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Unmanned _ Telescopic Observations _ James Webb Space Telescope

Posted by: Redstone Aug 23 2005, 02:01 PM

The manufacture of the JWST mirror blanks

Despite this milestone, the fate of JWST is still somewhat precarious, because although the scientific bang from the telescope is expected to be huge, to a staggering $4.5 billion. A on the squeeze in NASA's space-based astronomy plans gives some background.

The JWST home page can be found

The Space Telescope Science Institute, which runs Hubble, also has a site As does

Posted by: djellison Aug 23 2005, 02:10 PM

Just how does it end up costing $4.5B ( which will become $5B I'm sure)

That's just - wow. That's TEN Mer's.


I'm not saying "drop the scope, build Ten MER's" - but even the challenge of getting that mirror light enough, and deploying accurately enough surely cant cost $4.5B


Posted by: Redstone Aug 23 2005, 02:42 PM

Well, a 6.5m telescope is pretty big even on the ground. And the plan is to send it to L2, not LEO, so with no repair capability, it has to be REALLY well designed, with huge redundancy and margin etc. Plus, the thing weighs nearly seven tonnes.

A little more info at

Back in 2003, it I'll see if I can find some more info on what is driving up the cost.

Posted by: Bob Shaw Aug 23 2005, 03:03 PM

The JWST has always struck me as being a prime example of why men in space (or at least very capable robonauts) are a good idea. The mechanical requirements of unfolding those mirror segments and the sunshade, plus the inevitable limits on attitude-control and instrumentation really do demand some up-close-and-personal TLC. Hubble never really needed men (it was launched 'built') and the upgrades were always the jam on the cake (OK, they got the mirror wrong, and that fix *did* need men, but you can't say that such activities were a part of the rationale behind Hubble and the Shuttle - it was sheer luck that after a really bad start something could be done at all!). JWST, however, is exactly the sort of structure which could do with a quick tap from a guy with a rubber mallet when the main wossisname joint flange sub-assembly secondary cotter-pin stiffens up!

Personally, I'd put JWST on the back burner until it can be man-tended, and spend the money in the meantime on a series of state-of-the-art but disposable Hubbles II, III and IV. JWST smells too strongly of too many eggs in one basket for me, and after the Galileo antenna I'd as soon not have to trust my faith in interplanetary origami.

Posted by: dilo Aug 23 2005, 09:22 PM

4.5 billion is a lot. If I'm not wrong, this is 2 B$ above Hubble, and still surpassing it even considering the cost of shuttle servicing missions.
How is possible? clearly, the aveniristic technology require strong investment... but consider that this will have many applications and can be an investment for future space telescopes!

Posted by: Redstone Aug 26 2005, 09:50 PM

It seems JWST is safe from outright cancellation for the moment. has some detail on how the project hopes to rein in the budget for JWST. Part of it is limiting testing. Scary. The other part is reducing the amount of polishing of the mirrors which will greatly slow down JWST's ability to image in the optical part of the spectrum. JWST was always billed as a near IR telescope, but the lack of any overlap with Hubble is going to hurt.

Launch is also delayed, probably to 2013.

Posted by: antoniseb Aug 26 2005, 10:31 PM

QUOTE (Redstone @ Aug 26 2005, 04:50 PM)
JWST was always billed as a near IR telescope, but the lack of any overlap with Hubble is going to hurt.

The overrun is about a billion dollars (so far), and the reduced mirror polishing will save $150M. They've got a few other cost cutting things to do, or somehow get more funding.

Does anyone know how much of the budget is a one time expense to do research on electro-mechanical devices that work at near absolute zero temperatures? I am kind of curious to know where the money for this project has gone, as it will give some guidance for future large space telescopes such as SIM and Terrestrial Planet Finder.

Posted by: Bob Shaw Aug 26 2005, 10:39 PM

IMHO, JWST should be put on hold, and then back out to competition - it's just going the way of the ISS, descoped and over budget, when Burt Rutan and Co would just build the damn thing, and hit it with a hammer as required until it was the right shape. If JWST fails, then (near) optical space astronomy goes down the tubes, period.

Failing that, a bunch of throwaway Hubbles (maybe with a He replenishment capability, but that's all).

Really, it's nuts to NOT make JWST man-tended!

Posted by: Redstone Oct 9 2005, 04:16 PM

First JWST mirror segment delivered for polishing.

The mirrors will be polished to tolerances as tight as 20 nanometers, or less than one millionth of an inch.

After initial polishing, the segments will be tested at roughly minus 400 degrees Fahrenheit (near absolute zero) in a cryogenic test chamber at NASA's Marshall Space Flight Center in Huntsville, Ala., and returned to Tinsley for further refinement and polishing. The entire polishing process takes about two-and-a-half years.

blink.gif No wonder this telescope costs a fortune.

Posted by: BruceMoomaw Oct 9 2005, 10:07 PM

"Really, it's nuts to NOT make JWST man-tended!"

Not when you consider that both its sensitivity and its available observation time are tremendously reduced if you put it anywhere near the radiated warmth of Earth. Considering that, it's still more scientifically cost-effective to put it at the Earth-Sun L2 point, even though it's beyond range of human repairmen. (Keep in mind that, once the design work for the first one has been done, the cost of an identical replacement would be considerably less.)

Posted by: SigurRosFan Oct 9 2005, 10:24 PM

"The James Webb Space Telescope is a large, infrared-optimized space telescope scheduled for launch no earlier than June 2013."

Posted by: Redstone Nov 21 2005, 01:53 PM The article also says that the telescope will not be "descoped" to any great degree. Only some testing and instrumentation for low priority science will be removed. Cost is still $4.5 billion, but now has less risk, and a more even funding profile. And launch is likely to be on an Ariane 5, with a launch deal set for 2006.

With HSM 4 now more and more likely, this delay doesn't bother me so much. HST will last that long, and there will still be overlap between the two observatories.

