hitting orbital debris on the way or similar). But one would expect unknown unknowns to impact both.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: bolun on 12/18/2021 12:50 pm
Webb encapsulated inside Ariane 5

18/12/2021

The James Webb Space Telescope is confirmed for the target launch date of 24 December, at 12:20 GMT / 13:20 CET.

Late yesterday, teams at the launch site successfully completed encapsulation of the observatory inside the Ariane 5 rocket that will launch it to space. Webb’s launch final readiness review will be held on Tuesday 21 December and, if successful, roll-out is planned for Wednesday 22 December.

https://www.esa.int/ESA_Multimedia/Images/2021/12/Webb_encapsulated_inside_Ariane_5

Image credit: ESA-Manuel Pedoussaut
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: freddo411 on 12/18/2021 01:17 pm
If I may ask (and I'm not sure if this is at all on topic), how did launching two MERs at the same time insure against unknown unknowns?
I can see it helping against known unknowns (hitting orbital debris on the way or similar). But one would expect unknown unknowns to impact both.

It's fair to say that a design flaw in one copy would also be in the other.   

Note that they didn't launch at exactly the same time, so things that happened to the first rover might inform operation of the second rover.  Sometimes a work around can allow the second copy to function adequately once the flaw becomes apparent in the first.

Also consider randomness.   Some design flaws don't manifest until specific, perhaps rare, events happen.   For example, the tiles on the shuttle causing failure.    So having two copies might allow one to survive

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: freddo411 on 12/18/2021 01:43 pm

However, I don’t think learning curves apply much to MERS as the rovers were built in parallel, not serially.

A more relevant example might by the Mars Insight lander mission, which reused the design of the Mars Phoenix lander.  Phoenix cost $420M total, while Mars Insight was coming in at $675M total before its two-year launch delay.  So there were no huge savings from reusing the lander design, certainly not enough to offset the costs of the other differences between the two missions.

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No one in this thread has credibly argued that two copies of MERS cost anything like 2x the price of 1 MER.

MERS was budgeted and managed as one mission, so aside from Opportunity’s many mission extensions over Spirit, you won’t find separate costs for each rover.

I covered NASA Space Science at OMB at the time the decision was made to fund two MERS rovers.  The decision to fund two MERS rovers was driven by the desire to insure against unknown unknowns in the wake of the failure of the Mars Climate Orbiter and Mars Polar Lander missions.  It had nothing to do with cost savings.  We did not expect any.


I appreciate your thoughtful reply and references. 

I intentionally reference the MERS rovers because it is an excellent example of my point; namely that producing two copies of a design *in parallel* costs only marginally more than producing one copy.   

As to the reason to make a second copy, it's not a cost saving measure ( in fact it obviously costs a bit more) it's to provide contingencies -- as you say above about MERS.

Addressing some of your comments:

* "development" as a category of expenses in these NASA missions is broad.   It covers much, much more than simply producing and assembling hardware.   Is it not clear that producing #2 in parallel isn't 2x the development budget category?   To your points, in the case of JWST maybe actual cost to make #2 might be $1 or $2 or $4 billion ... but there isn't enough information to say with certainty.  Even if you'd like to apply the learning curve heuristics, you'd need to know the dollars spent on production and assembly which aren't broken out.

* I acknowledge that actually launching and operating a second telescope would have significant expenses.   That's a separate issue from producing a second copy in parallel.


Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/18/2021 01:49 pm
I intentionally reference the MERS rovers because it is an excellent example of my point; namely that producing two copies of a design *in parallel* costs only marginally more than producing one copy.   

But it doesn't prove that. You have provided no proof that it does.

You're making silly arguments. For starters, there were not duplicate facilities to produce two JWSTs at the same time. When the mirrors were assembled at Goddard there was only one clean room big enough to handle it, and it was built back in the 1980s. If you wanted to build two JWSTs, you'd have to build another whole new clean room. If anything, producing two would cost more because it would require additional facilities.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: freddo411 on 12/18/2021 02:09 pm
I intentionally reference the MERS rovers because it is an excellent example of my point; namely that producing two copies of a design *in parallel* costs only marginally more than producing one copy.   

But it doesn't prove that. You have provided no proof that it does.

You're making silly arguments. For starters, there were not duplicate facilities to produce two JWSTs at the same time. When the mirrors were assembled at Goddard there was only one clean room big enough to handle it, and it was built back in the 1980s. If you wanted to build two JWSTs, you'd have to build another whole new clean room. If anything, producing two would cost more because it would require additional facilities.

The MERS program produced two rovers.   The cost definitively is in the range of other missions (less than some, more than others).    That's the argument.   Not a proof.      You haven't proved otherwise.

Producing the parts for the JWST copy would not require the specific clean room at Goddard.   Final assembly of #2 could occur in another existing clean room facility, in a newly built facility, or in the Goddard facility after #1 was complete.


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You're making silly arguments.


This doesn't add to the discussion here.



Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ulm_atms on 12/18/2021 02:33 pm
I intentionally reference the MERS rovers because it is an excellent example of my point; namely that producing two copies of a design *in parallel* costs only marginally more than producing one copy.   

But it doesn't prove that. You have provided no proof that it does.

You're making silly arguments. For starters, there were not duplicate facilities to produce two JWSTs at the same time. When the mirrors were assembled at Goddard there was only one clean room big enough to handle it, and it was built back in the 1980s. If you wanted to build two JWSTs, you'd have to build another whole new clean room. If anything, producing two would cost more because it would require additional facilities.

The MERS program produced two rovers.   The cost definitively is in the range of other missions (less than some, more than others).    That's the argument.   Not a proof.      You haven't proved otherwise.

Producing the parts for the JWST copy would not require the specific clean room at Goddard.   Final assembly of #2 could occur in another existing clean room facility, in a newly built facility, or in the Goddard facility after #1 was complete.


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You're making silly arguments.


This doesn't add to the discussion here.

Blackstar, well, he is one of those people on here that I give way more weight to then most on this forum...especially on the NASA science front.  I have learned what he says is truth 99.99% of the time.

If NASA built a NEW clean room for a specific payload to make two, you now have the operations and maintenance funds that now have to be spent to keep the new facility going on top of actually building the new facility.  You also then have to hire/train double the people for building the second one as I bet the people building the first one would like days off.  Then it has to be launched on a rocket which this time requires payment and not a trade like JWST did with ESA.  All this really starts adding up over the decades with two in parallel.

The problem with JWST is that it was something never done before so more $$$ then something that has been done multiple times.  Add a second in process at the same time, and if you hit issues (and JWST did hit issues over the years)....you now have to redo/fix/test two full sets.  It really does snowball over the time frame JWST has lived in.

If the 1st one cost $8.8B to build, I can see the second one costing a little less but not sub $1B less (my guess...$5-6B not including launch and operation after launch).

Remember...JWST cost's exploded from what was proposed...I'm pretty sure a second/parallel one would have the same issue over all this time.

And for the MERS convo....A robot (for which NASA and all the world have made A LOT of) is fundamentally easier then a never before done IR telescope that is basically the most complicated origami'd device ever conceived and requires a precision that the robots/rovers don't even come close too.  If you want an apple to apple comparison...use JWST and Hubble programs to compare...that would be a lot closer to compare to.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/18/2021 03:52 pm

Producing the parts for the JWST copy would not require the specific clean room at Goddard.   Final assembly of #2 could occur in another existing clean room facility, in a newly built facility, or in the Goddard facility after #1 was complete.



There isn't another equivalent facility. The remaining options all costs significantly more money.

MER is not a relevant example because they were produced simultaneously.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/18/2021 03:57 pm

Note that they didn't launch at exactly the same time, so things that happened to the first rover might inform operation of the second rover.  Sometimes a work around can allow the second copy to function adequately once the flaw becomes apparent in the first.

Also consider randomness.   Some design flaws don't manifest until specific, perhaps rare, events happen.   For example, the tiles on the shuttle causing failure.    So having two copies might allow one to survive

10 days apart is " exactly the same time" for this discussion.  Both vehicles were completed at the same time.  The second one just dwelled in the facility a little longer.  The launch period didn't allow for any fixes.

The reason for two was to increase the chance of mission success.   And not to avoid inherent design flaws.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/18/2021 04:09 pm
If I may ask (and I'm not sure if this is at all on topic), how did launching two MERs at the same time insure against unknown unknowns?

Because unexpected/uncontrollable exogenous events could sideline one rover before mission complete but not the other.  Examples include a rare Atlas launch failure, a bad event upset en route, or getting especially unlucky landing terrain.  In the early days of the planetary program, NASA sent duplicate landers to the Moon to deal with similar unknown unknowns and help ensure success during the space race with the Soviets.  We similarly wanted to help ensure a Mars Exploration Program success and get the program back on track after the twin MCO and MPL failures.

Both MERS rovers were successful in their planned mission.  But exogenous conditions during the mission extensions — Spirit’s wheels getting stuck in soft ground — did sideline Spirit nine years before Opportunity was also lost.  By buying two rovers, that’s the kind of thing we were insuring NASA and the program against during the planned mission.

Two rovers was Administrator Dan Goldin’s idea (or at least he made the argument to us).  We agreed.

Quote
I can see it helping against known unknowns (hitting orbital debris on the way or similar).  But one would expect unknown unknowns to impact both.

There are unknown unknowns that would have impacted both.  Planet-wide dust storm of the kind that likely took down Opportunity, for example.  But there’s a lot that wouldn’t.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/18/2021 04:37 pm
There isn't another equivalent facility. The remaining options all costs significantly more money.

Anyway, the big clean room at Goddard is unique. It was originally designed to do simultaneous processing of two Hubble-sized shuttle payloads. The assumption was that shuttle would be flying so often that Goddard would have to do a lot of payload processing. Of course, that never happened. But because it is so big--designed for two payloads--it could handle JWST.

Now we were told back around 2017 or so that the facility was designed with, I think, a 40-year lifetime. At that point, they're going to have to take apart all the filters and scrubbing systems and replace them. Major facility overhaul. I'm guessing that's coming up really soon.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/18/2021 05:12 pm
I intentionally reference the MERS rovers because it is an excellent example of my point; namely that producing two copies of a design *in parallel* costs only marginally more than producing one copy.

MERS doesn’t prove that because we don’t have a cost breakdown for each rover’s build.  We don’t know if the cost split is 50/50 or 90/10 or something else.

As I recall, going with two rovers basically doubled the cost of the MERS mission.  If I’m recalling correctly, that would indicate that the cost split was closer to 50/50.  The fact that Mars Insight cost more than Mars Phoenix despite reusing Phoenix lander design also indicates that the cost split on these second builds is closer to 50/50.  And a century of data on the learning curve also indicates that the cost split is closer to 50/50 for second builds of large aerospace assemblies or satellites.  The most we can realistically hope to save on the second build is ~20% over the first build.

To be clear, as other have pointed out, we could not build parallel JWSTs like we did with the (much smaller) MERS rovers.  The facilities don’t exist for that.  Paying for a second set of facilities would balloon the cost of a JWST II build way past the cost of the JWST I build,

Quote
As to the reason to make a second copy, it's not a cost saving measure ( in fact it obviously costs a bit more) it's to provide contingencies -- as you say above about MERS.

Sure, but we could afford to do that on MERS.  It was a mission measured in the hundreds of millions of dollars.  I could make that work budgetarily without impacting other planetary missions.

NASA could not afford a JWST II.  It will have cost billions with a “b”.  Paying for it would have eaten two Roman space telescopes alive.  JWST I and II would have been the only astrophysics flagships in work for another couple decades.

Quote
* "development" as a category of expenses in these NASA missions is broad.   It covers much, much more than simply producing and assembling hardware.   Is it not clear that producing #2 in parallel isn't 2x the development budget category?   To your points, in the case of JWST maybe actual cost to make #2 might be $1 or $2 or $4 billion ... but there isn't enough information to say with certainty.  Even if you'd like to apply the learning curve heuristics, you'd need to know the dollars spent on production and assembly which aren't broken out.

Development is the build.  It is production and assembly.  All NASA (and DOD, etc.) space programs go through distinct phases marked by major review gates before proceeding to the next phase.  When NASA says “we’ve completed Critical Design Review [or whatever the review is]”, that means they’re largely done with the design phase and are ready to proceed with the development phase and bend metal or polish optics or whatever is needed to build the thing.  When NASA says “this is what we spent during development”, NASA is saying “this is what it cost to build this thing” (as opposed to design, launch, or operate it).

To be clear, there may be some long-lead items purchased during the design phase and there may be some redesign work going on during the development.  But to first order, development costs are build costs.  JWST experienced a lot of workmanship issues that could be avoided on a second build.  But the $9.5B cost of the first build, a century of data on the learning curve showing the best savings we can hope for on a second build are around ~20%, the example of the Phoenix/Insight landers, and just common sense tell us we’re not going to get the cost for the second build down around $1B or less.  There’s nothing that drops the cost of a second build by an order of magnitude (10x) over the cost of a first build.  It might have been closer to $7B or $9B, but the cost of a second JWST build would have been around $8B.

Finally, just to put this conversation to rest, the only other JWST cost breakdowns available don’t show any obvious, multi-billion dollar savings for a second build.  There’s this pie chart by program function:

https://www.spiedigitallibrary.org/ContentImages/Proceedings/10698/1069823/FigureImages/00171_PSISDG10698_1069823_page_2_1.jpg

Aside from “Mission Ops and Ground”, there’s no wedge on that pie chart that a second JWST build wouldn’t have to pay for.

And there’s this pie chart by subsystem/contract:

https://i.imgur.com/HSgw1yI.png

There’s a couple “Miscellaneous” categories and a “Technology Development” category that add up to about 10%.  But a second JWST build would have to pay for everything else.

EDIT/ADD:  I forgot to mention upstream... The Roman space telescope baselined the use of a donated Hubble-class telescope from the NRO and that hasn’t resulted in any big savings that made Roman cost a small fraction of its original estimates.  In fact, Roman has steadily gone up in cost.  The 2010 decadal survey estimate for what became Roman was $1.6B.  The initial 2015 NASA cost estimate for Roman that baselined the use of the donated NRO telescope was $2B.  Roman is now up to $3.9B after its preliminary design review and despite a major independent review and descope.  It’s not quite the same as a second build.  But the fact that Roman hasn’t seen any cost savings despite leveraging a prior, proven NRO design and build is a strong indication that a JWST II build wouldn’t see significant savings over the cost of building JWST.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/19/2021 12:29 am
Real Engineering has a nice rundown of the JWST:

https://www.youtube.com/watch?v=aICaAEXDJQQ
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/19/2021 01:54 am
The most common refrain in discussing the difficulties in developing James Webb have been the ultra complex, ultra precise systems that have to fit in a very tight mass budget: the mirrors, the mirror adjustment systems, the sun shield tensioners, the cryo coolers, and on and on that goes. At the same time, everyone who says "we should use more capable spacecraft so that mass constraints aren't such a vicious engineering problem for these things" gets shot down with "weight is not the problem!" So, somebody is not being truthful, and I am not enjoying trying to play the game of "guess who's full of crap."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: baldusi on 12/19/2021 02:05 am

Lumping all costs together into development is confusing the issue.   Clearly, it’s very expensive to figure out how to build JWST, this has zero to do with the production cost of the second copy.

The scale of MERS  and/or JWST has virtually nothing to do with the cost of making a second copy.  Why would it?

I don’t give much weight to your production learning curve heuristic in the JWST case.  It’s not really production ... it’s actually a bespoke one off.

No one in this thread has credibly argued that two copies of MERS cost anything like 2x the price of 1 MER.  It is plausible the simultaneously making 2 copies of JWST would have cost marginally more than making one.

Question to the thread:   Was there a ground based copy of JWST made?

You have to wrap your head around the fact that for one-off, you use a lot of ad-hoc production. Methods that are extremely handcrafted, to specifications that are never again required. So, specially with a decade long development, doing a second copy might well require rebuilding a whole factory, building a new one or paying one to be mothballed until it is equired again. In that time, people might have found new jobs, retired or even died. And it's not like you can ask anyone to have the craft to manufacture the parts to micron precision at 4Kelvin.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Exastro on 12/19/2021 02:19 am

Lumping all costs together into development is confusing the issue.   Clearly, it’s very expensive to figure out how to build JWST, this has zero to do with the production cost of the second copy.

You have to wrap your head around the fact that for one-off, you use a lot of ad-hoc production. Methods that are extremely handcrafted, to specifications that are never again required. So, specially with a decade long development, doing a second copy might well require rebuilding a whole factory, building a new one or paying one to be mothballed until it is equired again. In that time, people might have found new jobs, retired or even died. And it's not like you can ask anyone to have the craft to manufacture the parts to micron precision at 4Kelvin.


Seems like if you go through the whole JWST build process and then start over at the beginning for the second unit, the second one might well cost as much as the first if enough of the skills and intricate process details developed the first time through don't get preserved.  But if you simply build two of each part instead of one as you go along, that ought to should be greatly mitigated.  Or so I'd imagine.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Don2 on 12/19/2021 06:16 am
The rule of thumb for planetary probes built simultaneously is that building two costs 50% more than building one. This was mentioned in a study of ice giants missions from a few years ago which considered the possibility of building two identical spacecraft for Uranus and Neptune.

Applying that to JWST suggests a cost of $5 billion for a second one. However, some knowledgeable people here are insisting that there is no facility big enough to build two JWSTs side by side. Because JWST is a very big project then building a second one could lead to a shortage of people or facilities. A shortage would lead to price increases and that could result in the second one costing more than the first.

For instance, there probably isn't a huge amount of mirror grade beryillium available. The oxides are toxic and I believe it requires special facilities to machine.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/19/2021 06:56 am
The most common refrain in discussing the difficulties in developing James Webb have been the ultra complex, ultra precise systems that have to fit in a very tight mass budget: the mirrors, the mirror adjustment systems, the sun shield tensioners, the cryo coolers, and on and on that goes. At the same time, everyone who says "we should use more capable spacecraft so that mass constraints aren't such a vicious engineering problem for these things" gets shot down with "weight is not the problem!" So, somebody is not being truthful, and I am not enjoying trying to play the game of "guess who's full of crap."

Complexity drives cost on these scopes, and different things contribute to complexity.  Lack of large mass margins did drive some complexity on JWST.  But so did the insane 50K cooling requirement.  And so did the insane resolution of 2um (diffraction limited).  So, yes, using your favorite HLV would have relaxed some mass constraints and reduced some complexity.  But the biggest HLV in the world would not have relaxed the cooling and resolution constraints that were also driving JWST’s complexity higher and higher.  (As I joked in another thread, launching JWST on Starship doesn’t mean you could make JWST’s mirrors out of whatever stainless steel Starship uses.)

Complexity contributes to other costs, like marching army and ground tests.  But again, mass constraints were only one factor contributing to JWST’s complexity.  And no matter how big your LV, a project like JWST will have to keep experts and experienced technicians around for years and will have to do a lot of validation and verification to make sure everything works as advertised before it flies.  LV size can’t eliminate those cost centers.

You’re asking for a simple, either/or explanation.  Unfortunately, the accurate answer to these kinds of questions is a complex both/and explanation.  This paper gets into it a little more deeply and illustrates how different yet interconnected some of these factors can be.

https://ntrs.nasa.gov/api/citations/20180003980/downloads/20180003980.pdf

Hope this helps.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/19/2021 07:11 am
The most common refrain in discussing the difficulties in developing James Webb have been the ultra complex, ultra precise systems that have to fit in a very tight mass budget: the mirrors, the mirror adjustment systems, the sun shield tensioners, the cryo coolers, and on and on that goes. At the same time, everyone who says "we should use more capable spacecraft so that mass constraints aren't such a vicious engineering problem for these things" gets shot down with "weight is not the problem!" So, somebody is not being truthful, and I am not enjoying trying to play the game of "guess who's full of crap."

Complexity drives cost on these scopes, and different things contribute to complexity.  Lack of large mass margins did drive some complexity on JWST.  But so did the insane 50K cooling requirement.  And so did the insane resolution of 2um (diffraction limited).  So, yes, using your favorite HLV would have relaxed some mass constraints and reduced some complexity.  But the biggest HLV in the world would not have relaxed the cooling and resolution constraints that were also driving JWST’s complexity higher and higher.  (As I joked in another thread, launching JWST on Starship doesn’t mean you could make JWST’s mirrors out of whatever stainless steel Starship uses.)

Complexity contributes to other costs, like marching army and ground tests.  But again, mass constraints were only one factor contributing to JWST’s complexity.  And no matter how big your LV, a project like JWST will have to keep experts and experienced technicians around for years and will have to do a lot of validation and verification to make sure everything works as advertised before it flies.  LV size can’t eliminate those cost centers.

You’re asking for a simple, either/or explanation.  Unfortunately, the accurate answer to these kinds of questions is a complex both/and explanation.  This paper gets into it a little more deeply and illustrates how different yet interconnected some of these factors can be.

https://ntrs.nasa.gov/api/citations/20180003980/downloads/20180003980.pdf

Hope this helps.

Thanks for the link, it actually is very helpful. And, frustratingly, almost every single major cost driver in the system did, in fact, reduce to the lack of available reserve mass. I am earnestly frustrated at every claim that's suggested otherwise, because the entire design tradespace of JWST was wholly contingent on it, from the complex integrated cooling scheme to the complex engineering that pursued lightening of parts and clawing back mass reserves wherever possible. The story of JWST is one of complexity begotten by a lack of room for mass growth. The lack of sufficient, available testing facilities obviously didn't help, either.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/19/2021 12:29 pm
The rule of thumb for planetary probes built simultaneously is that building two costs 50% more than building one. This was mentioned in a study of ice giants missions from a few years ago which considered the possibility of building two identical spacecraft for Uranus and Neptune.

Having just done the planetary decadal survey, I would not put too much faith in that assertion.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/19/2021 12:43 pm
The lack of sufficient, available testing facilities obviously didn't help, either.

This is a limiting factor for anything bigger than existing fairing.  There are no assembly clean rooms large enough.  No thermovac chambers.  No easy method of transportation.  No processing facilities.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/19/2021 12:46 pm

Thanks for the link, it actually is very helpful. And, frustratingly, almost every single major cost driver in the system did, in fact, reduce to the lack of available reserve mass

Wrong, it does not say that.  It said "lack of system resources".  This is more than just mass.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 12/19/2021 12:53 pm
The most common refrain in discussing the difficulties in developing James Webb have been the ultra complex, ultra precise systems that have to fit in a very tight mass budget: the mirrors, the mirror adjustment systems, the sun shield tensioners, the cryo coolers, and on and on that goes. At the same time, everyone who says "we should use more capable spacecraft so that mass constraints aren't such a vicious engineering problem for these things" gets shot down with "weight is not the problem!" So, somebody is not being truthful, and I am not enjoying trying to play the game of "guess who's full of crap."

Complexity drives cost on these scopes, and different things contribute to complexity.  Lack of large mass margins did drive some complexity on JWST.  But so did the insane 50K cooling requirement.  And so did the insane resolution of 2um (diffraction limited).  So, yes, using your favorite HLV would have relaxed some mass constraints and reduced some complexity.  But the biggest HLV in the world would not have relaxed the cooling and resolution constraints that were also driving JWST’s complexity higher and higher.  (As I joked in another thread, launching JWST on Starship doesn’t mean you could make JWST’s mirrors out of whatever stainless steel Starship uses.)

Complexity contributes to other costs, like marching army and ground tests.  But again, mass constraints were only one factor contributing to JWST’s complexity.  And no matter how big your LV, a project like JWST will have to keep experts and experienced technicians around for years and will have to do a lot of validation and verification to make sure everything works as advertised before it flies.  LV size can’t eliminate those cost centers.

You’re asking for a simple, either/or explanation.  Unfortunately, the accurate answer to these kinds of questions is a complex both/and explanation.  This paper gets into it a little more deeply and illustrates how different yet interconnected some of these factors can be.

https://ntrs.nasa.gov/api/citations/20180003980/downloads/20180003980.pdf

Hope this helps.

Thanks for the link, it actually is very helpful. And, frustratingly, almost every single major cost driver in the system did, in fact, reduce to the lack of available reserve mass. I am earnestly frustrated at every claim that's suggested otherwise, because the entire design tradespace of JWST was wholly contingent on it, from the complex integrated cooling scheme to the complex engineering that pursued lightening of parts and clawing back mass reserves wherever possible. The story of JWST is one of complexity begotten by a lack of room for mass growth. The lack of sufficient, available testing facilities obviously didn't help, either.
NGST was originally an 8m diameter mirror with a 3300kg mass constraint. JWST today has relaxed to a 6.5m diameter mirror and 6800kg mass.
You can see what you want to see, but JWST's costs were driven by the precision required in the optics and instruments, and the operation at cryogenic temperatures. Hogging out the mirror backfaces or using low-mass trusses or etc were not the main cost drivers.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: bolun on 12/19/2021 01:17 pm
Dec 18, 2021

MEDIA ADVISORY M21-167

NASA Sets Coverage, Invites Public to View Webb Telescope Launch

NASA will provide coverage of prelaunch, launch, and postlaunch activities for the James Webb Space Telescope, the world’s largest and most powerful space science telescope.

Webb is targeted to launch at 7:20 a.m. EST Friday, Dec. 24, on an Arianespace Ariane 5 rocket from Europe’s Spaceport in Kourou, French Guiana, on the northeastern coast of South America.

Live launch coverage in English will begin at 6 a.m. on NASA TV, the NASA app, and the agency’s website. The public can also watch live on Facebook, Twitter, YouTube, Twitch, and Daily Motion. NASA also will offer a launch broadcast in Spanish beginning at 6:30 a.m. on the agency’s website and Spanish-language social media accounts. NASA will hold a prelaunch media briefing at 2 p.m. on Tuesday, Dec. 21, and a postlaunch news conference approximately 30 minutes after the live launch broadcast ends on Friday, Dec. 24.

The Webb mission, an international partnership with ESA (European Space Agency) and the Canadian Space Agency, will explore every phase of cosmic history – from within the solar system to the most distant observable galaxies in the early universe, and everything in between. Webb will reveal new and unexpected discoveries and help humanity understand the origins of the universe and our place in it.

Full mission coverage is as follows. All times are Eastern, and information is subject to change.

NASA Press Briefings

At 2 p.m. Tuesday, Dec. 21, NASA will hold a virtual prelaunch media briefing with the following participants:

- NASA Deputy Administrator Pam Melroy
- Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate, NASA Headquarters in Washington
- Greg Robinson, Webb program director, NASA Headquarters
- Beatriz Romero, Webb project director for launch services, Arianespace in Paris

On Friday, Dec. 24, approximately 30 minutes after Webb’s launch broadcast ends, a joint news conference will take place in Kourou.

Both briefings will stream on NASA TV, the NASA app, and the agency’s website.

To participate by telephone, media must RSVP no later than two hours before the start of each briefing to Laura Betz at: [email protected] Media and members of the public may also ask questions on social media using #UnfoldtheUniverse.

NASA’s media accreditation policy for virtual and onsite activities is available online.

NASA TV Launch Coverage in English

NASA TV live coverage will begin at 6 a.m. Friday, Dec. 24. For NASA TV downlink information, schedules, and links to streaming video, visit:

https://www.nasa.gov/live

On launch day, a “clean feed” of the launch without commentary will be available by satellite feed. The uplink will begin at 7 a.m. and continue for an hour after launch. The clean feed will also be available on the Washington AVOC.

Launch coverage audio will be available via this satellite feed as well, with audio channels for English-, French-, and Spanish-language launch commentary, as well as "mission audio" without commentary.

Please contact [email protected] to receive the satellite coordinates.

NASA Launch Coverage in English

Launch day coverage will be available on the agency’s website. Coverage will include livestreaming and blog updates. On-demand streaming video and photos of the launch will be available shortly after liftoff. Follow coverage online at:

https://blogs.nasa.gov/webb

NASA Launch Coverage in Spanish: Desplegando el Universo

Hosted by Begoña Vila, Webb instrument systems engineer, NASA’s broadcast of the launch in Spanish will include interviews with Hispanic members of the mission and live commentary from Kourou by Vila and ESA engineer Julio Monreal.

The show, which will begin at 6:30 a.m. Friday, Dec. 24, will be available on NASA en español’s YouTube, Twitter, and Facebook accounts, as well as on NASA’s website.

Media and educational institutions interested in sharing the stream of the show can contact María José Viñas at: [email protected]

The agency has also released the first episode of NASA’s Curious Universe podcast in Spanish. The episode, "Desplegando el universo con el telescopio espacial James Webb," is available on Apple Podcasts, Google Podcasts, and SoundCloud.

Media Interview Requests

Members of the media seeking interviews about Webb’s launch should fill out NASA’s request form.

Public Participation

Members of the public can register to attend launch virtually. NASA’s virtual guest program for the mission includes curated launch resources, notifications about related opportunities or changes, and a stamp for the NASA virtual guest passport following a successful launch.

Virtual NASA Social

As NASA prepares for Webb to #UnfoldTheUniverse, the agency invites the public to join the James Webb Space Telescope social event on Facebook. Participants will be joined by NASA, ESA, the Canadian Space Agency, and the Space Telescope Science Institute. Stay up to date on the latest mission activities, interact with Webb experts in real-time, and watch the live launch broadcast with an interactive chat.

Watch and Engage on Social Media

Stay connected with the mission and let people know you are following the launch on Twitter, Facebook, and Instagram with #UnfoldTheUniverse. Follow and tag these accounts:

Twitter: @NASA, @NASAWebb
Facebook: NASA, NASAWebb
Instagram: NASA, @NASAWebb
For more information about the Webb mission, visit:

https://nasa.gov/webb

-end-

https://www.nasa.gov/press-release/nasa-sets-coverage-invites-public-to-view-webb-telescope-launch
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/19/2021 04:36 pm
NGST was originally an 8m diameter mirror with a 3300kg mass constraint. JWST today has relaxed to a 6.5m diameter mirror and 6800kg mass.
You can see what you want to see, but JWST's costs were driven by the precision required in the optics and instruments, and the operation at cryogenic temperatures. Hogging out the mirror backfaces or using low-mass trusses or etc were not the main cost drivers.

The cost drivers in JWST almost all reduce to the extremely complex interplay between the instruments and the spacecraft bus, and the spacecraft bus and its sunshield ate up the lion's share of the budget. That complexity could have been avoided with heavier solutions.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/19/2021 04:39 pm
Thanks for the link, it actually is very helpful. And, frustratingly, almost every single major cost driver in the system did, in fact, reduce to the lack of available reserve mass.

No.  Mass constraints are a cost driver.  But they are not the only cost driver.  Read it again:

Quote
By having many simultaneous challenges, it made things more time consuming and expensive. For example, being a 50 Kelvin observatory adds the complexity of needing to design and test for these temperatures with all of the material property issues (eg, CTE, damping, etc) that come with this.
The additional factor though was that Webb needed to be diffraction limited at 2um which is slightly challenging by itself but even more so when you combine it with the need to be 50 Kelvin. In many ways, these requirements _along with the tight constraints on mass_ led to the choice of beryllium as the mirror material which was optimal for this temperature but requires more time and money for fabrication as the removal rates are slower and you have to control stresses. In addition, these combined requirements led to the need to cryo polish each mirror to remove the distortions of going cold. Had the system been diffraction limited at a longer wavelength or been warm, a faster material fabrication choice like ULE could have been usen and cryo polishing may not have been needed.

The paper mentions the stringent thermal requirement first.  Then it mentions the stringent requirement on resolution.  Only after that does it mention mass constraints, and then only in the context of the other two requirements.  Mass is a factor driving complexity, but it’s not the only factor or even the most important factor in that paper.

The complexity of the thermal and resolution requirements that drove JWST’s costs were magnified by mass constraints.  But it is false to claim that the thermal and resolution requirements could “reduce to the lack of available reserve mass.”

Quote
I am earnestly frustrated at every claim that's suggested otherwise, because the entire design tradespace of JWST was wholly contingent on it, from the complex integrated cooling scheme to the complex engineering that pursued lightening of parts and clawing back mass reserves wherever possible. The story of JWST is one of complexity begotten by a lack of room for mass growth.

No matter how much we relax mass constraints, keeping a scope that big at 50K for years in space is unprecedented and requires new and complex cooling systems.  We just can’t hook it up to my cheapo basement freezer and send it to L2.  No matter how much we relax mass constraints, maintaining a diffraction-limited resolution of 2um on a 6+m space scope is unprecedented and requires new, precise, and complex optics.  We can’t just scale up my older kid’s cheapo refracting telescope.  Relaxing mass constraints helps, but it is absolutely false to claim that every driver of complexity and cost reduces to mass.  They do not.  At all.

Quote
The lack of sufficient, available testing facilities obviously didn't help, either.

Which has nothing to do with LV payload size or mass constraints.  In fact, if the mass and volume constraints on JWST were allowed to grow beyond certain limits, JWST would not have fit in certain testing facilities.  Building new testing facilities to accommodate a fat JWST would have wiped out any savings from relaxing mass constraints and then some.  Above certain limits, a fat JWST would have been a more, not less, expensive scope.  It’s just not true that relaxing mass constraints solves all problems.  It doesn’t and may introduce more.

This is reflected in spacecraft cost models, which typically use a combination of mass and an estimation of system complexity as their inputs.  If you drive mass thru the roof in an effort to make the system as simple as possible, you’ll often wind up with a more expensive spacecraft than if you try to find the sweet spot between mass and complexity.

The cost drivers in JWST almost all reduce to the extremely complex interplay between the instruments and the spacecraft bus, and the spacecraft bus and its sunshield ate up the lion's share of the budget. That complexity could have been avoided with heavier solutions.

No, this is again a false statement.  Heavier solutions could have mitigated some of the complexity driving JWST’s cost.  But heavier solutions would not have eliminated that complexity.  JWST was going to be a complex, multi-billion dollar scope no matter how fat.  That could not be avoided.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/19/2021 04:51 pm
The paper mentions the stringent thermal requirement first.  Then it mentions the stringent requirement on resolution.  Only after that does it mention mass constraints, and then only in the context of the other two requirements.  Mass is a factor driving complexity, but it’s not the only factor or even the most important factor in that paper.

The complexity of thermal and resolution requirements that drove JWST’s costs were magnified by mass constraints.  But it is false to claim that the thermal and resolution requirements could “reduce to the lack of available reserve mass.”

...

No matter how much we relax mass constraints, keeping a big scope at 50K for years in space is unprecedented and requires new and complex cooling systems.  We just can’t hook it up to my basement freezer and send it to L2.  No matter how much we relax mass constraints, maintaining a diffraction-limited resolution of 2um on a 6+m space scope is unprecedented and requires new, precise, and complex optics.  We can’t just scale up my older kid’s refracting telescope.  Relaxing mass constraints helps, but it is absolutely false to claim that every driver of complexity and cost reduces to mass.  They do not.  At all.

The thermals management between the instrumentation and the spacecraft bus are what drove the exotic solutions that JWST employs to achieve its operational specifications. It is stated in the paper that these components are heavily integrated because there was not enough reserve mass to use modular bits that could be traded out, frequently forcing re-engineering of large sections the spacecraft if one part wasn't cutting it. This was a mass constraint induced engineering challenge. The cryo-cooler and spacecraft bus all working together the way they do, with the consequent complex modeling it required for thermal paths and all the other associated difficulties with complex systems was, likewise, a mass constraint induced engineering challenge. The section immediately prior to the 50 kelvin excerpt you quoted says all this.

Quote
Another area that drove complexity was the lack of system resources.  The lack of large mass reserves drove the need for extensive lightweighting and the thermal heat dissipation margins led to extra design trades and even the addition of a deployable radiator.  In both cases, large trade studies had to be undertaken to find ways to build back up margins and these then delayed the final design and consumed resources.   
 
Another key point is the need to be lightweight with tight performance requirements also drove the need for extensive work on dealing with the effects of gravity for everything from mirrors to structures and from wavefront performance to alignment.  Once the effects gravity became relevant, it required extensive modeling, model validation, and error budgets needed to accommodate this.  These kinds of challenges did not occur on earlier missions like hubble which had the mass to avoid them.

Quote
Which has nothing to do with LV payload size or mass constraints.  In fact, if the mass and volume constraints on JWST were allowed to grow beyond certain limits, JWST would not have fit in certain testing facilities.  Building new testing facilities to accommodate a fat JWST would have wiped out any savings from relaxing mass constraints and then some.  Above certain limits, a fat JWST would have been a more, not less, expensive scope.  It’s just not true that relaxing mass constraints solves all problems.  It doesn’t and may introduce more.

It was an acknowledgement of the problem with a lack of facilities adding onto the schedule, and consequently, payroll, of the project, which was cited as one of the other substantial contributing factor's to the observatory's high costs.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: PahTo on 12/19/2021 05:01 pm

Mods:
Would you please split this thread in to a dedicated "updates" thread now that we're apparently so close to launch?
Thx.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/19/2021 05:08 pm
The lack of sufficient, available testing facilities obviously didn't help, either.

This is a limiting factor for anything bigger than existing fairing.  There are no assembly clean rooms large enough.  No thermovac chambers.  No easy method of transportation.  No processing facilities.

What about Plum Brook?

Wrong, it does not say that.  It said "lack of system resources".  This is more than just mass.

Is that different than the aforementioned lack of facilities?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/19/2021 05:11 pm
The most common refrain in discussing the difficulties in developing James Webb have been the ultra complex, ultra precise systems that have to fit in a very tight mass budget: the mirrors, the mirror adjustment systems, the sun shield tensioners, the cryo coolers, and on and on that goes. At the same time, everyone who says "we should use more capable spacecraft so that mass constraints aren't such a vicious engineering problem for these things" gets shot down with "weight is not the problem!" So, somebody is not being truthful, and I am not enjoying trying to play the game of "guess who's full of crap."

I'm going to side with the budget guy and the guy who actually puts spacecraft on rockets. They seem to actually have some experience.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/19/2021 05:14 pm
What about Plum Brook?

Lacks a high quality clean room necessary for large optics. Also lacks a runway that can handle C-5s.

I got a nice tour of Plum Brook--now called the Neil A. Armstrong Test Facility--back in 2012. The then director was trying to get a number of facility upgrades to enable them to handle more payloads. I don't think it happened.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/19/2021 05:18 pm
I'm going to side with the budget guy and the guy who actually puts spacecraft on rockets. They seem to actually have some experience.

I don't understand. Outside of the test time, the reports say, over and over again, that decisions driven by weight made the engineering more difficult. Why are the contributions of weight savings driven engineering program decisions, which are cited frequently in the reports as cost growth drivers, consistently played down here?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: etudiant on 12/19/2021 06:41 pm
Thanks for the link, it actually is very helpful. And, frustratingly, almost every single major cost driver in the system did, in fact, reduce to the lack of available reserve mass.

No.  Mass constraints are a cost driver.  But they are not the only cost driver.  Read it again:

Quote
By having many simultaneous challenges, it made things more time consuming and expensive. For example, being a 50 Kelvin observatory adds the complexity of needing to design and test for these temperatures with all of the material property issues (eg, CTE, damping, etc) that come with this.
The additional factor though was that Webb needed to be diffraction limited at 2um which is slightly challenging by itself but even more so when you combine it with the need to be 50 Kelvin. In many ways, these requirements _along with the tight constraints on mass_ led to the choice of beryllium as the mirror material which was optimal for this temperature but requires more time and money for fabrication as the removal rates are slower and you have to control stresses. In addition, these combined requirements led to the need to cryo polish each mirror to remove the distortions of going cold. Had the system been diffraction limited at a longer wavelength or been warm, a faster material fabrication choice like ULE could have been usen and cryo polishing may not have been needed.

The paper mentions the stringent thermal requirement first.  Then it mentions the stringent requirement on resolution.  Only after that does it mention mass constraints, and then only in the context of the other two requirements.  Mass is a factor driving complexity, but it’s not the only factor or even the most important factor in that paper.

The complexity of thermal and resolution requirements that drove JWST’s costs were magnified by mass constraints.  But it is false to claim that the thermal and resolution requirements could “reduce to the lack of available reserve mass.”

Quote
I am earnestly frustrated at every claim that's suggested otherwise, because the entire design tradespace of JWST was wholly contingent on it, from the complex integrated cooling scheme to the complex engineering that pursued lightening of parts and clawing back mass reserves wherever possible. The story of JWST is one of complexity begotten by a lack of room for mass growth.

No matter how much we relax mass constraints, keeping a big scope at 50K for years in space is unprecedented and requires new and complex cooling systems.  We just can’t hook it up to my cheapo basement freezer and send it to L2.  No matter how much we relax mass constraints, maintaining a diffraction-limited resolution of 2um on a 6+m space scope is unprecedented and requires new, precise, and complex optics.  We can’t just scale up my older kid’s cheapo refracting telescope.  Relaxing mass constraints helps, but it is absolutely false to claim that every driver of complexity and cost reduces to mass.  They do not.  At all.

Quote
The lack of sufficient, available testing facilities obviously didn't help, either.

Which has nothing to do with LV payload size or mass constraints.  In fact, if the mass and volume constraints on JWST were allowed to grow beyond certain limits, JWST would not have fit in certain testing facilities.  Building new testing facilities to accommodate a fat JWST would have wiped out any savings from relaxing mass constraints and then some.  Above certain limits, a fat JWST would have been a more, not less, expensive scope.  It’s just not true that relaxing mass constraints solves all problems.  It doesn’t and may introduce more.

This is reflected in spacecraft cost models, which typically use a combination of mass and an estimation of system complexity as their inputs.  If you drive mass thru the roof in an effort to make the system as simple as possible, you’ll often wind up with a more expensive spacecraft than if you try to find the sweet spot between mass and complexity.

It seems that the arguments for the relative irrelevance of mass for the cost of the JWST are focusing on the lack of testing facilities. That is perhaps a roundabout way of pleading for in space testing facilities, which might be more economical as well as broadly useful, provided only that cheap transportation becomes available.
Afaik, the EELT, a 30 meter ground based scope under construction in Chile, is expected to cost $2B+/-. That is a small fraction of the JWST cost. The EELT is equally unattended, the observation systems run under computer control, with the astronomers monitoring from residences at lower, more oxygen dense altitudes. So we are paying a big price for in space observations, which I hope and believe can be greatly reduced by the SH/SS.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: vjkane on 12/19/2021 07:07 pm
It seems that the arguments for the relative irrelevance of mass for the cost of the JWST are focusing on the lack of testing facilities. That is perhaps a roundabout way of pleading for in space testing facilities, which might be more economical as well as broadly useful, provided only that cheap transportation becomes available.
Afaik, the EELT, a 30 meter ground based scope under construction in Chile, is expected to cost $2B+/-. That is a small fraction of the JWST cost. The EELT is equally unattended, the observation systems run under computer control, with the astronomers monitoring from residences at lower, more oxygen dense altitudes. So we are paying a big price for in space observations, which I hope and believe can be greatly reduced by the SH/SS.
The managers of the EELT can easily do routine maintenance, make repairs, etc. So the cost of 99% reliability unattended for years doesn't have to be carried for this project. Also, EELT operates in a nice atmosphere (no out gassing!), most of the equipment and facility can be designed for nice temperature ranges, and there's no radiation problems.   

If you simply put EELT on an SH/SS, it would fail immediately. Space is hard. Extreme reliability is hard. Launch costs are trivial once you get to these scale of projects.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: etudiant on 12/19/2021 07:11 pm
It seems that the arguments for the relative irrelevance of mass for the cost of the JWST are focusing on the lack of testing facilities. That is perhaps a roundabout way of pleading for in space testing facilities, which might be more economical as well as broadly useful, provided only that cheap transportation becomes available.
Afaik, the EELT, a 30 meter ground based scope under construction in Chile, is expected to cost $2B+/-. That is a small fraction of the JWST cost. The EELT is equally unattended, the observation systems run under computer control, with the astronomers monitoring from residences at lower, more oxygen dense altitudes. So we are paying a big price for in space observations, which I hope and believe can be greatly reduced by the SH/SS.
The managers of the EELT can easily do routine maintenance, make repairs, etc. So the cost of 99% reliability unattended for years doesn't have to be carried for this project. Also, EELT operates in a nice atmosphere (no out gassing!), most of the equipment and facility can be designed for nice temperature ranges, and there's no radiation problems.   

If you simply put EELT on an SH/SS, it would fail immediately. Space is hard. Extreme reliability is hard. Launch costs are trivial once you get to these scale of projects.

No argument to any of that.;
My only point is that addressing those issues is a whole lot easier/cheaper if you don't have to watch every ounce.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/19/2021 07:52 pm
I'm going to side with the budget guy and the guy who actually puts spacecraft on rockets. They seem to actually have some experience.

I don't understand.

Let me explain:

VSECOTSPE has repeatedly explained to you why you are wrong. You do realize that he's actually somebody who has worked in the space program on these issues, right? Jim has also explained to you why you are wrong. You do realize that he has worked in the space program on numerous high-profile space missions, right? VSECOTSPE even cited a report, which you have repeatedly misinterpreted despite his attempts to respond.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/19/2021 08:22 pm
This was a mass constraint induced engineering challenge.

No.  Per the text you quoted, it was the thermal requirement _in combination with_ the mass constraint. 

Quote
The lack of large mass reserves drove the need for extensive lightweighting _and_ the thermal heat dissipation margins led to extra design trades and even the addition of a deployable radiator.
 

It’s thermal _and_ mass.  It’s not mass only.  It’s both/and, not either/or.

I have an astrophysics degree and used to man the night shift on a scope with a LN2 dewar wrapped around a LHe dewar.  No matter how big we made the dome that housed that whole scope, it was still going to have this complex, Matrioshka doll cooling system that was labor-intensive to tend to.  That was driven by the need to cool the detectors down the a temperature where they would be sensitive to the sub-IR photons that we wanted to take data on.  It had nothing to do with any size or mass constraint.  We could simplify and simplify JWST with no mass or volume constraints, and it would still run up against a similar, minimum, multi-billion dollar level of complexity with regard to achieving its extreme thermal requirement.

Just compare similar scopes.  HST has a collecting area of 4.5m^2, a diffraction limit of 0.05 arcseconds, and is uncooled.  JWST has a collecting area of 33.2m^2, a diffraction limit of 0.004 arcseconds, and has to be cooled down to 50 degrees Kelvin.  JWST is literally an order of magnitude more capable than HST in collecting area and an order of magnitude more capable in resolution, and it adds a severe cooling requirement on top of that. 

HST cost $2.4B thru launch.  (I’m obviously not counting subsequent servicing missions or operations.)  Even before mass constraints enter the picture — based just on the order of magnitude difference in the scopes’s capabilities and the unprecedented cooling requirement on JWST — we would expect JWST development to cost some multiple of HST.  And at about ~$9.5B (including ESA/CSA contributions), JWST’s development cost is almost 4x HST’s cost thru launch.  Surprise, surprise.

I’m not denying that if JWST could have launched on Starship, SLS, or pick your favorite heavy lifter with a bigger diameter shroud, it would not have reduced complexity and shaved a billion dollars or two or three off JWST’s cost.  But just given how much more capable JWST is over HST, it’s utterly unrealistic to expect JWST’s cost to drop down into HST territory, or be even cheaper than HST, no matter how big the launcher.

(For the record, the year before I arrived, OMB approved a funding start for JWST based on an utterly unrealistic total cost that was a fraction of HST.  That was done by my old boss who came from a launch vehicle background.  I’d like to think that wouldn’t have happened under my watch given my astrophysics background.)

The latest astrophysics decadal survey is recommending another 6m flagship scope.  It will launch in the era of Starship, New Glenn, and maybe Vulcan Heavy (hopefully not SLS).  The decadal (really Aerospace Corporation) estimated its cost at $11B.  Again, mass constraints are a factor but obviously not the only driver.

The costs of these big, complex, state-of-the-art leaping, Nobel Prize-potential scopes are driven first and foremost by their science requirements.  Access to bigger and lower cost launch will help a lot of things we want to do in space, including certain things in astrophysics.  But it’s not going to fundamentally revolutionize the costs of these flagship scopes.

Quote
It was an acknowledgement of the problem with a lack of facilities adding onto the schedule, and consequently, payroll, of the project, which was cited as one of the other substantial contributing factor's to the observatory's high costs.

Good, but again, that has nothing to do with launch mass constraints.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: whitelancer64 on 12/19/2021 08:32 pm

*snip*

Question to the thread:   Was there a ground based copy of JWST made?

I looked this up the other day, and the answer is no.

There was (is? I'm not sure of its fate) a pathfinder backplane that is not flight capable. There were two flight spares built for the primary mirror segments (one without the gold coating) and one for the secondary mirror, which were used to practice handling and installation on the pathfinder backplane, as well as other pathfinder operations for mirror testing and calibration. There were also ten gold-coated primary mirror simulators that were made out of aluminum which were used during thermal testing.

https://en.wikipedia.org/wiki/OTE_Pathfinder#Components

Attached images are of the completed installation of the two flight spare mirrors on the pathfinder backplane in 2014.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/19/2021 09:03 pm
-snip-

Thank you for the answers. They were very helpful for my understanding.  :)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/19/2021 09:15 pm
It seems that the arguments for the relative irrelevance of mass for the cost of the JWST are focusing on the lack of testing facilities. That is perhaps a roundabout way of pleading for in space testing facilities

No.

First, we do acoustic vibration testing on the ground because that’s a test of whether the spacecraft can survive the lunch environment.  You can’t launch and then test that in space.

Second, if you find a problem testing in space, then you have to bring the scope back down, fix it, and launch again — and design the spacecraft to survive multiple launches and have a space transportation system that can pull this off (maybe Starship can if it achieves its potential).  That’s all a no-go.  Realistically, you’re only going to do the kinds of testing we do on the ground in space if you’re also building in space.

Third, I don’t think we have a clue how we would create hyper-clean lab environments at the scale these scopes need, do vacuum testing in space (there’s an oxymoron) at the scale these scopes need, or do hyper-precise optical bench testing in space at the scale these scopes need.

Realistically, this kind of in-space construction and qualification activity will show up in ever bigger and higher wavelength RF arrays (for comms, PNG, radar, and eventually research) before it transitions to the more difficult IR, optical, and higher wavelengths.

And even before RF, it will probably show up in arrays requiring even less precision, like solar arrays and thermal radiator arrays.  And although a couple companies are working on in-space construction of those kinds of arrays, we aren’t seeing that happening yet, either.

The only in-space assembly and repair currently being done is space is where a satellite with a fresh propulsion system latches onto an old comsat running low on propellant and either extends its useful life by a few years (or in theory deorbits it).

Based on all the above, building and testing scopes like JWST in space is probably at least a few decades away.

Quote
Afaik, the EELT, a 30 meter ground based scope under construction in Chile, is expected to cost $2B+/-. That is a small fraction of the JWST cost.

ELT has at least six more years of construction before first light in 2027.  Exactly a year ago to the day, its total cost estimate was $1.6B.  This year it’s $2.0B.  Assuming ELT continues to grow at $400M per year for the next six years, ELT will cost between $4B and $5B before first light.  They’ll probably have delays and marching army costs past 2027 that drive the cost over $5B.

The world’s other 30m telescope in Hawaii, unimaginatively called the Thirty-Meter Telescope, is up to $2.4B so far.

ELT’s collecting area is many orders of magnitude greater than HST, and its resolution is exactly an order of magnitude better than HST.   Based on that, ELT’s cost before first light will be some multiple of HST’s $2.4B cost through launch.  ~$4B-$5B or more would be at least 2x HST’s cost through launch.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/19/2021 09:29 pm
NGST was originally an 8m diameter mirror with a 3300kg mass constraint. JWST today has relaxed to a 6.5m diameter mirror and 6800kg mass.
You can see what you want to see, but JWST's costs were driven by the precision required in the optics and instruments, and the operation at cryogenic temperatures. Hogging out the mirror backfaces or using low-mass trusses or etc were not the main cost drivers.

The cost drivers in JWST almost all reduce to the extremely complex interplay between the instruments and the spacecraft bus, and the spacecraft bus and its sunshield ate up the lion's share of the budget. That complexity could have been avoided with heavier solutions.

Wrong conclusion
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/19/2021 09:35 pm
What about Plum Brook?

Not clean enough.  It is concrete.  Also, inadequate airport.  That is why JSC’s SES was modified.  But it could only do the Telescope without the spacecraft  bus.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/19/2021 09:36 pm
The most common refrain in discussing the difficulties in developing James Webb have been the ultra complex, ultra precise systems that have to fit in a very tight mass budget: the mirrors, the mirror adjustment systems, the sun shield tensioners, the cryo coolers, and on and on that goes. At the same time, everyone who says "we should use more capable spacecraft so that mass constraints aren't such a vicious engineering problem for these things" gets shot down with "weight is not the problem!" So, somebody is not being truthful, and I am not enjoying trying to play the game of "guess who's full of crap."

Look in the mirror
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Don2 on 12/19/2021 09:37 pm
The rule of thumb for planetary probes built simultaneously is that building two costs 50% more than building one. This was mentioned in a study of ice giants missions from a few years ago which considered the possibility of building two identical spacecraft for Uranus and Neptune.

Having just done the planetary decadal survey, I would not put too much faith in that assertion.

I am referring to the Ice Giants Pre-Decadal survey mission study report. You can find it here:
https://www.lpi.usra.edu/icegiants/mission_study/Full-Report.pdf

See Section 4.9.8 Cost, Page 150

The report considers dual spacecraft on a single launch vehicle visiting both planets.
They assume:

 1/ "The two spacecraft would be identical and built together"

They estimate the savings from building two copies by tracking nonrecurring and recurring engineering costs for all elements. Using that method they produce a cost of 2707 million in 2015$.

For an orbiter + Probe at both Uranus and Neptune, the project cost using simple summing of the elements is 3672 million in 2015$. The report states this is a "worst-case situation, where there are no cost savings due to building multiple flight elements or common instruments, software, etc."

The cost assuming savings from building two copies is 74% of the worst case cost, which means that the second probe costs 48% of the first one. Feel free to check these numbers on your calculator.

The report states that:
"Our first method utilizes the fact that Team X identifies both nonrecurring (NRE) and recurring engineering (RE) costs for all WBS elements. So, for two identical copies of a WBS element, the cost is estimated as 2*RE+NRE."

The report also states:
"Costs are scaled for Science, MOS/GDS, Mission Design, and other elements of the WBS using rules of thumb. For example, the cost during cruise for science and MOS/GDS for a dual orbiter is estimated to be 1.5 times the cost of the science and MOS/GDS during cruise for the single orbiter case. "

It is interesting that there are also savings in operations costs for a two spacecraft scenario.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/19/2021 09:42 pm
Thanks for the link, it actually is very helpful. And, frustratingly, almost every single major cost driver in the system did, in fact, reduce to the lack of available reserve mass.

No.  Mass constraints are a cost driver.  But they are not the only cost driver.  Read it again:

Quote
By having many simultaneous challenges, it made things more time consuming and expensive. For example, being a 50 Kelvin observatory adds the complexity of needing to design and test for these temperatures with all of the material property issues (eg, CTE, damping, etc) that come with this.
The additional factor though was that Webb needed to be diffraction limited at 2um which is slightly challenging by itself but even more so when you combine it with the need to be 50 Kelvin. In many ways, these requirements _along with the tight constraints on mass_ led to the choice of beryllium as the mirror material which was optimal for this temperature but requires more time and money for fabrication as the removal rates are slower and you have to control stresses. In addition, these combined requirements led to the need to cryo polish each mirror to remove the distortions of going cold. Had the system been diffraction limited at a longer wavelength or been warm, a faster material fabrication choice like ULE could have been usen and cryo polishing may not have been needed.

The paper mentions the stringent thermal requirement first.  Then it mentions the stringent requirement on resolution.  Only after that does it mention mass constraints, and then only in the context of the other two requirements.  Mass is a factor driving complexity, but it’s not the only factor or even the most important factor in that paper.

The complexity of thermal and resolution requirements that drove JWST’s costs were magnified by mass constraints.  But it is false to claim that the thermal and resolution requirements could “reduce to the lack of available reserve mass.”

Quote
I am earnestly frustrated at every claim that's suggested otherwise, because the entire design tradespace of JWST was wholly contingent on it, from the complex integrated cooling scheme to the complex engineering that pursued lightening of parts and clawing back mass reserves wherever possible. The story of JWST is one of complexity begotten by a lack of room for mass growth.

No matter how much we relax mass constraints, keeping a big scope at 50K for years in space is unprecedented and requires new and complex cooling systems.  We just can’t hook it up to my cheapo basement freezer and send it to L2.  No matter how much we relax mass constraints, maintaining a diffraction-limited resolution of 2um on a 6+m space scope is unprecedented and requires new, precise, and complex optics.  We can’t just scale up my older kid’s cheapo refracting telescope.  Relaxing mass constraints helps, but it is absolutely false to claim that every driver of complexity and cost reduces to mass.  They do not.  At all.

Quote
The lack of sufficient, available testing facilities obviously didn't help, either.

Which has nothing to do with LV payload size or mass constraints.  In fact, if the mass and volume constraints on JWST were allowed to grow beyond certain limits, JWST would not have fit in certain testing facilities.  Building new testing facilities to accommodate a fat JWST would have wiped out any savings from relaxing mass constraints and then some.  Above certain limits, a fat JWST would have been a more, not less, expensive scope.  It’s just not true that relaxing mass constraints solves all problems.  It doesn’t and may introduce more.

This is reflected in spacecraft cost models, which typically use a combination of mass and an estimation of system complexity as their inputs.  If you drive mass thru the roof in an effort to make the system as simple as possible, you’ll often wind up with a more expensive spacecraft than if you try to find the sweet spot between mass and complexity.

It seems that the arguments for the relative irrelevance of mass for the cost of the JWST are focusing on the lack of testing facilities. That is perhaps a roundabout way of pleading for in space testing facilities, which might be more economical as well as broadly useful, provided only that cheap transportation becomes available.
Afaik, the EELT, a 30 meter ground based scope under construction in Chile, is expected to cost $2B+/-. That is a small fraction of the JWST cost. The EELT is equally unattended, the observation systems run under computer control, with the astronomers monitoring from residences at lower, more oxygen dense altitudes. So we are paying a big price for in space observations, which I hope and believe can be greatly reduced by the SH/SS.

That is idiotic.  There is no such thing as “in space testing”.  the testing is to make sure the payload can survive the into orbit and the space environmet before it arrives in it.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RotoSequence on 12/19/2021 09:53 pm
NGST was originally an 8m diameter mirror with a 3300kg mass constraint. JWST today has relaxed to a 6.5m diameter mirror and 6800kg mass.
You can see what you want to see, but JWST's costs were driven by the precision required in the optics and instruments, and the operation at cryogenic temperatures. Hogging out the mirror backfaces or using low-mass trusses or etc were not the main cost drivers.

The cost drivers in JWST almost all reduce to the extremely complex interplay between the instruments and the spacecraft bus, and the spacecraft bus and its sunshield ate up the lion's share of the budget. That complexity could have been avoided with heavier solutions.

Wrong conclusion

I cannot possibly see how James Webb would not have been easier and cheaper (note, not "cheap") to engineer if modularity could have been budgeted for.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/19/2021 10:02 pm
NGST was originally an 8m diameter mirror with a 3300kg mass constraint. JWST today has relaxed to a 6.5m diameter mirror and 6800kg mass.
You can see what you want to see, but JWST's costs were driven by the precision required in the optics and instruments, and the operation at cryogenic temperatures. Hogging out the mirror backfaces or using low-mass trusses or etc were not the main cost drivers.

The cost drivers in JWST almost all reduce to the extremely complex interplay between the instruments and the spacecraft bus, and the spacecraft bus and its sunshield ate up the lion's share of the budget. That complexity could have been avoided with heavier solutions.

Wrong conclusion

I cannot possibly see how James Webb would not have been easier and cheaper (note, not "cheap") to engineer if modularity could have been budgeted for.

It was modular.  The Telescope and Spacecraft were built separately.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/19/2021 10:11 pm
Also, space telescopes (and spacecraft) are no different than software.  They grow to use the available resources.  The next telescope, whether is flies on SLS or Starship, will be like JWST (and HST, OAO, etc)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/19/2021 11:00 pm
I cannot possibly see how James Webb would not have been easier and cheaper (note, not "cheap") to engineer if modularity could have been budgeted for.

It was modular.  The Telescope and Spacecraft were built separately.

The primary also takes advantage of modular weight savings by breaking the mirror down into 18 independently actuated hexagonal elements.  A smaller mirror is easier to keep stiff than a large mirror.  Keeping the primary stiff would have made it _a lot_ heavier had it been monolithic instead of modular.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: etudiant on 12/19/2021 11:33 pm
Thanks for the link, it actually is very helpful. And, frustratingly, almost every single major cost driver in the system did, in fact, reduce to the lack of available reserve mass.

No.  Mass constraints are a cost driver.  But they are not the only cost driver.  Read it again:

Quote
By having many simultaneous challenges, it made things more time consuming and expensive. For example, being a 50 Kelvin observatory adds the complexity of needing to design and test for these temperatures with all of the material property issues (eg, CTE, damping, etc) that come with this.
The additional factor though was that Webb needed to be diffraction limited at 2um which is slightly challenging by itself but even more so when you combine it with the need to be 50 Kelvin. In many ways, these requirements _along with the tight constraints on mass_ led to the choice of beryllium as the mirror material which was optimal for this temperature but requires more time and money for fabrication as the removal rates are slower and you have to control stresses. In addition, these combined requirements led to the need to cryo polish each mirror to remove the distortions of going cold. Had the system been diffraction limited at a longer wavelength or been warm, a faster material fabrication choice like ULE could have been usen and cryo polishing may not have been needed.

The paper mentions the stringent thermal requirement first.  Then it mentions the stringent requirement on resolution.  Only after that does it mention mass constraints, and then only in the context of the other two requirements.  Mass is a factor driving complexity, but it’s not the only factor or even the most important factor in that paper.

The complexity of thermal and resolution requirements that drove JWST’s costs were magnified by mass constraints.  But it is false to claim that the thermal and resolution requirements could “reduce to the lack of available reserve mass.”

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I am earnestly frustrated at every claim that's suggested otherwise, because the entire design tradespace of JWST was wholly contingent on it, from the complex integrated cooling scheme to the complex engineering that pursued lightening of parts and clawing back mass reserves wherever possible. The story of JWST is one of complexity begotten by a lack of room for mass growth.

No matter how much we relax mass constraints, keeping a big scope at 50K for years in space is unprecedented and requires new and complex cooling systems.  We just can’t hook it up to my cheapo basement freezer and send it to L2.  No matter how much we relax mass constraints, maintaining a diffraction-limited resolution of 2um on a 6+m space scope is unprecedented and requires new, precise, and complex optics.  We can’t just scale up my older kid’s cheapo refracting telescope.  Relaxing mass constraints helps, but it is absolutely false to claim that every driver of complexity and cost reduces to mass.  They do not.  At all.

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The lack of sufficient, available testing facilities obviously didn't help, either.

Which has nothing to do with LV payload size or mass constraints.  In fact, if the mass and volume constraints on JWST were allowed to grow beyond certain limits, JWST would not have fit in certain testing facilities.  Building new testing facilities to accommodate a fat JWST would have wiped out any savings from relaxing mass constraints and then some.  Above certain limits, a fat JWST would have been a more, not less, expensive scope.  It’s just not true that relaxing mass constraints solves all problems.  It doesn’t and may introduce more.

This is reflected in spacecraft cost models, which typically use a combination of mass and an estimation of system complexity as their inputs.  If you drive mass thru the roof in an effort to make the system as simple as possible, you’ll often wind up with a more expensive spacecraft than if you try to find the sweet spot between mass and complexity.

It seems that the arguments for the relative irrelevance of mass for the cost of the JWST are focusing on the lack of testing facilities. That is perhaps a roundabout way of pleading for in space testing facilities, which might be more economical as well as broadly useful, provided only that cheap transportation becomes available.
Afaik, the EELT, a 30 meter ground based scope under construction in Chile, is expected to cost $2B+/-. That is a small fraction of the JWST cost. The EELT is equally unattended, the observation systems run under computer control, with the astronomers monitoring from residences at lower, more oxygen dense altitudes. So we are paying a big price for in space observations, which I hope and believe can be greatly reduced by the SH/SS.

That is idiotic.  There is no such thing as “in space testing”.  the testing is to make sure the payload can survive the into orbit and the space environment before it arrives in it.

Are we not arguing at cross purposes here?
The claim is that cheap ($100/kg) access to space with a return capability allows for a good debug of the expensive science  gear.
Frankly, if the launch packaging is so iffy that it is first rank failure item, the program manager needs help.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/19/2021 11:35 pm
A lovely piece, but I could weep.
No backup at all, on a complex product where the track record for similar deployments is iffy.

frankly, SpaceX's SS can't come soon enough, NASA science spends most of their scarce $$ on product engineering because of launch constraints.
Lift those and the same $$ can do 10x more and better science.
Most of the costs on the Webb had little to do with launch constraints.  Most of the costs were associated with building a telescope that has to be so precisely built and maintain its shape with the thermal environment it is operating in.  The cost of developing the cameras to operate in this environment has also been a major challenge.  Starship would not have changed that.  A telescope of that size and capability would have been incredibly expensive even if it didn't have to unfold on the way to its operational location.

But a fixed main mirror and a fixed sunshield, had the fairing been sufficiently roomy, would reduce the risk factor considerably. Maybe the telescope would have cost only 1/3 less but its chance of success would be much bigger, and that surely counts for a lot.

A fixed sunshield could probably be built with smaller dimensions and SpaceX could probably also design a bigger fairing for an expendable Starship. That way there would be perhaps one or two major deployments instead of the many complex ones we see now. 

Crossing fingers and eating peanuts. (Too much) Excitement guaranteed. It will be unbearable if it doesn't work out. Not just for the loss of science but also because it will harden the resistance to big science. Many elected representatives will be swayed from funding future missions if this one fails.
A fixed sunshade would not have been any smaller.  It is sized for just how big it needs to be to keep the telescope cold enough.  And fully deployed with layers separated it might not survive the launch forces stretched out.  It is very fragile.  Packed up protects the thin film and support structure better during the high vibration and acceleration of launch.

The thin film sunshade, I think, is bigger than a fixed one would be because it has the extraction booms beyond the area of the actual sunshade.

If it were a fixed sunshade it obviously would not be made out of fragile thin film layers. I imagine that it would rather be a sturdy, multi-layered honeycomb structure, with several pretty well thermically isolated layers. Maybe heavier but also much simpler than the contraption we have now, which makes me very nervous.
See the linked NASA page with a picture of the sun shield during a test deployment.  Very little extends beyond the actual shield.  So no a fixed shield would not be any smaller.

https://jwst.nasa.gov/content/observatory/sunshield.html (https://jwst.nasa.gov/content/observatory/sunshield.html)


Look at the cross section diagram of the shield and you will also see why the layers need to be thin for the rejection of heat out the side.  The very thin film is used because it is a design that can do the job by minimizing the heat storage capacity of each layer.  You want as much of the energy provided by solar radiation dumped out the side as fast as possible.  Any thicker layers would absorb more heat over time and make it harder to quickly reject heat out of the side of the shield.  The layers would get warmer and radiate more energy to the next layer complicating the problem.  You have to remember the cooling requirements are far beyond any spacecraft of this size ever built before.  This is a significantly different thermodynamic problem than reentry heat shields.

Thanks for your comprehensive and convincing reply.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/20/2021 12:35 am

Are we not arguing at cross purposes here?
The claim is that cheap ($100/kg) access to space with a return capability allows for a good debug of the expensive science  gear.
Frankly, if the launch packaging is so iffy that it is first rank failure item, the program manager needs help.

No.    For many reasons, among them refllght is a fallacy.

Wrong about the launch packaging.  To make such a comment means you have no knowledge of the processes or engineering involved.  And Starship is not going to change them.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: baldusi on 12/20/2021 02:51 am
You also have to think about zero-g and no atmosphere to reject heat. Heavier elements require more mass for reaction wheels, bigger thrusters (which are a source of contaminants), and more propellant. Also, having more mass means longer time to reach thermal equilibrium, higher thermal expansion stress, and more heat rejection and radiation.
Bigger everything also requires more cooling (remember that this is to be cooled to 50K), and more power (more solar panels). This increases the momentum, which requires bigger wheels and thrusters and you are at it again. So adding significant mass to "reduce cost" has an exponential effect on the whole craft.
On the optics side, heavier mirrors would require bigger actuators and more time to reach the correct wavefront, etc.
You can trade mass for cost on "dumb" systems, not on the most sophisticated optical and thermal instrument ever devised by humans.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Dizzy_RHESSI on 12/20/2021 01:40 pm
ELT has at least six more years of construction before first light in 2027.  Exactly a year ago to the day, its total cost estimate was $1.6B.  This year it’s $2.0B.  Assuming ELT continues to grow at $400M per year for the next six years, ELT will cost between $4B and $5B before first light.  They’ll probably have delays and marching army costs past 2027 that drive the cost over $5B.

The world’s other 30m telescope in Hawaii, unimaginatively called the Thirty-Meter Telescope, is up to $2.4B so far.

ELT’s collecting area is many orders of magnitude greater than HST, and its resolution is exactly an order of magnitude better than HST.   Based on that, ELT’s cost before first light will be some multiple of HST’s $2.4B cost through launch.  ~$4B-$5B or more would be at least 2x HST’s cost through launch.

ELT will not cost that much. Maybe after 20 or 30 years of operations and a generation of new instruments, but not for construction. ESO literally could not afford it, they do not have the flexibility that NASA has. It's not a good idea to extrapolate based on a single year. If we do the same with JWST after it was delayed twice in 2018 we would conclude its launch date is being delayed at a rate of 2 years per year, so it would never launch. The best estimate of the cost is whatever ESO say it is, even that is inaccurate we are not going to obtain a more precise estimate by guesswork. TMT may well end up having a higher construction cost than ELT, because it has been set back several years.

And as for the cost of HST, that estimate is not corrected for inflation. The recent decadal survey quotes an estimate of 9.4 billion in 2020 dollars, not including servicing or operations.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ttle2 on 12/20/2021 02:27 pm
Just compare similar scopes.  HST has a collecting area of 4.5m^2, a diffraction limit of 0.05 arcseconds, and is uncooled.  JWST has a collecting area of 33.2m^2, a diffraction limit of 0.004 arcseconds, and has to be cooled down to 50 degrees Kelvin.  JWST is literally an order of magnitude more capable than HST in collecting area and an order of magnitude more capable in resolution, and it adds a severe cooling requirement on top of that. 

JWST definitely doesn't have an order of magnitude better resolution than HST, in fact it will be a bit worse than HST (6.5 m diffraction limited at 2 um vs. 2.4 m diffraction limited at ~500 nm).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/20/2021 06:41 pm
ELT will not cost that much. Maybe after 20 or 30 years of operations and a generation of new instruments, but not for construction. ESO literally could not afford it, they do not have the flexibility that NASA has.  It's not a good idea to extrapolate based on a single year.

ELT will come in at least around ~$5B (or more) or they’ll cancel it.  I’m not saying they‘re going to have exactly $400M increases each year.  But any development or construction project has an ideally efficient Gaussian-ish distribution of work and spending over time.  ELT is still early in construction and not over the hump of that curve.   The fact that they’re already seeing $400M increases year-on-year on a $1B to $2B budget (25% to 50% increases six years out) means it’s going to get worse before it gets better.

I don’t know ESO’s budget, but they’ll do the same as NASA does when confronted with these realities — they’ll seek offsetting contributions from partners (as they’ve already done) and/or they’ll extend the construction schedule to fit the program’s annual budget (which further drives up marching army costs and delays future programs that need that budget wedge to start but at least fits the budget). Another option is technical descopes, as we’ve seen on Roman, but there’s a limit to how much technical content you can take out of any program and descopes need technically and politically talented leadership to pull off.

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If we do the same with JWST after it was delayed twice in 2018 we would conclude its launch date is being delayed at a rate of 2 years per year, so it would never launch

I wouldn’t make predictions based on delays a year or two before launch or first light, either.  But ELT is more than half a decade from first light.  Whether due to bad estimates or technical issues, cost increases or schedule delays of this magnitude this early in a program are highly predictive of further cost increases and schedule delays.  The worst is yet to come.

I wrote this in late August _2014_ about SLS, its schedule slips at the time, and its likely launch date:

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The project was started in 2011, and the 2010 NASA Authorization Act required SLS to launch by 2016. It is now four years later, and the likely launch date for EM-1 has slipped to 2018 or later, a slip of two years in the first launch of SLS. That’s one year of schedule slippage for every two years that the project has existed. If the SLS schedule continues to slip at this rate over the next four years, the date of the first SLS launch will slip from 2018 to 2020. And then from 2018 to 2020, SLS will slip one more year or so before finally launching for the first time somewhere in the 2021-2022 timeframe.

In late August 2014, a program manager was publicly saying SLS would launch in 2017 and detailed NASA probabilistic assessments gave SLS a 1-in-3 chance of a 2018 launch.  I just looked at the fact that the launch date was slipping one year for every two years of calendar time that passed, extrapolated, and predicted a launch in 2021-2022.  Guess what?  We’re finally looking at an SLS launch in early 2022.  Surprise, surprise.

Employed early enough and by dispassionate, experienced analysts, good rules of thumb beat the accuracy of what advocates inside the program say and what needlessly complex, garbage-in/garbage-out analysis spits out, any day.

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The best estimate of the cost is whatever ESO say it is

No, absolutely not.  When has any program or it’s parent agency — HST, JWST, Roman, SLS, Orion, any number of DOD programs, any number of big ground scopes, etc. — been accurate about its total cost/schedule a half decade plus out?

You don’t go to programs and their parent agencies for accurate projections.  They’re advocates so they’re biased.  They have political masters they have to keep placated which further warps their projections.  And they don’t cultivate (but they should and pay attention to it) the outside-in expertise for doing these kinds of projections across lots of programs.

If you want accurate projections, you look to the independent, dispassionate estimators who do this kind of work every day.  It’s the GAOs, IGs, and Aerospace Corps of the world that will give you the most accurate picture of a program, not the the program’s management or its agency management.  OMB staff also become good at this kind of stuff, but their analyses serve the White House budget process and are embargoed.  I don’t know what the equivalent of the GAO, NASA IG, or Aerospace Corporation is for ESO or Europe.  But I would look to those kinds of organizations in Europe for the most accurate assessment of ELT’s cost/schedule.

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And as for the cost of HST, that estimate is not corrected for inflation. The recent decadal survey quotes an estimate of 9.4 billion in 2020 dollars, not including servicing or operations.

You’re absolutely right that that I did not account for inflation.  I was just trying to quickly make a broad point that inflating the figure would have just reinforced.

But if the $2.4B figure I looked up of HST cost thru launch in 1990 is accurate, there’s no way that inflates to $9.4B by 2020.  That would require a steady inflation rate of ~5% year-over-year, which the US and most of the world did not see during that time period.  We may be headed in that direction going forward now, but there were huge deflationary forces in the 90s from the introduction of desktop computer and networking technology, a major recession in the aughts, and continued deflationary fears until very recently.  I could believe $5B or so, which would imply a ~3% inflation rate, which is much closer to (but probably still a little higher than) inflation rates during those decades.

JWST definitely doesn't have an order of magnitude better resolution than HST, in fact it will be a bit worse than HST

You’re right that they are about the same in comparable IR wavelengths.  I was trying to make a point about the crazy precision JWST needs to do that for the much farther/fainter objects than HST can gather/detect.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/20/2021 07:27 pm

Are we not arguing at cross purposes here?
The claim is that cheap ($100/kg) access to space with a return capability allows for a good debug of the expensive science  gear.


For many reasons, among them refllght is a fallacy. Most details on this nonsense.

a.  It is still cheaper to test on earth than "in space"
b.  Many spacecraft are in non retrievable orbits.
c.  Retrieval is not simple.   Have to approach the spacecraft with a dirty spacecraft spewing propellants and other items.  Once retrieved, it will be placed in a container of unknown cleanliness.  It will be subject to radiant heating during entry.  Also it will be basked in outside air when the compartment is repressurized during entry.   It will see landing loads (not a common spacecraft load).  Removal and transport to processing facility will subject it to contamination.  It will be hard to return it to the factory since it likely will have propellants still onboard.
d.  The claim is iffy
E.  The testing is for the spacecraft as a whole and not individual items.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Dizzy_RHESSI on 12/20/2021 11:25 pm
ELT will come in at least around ~$5B (or more) or they’ll cancel it.  I’m not saying they‘re going to have exactly $400M increases each year.  But any development or construction project has an ideally efficient Gaussian-ish distribution of work and spending over time.  ELT is still early in construction and not over the hump of that curve.   The fact that they’re already seeing $400M increases year-on-year on a $1B to $2B budget (25% to 50% increases six years out) means it’s going to get worse before it gets better.

But we aren't seeing "year-on-year" increases. You claim it happened in a single year and have linearly extrapolated that. A revised estimate being announced in one particular year does not mean the cost has risen that much in that year alone nor does it mean that is representative. I think you need to check your data, a press release from one year ago states the cost was revised up to 1.3 billion euros, a rise of 10%. As it explains in the article, part of the reason was that they abandoned the phased approach. If we trace back the announcements we see that in 2012 the total estimate was 1083 million euros, which is 1.17 billion today. With instruments and operations the cost will be higher, not 5 billion. Costs have risen, but certainly not by 400 million a year. It's not even 400 million over nearly a decade.

https://www.eso.org/public/announcements/ann20034/

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But I would look to those kinds of organizations in Europe for the most accurate assessment of ELT’s cost/schedule.

Please point me to the rigorous independent estimate if you are aware of such a thing. So far in the running for best estimate we have ESO's modelling and your linear extrapolation based on seemingly false data.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: daveglo on 12/21/2021 12:58 am
Get in, we're going to space!

On Dec. 18, our team lowered the @ariane5 (https://twitter.com/ariane5?ref_src=twsrc%5Etfw) nosecone down over Webb using a laser-guided crane system, and locked it in place for launch. Liftoff is set for Dec. 24 at 7:20 AM ET. #UnfoldTheUniverse (https://twitter.com/hashtag/UnfoldTheUniverse?src=hash&amp;ref_src=twsrc%5Etfw) pic.twitter.com/ElHz9FEPFh (https://t.co/ElHz9FEPFh)</p>&mdash; NASA Webb Telescope (@NASAWebb) December 20, 2021 (https://twitter.com/NASAWebb/status/1473013535278047238?ref_src=twsrc%5Etfw)

Maybe I can turn the conversation to the actual, ya know, LAUNCH?  Instead of long-winded theoretical hyperbole?  Please?  Y'all can always make a new thread.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Star One on 12/21/2021 09:06 am
Taking Light Apart with the JWST:

https://youtu.be/gRG80Wr1ETo
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 12/21/2021 09:08 am
Maybe I can turn the conversation to the actual, ya know, LAUNCH?  Instead of long-winded theoretical hyperbole?  Please?  Y'all can always make a new thread.

At this point it might be easier if you create a new update thread. ("James Webb Space Telescope - Updates only") Copy over your last update to seed it.

edit:

And then PM Bolun (https://forum.nasaspaceflight.com/index.php?action=profile;u=14026) and Star One (https://forum.nasaspaceflight.com/index.php?action=profile;u=40487) and let them know about it, and ask them to each copy their last couple of posts.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: eeergo on 12/21/2021 09:18 am
Maybe I can turn the conversation to the actual, ya know, LAUNCH?  Instead of long-winded theoretical hyperbole?  Please?  Y'all can always make a new thread.

At this point it might be easier if you create a new update thread. ("James Webb Space Telescope - Updates only") Copy over your last few updates to seed it.

edit:

And then PM Bolun (https://forum.nasaspaceflight.com/index.php?action=profile;u=14026) and Star One (https://forum.nasaspaceflight.com/index.php?action=profile;u=40487) and let them know about it, and ask them to each copy their last couple of posts.

There is such a thread in the ESA launchers subforum, as usual for any launch: https://forum.nasaspaceflight.com/index.php?topic=49417.new#new

This thread is supposed to be about the payload itself, and the post-launch mission.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/21/2021 05:26 pm
But we aren't seeing "year-on-year" increases.

Forget the budget figures.  Just in terms of schedule, ELT is slipping year-for-year.

In mid-2018, ELT was scheduled to see first light in 2024:

https://www.nextbigfuture.com/2018/08/giant-30-40-ground-telescopes-will-begin-direct-imaging-many-more-exoplanets-around-2024.html

https://www.popularmechanics.com/space/telescopes/a20264196/foundation-construction-extremely-large-telescope-chile/

https://www.newsweek.com/extremely-large-telescope-astronomy-european-southern-observatory-917745

In three years, that schedule moved right by three years.  In mid-2021, ELT was was scheduled to see first light in 2027:

https://www.eso.org/public/usa/announcements/ann21008/

Year-for-year slips are obviously never good.  It either means that the project is not making progress or that the amount of work in front of the project is growing as fast or faster than the work being completed due to unknowns, realized threats, bad estimates, corruption, etc.

In the specific case of ELT, here are some of the reasons why the schedule is slipping:

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A rough sea

Likening the giant project’s current challenges to that of “a boat heaving on a rough sea”, Tamai [ELT Program Manager Roberto Tamai] outlined setbacks including a key contractor becoming insolvent, social unrest in Chile last year, and inevitably the impact of the Covid-19 pandemic and travel restrictions on site activities, inspections, and interaction between the hundreds of contractors and sub-contractors working on ELT.

https://optics.org/news/11/12/24

To be fair, that same article states that the project is making progress on the adaptive quaternary and the primary’s mirror blanks.

But you obviously can’t make progress overall with contractors going belly up or with a pandemic or civil unrest (yikes!) restricting access.  None of that is necessarily even the project’s fault.  It’s just what’s been happening.  Hopefully it has changed or will change soon.

The more I look into ELT, the worse it gets.  Looking at the budget, I didn’t see how they get out of it for less than a handful of billions of dollars.   Now looking at the schedule, I don’t even see where the work being done closes with work that needs to be done.  (Again, hopefully that’s changing.)  To be clear, that doesn’t mean the managers are evil or incompetent.  And it doesn’t mean that the project is not worth doing at the higher cost.  It just means that the project appears to be in trouble, and based on experience with more projects like this than I can count, it will get worse before it gets better.

You’re free to hold a different view based on what the project and ESO are saying.  I’m just advising to take their claims with a large grain of salt.  Internal advocates usually turn out to be wrong (by a lot), and the budget and schedule indicators and management reveals on this project are pointing in the wrong direction.

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Please point me to the rigorous independent estimate if you are aware of such a thing.

That was a reference to NASA’s probabilistic schedule estimate for SLS that was off by four years.  I was providing it as an illustrative example of how internal advocates and complex analysis on these projects are almost always way off in their estimates while independent experience and rules of thumb based on decades of prior projects are much more accurate.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Dizzy_RHESSI on 12/23/2021 11:24 am
Forget the budget figures...