And SIM, which is seen as a casualty of the JWST overruns, has been giving a funding boost by Congress, and is on track for a 2012 launch, according to

Posted by: AlexBlackwell Mar 8 2006, 08:56 PM

I moved this from a thread I started to this one. Thanks to ljk4-1 for pointing it out to me.

I apologize if there is already a thread on JWST; I didn't take the time to look (very hard). However, if there isn't, I'll kick-start it by pointing out Tony Reichhardt's excellent news article in the March 9, 2006, issue of Nature:

US astronomy: Is the next big thing too big?
Tony Reichhardt
Nature 440, 140-143 (2006).


So no one is denying that the JWST will be a first-rate telescope, perhaps even a revolutionary one. Just last August an independent assessment team charged by the project to review the telescope's science potential reported that "the scientific case for the JWST mission has become even stronger" since the Decadal Survey's endorsement in 2000. But what of its expense? NASA's latest budget puts the project's price tag, including $1 billion for a decade's worth of operations, at $4.5 billion. That's more than the entire annual research and development budget of the National Science Foundation; it represents more than $1 million for each full member of the American Astronomical Society.

Nature also has an editorial ("") on the subject in the same issue. Following is an excerpt:

It is now clear that when NASA first requested funds for a Next Generation Space Telescope a decade ago, the project's advertised price of under $1 billion was little more than a fiction. But it was a fiction that the space agency, the Congress and many in the astronomy community wanted to believe.

And, of course, there's the recent NASAWatch/Spaceref article ""

Posted by: BruceMoomaw Mar 14 2006, 03:07 AM

My attempt to attach this article failed; it overloaded available space on this site. I'll have to do a summary of it later -- it makes a great many important points about the current space science proram.

Posted by: BruceMoomaw Mar 14 2006, 03:47 AM

Particularly interesting quotes from the article:

(1) "At the beginning of the millennium, US astronomers thought that their most-wanted project would cost $1 billion...NASA's latest budget puts the project's price tag, including $1 billion for a decade's worhthof operations, at $4.5 billion. That's more than the entire annual research and development budget of the National Science Foundation; it represents more than $1 million for each full member of the American Astronomical Society." Which, I think, makes my point again about the low cost-effectiveness of most space science, and the immense difficulty it would have competing for government funding in any honest competition with other kinds of scientific research.

(2) One part of the problem DOES seem to be NASA HQ's fault. "A delay in the government's decision to move from a US launcher to the Ariane added an estimated $300 million as highly paid engineers were unable to move forward until they knew which rocket they were designing for. The situation is particularly embarrassing given that the cost of delaying the decision ended up being greater than the cost of the launch." Ah, the rationality of government. Still, this is only 1/12 of the total cost rise.

(3) As for the other causes of the cost underestimate: "The Decadal Survey guessed the cost as $1 billion. Studies in the mid-1990s had pegged the price as between $500 million and $1 billion. These were based on the hope -- unfulfilled, as it happened -- that the Webb Telescope might take advantage of advances in building low-cost spaceraft developed by the military."

However: "Garth Illingworth of UC-Santa Cruz, who chaired the 1990 panel [which much more acurately predicted its current cost], chalks the anomalously low estimates from the 1990s up to a 'lack of reality' inherent in the 'faster, better, cheaper' philosophy of Dan Goldin...Reinhard Genzel of Germany's Max Planck Institute for Extraterrestrial Physics in Garchning says it was clear at the time that a $500 million estimate for the Webb Telescope was a 'political price'...

"Today, Illingworth inveighs against the 'extraordinarily bad, artificial cost estimates' of the Goldin era. But the 2000 Decadal Survey seems to have been happy to accept them. The world of big science is well used to projects being lowballed -- a process that gets schemes started on the basis of a low-cost estimate, with the implicit hope that by the time the true costs are known inertia and vested interests will make it impossible to pull out. Lowballing is not a practice anyone would like to defend on principle, but histories like the Hubble's show it can work." That is, our old friend the Camel's Nose again -- exactly the same technique NASA used to get Shuttle and Station funded.

(4) Where Hubble is concerned: "[Hubble project scientist Robert] O'Dell recalls that in 1972, Hubble's total price including its first year of operations was projected to be...$1 billion in today's prices. According to Robert Smith, a historian at Canada's Univ. of Alberta who wrote a political history of the telescope...'the development cost of Hubble to date is certainly more than $4 billion.'

"NASA's Eric Smith adds that when new instruments and operating expenses are added, that comes to $9 billion. This doesn't include the cost of four space shuttle servicing missions to Hubble, and a fifth being planned -- the cost of a shuttle launch can be put at about $500 million. All in all, building, launching, using and refurbishing Hubble has probably been the most expensive undertaking ever made in the name of pure science; the mission is still, remarkably, costing over $300 million a year." (And that's ignoring the fact that the true cost of each Shuttle mission, using honest accounting, is over $1 billion!)

(5) Charles Beichman of JPL, a leading light of the cancelled Terrestrial Planet Finder mission...thinks that the Webb Telescope will be 'a fine machine. It will do fantastic science.' In fact, he is on one of the instrument teams. But when he goes to professional meetings, he sees more young astronomers attending sessions on planet-finding than on Hubble or the Webb Telescope." Of course, Beichman couldn't POSSIBLY be a biased witness in this matter. Heavens, no. But I do find it at least plausible that the examination of other solar systems is considered, on balance, more romantic -- and thus more interesting -- by genuine astronomers than cosmology or other fields of space astronomy are, just as it is by the nonscientific public.

Still, as the article says, "anyone who doesn't realize that TPF would be costlier than the Webb Telescope is dreaming." I shudder to think what the real cost of THAT endeavor will end up being -- which is why I have no objection at all to protractedly deferring it until Kepler and/or SIM have given us the initial census of the frequency of potentially habitable planets which we need to make even the most basic decisions as to the design of TPF.