The claims I objected to were about cost, not schedule. I'm not really interested in trying to have a discussion where the goalposts are constantly shifting, this is already off-topic.

I was providing it as an illustrative example of how internal advocates and complex analysis on these projects are almost always way off in their estimates while independent experience and rules of thumb based on decades of prior projects are much more accurate.

An illustrative example that was beside the point. You strongly rejected my claim that ESO's cost estimate was the best one we have for ELT, not SLS or anything else. There are no independent estimates, apart from your attempt. Your estimate was not based on decades of experience, it is just a linear extrapolation.  I never said ESO's estimate was perfect, I said it was more precise than any value you can deduce from guesswork. It was certainly proven to be the case for your estimate when we found out the values you were using in your regression were false, even ignoring the problems with the method. You can criticise historical internal estimates all day, but it does not follow that therefore any independent estimate must be better.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 12/23/2021 11:50 am
Didn't see this posted yet.

Faux blueprint of JWST, high enough resolution enough to make a decent poster: https://www.nasa.gov/image-feature/blueprints-of-the-james-webb-space-telescope/ (https://www.nasa.gov/image-feature/blueprints-of-the-james-webb-space-telescope/) for the description, with the image attached below.

Tried google-translating the latin labels. The results were odd ("Greatest hate ever", "Live life without fans"). Not sure if it's a G-trans issue, or if someone was having fun and they're in-jokes. If anyone who understands latin (or just has more patience with google-trans) wants to have a shot at it, it can't possibly be any more off-topic.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Don2 on 12/23/2021 06:25 pm
Instrument cost and complexity looks to have been a very significant factor in the JWST cost blowout. The reference provided by VSECOTSPE, which I link to below, show that the instruments  made up 25% of the total cost, which would be $2.0 billion based on the $8 billion cost cap. That is as much as an entire flagship mission.

https://ntrs.nasa.gov/api/citations/20180003980/downloads/20180003980.pdf

The instruments are far more complex than the Spitzer ones, and it looks like the difficulty of developing and testing them was a surprise. Apparently, NIRCAM spent over two years in cryogenic testing.

There was a proposal early on to drop the mid-infrared instrument. This would have meant that the telescope could have been much warmer, since it would not have needed to be sensitive to wavelengths longer than 5 microns.

From an online blackbody calculator the radiance of a 300K telescope at 1.8 micron is 2e-05 w/m**2/sr/micron. To achieve the same background at 5 micron requires a temperature of 135K, which is significantly above the boiling point of liquid nitrogen at 1 atmosphere. This would have simplified testing.

https://www.spectralcalc.com/blackbody_calculator/blackbody.php

Dropping the mid-infrared would have lead to a painful loss of science. Dust emits at longer wavelengths, and highly redshifted red supergiant stars would no longer be visible. However, the core program of spotting the earliest stars, which are thought to be blue supergiants, would still have been feasible.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: VSECOTSPE on 12/24/2021 04:54 am
The claims I objected to were about cost, not schedule.

As the saying goes, time is money.  This is especially true of development projects, where delays require management to maintain workforce longer, which drives up costs.  If a project is experiencing delays, costs are going up.  When costs are going up, a project is almost always experiencing delays.  Look up earned value management for the modern tool used to track this long-understood relationship between work, schedule, and cost.

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I'm not really interested in trying to have a discussion where the goalposts are constantly shifting

Not shifting goalposts.  Just using a related line of evidence to demonstrate that the project is experiencing trouble.  If you don’t like numbers, I also quoted the program manager. 

Quote
You strongly rejected my claim that ESO's cost estimate was the best one we have for ELT, not SLS or anything else. There are no independent estimates, apart from your attempt. Your estimate was not based on decades of experience, it is just a linear extrapolation.

I reject that ELT will cost a billion dollars and change as ESO claims.  The schedule for first light has slipped by three years in the past three years.  Paying a workforce for three more years will cost a lot of money.  A major contractor has gone belly up according to the PM.  That work will take time and money to re-compete, on top of any losses to the defunct contractor.  Civil unrest is restricting access to the work site according to the PM.  Those delays will cost money.  The PM is also complaining about Covid, which has caused substantial delays on other projects that cost money.  When I looked at ELT’s recent cost growth, I saw a multi-billion dollar project.  That is supported by the multi-year schedule slippage and the PM’s reveals.  I see no evidence that supports ESO’s estimate.

Quote
I never said ESO's estimate was perfect, I said it was more precise than any value you can deduce from guesswork.

Not guesswork.  See directly above.  You’re right about avoiding overly precise estimates on anything.  But dollars to donuts, ELT will come in closer to my estimate than ESO’s.

Quote
You can criticise historical internal estimates all day

I’m not sure ESO’s internal estimates have a relationship with history.  For example, ESO’s original estimate for ELT, a 40m primary scope, was 1.0B euros, while ESO’s estimate for OWL, a 100m primary scope, was 1.5B Euros.  This implies that a scope with ~6x the collecting area is only ~50% more expensive.  That’s not credible, in terms of common sense or parameterizations based on historical actuals, which show an order of magnitude difference in cost between scopes of those sizes.

Quote
but it does not follow that therefore any independent estimate must be better.

Where have internal project/program estimates on any large, complex, flagship-scale project — cost, schedule, flight safety — ever accurately predicted actuals at development complete or program end?

Jim Webb himself — the person, not the telescope — doubled NASA’s internal estimate for the Apollo Program when he was NASA Administrator before releasing the estimate externally.  (Webb supposedly did this in the drive over to the White House to brief President Kennedy, but I imagine that bit is not historically accurate.)  Webb was an attorney by trade.  His outside looking-in estimate turned out to be right.  NASA’s detailed, bottoms-up estimate involved the work of an army of engineers and technicians.  And it turned out to be wrong.  Guess where Webb had worked prior?  Not NASA.  OMB.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: turbopumpfeedback2 on 12/24/2021 04:56 am
Good luck JWST.

I hope my nightmares will not get realized (one booster not starting, another starting, very scary dream)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 12/24/2021 09:33 am
Good luck JWST.

I hope my nightmares will not get realized (one booster not starting, another starting, very scary dream)

My concern would be for the sun shield deployment above anything else.  Then again, the Webb was delayed and that issue minimized... hopefully.  With a touch of luck this 'scope will work; I have my share of complaints but if it flies I'll be merry.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Don2 on 12/24/2021 08:27 pm
I've been thinking about the ways that Starship might change things, and specifically how Elon Musk might tackle a project like JWST. Both JWST and Starship are novel designs. This makes cost estimation difficult because cost estimation makes comparisons with prior designs which have known costs. This makes it difficult to ensure that the project is realistic when it starts.

JWST spent 20 years designing and ground testing components before flight. For Starship Elon is building multiple flying prototypes which started off doing very limited things. The prototypes are becoming more capable over time as they iterate towards a fully capable system. The SpaceX strategy of flying hardware and fixing it when it doesn't work the first time is very different from the way JWST has been built.

One way Elon might do a telescope would be to install it in the nose of a Starship. The Starship would make three month long flights to low Earth orbit and would fly twice a year. Each time it flew it would get a new instrument. Instead of building complex multi-mode instruments like JWST, each instrument would have limited functionality but they would be replaced each time the telescope flew. Over time they would offer the same features as JWST but not all on one flight.

The telescope could also be upgraded periodically. Starship offers an 8m wide payload bay, so eventually it could accommodate a rather large telescope. It would probably be sensible to start with a small room temperature telescope until pointing, vibration and other accommodation issues are worked out. It would probably not be possible to ever match both the size and low temperature of JWST on a Starship attached telescope.

A strategy of modest incremental improvements rather than giant technical leaps would help to keep costs under control. Also, the telescope could be returned to Earth and fixed if it didn't work, which would reduce the need for ground testing.

NASA did something similar in the Shuttle era with some of the astronomy focused Spacelab missions.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RonM on 12/24/2021 08:46 pm
https://www.youtube.com/watch?v=cp_7AJseYYc
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/24/2021 08:46 pm

One way Elon might do a telescope would be to install it in the nose of a Starship. The Starship would make three month long flights to low Earth orbit and would fly twice a year.

That would make JWST entirely pointless because it couldn't get cold in LEO. Might as well spray black paint on the mirrors.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ulm_atms on 12/24/2021 09:04 pm

One way Elon might do a telescope would be to install it in the nose of a Starship. The Starship would make three month long flights to low Earth orbit and would fly twice a year.

That would make JWST entirely pointless because it couldn't get cold in LEO. Might as well spray black paint on the mirrors.

I like this comment but want to explain further.

LEO is too warm for JWST.  The Earth radiates A LOT of heat...good old albedo and all.  JWST will have the shade facing the Sun but would then be facing Earth.....not a good combo for it's mission.  The lagrange point it is going to allows it to be cool enough for it's mission(within the refrigeration limits of it's systems)....simple as that really.

Off-Topic.....but can we please stop bringing up theoretical Starship scenarios in EVERY SINGLE THREAD please?  It would be appreciative.....highly...  Please put them in the Starship threads where they belong.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Graham on 12/24/2021 09:05 pm

One way Elon might do a telescope would be to install it in the nose of a Starship. The Starship would make three month long flights to low Earth orbit and would fly twice a year.

That would make JWST entirely pointless because it couldn't get cold in LEO. Might as well spray black paint on the mirrors.

Well said Lee. What is the obsession with throwing Starship at everything? It’ll be a great asset if it achieves promised flight rates and capabilities, but it’s not a catch all for every single issue.

Webb is a true engineering marvel that can only work in the way it is designed, you can’t just strap it into a Starship and have it work the same way.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: vjkane on 12/24/2021 10:46 pm
Off-Topic.....but can we please stop bringing up theoretical Starship scenarios in EVERY SINGLE THREAD please?  It would be appreciative.....highly...  Please put them in the Starship threads where they belong.
Not off topic. This is a discussion thread for JWST. There are other threads for Starship scenarios. Bluntly, having Starship jump into every discussion keeps knowledgeable potential posters from posting. I post much less here than I otherwise would, and in private communications I know that others with much more expertise stay away. Why post something if the solution to everything is Starship, or Starship could do it so much better? Other places to discuss this.

My Christmas wish is for the moderators to remove any post mentioning Starship except for those threads dedicated to it.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Don2 on 12/25/2021 12:36 am

One way Elon might do a telescope would be to install it in the nose of a Starship. The Starship would make three month long flights to low Earth orbit and would fly twice a year.

That would make JWST entirely pointless because it couldn't get cold in LEO. Might as well spray black paint on the mirrors.

In future please read my post before replying to it. In the original post I said:

"It would probably not be possible to ever match both the size and low temperature of JWST on a Starship attached telescope. "

Why do I say "probably not"? Because the Wide Field Infra-red Survey Explorer mission operated a low temperature telescope in low Earth orbit using solid hydrogen coolant. A telescope using liquid helium coolant would be viable in low Earth orbit if the mission was short, but of course the size would have to be limited ( WISE's mirror was only 40cm diameter) because it would have to be contained inside an insulated structure.

If you read the post again you will see that I was speculating about how Elon might do 'a telescope', not about an exact copy of JWST mounted on a Starship.

You and the other people replying to the post have missed the point I was trying to make, which was to do with the different strategies for achieving leaps in technology. I wasn't trying to hype Starship, and I won't mention it again in this thread because of all the rude replies it generated.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Timber Micka on 12/25/2021 01:41 am
It is hard to put into words the importance of this mission.

What scares me the most about this mission is that if it fails, we will never see a purely scientific project of this magnitude again in our lifetime. There will still be ITER and a manned mission to Mars, but these are not purely scientific projects. The first is an industrial project as well, and the second is more sentimental than scientific.

JWST absolutely has to work.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Surfdaddy on 12/25/2021 02:21 am
It is hard to put into words the importance of this mission.

What scares me the most about this mission is that if it fails, we will never see a purely scientific project of this magnitude again in our lifetime. There will still be ITER and a manned mission to Mars, but these are not purely scientific projects. The first is an industrial project as well, and the second is more sentimental than scientific.

JWST absolutely has to work.

Which is why I would suggest that Don2's post WAS relevant. He's suggesting that one way to build things is spending 20 years and 10 billion dollars on a must-work-first-time mission, versus possible future approaches of successive trial builds/test/refinements.

I do hope JWST flies, deploys, and works perfectly.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: vjkane on 12/25/2021 03:34 am
Which is why I would suggest that Don2's post WAS relevant. He's suggesting that one way to build things is spending 20 years and 10 billion dollars on a must-work-first-time mission, versus possible future approaches of successive trial builds/test/refinements.

I do hope JWST flies, deploys, and works perfectly.
But those posts are not about JWST, but possible future missions of which there are an almost infinity set of possibilities. This thread is about JWST, not possible future missions. Please set up a separate thread to discuss possible Starship enabled astronomy missions.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/25/2021 03:37 am
I do hope JWST flies, deploys, and works perfectly.

Perhaps the only thing we can all agree on.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: markbike528cbx on 12/25/2021 03:41 am
It is hard to put into words the importance of this mission.

What scares me the most about this mission is that if it fails, we will never see a purely scientific project of this magnitude again in our lifetime. There will still be ITER and a manned mission to Mars, but these are not purely scientific projects. The first is an industrial project as well, and the second is more sentimental than scientific.

JWST absolutely has to work.

I would question why we NEED a "purely scientific project of this magnitude "

Freeman Dyson once lectured about the fallacy of "Big Science" -  his example as I recall was Hubble and the other "Great Observatories"
http://www.columbia.edu/~jeh1/Documents/Hansen.1990.RemarksOnMissionToPlanetEarth.U.S.Senate.6September.pdf  See appendix A of the PDF .
Based on Wooster College May 9, 1988 commencement address and lectures ('On Being the Right Size: Reflectlons on the Ecology of Scientific Projects) given in Seattle in May 1988.

"The fundamental flaw in the Great Observatory program is ecological.
The Great Observatories are too big and too slow and too
expensive to fit comfortably into the ecology of
science. They take so long to fund, to build
and to launch that they are unable to keep
pace with the rapid growth of science."  - Freeman Dyson  1988

Big is not better, small is not worse.

That said, big observatories do push the boundaries of instrumentation, mostly because they have to, in order to justify the  funding.   
Do I regret the Hubble "Deep Fields", https://esahubble.org/science/deep_fields/  ? Hell no.   

Do I hope the JWST reaches beyond our current imaginations?  Sure.   
Is it a good way to spend that much money and entire careers?  Maybe not.

Will a failure of the JWST cripple science or even BIG SCIENCE.  Nope. 
Everybody wants a flagship, no matter how flawed [Vasa, Mary Rose, BTA-6 etc].

Relax.

https://en.wikipedia.org/wiki/Vasa_(ship)
https://en.wikipedia.org/wiki/Mary_Rose
https://en.wikipedia.org/wiki/BTA-6
https://www.nasa.gov/audience/forstudents/postsecondary/features/F_NASA_Great_Observatories_PS.html
Voyager timeline, project start to end of planetary missions  15 years.
JWST timeline. 25 years to launch, no science yet.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/25/2021 04:36 am
Freeman Dyson once lectured about the fallacy of "Big Science" -  his example as I recall was Hubble and the other "Great Observatories"

History seems to have proven him wrong.  HST is one of the most, if not the most prolific scientific instrument of all time.

When it comes to telescopes, aperture rules. JWST is the size it is because that's what's needed to answer the questions it was designed to answer.  In fact, if anything, it might be a little too small.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/25/2021 07:01 am
4 hours 18 minutes to launch.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 12/25/2021 07:17 am
It is hard to put into words the importance of this mission.

What scares me the most about this mission is that if it fails, we will never see a purely scientific project of this magnitude again in our lifetime. There will still be ITER and a manned mission to Mars, but these are not purely scientific projects. The first is an industrial project as well, and the second is more sentimental than scientific.

JWST absolutely has to work.
I think we will see large scale scientific projects even if the Webb fails.  The proposed $23 billion successor to the super collider at CERN comes to mind.  I don't think the outcome of Webb will affect that in any way.  I do believe that the US will start planning a worthy successor to Webb shortly after a failed outcome. It would probably take a few budget cycles to get it approved,  But I believe we would do it.  I think ITER will be canceled eventually because just like SLS it is already obsolete before it is finished.  And I don't think even that will hurt future large scale projects.  Economic conditions will have a bigger impact on whether or not we do the next big project,
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Surfdaddy on 12/25/2021 07:56 am
This even makes a Space Shuttle launch look inexpensive.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Kaputnik on 12/25/2021 08:40 am
This even makes a Space Shuttle launch look inexpensive.

Depends what's in the payload bay.
But yes, this just be the single most expensive launch in history. Happy to be corrected on that.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 12/25/2021 09:26 am
Slight less than 1 hour 55 min now according to streams.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 12/25/2021 10:57 am
When it comes to telescopes, aperture rules. JWST is the size it is because that's what's needed to answer the questions it was designed to answer.

According to reports at the time, the size came more from Dan Goldin than from the requests from researchers. He publicly mocked one of the PIs for only wanting a 4m telescope as a successor to Hubble.



Also, can we stop talking about it hypothetically failing. At least for 24hrs. I'm not superstitious but... just let them get it into its transfer orbit at least.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 12/25/2021 11:02 am
17 minutes to liftoff
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: eric z on 12/25/2021 11:34 am
  Awesome Launch! Go Webb! I love Ariane. ;D
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/25/2021 11:34 am

NASA did something similar in the Shuttle era with some of the astronomy focused Spacelab missions.

No, it did not.  They were in related missions. And only few 3 times
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/25/2021 11:46 am
Ariane did its job perfectly, tous les paramètres normaux, merci beaucoup ESA, and Merry Christmas to all working on JWST!

Phew!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/25/2021 11:52 am
JWST solar array unfolded, power is being supplied. Quite a lot of small objects twirling around at separation, I was surprised to see that.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/25/2021 11:57 am
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/25/2021 11:59 am
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/25/2021 12:07 pm
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: bolun on 12/25/2021 12:22 pm
https://twitter.com/NASAWebb/status/1474724813579165699

Quote
#NASAWebb’s solar array has successfully deployed, and Webb’s batteries are charging up ⚡ #UnfoldTheUniverse
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: bolun on 12/25/2021 12:22 pm
https://twitter.com/esaoperations/status/1474728914979377158

Quote
Full data link 〰️ up and down 〰️ established with @esa_webb! Mission controllers at @spacetelescope in Baltimore now in command via ESA #ESOC and @ASI_spazio #Malindi station

#ChattingWithWebb
#JWST
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: archipeppe68 on 12/25/2021 12:32 pm
This is my personal contribution to such Historical and also emotional (like Chris Bergin knows well), the biggest Christmas' Gift ever!!

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Kaputnik on 12/25/2021 12:52 pm
What a great Christmas present. Could have done without the stress though! Been on the mulled wine all morning.

Certainly a better Christmas present than we got in 2003 (Beagle 2)

Question- does JWST have engineering cameras? I'm guessing not, from the lack of onboard views.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 12/25/2021 01:49 pm
JWST's high gain antenna had yet to deploy, so there would be nothing other than important telemetry yet.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/25/2021 02:02 pm
This makes me happy.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: apollo16uvc on 12/25/2021 02:04 pm
DSN is communicating with webb:

(https://cdn.discordapp.com/attachments/694894769167663228/924315935660204133/image0.jpg)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: baldusi on 12/25/2021 05:45 pm
Is there a timeline of events (deployments, maneuvers to L2, etc.)?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: seb21051 on 12/25/2021 05:50 pm
https://www.youtube.com/watch?v=cp_7AJseYYc&ab_channel=ScottManley

https://www.youtube.com/watch?v=RzGLKQ7_KZQ&ab_channel=JamesWebbSpaceTelescope%28JWST%29
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Joseph Peterson on 12/25/2021 06:05 pm
Is there a timeline of events (deployments, maneuvers to L2, etc.)?

Hopeful this helps:

https://webbtelescope.org/contents/media/images/4180-Image
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: mtakala24 on 12/25/2021 06:36 pm
Is there a timeline of events (deployments, maneuvers to L2, etc.)?

Hopeful this helps:

https://webbtelescope.org/contents/media/images/4180-Image

This does not make sense, as the official timeline on the website has the high gain antenna deployment later than the MCC1a.
https://jwst.nasa.gov/content/webbLaunch/deploymentExplorer.html
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: kdhilliard on 12/25/2021 07:46 pm
...
https://webbtelescope.org/contents/media/images/4180-Image
This does not make sense, as the official timeline on the website has the high gain antenna deployment later than the MCC1a.
https://jwst.nasa.gov/content/webbLaunch/deploymentExplorer.html
? They are consistent, both showing the MCC-1a burn prior to the high gain antenna deploy.

Are you saying that order is surprising?

The Deployment Explorer you linked shows Solar Array deploy and Gimballed Antenna Assy deploy as the only two "automatic" deployments.  "All other deployments will be controlled by commands from the ground."

It does not say how MCC1a is commanded, only stating:
Quote
MCC1a

Mid Course Correction Burn 1a

Nominal Event Time: Launch + 12.5 hours

This burn fine-tunes Webb's trajectory after launch. The duration of the burn will depend on Ariane 5 launcher performance.

The James Webb Space Telescope is launched on a direct path to an orbit around the second Sun-Earth Lagrange Point (L2), but it needs to make its own mid-course thrust correction maneuvers to get there. This is by design, because if Webb gets too much thrust from the Ariane rocket, it can’t turn around to thrust back toward Earth because that would directly expose its telescope optics and structure to the Sun, overheating them and aborting the science mission before it can even begin. Therefore, Webb gets an intentional slight under-burn from the Ariane and uses its own small thrusters and on-board propellant to make up the difference.

There will be three mid-course correction (MCC) maneuvers: MCC-1a, MCC-1b, and MCC-2. The first burn, MCC-1a, is the most important and the only other time-critical operation aside from solar array deployment during Webb’s commissioning period.

Do we know if JWST will calculate its own MCC-1a burn, or if parameters for that burn can be received with the HGA platform stowed?  STScI's JWST Communications Subsystem (https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-spacecraft-bus/jwst-communications-subsystem) page states that Webb's other antenna, the "0.2 m S-band medium-gain antenna (MGA)" is mounted on the same articulated platform as the 0.6 m Ka-band high-gain antenna (HGA).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Hobbes-22 on 12/25/2021 08:02 pm
Is there a timeline of events (deployments, maneuvers to L2, etc.)?

https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html (https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/25/2021 08:12 pm
Is there a timeline of events (deployments, maneuvers to L2, etc.)?

https://planet4589.org/space/misc/webb/time.html
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Joseph Peterson on 12/25/2021 09:04 pm
Is there a timeline of events (deployments, maneuvers to L2, etc.)?

https://planet4589.org/space/misc/webb/time.html

This has far more detail than the link I had and is easy to read.  Thanks for posting.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/25/2021 09:04 pm
...
https://webbtelescope.org/contents/media/images/4180-Image
This does not make sense, as the official timeline on the website has the high gain antenna deployment later than the MCC1a.
https://jwst.nasa.gov/content/webbLaunch/deploymentExplorer.html
? They are consistent, both showing the MCC-1a burn prior to the high gain antenna deploy.

Are you saying that order is surprising?

The Deployment Explorer you linked shows Solar Array deploy and Gimballed Antenna Assy deploy as the only two "automatic" deployments.  "All other deployments will be controlled by commands from the ground."

It does not say how MCC1a is commanded, only stating:
Quote
MCC1a

Mid Course Correction Burn 1a

Nominal Event Time: Launch + 12.5 hours

This burn fine-tunes Webb's trajectory after launch. The duration of the burn will depend on Ariane 5 launcher performance.

The James Webb Space Telescope is launched on a direct path to an orbit around the second Sun-Earth Lagrange Point (L2), but it needs to make its own mid-course thrust correction maneuvers to get there. This is by design, because if Webb gets too much thrust from the Ariane rocket, it can’t turn around to thrust back toward Earth because that would directly expose its telescope optics and structure to the Sun, overheating them and aborting the science mission before it can even begin. Therefore, Webb gets an intentional slight under-burn from the Ariane and uses its own small thrusters and on-board propellant to make up the difference.

There will be three mid-course correction (MCC) maneuvers: MCC-1a, MCC-1b, and MCC-2. The first burn, MCC-1a, is the most important and the only other time-critical operation aside from solar array deployment during Webb’s commissioning period.

Do we know if JWST will calculate its own MCC-1a burn, or if parameters for that burn can be received with the HGA platform stowed?  STScI's JWST Communications Subsystem (https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-spacecraft-bus/jwst-communications-subsystem) page states that Webb's other antenna, the "0.2 m S-band medium-gain antenna (MGA)" is mounted on the same articulated platform as the 0.6 m Ka-band high-gain antenna (HGA).

Ground calculated
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/25/2021 09:50 pm
Ground calculated

Jim, is there a resource on how they determine the state vector from the ground? I know about using Doppler shift to determine radial velocity but not the rest and I've often wondered how they do that.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jimvela on 12/25/2021 10:03 pm
Ground calculated

Jim, is there a resource on how they determine the state vector from the ground? I know about using Doppler shift to determine radial velocity but not the rest and I've often wondered how they do that.

Different Jim.

Start here:
https://deepspace.jpl.nasa.gov/files/810-007/103.pdf

Nav team will take DSN tracking data and use that to generate the products needed for mission planning e.g. ephermeris creation.

At least that's how it works on all the missions that I've supported which used DSN for tracking.

No direct knowledge of the JWST team's specific operations.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: zubenelgenubi on 12/26/2021 12:22 am
MCC1a burn at L + 12.5 hr.  Successful?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 12/26/2021 01:00 am
Yes.

https://blogs.nasa.gov/webb/2021/12/25/the-first-mid-course-correction-burn/

Burn lasted 65 minutes, as planned...which is why we just got word just before 9 p.m. EST.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: zubenelgenubi on 12/26/2021 01:41 am
Burn lasted 65 minutes, as planned...
Wow, 65 minutes!

Besides electric/ion propulsion, is this the longest rocket burn?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/26/2021 01:49 am
Cassini  did over 90 minutes for Saturn orbit insertion.  Juno had a long burn.  It isn’t uncommon.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: zubenelgenubi on 12/26/2021 04:23 am
...Solar Array deploy and Gimballed Antenna Assy deploy as the only two "automatic" deployments.  "All other deployments will be controlled by commands from the ground."
GAA deploy is what time Dec 26?  Timeline doesn't go into hours:minutes detail.



I just noticed that I have given over 30,000 likes! 👍
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/26/2021 05:06 am
...Solar Array deploy and Gimballed Antenna Assy deploy as the only two "automatic" deployments.  "All other deployments will be controlled by commands from the ground."
GAA deploy is what time Dec 26?  Timeline doesn't go into hours:minutes detail.


That's because it's not necessarily specific. Times can vary based on many factors, including human commanding.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: catdlr on 12/26/2021 05:17 am
I posted this sometime long ago, but it's useful now to see the time and events of deployments. Start at 3:20 in the video to view the process.

https://youtu.be/v6ihVeEoUdo
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: catfry on 12/26/2021 09:02 am
Burn lasted 65 minutes, as planned...
Wow, 65 minutes!

Besides electric/ion propulsion, is this the longest rocket burn?

Rosetta had some very long rendezvous burns lasting many hours. I looked it up and the longest was 6 hours and 40 min of continuous thrust (conventional hydrazine thruster). Part of it is just that the engines are so small and there isn't that much gained from putting a bigger one on once you are in orbit, and time isn't as much of a factor.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jak Kennedy on 12/26/2021 10:34 am
So I have a question about L2. Is the James Webb telescope circling L2 outside the earths shadow or are all the graphics exaggerated? I'm guessing that if it is, that's because a larger L2 orbit is more stable? Could the telescope orbit L2 inside earths shadow by using more fuel?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 12/26/2021 11:14 am
L2 is a good way beyond earth shadow distance I think. Perhaps a wide orbit is more stable and requires less station keeping? Was there something about being above/below main dust disc of solar system?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Hobbes-22 on 12/26/2021 11:47 am
So I have a question about L2. Is the James Webb telescope circling L2 outside the earths shadow or are all the graphics exaggerated? I'm guessing that if it is, that's because a larger L2 orbit is more stable? Could the telescope orbit L2 inside earths shadow by using more fuel?

It's far outside Earth's shadow, it'll orbit L2 at a distance of about 300,000 km.
Orbiting inside Earth's shadow would require a switch from solar panels to RTG.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Greg Hullender on 12/26/2021 12:56 pm
So I have a question about L2. Is the James Webb telescope circling L2 outside the earths shadow or are all the graphics exaggerated? I'm guessing that if it is, that's because a larger L2 orbit is more stable? Could the telescope orbit L2 inside earths shadow by using more fuel?
The JWEST can't handle any eclipse--neither from the Earth nor the moon. Here's a NASA paper (https://ntrs.nasa.gov/api/citations/20190028885/downloads/20190028885.pdf) that outlines the challenges in finding orbits that accomplish this with a minimum of orbital corrections.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ETurner on 12/26/2021 01:26 pm

[...] The very thin film is used because it is a design that can do the job by minimizing the heat storage capacity of each layer.  You want as much of the energy provided by solar radiation dumped out the side as fast as possible.  Any thicker layers would absorb more heat over time and make it harder to quickly reject heat out of the side of the shield.  The layers would get warmer and radiate more energy to the next layer complicating the problem. [...]
The idea that greater mass would require greater cooling capacity is a fallacy. The heat input that sizes the cooling systems is independent of mass -- area exposed to the Sun is unchanged, heat dissipated by electronics is unchanged, radiating areas are unchanged, etc. Thermal inertia scales with mass but merely slows cooling and heating (which also reduces thermal stresses).

Allowing more mass would allow a less exquisite, more robust (and probably simpler) thermal shield. It’s probably worth waiting a little longer for the vehicle to cool.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: freddo411 on 12/26/2021 01:42 pm
So I have a question about L2. Is the James Webb telescope circling L2 outside the earths shadow or are all the graphics exaggerated? I'm guessing that if it is, that's because a larger L2 orbit is more stable? Could the telescope orbit L2 inside earths shadow by using more fuel?

It's far outside Earth's shadow, it'll orbit L2 at a distance of about 300,000 km.
Orbiting inside Earth's shadow would require a switch from solar panels to RTG.

Really?   Eclipses are generally short events, especially when large distances are involved.    Short term power cuts from the solar panels could be handled with batteries.    Is there a reason not to use a battery?

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ETurner on 12/26/2021 01:52 pm

[...] Heavier elements require more mass for reaction wheels, bigger thrusters (which are a source of contaminants), and more propellant. Also, having more mass means longer time to reach thermal equilibrium, higher thermal expansion stress, and more heat rejection and radiation.
Bigger everything also requires more cooling (remember that this is to be cooled to 50K), and more power (more solar panels). This increases the momentum, which requires bigger wheels and thrusters and you are at it again. So adding significant mass to "reduce cost" has an exponential effect on the whole craft.
On the optics side, heavier mirrors would require bigger actuators and more time to reach the correct wavefront, etc.
You can trade mass for cost on "dumb" systems, not on the most sophisticated optical and thermal instrument ever devised by humans.


“Heavier elements require more mass for reaction wheels”
  --  In other words, the masses scale (with less need for miniaturization).

“bigger thrusters (which are a source of contaminants), and more propellant”
  --  In other words, the masses scale (with less need for miniaturization).
      (Exercise for engineers: consider how to trade mass for protection against contaminants from point sources.)

“Also, having more mass means longer time to reach thermal equilibrium, higher thermal expansion stress”
  --  Slower equilibration means lower thermal gradients, pretty much cancelling any increase in thermal stress.

“[more mass means] more heat rejection and radiation... Bigger everything also requires more cooling”
  -- This is a fallacy. See comment above.

‘This increases the momentum, which requires bigger wheels and thrusters and you are at it again”
  --  In other words, the masses scale (with less need for miniaturization).

“So adding significant mass to "reduce cost" has an exponential effect on the whole craft.”
  -- Your points to not support this, and “exponential” is hyperbole, not a scaling law.

“On the optics side, heavier mirrors would require bigger actuators”
  -- There is no gravity.

“and more time to reach the correct wavefront, etc”
  -- This does not matter. The motion times are negligible.

“You can trade mass for cost on "dumb" systems, not on the most sophisticated optical and thermal instrument ever devised by humans.”
  -- Not substantiated by your remarks.

Most of your points argue (if anything) that more mass in Part A may require proportionally more mass in Part B, but why think that this is a problem, much less super-duper exponential problem? Mass can be cheap, and exquisite engineering (analysis, design iteration, fabrication, testing) is expensive. In JWST, > $1000/gm.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: JohnLloydJones on 12/26/2021 02:09 pm
So I have a question about L2. Is the James Webb telescope circling L2 outside the earths shadow or are all the graphics exaggerated? I'm guessing that if it is, that's because a larger L2 orbit is more stable? Could the telescope orbit L2 inside earths shadow by using more fuel?

It's far outside Earth's shadow, it'll orbit L2 at a distance of about 300,000 km.
Orbiting inside Earth's shadow would require a switch from solar panels to RTG.

Really?   Eclipses are generally short events, especially when large distances are involved.    Short term power cuts from the solar panels could be handled with batteries.    Is there a reason not to use a battery?

There are thermal considerations as well as the power issue.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/26/2021 02:16 pm

(with less need for miniaturization).

  --  Slower equilibration means lower thermal gradients, pretty much cancelling any increase in thermal stress.



This false logic permeates throughout your post.  There is no "miniaturization" on JWST.  It is one of the largest spacecraft and has some of the largest components.

More mass fixes everything is also a fallacy.

Take your nonsense and fantasies to another thread.  This one is about the real spacecraft.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: freddo411 on 12/26/2021 02:29 pm
So I have a question about L2. Is the James Webb telescope circling L2 outside the earths shadow or are all the graphics exaggerated? I'm guessing that if it is, that's because a larger L2 orbit is more stable? Could the telescope orbit L2 inside earths shadow by using more fuel?

It's far outside Earth's shadow, it'll orbit L2 at a distance of about 300,000 km.
Orbiting inside Earth's shadow would require a switch from solar panels to RTG.

Really?   Eclipses are generally short events, especially when large distances are involved.    Short term power cuts from the solar panels could be handled with batteries.    Is there a reason not to use a battery?

There are thermal considerations as well as the power issue.

Indeed.   I suspect that having a stable (always in the sun) thermal environment is the true driver of the no eclipse requirement.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Hobbes-22 on 12/26/2021 02:38 pm
So I have a question about L2. Is the James Webb telescope circling L2 outside the earths shadow or are all the graphics exaggerated? I'm guessing that if it is, that's because a larger L2 orbit is more stable? Could the telescope orbit L2 inside earths shadow by using more fuel?

It's far outside Earth's shadow, it'll orbit L2 at a distance of about 300,000 km.
Orbiting inside Earth's shadow would require a switch from solar panels to RTG.

Really?   Eclipses are generally short events, especially when large distances are involved.    Short term power cuts from the solar panels could be handled with batteries.    Is there a reason not to use a battery?

JWST does have a battery on board (about 1 kWh, IIRC). my sentence "Orbiting inside Earth's shadow would require a switch from solar panels to RTG." refers to a permanent orbit inside Earth's shadow, not eclipses. I don't know what the constraints are for eclipses, could be thermal (rapid cooldown of the hot side of the spacecraft. Maybe they're worried about the hydrazine freezing).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: dsmillman on 12/26/2021 03:32 pm
We now have the High Gain Antenna deployed:

"Webb Antenna Released and Tested

Shortly after 10 am EST on Dec. 26, the Webb team began the process of releasing the gimbaled antenna assembly, or GAA, which includes Webb’s high-data-rate dish antenna. This antenna will be used to send at least 28.6 Gbytes of science data down from the observatory, twice a day. The team has now released and tested the motion of the antenna assembly — the entire process took about one hour.

Separately, overnight, the temperature sensors and strain gauges on the telescope were activated for the first time. Temperature and strain data are now available to engineers monitoring Webb’s thermal and structural systems."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Torbjorn Larsson, OM on 12/26/2021 03:34 pm
It was an exciting Webbcast!

Burn lasted 65 minutes, as planned...
Wow, 65 minutes!

Besides electric/ion propulsion, is this the longest rocket burn?

I'm happy to read confirmation that it was the correct burn length for this second somewhat  time critical event after the solar panel deploy. No comments yet on how nominal it was, but that reads promising.

Isn't the burn length a consequence for the need to "undershoot" the final transfer orbit velocity (due to thermal constraints on Webb position)?

Off topic for this telescope, but its launch article has a description of science context that can be nitpicked:

Quote
COBE provided critical evidence to support the Big Bang Theory of the universe’s creation, including that the cosmic microwave background radiation has a near-perfect black-body spectrum, and that it has very faint anisotropies.

The cosmic background black body spectra is a consequence of the Hot Big Bang, but the weak anisotropies is evidence for the preceding inflation era. To quote the recent timely - for Webb -  release of the US NAS Astronomical and Astrophysics Decadal Survey ["Pathways to Discovery in Astronomy and Astrophysics for the 2020s (2021)", Appendix C Panel on Cosmology]:

Quote
The question of what process set the Hot Big Bang in motion and created the seeds of structure has been with us for many decades. Early theoretical developments, together with observations over the past two decades, have established the inflationary paradigm as the dominant picture in the field.

[FWIW, the last BICEP3/Keck data preferred a simple Higgs scalar field, and the paper notes that we should know if this has the correct amount of gravitational backreaction from tensor B-modes within a decade. If that happens, it will be "the" picture of what process produced our current Hot Big Bang universe.]
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ETurner on 12/26/2021 03:49 pm

(with less need for miniaturization).

  --  Slower equilibration means lower thermal gradients, pretty much cancelling any increase in thermal stress.



This false logic permeates throughout your post.  There is no "miniaturization" on JWST.  It is one of the largest spacecraft and has some of the largest components.

More mass fixes everything is also a fallacy.

Take your nonsense and fantasies to another thread.  This one is about the real spacecraft.


This false logic permeates throughout your post.
-- Sorry to get everything wrong like that. Scaling laws, etc., all wrong! There was nothing at all for me to correct in the post that I quoted.

“There is no "miniaturization" on JWST.”
  -- Sorry, bad choice of words. Let’s call it “stringent mass minimization.” Good enough?

“has some of the largest components.”
  -- Yes I definitely chose the wrong word to express my point. I had noticed that the vehicle is large.

More mass fixes everything is also a fallacy.
  -- And “more mass fixes everything” also a straw man.

Take your nonsense and fantasies to another thread.  This one is about the real spacecraft.
  -- I try to be polite, so no comment.

Your straw-man arguments aside, I appreciate your many insights into the concrete side of current spacecraft development and operations, many of which will continue to be of crucial importance for the foreseeable future. You know of many challenges and constraints that others overlook. You also have ingrained assumptions that are sometimes off-target. As do we all.

[Edit: Fixed messed up quotes]
[Edit 2, to avoid cluttering the thread downstream: “pretty much cancelling any increase in thermal stress” is confused. Rather, scaling says that holding thermal radiated power per unit area constant while allowing material thickness to vary, the thermal gradients in that material will be constant.]
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/26/2021 03:59 pm
“There is no "miniaturization" on JWST.”
  -- Sorry, bad choice of words. Let’s call it “stringent mass minimization.” Good enough?

still false
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ETurner on 12/26/2021 04:34 pm
“There is no "miniaturization" on JWST.”
  -- Sorry, bad choice of words. Let’s call it “stringent mass minimization.” Good enough?

still false
And now I can’t make out what what you are trying to say. That there was no stringent mass minimization, or that there was, but mass constraints have no impact on costs, or...?  Most of my points were simple corrections of mistakes in a previous post. Your responses so far have been more hostile than informative.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: bolun on 12/26/2021 05:49 pm
https://twitter.com/esa/status/1475094447826345988

Quote
Image of @ariane5 #VA256 upper stage and the NASA/ESA/CSA James #Webb Space Telescope IN SPACE, as seen by friends at the #Tautenburg Schmidt telescope in Germany, at 23:23 GMT/00:23 CET last night (pic: S. Melnikov, C. Högner and B. Stecklum, via @markmccaughrean)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: cohberg on 12/26/2021 05:52 pm
Quote from: Jonathan McDowell @planet4589
Here's the full story of the early JWST solar array deploy that surprised those using the prelaunch timeline. As I suggested it was 'not a xed time, but a fixed set of conditions' - I hadn't guessed that it was 'angular rate' (stability of pointing) though.

Quote from: @SouthernWave1
Replying to @planet4589 @Dr_ThomasZ and 2 others
SA deployment is triggered by JWST based on angular rate measurements. Once the rates are damped below a threshold by the RCS thrusters, JWST sends an internal command to release the array. Since the tip off rates were benign, this happened more quickly than conservative predicts

http://twitter.com/planet4589/status/1475160224956923911

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 12/27/2021 12:34 pm
Jim, is there a resource on how they determine the state vector from the ground? I know about using Doppler shift to determine radial velocity but not the rest and I've often wondered how they do that.
Not Jim, but the principles are straightforward, at least once the distances are large.  Doppler gives the range rate, and the signal delay ground-spacecraft-ground gives the absolute range.  For plane-of-sky, they measure the difference in phase between two widely spaced antennas.  This requires extremely careful calibration, so they observe a nearby quasar first (and after, I think).  A few such observations, combined with the Earth turning, and a full ephemeris can be fit.

For correcting launch dispersions they might use something else, as the spacecraft may be too close to see from multiple antennas.  Optical images for plane-of-sky?  Residuals from the inertial nav system of the spacecraft?  Maybe only correct the radial component, as that's likely the most variable due to rocket cutoff residuals?  It's a good question. 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Herb Schaltegger on 12/27/2021 01:27 pm
It's a good question.

Indeed it is. I’m working so don’t have time to dig through my saved links and resources, but I believe this particular issue was solved for Apollo (state vectors for guidance maneuvers were provided by ground controllers in most - all? - cases). Some of the many millions of pages of Apollo documents have described the procedures in great detail - I just don’t know if I can find them. Maybe this reminder will help cue someone into an NTRS search today while I’m otherwise occupied.

The same techniques, refined with time and increases in computing power to reduce calculation times, were used for interplanetary missions through the 70’s and beyond to the present day.

EDIT: Here’s a quick starter search if anyone wants some light reading. ;)

https://ntrs.nasa.gov/search?q=Apollo%20state%20vector%20determination
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Alpha Control on 12/27/2021 02:11 pm
I'm interested to know if there are any cameras on James Webb that can provide views of the structure and visual status of the sun shields and so forth. Obviously there are sensors that that the engineers use to obtain system status.

I'm thinking along the lines of the hazard cameras on Mars 2020 Rover. Those B&W photos showing wheels on the ground on Mars were a great thing to see. Hoping that JWST has cameras for similar "key moment" photos.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/27/2021 02:13 pm
I'm interested to know if there are any cameras on James Webb that can provide views of the structure and visual status of the sun shields and so forth. Obviously there are sensors that that the engineers use to obtain system status.


none
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Alpha Control on 12/27/2021 02:16 pm
I'm interested to know if there are any cameras on James Webb that can provide views of the structure and visual status of the sun shields and so forth. Obviously there are sensors that that the engineers use to obtain system status.


none

Thanks Jim!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: fast on 12/27/2021 02:26 pm
I'm interested to know if there are any cameras on James Webb that can provide views of the structure and visual status of the sun shields and so forth. Obviously there are sensors that that the engineers use to obtain system status.


none

Probably because of 30 yeard old concept design.
This days its normal and logical to have them, but old basic design and weight restrictions did not allow as explaned at 16.10 here: https://youtu.be/KGeWg_K8UiI
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: deadman1204 on 12/27/2021 02:37 pm
I'm interested to know if there are any cameras on James Webb that can provide views of the structure and visual status of the sun shields and so forth. Obviously there are sensors that that the engineers use to obtain system status.


none

Probably because of 30 yeard old concept design.
This days its normal and logical to have them, but old basic design and weight restrictions did not allow as explaned at 16.10 here: https://youtu.be/KGeWg_K8UiI
But Lucy doesn't have them either.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 12/27/2021 02:52 pm
What was the approximate start date to sun shield deployment?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/27/2021 02:53 pm
This days its normal and logical to have them,

That is not true.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: daedalus1 on 12/27/2021 02:54 pm
What was the approximate start date to sun shield deployment?

https://planet4589.org/space/misc/webb/time.html
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: hoku on 12/27/2021 02:57 pm
Is there a timeline of events (deployments, maneuvers to L2, etc.)?
The attached slides from Eric Smith's Sep (?) 2021 AAAC presentation summarise the Spacecraft Commissioning activities up to Launch+30d

https://science.nasa.gov/science-red/s3fs-public/atoms/files/Smith%20Webb-Update%20APAC%20Oct-2021.pdf (https://science.nasa.gov/science-red/s3fs-public/atoms/files/Smith%20Webb-Update%20APAC%20Oct-2021.pdf)

edit: link to presentation added
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Star One on 12/27/2021 04:08 pm
I'm interested to know if there are any cameras on James Webb that can provide views of the structure and visual status of the sun shields and so forth. Obviously there are sensors that that the engineers use to obtain system status.


none

Probably because of 30 yeard old concept design.
This days its normal and logical to have them, but old basic design and weight restrictions did not allow as explaned at 16.10 here: https://youtu.be/KGeWg_K8UiI
But Lucy doesn't have them either.
I hope this thread doesn’t get derailed over cameras the same way the Lucy thread was.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Alpha Control on 12/27/2021 04:25 pm
I'm interested to know if there are any cameras on James Webb that can provide views of the structure and visual status of the sun shields and so forth. Obviously there are sensors that that the engineers use to obtain system status.

none

Probably because of 30 yeard old concept design.
This days its normal and logical to have them, but old basic design and weight restrictions did not allow as explaned at 16.10 here: https://youtu.be/KGeWg_K8UiI
But Lucy doesn't have them either.
I hope this thread doesn’t get derailed over cameras the same way the Lucy thread was.
I don't see any reason for concern. I asked a legitimate question, and received good answers. I'm fine.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: centaurinasa on 12/27/2021 04:30 pm
https://twitter.com/NASAWebb/status/1475138567454265352
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 12/27/2021 04:47 pm
What was the approximate start date to sun shield deployment?
Tomorrow.  Where is WEBB is a pretty cool resource.

(Still don't know why its "Cruising Speed" field doesn't continuously update.)

https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Stan-1967 on 12/27/2021 05:10 pm

(Still don't know why its "Cruising Speed" field doesn't continuously update.)


It probably is continuously updating, but you are not seeing much change when the web page only is displaying 4 significant digits.  As Webb gets further from Earth, the gravitational "gradient" get's pretty flat, so it could take several hours to see a change on the display.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: dsmillman on 12/27/2021 05:43 pm

(Still don't know why its "Cruising Speed" field doesn't continuously update.)


It probably is continuously updating, but you are not seeing much change when the web page only is displaying 4 significant digits.  As Webb gets further from Earth, the gravitational "gradient" get's pretty flat, so it could take several hours to see a change on the display.

The "Cruising Speed" was updating every 30 to 60 minutes on Saturday in the hours after launch.
Since the Webb velocity was decreasing rapidly during this period, the update period should  have been one minute or less.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: zubenelgenubi on 12/27/2021 06:22 pm
MCC1b burn later today?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/27/2021 06:52 pm
MCC1b burn later today?

That appears to be the plan.

https://blogs.nasa.gov/webb/

"In the same way, MCC-1b, scheduled for 2.5 days after launch, and MCC-2, scheduled for about 29 days after launch (but neither time-critical), ..."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 12/27/2021 07:58 pm

(Still don't know why its "Cruising Speed" field doesn't continuously update.)



The "Cruising Speed" was updating every 30 to 60 minutes on Saturday in the hours after launch.
Since the Webb velocity was decreasing rapidly during this period, the update period should  have been one minute or less.

It probably is continuously updating, but you are not seeing much change when the web page only is displaying 4 significant digits.  As Webb gets further from Earth, the gravitational "gradient" get's pretty flat, so it could take several hours to see a change on the display.

=======================================================================

No...I thought of that.  Of course, the decrease is not linear, but between yesterday and today, it's not 'way off linear.  It dropped from 0.8663 mph to 0.7406 mph in somewhere between 1,000 and 1,500 minutes, which should mean a drop of 0.0001 about once every minute or so.  It almost looks like it's being manually adjusted every hour or two.

...which is no big deal.  I just don't know why they wouldn't program it to be real-time, continuously updating.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/27/2021 09:34 pm
MCC1b burn later today?

That appears to be the plan.

https://blogs.nasa.gov/webb/

"In the same way, MCC-1b, scheduled for 2.5 days after launch, and MCC-2, scheduled for about 29 days after launch (but neither time-critical), ..."

I love the informative blog posts on that site. Just perfect for the curious layman. Great explanation of the thruster rationale in the latest posting.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Stan-1967 on 12/27/2021 09:54 pm


It almost looks like it's being manually adjusted every hour or two.

...which is no big deal.  I just don't know why they wouldn't program it to be real-time, continuously updating.

Thinking about it more, it probably is being manually updated as new measurement are being made by any of NASA's DSN sites, or backups the ESA might be sharing.  If that is so, the website is probably displaying the "theoretical" orbit calculations, not actual measurements.  Refinements on position/distance & velocity have to be confirmed by ground stations to make the calculations for the orbital correction maneuvers. 

see post 289 & 290.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 12/27/2021 11:05 pm
If "Day 2.5" is a precise time-mark, then MCC 1b would begin in about 15 minutes.  I'll be watching the blog site.

...although Karen Fox' blog notes, regarding MCC 1b tonight and MCC 2 on Day 29, that "...neither is time-critical...."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: mn on 12/27/2021 11:37 pm
If "Day 2.5" is a precise time-mark, then MCC 1b would begin in about 15 minutes.  I'll be watching the blog site.

...although Karen Fox' blog notes, regarding MCC 1b tonight and MCC 2 on Day 29, that "...neither is time-critical...."

And there is the update of the successful burn

https://blogs.nasa.gov/webb/2021/12/27/webbs-second-mid-course-correction-burn/

Quote
At 7:20 pm EST – 60 hours after liftoff — Webb’s second mid-course correction burn began. It lasted 9 minutes and 27 seconds and is now complete. This burn is one of three planned course corrections to put the telescope precisely in orbit around the second Lagrange point, commonly known as L2.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 12/28/2021 01:31 am
Jim, is there a resource on how they determine the state vector from the ground? I know about using Doppler shift to determine radial velocity but not the rest and I've often wondered how they do that.
Not Jim, but the principles are straightforward, at least once the distances are large.  Doppler gives the range rate, and the signal delay ground-spacecraft-ground gives the absolute range.  For plane-of-sky, they measure the difference in phase between two widely spaced antennas.  This requires extremely careful calibration, so they observe a nearby quasar first (and after, I think).  A few such observations, combined with the Earth turning, and a full ephemeris can be fit.

For correcting launch dispersions they might use something else, as the spacecraft may be too close to see from multiple antennas.  Optical images for plane-of-sky?  Residuals from the inertial nav system of the spacecraft?  Maybe only correct the radial component, as that's likely the most variable due to rocket cutoff residuals?  It's a good question. 
Here's how they did near-Earth corrections on Apollo.  From DOPPLER OBSERVABLE MODELING FOR THE APOLLO REAL-TIME ORBIT DETERMINATION PROGRAM (https://ntrs.nasa.gov/api/citations/19700026614/downloads/19700026614.pdf):
Quote
The Doppler count is recorded by the tracking stations. The real-time orbit determination program uses its current estimate of the vehicle's position and velocity to compute a corresponding value of Doppler count. The difference between the observed and computed values of Doppler count, called the residual, is computed and used by the orbit determination program to obtain an improved estimate of the vehicle's position and velocity.
It seems likely (though I have no inside knowledge) that they could easily use the same technique for modern launch dispersion calculations.  It needs only doppler data (in theory at least 6 points, since they are solving for 6 variables).  The plane-of-sky position should be obtainable with reasonable accuracy since there will be several thousand-km baselines obtained by observation from different antennas and Earth rotation.  Unlike spacecraft at distant locations (such as Mars) these baselines are a significant fraction of the distance to the spacecraft, and should result in accurate solutions. Fancy phase-comparison techniques should not be needed for state estimates good enough for launch dispersion corrections.

ADDED:  Yes, this is exactly how it works.  From More Than You Wanted to Know About Webb’s Mid-Course Corrections! (https://blogs.nasa.gov/webb/2021/12/27/more-than-you-wanted-to-know-about-webbs-mid-course-corrections/):
Quote
The burn wasn’t scheduled immediately after launch to give time for the flight dynamics team to receive tracking data from three ground stations, widely separated over the surface of the Earth, thus providing high accuracy for their determination of Webb’s position and velocity, necessary to determine the precise parameters for the correction burn. Ground stations in Malindi Kenya, Canberra Australia, and Madrid Spain provided the necessary ranging data.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gongora on 12/28/2021 03:05 am
Updates thread: https://forum.nasaspaceflight.com/index.php?topic=55472.0
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: mn on 12/28/2021 03:44 am
....

https://blogs.nasa.gov/webb/
...

I love the informative blog posts on that site. Just perfect for the curious layman. Great explanation of the thruster rationale in the latest posting.

Very interesting indeed, so they explain that they always need need to remain on the sun side of L2 so they can use the thrusters to push back towards L2. If they overshoot and end up on the wrong side of L2 there are no thrusters on this side to push the spacecraft back towards L2.

https://blogs.nasa.gov/webb/2021/12/27/more-than-you-wanted-to-know-about-webbs-mid-course-corrections/

Quote
This means the thrusters can only push Webb away from the Sun, not back toward the Sun (and Earth). We thus design the launch insertion and the MCCs to always keep us on the uphill side of the gravitational potential,  we never want to go over the crest – and drift away downhill on the other side, with no ability to come back
.

Does this mean really no way or it would be a big headache?

Could they hypothetically rotate the spacecraft, fire the thrusters and then turn back around (And wait for the camera systems to cool off again)? Or is that not possible for some reason?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/28/2021 04:09 am
....

https://blogs.nasa.gov/webb/ (https://blogs.nasa.gov/webb/)
...

I love the informative blog posts on that site. Just perfect for the curious layman. Great explanation of the thruster rationale in the latest posting.

Very interesting indeed, so they explain that they always need need to remain on the sun side of L2 so they can use the thrusters to push back towards L2. If they overshoot and end up on the wrong side of L2 there are no thrusters on this side to push the spacecraft back towards L2.

https://blogs.nasa.gov/webb/2021/12/27/more-than-you-wanted-to-know-about-webbs-mid-course-corrections/ (https://blogs.nasa.gov/webb/2021/12/27/more-than-you-wanted-to-know-about-webbs-mid-course-corrections/)

Quote
This means the thrusters can only push Webb away from the Sun, not back toward the Sun (and Earth). We thus design the launch insertion and the MCCs to always keep us on the uphill side of the gravitational potential,  we never want to go over the crest – and drift away downhill on the other side, with no ability to come back
.

Does this mean really no way or it would be a big headache?

Could they hypothetically rotate the spacecraft, fire the thrusters and then turn back around (And wait for the camera systems to cool off again)? Or is that not possible for some reason?

The reason given is that pointing the optics and instruments in the direction of the sun would destroy them.


"If Webb gets too much thrust, it can’t turn around to move back toward Earth because that would directly expose its telescope optics and structure to the Sun, overheating them and aborting the science mission before it can even begin."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 12/28/2021 10:26 am
At last check of "Where is WEBB?", its Cruising Speed was down to 0.669 miles per second, or 2,408 miles per hour, or 47 mph slower than the top speed of the SR-71 Blackbird.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/28/2021 02:33 pm
I think this is scheduled for today:

Deploy L and R forward unitized pallet structures
Deploy L and R aft unitized pallet structures
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: kessdawg on 12/28/2021 03:01 pm
The nerd in me can't wait for the temperature on the "Where is Webb" site to start updating!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/28/2021 05:56 pm
Forward Pallet Structure Lowered, Beginning Multiple-Day Sunshield Deployment

https://blogs.nasa.gov/webb/
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: JonAl on 12/28/2021 07:58 pm
Can't understand nasa's "where is JWST web" speed, please clarify
If JWST distance to L2 today is 655471 miles and speed is 0,7589 miles/second it would take:
655471ml/0,7589ml/s=863712 seconds=863712/60/60/24=10 days to reach L2, while graphic shows only 2,5 days travelled in a 30 day journey
Besides, being escape speed from earth 6,95ml/s, how can it be traveling at not even 1 ml/s
Can anybody clarify why?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Svetoslav on 12/28/2021 08:02 pm
I got a question from a friend... I'll be glad if someone can answer him. To quote:

Quote
"I have a question for you. I inquired on the Internet, but could not answer. I heard that "James Webb" will be positioned at the L2 point of Lagrange, why exactly there? Aren't L4 and L5 more appropriate? L4 and L5 are more stable points compared to L1 and L2. Therefore, the space object that will be in them (in the case of the James Webb telescope) will have to perform various maneuvers to stay in these areas.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/28/2021 08:03 pm
Can't understand nasa's "where is JWST web" speed, please clarify
If JWST distance to L2 today is 655471 miles and speed is 0,7589 miles/second it would take:
655471ml/0,7589ml/s=863712 seconds=863712/60/60/24=10 days to reach L2, while graphic shows only 2,5 days travelled in a 30 day journey
Besides, being escape speed from earth 6,95ml/s, how can it be traveling at not even 1 ml/s
Can anybody clarify why?

It's coasting up a hill (Earth's gravity well) and slowing down the entire time.  IIRC, it was 9-somthing miles/second at separation.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/28/2021 08:09 pm
I got a question from a friend... I'll be glad if someone can answer him. To quote:

Quote
"I have a question for you. I inquired on the Internet, but could not answer. I heard that "James Webb" will be positioned at the L2 point of Lagrange, why exactly there? Aren't L4 and L5 more appropriate? L4 and L5 are more stable points compared to L1 and L2. Therefore, the space object that will be in them (in the case of the James Webb telescope) will have to perform various maneuvers to stay in these areas.


To keep the sun, earth and moon on the back side of the spacecraft
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/28/2021 08:11 pm
I got a question from a friend... I'll be glad if someone can answer him. To quote:

Quote
"I have a question for you. I inquired on the Internet, but could not answer. I heard that "James Webb" will be positioned at the L2 point of Lagrange, why exactly there? Aren't L4 and L5 more appropriate? L4 and L5 are more stable points compared to L1 and L2. Therefore, the space object that will be in them (in the case of the James Webb telescope) will have to perform various maneuvers to stay in these areas.

To keep the sun, earth and moon on the back side of the spacecraft

In other words, to keep the cold side away from heat sources, correct?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/28/2021 08:11 pm
Can't understand nasa's "where is JWST web" speed, please clarify
If JWST distance to L2 today is 655471 miles and speed is 0,7589 miles/second it would take:
655471ml/0,7589ml/s=863712 seconds=863712/60/60/24=10 days to reach L2, while graphic shows only 2,5 days travelled in a 30 day journey
Besides, being escape speed from earth 6,95ml/s, how can it be traveling at not even 1 ml/s
Can anybody clarify why?

Only circular orbits have a constant speed.  Elliptical orbits have slow speeds at apogee and fast speeds at perigee
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: DanClemmensen on 12/28/2021 08:12 pm
I got a question from a friend... I'll be glad if someone can answer him. To quote:

Quote
"I have a question for you. I inquired on the Internet, but could not answer. I heard that "James Webb" will be positioned at the L2 point of Lagrange, why exactly there? Aren't L4 and L5 more appropriate? L4 and L5 are more stable points compared to L1 and L2. Therefore, the space object that will be in them (in the case of the James Webb telescope) will have to perform various maneuvers to stay in these areas.
Remember: This is Earth-Sun L2, not Earth-Moon L2. Earth-Sun L4 and L5 are 93 million miles away from Earth. L2 is a lot closer, so less power needed to transmit the multiple Gigabytes of data per day. From L2, the Earth is directly behind JWST's sun shield. I speculate that this simplifies the design and mounting of the hi-gain antenna, on the Earth-facing side of the sun shield.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: daveglo on 12/28/2021 08:15 pm
I got a question from a friend... I'll be glad if someone can answer him. To quote:

Quote
"I have a question for you. I inquired on the Internet, but could not answer. I heard that "James Webb" will be positioned at the L2 point of Lagrange, why exactly there? Aren't L4 and L5 more appropriate? L4 and L5 are more stable points compared to L1 and L2. Therefore, the space object that will be in them (in the case of the James Webb telescope) will have to perform various maneuvers to stay in these areas.
Remember: This is Earth-Sun L2, not Earth-Moon L2. Earth-Sun L4 and L5 are 93 million miles away from Earth. L2 is a lot closer, so less power needed to transmit the multiple Gigabytes of data per day. From L2, the Earth is directly behind JWST's sun shield. I speculate that this simplifies the design and mounting of the hi-gain antenna, on the Earth-facing side of the sun shield.

Also of note regarding L4 and L5:  These points are also occupied by small asteroids/rocks BECAUSE they are so stable.  Not good companions for a precision telescope.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: russianhalo117 on 12/28/2021 09:31 pm
Can't understand nasa's "where is JWST web" speed, please clarify
If JWST distance to L2 today is 655471 miles and speed is 0,7589 miles/second it would take:
655471ml/0,7589ml/s=863712 seconds=863712/60/60/24=10 days to reach L2, while graphic shows only 2,5 days travelled in a 30 day journey
Besides, being escape speed from earth 6,95ml/s, how can it be traveling at not even 1 ml/s
Can anybody clarify why?

The tracker has many flaws. Take it as a grain of salt. The days travelled since launch is the only thing that is actually correct other than the satellite name. One other primary flaw is shown below:

Just a caution if you're using the WhereIsWebb page: The "distance from Earth" isn't radial distance. It's distance travelled over its trajectory. Don't read more into it than as a progress bar.

Quote
The distance shown is the approximate distance travelled as opposed to altitude.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/29/2021 12:33 am
Next up:

Spacecraft-to-Optical Telescope Element launch release mechanism
Spacecraft-to-ISIM Electronics Compartment launch release mechanism   
Raise DTA (deployable telescope tower assembly)
Release CJAA (Cryocooler Jitter Attenuation Assy)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/29/2021 01:49 pm
Webb has extra fuel because of an accurate launch - fuel for longer than 10 years of science.

https://blogs.nasa.gov/webb/2021/12/29/nasa-says-webbs-excess-fuel-likely-to-extend-its-lifetime-expectations/

My guess is that they'll end up with even more (or to put it another way, they'll learn how to use less than they predicted). That has happened with a number of NASA spacecraft. They launch with margins to cover contingencies, then they learn how to operate the spacecraft more efficiently.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: DaveMorgan on 12/29/2021 03:22 pm
Good News - they have just started displaying temperatures on their website

Bad News - from my reading of the pop-up - the temps only update once per day :(
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 12/29/2021 04:07 pm
Good News - they have just started displaying temperatures on their website
Bad News - from my reading of the pop-up - the temps only update once per day

Also, if you switch between metric and Freedom units, the input is obviously whole degrees Fahrenheit, even with the two decimal-place display, and therefore the Celsius conversion is false precision.



In spite of my criticism of the page's oddities, I appreciate that it exists.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: JohnLloydJones on 12/29/2021 06:11 pm
Good News - they have just started displaying temperatures on their website
Bad News - from my reading of the pop-up - the temps only update once per day

Also, if you switch between metric and Freedom units, the input is obviously whole degrees Fahrenheit, even with the two decimal-place display, and therefore the Celsius conversion is false precision.



In spite of my criticism of the page's oddities, I appreciate that it exists.

The page is a nice way to engage the public, but under the slick appearance, there's a good deal of smoke and mirrors. The page updates itself every few minutes and it's instructive to see what data it fetches. Apart from the temperatures (which are sent in Celsius regardless of the display option) there is the deployment step and the "launchDateTimeString". In other words those fancy spinning values showing distance are simply calculated from the launch time and some inbuilt model*. As mentioned, the temperatures seem to originate in round numbers on the Fahrenheit scale even if they were converted to Celsius to send to the page.

Note*: I cannot eliminate the possibility that the model can get periodic updates when the page is refreshed, but even so...
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbeale on 12/29/2021 11:00 pm
I understand the online JWST dashboard page is just reporting a nominal distance based on a pre-calculated trajectory. However I am curious about the actual spacecraft control: to calculate a correction burn, I assume you need both the thrust that the engine delivers, and the (time-varying) total mass of the spacecraft. How accurately is the fuel flow rate, specific impulse, and the mass of the spacecraft known?  For example it seems to me difficult to measure the total mass at any time after liftoff, except indirectly through tracking during and after a burn, but that only gives you a trajectory which is a function of both thrust and mass, and doesn't give you those parameters separately (?)  Or is tracking good enough to also detect changes due to radiation pressure over short time periods?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 12/29/2021 11:07 pm
Mass will only change through thruster burns, and those are precisely metered.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Billium on 12/29/2021 11:15 pm
The temperatures on the “hot” side are lower than I expected. I take it the sensors aren’t actually exposed to the sun, obviously. It’s hard to visualize exactly where the reading is coming from. The craft seems to dissipate the heat pretty well, even on the hot side.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/29/2021 11:20 pm
Quite a lot of members are posting discussion items on the "updates" thread... - I hope you will move your posts into this one and try to leave the other thread for updates only.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 12/29/2021 11:48 pm
I understand the online JWST dashboard page is just reporting a nominal distance based on a pre-calculated trajectory. However I am curious about the actual spacecraft control: to calculate a correction burn, I assume you need both the thrust that the engine delivers, and the (time-varying) total mass of the spacecraft. How accurately is the fuel flow rate, specific impulse, and the mass of the spacecraft known?  For example it seems to me difficult to measure the total mass at any time after liftoff, except indirectly through tracking during and after a burn, but that only gives you a trajectory which is a function of both thrust and mass, and doesn't give you those parameters separately (?)  Or is tracking good enough to also detect changes due to radiation pressure over short time periods?
From More Than You Wanted to Know About Webb’s Mid-Course Corrections! (https://blogs.nasa.gov/webb/2021/12/27/more-than-you-wanted-to-know-about-webbs-mid-course-corrections/):
Quote
The burn wasn’t scheduled immediately after launch to give time for the flight dynamics team to receive tracking data from three ground stations, widely separated over the surface of the Earth, thus providing high accuracy for their determination of Webb’s position and velocity, necessary to determine the precise parameters for the correction burn. Ground stations in Malindi Kenya, Canberra Australia, and Madrid Spain provided the necessary ranging data. There was also time to do a test firing of the required thruster before executing the actual burn.
The practice burn will induce an acceleration.  This does not give you the exact thrust, or the exact mass, independently.  But it does give you the acceleration, which is what they need to compute a course correction.  The change in mass during the burn will be quite well approximated as long as the mass is roughly correct, since these burns use little fuel.  Using solar radiation pressure to compute mass is very error prone.  The reflectivities of the surfaces are not known to enough digits and also age.  Instead they know the mass at launch (it's carefully weighed) of about 6000 kg.  It carries 300 kg of propellant.  If the fuel gauge is accurate to 1% (just a guess) that's 3 kg uncertainty out of 6000, or about 0.05%.  That's much better than the uncertainty in the thruster thrust.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/30/2021 12:02 am
There are no propellant gauges on spacecraft
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/30/2021 12:11 am
I understand the online JWST dashboard page is just reporting a nominal distance based on a pre-calculated trajectory. However I am curious about the actual spacecraft control: to calculate a correction burn, I assume you need both the thrust that the engine delivers, and the (time-varying) total mass of the spacecraft. How accurately is the fuel flow rate, specific impulse, and the mass of the spacecraft known?  For example it seems to me difficult to measure the total mass at any time after liftoff, except indirectly through tracking during and after a burn, but that only gives you a trajectory which is a function of both thrust and mass, and doesn't give you those parameters separately (?)  Or is tracking good enough to also detect changes due to radiation pressure over short time periods?

They know the thrust from preflight testing and post launch firings.  They know chamber pressure.    They know the mass from prelaunch.  They can measure velocity change due to a firing.  They can compute thrust and mass loss.  They check this against predicted.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbeale on 12/30/2021 12:24 am
If the fuel flow vs time, and/or the remaining total fuel was precisely known, that would answer the question. I guess I'm curious how precisely known either of those things are. I'd assumed for small thrusters, there is a valve to a pressurized tank, but I don't know what additional sensors there are, or how consistent the fuel flow rates and exhaust velocities are under every circumstance.
I guess you could use something like a load cell on the nozzle mounting to directly measure thrust while operating, but maybe it isn't useful if you end up with better accuracy just from tracking data.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/30/2021 01:35 am
If the fuel flow vs time, and/or the remaining total fuel was precisely known, that would answer the question. I guess I'm curious how precisely known either of those things are. I'd assumed for small thrusters, there is a valve to a pressurized tank, but I don't know what additional sensors there are, or how consistent the fuel flow rates and exhaust velocities are under every circumstance.
I guess you could use something like a load cell on the nozzle mounting to directly measure thrust while operating, but maybe it isn't useful if you end up with better accuracy just from tracking data.

No tank gauge.  Spacecraft  IMU would provide accel data.   And again thrust known by chamber pressure.  The rest of my previous post lists the rest of the data.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: watermod on 12/30/2021 06:25 am
A question generic to space science platforms but brought up by my wife in context of the Web Telescope.
When 100s of millions to 10s of billions of dollars are spent designing a platform that scientist have to queue up to use, AND, the major cost is design, WHY are 5 or 10 not made and launched instead of 1?

Consider Webb.  It's built!  Run off a few more.   If something goes wrong with one the others will work.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ttle2 on 12/30/2021 07:10 am
A question generic to space science platforms but brought up by my wife in context of the Web Telescope.
When 100s of millions to 10s of billions of dollars are spent designing a platform that scientist have to queue up to use, AND, the major cost is design, WHY are 5 or 10 not made and launched instead of 1?

Consider Webb.  It's built!  Run off a few more.   If something goes wrong with one the others will work.

This has been discussed many times before in many threads and a lot of reasons have been listed:

- First of all, the savings will not be that great. Even a direct copy of JWST would cost billions.
- There are no facilities nor people to build another copy concurrently.
- Even if you could get another one for, let's say $2B (you can't), where would the money come from? Assuming the total NASA science funding didn't increase, which mission would you drop?

The whole idea that all proposals should be allowed time on JWST (or some other state-of-the-art instrument) is, to me, very odd.  Not every proposed observation is worth doing. Another thing is that the discussion tends to get focused completely on fancy instruments and not people who actually use them. It is very difficult to find a permanent job in astronomy, so most PhDs end up leaving the field (possibly after a postdoc or two). The last thing needed is more instruments with no people to use the collected data for actually doing science.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: fast on 12/30/2021 07:48 am
A question generic to space science platforms but brought up by my wife in context of the Web Telescope.
When 100s of millions to 10s of billions of dollars are spent designing a platform that scientist have to queue up to use, AND, the major cost is design, WHY are 5 or 10 not made and launched instead of 1?

Consider Webb.  It's built!  Run off a few more.   If something goes wrong with one the others will work.



It is about the product design and production process selected. You aim either at cutting edge performance or optimised for mass production design.
There always options in between, but than they will come at cost of performance. And in case performance is paramount you end up with unique design without ability to reproduce and just accept the risk of falure.

In the end JWST falure will not be the end of the world, mereley 0.0....01% of earth population will even notice it, and all will just move on.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 12/30/2021 01:06 pm
I *think* these are the things that are due today that haven't been done.

Release CJAA (Cryocooler Jitter Attenuation Assy)   
Release CCA (Cooler Compressor Assy)   
Deploy solar trim tab (Aft Momentum Flap)
Release sunshade restraints
Retract sunshade central covers

Maybe the first one was done yesterday, and not reported.  It was scheduled for yesterday.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 12/30/2021 01:17 pm
There are no propellant gauges on spacecraft
It may be true that there is no part labeled "propellant gauge", but there are several ways of figuring out how much fuel is in the tank:
(a) The obvious - you know how much you've started with, and how much you've used.  Reasonable accurate at the beginning, but errors in measuring usage add up, so less accurate at the end.
(b) There is almost always a pressure sensor on the tank.  As the the tank is emptied, the ullage gas expands, and its pressure goes down.  This method needs to know the tank temperature, but that's almost always measured anyway.  Most accurate when tank is full.
(c) Combination of a tank heater and temperature sensor.  Run the heater to supply some energy, which is electrical and can be measured very accurately.  The temperature rise will depend on the thermal mass of fuel in the tank. Most accurate when the tank closer to empty.  Requires calibration from vacuum testing of the spacecraft.

I believe all three are common on comsats, where fuel amounts are a big deal.  Ending life with fuel in the tank costs millions of dollars in opportunity costs, but running out prematurely leaves the craft drifting in GEO, which is very bad.

Between these techniques, operators have a quite good idea of how much fuel is left.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/30/2021 01:28 pm
There are no propellant gauges on spacecraft
It may be true that there is no part labeled "propellant gauge", but there are several ways of figuring out how much fuel is in the tank:
(a) The obvious - you know how much you've started with, and how much you've used.  Reasonable accurate at the beginning, but errors in measuring usage add up, so less accurate at the end.
(b) There is almost always a pressure sensor on the tank.  As the the tank is emptied, the ullage gas expands, and its pressure goes down.  This method needs to know the tank temperature, but that's almost always measured anyway.  Most accurate when tank is full.
(c) Combination of a tank heater and temperature sensor.  Run the heater to supply some energy, which is electrical and can be measured very accurately.  The temperature rise will depend on the thermal mass of fuel in the tank. Most accurate when the tank closer to empty.  Requires calibration from vacuum testing of the spacecraft.

I believe all three are common on comsats, where fuel amounts are a big deal.  Ending life with fuel in the tank costs millions of dollars in opportunity costs, but running out prematurely leaves the craft drifting in GEO, which is very bad.

Between these techniques, operators have a quite good idea of how much fuel is left.

A.  That is what I stated earlier

B.  That doesn’t work.  Most tanks are not blow down but gas is added as propellant is used.

C.  They don’t heat the tanks.  Plus it wouldn’t since the propellant is in zero g and floating most of the time or attached to a propellant acquisition device within the tank.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 12/30/2021 02:13 pm
There are no propellant gauges on spacecraft
It may be true that there is no part labeled "propellant gauge", but there are several ways of figuring out how much fuel is in the tank: [...]
(b) There is almost always a pressure sensor on the tank.  As the the tank is emptied, the ullage gas expands, and its pressure goes down.  This method needs to know the tank temperature, but that's almost always measured anyway.  Most accurate when tank is full.
[...]
B.  That doesn’t work.  Most tanks are not blow down but gas is added as propellant is used.
The Webb tanks are blowdown, according to JWST documentation.  See JWST Propulsion (https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-spacecraft-bus/jwst-propulsion).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: mn on 12/30/2021 02:44 pm
I understand the online JWST dashboard page is just reporting a nominal distance based on a pre-calculated trajectory. However I am curious about the actual spacecraft control: to calculate a correction burn, I assume you need both the thrust that the engine delivers, and the (time-varying) total mass of the spacecraft. How accurately is the fuel flow rate, specific impulse, and the mass of the spacecraft known?  For example it seems to me difficult to measure the total mass at any time after liftoff, except indirectly through tracking during and after a burn, but that only gives you a trajectory which is a function of both thrust and mass, and doesn't give you those parameters separately (?)  Or is tracking good enough to also detect changes due to radiation pressure over short time periods?

I want to add my non expert two cents to everything the experts have already explained.

Without knowing all the details, we do know that NASA has been guiding spacecraft into orbits around other planets, moons, asteroids and random points in space (like L2), for many many years, including numerous 'course correction burns' on the way, with amazing success (with just a few tiny number of notable mistakes).

Every time a spacecraft enters it's intended final orbit successfully I just listen in amazement. I have to give a tip of the hat to the people at NASA JPL (and I'm sure many other teams, JPL just stands out in my mind). The wizards of space is what I call them.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Herb Schaltegger on 12/30/2021 03:02 pm
(Deleted due to unnecessary snark)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/30/2021 03:15 pm
There are no propellant gauges on spacecraft
It may be true that there is no part labeled "propellant gauge", but there are several ways of figuring out how much fuel is in the tank: [...]
(b) There is almost always a pressure sensor on the tank.  As the the tank is emptied, the ullage gas expands, and its pressure goes down.  This method needs to know the tank temperature, but that's almost always measured anyway.  Most accurate when tank is full.
[...]
B.  That doesn’t work.  Most tanks are not blow down but gas is added as propellant is used.
The Webb tanks are blowdown, according to JWST documentation.  See JWST Propulsion (https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-spacecraft-bus/jwst-propulsion).

Sorry, was getting mixed up with Europa Clipper.  JWST SCAT and attitude thrusters share the same hydrazine tank.  It uses a diaphragm PMD.  So pressure is the only way to measure prop utilization, since trying to add up impulses from attitude thrusters is virtually impossible.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 12/30/2021 03:16 pm
There are no propellant gauges on spacecraft
It may be true that there is no part labeled "propellant gauge", but there are several ways of figuring out how much fuel is in the tank: [...]
(c) Combination of a tank heater and temperature sensor.  Run the heater to supply some energy, which is electrical and can be measured very accurately.  The temperature rise will depend on the thermal mass of fuel in the tank. Most accurate when the tank closer to empty.  Requires calibration from vacuum testing of the spacecraft.
C.  They don’t heat the tanks.  Plus it wouldn’t [work] since the propellant is in zero g and floating most of the time or attached to a propellant acquisition device within the tank.
This method not working would be quite surprising to Lockheed, who rate this the most accurate method of gauging a near-empty tank (see Review of Propellant Gauging Methods (http://yspm.net/pdf/4_review.pdf), Dr. Lendler, Lockheed).  It works because the propellant for thrusters must be gathered around the tank outlet, not free floating.

I have not been able to find a source on whether Webb has tank heaters. The spacecraft bus is in constant sunlight, so it may not be needed to keep the tanks from freezing.  On the other hand SOHO, also in constant sunlight, had problems with propellants freezing, and recovery after an anomaly required the use of tank and propellant line heaters.  So they might be there just in case, or for measuring propellant, or both. Perhaps someone on the JWST team can comment?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/30/2021 03:20 pm
I have not been able to find a source on whether Webb has tank heaters. The spacecraft bus is in constant sunlight, so it may not be needed to keep the tanks from freezing.  On the other hand SOHO, also in constant sunlight, had problems with propellants freezing, and recovery after an anomaly required the use of tank and propellant line heaters.  So they might be there just in case, or for measuring propellant, or both. Perhaps someone on the JWST team can comment?

It has tank heaters.

They don't use heat to measure propellant. 

Like I said, I was thinking of Europe Clipper, which has a larger propellant system.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbeale on 12/30/2021 04:08 pm
When a spring-driven deployment like "Aft Momentum Flap" occurs, I assume that changes the orientation of the spacecraft relatively quickly as the flap swings around. I assume attitude control must be self-contained, if the high-gain antenna has a beamwidth only as wide as the earth's disc from L2. Now maybe that one causes only a small change, and maybe the IMU rate sensors are good enough to know precisely, but I'm just curious if alignment using a star tracker works no matter how many degrees off of nominal you suddenly push it, or is there some finite window of capture angles, after which you get lost?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/30/2021 04:20 pm
a.   I assume attitude control must be self-contained,
 b. if the high-gain antenna has a beamwidth only as wide as the earth's disc from L2.
c. Now maybe that one causes only a small change, and maybe the IMU rate sensors are good enough to know precisely,
d. but I'm just curious if alignment using a star tracker works no matter how many degrees off of nominal you suddenly push it, or is there some finite window of capture angles, after which you get lost?

a.  It is.  Can't do it remotely.
b.  There is a medium gain antenna, so direct pointing is not required.
c.  They are
d.  Star and sun sensors are used to find which way it is pointing and update the IMU.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jimvela on 12/30/2021 04:29 pm
When a spring-driven deployment like "Aft Momentum Flap" occurs, I assume that changes the orientation of the spacecraft relatively quickly as the flap swings around. I assume attitude control must be self-contained, if the high-gain antenna has a beamwidth only as wide as the earth's disc from L2. Now maybe that one causes only a small change, and maybe the IMU rate sensors are good enough to know precisely, but I'm just curious if alignment using a star tracker works no matter how many degrees off of nominal you suddenly push it, or is there some finite window of capture angles, after which you get lost?

[Disclaimer- no direct knowledge of JWST]
On all of the star tracker systems I've worked with, they work just fine as far as locking on the star field at any attitude.
There are things like dazzling or obscuring the tracker FOV that can cause problems, but none of the systems I've worked with would have any difficulty with a few degrees per second of motion of the vehicle.  (and generally speaking, they all would work at surprisingly high rates when locked up and providing a solution against the star field.)

All of the spacecraft I've supported had ADCS loops that were running at rates like 10Hz or above, and again would have little difficulty dealing with attitude disruption transients like a mechanism deployment, and even less so for standard deployments that we'd have simulated many, many times pre-launch.

Generally the ADCS systems fused multiple sensor suites including the tracker data, IMU/gyro data, sun sensors, etc.  These all have complexities and behavioral uniqueness around attitude transients- but something like a standard mechanism deployment would have been simulated and tested to death long before launch.

As someone who does test this stuff for a living, I'd be really interested to know how the telemetry from the event compares to the simulated deployment pre-launch.  There's TONS of stuff to learn about how your system flies when you finally get to see it behaving in flight.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 12/30/2021 05:17 pm
I have not been able to find a source on whether Webb has tank heaters. The spacecraft bus is in constant sunlight, so it may not be needed to keep the tanks from freezing.  On the other hand SOHO, also in constant sunlight, had problems with propellants freezing, and recovery after an anomaly required the use of tank and propellant line heaters.  So they might be there just in case, or for measuring propellant, or both. Perhaps someone on the JWST team can comment?

It has tank heaters.

They don't use heat to measure propellant.
This makes sense, at least initially - early in mission life, both the book-keeping and the pressure-measuring are more accurate.  But since the tank has heaters, later in the mission they may want to switch to the heat-temperature system.  That's what the StarDust mission did (https://www.researchgate.net/profile/Boris-Yendler/publication/264840565_Fuel_Estimation_for_Stardust-NExT_Mission/links/5654984f08ae1ef92976b85c/Fuel-Estimation-for-Stardust-NExT-Mission.pdf), even though not designed for it, when the exact amount of propellant was important for an extended mission.  Below is a diagram from that paper (PVT is the pressure method, PGS the thermal method). Note they had a comsat guy do the analysis - this makes sense since this technique is more usual for comsats.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Bogeyman on 12/30/2021 08:22 pm
Does JWST have a camera on board to show the telescope itself? Like, how to confirm that the sunshield is fully deployed etc.?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 12/30/2021 08:24 pm
Does JWST have a camera on board to show the telescope itself? Like, how to confirm that the sunshield is fully deployed etc.?
No
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbeale on 12/30/2021 08:33 pm
Is it known what visual magnitude the fully deployed JWST sunshield is expected to be as viewed from earth, either at deployment, or at L2? Is it within the range of some reasonable sized telescope? I understand the sheets have some significant embossed texture, but I don't know what the overall reflectance vs. angle looks like.