In summary, it is very hard to blame the Webb Telescope problem itself on NASA HQ -- although of course the cuts in space science spending as a whole can be blamed on the hypertrophied (or, to be more accurate, metastasized) manned space program. But where Webb's tendency to hog most of whatever the actual space astronomy budget turns out to be is concerned, I think that space astronomers -- to quote Popeye the Sailor -- "buttered their bread and now they've got to sleep in it."

Posted by: AlexBlackwell Mar 14 2006, 05:02 PM

To keep things tidy and prevent sprawling, disconnected threads, I moved Bruce's two posts to the JWST thread.

Posted by: GravityWaves Apr 1 2006, 07:27 PM

QUOTE (dilo @ Aug 23 2005, 06:22 PM) *
4.5 billion is a lot. If I'm not wrong, this is 2 B$ above Hubble, and still surpassing it even considering the cost of shuttle servicing missions.
How is possible? clearly, the aveniristic technology require strong investment... but consider that this will have many applications and can be an investment for future space telescopes!

Guys have you seen the JWST talking points e-mail ? I think NASA watch had it on the website

Posted by: ljk4-1 May 16 2006, 02:44 PM

James Webb Telescope Sunshield Membrane Passes Tests

Redondo Beach CA (SPX) May 15, 2006 - Northrop Grumman announced Monday its
engineering team has successfully completed a series of tests on a key element
of the James Webb Space Telescope.

Posted by: ljk4-1 May 31 2006, 05:53 PM

ATK To Provide More Components For James Webb Space Telescope

Minneapolis MN (SPX) May 31, 2006

Alliant Techsystems announced Tuesday it has received a $65 million contract to provide more components and subsystems to Northrop Grumman for NASA's James Webb Space Telescope.

Posted by: ljk4-1 Jun 9 2006, 07:28 PM

Astrophysics, abstract

From: Jonathan Gardner [view email]

Date: Wed, 7 Jun 2006 21:05:29 GMT (12223kb)

The James Webb Space Telescope

Authors: Jonathan P. Gardner, John C. Mather, Mark Clampin, Rene Doyon, Matthew A. Greenhouse, Heidi B. Hammel, John B. Hutchings, Peter Jakobsen, Simon J. Lilly, Knox S. Long, Jonathan I. Lunine, Mark J. McCaughrean, Matt Mountain, John Nella, George H. Rieke, Marcia J. Rieke, Hans-Walter Rix, Eric P. Smith, George Sonneborn, Massimo Stiavelli, H. S. Stockman, Rogier A. Windhorst, Gillian S. Wright

Comments: 96 pages, including 48 figures and 15 tables, accepted by Space Science Reviews

The James Webb Space Telescope (JWST) is a large (6.6m), cold (50K), infrared-optimized space observatory that will be launched early in the next decade. The observatory will have four instruments: a near-infrared camera, a near-infrared multi-object spectrograph, and a tunable filter imager will cover the wavelength range, 0.6 to 5.0 microns, while the mid-infrared instrument will do both imaging and spectroscopy from 5.0 to 29 microns.

The JWST science goals are divided into four themes. The End of the Dark Ages: First Light and Reionization theme seeks to identify the first luminous sources to form and to determine the ionization history of the early universe.

The Assembly of Galaxies theme seeks to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present day.

The Birth of Stars and Protoplanetary Systems theme seeks to unravel the birth and early evolution of stars, from infall on to dust-enshrouded protostars to the genesis of planetary systems.

The Planetary Systems and the Origins of Life theme seeks to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for the origins of life in those systems.

To enable these observations, JWST consists of a telescope, an instrument package, a spacecraft and a sunshield. The telescope consists of 18 beryllium segments, some of which are deployed. The segments will be brought into optical alignment on-orbit through a process of periodic wavefront sensing and control.

The JWST operations plan is based on that used for previous space observatories, and the majority of JWST observing time will be allocated to the international astronomical community through annual peer-reviewed proposal opportunities.

Posted by: Decepticon Jun 16 2006, 10:29 PM

I'm looking forward to seeing alpha centauri images with this telescope. smile.gif

Posted by: DonPMitchell Jun 16 2006, 10:35 PM

JWST is a partnership between ESA, NASA, and the Canadian Space Agency.

How much are various partners putting into this? How much is NASA being asked to pay?

Posted by: GravityWaves Jul 5 2006, 01:09 AM

QUOTE (DonPMitchell @ Jun 16 2006, 07:35 PM) *
How much are various partners putting into this? How much is NASA being asked to pay?

Canadians have already helped with the Shuttle arm and ESA has already worked with NASA on Hubble, Cassini-Huygens, Soho and other missions
to save money JWST will be launched by Ariane-5 in French Guiana S.America

Posted by: Littlebit Jan 22 2007, 03:27 PM

James Webb Space Telescope Mirror Backplane Prototype Passes Critical NASA Space Readiness Tests

A prototype structure that holds the primary mirrors for the optical element of the James Webb Space Telescope (JWST) passed a key readiness milestone after undergoing a series of rigorous cryogenic tests at NASA's Marshall Space Flight Center in Huntsville, Ala.

Posted by: SigurRosFan Feb 9 2007, 05:36 PM


Engineers have finished making the 18 hexagonal elements that will come together to form the telescope's 6.6m primary mirror.

Posted by: GravityWaves Feb 19 2007, 02:12 PM

"6.6m (22ft) in diameter", that's fantastic !

Posted by: ollopa May 21 2007, 01:09 PM

NASA, ESA and the CSA are holding a technical review of the JWST in Dublin, Ireland, next month. Approximately 300 people will attend the meeting, which will be held in the Royal Hospital Kilmainham from Monday June 11th – Thursday June 14th. In addition to NASA, ESA and CSA personnel, representatives from a large number of US and European space technology companies will be present.

The JWST Chief Project Scientist John Mather will give two public lectures while in Dublin, one will be in association with the Royal Irish Academy.

We are currently transporting a full-scale model of the James Webb Space Telescope to Dublin (it will be placed in the grounds of the Royal Hospital Kilmainham and National Museum of Modern Art) for at least 6 weeks.