EDIT: I guess this answers the "before" part of that question: unfiltered magnitude of 14.7 as of 29 Dec 21:26 UTC, which had not very much area deployed at that time, and I guess it was something like 40% of the way to L2 at that time.
https://www.virtualtelescope.eu/2021/12/30/the-james-webb-telescope-imaged-on-its-way-to-the-stars-29-dec-2021/

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: TxDoc on 12/30/2021 11:54 pm
Clip of James Webb Telescope Gliding Through Space as Astronomer Captures Video


https://www.newsweek.com/astronomer-captures-video-james-webb-telescope-gliding-through-space-1664307?amp=1

Sent from my moto z4 using Tapatalk

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbeale on 12/31/2021 12:27 am
For some reason I did not see any movie or animation on the Newsweek page, only the still frame. However the VirtualTelescope.eu web page (I think the original source) did show an animated GIF that I could view, at this link:
https://www.virtualtelescope.eu/wordpress/wp-content/uploads/2021/12/JWT_29dec2021_pw17.gif?x93759

It's neat that this can be done with a 17" f/6.8 telescope.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: TxDoc on 12/31/2021 01:31 am
Live SkyTour stream topic JWST

https://youtu.be/-2DZ-7CwoCA

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Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Vahe231991 on 12/31/2021 01:58 am
If the COVID pandemic had not broken out, would the JWST have been launched in March 2021 instead of this month, given that in 2019 NASA announced that the launch of the telescope was being delayed from 2020 to 2021?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Joseph Peterson on 12/31/2021 09:50 am
If the COVID pandemic had not broken out, would the JWST have been launched in March 2021 instead of this month, given that in 2019 NASA announced that the launch of the telescope was being delayed from 2020 to 2021?

It is JWST, so almost certainly not.

That said based on the death toll of my elders COVID did have an impact.  Whether that impact was only a couple months or eight months is something us mere mortals can never calculate, but there was an impact.

Now that JWST has launched either could be true, or both could be false.  What matters now is what has always been critical, Mechaorigami unfolding as planned.  I don't know about you, but I'm on the edge of my seat awaiting each update.

So far so good yet I am kicking myself.

I should have done more yoga in preparation to cross all of my body parts for multiple months.

In hindsight I should have written this the the form of haiku.  The moment is passed and there's nothing to prove.  Instead I must wait to see what JWST can do.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 12/31/2021 12:03 pm
If the COVID pandemic had not broken out, would the JWST have been launched in March 2021 instead of this month, given that in 2019 NASA announced that the launch of the telescope was being delayed from 2020 to 2021?

It would have been earlier. They stopped work in California at least once due to the pandemic. I don't know if there's a way to predict when it would have been, only that it would have been earlier.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 12/31/2021 01:45 pm
If the COVID pandemic had not broken out, would the JWST have been launched in March 2021 instead of this month, given that in 2019 NASA announced that the launch of the telescope was being delayed from 2020 to 2021?
When Hubble was delayed, there were problems found during the delay that it otherwise would have been present at launch.  I have no idea if this is true of Webb ("problem found and averted at last second" does not make a good press release), but it's possible.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 12/31/2021 08:58 pm
A comment on the updates thread: just posting twitter links is not helpful for all of us on mobile devices who aren't members of twitter. I just see a link. Actual text in the message body is much more useful.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: StormtrooperJoe on 01/01/2022 12:00 am
Does anyone know how many of those single points of failure JWST has passed? With the recent deployment of the port boom, we must be through a good portion of them.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Toast on 01/01/2022 12:01 am
Didn't want to clutter up the updates thread, so I'll put this here.

https://blogs.nasa.gov/webb/2021/12/31/first-of-two-sunshield-mid-booms-deploys/

Quote
Switches that should have indicated that the cover rolled up did not trigger when they were supposed to. However, secondary and tertiary sources offered confirmation that it had. Temperature data seemed to show that the sunshield cover unrolled to block sunlight from a sensor, and gyroscope sensors indicated motion consistent with the sunshield cover release devices being activated.

After analysis, mission management decided to move forward with the regularly planned deployment sequence. The deployment of the five telescoping segments of the motor-driven mid-boom began around 1:30 p.m. EST, and the arm extended smoothly until it reached full deployment at 4:49 p.m.

As Webb’s deployment steps are all human-controlled, the schedule for deployments could continue to change – as today’s activities showed. Shortly before 6:30 p.m., the team decided to proceed with deploying the starboard mid-boom tonight, and the initial steps of that deployment began just after 7 p.m.

So looks like a (thankfully minor) problem with a the sunshield cover release sensor. Other sensors were able to provide data supporting continuing with deployment.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: lcs on 01/01/2022 03:38 am
A comment on the updates thread: just posting twitter links is not helpful for all of us on mobile devices who aren't members of twitter. I just see a link. Actual text in the message body is much more useful.

Webb's sunshield was secured for flight with 107 individual pins, called 'non explosive actuators' which were designed to keep all 5 layers of the sunshield tidy for launch. With the completion of this deployment, all of them have now been successfully released.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/01/2022 11:06 am
A comment on the updates thread: just posting twitter links is not helpful for all of us on mobile devices who aren't members of twitter. I just see a link. Actual text in the message body is much more useful.

Webb's sunshield was secured for flight with 107 individual pins, called 'non explosive actuators' which were designed to keep all 5 layers of the sunshield tidy for launch. With the completion of this deployment, all of them have now been successfully released.

Did each one of those pins count as a single point failure? I know that the spacecraft has something like 340 single points of failure.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 01/01/2022 12:19 pm
Yes, each and all of them had to release properly or the mission would fail (source, youtube vid interview with the lady who was responsible for the pins).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/01/2022 12:46 pm
Yes, each and all of them had to release properly or the mission would fail (source, youtube vid interview with the lady who was responsible for the pins).

That's what I thought. I am only wondering if there's a way to countdown how many single point failures are still left, not that it's really important: until the last one, it's still a nail-biter.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 01/01/2022 12:57 pm
I heard there were temperature sensors aboard; in lieu of web cameras this sounds like a way of monitoring the sun shield's health, specifically effectiveness.  Has the Webb cooled down much since it began deployment?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Johnnyhinbos on 01/01/2022 12:59 pm
Yes, each and all of them had to release properly or the mission would fail (source, youtube vid interview with the lady who was responsible for the pins).
Do you have a link to this video?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 01/01/2022 02:30 pm
I heard there were temperature sensors aboard; in lieu of web cameras this sounds like a way of monitoring the sun shield's health, specifically effectiveness.  Has the Webb cooled down much since it began deployment?

You might enjoy following "Where is WEBB?"  https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

The 4 temperature sensors didn't come to life until early in the deployment sequence.  Right now there is a 325°F difference across the sunshield, between point a and point d.  We'll see how that difference increases once the layers are separated.

Update:  4.5 hours later, that 325°F difference has increased to 431°F as the temperature at a is up to 134°F.

The temperature at d, now at -297°F, will ultimately need to be 80°-100°F lower, with the cryocooler further lowering the temp at the sensitive MIRI.  I guess we'll see this as the sunshield layers get separated tomorrow, some time elapses and we get farther from earth.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 01/01/2022 04:20 pm
First, the disclaimer:  IANARS...just a semi-retired Civil Engineer (a dirt monger).  But space has fascinated me since Sputnik and International Geophysical Year (1958).  So, what follows contains no high science, just a little musing from a guy who's little more than a layman at this.

Looking at the "Where is WEBB?" site, I had been visualizing Webb's journey to a "halo" orbit around Sun-Earth L2 as something like my tossing a raw egg from the ground up to a guy waiting at a 5th floor window.  I toss it nearly vertically at 64 fps.  After 1 second, its velocity is down to 32 fps and it's gone up 48 feet.  After 2 seconds, its velocity is down to 0 and it's gone up another 16 feet, for a total of 64 feet, where my waiting buddy casually reaches out and catches it in the palm of his hand.  Yes, I understand that g is not 32 feet/second2 for Webb, but slowly declining as the square of the distance from the center of our planet.  And I know that the sun's gravity, 28 times that of earth's, figures in to the whole idea of a Lagrange Point.  But, my egg toss metaphor seemed to somewhat fit the ever-slowing Cruise Velocity of Webb, as it closed half the distance to L2 in less than one-quarter of the month-long journey.

But, the closet scientist in me knew that this is not a "vertical" journey like the egg toss, but Webb's separating from the Earth and its solar orbit to take up a special kind of solar orbit of its own.  But it is also going to trace out a "halo orbit" around L2.  I was really having a challenge trying to wrap my brain around that.

And then I stumbled upon this:  https://www.youtube.com/watch?v=6cUe4oMk69E&list=TLGG8tIphgpDAHkwMTAxMjAyMg

And it became much clearer to me.

I hope it is of some benefit to some of the group.  And to the astrophysicists et al. to whom this is basic stuff, my hat's off to you, for working in such an awesome medium.  Pardon those of us who just flirt with the edges of it, and get our minds pleasantly blown.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/01/2022 06:49 pm
Looking at the "Where is WEBB?" site, I had been visualizing Webb's journey to a "halo" orbit around Sun-Earth L2 as something like my tossing a raw egg from the ground up to a guy waiting at a 5th floor window.

Not an expert, but with college physics, it's somewhat like your example of throwing an egg. As you say the sun's gravity remains near constant while the earth's reduces as r^2. At L2 the gravity forces balance the centripetal force of orbit around sun. There's a small force remaining which is pulling towards the earth - L2 axis and this provides the force to make craft orbit L2.

The difference from throwing egg up is that the effective force is not constant. At L2 it is zero and it increases as dr^2 where dr is the distance from L2 (I haven't done any calculations of this but just as I visualize it now). With the egg in constant gravity, it falls down pretty quickly but I'm guessing that with dr^2 force, the last bit, as it rises, happens more and more slowly, the closer it gets. This slowness maybe is what makes it so handy that only very small puffs of thrust keep it balanced there for long periods of time. The last corrective thrust when arriving at L2 is a very fine tuning so that it rises only to the required height and not any further. To follow the egg example, if you threw it too hard it would rise up, slowing and slowing but just when it was about to stop, it would start speeding up upwards again, not something we see in constant gravity.

Is the force going as dr^2 or is it going as dr? Now I think more about it, it might be dr, since the force is negative at altitude lower than L2 but positive at altitude above L2. I guess centripetal force might cancel dr^2 to make it dr. Hand waving without having done any calculations.
 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/01/2022 06:56 pm
see diagram "The Journey to L2" in https://astronomy.com/magazine/news/2021/10/the-james-webb-space-telescope-lives (https://astronomy.com/magazine/news/2021/10/the-james-webb-space-telescope-lives)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 01/01/2022 07:07 pm
see diagram "The Journey to L2" in https://astronomy.com/magazine/news/2021/10/the-james-webb-space-telescope-lives (https://astronomy.com/magazine/news/2021/10/the-james-webb-space-telescope-lives)

See also this link:  http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/lagptsolar.html#c1

Notably, this quoted paragraph from it:  "The Lagrange points L1, L2 and L3 would not appear to be so useful because they are unstable equilibrium points. Like balancing a pencil on its point, keeping a satellite there is theoretically possible, but any perturbing influence will drive it out of equilibrium. However, in practice these Lagrange points have proven to be very useful indeed since a spacecraft can be made to execute a small orbit about one of these Lagrange points with a very small expenditure of energy. They have provided useful places to "park" a spacecraft for observations. These orbits around L1 and L2 are often called "halo orbits".

The "contour lines" of equal gravitational potential were helpful to me, as a frequent user of topographical contour lines.  L4 and L5 are "depressions" and thus "stable".  L1 and L2 are "saddle points"..."low points" in one direction but "high points" in the direction 90° from that. Thus, they are "unstable," but happily the energy to maintain the "halo orbit" is minimal.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: MTom on 01/01/2022 07:17 pm
What will be the speed of JWST relative to L2 while orbiting around them?
And will it be the same can be seen in "Where is webb" site after L2 insertion burn?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 01/01/2022 08:13 pm
Yes, each and all of them had to release properly or the mission would fail (source, youtube vid interview with the lady who was responsible for the pins).
Do you have a link to this video?

Have been looking but cannot find it. The engineer is Amy Lo of Northrop Grumman.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 01/01/2022 08:58 pm
1.  What will be the speed of JWST relative to L2 while orbiting around them?
2.  And will it be the same can be seen in "Where is webb" site after L2 insertion burn?

1.  Per this reference (https://physics.stackexchange.com/questions/41814/james-webb-space-telescopes-halo-orbit-at-lagrange-point-l2), the period of the "halo orbit" is "about half a year".  It is elliptical, with a periapsis of about 160,000 miles and apoapsis of about 517,000 miles.  That gives the circumference--the length of one full "orbit"--of about 2,277,500 miles.  In 180 days, that's an average of about 527 mph...obviously more at periapsis and less at apoapsis.  But, as noted in the neat video in the earlier post, this "halo orbit" is superimposed on the overall solar orbit, with an orbital speed of (if I haven't screwed up the math) of about 34,000 mph.

2.  I doubt it.  The "Cruise Speed" in "Where is WEBB?" (so far, anyway) appears to display the rate at which the Earth-Webb distance is increasing, in miles per hour.  Once Webb is in the "halo orbit," its distance from Earth will be nearly constant, slightly less than 900,000 miles.  Maybe on Day 30 they will change the function to "Orbital Velocity Relative to Sun-Earth L2" but I don't recall seeing anything to suggest this.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: MTom on 01/01/2022 09:27 pm
The "Cruise Speed" in "Where is WEBB?" (so far, anyway) appears to display the rate at which the Earth-Webb distance is increasing, in miles per hour.
Are you sure about it? (I don't know it, this is only a question from me)
I guess, in the early days there isn't a big difference between the speed how the distance increasing and the speed of spacecraft on the trajectory (without the speed on overall solar orbit).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 01/01/2022 10:07 pm
The "Cruise Speed" in "Where is WEBB?" (so far, anyway) appears to display the rate at which the Earth-Webb distance is increasing, in miles per hour.
Are you sure about it? (I don't know it, this is only a question from me)
I guess, in the early days there isn't a big difference between the speed how the distance increasing and the speed of spacecraft on the trajectory (without the speed on overall solar orbit).

I just looked at a one minute increment and the Distance From Earth increased 23.7 miles.  That's 1,422 mph.  The Cruise Speed was noting 0.3977 miles per second, which is 1,432 mph.  I can't tell you any more than that.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: fthomassy on 01/01/2022 10:18 pm
The "Cruise Speed" in "Where is WEBB?" (so far, anyway) appears to display the rate at which the Earth-Webb distance is increasing, in miles per hour.
Are you sure about it? (I don't know it, this is only a question from me)
I guess, in the early days there isn't a big difference between the speed how the distance increasing and the speed of spacecraft on the trajectory (without the speed on overall solar orbit).
The site states that distance, and one would suppose speed, is measured along the flight path. So they could continue this while in the L2 Halo orbit. But the site also states that updates will switch to temperature only after MCC2 (final insertion).

See “About This Page” link for more complete information.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/01/2022 10:35 pm
Just ignore the velocity.  It is for the public .
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: DaveS on 01/01/2022 11:51 pm
Just ignore the velocity.  It is for the public .
So like the names of every single mission NASA has ever launched?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/01/2022 11:58 pm
Just ignore the velocity.  It is for the public .
So like the names of every single mission NASA has ever launched?

yep
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Joseph Peterson on 01/02/2022 04:17 am
... with a periapsis of about 160,000 wiles and apoapsis of about 517,000 miles. 

I am familiar with the area unit, Wales, but not the distance unit, wiles.  Can you tell me how long a wile is in terms of the percentage of the maximum velocity of a spherical sheep in a vacuum per fortnight?



For those that don't get the joke, I am referencing El Reg unit conversions (https://www.theregister.com/Design/page/reg-standards-converter.html) while pretending not to understand the obvious typo.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: DanClemmensen on 01/02/2022 04:52 am
... with a periapsis of about 160,000 wiles and apoapsis of about 517,000 miles. 

I am familiar with the area unit, Wales, but not the distance unit, wiles.  Can you tell me how long a wile is in terms of the percentage of the maximum velocity of a spherical sheep in a vacuum per fortnight?



For those that don't get the joke, I am referencing El Reg unit conversions (https://www.theregister.com/Design/page/reg-standards-converter.html) while pretending not to understand the obvious typo.
:) The Wile is a unit of ensnarement, as in "beware of her wiles".   A Web(b) would have a large ensnarement value.  :)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Joseph Peterson on 01/02/2022 05:04 am
... with a periapsis of about 160,000 wiles and apoapsis of about 517,000 miles. 

I am familiar with the area unit, Wales, but not the distance unit, wiles.  Can you tell me how long a wile is in terms of the percentage of the maximum velocity of a spherical sheep in a vacuum per fortnight?



For those that don't get the joke, I am referencing El Reg unit conversions (https://www.theregister.com/Design/page/reg-standards-converter.html) while pretending not to understand the obvious typo.
:) The Wile is a unit of ensnarement, as in "beware of her wiles".   A Web(b) would have a large ensnarement value.  :)

Clever girl.

Jurassic Park quotes aside, I am looking forward to JWST ensnaring images of the earliest stars.  It will be great to know which greats predate Ben Turpin (https://en.wikipedia.org/wiki/Ben_Turpin).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 01/02/2022 07:14 am
Yes, each and all of them had to release properly or the mission would fail (source, youtube vid interview with the lady who was responsible for the pins).
Do you have a link to this video?

kdhilliard found it for me. Thanks!

Quoting him:

  https://youtube.com/watch?v=7bz03OnyD2A
  29 Days on the Edge
  NASA Goddard
  Oct 25, 2021

Amy Lo, Webb Deputy Director for Vehicle Engineering, is in there, but it's Krystal Puga, Webb Release Mechanism Hardware Manager, who discuses the sunshield deployment in detail.  Particularly at 6:19 (https://youtube.com/watch?v=7bz03OnyD2A&t=6m19s):
Quote
Now comes the critical point.  All hundred and seven sunshield release mechanisms need to fire on queue.  One hundred and seven!  They free the five sunshield layers allowing them to extend as the mid-booms deploy.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 01/02/2022 10:12 am
... with a periapsis of about 160,000 wiles and apoapsis of about 517,000 miles. 

I am familiar with the area unit, Wales, but not the distance unit, wiles.  Can you tell me how long a wile is in terms of the percentage of the maximum velocity of a spherical sheep in a vacuum per fortnight?



For those that don't get the joke, I am referencing El Reg unit conversions (https://www.theregister.com/Design/page/reg-standards-converter.html) while pretending not to understand the obvious typo.
:) The Wile is a unit of ensnarement, as in "beware of her wiles".   A Web(b) would have a large ensnarement value.  :)

Clever girl.

Jurassic Park quotes aside, I am looking forward to JWST ensnaring images of the earliest stars.  It will be great to know which greats predate Ben Turpin (https://en.wikipedia.org/wiki/Ben_Turpin).

FIXED, you wily bastards!!
 ::)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: allins on 01/02/2022 03:50 pm
Yes, each and all of them had to release properly or the mission would fail (source, youtube vid interview with the lady who was responsible for the pins).
Do you have a link to this video?

kdhilliard found it for me. Thanks!

There's also a 60 Minutes segment.  The pins are discussed around 8:20.

https://www.cbsnews.com/news/james-webb-space-telescope-60-minutes-2021-12-12/


Quoting him:

  https://youtube.com/watch?v=7bz03OnyD2A
  29 Days on the Edge
  NASA Goddard
  Oct 25, 2021

Amy Lo, Webb Deputy Director for Vehicle Engineering, is in there, but it's Krystal Puga, Webb Release Mechanism Hardware Manager, who discuses the sunshield deployment in detail.  Particularly at 6:19 (https://youtube.com/watch?v=7bz03OnyD2A&t=6m19s):
Quote
Now comes the critical point.  All hundred and seven sunshield release mechanisms need to fire on queue.  One hundred and seven!  They free the five sunshield layers allowing them to extend as the mid-booms deploy.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 01/02/2022 04:06 pm
Unsure if this has been asked recently: where are the thermal sensors on Webb exactly?  From the streams I have seen there seem to be at least 4, with 2 each on the sun and shade sides.  For the shade side, what few images about them I find seem to point at the secondary mirror and base of primary; is that right?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: launchwatcher on 01/02/2022 04:11 pm
Unsure if this has been asked recently: where are the thermal sensors on Webb exactly?  From the streams I have seen there seem to be at least 4, with 2 each on the sun and shade sides.  For the shade side, what few images about them I find seem to point at the secondary mirror and base of primary; is that right?
https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html has a "temperatures are now available" popup if you click on on the "hot side" and "cold side" links which lists:

a) Sunshield UPS Average Temperature (hot side: Sunshield Structure)

b) Spacecraft Equipment Panel Average Temperature (hot side: Spacecraft Bus)

c) Primary Mirror Average Temperature (cold side: Mirrors)

d) Instrument Radiator Temperature (cold side: ISIM)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: mn on 01/02/2022 04:29 pm
Unsure if this has been asked recently: where are the thermal sensors on Webb exactly?  From the streams I have seen there seem to be at least 4, with 2 each on the sun and shade sides.  For the shade side, what few images about them I find seem to point at the secondary mirror and base of primary; is that right?
https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html has a "temperatures are now available" popup if you click on on the "hot side" and "cold side" links which lists:

a) Sunshield UPS Average Temperature (hot side: Sunshield Structure)

b) Spacecraft Equipment Panel Average Temperature (hot side: Spacecraft Bus)

c) Primary Mirror Average Temperature (cold side: Mirrors)

d) Instrument Radiator Temperature (cold side: ISIM)

Just remember that this page shows just 4 of the many sensors.

Quote
Of the many temperature monitoring points on the observatory, this page displays 2 "hot side" and 2 "cold side" temperatures that are a good indication of overall temperature status and trends.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 01/02/2022 07:33 pm
Unsure if this has been asked recently: where are the thermal sensors on Webb exactly?  From the streams I have seen there seem to be at least 4, with 2 each on the sun and shade sides.  For the shade side, what few images about them I find seem to point at the secondary mirror and base of primary; is that right?
https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html has a "temperatures are now available" popup if you click on on the "hot side" and "cold side" links which lists:

a) Sunshield UPS Average Temperature (hot side: Sunshield Structure)

b) Spacecraft Equipment Panel Average Temperature (hot side: Spacecraft Bus)

c) Primary Mirror Average Temperature (cold side: Mirrors)

d) Instrument Radiator Temperature (cold side: ISIM)

Excellent - so obviously making sure the mirror and instruments monitored prioritized.


Although Webb won't be imaging for a while, what is known about it's first round of scientific operations?  I recall somewhere that was presented but it's buried somewhere.  All I can remember was how Jupiter observations (unsure if of the moons or planet, both?) were part of it, but naturally not exclusively.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 01/02/2022 07:47 pm
Although Webb won't be imaging for a while, what is known about it's first round of scientific operations?  I recall somewhere that was presented but it's buried somewhere.  All I can remember was how Jupiter observations (unsure if of the moons or planet, both?) were part of it, but naturally not exclusively.

List of Cycle 1 observations? https://www.stsci.edu/jwst/science-execution/approved-programs/cycle-1-go (https://www.stsci.edu/jwst/science-execution/approved-programs/cycle-1-go)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ttle2 on 01/02/2022 08:44 pm
Although Webb won't be imaging for a while, what is known about it's first round of scientific operations?  I recall somewhere that was presented but it's buried somewhere.  All I can remember was how Jupiter observations (unsure if of the moons or planet, both?) were part of it, but naturally not exclusively.

List of Cycle 1 observations? https://www.stsci.edu/jwst/science-execution/approved-programs/cycle-1-go (https://www.stsci.edu/jwst/science-execution/approved-programs/cycle-1-go)

Besides the General Observer (GO) program listed above, there are also Director's Discretionary Early Release Science (DD-ERS) and Guaranteed Time Observation (GTO) programs, though they are smaller than the GO allocation:

https://www.stsci.edu/jwst/science-execution/approved-ers-programs
https://www.stsci.edu/jwst/science-execution/approved-programs/cycle-1-gto
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbeale on 01/03/2022 02:43 am
It would be fun to see a plot of the a,b,c,d temperature readings over time, but it seems the online dashboard only gives you a current daily snapshot.  Just as a note-to-self, as of right now at 2022-JAN-02 1940 PST it reads:
a 57.78C  136F
b 17.78C  64F
c -116.11C  -177F
d -192.22C  -314F
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ddspaceman on 01/03/2022 03:07 am
https://twitter.com/Dr_ThomasZ/status/1477795233265975298

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: litton4 on 01/03/2022 02:01 pm
Not seen this before - a cool down analysis: (not sure of the source)

Quote
that water band is critical and 99% defines the cooldown sequence…….

the biggest enemy of any cold detector in space is water-ice and you don’t want any (any significant amount) on the detectors because of its effect on the signal ie signal-noise.

When the satellite is launched it has a little bit of surface water contamination (not much due tho the controlled environments in the ground), but unfortunately there can be quite a lot of moisture within some of the structures, especially the composite materials used for strength and weight-saving.

So as soon as these “damp” materials hit the vacuum of space, all the moisture starts wicking and evaporating away (which is good). It behaves as an orbital body, so unless it is ejected with high velocity it will generally follow the same orbit as the satellite (which can be bad in a circular orbit, less so for L2). The worst thing that can happen is that the water vapor reaches any cold surface that is at or below that water band temperature. If it does, it freezes to the surface. This is bad news for these sort of missions because the coldest bits are usually the detectors, so the risk of water-ice collecting on the detectors has to be minimised.

To do this there is an extended “warm phase” at the start of the mission, which you can see on the plot up to about Day 32. During these 32 days dedicated heaters (or decontamination heaters) are kept on which keeps the sensitive parts above the water-ice temperature. The period is calculated, along with a “decontamination analysis”, such that sufficient embedded water is wicked/ evaporated/ dissipated into space and away from the satellite.

Around L+32 days the heaters are switched off, and the “cold bits” of the payload are allowed to start cooling below the water-ice temperature. This is a “passive cooling” phase.

At this stage, the satellite is not ready for science so the cryo-coolers used to achieve final detector temperature are not needed. These are switched on around Day 80, once everything else is passively sufficiently cooled and the satellite is close to its final operational orbit and configuration. This “active cooling” phase takes the detectors down to their operating temps in the 5-20K range. I’m not sure what MIRI CCC is on that graph, but it could be Cryo Contamination Cover or similar, so possibly MIRI has yet one more way to keep water-ice away until the last minute.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Hamish.Student on 01/03/2022 02:23 pm
Sorry for what is probably a basic and obvious question. Obviously, as metal cools it shrinks. The engineers at NASA know this, and so the design of JWST would take into account thermal shrinking as the observatory cools. I wonder how this is done? I assume they would tweak tolerances as needed to make this work at the designed temperature? Simplistic example: This piece needs to be 1m, and it will shrink 10% over the cooling, thus at ambient Earth temperature it is 1.1m. Are there other ways around this? Or is the effect enough that it is negligible? 
Thankyou in advance!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/03/2022 02:36 pm
Sorry for what is probably a basic and obvious question. Obviously, as metal cools it shrinks. The engineers at NASA know this, and so the design of JWST would take into account thermal shrinking as the observatory cools. I wonder how this is done? I assume they would tweak tolerances as needed to make this work at the designed temperature? Simplistic example: This piece needs to be 1m, and it will shrink 10% over the cooling, thus at ambient Earth temperature it is 1.1m. Are there other ways around this? Or is the effect enough that it is negligible? 
Thankyou in advance!

Much of the telescope structure is composite that has a low thermal expansion coefficient.  They have the ability to adjust the components in the optic path that would be affected by changes.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Hamish.Student on 01/03/2022 02:38 pm
Sorry for what is probably a basic and obvious question. Obviously, as metal cools it shrinks. The engineers at NASA know this, and so the design of JWST would take into account thermal shrinking as the observatory cools. I wonder how this is done? I assume they would tweak tolerances as needed to make this work at the designed temperature? Simplistic example: This piece needs to be 1m, and it will shrink 10% over the cooling, thus at ambient Earth temperature it is 1.1m. Are there other ways around this? Or is the effect enough that it is negligible? 
Thankyou in advance!

Much of the telescope structure is composite that has a low thermal expansion coefficient.  They have the ability to adjust the components in the optic path that would be affected by changes.
 

I was wondering that, but I discounted it because I assumed it would add extra complexity they would want to avoid. Thanks for the info!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: cdebuhr on 01/03/2022 02:45 pm
Sorry for what is probably a basic and obvious question. Obviously, as metal cools it shrinks. The engineers at NASA know this, and so the design of JWST would take into account thermal shrinking as the observatory cools. I wonder how this is done? I assume they would tweak tolerances as needed to make this work at the designed temperature? Simplistic example: This piece needs to be 1m, and it will shrink 10% over the cooling, thus at ambient Earth temperature it is 1.1m. Are there other ways around this? Or is the effect enough that it is negligible? 
Thankyou in advance!

Much of the telescope structure is composite that has a low thermal expansion coefficient.  They have the ability to adjust the components in the optic path that would be affected by changes.
 

I was wondering that, but I discounted it because I assumed it would add extra complexity they would want to avoid. Thanks for the info!
A precision optical system such as this needs to be in very precise alignment (on the order of a few dozen nm in this case, I believe) ... way beyond what would survive launch.  Final alignments are done as part of deployment and commissioning.  There's going to be literally hundreds on positioning actuators on the optical components, some needed for normal operations, some just for alignments.  For example, each one of the 18 primary mirror segments is actuated on 7 axes (3 position, 3 rotation, 1 of curvature).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/03/2022 03:11 pm
Sorry for what is probably a basic and obvious question. Obviously, as metal cools it shrinks. The engineers at NASA know this, and so the design of JWST would take into account thermal shrinking as the observatory cools. I wonder how this is done? I assume they would tweak tolerances as needed to make this work at the designed temperature? Simplistic example: This piece needs to be 1m, and it will shrink 10% over the cooling, thus at ambient Earth temperature it is 1.1m. Are there other ways around this? Or is the effect enough that it is negligible? 
Thankyou in advance!

Much of the telescope structure is composite that has a low thermal expansion coefficient.  They have the ability to adjust the components in the optic path that would be affected by changes.
 

I was wondering that, but I discounted it because I assumed it would add extra complexity they would want to avoid. Thanks for the info!
A precision optical system such as this needs to be in very precise alignment (on the order of a few dozen nm in this case, I believe) ... way beyond what would survive launch.  Final alignments are done as part of deployment and commissioning.  There's going to be literally hundreds on positioning actuators on the optical components, some needed for normal operations, some just for alignments.  For example, each one of the 18 primary mirror segments is actuated on 7 axes (3 position, 3 rotation, 1 of curvature).

A 126 variable optimization problem sounds like there might be just a hint of math and data collection behind it.  I'm guessing they have some very specific observations planned to help them find the right places to put all those knobs?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 01/03/2022 04:43 pm
Sorry for what is probably a basic and obvious question. Obviously, as metal cools it shrinks. The engineers at NASA know this, and so the design of JWST would take into account thermal shrinking as the observatory cools. I wonder how this is done? I assume they would tweak tolerances as needed to make this work at the designed temperature? Simplistic example: This piece needs to be 1m, and it will shrink 10% over the cooling, thus at ambient Earth temperature it is 1.1m. Are there other ways around this? Or is the effect enough that it is negligible? 
Thankyou in advance!

Much of the telescope structure is composite that has a low thermal expansion coefficient.  They have the ability to adjust the components in the optic path that would be affected by changes.
 

I was wondering that, but I discounted it because I assumed it would add extra complexity they would want to avoid. Thanks for the info!
A precision optical system such as this needs to be in very precise alignment (on the order of a few dozen nm in this case, I believe) ... way beyond what would survive launch.  Final alignments are done as part of deployment and commissioning.  There's going to be literally hundreds on positioning actuators on the optical components, some needed for normal operations, some just for alignments.  For example, each one of the 18 primary mirror segments is actuated on 7 axes (3 position, 3 rotation, 1 of curvature).

A 126 variable optimization problem sounds like there might be just a hint of math and data collection behind it.  I'm guessing they have some very specific observations planned to help them find the right places to put all those knobs?
Each segment can be treated individually (as they will all be aligned to the same desired datum) so you have 18 7-way problems to solve rather than one 126-way. You also have a predetermined target state to aim for rather than an undefined optimum state to locate, also making the task easier.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Herb Schaltegger on 01/03/2022 04:55 pm
Sorry for what is probably a basic and obvious question. Obviously, as metal cools it shrinks. The engineers at NASA know this, and so the design of JWST would take into account thermal shrinking as the observatory cools. I wonder how this is done? I assume they would tweak tolerances as needed to make this work at the designed temperature? Simplistic example: This piece needs to be 1m, and it will shrink 10% over the cooling, thus at ambient Earth temperature it is 1.1m. Are there other ways around this? Or is the effect enough that it is negligible? 
Thankyou in advance!
Much of the telescope structure is composite that has a low thermal expansion coefficient.  They have the ability to adjust the components in the optic path that would be affected by changes.
 

I was wondering that, but I discounted it because I assumed it would add extra complexity they would want to avoid. Thanks for the info!
A precision optical system such as this needs to be in very precise alignment (on the order of a few dozen nm in this case, I believe) ... way beyond what would survive launch.  Final alignments are done as part of deployment and commissioning.  There's going to be literally hundreds on positioning actuators on the optical components, some needed for normal operations, some just for alignments.  For example, each one of the 18 primary mirror segments is actuated on 7 axes (3 position, 3 rotation, 1 of curvature).

A 126 variable optimization problem sounds like there might be just a hint of math and data collection behind it.  I'm guessing they have some very specific observations planned to help them find the right places to put all those knobs?
Each segment can be treated individually (as they will all be aligned to the same desired datum) so you have 18 7-way problems to solve rather than one 126-way. You also have a predetermined target state to aim for rather than an undefined optimum state to locate, also making the task easier.

I doubt they will solve this analytically at all, except as a first-pass estimate. They will likely use focus or guide stars and stellar objects, and drive the actuators algorithmically to yield as close-to-ideal focus as possible.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/03/2022 05:57 pm
Sorry for what is probably a basic and obvious question. Obviously, as metal cools it shrinks. The engineers at NASA know this, and so the design of JWST would take into account thermal shrinking as the observatory cools. I wonder how this is done? I assume they would tweak tolerances as needed to make this work at the designed temperature? Simplistic example: This piece needs to be 1m, and it will shrink 10% over the cooling, thus at ambient Earth temperature it is 1.1m. Are there other ways around this? Or is the effect enough that it is negligible? 
Thankyou in advance!

Much of the telescope structure is composite that has a low thermal expansion coefficient.  They have the ability to adjust the components in the optic path that would be affected by changes.
 

I was wondering that, but I discounted it because I assumed it would add extra complexity they would want to avoid. Thanks for the info!
A precision optical system such as this needs to be in very precise alignment (on the order of a few dozen nm in this case, I believe) ... way beyond what would survive launch.  Final alignments are done as part of deployment and commissioning.  There's going to be literally hundreds on positioning actuators on the optical components, some needed for normal operations, some just for alignments.  For example, each one of the 18 primary mirror segments is actuated on 7 axes (3 position, 3 rotation, 1 of curvature).

A 126 variable optimization problem sounds like there might be just a hint of math and data collection behind it.  I'm guessing they have some very specific observations planned to help them find the right places to put all those knobs?
Each segment can be treated individually (as they will all be aligned to the same desired datum) so you have 18 7-way problems to solve rather than one 126-way. You also have a predetermined target state to aim for rather than an undefined optimum state to locate, also making the task easier.

That doesn't sound possible, since each segment contributes light to every pixel.  How can you separate them to treat them individually?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Mike_1179 on 01/03/2022 06:38 pm
From the Update thread:

Undoubtedly, but there's no way they'd stop using a healthy $10B observatory, so most people consider these mission extensions formalities, assuming the instrument is still viable.

Let me add a caveat to that: the approval may be considered little more than a formality, but the budget to do it is not. Put another way, if the telescope is still healthy, they will get approval to continue, but they may not get all the money they request to continue in the way that they want to. They probably will get all of the requested budget, but NASA still undertakes a formal review of all that.

Several years ago we did a big study on the process by which missions are approved to continue, known as the senior review process. I have this vague recollection that certain really big astronomy projects are exempted from the senior review process but still undergo their own type of mission extension review. But the point is that nobody gets automatic money, they have to apply to continue.

Is that what happened to SOFIA?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/03/2022 06:49 pm
From the Update thread:

Undoubtedly, but there's no way they'd stop using a healthy $10B observatory, so most people consider these mission extensions formalities, assuming the instrument is still viable.

Let me add a caveat to that: the approval may be considered little more than a formality, but the budget to do it is not. Put another way, if the telescope is still healthy, they will get approval to continue, but they may not get all the money they request to continue in the way that they want to. They probably will get all of the requested budget, but NASA still undertakes a formal review of all that.

Several years ago we did a big study on the process by which missions are approved to continue, known as the senior review process. I have this vague recollection that certain really big astronomy projects are exempted from the senior review process but still undergo their own type of mission extension review. But the point is that nobody gets automatic money, they have to apply to continue.

Is that what happened to SOFIA?


Actually, no, not exactly. (And I'll be honest that astrophysics policy isn't something I'm very familiar with. Planetary science policy is much more my wheelhouse.)

I think--and maybe somebody can correct me--that Hubble may have been exempted from the main senior review process but underwent its own form of senior review. I don't know if the same was also done for Chandra and Spitzer. The really big astrophysics programs are sorta different than everything else because they are tied to institutions. If you shut down Hubble, do you also shut down the Space Telescope Science Institute? (No, but you sorta see how the linkage is relevant, right?)

However, SOFIA was supposed to be part of the normal astrophysics senior review process and then Congress stepped in several years ago and exempted it because they wanted to protect it. Somebody in Congress feared that SOFIA would fare poorly in the senior review process and would not get funded. Automatic continuance, regardless of the scientific merit of the program. SOFIA has a lot of politics behind it in large part because of the international aspect, and very little of that is public.

I will add that NASA's senior review process is a great way to evaluate their ongoing missions. They look at their science productivity and determine if the money is being spent productively. Almost every working spacecraft will be approved to continue, but NASA makes sure that they are getting the most out of them. 


Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/03/2022 07:12 pm
Ugh, my post got eaten by solar flares and my description got lost.

Here's the report we did on how NASA extends its science missions beyond their primary phase. Maybe I'll update this and add in my explanation again. But not now.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: photonic on 01/03/2022 08:08 pm

[...]

That doesn't sound possible, since each segment contributes light to every pixel.  How can you separate them to treat them individually?

The whole procedure is called 'Wavefront sensing and control' and is explained in this paper (https://www.researchgate.net/publication/258718428_Wavefront_Sensing_and_Controls_for_the_James_Webb_Space_Telescope) (click on 'download full-text PDF' in the top right).

Initially, the 18 segment will be very misaligned, so you will see 18 separate spots when imaging a bright star. A first step is to identify which spot belongs to which segment, which is pretty simple if you tilt each of them a little bit one at a time. After the spots are identified, they are first placed in an nice array, so that you can do the focusing of all segments in parallel. They are then overlapped in several steps (first with coarse, then with fine actuators). For controlling the so-called 'piston' degree of freedom (how far individual segments differ in height), they use a sort of white light interference technique (see the bit about the 'barber pole' patterns). This is done in pairs of two segments, and uses dedicated hardware (prisms/gratings). They finally do some sort of image analysis to get out some remaining aberrations (e.g. by changing the position of the secondary mirror) which is beyond my understanding of optics.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Urx on 01/03/2022 08:34 pm
Sorry for what is probably a basic and obvious question. Obviously, as metal cools it shrinks. The engineers at NASA know this, and so the design of JWST would take into account thermal shrinking as the observatory cools. I wonder how this is done? I assume they would tweak tolerances as needed to make this work at the designed temperature? Simplistic example: This piece needs to be 1m, and it will shrink 10% over the cooling, thus at ambient Earth temperature it is 1.1m. Are there other ways around this? Or is the effect enough that it is negligible? 
Thankyou in advance!

Much of the telescope structure is composite that has a low thermal expansion coefficient.  They have the ability to adjust the components in the optic path that would be affected by changes.
 

I was wondering that, but I discounted it because I assumed it would add extra complexity they would want to avoid. Thanks for the info!
A precision optical system such as this needs to be in very precise alignment (on the order of a few dozen nm in this case, I believe) ... way beyond what would survive launch.  Final alignments are done as part of deployment and commissioning.  There's going to be literally hundreds on positioning actuators on the optical components, some needed for normal operations, some just for alignments.  For example, each one of the 18 primary mirror segments is actuated on 7 axes (3 position, 3 rotation, 1 of curvature).

A 126 variable optimization problem sounds like there might be just a hint of math and data collection behind it.  I'm guessing they have some very specific observations planned to help them find the right places to put all those knobs?
Each segment can be treated individually (as they will all be aligned to the same desired datum) so you have 18 7-way problems to solve rather than one 126-way. You also have a predetermined target state to aim for rather than an undefined optimum state to locate, also making the task easier.