The School of Cosmic Physics at the Dublin Institute for Advanced Studies is directly involved in developing one of the four main instruments on board JWST - the MIRI - and is hosting next month's meeting.

As this is a technical event, there are limited public events associated with it, but I will post more precise details shortly.

Posted by: helvick May 21 2007, 06:24 PM

Great stuff - finally something to go to that is close to home. smile.gif

Posted by: djellison May 21 2007, 08:18 PM

This thread will be useless without pics. You have your assignment. Do it smile.gif


Posted by: helvick May 21 2007, 08:32 PM

I'm on it boss. smile.gif

Posted by: jaredGalen May 23 2007, 10:23 AM

Some one has posted some pics (2) of the Full scale model here

I'm in dublin, this is fantastic about the technical review meeting here in Dublin. Can't wait to see the model for real smile.gif

Posted by: djellison May 23 2007, 10:35 AM

That's two of you.


Do it. smile.gif


Posted by: AlexBlackwell May 23 2007, 07:29 PM
By Brian Berger
Space News Staff Writer,
posted: 23 May 2007
6:00 am ET

Posted by: jaredGalen Jun 6 2007, 11:11 AM

Anyone have new info on events associated with next weeks technical review of the JWST in Dublin?

Posted by: helvick Jun 8 2007, 02:27 PM

I stopped by the Royal Hospital today at lunchtime and found the crew busily putting the replica together - it really is a shock to see just how big it actually is. The idea that something that huge can be launched and will be able to go through that unfolding manouver is astonishing. I'll be going back on Sunday when it's more complete and once or twice next week depending on when it is actually finished to get shots of the fully built model. These shots are all a bit rough and ready as I was in a bit of a rush but they'll give you an idea of the scale.


Posted by: ollopa Jun 9 2007, 01:17 AM

Members of this forum are especially welcome to the following. Just register as UMSF:


The next generation of Irish astronomers will take time off from their
Leaving Cert and Junior Cert examinations on Monday to brief journalists
about Ireland's big involvement in a dramatic new space telescope project
that is to revolutionise space research.

Students sitting their Science examinations this week will be graduate
researchers at university by the time the new telescope is launched in 2013
and they will be ideally placed to continue Ireland's strong tradition of
space research.

The students will brief journalists in front of a huge full-scale model of
the two-storey-high James Webb Space Telescope (JWST), which is to be
launched aboard Europe's powerful “Ariane-5” rocket to replace the
legendary Hubble Space Telescope. A large model of the Ariane rocket will
also be on hand.

The briefing coincides with a major international meeting at the ROYAL
HOSPITAL KILMAINHAM (RHK), which is attracting scientists and engineers
from all over the world. The meeting is hosted by the DUBLIN INSTITUTE FOR ADVANCED STUDIES, a leading centre for research into our cosmic origins.

The full-scale space telescope model was developed by aerospace contractors Northrop Grumman to give a better understanding of the size, scale and complexity of the project. The model is constructed mainly of aluminum and steel, it weighs six tonnes and is the size of two tennis-courts.

The model was transported by ship from the United States after it was
unveilled on the National Mall in Washington DC last month. It required
four container lorries to bring it from Dublin Port to Kilmainham, and a
large crew – including many FÁS apprentices – are spending four days
assembling the model in a large meadow at the back of the RHK.


WHEN: Monday, 11 June 2006

WHERE: Royal Hospital Kilmainham (RHK)

The Johnston Room

TIME: 11.30 a.m.

TO MEET: Professor Tom Ray, Dublin Institute for Advanced Studies

Dr John C Mather, joint winner of the 2006
Nobel Prize for Physics. This year, Dr. Mather was listed among Time
Magazine's 100 Most Influential People in the World.

Tony Mc Donald, Enterprise Ireland

Chair: Leo Enright, Chairman, Discover Science and Engineering.

Posted by: ollopa Jun 9 2007, 01:53 AM

Currently - and remember these things can change - the following sessions on Monday morning are open to non-mission attendees. You will have to register, but staff have been told to expect UMSF members. If you have a problem, ask to speak with Dympna O'Callaghan. If you feel the need to attend other sessions, talk to Dympna on Monday. This is not a general invite to the public, but we at the Institute for Advanced Studies are very keen to facilitate anyone with a serious interest in astrophysics.

Great Hall (Main meeting room)

Registration Johnston Room (from 8:30)

Dublin Institute for Advanced Studies Welcome (Ray)

JWST Science Objectives (Gardner)

JWST Mission Overview and Status (Menzel)

JWST Observatory Overview and Status (Lynch)


OTE and Wavefront Sensing Overview (Feinberg)

NIRCam (Rieke)

NIRSpec (Jakobsen)

Lunch (Baroque Chapel)

Posted by: helvick Jun 9 2007, 01:31 PM

I just re-arranged my Monday schedule so I'll be there. smile.gif

I'll take notes and post a report afterwards.

Posted by: helvick Jun 9 2007, 05:19 PM

I went back to check on the model's progress and found that the construction team were just putting the last few pieces into place. The pictures really don't do it justice but you can get a good idea of scale by how small the crew on the boom lift look.

I also added another bunch of shots to the

Posted by: climber Jun 9 2007, 06:01 PM

Thanks helvick.
I'll come to Ireland by mid august. Do you know if it'll still be there?

Posted by: helvick Jun 9 2007, 09:43 PM

My understanding is that it is going to remain for around six weeks so it almost certainly will not still be here, unfortunately. One of the local web sites said it would be here until July 19th which more or less matches up. I don't have any official information though, maybe Ollopa can be more definite.

It is scheduled to be displayed at the Rochester Museum & Science Center, in Rochester, New York starting on August the 26th so it will definitely have to be deconstructed at least 10 days before so that it can be shipped back across the Atlantic. I find it really amusing that it has to travel by ship - it's too big to fly. smile.gif

Posted by: nprev Jun 10 2007, 12:22 AM

Helvick, do you know the rest of its schedule? Hoping it'll make a stop in Los Angeles...