That doesn't sound possible, since each segment contributes light to every pixel.  How can you separate them to treat them individually?

I was wondering about that as well and followed up on a link in this thread and that lead me to https://www.aura-astronomy.org/blog/2021/12/22/why-will-it-take-six-months-to-see-jwsts-first-science-images/ (https://www.aura-astronomy.org/blog/2021/12/22/why-will-it-take-six-months-to-see-jwsts-first-science-images/).

The sequence of 4 pictures inside the deployment circle explains the process more easily than lots of words.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Herb Schaltegger on 01/03/2022 08:53 pm

[...]

That doesn't sound possible, since each segment contributes light to every pixel.  How can you separate them to treat them individually?

The whole procedure is called 'Wavefront sensing and control' and is explained in this paper (https://www.researchgate.net/publication/258718428_Wavefront_Sensing_and_Controls_for_the_James_Webb_Space_Telescope) (click on 'download full-text PDF' in the top right).

Initially, the 18 segment will be very misaligned, so you will see 18 separate spots when imaging a bright star. A first step is to identify which spot belongs to which segment, which is pretty simple if you tilt each of them a little bit one at a time. After the spots are identified, they are first placed in an nice array, so that you can do the focusing of all segments in parallel. They are then overlapped in several steps (first with coarse, then with fine actuators). For controlling the so-called 'piston' degree of freedom (how far individual segments differ in height), they use a sort of white light interference technique (see the bit about the 'barber pole' patterns). This is done in pairs of two segments, and uses dedicated hardware (prisms/gratings). They finally do some sort of image analysis to get out some remaining aberrations (e.g. by changing the position of the secondary mirror) which is beyond my understanding of optics.

Exactly, as I indicated above. Thanks for the detailed link. This whole process was first worked out (publicly at least) when Earth-based multi-mirror telescopes were designed and built several decades ago.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 01/03/2022 10:15 pm
Bottom sun shield layer tensioned, yay! - I feel that my own tension is easing...

 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/03/2022 11:42 pm
Ugh, my post got eaten by solar flares and my description got lost.

Here's the report we did on how NASA extends its science missions beyond their primary phase. Maybe I'll update this and add in my explanation again. But not now.

Okay, let me try to write again what got eaten when the Matrix glitched.

(We did that study of the mission extension/senior review process back in 2016, which I find a bit hard to believe. But the past two years have either been a million years long or they have not happened at all. I haven't decided which--all I know is they sucked.)

For context, in general, a science mission has a designated primary mission phase. To go beyond that primary mission phase into an extended mission phase they have to go through a senior review process. That's essentially like writing a grant proposal where they say "Here is the science we want to do in the extended mission phase, and here is how much money we want from NASA to do that science. And here's the breakdown of how we're going to spend that money. And here's what we can do if you give us X dollars more than we are asking for. And here's what we can do if you give us Y dollars less than we are asking for." The senior review looks at the proposal, asks questions, and then almost always grants the request for extension, but doesn't always give them the money they want. Extended missions used to be funded for 2 additional years and then teams had to apply again. Now they are funded for 3 additional years before they have to apply again.

Now suppose the primary mission phase does not line up with when the next senior review is taking place. Suppose your primary mission ends in 2023 and the next senior review is in 2024. I think that NASA can provide bridging funds to extend a mission to 2024 and then require them to go through the senior review process. Generally, they want all the missions in a division (like astro, helio, planetary, Earth science) to come up for review at the same time. NASA used to stagger them so that 2 divisions did their reviews in even years and the other 2 did them in odd years. I don't know how they stagger them now but that info should be public somewhere.

The committee's primary recommendation in that 2016 report was that NASA should extend their senior review process from every two years to every three years. Now that may not seem like a big deal, but it really is a big deal. The reason is that the small PI-led missions can spend up to 6 months preparing for a senior review, and 6 months out of 24 months is a lot. That means that a quarter of your time you are not really doing science, you're preparing to ask for the opportunity to do more science. It's inefficient. 6 months out of 36 months is much better. It improves the overall efficiency and return from the missions (especially the small PI-led missions). We considered making it every 4 years, but that seemed like too much, and it might have committed NASA to longer funding times than they wanted to commit. Three years seemed right. It was also justified by the fact that missions are lasting longer.

If you look in that report, it might mention if the really big astrophysics missions are exempted and have their own process. I can't remember and I'm too lazy to look myself. They do get reviewed, however, and the reviews are how NASA makes sure that they are being as productive and well-managed as possible. (As a sidenote, it is possible, although I think it's pretty rare, for another team to propose that they run a mission instead. So the whole process is a way to keep mission teams on their toes and trying to produce the best science out of their missions that they can.)

There are differences in the details, of course. When we did that study, one of the things that had ruffled feathers at NASA was that their own Inspector General said that they should have held a senior review for the MAVEN mission even though it had not yet finished its primary mission phase. That was a rather stupid criticism from the IG. One of the things you have to keep in mind about agency Inspectors General is that they will criticize their agency for violating this or that policy or rule even when there is a perfectly good reason to do so. That's like criticizing Picasso for drawing outside the lines. Not all the missions going up for review line up on the same schedule and planetary has it a bit harder than the rest because of the time it takes to get to their targets, whereas Earth science missions turn on soon after reaching orbit. New Horizons was another case where I think they wanted a much longer mission extension because of the time between targets, but I forget the details.

Something that I remember from that study that will almost certainly apply to JWST is that the science productivity of the mission will increase over time as they figure out how to optimize the use of the telescope. In other words, they will get better at it by year 2, 3, 4 than they will be in year 1. What we heard from some mission PIs was that they spent much of their primary mission phase figuring out how to use their spacecraft, and then in the extended mission phase they were really good at it. I'm sure JWST's team will do the same. That applies to how operations interacts with the science return. For example, they'll figure out that if they turn on instruments in the order ACB it works better than turning them on ABC, or they'll learn how to optimize fuel usage and so on.

Finally, keep in mind that NASA is aware of all this kind of stuff because they have so much experience with it. That means that it is reflected in their future planning and budgets. As an example, NASA has a funding line for mission extensions, which they assume will happen so they don't have to scramble to find the money for them. I am sure that somewhere in the planning for JWST people talked about what they will do if the telescope lasts 15 years. They don't have to think about that today, but it's not like they will scramble and figure out what to do when the operations people come back and tell them that the fuel will last for 13 years at the current rate.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 01/04/2022 12:51 am
Question I wanted to ask, but felt some might consider it jinxing the current deployment... (No reason to add to people's stress.)

Assuming the deployment of the sunshield had failed after the previous step (booms deployed, but tensioning failed), so the telescope has a "single" layer sunshield, but the rest of the optics unpacks correctly. Or alternatively, everything deploys but the cooling system fails.

How much science could the spacecraft still do? Obviously it's still a large telescope, and it can still work in red through near-IR. But can the instruments delivery useful data at all outside of their intended operating temperature range (sub-50K)? Go further, what if the sunshield booms hadn't deployed and the mirror assembly is exposed to sunlight unless angled directly away from the sun?

There's a lot of commentary about "single-points-of-failure", but how many are actually mission-ending rather than mission-limiting?

[edit: Redliox asked a similar question in the updates thread.]
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Mark S on 01/04/2022 01:27 am
Bottom sun shield layer tensioned, yay! - I feel that my own tension is easing...

Hm. The NASA animations show the top layer being tensioned first. Assuming that the top layer is the one closest to the mirror and farthest from the spacecraft portion of the telescope. At least the top layer slides up the poles first (deploying?). I guess the actual tensioning could be done in any order once the layers are deployed, and would not really be visible in the animation.

Seems like forever since anything changed on the "Where's Webb" page, but I know logically that it's only been a few days. The last completed step is still listed as "Sunshield STARBOARD Mid-Boom" at 6th+ day.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbeale on 01/04/2022 01:29 am
Reported temperature readings (deg. C) on JWST dashboard. Cold side got colder, especially (c) mirror temp.

    day       a       b         c       d
2022-01-02   57.78   17.78   -116.11   -192.22
2022-01-03   58.89   18.89   -131.67   -194.44

a) Sunshield UPS Average Temperature (hot side: Sunshield Structure)
b) Spacecraft Equipment Panel Average Temperature (hot side: Spacecraft Bus)
c) Primary Mirror Average Temperature (cold side: Mirrors)
d) Instrument Radiator Temperature (cold side: ISIM)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: daveglo on 01/04/2022 01:58 am
Reported temperature readings (deg. C) on JWST dashboard. Cold side got colder, especially (c) mirror temp.

    day       a       b         c       d
2022-01-02   57.78   17.78   -116.11   -192.22
2022-01-03   58.89   18.89   -131.67   -194.44

a) Sunshield UPS Average Temperature (hot side: Sunshield Structure)
b) Spacecraft Equipment Panel Average Temperature (hot side: Spacecraft Bus)
c) Primary Mirror Average Temperature (cold side: Mirrors)
d) Instrument Radiator Temperature (cold side: ISIM)

Converted to degF and added some earlier data.

    day       a       b         c       d
2022-01-01   134.00   ?????   ?????   -297.00
2022-01-02   136.00   64.00   -177.00   -314.00
2022-01-03   138.00   66.00   -205.00   -318.00


What do you think the odds are that this is pre-programmed data, loosely based on a simulation, and having very little to do with reality?  Am I being too cynical?   :o
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbeale on 01/04/2022 02:21 am
There's a YouTube video with a capture of the dashboard a day earlier (Dec.31) from which I scraped:
82, 47, -49, -229 F at L+6:12:50 so in deg.C that would be:

T      day         a       b         c         d
L+6  2021-12-31   27.78    8.33    -45.0     -145.0
L+7  2022-01-01   56.67                      -182.78
L+8  2022-01-02   57.78   17.78    -116.11   -192.22
L+9  2022-01-03   58.89   18.89    -131.67   -194.44


I'd like to think it's measured data, but I don't personally know.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/04/2022 11:33 am
I looked up the formula for L2 balancing of gravitation and centripetal force. On https://en.wikipedia.org/wiki/Hill_sphere (https://en.wikipedia.org/wiki/Hill_sphere) section "Derivation", it gives this.
Acceleration (w.r.t Earth centre) is a = Re^2/Me[ 1/r^2 - 3Ms*r ] where Me is mass of earth, Ms is mass of sun and Re is Earth-Sun distance. Acceleration is zero at L2 point and is close to a linear function of distance for positions near L2. E.g. if Webb is 95% of L2 distance, the pull towards Earth is about 0.6g. If distance is 99% of L2, then pull is 0.12g.
The trick is to get close to L2 so the pull is close to zero.


Not an expert, but with college physics, it's somewhat like your example of throwing an egg. As you say the sun's gravity remains near constant while the earth's reduces as r^2. At L2 the gravity forces balance the centripetal force of orbit around sun. There's a small force remaining which is pulling towards the earth - L2 axis and this provides the force to make craft orbit L2.
...
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/04/2022 11:41 am
If they needed to remove ice, could they tilt just sightly towards Sun, e.g. pointing at 85 degrees away from Sun, while rotating at some rate so heating is somewhat constant?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/04/2022 12:28 pm
If they needed to remove ice, could they tilt just sightly towards Sun, e.g. pointing at 85 degrees away from Sun, while rotating at some rate so heating is somewhat constant?

Would likely overheat some parts of the spacecraft/telescope.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: launchwatcher on 01/04/2022 01:24 pm
If they needed to remove ice, could they tilt just sightly towards Sun, e.g. pointing at 85 degrees away from Sun, while rotating at some rate so heating is somewhat constant?
Depends on the axis of rotation. 

85 degrees is at the edge of its intended field of view - the Sun-Webb-target angle can range from 85 degrees to 135 degrees.

See:  https://www.youtube.com/watch?v=y0bOi3kVIBs
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: litton4 on 01/04/2022 01:59 pm
Encouraging 3 out of 5 layers went off without a hitch (of course it's preferable).  Although things seem on a good roll, any worst case scenarios if only 3 or 4 layers work?  Is there any calculation on how effective only partial shielding (I will say 3/5 or 4/5 shielding seems pretty darn good [for odds of space-age tin foil not shredding] outside of 5/5) could be is necessary?

Correct me if I'm wrong, but I saw a quote that the 5th layer is an "extra" redundant layer to copy with degradation over time (micro meteorite impacts etc), so could cope with a problem on some layers.....
The layers are also divided into segments to stop tears from spreading.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 01/04/2022 02:40 pm
If they needed to remove ice, could they tilt just sightly towards Sun, e.g. pointing at 85 degrees away from Sun, while rotating at some rate so heating is somewhat constant?

Would likely overheat some parts of the spacecraft/telescope.
Is the overheating recoverable (i.e. requires re-chill and re-commissioning to occur before resuming operations), or does exceeding a certain temperature and/or rate of heating cause permanent deformation or other damage to components that is unrecoverable?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/04/2022 02:46 pm
If they needed to remove ice, could they tilt just sightly towards Sun, e.g. pointing at 85 degrees away from Sun, while rotating at some rate so heating is somewhat constant?

Would likely overheat some parts of the spacecraft/telescope.
Is the overheating recoverable (i.e. requires re-chill and re-commissioning to occur before resuming operations), or does exceeding a certain temperature and/or rate of heating cause permanent deformation or other damage to components that is unrecoverable?

I don't know
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/04/2022 04:10 pm
If they needed to remove ice, could they tilt just sightly towards Sun, e.g. pointing at 85 degrees away from Sun, while rotating at some rate so heating is somewhat constant?
Just thinking about it, no it wouldn't work. top end of mirror would be illuminated first, long before the rest of mirror. Large temp differentials across structure.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/04/2022 04:11 pm
Great news that sun shield is fully deployed!

BTW, what are the mirrored panels that fold out underneath the booms (on sun side)?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/04/2022 04:16 pm
Great news that sun shield is fully deployed!

BTW, what are the mirrored panels that fold out underneath the booms (on sun side)?

hard sun shield
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/04/2022 04:50 pm
Next major tasks on the list:

Deploy DRSA-V Deployable Radiator Shade Assy/Vert.
Deploy Star Tracker Support Assy
Deploy SMSS (Secondary Mirror Support Structure)
SMA (Secondary Mirror Assembly) deployment
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/04/2022 04:59 pm
Correct me if I'm wrong, but I saw a quote that the 5th layer is an "extra" redundant layer to copy with degradation over time (micro meteorite impacts etc), so could cope with a problem on some layers.....
The layers are also divided into segments to stop tears from spreading.

I got to see it a couple of times out at Northrop Grumman--first when they were deploying it, and then a few weeks later when they were folding it back up. We got an explanation from one of the designers about the layers and how it is all threaded and separated. It's actually a very carefully designed structure. I don't remember the specifics, but I think you are right about there being an extra layer and the design being redundant from tears. They also modeled what micrometeorite punctures would do for the thermal control/redundancy, whatever you call it. I think (and this is probably discussed in some JWST video somewhere) that they don't expect a complete puncture all the way through. There would be angles, and that will provide redundancy.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Mike_1179 on 01/04/2022 05:34 pm

They also modeled what micrometeorite punctures would do for the thermal control/redundancy, whatever you call it. I think (and this is probably discussed in some JWST video somewhere) that they don't expect a complete puncture all the way through. There would be angles, and that will provide redundancy.

Do those layers of kapton work as Whipple shields, or are they not substantial enough?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/04/2022 05:48 pm

They also modeled what micrometeorite punctures would do for the thermal control/redundancy, whatever you call it. I think (and this is probably discussed in some JWST video somewhere) that they don't expect a complete puncture all the way through. There would be angles, and that will provide redundancy.

Do those layers of kapton work as Whipple shields, or are they not substantial enough?

I really don't remember. There is some kind of redundancy there, but I don't remember what/how. The only thing I remember him saying was that micrometeorites won't hit at a 90 degree angle.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gdelottle on 01/04/2022 07:19 pm
JWST is known to have 344 single points of failure. Does anyone know if a complete list of these SPFs is available and how many of them have been successfully passed to date?  Even a rough estimate would be interesting.

I don't write much but I have a great interest, partially professional, in this area.

Thanks and sorry if this question has been already asked (and answered).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CruddyCuber on 01/04/2022 07:28 pm
JWST is known to have 344 single points of failure. Does anyone know if a complete list of these SPFs is available and how many of them have been successfully passed to date?  Even a rough estimate would be interesting.

I don't write much but I have a great interest, partially professional, in this area.

Thanks and sorry if this question has been already asked (and answered).

The most recent rough estimate I can find is 75%:

https://twitter.com/NASAWebb/status/1478412564983959553
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/04/2022 08:34 pm
JWST is known to have 344 single points of failure. Does anyone know if a complete list of these SPFs is available and how many of them have been successfully passed to date?  Even a rough estimate would be interesting.

On Nasa tv, they mentioned the flexible membrane part being the most difficult and that the rigid parts were more standard and hence less subject to unknowns.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Greg Hullender on 01/04/2022 09:32 pm
We're used to NASA missions that get extended to many times the nominal mission, like the Opportunity mission that was nominally just 90 days but ended up lasting almost 15 years. Obviously Webb won't last 300 years--even if they figure out a way to refuel it--but I'm wondering what, other than fuel, is most likely to limit the mission duration.

For example, I saw comments that the sunshield was designed to handle 10 years of micrometeoroid impacts, so that's one possible limit, although--as with other things--I wonder if it'll really outlast that by a big margin. Do we have any basis (other than sheer guesswork) to think one way or another?

I note that the instruments on Hubble tend to fail after a while--maybe from long-term exposure to cosmic radiation. Does anyone have a feel for how long the Webb instruments are likely to last?

Or is there some other part of the telescope that's apt to fail earlier than the rest?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: arachnitect on 01/04/2022 10:28 pm
We're used to NASA missions that get extended to many times the nominal mission, like the Opportunity mission that was nominally just 90 days but ended up lasting almost 15 years. Obviously Webb won't last 300 years--even if they figure out a way to refuel it--but I'm wondering what, other than fuel, is most likely to limit the mission duration.

For example, I saw comments that the sunshield was designed to handle 10 years of micrometeoroid impacts, so that's one possible limit, although--as with other things--I wonder if it'll really outlast that by a big margin. Do we have any basis (other than sheer guesswork) to think one way or another?

I note that the instruments on Hubble tend to fail after a while--maybe from long-term exposure to cosmic radiation. Does anyone have a feel for how long the Webb instruments are likely to last?

Or is there some other part of the telescope that's apt to fail earlier than the rest?

The cryocooler for the MIRI instrument is probably a weak point. It's a closed loop system so it doesn't have a fixed lifespan, but the compressor has moving parts that could fail or the helium could leak out.

I don't know what portion of the observatory's science value is attached to MIRI.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/04/2022 10:30 pm
We're used to NASA missions that get extended to many times the nominal mission, like the Opportunity mission that was nominally just 90 days but ended up lasting almost 15 years. Obviously Webb won't last 300 years--even if they figure out a way to refuel it--but I'm wondering what, other than fuel, is most likely to limit the mission duration.

For example, I saw comments that the sunshield was designed to handle 10 years of micrometeoroid impacts, so that's one possible limit, although--as with other things--I wonder if it'll really outlast that by a big margin. Do we have any basis (other than sheer guesswork) to think one way or another?

Maybe Jim can provide a more useful answer, but something that I picked up a number of years ago is that "designed to last X" really means "tested to last X." They test it to a point where they have a certain probability (50%?) that it will last X years. Actually testing it for a longer period may be too expensive, but that doesn't mean that it will die at that X year period.

However, there are examples of NASA spacecraft that pretty much died at their lifetime. I cannot remember the examples, but a number of years ago I heard about a couple of them that exceeded their design lifetime by only a month or two and then died. So it's not the case that all NASA spacecraft last much longer than their predicted lifetimes.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/04/2022 10:39 pm
Reaction wheels, star trackers, basic electronics (see HST), batteries, mechanisms in instruments to name a few
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Nomadd on 01/05/2022 12:17 am
Reaction wheels, star trackers, basic electronics (see HST), batteries, mechanisms in instruments to name a few
Would fuel exhaustion for maneuvering also kill reaction wheel desaturation, since I'm guessing it's too far from Earth to use the Hubble magnetic torque bar system? I have little or no idea how long the scope would be useful without station keeping anyhow.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jimmy_C on 01/05/2022 12:42 am
Here is an interesting video about reaction wheels that failed over the years on satellites. Energic solar events were correlated with reaction wheel failures on the Far Ultraviolet Spectroscopic Explorer, Kepler, Dawn, and Hayabusa. They don't know for sure, and Webb's reaction wheels may not be affected, but it's one possible source of issues.

Scientists May Have Figured Out Why So Many Spacecraft Were Failing
 (https://www.youtube.com/watch?v=KibT-PEMHUU)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbeale on 01/05/2022 01:25 am
Interesting to see that all four displayed temperatures are colder today, than they were yesterday.
Until today, the two "hot side" values had been steadily going up.

Reported temperature readings on JWST dashboard (deg. C)
T      Day       A       B         C        D
L+6  2021-12-31 27.78    8.33    -45.0    -145.0
L+7  2021-01-01 56.67                     -182.78
L+8  2022-01-02 57.78   17.78   -116.11   -192.22
L+9  2022-01-03 58.89   18.89   -131.67   -194.44
L+10 2022-01-04 53.33   11.67   -147.22   -197.22
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/05/2022 02:02 am
Here is an interesting video about reaction wheels that failed over the years on satellites. Energic solar events were correlated with reaction wheel failures on the Far Ultraviolet Spectroscopic Explorer, Kepler, Dawn, and Hayabusa. They don't know for sure, and Webb's reaction wheels may not be affected, but it's one possible source of issues.


those were from a specific manufacturer
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/05/2022 02:03 am
Reaction wheels, star trackers, basic electronics (see HST), batteries, mechanisms in instruments to name a few

Forgot solar array
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/05/2022 02:03 am
Reaction wheels, star trackers, basic electronics (see HST), batteries, mechanisms in instruments to name a few
Would fuel exhaustion for maneuvering also kill reaction wheel desaturation, since I'm guessing it's too far from Earth to use the Hubble magnetic torque bar system? I have little or no idea how long the scope would be useful without station keeping anyhow.

That is the prime use of propellant.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: litton4 on 01/05/2022 08:46 am
Interesting to see that all four displayed temperatures are colder today, than they were yesterday.
Until today, the two "hot side" values had been steadily going up.

Reported temperature readings on JWST dashboard (deg. C)
T      Day       A       B         C        D
L+6  2021-12-31 27.78    8.33    -45.0    -145.0
L+7  2021-01-01 56.67                     -182.78
L+8  2022-01-02 57.78   17.78   -116.11   -192.22
L+9  2022-01-03 58.89   18.89   -131.67   -194.44
L+10 2022-01-04 53.33   11.67   -147.22   -197.22


Cloudy day?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Mike_1179 on 01/05/2022 12:57 pm
Interesting to see that all four displayed temperatures are colder today, than they were yesterday.
Until today, the two "hot side" values had been steadily going up.

Reported temperature readings on JWST dashboard (deg. C)
T      Day       A       B         C        D
L+6  2021-12-31 27.78    8.33    -45.0    -145.0
L+7  2021-01-01 56.67                     -182.78
L+8  2022-01-02 57.78   17.78   -116.11   -192.22
L+9  2022-01-03 58.89   18.89   -131.67   -194.44
L+10 2022-01-04 53.33   11.67   -147.22   -197.22


Cloudy day?

Did they change the spacecraft orientation to allow certain parts to heat up or cool down to aid in deployment? I know they said they had some motors that got hotter than they wanted, so perhaps they rotated to a orientation to help cool those motors and we can see that based on where these thermocouples are located.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: litton4 on 01/05/2022 01:22 pm
Here is an interesting video about reaction wheels that failed over the years on satellites. Energic solar events were correlated with reaction wheel failures on the Far Ultraviolet Spectroscopic Explorer, Kepler, Dawn, and Hayabusa. They don't know for sure, and Webb's reaction wheels may not be affected, but it's one possible source of issues.


those were from a specific manufacturer

Didn't they change to ceramic bearings or something as a result of this finding?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: deadman1204 on 01/05/2022 01:53 pm
Here is an interesting video about reaction wheels that failed over the years on satellites. Energic solar events were correlated with reaction wheel failures on the Far Ultraviolet Spectroscopic Explorer, Kepler, Dawn, and Hayabusa. They don't know for sure, and Webb's reaction wheels may not be affected, but it's one possible source of issues.


those were from a specific manufacturer

Wasn't it more than a specific manufacturer, but all from the same batch or something similar?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 01/05/2022 02:03 pm
Here is an interesting video about reaction wheels that failed over the years on satellites. Energic solar events were correlated with reaction wheel failures on the Far Ultraviolet Spectroscopic Explorer, Kepler, Dawn, and Hayabusa. They don't know for sure, and Webb's reaction wheels may not be affected, but it's one possible source of issues.
those were from a specific manufacturer
Didn't they change to ceramic bearings or something as a result of this finding?
Yes, they did, and there have been no failures with the new models.

I suspect that this does not affect Webb in any case.  As someone once explained, there are $105 reaction wheels, and $106 reaction wheels.  The cheaper ones use physical bearings, the expensive ones use magnetic no-contact bearings.  Many science missions on a limited budget could not afford 4 or more of the fancy ones, and so used cheaper ones, which were the ones that failed.  Webb has 6 reaction wheels, so even more redundant, and I'd guess they are the fancy ones.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: daveglo on 01/05/2022 02:29 pm
Interesting to see that all four displayed temperatures are colder today, than they were yesterday.
Until today, the two "hot side" values had been steadily going up.

Reported temperature readings on JWST dashboard (deg. C)
T      Day       A       B         C        D
L+6  2021-12-31 27.78    8.33    -45.0    -145.0
L+7  2022-01-01 56.67                     -182.78
L+8  2022-01-02 57.78   17.78   -116.11   -192.22
L+9  2022-01-03 58.89   18.89   -131.67   -194.44
L+10 2022-01-04 53.33   11.67   -147.22   -197.22


DegF (eliminates those pesky decimals):

T      Day       A       B         C        D
L+6  2021-12-31 82.0    47.0    -49.00    -229.0
L+7  2022-01-01 134.0                     -297.0
L+8  2022-01-02 136.0   64.00   -177.00   -314.0
L+9  2022-01-03 138.0   66.00   -205.00   -318.0
L+10 2022-01-04 128.0   53.00   -233.00   -323.0
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 01/05/2022 02:57 pm
Also eliminates my comprehension. :-)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: TxDoc on 01/05/2022 03:29 pm
Mirror Deployment
https://youtu.be/-EnlaXnFcGs

Sent from my moto z4 using Tapatalk

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: launchwatcher on 01/05/2022 03:55 pm
Interesting to see that all four displayed temperatures are colder today, than they were yesterday.
Until today, the two "hot side" values had been steadily going up.

Reported temperature readings on JWST dashboard (deg. C)
T      Day       A       B         C        D
L+6  2021-12-31 27.78    8.33    -45.0    -145.0
L+7  2021-01-01 56.67                     -182.78
L+8  2022-01-02 57.78   17.78   -116.11   -192.22
L+9  2022-01-03 58.89   18.89   -131.67   -194.44
L+10 2022-01-04 53.33   11.67   -147.22   -197.22


Cloudy day?

Did they change the spacecraft orientation to allow certain parts to heat up or cool down to aid in deployment? I know they said they had some motors that got hotter than they wanted, so perhaps they rotated to a orientation to help cool those motors and we can see that based on where these thermocouples are located.
An orientation change to reduce motor temperature was mentioned in the January 3rd media briefing.

Quote
One issue was a set of six motors used during sunshield tensioning. Due to sunlight shining upon the motors, they had a slightly higher temperature than expected, so engineers reoriented Webb to put the motors more in the shade.

The shading procedure ran Sunday (Jan. 2) and the motor temperature dropped as expected.

https://www.space.com/james-webb-space-telescope-begins-tensioning-sunshield
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: hoku on 01/05/2022 03:55 pm
Mirror Deployment
<snap>

Sent from my moto z4 using Tapatalk

Just as depicted by Kodak in the lenticular image cards they handed out in 2001...  ;)

Bonus points for spotting the unit conversation mistake on the back of the card  8)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/05/2022 04:22 pm
The optics in the cameras looks quite complex. Lots of mirror bounces. Lots of alignment.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: rsnellenberger on 01/05/2022 04:45 pm
Now, JWST can remain in this configuration and still produce good science
Can MIRI reach its 7K operating temp without Aft Deployed Instrument Radiator deployment?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Greg Hullender on 01/05/2022 04:57 pm
Now, JWST can remain in this configuration and still produce good science
Can MIRI reach its 7K operating temp without Aft Deployed Instrument Radiator deployment?
I think it might be more accurate to say that now we've reached the point where we actually have a working telescope even if there are subsequent failures. Possibly a severely crippled telescope, but prior to this point, failures meant we'd have nothing at all. When you look at it that way, today's secondary-mirror deployment was a pretty big milestone. But with only three or four days to full deployment, it's hard to make a big deal out of it.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/05/2022 05:04 pm
Now, JWST can remain in this configuration and still produce good science
Can MIRI reach its 7K operating temp without Aft Deployed Instrument Radiator deployment?
I think it might be more accurate to say that now we've reached the point where we actually have a working telescope even if there are subsequent failures. Possibly a severely crippled telescope, but prior to this point, failures meant we'd have nothing at all. When you look at it that way, today's secondary-mirror deployment was a pretty big milestone. But with only three or four days to full deployment, it's hard to make a big deal out of it.

The optical alignment process remains crucial.  If that isn't successful, we've still got nothing.  As Jim pointed out, the wings are only a nicety, not a requirement (unlike the secondary mirror), but getting the optics collimated is not optional.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/05/2022 05:15 pm
The optics in the cameras looks quite complex. Lots of mirror bounces. Lots of alignment.

$10 billion buys a lot of complexity.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: litton4 on 01/05/2022 05:20 pm
Now, JWST can remain in this configuration and still produce good science
Can MIRI reach its 7K operating temp without Aft Deployed Instrument Radiator deployment?
I think it might be more accurate to say that now we've reached the point where we actually have a working telescope even if there are subsequent failures. Possibly a severely crippled telescope, but prior to this point, failures meant we'd have nothing at all. When you look at it that way, today's secondary-mirror deployment was a pretty big milestone. But with only three or four days to full deployment, it's hard to make a big deal out of it.

The optical alignment process remains crucial.  If that isn't successful, we've still got nothing.  As Jim pointed out, the wings are only a nicety, not a requirement (unlike the secondary mirror), but getting the optics collimated is not optional.

I think there are something like 6 actuators for each mirror segment, including a centre one that can adjust the curvature....
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/05/2022 05:34 pm
Now, JWST can remain in this configuration and still produce good science
Can MIRI reach its 7K operating temp without Aft Deployed Instrument Radiator deployment?
I think it might be more accurate to say that now we've reached the point where we actually have a working telescope even if there are subsequent failures. Possibly a severely crippled telescope, but prior to this point, failures meant we'd have nothing at all. When you look at it that way, today's secondary-mirror deployment was a pretty big milestone. But with only three or four days to full deployment, it's hard to make a big deal out of it.

The optical alignment process remains crucial.  If that isn't successful, we've still got nothing.  As Jim pointed out, the wings are only a nicety, not a requirement (unlike the secondary mirror), but getting the optics collimated is not optional.

I think there are something like 6 actuators for each mirror segment, including a centre one that can adjust the curvature....

Each main mirror has seven and the secondary has six (I think).  They've got to get all those in the right places or it's HST prior to COSTAR all over again.  I'll be waiting impatiently.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Herb Schaltegger on 01/05/2022 06:17 pm
Now, JWST can remain in this configuration and still produce good science
Can MIRI reach its 7K operating temp without Aft Deployed Instrument Radiator deployment?
I think it might be more accurate to say that now we've reached the point where we actually have a working telescope even if there are subsequent failures. Possibly a severely crippled telescope, but prior to this point, failures meant we'd have nothing at all. When you look at it that way, today's secondary-mirror deployment was a pretty big milestone. But with only three or four days to full deployment, it's hard to make a big deal out of it.

The optical alignment process remains crucial.  If that isn't successful, we've still got nothing.  As Jim pointed out, the wings are only a nicety, not a requirement (unlike the secondary mirror), but getting the optics collimated is not optional.

I think there are something like 6 actuators for each mirror segment, including a centre one that can adjust the curvature....

Each main mirror has seven and the secondary has six (I think).  They've got to get all those in the right places or it's HST prior to COSTAR all over again.  I'll be waiting impatiently.

This is over-stating it, I think. Again, multi-mirror telescope collimation and operation is not new except in microgravity. In principle, so long as you can characterize any partial misalignment of a segment, you can work around it. Characterize the optical effects with guide stars and known stellar objects, then algorithmically deal with the results.

Ideally everything will work perfectly now now and for a decade to come, but multiple segments means some degree of general redundancy and the ability to work around and in spite of some kinds of potential issues like this.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/05/2022 06:43 pm
Now, JWST can remain in this configuration and still produce good science
Can MIRI reach its 7K operating temp without Aft Deployed Instrument Radiator deployment?
I think it might be more accurate to say that now we've reached the point where we actually have a working telescope even if there are subsequent failures. Possibly a severely crippled telescope, but prior to this point, failures meant we'd have nothing at all. When you look at it that way, today's secondary-mirror deployment was a pretty big milestone. But with only three or four days to full deployment, it's hard to make a big deal out of it.

The optical alignment process remains crucial.  If that isn't successful, we've still got nothing.  As Jim pointed out, the wings are only a nicety, not a requirement (unlike the secondary mirror), but getting the optics collimated is not optional.

I think there are something like 6 actuators for each mirror segment, including a centre one that can adjust the curvature....

Each main mirror has seven and the secondary has six (I think).  They've got to get all those in the right places or it's HST prior to COSTAR all over again.  I'll be waiting impatiently.

This is over-stating it, I think. Again, multi-mirror telescope collimation and operation is not new except in microgravity. In principle, so long as you can characterize any partial misalignment of a segment, you can work around it. Characterize the optical effects with guide stars and known stellar objects, then algorithmically deal with the results.

Ideally everything will work perfectly now now and for a decade to come, but multiple segments means some degree of general redundancy and the ability to work around and in spite of some kinds of potential issues like this.

Well, if actuators fail and if the current alignment is as bad as was described above (above it was stated that they are likely nowhere near where they need to be), that could be a big problem - bigger than HST, potentially since it's a multi-mirror scope and you could have multiple images.

Hopefully, all these actuators will work and that won't be a problem.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: jbeale on 01/05/2022 07:35 pm
As far as the potential for actuators and other mechanical parts failing- I'm curious. Obviously JWST as a whole is a dramatically new thing, but apart from the now-deployed 5-layer sunshield, how many moving parts on JWST have not been used before in space? I'd assume designers would want to use already proven devices and subsystems wherever possible. It seems to me NASA and its contractors already have quite a bit of space-proven technology, given the number of successful missions so far.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ttle2 on 01/05/2022 08:01 pm
Well, if actuators fail and if the current alignment is as bad as was described above (above it was stated that they are likely nowhere near where they need to be), that could be a big problem - bigger than HST, potentially since it's a multi-mirror scope and you could have multiple images.

Hopefully, all these actuators will work and that won't be a problem.

I believe the mirrors have to move something like 1 cm from their launch positions before they can even start the finer alignment process. So yes, if they failed to move at all, the telescope would be so very badly out of focus that deconvolving couldn't be effective.

But on-orbit focusing is of course not unique to JWST; all major telescopes need that. 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gparker on 01/05/2022 09:08 pm
Well, if actuators fail and if the current alignment is as bad as was described above (above it was stated that they are likely nowhere near where they need to be), that could be a big problem - bigger than HST, potentially since it's a multi-mirror scope and you could have multiple images.

Hopefully, all these actuators will work and that won't be a problem.
There is some redundancy and graceful degradation in the mirror actuators. A failure is not necessarily catastrophic.

The biggest actuator risk is from those on the secondary mirror before initial commissioning is complete. In many of those cases the secondary mirror would be too far out of position for the other actuators to compensate.

The primary mirror actuators are less of a risk. If a single motor fails then the other actuators can put that segment in a position that either corrects most of the error or (if it's too bad) parks it out of the way so later image processing can mostly neutralize it. The options depend on which actuator failed and how far the commissioning process got.

After commissioning the mirrors will be realigned periodically (several weeks to several months). These adjustments are small compared to the deployment movements. In case of a failure it's easier to compensate using the other actuators and the image degradation is less if they can't. (I suppose an actuator could be stuck on and drive a mirror far out of position. Each actuator motor has redundant electronics which should help prevent that.)

Actuator Usage and Fault Tolerance of the James Webb Space Telescope Optical Telescope Element Mirror Actuators (slideshow summary of the paper (https://slideplayer.com/slide/3971867/))
Wavefront Sensing and Controls for the James Webb Space Telescope
 (https://www.researchgate.net/publication/258718428_Wavefront_Sensing_and_Controls_for_the_James_Webb_Space_Telescope)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ulm_atms on 01/05/2022 09:57 pm
Super basic question...  Have these specific actuators been used in space before?  Just wondering if they have some type of baseline from previous use or if this is the very first time with them in space.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: dmgaba on 01/06/2022 12:49 am
For a very detailed view of most aspects of the post-deployment commissioning I found this slide set from a December 2020 presentation to the JWST Users Committee (see attached PDF). 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gparker on 01/06/2022 06:31 am
Super basic question...  Have these specific actuators been used in space before?  Just wondering if they have some type of baseline from previous use or if this is the very first time with them in space.

They're probably new. The slideshow (https://slideplayer.com/slide/3971867/) mentioned above describes motor tests in 2011 that didn't go as well as they would have liked: they often degraded beyond spec before reaching 2X design life. After a redesign the motors reached 7X design life with no signs of trouble.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gdelottle on 01/06/2022 10:19 am
They're probably new. The slideshow (https://slideplayer.com/slide/3971867/) mentioned above describes motor tests in 2011 that didn't go as well as they would have liked: they often degraded beyond spec before reaching 2X design life. After a redesign the motors reached 7X design life with no signs of trouble.

does anyone know when such design details were frozen? 2005? 2010? Maybe even later?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Citabria on 01/06/2022 12:55 pm
Bonus points for spotting the unit conversation mistake on the back of the card  8)
Hahahaha. AU in miles is wrong... to 9 significant figures!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: litton4 on 01/06/2022 01:02 pm
Does anyone know if they are covering the radiator deployment (today?) and the primary mirror wings (Friday, Saturday?) on NASA TV?

I don't see anything in the schedule, apart from replays of the launch listed.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Gregster on 01/06/2022 01:27 pm
Does anyone know if they are covering the radiator deployment (today?) and the primary mirror wings (Friday, Saturday?) on NASA TV?

I don't see anything in the schedule, apart from replays of the launch listed.

NASA TV will provide live coverage of the unfolding of the second primary mirror wing marking the end of the observatory deployments on Saturday Jan. 8. Time of the coverage TBD. The event will be followed by a media briefing per https://www.nasa.gov/nasalive.
 
No other coverage is listed at this moment.
 
Times for the events will be posted on https://blogs.nasa.gov/webb/
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Star One on 01/06/2022 02:08 pm
The real reason for the sun shield revealed.

https://xkcd.com/2564/
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/06/2022 02:28 pm
Well, if actuators fail and if the current alignment is as bad as was described above (above it was stated that they are likely nowhere near where they need to be), that could be a big problem - bigger than HST, potentially since it's a multi-mirror scope and you could have multiple images.

Hopefully, all these actuators will work and that won't be a problem.

I believe the mirrors have to move something like 1 cm from their launch positions before they can even start the finer alignment process. So yes, if they failed to move at all, the telescope would be so very badly out of focus that deconvolving couldn't be effective.

I found it a bit shocking that they can move 1cm, so I looked it up:

https://www.esmats.eu/amspapers/pastpapers/pdfs/2006/warden.pdf

"The length of the actuator was calculated based on a nominal deployed actuator length of 138.8 mm. The bipod assembly is required to retract 12.5 mm to the stowed position and extend 5.0 mm to the maximum deployed position."

Wow!

Yeah - those actuators had better work!  Fortunately, they tested them like crazy.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: SteveU on 01/06/2022 02:40 pm
Sorry if this has already been discussed.  Will the mirrors need to be adjusted in the future (will they fall out of alignment as they age?) 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: mn on 01/06/2022 03:09 pm
Sorry if this has already been discussed.  Will the mirrors need to be adjusted in the future (will they fall out of alignment as they age?)

Yes they will be adjusted periodically.

See this post: https://forum.nasaspaceflight.com/index.php?topic=54269.msg2328280#msg2328280
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: capoman on 01/06/2022 05:02 pm
Heat radiator successfully deployed.

https://blogs.nasa.gov/webb/2022/01/06/webbs-specialized-heat-radiator-deployed-successfully/

Mirror wings up next.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: SteveU on 01/06/2022 05:02 pm
Sorry if this has already been discussed.  Will the mirrors need to be adjusted in the future (will they fall out of alignment as they age?)

Yes they will be adjusted periodically.

See this post: https://forum.nasaspaceflight.com/index.php?topic=54269.msg2328280#msg2328280
Thanks - can't believe I missed that post - or I saw it and immediately forgot it!!!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: capoman on 01/06/2022 05:11 pm
Interesting blog entry on why there are no deployment cameras, a question we are all probably wondering about.

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

All makes sense, but I bet they wish they had them when the shield cover sensors weren't working properly.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/06/2022 06:18 pm
Interesting blog entry on why there are no deployment cameras, a question we are all probably wondering about.