Posted by: ollopa Jun 10 2007, 12:53 AM

QUOTE (helvick @ Jun 9 2007, 10:43 PM) *
It is scheduled to be displayed at the Rochester Museum & Science Center, in Rochester, New York starting on August the 26th.

That was actually a couple of years ago. We're still talking to Grumman about the exact repatriation date. Six weeks is just a ball-park number, however we will almost certainly move it from Kilmainham on or before the w/e of June 23rd. I'll keep you posted on a new location (top secret just now!).

Posted by: ollopa Jun 10 2007, 11:25 PM

Direct from its Washington premier just last month, the next really big thing in space exploration has arrived in Dublin this week to highlight the past, present and future of Ireland's contribution to space research. Construction crews at the Royal Hospital in Kilmainham spent three days assembling a full-scale model of the two-storey-high behemoth that will replace the legendary Hubble Space Telescope as humanity's sharpest eye on the cosmos.

The Dublin Institute for Advanced Studies, through it's School of Cosmic Physics, has been actively involved in space missions since the earliest days of space exploration, and this week it is hosting an international meeting of the scientists and engineers who are designing a revolutionary new observatory, the James Webb Space Telescope (JWST). Approximately 300 people will attend the meeting, which will be held in the Royal Hospital Kilmainham from Monday June 11th. to Thursday June 14th .

The JWST is named after the public servant who led America's project to land astronauts on the Moon, but it is a truly international enterprise. The Dublin Institute is providing optical filters for a key instrument aboard the telescope.

“We are immensely proud to be involved in this exciting new project,” said Professor Tom Ray, who works with a team of graduate students in the Institute's School of Cosmic Physics to understand how stars like our own Sun came to be in the first place. The new telescope will also study supermassive black holes and help in the search for planets that might harbour life.

The Dublin Institute for Advanced Studies is involved in the telescope project through Ireland's membership of the European Space Agency, and special funding for this Irish contribution came from Enterprise Ireland. Barry Fennell of EI’s International Science & Technology Dept explained that while Ireland contributes to ESA, it also gets much in return: “In the last 7 years, over 50 Irish companies and 10 University research teams have secured contracts with a cumulative value of €35 million. In addition, commercial business being generated by Irish companies and academics directly from ESA-supported developments is estimated to be worth about €25 million a year”.

The large telescope model was brought to Ireland with the help of the Northrop Grumman corporation, prime contractors for the space telescope project. Additional sponsorship came from Omega Air, the Dublin-based aviation services company, and from FÁS, whose skilled apprentices found themselves working on something out of this world.

The Dublin Institute for Advanced Studies plans to use the huge model of the space telescope as the centrepiece of a summer-long campaign to raise public awareness of Ireland's involvement in cutting-edge science. The Institute is probably best-known to Dubliners as the custodian of Dunsink Observatory, a much-loved Dublin landmark with a unique place in the history of astronomy.


Posted by: nprev Jun 11 2007, 01:25 AM

This is gonna sound trite, but damn that thing is big! Exciting times ahead... smile.gif

Posted by: dilo Jun 11 2007, 06:00 AM

What an impressive shot, allopa!
I'm fascinated by the contrast between past and future there...

Posted by: helvick Jun 11 2007, 09:39 PM

As promised by Ollopa UMSF folks were allowed to attend. As it transpired I think I could have stayed for the entire day but I had to get back to work for the afternoon so I missed out on the sessions after lunch. These are just my notes so they come with absolutely no warranty whatsoever. smile.gif

Todays Agenda:

  1. Welcome - Tony Ray (DIAS) and John Mather.
  2. JWST Science Objectives - Gardiner
  3. Mission overview, Observatory Overview and Reformulation Summary - Menzel & Giampaoli
  4. OTE and Wavefront Sensing Overview - Feinberg
  5. NIRCam (Rieke)
  6. NIRSpec (Jakobsen
  1. FGS-TF (Hutchings)
  2. MIRI (Wright)
  3. Cooler (Larson)
  4. JWST Integration & Test (Diaz & Drury)
  5. Operations & Observing Policies (Johns & Sonneborn)
  6. Progress & Status (Sabelhaus)
John Mather – introduction
Gave a quick introduction and commented that he is glad to see the telescope that originally was scetched out on a blackboard in 1996 finally getting built with a remarkably similar set of features to the original rough design. He cracked a joke about the fact that the original budget was laughed at by some people who have since been proven correct but emphasized that in adjusted terms the project is now 2x the original budget – so it is over the original estimate but it is now realistic and being held tightly.

He made some brief comments about the relevance to JWST's mission of Spitzers recent work, the Hubble Ultra Deep Field and transit Exoplanets. He also made mention of the recent (probable) pair-instability super nova (SN 2006 GY) (he called it a Super Duper Nova smile.gif ) that has shown that this type of nova may be much more common than had been thought. Their immense brightness and this indication of their frequency pushes back JWST's reach even further out the edge.

You could tell that he was very pleased with the project. He then handed over briefly to Gillian Wright (I think) the co-Lead of the MIRI Science Team who briefly thanked the combined team for enabling a full day free of ITAR restrictions so everyone could attend. I was surprised that this got to the top of the agenda but I'm not complaining – I got a free pass in partly because of folks figuring this out. At that point she handed over to John Gardiner – GSFC Senior Project Scientist for the JWST

JWST Science Objectives - Gardiner
STScI will be managing the operations for JWST. (and as an aside go to for outline data)

JG gave a general purpose JWST overview for the masses – not much new in this but it was a nice intro for those outsiders (like me) who were allowed in for the day.

I didn't pick up much new (ie that isn't on the STScI web site) for the first three mission objectives:But he had quite an interesting segment on the final item. In particular he specifically indicated that JWST will be targeting ExoMoons aswell as ExoPlanets for detection and spectroscopic analysis via combinations of inferior and anterior transits. He mentioned the recent Spitzer 8micron planetary surface mapping of HD 189733b and indicated that JWST should be able to do something similar for Earth like planets in the habitable zone of comparable stars.

He mentioned that coronograph assisted imaging should significantly expand the percentage of systems where JWST will be able to go planet hunting but did not go into much detail. (Later on in the morning Peter Jakobsen pointed out that the lack of a coronograph on NIRSpec means that the there are some additional constraints on what can be done in terms of analysis of non transit exoplanets)

Mission overview, Observatory Overview and Reformulation Summary - Menzel & Giampaoli
This was mega detailed and I probably missed more than 50% because I simply couldn't keep up while making notes. Fantastic stuff though from my point of view and I'd go back to one of Mike's talks in a heartbeat, he reminds me a bit of Rob Manning – seriously passionate about his machines. Mike said that the data was slightly edited to comply with ITAR because all of us foreigners where there but honestly I wouldn't have noticed if he hadn't specifically pointed out the one spot where some hard numbers had been removed. Anyway some details.

All 10 enabling technologies for the mission have now completed "Technology non-advocate review" and are ready for TRL6 more than 12 months ahead of schedule.

The major news however is the re-formulation of the project to mitigate some cost and program risks. Mike gave an incredibly detailed explanation of the changes that have been made, whay the were needed and what the impact would be. These were mostly in the arena of decoupling various test processes, equipment and resources (such as test facilities) so that schedule dependencies and interlocks could be removed. The argument and description of the final result was compelling and the major concern that I had when first hearing of this reformulation (that testing was being reduced or that the team was accepting lower specifications) certainly seem to me to not be true now that I have seen this new plan. In particular these changes have enabled the addition of more vibration analysis, cryocycling and cryometrology testing because programmatic interlocks and resource scheduling are now much simpler.

Some interesting news on the spacecraft design front are the physical changes that have been introduced with the B2 structural changes. For reference B1 is basically the layout that the large scale model is built to. In particular the following significant (ie visibly noticeable) items have been modified:

The Sunshield has changed from a 3-2-2 layout to a 4-2 layout.

Sunshield deployment mechanics now follows a 10 folding stage process using what NG call a unitized pallet system (this appears to me to be a rigid shell like shield enclosure for launch and final structure rigidity). This is down from the 24 folding stages in the video we've all seen so this seems to represent a major simplification in the deployment mechanics.

The deployed cryo-cooler\radiator system from B1 is now a fixed unit, again reducing the deployment mechanical complexity.

The Solar panels have been moved to a single tail-dragger format from the dual side wing format on the B1 layout.

The Bib (rhomboidal stray light shield at the base of the main mirror) and the Frill (stray light shield around the top rim of the main mirror) have been made larger.

Lots of mass savings have been made – in total about 100kg gross has been removed but some of that has been clawed back elsewhere.

Tuned Magnetic Dampers have been added to the secondary mirror mount – these were needed to closeout on a couple of problematic harmonics from the reaction wheels that were preventing the team meeting 70% engineering margins. (I think)

Overall project performance metrics are green or will be following the B2 structural changes.

Mass is now 5315kg vs a launcher limit of 6530kg. This is a margin of 22.9% vs a required margin of 19.7%. Even adding in some desirable additional items and this only drops to 21.1% which is still healthy.

Power subsystem is fine. No news move along.

The desirable addional items include spreader rings for the solar shield to improve it's 3D structure, modifications to the shiled spreader bars and a trailing aft shield\trim tab that can be used for spacecraft balancing (at least I think that's what he said).

Mike then gave more depth on a specific problem relating to the cables that connect the ambient portion of the ISIM (at ~300K) and the cryosection (at ~35K). These are only 4m long and there is a 270K temperature drop across them that is not currently adequately cooled. They are adding a four stage cooling system to these to resolve this.

Finally he put up a slide showing the underside (sun facing side) of the spacecraft bus showing the potential location for a lightweight grapple fixture that could (in theory) be used to facilitate a repair mission at some stage. This is a ~2kg mounting so adding it isn't a major deal in itself. The audience gave it a mixed reaction and Mike certainly seemed to be presenting it as "someone else's idea, not mine".

Bob Giampaoli gave a brief update on some of the current work on the deployment mechanics that is ongoing. He specifically invited anyone who was interested to visit the JWST Solar-shield full scale mock-up at the HiBay at NG in Redondo Beach where they will be working on the detailed folding\unfolding mechanism until the end of the year.

They are not using pyro's at all for the unfolding\deployment. All mechanical using common locking equipment and deployment motors. I found this very interesting especially since there are a number of points where a single failure will be catastrophic.

The addition of the TMD's has also resolved issues for the deployment of the secondary mirror booms – makes it much easier to find an acceptable trade off between the stiffness required for the mirror mount and the flexibility required to deploy.

Overall the design is coming in within the Ariane's limits with some minor deviations that they expect to iron out pretty soon.

OTE and Wavefront Sensing Overview - Lee Feinberg

I was unable to capture the hard numbers properly on this and haven't had a chance to double check them so be especially careful of errors here. If it looks or smells wrong to you, then it probably is.

The WSC system is the tuning and aiming system that melds those 18 Beryllium hexagonal mirrors into one near perfect optical element. It leverages the NIRCAM as its imaging sensor. The use of adjustable optics here is to eliminate vibration and keep the mirror PSF stable to within 2%. The WSC will periodically (every 14 days) carry out a full re-work of it's magic to ensure that everything remains precise. Each of the 18 elements have an independent 6 degree of freedom mount using redundant actuators and a single radius of curvature control actuator. Mirror element assembly is at the point where they are just beginning to be polished, all the base machining and light weighting has been done.

Lee gave numbers on the progressive improvement in optical accuracy as the WSC process steps through its refining stages =>Basic Alignment => Focus adjustment => Coarse Phasing => Fine Phasing (to <1 Lambda) => Multi field Alignment (<0.5 Lambda ?). The final RMS deviation for a point source is < 0.35 micron. I think, I was struggling to keep up with this.