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

All makes sense, but I bet they wish they had them when the shield cover sensors weren't working properly.

While I understand their explanation, I don't think they were thinking the way we're (or, possibly, "I'm") thinking.

They're thinking, "what do cameras add to engineering analysis if anything goes wrong or during the process of things going right?"

I'm thinking, "how can I get an overview picture of the fully-deployed spacecraft I paid for?"

One of my desktop backgrounds is attached.  The picture itself is worth what I paid for this (to me), and the science generated by it is a massive bonus on top of that.


Pictures like this mean a lot to me and a picture in a ground-based clean-room just isn't the same.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/06/2022 06:28 pm

I'm thinking, "how can I get an overview picture of the fully-deployed spacecraft I paid for?"


there is no way to do that
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/06/2022 06:28 pm
Pictures like this mean a lot to me and a picture in a ground-based clean-room just isn't the same.

Once it starts producing world-class science images, nobody will care about that.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Vettedrmr on 01/06/2022 06:30 pm
I'm thinking, "how can I get an overview picture of the fully-deployed spacecraft I paid for?"

One of my desktop backgrounds is attached.  The picture itself is worth what I paid for this (to me), and the science generated by it is a massive bonus on top of that.


Pictures like this mean a lot to me and a picture in a ground-based clean-room just isn't the same.

I love that photo as well.  BUT, you/we physically can't get a photo like that of JWST when fully deployed.  At best you'd get a photo of the sunshield; everything in the shade of the sunshield would be completely black. 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Yiosie on 01/06/2022 06:36 pm
I'm thinking, "how can I get an overview picture of the fully-deployed spacecraft I paid for?"

One of my desktop backgrounds is attached.  The picture itself is worth what I paid for this (to me), and the science generated by it is a massive bonus on top of that.


Pictures like this mean a lot to me and a picture in a ground-based clean-room just isn't the same.

I love that photo as well.  BUT, you/we physically can't get a photo like that of JWST when fully deployed.  At best you'd get a photo of the sunshield; everything in the shade of the sunshield would be completely black.

These renders modified by Doug Ellison on Twitter illustrate this:

https://twitter.com/doug_ellison/status/1478445088065810435

https://twitter.com/doug_ellison/status/1478488542732980226
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/06/2022 06:52 pm

I'm thinking, "how can I get an overview picture of the fully-deployed spacecraft I paid for?"


there is no way to do that

It wouldn't have to be a free-flyer picture like that one, it could be three pictures - right and left halves of the sunshield (it's probably fore and aft, isn't it...don't remember), and one shot of the main mirror and tower taken by starlight using a long-exposure of the fully-deployed mirror taken from the area around the secondary when the sun isn't directly behind it.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/06/2022 06:54 pm
Pictures like this mean a lot to me and a picture in a ground-based clean-room just isn't the same.

Once it starts producing world-class science images, nobody will care about that.

I have a shot of HST too.  ;-)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Surfdaddy on 01/06/2022 06:57 pm
I'm thinking, "how can I get an overview picture of the fully-deployed spacecraft I paid for?"

One of my desktop backgrounds is attached.  The picture itself is worth what I paid for this (to me), and the science generated by it is a massive bonus on top of that.


Pictures like this mean a lot to me and a picture in a ground-based clean-room just isn't the same.

I love that photo as well.  BUT, you/we physically can't get a photo like that of JWST when fully deployed.  At best you'd get a photo of the sunshield; everything in the shade of the sunshield would be completely black. 

True, but the Chinese got a great selfie of their rover and also a great selfie of their Mars Orbiter with a small free flying camera. And their missions didn't cost $10Billion, either.

I don't think we should underestimate the value of a look at the spacecraft and the environment. Think of the Earthrise from Apollo 8, the view of McCandless floating in his suit and MMU, and the video of SpaceX second stages going into orbit.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/06/2022 07:18 pm

True, but the Chinese got a great selfie of their rover and also a great selfie of their Mars Orbiter with a small free flying camera. And their missions didn't cost $10Billion, either.

I don't think we should underestimate the value of a look at the spacecraft and the environment. Think of the Earthrise from Apollo 8, the view of McCandless floating in his suit and MMU, and the video of SpaceX second stages going into orbit.

who cares?  A free flyer would be a necessary risk to JWST.  There is no planet to reenter it or leave it in the dirt.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/06/2022 07:21 pm

It wouldn't have to be a free-flyer picture like that one, it could be three pictures - right and left halves of the sunshield (it's probably fore and aft, isn't it...don't remember), and one shot of the main mirror and tower taken by starlight using a long-exposure of the fully-deployed mirror taken from the area around the secondary when the sun isn't directly behind it.

Where are the first two cameras?
There is no room around the secondary.

And still not worth the engineering, mass, complexity and cost for the effort for 3 photos
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/06/2022 07:23 pm

It wouldn't have to be a free-flyer picture like that one, it could be three pictures - right and left halves of the sunshield (it's probably fore and aft, isn't it...don't remember), and one shot of the main mirror and tower taken by starlight using a long-exposure of the fully-deployed mirror taken from the area around the secondary when the sun isn't directly behind it.

Where are the first two cameras?

Top of the tower.

Quote
There is no room around the secondary.
It's huge.  The camera can be tiny.

Quote
And still not worth the engineering, mass, complexity and cost for the effort for 3 photos

To you.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 01/06/2022 07:27 pm
True, but the Chinese got a great selfie of their rover and also a great selfie of their Mars Orbiter with a small free flying camera. And their missions didn't cost $10Billion, either.

I don't think we should underestimate the value of a look at the spacecraft and the environment. Think of the Earthrise from Apollo 8, the view of McCandless floating in his suit and MMU, and the video of SpaceX second stages going into orbit.
A free flyer would be a[n] [un]necessary risk to JWST.  There is no planet to reenter it or leave it in the dirt.
I completely agree that a free-flying camera is not worth the trouble, but I don't think it's a re-contact risk.  Webb absolutely has to stay on this side of the gravitational hill that is L2, since its thrusters can only push in the anti-sunward direction.  But that means any nearby free-floating object that does not do any orbital maintenance will slide down the hill, away from Webb.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: kenny008 on 01/06/2022 07:37 pm

It wouldn't have to be a free-flyer picture like that one, it could be three pictures - right and left halves of the sunshield (it's probably fore and aft, isn't it...don't remember), and one shot of the main mirror and tower taken by starlight using a long-exposure of the fully-deployed mirror taken from the area around the secondary when the sun isn't directly behind it.

Where are the first two cameras?

Top of the tower.

Quote
There is no room around the secondary.
It's huge.  The camera can be tiny.

Quote
And still not worth the engineering, mass, complexity and cost for the effort for 3 photos

To you.

Or to those on the project team, as evidenced by the blog article you were originally responding to.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: matthewkantar on 01/06/2022 07:53 pm
We can make this nuttily complicated observatory and set it up a million miles from home, but taking a snap shot of it with a few cameras the size of coin? Impossible!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: dafixer on 01/06/2022 08:08 pm
They (NASA) addressed the camera question in the live broadcast yesterday when they were deploying the secondary mirror. My summary of the discussion was:
1) That the mirror side of Webb is in the dark so there's nothing to see. If they tried to luminate it to take a picture there was concern about damaging the telescope optics. There were very good technical reasons for not attaching a camera to photograph the dark side of the telescope since it would require a camera that can operate at cryogenic temps and the camera would become a hot spot in an area that should otherwise be as cold as possible.
2) A camera on the sun side of the telescope has limited value as that side of the telescope is highly reflective (as evidenced by the Ariane footage of Webb flying off into the sunset). So taking a picture of the sun side of the scope would be akin to taking a photo of a house of mirrors.

They made a convincing argument on why actual photos weren't necessary and of very limited value.


 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 01/06/2022 08:57 pm
We will be receiving lots of photos of the reflective mirrors in the coming years, so no worry     ;)

Only the two sides of the main mirror to go now, we are itchingly close to full deployment, such fantastic news!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/06/2022 09:01 pm

Top of the tower.

And there isn't enough light for a photo from that side and too cold

It's huge. 


Yes, so much that there is no place for a camera and they aren't going to clip it on the mirror directly


To you.

To those that matter
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/06/2022 09:05 pm

I completely agree that a free-flying camera is not worth the trouble, but I don't think it's a re-contact risk.
[/quote]

it is until it reaches L2 and then who knows after few years. 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jack Daniel on 01/06/2022 09:24 pm
My ill-considered opinion on the camera matter is basically as follows:

I would love the pictures, but is it really worth the additional cost for the various risk-assessments that would have to be made? It won't just be finding a place to clip a gopro to, you'll need the data storage and transfer devices, batteries and so forth, you'll need to make sure that all of that equipment is secure, and won't be affected by the vibrations on launch, too; you'll need to fabricate brackets for that. You'll need cameras that are suitable for the extreme cold/heat, and any number of additional minor complications that I'm too dumb to think of.
As with everything, it comes to a cost benefit analysis. They have the telemetry they need, so this would really mainly be for an engagement purpose for people like us. That's worthy, but we're already pretty engaged without it, and there are already enough complications.

The point of this mission is the pictures (or data in general) it will produce, not the pictures of it. I'd love to see the IXPE deployment; that looked amazing, but I don't really need to see it, that's not what it's for. These aren't for looking at, they are the ones who look.

Feel free to tear this opinion apart though, I'm easily swayed.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: John Santos on 01/06/2022 09:30 pm

I completely agree that a free-flying camera is not worth the trouble, but I don't think it's a re-contact risk.

it is until it reaches L2 and then who knows after few years.
[/quote]

A free-flying camera would fall back down the hill after it reaches L2, unless it also has a thruster with sufficient fuel to match JWST's MCC2 burn.

The camera might be tiny and simple, but it would need a thruster (cold gas should be fine) to orient and fly around the telescope, plus a honking big transmitter and antenna to send back video or even stills from (currently) 2.6 times the distance to the moon.

I think in real life, after the final deployments in two days, they would let it drift away.  It would be several kilometers distant in a few hours, and then it would be safe to give a short thrust to increase the distance, and then burn to exhaustion to slow it down and ensure it never comes close again.

However, if it failed in any way, it could become an uncontrolled piece of space junk in close proximity to the most expensive and fragile spacecraft ever launched.

The people building Webb aren't idiots and they did look closely at including a camera or set of cameras and did testing to determine what they would need and how well the available cameras would work.  They did all the risk/benefit analysis including answering as many known unknowns as possible and thinking long and hard about the unknown unknowns before deciding not to include one.

I would love to see images too, but they would be of little value and great risk.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Kaputnik on 01/06/2022 09:32 pm
I'm thinking, "how can I get an overview picture of the fully-deployed spacecraft I paid for?"

One of my desktop backgrounds is attached.  The picture itself is worth what I paid for this (to me), and the science generated by it is a massive bonus on top of that.


Pictures like this mean a lot to me and a picture in a ground-based clean-room just isn't the same.

I love that photo as well.  BUT, you/we physically can't get a photo like that of JWST when fully deployed.  At best you'd get a photo of the sunshield; everything in the shade of the sunshield would be completely black. 

True, but the Chinese got a great selfie of their rover and also a great selfie of their Mars Orbiter with a small free flying camera. And their missions didn't cost $10Billion, either.

I don't think we should underestimate the value of a look at the spacecraft and the environment. Think of the Earthrise from Apollo 8, the view of McCandless floating in his suit and MMU, and the video of SpaceX second stages going into orbit.

It's clear that PR was a huge priority for China. "Look at me! I'm on Mars!". NASA don't have to do that.

I'm not saying that the photos you cite are not of great cultural importance. But an engineering camera is probably not going to create such an image. The HiRISE shots of Mars landers during descent are impressive, but did not lodge in public perception. Even the higher resolution descent imagery from Perseverance was only of passing interest to non space nerds.
I think the presence of humans and/or Earth as a backdrop is a common factor in most of the really iconic images, and some fuzzy, overexposed, wide angle shots of glittering mylar can't compete. And that's all that we'd likely have got from a JWST engineering camera.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 01/06/2022 09:50 pm
Re: Selfie-cams.

PR fluff vs teh sceince! is a battle within NASA that goes back to Carl Sagan and the Voyager probes. People fought to keep the planetary imaging cameras off them, in place of "real instruments". Imagine the next generation of planetary science researchers had been denied those amazing images.

And I suspect a big part of the opposition is similar to the internal scorn heaped on the publicly chosen mission names by the likes of Jim. (IMO, those 8yr olds from Poughkeepsie have a vastly better track record than the mission scientists themselves and their god-awful backronyms.)



I love that photo as well.  BUT, you/we physically can't get a photo like that of JWST when fully deployed.  At best you'd get a photo of the sunshield; everything in the shade of the sunshield would be completely black.
These renders modified by Doug Ellison on Twitter illustrate this:
https://twitter.com/doug_ellison/status/1478445088065810435

https://twitter.com/doug_ellison/status/1478488542732980226

Those 'shops don't make a lot of sense. A reflective surface can't be darker than the surrounding sky. Even if it was relatively non-reflective, it would be as bright as the average of the sky around it. (A better image would be the "colour of the sky" used in the background image, but without stars. An occulted starfield, not a shadow.)

Given the reflectivity, especially the perfect reflection of the main mirror, the NASA render is closer. Possibly too bright, but much much more realistic.

https://twitter.com/NASAWebb/status/1479161843595759618/photo/1
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: AS_501 on 01/06/2022 10:27 pm
I understand the orbital mechanics benefits of putting JWST at L2.  But don't the Lagrange points tend to attract free-floating solar system dust, droppings from comets and asteroids, etc. that could damage the telescope's optics?  Obviously not or NASA would not park the scope there in the first place.  My brain is locked up on this one.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RonM on 01/06/2022 10:35 pm
I understand the orbital mechanics benefits of putting JWST at L2.  But don't the Lagrange points tend to attract free-floating solar system dust, droppings from comets and asteroids, etc. that could damage the telescope's optics?  Obviously not or NASA would not park the scope there in the first place.  My brain is locked up on this one.

L4 and L5 are stable and collect debris. L1, L2, and L3 are metastable and require some effort to maintain position, so they don't collect debris.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jack Daniel on 01/06/2022 10:39 pm
I understand the orbital mechanics benefits of putting JWST at L2.  But don't the Lagrange points tend to attract free-floating solar system dust, droppings from comets and asteroids, etc. that could damage the telescope's optics?  Obviously not or NASA would not park the scope there in the first place.  My brain is locked up on this one.

Not as such; I think there's a Scott Manley video on this (of course there is), but L1/2/3 aren't actually stable. Any slight deviation from the exact point results in the orbiting object falling out of orbit slowly (hence why JWST need fuel to maintain its orbit - sort of - it's a touch more complicated because of the specific orbit, but that's not relevant right now). That means there is no aggregation of objects at that point.

L4 and 5 are more forgiving, and this is why we see a load of Trojans at roughly those points in Jupiter's orbit, and probably orbits of other planets too.

(if anyone smarter fancies improving/correcting, please do)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 01/06/2022 11:35 pm
Quote
I completely agree that a free-flying camera is not worth the trouble, but I don't think it's a re-contact risk.

it is until it reaches L2 and then who knows after few years.
The camera might be tiny and simple, but it would need [...] a honking big transmitter and antenna to send back video or even stills from (currently) 2.6 times the distance to the moon.
Nah.  The Chinese probes just sent their pictures by WiFi to the main spacecraft, which relayed them to Earth.  From Tianwen-1's first 'selfie' in space to celebrate China's National Day (http://www.technologynewschina.com/2020/10/tianwen-1s-first-selfie-in-space-to.html)
Quote
It can be separated from the probe under the ground control and takes one image per second with its two wide-angle lenses. The photos can be transmitted to the probe via WiFi communication and then transmitted back to the ground by the probe.
A simple, cheap, and not especially reliable off-the-shelf technology like WiFi can be used for this since it's not mission critical.  And once it's done its job, turn the wireless router off so it can't cause interference with more serious tasks.
Quote
[...] I would love to see images too, but they would be of little value and great risk.
I think this is the consensus (but not unanimous) opinion.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/07/2022 12:22 am
And I suspect a big part of the opposition is similar to the internal scorn heaped on the publicly chosen mission names by the likes of Jim. (IMO, those 8yr olds from Poughkeepsie have a vastly better track record than the mission scientists themselves and their god-awful backronyms.)


You have no idea who I am or what I think.  But I do know what I think of your posts, and they are no better than Gaetano Marano's.

 As far as naming spacecraft, it doesn't affect me since the documentation continues to use the real names vs the cute ones.


Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: tibber on 01/07/2022 02:18 am
We can make this nuttily complicated observatory and set it up a million miles from home, but taking a snap shot of it with a few cameras the size of coin? Impossible!
There are a number of good reasons to "want" pics and NASA knows that. During one of the deployment discussions, they talked about how much they wanted to have a camera... but...

There are many huge technical problems. Several have been mentioned in this thread:
Heat given off by the camera
building camera(s) that can operate in the temperatures on the cold side
the wires, electronics, weight, etc. (Perhaps not huge technical issues, but not trivial either.)

But the biggest problem is the dark side is DARK. The whole of the primary mirror will receive on average 1 photon per second during studies. (And reflect that photon into the secondary mirror.) That would take a very long time for a picture to form...

Ok, so let's think about how much light will reach JWST on the darkside from all the other light sources across the dark side. Probably still wouldn't illuminate dime sized camera lens enough to get a meaningful picture.

So add a flash... too much heat.
Make a bigger lens... too much weight, heat, placement, etc.

At some point, NASA realized that the additional cost for the beauty shots were too high against the potential PR and technical value.

At this point, while I would love pics, I realize I'd get the same view sitting in my closet, with my eyes closed, on a moonless night in a total blackout. :)

Cheers,
Tom
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 01/07/2022 02:31 am
they are no better than Gaetano Marano's.
There are names that should never be mentioned in public again.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Polaroid on 01/07/2022 04:08 am


To those that matter

Those who pay for it?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 01/07/2022 06:57 am
... with a periapsis of about 160,000 wiles and apoapsis of about 517,000 miles. 

I am familiar with the area unit, Wales, but not the distance unit, wiles.  Can you tell me how long a wile is in terms of the percentage of the maximum velocity of a spherical sheep in a vacuum per fortnight?



For those that don't get the joke, I am referencing El Reg unit conversions (https://www.theregister.com/Design/page/reg-standards-converter.html) while pretending not to understand the obvious typo.
:) The Wile is a unit of ensnarement, as in "beware of her wiles".   A Web(b) would have a large ensnarement value.  :)

It is a measurement unit created by the great professor Coyote. As in: Wile E. Coyote. He didn't quite understood why all his experiments failed, then realized that neither imperial nor metric really matched... and he invented his own units system. Didn't helped a lot, he ended in trial with the ACME corporation.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 01/07/2022 07:06 am
Beware of flying cameras... they are potential hazards.

https://twitter.com/f1/status/1035087654495215616

Silliest F1 retirement, ever. Also a potentially horrible, freak accident avoided only through sheer luck.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gdelottle on 01/07/2022 08:47 am
Apart from all other considerations, I wonder how much even a single camera installed for outreach purposes would have cost. Among design, system engineering, risk evaluation, AIV, commissioning, additional weight at launch, impact on the overall structure design, software, etc. etc. (the list is long) I guess it would be in the orders of the millions, if not the tens million dollar for an instrument like that, already regarded by some "the telescope that ate astronomy" (https://www.nature.com/articles/4671028a).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Jim on 01/07/2022 11:41 am


To those that matter

Those who pay for it?

They pay for the science
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Monkfish on 01/07/2022 12:57 pm
Are there cameras on the JWST that can image the deployment, failures or possible damage in the future. If not, why not?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: MTom on 01/07/2022 01:01 pm
Are there cameras on the JWST that can image the deployment, failures or possible damage in the future. If not, why not?

See the last pages

https://forum.nasaspaceflight.com/index.php?topic=54269.msg2328526#msg2328526
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: joncz on 01/07/2022 01:02 pm
Here's an exterior view of the JWST!

https://twitter.com/coreyspowell/status/1479154564037476354
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: centaurinasa on 01/07/2022 01:56 pm
https://twitter.com/ESA_Webb/status/1479412870878224386
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Mike_1179 on 01/07/2022 02:21 pm
Are there cameras on the JWST that can image the deployment, failures or possible damage in the future. If not, why not?

See the last pages

https://forum.nasaspaceflight.com/index.php?topic=54269.msg2328526#msg2328526

Also this blog post from NASA  https://blogs.nasa.gov/webb/2022/01/06/why-doesnt-webb-have-deployment-cameras/ (https://blogs.nasa.gov/webb/2022/01/06/why-doesnt-webb-have-deployment-cameras/)

And a Twitter thread from NASA https://twitter.com/NASAWebb/status/1479161843595759618?s=20 (https://twitter.com/NASAWebb/status/1479161843595759618?s=20)

I think they get the point that everyone expects there to be cameras on it but sometimes it just doesn't make sense to do something, no matter how cool it would be
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/07/2022 03:18 pm
Why would they not take the lid off the camera end by this stage? They could be checking out some bits while mirrors-wings are being done?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Vettedrmr on 01/07/2022 03:25 pm
Why would they not take the lid off the camera end by this stage? They could be checking out some bits while mirrors-wings are being done?

There's no need to rush, and doing things concurrently can add risk, even if they seem unrelated.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: AstroDave on 01/07/2022 03:56 pm
Interesting blog post from Wayne Hale.

https://waynehale.wordpress.com/2022/01/05/flying-new-spacecraft/
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: AS_501 on 01/07/2022 04:21 pm
Here's an exterior view of the JWST!

https://twitter.com/coreyspowell/status/1479154564037476354

Absolutely thrilling clip!  After JWST separated from the upper stage, Rob Navias said this would humanity's last view of the telescope.  Well, not exactly.  So what are the prospects for observing JWST when it reaches L2?  On the positive side the sunshield will reflect a lot of sunlight, but probably not flare like an Iridium satellite.  On the negative side JSWT is a million miles away.  My totally uneducated guess is no brighter than +15 or +16 magnitude.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Star One on 01/07/2022 04:29 pm
I understand the orbital mechanics benefits of putting JWST at L2.  But don't the Lagrange points tend to attract free-floating solar system dust, droppings from comets and asteroids, etc. that could damage the telescope's optics?  Obviously not or NASA would not park the scope there in the first place.  My brain is locked up on this one.

L4 and L5 are stable and collect debris. L1, L2, and L3 are metastable and require some effort to maintain position, so they don't collect debris.
Thanks for that explanation as I’ve always wondered why they don’t use some of the Lagrange points. Out of interest why are some stable and some metastable.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: daveglo on 01/07/2022 04:50 pm
Anyone wondering why we haven't heard or seen anything since the wing deployment process started?  It was supposed to be televised, but I can't find a stream.

If things started this morning as was originally posted, the port wing should be locked in place by now, shouldn't it?  Kind of odd not to have that announced.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/07/2022 04:59 pm
Anyone wondering why we haven't heard or seen anything since the wing deployment process started?  It was supposed to be televised, but I can't find a stream.

If things started this morning as was originally posted, the port wing should be locked in place by now, shouldn't it?  Kind of odd not to have that announced.

Wasn't supposed to be streamed and was supposed to take 3 hours.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: tibber on 01/07/2022 05:00 pm
Are there cameras on the JWST that can image the deployment, failures or possible damage in the future. If not, why not?

See the last pages

https://forum.nasaspaceflight.com/index.php?topic=54269.msg2328526#msg2328526

Also this blog post from NASA  https://blogs.nasa.gov/webb/2022/01/06/why-doesnt-webb-have-deployment-cameras/ (https://blogs.nasa.gov/webb/2022/01/06/why-doesnt-webb-have-deployment-cameras/)

And a Twitter thread from NASA https://twitter.com/NASAWebb/status/1479161843595759618?s=20 (https://twitter.com/NASAWebb/status/1479161843595759618?s=20)

I think they get the point that everyone expects there to be cameras on it but sometimes it just doesn't make sense to do something, no matter how cool it would be
Thanks for posting the links. The part in the blog about actually testing different cameras and positions on the full-scale mockups was interesting.

Cheers,
Tom
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: tibber on 01/07/2022 05:06 pm
Anyone wondering why we haven't heard or seen anything since the wing deployment process started?  It was supposed to be televised, but I can't find a stream.

If things started this morning as was originally posted, the port wing should be locked in place by now, shouldn't it?  Kind of odd not to have that announced.
From reading the various announcements and their history, it seems the plan all along was to broadcast during the second wing deployment, not the first. Then things shifted a day so I found things that still talk about broadcasting today (and hinting that it would be the second wing) and other updates that refer to tomorrow.

Cheers,
Tom
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: capoman on 01/07/2022 06:39 pm
Port mirror wing unfolded successfully!


https://blogs.nasa.gov/webb/2022/01/07/first-of-two-primary-mirror-wings-unfolds/

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: RonM on 01/07/2022 06:50 pm
I understand the orbital mechanics benefits of putting JWST at L2.  But don't the Lagrange points tend to attract free-floating solar system dust, droppings from comets and asteroids, etc. that could damage the telescope's optics?  Obviously not or NASA would not park the scope there in the first place.  My brain is locked up on this one.

L4 and L5 are stable and collect debris. L1, L2, and L3 are metastable and require some effort to maintain position, so they don't collect debris.
Thanks for that explanation as I’ve always wondered why they don’t use some of the Lagrange points. Out of interest why are some stable and some metastable.

There's a Coriolis acceleration on objects in L4 and L5 that keeps them in place. It's complicated but Scott Manley has a good video on it.

https://www.youtube.com/watch?v=7PHvDj4TDfM
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Polaroid on 01/08/2022 03:59 am


To those that matter

Those who pay for it?

They pay for the science

That is your incorrect opinion.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: russianhalo117 on 01/08/2022 04:32 am
To those that matter
Those who pay for it?
They pay for the science
That is your incorrect opinion.
FYI: Arguing with the knowledgeable Jim, whom is deeply in the know, is extremely unwise.

EDIT: to keep it classy and remove snark.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/08/2022 04:44 am
To those that matter
Those who pay for it?
They pay for the science
That is your incorrect opinion.
FYI: Arguing with the knowledgeable Jim, whom is deeply in the know, is extremely unwise and doesn't typically end well for those that continue the argument after my post.

This isn't a technical argument or one about deep knowledge.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: MATTBLAK on 01/08/2022 04:48 am
To those that matter
Those who pay for it?
They pay for the science
That is your incorrect opinion.
FYI: Arguing with the knowledgeable Jim, whom is deeply in the know, is extremely unwise and doesn't typically end well for those that continue the argument after my post.
"You don't tug on Superman's cape
You don't spit into the wind
You don't pull the mask off that old lone ranger
And you don't mess around with Jim..."
  ;)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Stan-1967 on 01/08/2022 05:14 am
FYI: Arguing with the knowledgeable Jim, whom is deeply in the know, is extremely unwise and doesn't typically end well for those that continue the argument after my post.
"You don't tug on Superman's cape
You don't spit into the wind
You don't pull the mask off that old lone ranger
And you don't mess around with Jim..."
  ;)


This all makes Jim seem so nefarious & larger than life.  I'll bet Jim would feed your dog bacon under the table if he was a guest in your home.  Can we stop with the ominous warnings?  Nothing bad will happen to anyone who gets in the crosshairs of Jim.  Mods won't silence you for just that, the thread will continue.  On topic hopefully.

Better to maybe think of Jim's terse factual rebukes as a gentle NSF Jedi hand wave telling you to stop your junk posting & go rethink your life....& post contents.

We need a countdown to Webbs first light.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Bogeyman on 01/08/2022 07:03 am
ESA just confirmed on Facebook that they did remove the lens cap - in response to some memes shared around ;)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gdelottle on 01/08/2022 09:26 am


To those that matter

Those who pay for it?

They pay for the science

That is your incorrect opinion.

Large science projects spend a quite large amount in EPO. This may include use of cameras designed for science to provide nice pics for the public as a follow up. But it's unlikely instrument design is complicated and modified just for that.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ttle2 on 01/08/2022 09:45 am

Large science projects spend a quite large amount in EPO. This may include use of cameras designed for science to provide nice pics for the public as a follow up. But it's unlikely instrument design is complicated and modified just for that.

I don't think images are taken specifically for PR that commonly (though that does happen sometimes; for example, when the telescope is finishing its commissioning, some photogenic target may be imaged for PR). However, science images are often processed separately to look nice for PR (setting colours etc.). To be honest, I often find the processed PR images overdone to the point of being gaudy, but to each his own.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gdelottle on 01/08/2022 10:07 am

Large science projects spend a quite large amount in EPO. This may include use of cameras designed for science to provide nice pics for the public as a follow up. But it's unlikely instrument design is complicated and modified just for that.

I don't think images are taken specifically for PR that commonly (though that does happen sometimes; for example, when the telescope is finishing its commissioning, some photogenic target may be imaged for PR). However, science images are often processed separately to look nice for PR (setting colours etc.). To be honest, I often find the processed PR images overdone to the point of being gaudy, but to each his own.

Right. But those images do not impact on the instrument design.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: KaarlisK on 01/08/2022 12:50 pm
Junocam (that was specifically built for public outreach) would disagree
https://en.m.wikipedia.org/wiki/JunoCam
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 01/08/2022 01:07 pm
IMO, 99% of us really enjoy rocketcams and other opportunities to visit space vicariously.  And there is some considerable value to that, as evidenced by the frequent provision of cameras on many public and private space missions.

The Webb folks have given us a fairly detailed, reasonable response as to why they ended up with no cameras.  It is sufficient for me.  My insignificant vote would be to (1) let this issue go, (2) enjoy the wonderful unfolding of this observatory and (3) eagerly await the images and science that flow from it.

I have SO enjoyed the fruits of Hubble for the last 30+ years.  Webb promises equally exciting images and an even deeper view back toward our beginnings.  So, what's to fuss about?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Stan-1967 on 01/08/2022 02:43 pm
Junocam (that was specifically built for public outreach) would disagree
https://en.m.wikipedia.org/wiki/JunoCam

I think this is a poor comparison.

Where are Juno’s selfies of the spacecraft?   All of its photos are of the subject of the mission, i.e Jupiter,  not the vehicle    So will it be with Webb
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: FlattestEarth on 01/08/2022 02:56 pm
What are the details of the "meticulous, two-hour process" for latching the mirror wing?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gparker on 01/08/2022 04:04 pm
What are the details of the "meticulous, two-hour process" for latching the mirror wing?

Design and Development of the Primary and Secondary Mirror Deployment Systems for the Cryogenic JWST (https://esmats.eu/amspapers/pastpapers/pdfs/2004/reynolds.pdf) (2004)
(Technically this is a description of an older design, but it should be pretty close to the flight hardware. "These architecture changes have resulted in some small impacts to the designs described in this paper, but essentially, the designs have stayed the same.")

Remember that the mirrors must remain precisely aligned to each other for good observations (tens of nanometers of wavefront error). That means the wing mirror latches must prevent any thermal or mechanical movement.

Each wing latch is ultimately secured by a drive screw that will eventually be tightened to 800 pounds of force. Needless to say you really don't want to cross-thread one of those screws. Presumably the "two-hour process" is lots of small movements and checks that everything is aligned correctly. For now those screws will only be tightened with a small amount of force. After the telescope has cooled the process will be completed, first loosening the drive screws to relieve any thermal stresses, then tightening them fully.

Fun fact: the secondary mirror struts (also described in that paper) will be secured in part by just being cold. The hinges have aluminum and titanium parts. Aluminum shrinks more than titanium when cooled, which provides clamping force to lock the hinges when at cryogenic temperatures.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gparker on 01/08/2022 04:16 pm
Super basic question...  Have these specific actuators been used in space before?  Just wondering if they have some type of baseline from previous use or if this is the very first time with them in space.

They're probably new. The slideshow (https://slideplayer.com/slide/3971867/) mentioned above describes motor tests in 2011 that didn't go as well as they would have liked: they often degraded beyond spec before reaching 2X design life. After a redesign the motors reached 7X design life with no signs of trouble.

Another detail: "While the use of a hexapod is not new technology, the actuator step size resolution required at cryogenic temperature is. … The key component of the actuator is a cryogenic capable geared stepper motor which was derived from the gear motor flown on the Spitzer Space Telescope and operated at 4.5K."
JWST Mirror Technology Development Results (https://ntrs.nasa.gov/api/citations/20070038371/downloads/20070038371.pdf) (2007)

So a new design to meet new requirements, but based in part on existing flight-proven hardware.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: tappa on 01/08/2022 04:18 pm
Apologies if this has been asked before.

From what I have read actuators will move the individual mirrors to focus. Would that mean that if the actuators fail over the life of JWST they can impact the working of the telescope? If correct, what is the expected life of the actuators? How many actuators failure can it handle before it results in significant degrading of Webb?


Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 01/08/2022 04:26 pm
Losing an actuator means one DoF of a mirror is now driven only by the other DoFs. When it comes to realignment, the rest of the mirrors would have to work around the limitation of the segments with the failed actuator. If more actuators fail, then it would likely be a decision of whether one or more mirrors should be driven far off axis to minimise their erroneous contribution to the image, or whether the erroneous contribution could be corrected in software and the mirrors should be left in place.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: photonic on 01/08/2022 04:31 pm
What are the details of the "meticulous, two-hour process" for latching the mirror wing?

The lady on the left in the webcast (deputy commissioning engineer?) mentioned that there are 3 or 4 latches that each constrain the wing in different degrees of freedom. She likened it to how you tighten a wheel on a car, you don't first tighten one screw all the way, but you do it little bits at a time while alternating between the screws. The end goal is to join the wing in a well defined way, without deforming the structure.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: testguy on 01/08/2022 04:45 pm
Just a thought, and I do not know if it is even feasible. 
But IF the sun shield is large enough and IF a Webb servicing mission could be performed without contaminating the telescope, then did the Webb designers add brackets and electrical connectors to allow for adding mirror segments some time in the future?  Also, would the optics even work?  I don’t thick the power requirements would need to be upgraded since the new segment actuators would not need to function at the same time as the existing actuators.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gparker on 01/08/2022 04:46 pm
Apologies if this has been asked before.

From what I have read actuators will move the individual mirrors to focus. Would that mean that if the actuators fail over the life of JWST they can impact the working of the telescope? If correct, what is the expected life of the actuators? How many actuators failure can it handle before it results in significant degrading of Webb?

Losing an actuator means one DoF of a mirror is now driven only by the other DoFs. When it comes to realignment, the rest of the mirrors would have to work around the limitation of the segments with the failed actuator. If more actuators fail, then it would likely be a decision of whether one or more mirrors should be driven far off axis to minimise their erroneous contribution to the image, or whether the erroneous contribution could be corrected in software and the mirrors should be left in place.

As for lifetime, three actuators were tested to 7X design life with no signs of degradation. And if I understand the description correctly, most of that design life seems to be the initial commissioning process. The ongoing alignment adjustments don't add up to much motor movement.

More details and references:
https://forum.nasaspaceflight.com/index.php?topic=54269.msg2328280#msg2328280
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: tibber on 01/08/2022 04:47 pm
Apologies if this has been asked before.

From what I have read actuators will move the individual mirrors to focus. Would that mean that if the actuators fail over the life of JWST they can impact the working of the telescope? If correct, what is the expected life of the actuators? How many actuators failure can it handle before it results in significant degrading of Webb?




A great slideshow about the actuators, their testing, redesign, and retesting. It also talks directly about how to adjust for premature failure: https://view.officeapps.live.com/op/view.aspx?src=https%3A%2F%2Fwebb.nasa.gov%2Fresources%2F2012SPIE8442-88OTEMotorFault%2520ToleranceBarto.pptx&wdOrigin=BROWSELINK

Basically, a sample of actuators was tested at 2x expected use and another at 6x expected use. Then they were inspected looking for wear and tear. A key bearing design was changed, another batch then tested and no failures were discovered at 7x the expected use over the lifetime of JWST.

Also after all the earth based testing, the actuators could be rebuilt in place.

Cheers,
Tom
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: KaarlisK on 01/08/2022 07:00 pm
Junocam (that was specifically built for public outreach) would disagree
https://en.m.wikipedia.org/wiki/JunoCam

I think this is a poor comparison.

Where are Juno’s selfies of the spacecraft?   All of its photos are of the subject of the mission, i.e Jupiter,  not the vehicle    So will it be with Webb
I wasn't making a comparison. I completely agree that Webb should not have cameras.
I was just saying that in general, outreach can and does affect instrument/spacecraft design. That part of the discussion wasn't just about Webb anymore.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: tibber on 01/08/2022 07:45 pm
Going back to the pics of JWST, in today's Q&A they mentioned that even for Hubble, JWST appears only as a point source of light. It can't be resolved.

Basically at a million miles, a tennis court looks like a single point today.

Cheers,
Tom
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 01/08/2022 10:04 pm
*sighs after hearing the main mirror is now fully deployed*

Phew!  I was fearful for the sunshield, but now I am glad the major items, if not the full deployment process, is complete.  It looks like the cost overruns for fixing the shield issues were worth it.  Obviously we'll know for sure once the science begins.  In the past, I had issues with items like Galileo's antenna, but especially headaches like the shuttle's and Hubble's flaws being giant targets of ridicule for NASA.  I'm now glad Webb won't be a part of that and hopefully an example of success (although I wouldn't say frugal spending).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: toren on 01/08/2022 10:14 pm
Big sigh of relief, and congratulations to all the teams involved.  I'm glad the skeptics turned out wrong.

Just hope that Starship and its to-be competitors come online so that we don't have to play billion dollar origami quite as much in the future.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: AS_501 on 01/08/2022 10:59 pm
To the JSWT Team from space fans all over the world:  "Roger Webb, we copy the shield and mirror are deployed.  You got a bunch of people about to turn blue.  We're breathing again.  Thanks a lot."   ;)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/08/2022 11:02 pm
Big sigh of relief, and congratulations to all the teams involved.  I'm glad the skeptics turned out wrong.

Just hope that Starship and its to-be competitors come online so that we don't have to play billion dollar origami quite as much in the future.

First of all, as discussed previously, a larger launch vehicle wouldn't have saved much money or much deployment. The sun shield is way bigger than Starship. Second, some of us would still like a 16m or larger space scope, which would require the same origami as this did, even if launched on a huge rocket.

Grateful that JWST is doing so well. All those dollars spent designing and testing seem to be paying off.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: tappa on 01/09/2022 05:24 am
First of all, as discussed previously, a larger launch vehicle wouldn't have saved much money or much deployment. The sun shield is way bigger than Starship. Second, some of us would still like a 16m or larger space scope, which would require the same origami as this did, even if launched on a huge rocket.

Grateful that JWST is doing so well. All those dollars spent designing and testing seem to be paying off.

Does that mean the R&D & experience from JWST would result in lower costs of the next space telescope? If so how much?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: woods170 on 01/09/2022 10:21 am
First of all, as discussed previously, a larger launch vehicle wouldn't have saved much money or much deployment. The sun shield is way bigger than Starship. Second, some of us would still like a 16m or larger space scope, which would require the same origami as this did, even if launched on a huge rocket.

Grateful that JWST is doing so well. All those dollars spent designing and testing seem to be paying off.

Does that mean the R&D & experience from JWST would result in lower costs of the next space telescope? If so how much?


No, it won't IMO. The next bigger thing is LUVOIR. But upscaling existing Webb technology is not guaranteed to work for LUVOIR. Upscaling existing technology for bigger systems usually doesn't work all that well. New problems emerge at bigger scales and those usually have significant impact on the existing approach to solve problems.

So, IMO, LUVOIR (if it ever gets off the ground) will have its own very significant development budget. IMO it is almost guaranteed to rival the budget of JWST.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 01/09/2022 01:14 pm
First of all, as discussed previously, a larger launch vehicle wouldn't have saved much money or much deployment. The sun shield is way bigger than Starship. Second, some of us would still like a 16m or larger space scope, which would require the same origami as this did, even if launched on a huge rocket.

Grateful that JWST is doing so well. All those dollars spent designing and testing seem to be paying off.

Does that mean the R&D & experience from JWST would result in lower costs of the next space telescope? If so how much?
The next space telescope will significantly push the limits of what we can do.  If it doesn't, there is no point in doing it.  At best, the lessons learned from JWST might lessen the increases in the budget of the next telescope at best.  I can imagine that once pictures are coming from JWST, the debate on how to go beyond its capabilities will pick up.  I can't wait for what I expect to be spectacular images and more of the debate on what to do next.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: capoman on 01/09/2022 01:48 pm
First of all, as discussed previously, a larger launch vehicle wouldn't have saved much money or much deployment. The sun shield is way bigger than Starship. Second, some of us would still like a 16m or larger space scope, which would require the same origami as this did, even if launched on a huge rocket.

Grateful that JWST is doing so well. All those dollars spent designing and testing seem to be paying off.

Does that mean the R&D & experience from JWST would result in lower costs of the next space telescope? If so how much?

A lot of the technology from Webb will be used in Luvoir. The sunshade, segmented mirrors etc., but as others have mentioned, scaling up will have it’s own challenges, and the main questions needed to be answered will be based on that, such as, how much stronger does the shield need to be, can segments be larger or do they need more segments, and also they will need to develop instruments that can go even deeper into the infra red, as that will be the main point of a larger telescope. They may need to be able to cool down instruments even closer to absolute zero. Much of what is learned with Webb going forward during operations will also assist with it’s design. I’m sure they are waiting on lots of info from Webb to even move design forward any significant amount. There is also launch constraints that are still unknowns, such as whether Starship or SLS become feasible options and what their limitations will be.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/09/2022 03:47 pm
and also they will need to develop instruments that can go even deeper into the infra red, as that will be the main point of a larger telescope. They may need to be able to cool down instruments even closer to absolute zero.