Finally and most importantly Lee walked through the various testing regimes, double checks and independent processes that will be used to prevent a repeat of the Hubble error. Main testing stages:

Tinsley (Polishing) – ambient testing
Marshall – ambient and cryo testing
Johnson SC – Full system testing (cryo again I think)
An independent Test Plan Integrity and Review Team are in place to make absolutely sure there are no mistakes.
The PDR for the OTE is in November.

One item that is interesting here is that Lee definitely said that the WSC process would be executed every 14 days but a number of documentations elsewhere say that wavefront control adjustments would only be needed at greater than 1 month intervals. I'm not sure when this changed. Overall it means that the mission will lose ~12 days observing time per year for this vs 6.

NIRCam and NIRSpec reports to follow tomorrow.

Posted by: helvick Jun 11 2007, 09:44 PM

Oh and I forgot to thank Ollapa for the inivtation - it was very much appreciated.

Posted by: djellison Jun 11 2007, 10:12 PM

Good job - your forum title has been appropriately adjusted smile.gif


Posted by: ollopa Jun 16 2007, 02:54 PM

It seems to be one of the worst-kept secrets in Astrophysics, but my spies tell me that ESA and NASA will finally sign the MOU for JWST at Le Bourget on Monday. I gather there will also be an agreement on LISA Pathfinder.

BTW, if anyone gets an early copy of AvWeek I'm curious to know if they included a pic of the model in Dublin. My snail-mail copy may not arrive till JWST launches!

Posted by: Analyst Jun 19 2007, 12:46 PM

QUOTE (helvick @ Jun 11 2007, 09:39 PM) *
NIRCam and NIRSpec reports to follow tomorrow.

Very interesting report. Waiting for the promised second part. smile.gif


Posted by: helvick Jun 19 2007, 07:22 PM

JWST Partner's Workshop - Dublin 11 June 2007 (Part II of III)

NIRCam –
Marcia Rieke University of Arizona (PI)
The instrument is quite advanced now compared to some of the other systems due to the critical role it plays as both a science instrument and as the sensor for calibration and Wavefront Sensing and Control. The CDR took place in May 2006 and the instrument is now (well) into the Engineering Test Unit phase.

Selection of the HgCdTe Rockwell sensor units has started and Dr Rieke made a point of the fact that they had no problems getting good characteristics for the short wavelength units but the long wavelength sensors are proving a bit harder. This latter difficulty extends to NIRSpec also as this requires similar characteristics.

Overall NIRCam represents 2-3 orders of magnitude increase in sensitivity in the wavelength it is designed to cover – in particular the design goal was to hit sensitivity in the nanoJansky range and that is being achieved (see below).

As NIRCam is used as the sensor for the Wavefront Sensing and Control capability it has to be fully redundant. This has resulted in a design with 2 fully independent halves to the instrument covering a total FOV of 2.2'x4.4'. That 10 square arcminute FOV makes it well suited for wide area surveys in search of (rare) first light event. Its dual purpose also means that (according to Dr Rieke) it has been exquisitely designed in an optical sense.

Dr Rieke mentioned that NIRCam could\would be used for surface characterization of KBO's. This is obvious enough and part of the "Planetary Systems and Origins of Life" theme for the mission but this was one of many instances where the presenters were at pains to point out that JWST would be useful as an observatory for Solar System objects.

NIRCam homepage -

For those unfamiliar with the instrument the basic design is a dichroic refractive optic camera covering the 0.6 to 5 micron wavelength range allowing for two concurrent observations in short and long(er) wavelengths. The incoming beam is split into 0.6-2.3micron short band and 2.4 – 5.2 micron long band). There are coronographs available in both long and short modules.

Each short wavelength channel is directed to a 4096x4096 pixel sensor array comprised of a grid of 4 separate 2048x2048 pixel HgCdTe Rockwell sensors. The corresponding long wavelength channel is directed to a 2048x2048 pixel single HgCdTe Rockwell sensor. There are a total of 40 megapixels between the two halves.

I've taken some key sensitivity & resolution data for NIRCam (from ) and attempted to compare them to Hubble's NICMOS ( from ) to try and put this instrument into some perspective.

This is entirely my reading of these two documents so I may be incorrect, if so let me know.

0.8-1.35micron NICMOS1 2.4e-7Jansky : NIRCam 1.1e-8Jansky (22x)
1.4-1.8 micron NICMOS1 5.7e-7Jansky : NIRCam 1.0e-8Jansky (57x)
0.8-1.35micron NICMOS3 4.5e-8Jansky : NIRCam 1.1e-8Jansky (4x)
2.3-2.5 micron NICMOS3 1.6e-6Jansky : NIRCam 2.5e-8Jansky (60x)

The resolution\FOV comparisons are:
NICMOS1 – 0.043" /pixel , 11" square FOV
NICMOS2 – 0.075" /pixel , 19" square FOV
NICMOS3 – 0.200" /pixel , 51" square FOV
NIRCam(short)– 0.0317"/pixel, 2'12" x 4'24" FOV
NIRCam(long) – 0.0648"/pixel, 2'12" x 4'24" FOV
NIRCam(short) covers approximately 288x the FOV of NICMOS1 at a slightly better angular resolution per pixel and 20-60x the sensitivity*. It covers 14x the FOV area of NICMOS3 at 6x finer angular resolution per pixel and 4-60x the sensitivity*. NIRCam(long) covers the same FOV at 1/4 the areal resolution.

* The sensitivity numbers (Jansky's) don't appear to be directly comparable to me. Anyone who can comment on the difference between sensitivity to achieve a "S/N of 5 over 5 orbits" (Hubble NICMOS) and "10 sigma over 10000 seconds" (NIRCam) please jump in. My understanding is that 10 sigma corresponds to an S/N of 100, if that is true then the above NIRCam numbers would need to be reduced by a factor of 20 in order to compare them with NICMOS. I believe that the 5 orbit number for Hubble equates to 5000 seconds but I'm not sure.