Huh?

You might want to look into that again.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ab2 on 01/09/2022 03:53 pm
Hello .. it is my first question here an I hope not an inapropriate place.

Why is she Sunshield layer 5 (Cold Side) not black -> infrared absorbing?

Does it not possibly induce(/reflect) bright infrared light from 'other' stars?

Should it not absorb any infrared radiation/light on its inner side to exclude
it as a relective error source?

Thanks for an answer. 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: briantipton on 01/09/2022 04:20 pm
First of all, as discussed previously, a larger launch vehicle wouldn't have saved much money or much deployment. The sun shield is way bigger than Starship. Second, some of us would still like a 16m or larger space scope, which would require the same origami as this did, even if launched on a huge rocket.

Grateful that JWST is doing so well. All those dollars spent designing and testing seem to be paying off.

Does that mean the R&D & experience from JWST would result in lower costs of the next space telescope? If so how much?


No, it won't IMO. The next bigger thing is LUVOIR. But upscaling existing Webb technology is not guaranteed to work for LUVOIR. Upscaling existing technology for bigger systems usually doesn't work all that well. New problems emerge at bigger scales and those usually have significant impact on the existing approach to solve problems.

So, IMO, LUVOIR (if it ever gets off the ground) will have its own very significant development budget. IMO it is almost guaranteed to rival the budget of JWST.

It is still early to talk about the "next telescope" like we know what it will be, but if we believe that the recommendation of the latest Decadal Survey will be acted on, the next flagship telescope will not be another jump up in mirror size from JWST. The report recommends a high-contrast direct imaging UV/O/IR observatory "with a target off-axis inscribed diameter of approximately 6 meters", so smaller than the either LUVOIR A or B proposals. And while it will certainly leverage some of the development from JWST, the report specifically recommends an extended period of technology development before even beginning the design phase to avoid a cost overrun on the scale of JWST (you could say that that recommendation itself is a key contribution of JWST to the next generation telescope).  Given the long time before design work will actually start on the next flagship mission, Starship and/or other Superheavy launch vehicles will be proven will before the design is underway and the benefits from larger payload volumes will be incorporated.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Greg Hullender on 01/09/2022 06:02 pm
For whatever telescope comes next, I really hope they consider multiple launches with in-space assembly, as in this NASA study:  Exoplanet Program: NASA in-Space Assembled Telescope (iSAT) Study (https://exoplanets.nasa.gov/exep/technology/in-space-assembly/iSAT_study/). That's a much better place to put time and effort than trying to design ever more complicated telescope origami.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 01/09/2022 06:11 pm
Hello .. it is my first question here an I hope not an inapropriate place.

Why is she Sunshield layer 5 (Cold Side) not black -> infrared absorbing?

Does it not possibly induce(/reflect) bright infrared light from 'other' stars?

Should it not absorb any infrared radiation/light on its inner side to exclude
it as a relective error source?

Thanks for an answer.
You don't want the shield absorbing and re-radiating any energy from the cold side.  Highly reflective hugely reduces any energy absorption.  Black would absorb much of the spectrum and re-radiate in the infrared.  It would be a tougher cooling problem. 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 01/09/2022 06:47 pm
A million thank you's to the people behind JWST! You reflect the best of humanity!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: woods170 on 01/09/2022 07:28 pm
It is still early to talk about the "next telescope" like we know what it will be,..

Wrong. The process that eventually led to what we now know as JWST started right around the time that Hubble was launched.

Now that JWST is in space and ready to do its thing, it very much IS the time to start thinking about the next telescope. You see, even if JWST, by some technical miracle, manages to stay operational for 20 years... it will take about that same amount of time to have the successor to JWST ready for launch.

Why do you think that LUVOIR, as a concept, has been around for several years now? It is because the people behind that idea recognize that it will take 2 decades to turn the concept into reality.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ab2 on 01/09/2022 08:03 pm
Thanks for the fast answer.

So having a reflective! 'cold side' in layer 5
does not possibly reflect some
light into the mirror-system?

As looking as an a pure amateur on to the design
I personally could imagine non targeted light sources
that reflect light indirect over the shield into the mirror
system.

Which would in my point of view introduce an error source.

But probably all light sources on this side are to faint
to influence measurement over this indirect way into the
mirror system.

 Greet and Cheers.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Eric Hedman on 01/09/2022 08:37 pm
Thanks for the fast answer.

So having a reflective! 'cold side' in layer 5
does not possibly reflect some
light into the mirror-system?

As looking as an a pure amateur on to the design
I personally could imagine non targeted light sources
that reflect light indirect over the shield into the mirror
system.

Which would in my point of view introduce an error source.

But probably all light sources on this side are to faint
to influence measurement over this indirect way into the
mirror system.

 Greet and Cheers.
Light reflected from the shield to the primary mirror won't be coming from a direction that will reflect it into the secondary mirror.  Most will reflect harmlessly off into space.  The same will be with light that reflects onto the secondary mirror.  With this design just about the only light that comes from the direction the telescope is pointed will hit the primary mirror and reflect to the secondary and from there into the camera sensors.  This design handles this extremely well.  The JWST design team really got this right.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ulm_atms on 01/09/2022 11:03 pm
First of all, as discussed previously, a larger launch vehicle wouldn't have saved much money or much deployment. The sun shield is way bigger than Starship. Second, some of us would still like a 16m or larger space scope, which would require the same origami as this did, even if launched on a huge rocket.

Grateful that JWST is doing so well. All those dollars spent designing and testing seem to be paying off.

Does that mean the R&D & experience from JWST would result in lower costs of the next space telescope? If so how much?

A lot of the technology from Webb will be used in Luvoir. The sunshade, segmented mirrors etc., but as others have mentioned, scaling up will have it’s own challenges, and the main questions needed to be answered will be based on that, such as, how much stronger does the shield need to be, can segments be larger or do they need more segments, and also they will need to develop instruments that can go even deeper into the infra red, as that will be the main point of a larger telescope. They may need to be able to cool down instruments even closer to absolute zero. Much of what is learned with Webb going forward during operations will also assist with it’s design. I’m sure they are waiting on lots of info from Webb to even move design forward any significant amount. There is also launch constraints that are still unknowns, such as whether Starship or SLS become feasible options and what their limitations will be.

Luvoir is a primarily UV scope.  Why would it have to be cooled that low?  I figure it would have the same basic requirements as Hubble for cooling.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: nacnud on 01/09/2022 11:07 pm
Luvoir will look at IR too, full name is Large Ultraviolet Optical Infrared Surveyor.

Edit: However 'the telescope is actively heated to a precise 270 K (−3 °C; 26 °F) to control thermal disturbances.' - Wikipedia
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gparker on 01/09/2022 11:34 pm
So having a reflective! 'cold side' in layer 5 does not possibly reflect some light into the mirror-system?

Light reflected from the shield to the primary mirror won't be coming from a direction that will reflect it into the secondary mirror.  Most will reflect harmlessly off into space.  The same will be with light that reflects onto the secondary mirror.  With this design just about the only light that comes from the direction the telescope is pointed will hit the primary mirror and reflect to the secondary and from there into the camera sensors.  This design handles this extremely well.  The JWST design team really got this right.

There are also black baffles and masks later in the optics path, closer to the detectors, that block stray light and reduce internal scattering. In general you want to reflect away whatever you can, to reduce heating, and then absorb whatever is left.

Section 2.4 of this paper describes one stray light path that the designers analyzed. Starlight goes through the hole in the center of the primary mirror, passes just outside the fine steering mirror, and reaches the internal instrument optics. The solution was to increase the size of the black mask around the edge of the fine steering mirror.
Pupil alignment considerations for large, deployable space telescopes (https://ntrs.nasa.gov/api/citations/20110015430/downloads/20110015430.pdf) (2011)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Steve G on 01/10/2022 03:25 am
A lot of media people have been alarmed at the $11 billion or so cost of the JWST, but in today's dollars, how much did Hubble cost? That includes launch, the required optics fix, operating costs, and the service missions, all flown on the costly shuttle with hundreds of hours of training by the crew plus the new equipment. Of course, Hubble is still operating, and the cost per year must be out there somewhere. Just trying to compare the two and I don't think the costs are much different by 2022 dollars.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/10/2022 03:38 am
A lot of media people have been alarmed at the $11 billion or so cost of the JWST, but in today's dollars, how much did Hubble cost? That includes launch, the required optics fix, operating costs, and the service missions, all flown on the costly shuttle with hundreds of hours of training by the crew plus the new equipment. Of course, Hubble is still operating, and the cost per year must be out there somewhere. Just trying to compare the two and I don't think the costs are much different by 2022 dollars.

Hubble has cost far more than JWST.

https://www.nasa.gov/content/about-facts-hubble-faqs

"What has the Hubble mission cost?

The Hubble mission has cost approximately $16 billion (adjusted for inflation to 2021 dollars) since its official start in 1977. This does not include the cost of space shuttle operations for Hubble’s deployment and servicing missions."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 01/10/2022 05:51 am
With every single Shuttle servicing missions costing $1.5 billion... it surely inflated the total cost.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 01/10/2022 10:17 am
A lot of media people have been alarmed at the $11 billion or so cost of the JWST, but in today's dollars, how much did Hubble cost? That includes launch, the required optics fix, operating costs, and the service missions, all flown on the costly shuttle with hundreds of hours of training by the crew plus the new equipment. Of course, Hubble is still operating, and the cost per year must be out there somewhere. Just trying to compare the two and I don't think the costs are much different by 2022 dollars.

Hubble has cost far more than JWST.

https://www.nasa.gov/content/about-facts-hubble-faqs

"What has the Hubble mission cost?

The Hubble mission has cost approximately $16 billion (adjusted for inflation to 2021 dollars) since its official start in 1977. This does not include the cost of space shuttle operations for Hubble’s deployment and servicing missions."
That's not quite a fair comparison, as the Hubble figure includes 30 years of active support and operations, compared to JHWST's 0 years. IIRC Hubble costs are around $100mn per annum (higher in the past than today), so that knocks aa minimum of $3bn off of the headline figure.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/10/2022 11:47 am
With every single Shuttle servicing missions costing $1.5 billion... it surely inflated the total cost.

"This does not include the cost of space shuttle operations for Hubble’s deployment and servicing missions..."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/10/2022 11:50 am
A lot of media people have been alarmed at the $11 billion or so cost of the JWST, but in today's dollars, how much did Hubble cost? That includes launch, the required optics fix, operating costs, and the service missions, all flown on the costly shuttle with hundreds of hours of training by the crew plus the new equipment. Of course, Hubble is still operating, and the cost per year must be out there somewhere. Just trying to compare the two and I don't think the costs are much different by 2022 dollars.

Hubble has cost far more than JWST.

https://www.nasa.gov/content/about-facts-hubble-faqs

"What has the Hubble mission cost?

The Hubble mission has cost approximately $16 billion (adjusted for inflation to 2021 dollars) since its official start in 1977. This does not include the cost of space shuttle operations for Hubble’s deployment and servicing missions."
That's not quite a fair comparison, as the Hubble figure includes 30 years of active support and operations, compared to JHWST's 0 years. IIRC Hubble costs are around $100mn per annum (higher in the past than today), so that knocks aa minimum of $3bn off of the headline figure.

https://www.planetary.org/articles/cost-of-the-jwst

"The James Webb Space Telescope (JWST) is expected to cost NASA $9.7 billion over 24 years. Of that amount, $8.8 billion was spent on spacecraft development between 2003 and 2021; $861 million is planned to support five years of operations. Adjusted for inflation to 2020 dollars, the lifetime cost to NASA will be approximately $10.8 billion."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: arachnitect on 01/10/2022 11:53 am
A lot of media people have been alarmed at the $11 billion or so cost of the JWST, but in today's dollars, how much did Hubble cost? That includes launch, the required optics fix, operating costs, and the service missions, all flown on the costly shuttle with hundreds of hours of training by the crew plus the new equipment. Of course, Hubble is still operating, and the cost per year must be out there somewhere. Just trying to compare the two and I don't think the costs are much different by 2022 dollars.

Hubble has cost far more than JWST.

https://www.nasa.gov/content/about-facts-hubble-faqs

"What has the Hubble mission cost?

The Hubble mission has cost approximately $16 billion (adjusted for inflation to 2021 dollars) since its official start in 1977. This does not include the cost of space shuttle operations for Hubble’s deployment and servicing missions."
That's not quite a fair comparison, as the Hubble figure includes 30 years of active support and operations, compared to JHWST's 0 years. IIRC Hubble costs are around $100mn per annum (higher in the past than today), so that knocks aa minimum of $3bn off of the headline figure.

https://www.planetary.org/articles/cost-of-the-jwst

"The James Webb Space Telescope (JWST) is expected to cost NASA $9.7 billion over 24 years. Of that amount, $8.8 billion was spent on spacecraft development between 2003 and 2021; $861 million is planned to support five years of operations. Adjusted for inflation to 2020 dollars, the lifetime cost to NASA will be approximately $10.8 billion."

ESA and CSA contributions were not insignificant on Webb, how does that compare to HST?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/10/2022 11:57 am
A lot of media people have been alarmed at the $11 billion or so cost of the JWST, but in today's dollars, how much did Hubble cost? That includes launch, the required optics fix, operating costs, and the service missions, all flown on the costly shuttle with hundreds of hours of training by the crew plus the new equipment. Of course, Hubble is still operating, and the cost per year must be out there somewhere. Just trying to compare the two and I don't think the costs are much different by 2022 dollars.

Hubble has cost far more than JWST.

https://www.nasa.gov/content/about-facts-hubble-faqs

"What has the Hubble mission cost?

The Hubble mission has cost approximately $16 billion (adjusted for inflation to 2021 dollars) since its official start in 1977. This does not include the cost of space shuttle operations for Hubble’s deployment and servicing missions."
That's not quite a fair comparison, as the Hubble figure includes 30 years of active support and operations, compared to JHWST's 0 years. IIRC Hubble costs are around $100mn per annum (higher in the past than today), so that knocks aa minimum of $3bn off of the headline figure.

https://www.planetary.org/articles/cost-of-the-jwst

"The James Webb Space Telescope (JWST) is expected to cost NASA $9.7 billion over 24 years. Of that amount, $8.8 billion was spent on spacecraft development between 2003 and 2021; $861 million is planned to support five years of operations. Adjusted for inflation to 2020 dollars, the lifetime cost to NASA will be approximately $10.8 billion."

ESA and CSA contributions were not insignificant on Webb, how does that compare to HST?

https://www.planetary.org/articles/cost-of-the-jwst

"That is only NASA’s portion. The European Space Agency provided the Ariane 5 launch vehicle and two of the four science instruments for an estimated cost of €700 million. The Canadian Space Agency contributed sensors and scientific instrumentation, which cost approximately CA$200 million."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: capoman on 01/10/2022 12:46 pm
Luvoir will look at IR too, full name is Large Ultraviolet Optical Infrared Surveyor.

Edit: However 'the telescope is actively heated to a precise 270 K (−3 °C; 26 °F) to control thermal disturbances.' - Wikipedia

Yeah, that was an error on my part. Luvior will not just be looking at IR as Webb does. It'll be a far more versatile scope covering many wavelengths, but will still need to accommodate IR needs such as cooling. Different instruments will likely  have different temperature requirements. This will actually make that telescope that much more complex.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: cdebuhr on 01/10/2022 01:19 pm
Luvoir will look at IR too, full name is Large Ultraviolet Optical Infrared Surveyor.

Edit: However 'the telescope is actively heated to a precise 270 K (−3 °C; 26 °F) to control thermal disturbances.' - Wikipedia

Yeah, that was an error on my part. Luvior will not just be looking at IR as Webb does. It'll be a far more versatile scope covering many wavelengths, but will still need to accommodate IR needs such as cooling. Different instruments will likely  have different temperature requirements. This will actually make that telescope that much more complex.
While LUVIOR will be investigating the IR, to say "as Webb does" is more than a little misleading.  LUVIOR will only be investigating into the NIR part of the spectrum, not into the mid-IR (like Webb), where all the trouble with thermal emissions from the telescope optics comes from.  With respect to the part of the EM spectrum being investigated, LUVIOR has a lot more in common with Hubble than it does Webb.  As for cooling of actual detectors, this is a solved problem, as Hubble sported some of these (NICMOS comes to mind, but I think there was at least one other).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/10/2022 01:21 pm
Does anyone know if the calibration images from the optical alignment process will be published?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: kenny008 on 01/10/2022 01:24 pm
My understanding from the post-deployment webcast is that they will not be publishing images until they complete all calibrations, and they can "show what it can do".
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/10/2022 03:02 pm
Will they post updates about actuation of mirror segments and opening instrument lid?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 01/10/2022 03:14 pm
With every single Shuttle servicing missions costing $1.5 billion... it surely inflated the total cost.

"This does not include the cost of space shuttle operations for Hubble’s deployment and servicing missions..."

Drats ! Sorry for that. Then again, it makes Hubble even more insanely expensive: well over $20 billion !
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: lrk on 01/10/2022 04:06 pm
Luvoir will look at IR too, full name is Large Ultraviolet Optical Infrared Surveyor.

Edit: However 'the telescope is actively heated to a precise 270 K (−3 °C; 26 °F) to control thermal disturbances.' - Wikipedia

Hmm.  If the telescope has an IR component, wouldn't you want it as cold as possible?  Being cold doesn't affect visible/UV observations, does it?  Although I imagine it would be much easier to engineer instruments that don't have to work at practically absolute zero. 

(also LUVOIR discussion probably belongs in a dedicated thread, but I didn't see an active one.)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: cdebuhr on 01/10/2022 04:24 pm
Luvoir will look at IR too, full name is Large Ultraviolet Optical Infrared Surveyor.

Edit: However 'the telescope is actively heated to a precise 270 K (−3 °C; 26 °F) to control thermal disturbances.' - Wikipedia

Hmm.  If the telescope has an IR component, wouldn't you want it as cold as possible?  Being cold doesn't affect visible/UV observations, does it?  Although I imagine it would be much easier to engineer instruments that don't have to work at practically absolute zero. 

(also LUVOIR discussion probably belongs in a dedicated thread, but I didn't see an active one.)
Depends on which part of the IR spectrum you're in.  Mid-IR (like JWST) - oh yeah.  The colder the better.  NIR (like LUVIOR, or Hubble for that matter)?  If you're hot enough to start emitting in that part of the spectrum, your telescope has much bigger problems.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: orsobubu on 01/10/2022 04:45 pm
The most fascinating phase of the telescope deployment for me is the sunshield, and in particular the first step, the restraints and pink covers releases, happened on December 30; I found lots of materials about the sunshield, but very little about the covers, which from what I understand have a spring mechanism that make them roll up in complicated and different phases to the edges of the two underlying pallets. Basically I found only this video at 3.00:

https://www.youtube.com/watch?v=zWBHO8FIP8Y

and this one at 6.00:

https://www.youtube.com/watch?v=7bz03OnyD2A

Does anyone have more information about these spectacular mechanisms I think have been neglected and very risky and difficult to control? Coincidentally, it seemed to me that one of the rare glitches in the entire deployment process involved this very phase! https://blogs.nasa.gov/webb/2021/12/31/first-of-two-sunshield-mid-booms-deploys/

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/10/2022 05:29 pm
With every single Shuttle servicing missions costing $1.5 billion... it surely inflated the total cost.

"This does not include the cost of space shuttle operations for Hubble’s deployment and servicing missions..."

Drats ! Sorry for that. Then again, it makes Hubble even more insanely expensive: well over $20 billion !


Yeah, but the dollar figures are really the wrong way to look at that issue. That stuff was relevant, but not really important. You have to consider the context of when the Hubble was approved and the overall thinking at NASA and the country at large (most importantly Congress). The shuttle was widely viewed as an enabler. It was going to make new things possible. And so the astrophysics community and the human spaceflight community made a pact, an agreement to work together on Hubble. There were a lot of compromises along the way (for instance, Hubble itself became more expensive so that humans could service it, but making human servicing possible meant that Hubble could be upgraded and its life extended). There was also an attitude of treating Hubble more like one of the great ground-based observatories, where it would be used by many people and upgraded over a long period of time. This was a much different approach than how earlier space telescopes had been built.

But all of that came with lots and lots of strings attached. The leaders of the shuttle program knew that they would have to fly a certain number of Hubble servicing missions over a period of time. They knew they would have to make those missions high priority, and they would even possibly get in the way of other missions. And the leaders of the astrophysics program knew that they would have to abide by the shuttle schedule and requirements and the added safety requirements and layers of bureaucracy. Everything was more complicated and yes, more expensive.

It's easier to run programs without those entanglements, which is why different groups are wary of getting into them too quickly.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: rustym on 01/10/2022 10:47 pm
Does anyone know how they point the JWT at a target?
1. Do they move just the mirror assembly separate from the sun-shield or do they maneuver the whole telescope?
2. If they move the whole thing how much does this limit its range before the sunshield becomes ineffective?
3. How do they keep it on target.

RM
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: LouScheffer on 01/10/2022 11:12 pm
Luvoir will look at IR too, full name is Large Ultraviolet Optical Infrared Surveyor.

Edit: However 'the telescope is actively heated to a precise 270 K (−3 °C; 26 °F) to control thermal disturbances.' - Wikipedia

Hmm.  If the telescope has an IR component, wouldn't you want it as cold as possible?  Being cold doesn't affect visible/UV observations, does it?  Although I imagine it would be much easier to engineer instruments that don't have to work at practically absolute zero. 

(also LUVOIR discussion probably belongs in a dedicated thread, but I didn't see an active one.)
It makes the mirror fabrication much easier if you can grind it at close to the operating temperature, and at temperatures you can easily reach for testing.  Also, much colder and a lot of volatiles will stick, something JWST is trying very hard to avoid.   So unless you *really* want mid-IR, it's better not to cool the mirror too much.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: cdebuhr on 01/10/2022 11:18 pm
Does anyone know how they point the JWT at a target?
1. Do they move just the mirror assembly separate from the sun-shield or do they maneuver the whole telescope?
2. If they move the whole thing how much does this limit its range before the sunshield becomes ineffective?
3. How do they keep it on target.

RM
Welcome to the forum!
1) They maneuver the whole spacecraft.
2) 50° of pitch (from -5° to +45°), 10° of roll (from -5° to +5°), and 360° of yaw.  Thanks to kdhilliard (next post) for clarifying and correcting my somewhat rusty recollection. I've seen these figures somewhere, but I can't remember them offhand.  I think its a range of something like 50-60 degrees pitch, 20-30 degrees roll, and 360 degrees yaw.  Do remember though that the thing is also orbiting the sun which means they can still view the whole sky, they just can't see the whole sky at any given time, as the telescope itself must always stay behind the sun shade.
3) The telescope is pointed using reaction wheels.  Coarse positioning is determined using fixed head star trackers on the main spacecraft bus.  These plus the reaction wheels gets the telescope pointing at its target.  Once on target, the spacecraft holds steady, with fine optical tacking being performed using the fine steering mirror, which is part of the main optical assembly.

Edit: correct my prior bad recollection of JWST maneuvering range.  Thanks to kdhilliard for reminding me that I too got this from Scott Manley's video.  I didn't check Manley's sources, but assume he got it right.  If I really needed to know, I'd check!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: kdhilliard on 01/10/2022 11:57 pm
Does anyone know how they point the JWT at a target?
...
1) They maneuver the whole spacecraft.
2) I've seen these figures somewhere, ...

50° of pitch (from -5° to +45°), 10° of roll (from -5° to +5°), and 360° of yaw.

This is discussed, with animation, at 6:17 into Scott Manley's JWST video from last month:
  https://youtube.com/watch?v=cp_7AJseYYc&t=6m17s
Quote from: Scott Manley
... And it can also roll by about plus or minus five degrees, which is necessary to stop rotation of the viewing field over long exposures, to make sure the light falls on the same pixels.  So it can't look directly away from the Sun, nor can it look a the inner planets.  When all these motions are accounted for, the spacecraft can observe about 39% of the sky at any time.  And over the complete year it will be able to see 100% of the sky, just not all at once.  There's also two constantly viewable regions about five degrees away from the celestial poles.

(I don't know the source of the range-of-motion video Manley shows.)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Perchlorate on 01/11/2022 01:34 am
On a Falcon 9 launch, I love hearing the dry callouts:  "Stage 1 transonic"  followed shortly by "Stage 1 landing leg deploy."

Later tonight, relative to the Earth, and based on the speed of sound at sea level, it will be "Webb transonic" as the Cruising Speed counter on "Where is WEBB" drops through 0.2114 miles per second.

I wonder what the speed will be just before L2 halo orbit insertion?  Even now, Webb's earth-relative velocity is down to about 2% of what it was when S2 cut off.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 01/11/2022 02:38 am
I wonder what the speed will be just before L2 halo orbit insertion?

The next two burns are tiny (~25 and 14m/s respectively), suggesting that Webb will be close to its final orbital velocity (~180m/s / 0.18km/s / 0.1mi/s WRT Earth, 30km/s WRT the sun). But what that will be on WhereIsWebb depends on what it's actually showing, which is not always what it says it's showing.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: mn on 01/11/2022 04:23 am
Does anyone know how they point the JWT at a target?
...
1) They maneuver the whole spacecraft.
2) I've seen these figures somewhere, ...

50° of pitch (from -5° to +45°), 10° of roll (from -5° to +5°), and 360° of yaw.

This is discussed, with animation, at 6:17 into Scott Manley's JWST video from last month:
  https://youtube.com/watch?v=cp_7AJseYYc&t=6m17s
Quote from: Scott Manley
... And it can also roll by about plus or minus five degrees, which is necessary to stop rotation of the viewing field over long exposures, to make sure the light falls on the same pixels.  So it can't look directly away from the Sun, nor can it look a the inner planets.  When all these motions are accounted for, the spacecraft can observe about 39% of the sky at any time.  And over the complete year it will be able to see 100% of the sky, just not all at once.  There's also two constantly viewable regions about five degrees away from the celestial poles.

(I don't know the source of the range-of-motion video Manley shows.)

The range of motion clips come from this video
https://youtube.com/v/y0bOi3kVIBs?t=36

Posted up thread here: https://forum.nasaspaceflight.com/index.php?topic=54269.msg2327671#msg2327671
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/11/2022 02:18 pm
For amusement, I found the trajectory of JWST from JPL Horizons system.
Using days from 1/1/2022 where Jan 1st is t=1, Jan 2nd is t=2, the distance can be fitted with a cubic equation, distance = 0.0001t^3 - 0.0138t^2 + 0.5559t + 6.5769.
This gives a maximum at day t = 29.78 and max distance of 1.3534e6 km. I used Excel which only gives 3 decimal places in the coefficients when fitting so not accurate.
L2 is at about 1.49e6 km, so it needs another small kick to get out to L2 distance.

Does anyone know how to select earth-centre as origin of coordinate system? I had to pick two surface locations 180deg apart and average the (x,y,z) to get earth-centre coordinates. I used pythagoras to get radial distance from earth-centre.

The "Where is Webb" page uses distance along the trajectory rather than radial distance so it's not too useful for this calculation.

Edit to add: I see that Horizons also gives the L2 location under the label SEML2 (sun-earth-moon).
Also, changed to use t instead of x in cubic
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: ccdengr on 01/11/2022 03:07 pm
Does anyone know how to select earth-centre as origin of coordinate system?
Select @earth (AKA code 500, geocentric)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Blackstar on 01/12/2022 02:58 am
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/12/2022 03:05 am


No.

I have video of it being destroyed in the late 60s.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Zed_Noir on 01/12/2022 03:58 am


No.

I have video of it being destroyed in the late 60s.


Correction, neutralized but not destroyed. It is still floating in the void.  ;)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: libra on 01/12/2022 08:16 am
What the freck is that thing ??!!!  :o
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: markbike528cbx on 01/12/2022 08:33 am
It is shown in the historical documentation video
https://memory-alpha.fandom.com/wiki/Planet_killer
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: woods170 on 01/12/2022 09:36 am


No.

I have video of it being destroyed in the late 60s.


Correction, neutralized but not destroyed. It is still floating in the void.  ;)

Also, this is NOT a party thread.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 01/12/2022 08:11 pm
Also, this is NOT a party thread.

...But it is a Trekkie thread on the side *gives Vulcan salute*
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Dizzy_RHESSI on 01/13/2022 12:19 pm
Luvoir will look at IR too, full name is Large Ultraviolet Optical Infrared Surveyor.

Edit: However 'the telescope is actively heated to a precise 270 K (−3 °C; 26 °F) to control thermal disturbances.' - Wikipedia

Hmm.  If the telescope has an IR component, wouldn't you want it as cold as possible?  Being cold doesn't affect visible/UV observations, does it?  Although I imagine it would be much easier to engineer instruments that don't have to work at practically absolute zero. 

(also LUVOIR discussion probably belongs in a dedicated thread, but I didn't see an active one.)

As LouScheffer said the primary concern is molecular contamination. UV performance is extremely sensitive to absorption by molecules which stick to the cold mirrors and detectors. There are other design considerations, telescope temperature was specifically studied by the LUVOIR team. They were also concerned about the added complexity of having to test everything at cryogenic temperatures and it is unclear whether the stability needed for high contrast imaging of exoplanets is compromised by low temperatures. The best mirror substrates (Zerodur and ULE) are optimised to have low expansion around room temperature.

https://asd.gsfc.nasa.gov/luvoir/technology/notes/ColdTemperatureTelescopeConsiderations-LUVOIRTechNote_Final.pdf
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: redliox on 01/16/2022 12:26 am
Since this is a discussion thread, felt this relevant here although almost put into the Pluto Planet one...

Although I don't think the Cycle 1 studies included specifically Pluto or Eris, but did of some Kuiper Belt studies, but what kind of resolution could Webb achieve of those 2 bodies?  Eris is at 97 AU.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/16/2022 01:58 am
Since this is a discussion thread, felt this relevant here although almost put into the Pluto Planet one...

Although I don't think the Cycle 1 studies included specifically Pluto or Eris, but did of some Kuiper Belt studies, but what kind of resolution could Webb achieve of those 2 bodies?  Eris is at 97 AU.

About the same as Hubble.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: niwax on 01/16/2022 03:19 pm
Does anyone know why the mirrors start out at a large offset to their final position? I was expecting each mirror to be adjusted slightly in a different direction, not moved all at once, at least now they're using the slow adjustment motors.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: KaarlisK on 01/16/2022 03:20 pm
Another question out of curiosity: why are two mirrors not moving?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/16/2022 03:28 pm
Another question out of curiosity: why are two mirrors not moving?

It says this right on the page:

"NOTE: Segment A3 and A6 will be moved separately at the end of the process because their position sensors are read out in a different way."
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: launchwatcher on 01/16/2022 03:40 pm
Does anyone know why the mirrors start out at a large offset to their final position? I was expecting each mirror to be adjusted slightly in a different direction, not moved all at once, at least now they're using the slow adjustment motors.
For launch, the mirrors were locked against mechanical stops, at one end of their potential range of motion.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: CMac on 01/18/2022 01:19 pm
Can they start the mirror focusing at this point while waiting for last two mirrors to complete deployment?
Looking forward to seeing an image showing all images from all mirrors. Hope they show one.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Vettedrmr on 01/18/2022 01:33 pm
I'm sure NASA will release images as soon as they're all calibrated and focused.  Last thing NASA needs is to release an early, but not completely focused, image to the public (shades of HST).
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: tibber on 01/18/2022 01:57 pm
Can they start the mirror focusing at this point while waiting for last two mirrors to complete deployment?
Looking forward to seeing an image showing all images from all mirrors. Hope they show one.
I suspect they "could, if" the instruments were cold enough to start up. And they seem to prefer all the mirrors are deployed first. Part of the concern is heat generated by moving too many parts at the same time.

Cheers,
Tom
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 01/18/2022 02:01 pm
I'm sure NASA will release images as soon as they're all calibrated and focused.  Last thing NASA needs is to release an early, but not completely focused, image to the public (shades of HST).

Given the public interest in the process (more so than previous telescopes precisely because of the Rube Goldberg nature of Webb, like the "7 minutes of terror" of the Mars skycranes), and how well NASA has handled the PR, I don't think releasing the focusing test images would create a bad impression. Quite the contrary, it would help maintain public interest during the coming "boring months" between deployment and operations. (Any news outlet that claimed the focusing images were a sign of disaster would be quickly "ratioed" by those ridiculing them.)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: edzieba on 01/18/2022 02:20 pm
Going by the simulated images from the calibration paper (https://doi.org/10.1117/12.925015 (https://doi.org/10.1117/12.925015)) images captured during the calibration process will consist of:
- A scatter of blurs
- An array of blurs
- An array ofdifferent blurs
- An array of points
- An array of points with a point in the middle
- A point

I could see those being released after the first imaging operations have produced actually-looks-like-an-image imagery, but the engineering captures are not very useful for public outreach.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Paul451 on 01/18/2022 02:25 pm
Going by the simulated images from the calibration paper (https://doi.org/10.1117/12.925015 (https://doi.org/10.1117/12.925015)) images captured during the calibration process will consist of:
- A scatter of blurs
- An array of blurs
- An array ofdifferent blurs
- An array of points
- An array of points with a point in the middle
- A point

AND IT WOULD BE SO EXCITING!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Vettedrmr on 01/18/2022 02:48 pm
I could see NASA releasing engineering images behind some kind of paywall (if they can even legally do that), but only restricted release (similar to L2).  But not to the general public.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: deadman1204 on 01/18/2022 09:27 pm
I could see NASA releasing engineering images behind some kind of paywall (if they can even legally do that), but only restricted release (similar to L2).  But not to the general public.

No, anything NASA releases is public domain. You know that within 5 minutes it would be on front page news, with people screaming about how jwst is broken.

Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/18/2022 09:49 pm
I could see NASA releasing engineering images behind some kind of paywall (if they can even legally do that), but only restricted release (similar to L2).  But not to the general public.

No, anything NASA releases is public domain. You know that within 5 minutes it would be on front page news, with people screaming about how jwst is broken.

A picture of a calibration target wouldn't be recognizable enough to the public to know if it's good or not good.  An out-of-focus galaxy with massive spherical aberration is recognizable.  But I think calibration targets would be interesting for one moment in public (the JWST first-light image) with an explanation that images of actual targets are to come.  I think people would be fine with that.  We'd be interested in the images in between but the public wouldn't.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Oersted on 01/18/2022 10:11 pm
I'd love to see one of the outer planets as a first image, of course preferably Saturn or Jupiter. Just to see what JWST is capable of, resolution-wise.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/18/2022 10:37 pm
I'd love to see one of the outer planets as a first image, of course preferably Saturn or Jupiter. Just to see what JWST is capable of, resolution-wise.

It can only see red, redder and redest. What do you want to see?  Resolution goes down as you get redder.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: webdan on 01/18/2022 10:43 pm
I'd love to see one of the outer planets as a first image, of course preferably Saturn or Jupiter. Just to see what JWST is capable of, resolution-wise.

Have to wait at least 6-8 months maybe earlier. Jupiter and Saturn are closing in to their solar conjunctions from us and won't be at oppositions until late September and August 2022 (respectively).

Of course JWST has a wider field of view, so likely earlier. But don't expect Hubble style images as Lee Jay mentions.

There's talk about viewing Mars in Dec... good article here:

https://www.nasa.gov/feature/how-the-webb-telescope-will-explore-mars (https://www.nasa.gov/feature/how-the-webb-telescope-will-explore-mars)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Stan-1967 on 01/18/2022 10:55 pm
I'd love to see one of the outer planets as a first image, of course preferably Saturn or Jupiter. Just to see what JWST is capable of, resolution-wise.

It can only see red, redder and redest. What do you want to see?  Resolution goes down as you get redder.

Webb can see more than just red, redder, & redest.  Just as Hubble had some limited IR capability, Webb will have some capability into the optical wavelengths.  I don't know if Webb images will use a band gap filter to remove optical wavelengths, but the raw photons being focused on the collector will include the optical ranges.  The Webb mirror excels in reflectance of IR wavelengths, hence the difference in the gold coating vs aluminum or silver for optical scopes.

As to resolution, were you thinking of the diffraction limit?  I think resolution stays proportional to the main objective diameter.

Edit:  Iregardless of any optical band gap filters, Webb's detectors in MIRI & NIRcam are exclusively sensitive to near & mid IR, so Lee Jay is correct, Webb see's red, redder, redest. 
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: cdebuhr on 01/18/2022 11:10 pm
I'd love to see one of the outer planets as a first image, of course preferably Saturn or Jupiter. Just to see what JWST is capable of, resolution-wise.

It can only see red, redder and redest. What do you want to see?  Resolution goes down as you get redder.

Webb can see more than just red, redder, & redest.  Just as Hubble had some limited IR capability, Webb will have some capability into the optical wavelengths.  I don't know if Webb images will use a band gap filter to remove optical wavelengths, but the raw photons being focused on the collector will include the optical ranges.  The Webb mirror excels in reflectance of IR wavelengths, hence the difference in the gold coating vs aluminum or silver for optical scopes.

As to resolution, were you thinking of the diffraction limit?  I think resolution stays proportional to the main objective diameter.
Webb is rated for wavelengths as short as 600 nm.  Shorter than that and the reflectance of the mirror system falls off a cliff (remember there are at least four bounces before you even think about entering an instrument, so take whatever reflectance you find and ^4).  As for instrument sensitivities, I don;t know offhand, but an awful lot of the science, if not most, on these sorts of observatories is through band-pass filters of all sorts depending on what spectral feature they're looking at.  In short, at most only a few percent of visible radiation shorter than 600nm will make it as far as the instruments, and that will likely get absorbed in the band-pass filters.  If raw resolution in the visible spectrum is what you're after, you're better off with a humongous ground-based observatory with modern adaptive optics.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/19/2022 12:41 am
  If raw resolution in the visible spectrum is what you're after, you're better off with a humongous ground-based observatory with modern adaptive optics.

I thought that didn't really work on planetary targets like Jupiter and Saturn because it only works over a narrow field of view and on relatively dim targets because of the guide star or laser. But I'm not up on this. Am I correct? If not, why do I never find good images of Jupiter or Saturn from the big ground-based scopes?
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: cdebuhr on 01/19/2022 12:52 am
  If raw resolution in the visible spectrum is what you're after, you're better off with a humongous ground-based observatory with modern adaptive optics.

I thought that didn't really work on planetary targets like Jupiter and Saturn because it only works over a narrow field of view and on relatively dim targets because of the guide star or laser. But I'm not up on this. Am I correct? If not, why do I never find good images of Jupiter or Saturn from the big ground-based scopes?
Whats that old advice?  "Better to remain silent and be thought a fool ...".  BTW, I'm talking about me not you!  Now that you mention it, I think you might be right there.  The the best of my knowledge, ground based with adaptive optics buries space-based through application of raw aperture on stellar targets.  For more expansive targets (like solar system objects), well ... I don't know that you're right, but I think you might be.  I think I've heard the same thing, but it had slipped my mind.  Thanks for the reminder!
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: webdan on 01/19/2022 12:59 am
Quote
Webb will have an approximately 6.5 meter diameter primary mirror, which would give it a significantly larger collecting area than the mirrors available on the current generation of space telescopes. Hubble's mirror is a much smaller 2.4 meters in diameter and its corresponding collecting area is 4.5 m2, giving Webb around 6.25 times (see calculation) more collecting area! Webb will have significantly larger field of view than the NICMOS camera on Hubble (covering more than ~15 times the area) and significantly better spatial resolution than is available with the infrared Spitzer Space Telescope.

https://www.jwst.nasa.gov/content/about/comparisonWebbVsHubble.html (https://www.jwst.nasa.gov/content/about/comparisonWebbVsHubble.html)
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: Lee Jay on 01/19/2022 01:40 am
Quote
Webb will have an approximately 6.5 meter diameter primary mirror, which would give it a significantly larger collecting area than the mirrors available on the current generation of space telescopes. Hubble's mirror is a much smaller 2.4 meters in diameter and its corresponding collecting area is 4.5 m2, giving Webb around 6.25 times (see calculation) more collecting area! Webb will have significantly larger field of view than the NICMOS camera on Hubble (covering more than ~15 times the area) and significantly better spatial resolution than is available with the infrared Spitzer Space Telescope.

https://www.jwst.nasa.gov/content/about/comparisonWebbVsHubble.html (https://www.jwst.nasa.gov/content/about/comparisonWebbVsHubble.html)

Look how carefully that's worded.

6.25 times the collection area than Hubble (but only 2.5 times the aperture), and better resolution than Spitzer (but not Hubble).

Hubble has better resolving power on its shortest wavelength than JWST does on its shortest wavelength.

JWST has an entirely different design basis than Hubble.  It's a successor, not a replacement.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2
Post by: gparker on 01/19/2022 03:25 am
Can they start the mirror focusing at this point while waiting for last two mirrors to complete deployment?
Looking forward to seeing an image showing all images from all mirrors. Hope they show one.
I suspect they "could, if" the instruments were cold enough to start up. And they seem to prefer all the mirrors are deployed first. Part of the concern is heat generated by moving too many parts at the same time.

Another problem is all of the mechanical parts that aren't fully cold yet. As they cool they'll move or shrink, which would spoil any precise mirror alignment. They'll wait until the telescope is at operating temperature before beginning the alignment process. The first alignment is expensive in terms of actuator lifetime, so they don't want to repeat it.
Title: Re: NASA - James Webb Space Telescope - Discussion Thread 2