Posted by: helvick Jun 19 2007, 08:55 PM

JWST Partner's Workshop - Dublin 11 June 2007 (Part III of III)

NIRSpec – Peter Jakobsen EADS Astrium

"A Pretty Picture is not Enough" or Imagery is Astronomy but Spectroscopy is Astrophysics. smile.gif

NIRSpec is a multi object dispersive spectrograph that uses a MEMS shutter array to enable it to take up to 100 spectral samples concurrently. Sampling in one of three resolutions (R=100, R=1000, R=2700) using 2 x 2048x2048 HgCdTe Rockwell sensors. The twin detectors do not abut perfectly so there is a detector gap in the layout which mostly just causes targeting complications for R=100 sampling but causes dropout in the middle of spectra for many R=1000 samples and all R=2700 samples. These dropouts will require re-shooting the target using a different array location to recover the dropout regions.

In addition to its MOS mode it also supports an Integral Field Spectrograph mode and a classical long slit spectrograph mode.

Physically it's a monster 185kg mass measuring ~1.8mx1.4x1m 2m on a side. The prism\refraction wheel is sufficiently massive that it acts as an (undesirable) reaction wheel for the observatory.
Internally it uses an all silicon carbide reflective optics (14 reflection) optical path.
FOV is 3.4' x 3.6' with a 0.2milliarc second nominal slitwidth.

The MEMS shutters consist of 4 arrays of 365x171 micro shutters. In operation targets selection requires the opening of three shutters in a line perpendicular to the spectral spread direction – the central shutter covers the target and the shutters on either side are used for background removal. Combined with the fact that 2nd and 3rd order effects prevent the use of multiple collinear (in array terms) targets the effective maximum number of concurrent samples is ~100.

The MEMS arrays make this a very powerful instrument however manufacturing the array is extremely difficult and it is clearly pushing the limits of today's micro mechanical manufacturing expertise. The arrays are individually electrostatically latched open and reset in bulk magnetically (to closed). Manufacturing challenges mean that the arrays have clear salt and pepper effect flaws – Peter Jakobsen did not say what the error rate was but it was very obvious in the sample images he displayed. I would estimate that it was probably in the order of 2-3%. In general the fail closed flaws are more frequent than fail open flaws and happily fail-closed shutter flaws result only in aiming\planning problems as the only effect is that certain individual shutter locations cannot be used. Fail open flaws are much more problematic as any open shutter could contaminate a spectral sampling anywhere else on the same horizontal line of the array and so fail-open flaws result in the loss of an entire row of sampling locations from the MOS array (actually they reduce the effectiveness of the row immediately above and below also). Fortunately fail-open flaws can be converted to fail-closed flaws pre flight so at launch there should be no fail open flaws. Peter Jakobsen gave no indication of the expected reliability of the array. The detectors and the MEMS array are supplied by NASA.

In addition to the MEMS arrays there is an IFU image slicer with a a 0.1" resolution of 3"x3" and 5 fixed non interfering slits of width 0.1", 0.2" and 0.4".

More details here. Page 9 shows the MEMS shutter array, IFU and fixed slit layouts and the direction of dispersion relative to the detector layout. The detector gap is not shown but corresponds approximately to the mid point gap between the MEMS shutters.

Peter Jakobsen closed out with some additional comments about exoplanet spectroscopy. My notes say that he said the challenge there is that they will need to get the S/N ratio past 10^4, specifically capturing >10^10 photons into the detector in <1hr time frame. This difficulty arises (in part) because NIRSpec does not have a coronograph.

Posted by: PhilCo126 Apr 22 2008, 04:00 PM

Just superb:

Posted by: climber Oct 18 2008, 03:55 PM

Air & Cosmos oct 17th issue says that a mockup of JWST is currently on display at Deutsches Museum:

Posted by: Oersted Dec 3 2008, 11:54 PM

I think this is the best deployment animation:

Posted by: bkellysky Jun 4 2010, 08:02 PM

A full-sized mockup of the James Webb Space Telescope is on display in lower Manhattan, New York City at Battery Park from now through June 6th. On Friday night, local astronomers will bring their telescopes to the site to show the planets and stars to people attending the panel discussion scheduled to include John Mather, John Grunsfeld, and Heidi Hammel, with journalist Miles O’Brien moderating. Neil deGrasse Tyson, will host the stargazing party.

bob kelly

Posted by: Ron Hobbs Jun 4 2010, 09:12 PM

Xinhua has some really great pictures of the mock-up

Posted by: bkellysky Jun 5 2010, 01:04 PM

Photo of the mock-up from the world science festival last night in Battery Park, New York City (too large to post here, see

(edited to add full url, since this post has fallen way down on my blog site!)


Posted by: Ron Hobbs Jun 5 2010, 03:44 PM


That is a great picture! Thanks.

Posted by: Big_Gazza Jul 7 2011, 10:42 AM

Oh dear, the spectre of cancellation of the JWST is being raised... mad.gif

I can think of a few expenditures that can be slashed to pay for the HST successor....

Posted by: Syrinx Jul 7 2011, 09:38 PM

I became ill when I read about this yesterday.

I think a lot of us want to say some things that would violate UMSF's posting terms.

I'll just say it made me consider (someday) moving to a different country. And I know my sentiment is shared by a lot of engineers.

Posted by: nprev Jul 7 2011, 11:08 PM

Let's all take a deep breath, calm down, and hope for the best...and keep firmly in mind.

Posted by: Explorer1 Jul 8 2011, 12:58 AM

Surely the components already made won't be trashed, will they? (Assuming this actually happens; remember Dawn's resurrections!)

Posted by: Hungry4info Jul 8 2011, 03:12 AM

If it goes like SIM(-lite), the hardware will probably be disposed of.

Posted by: Greg Hullender Jul 8 2011, 02:56 PM

If no one has any new facts to bring to the discussion, I'm not sure we can accomplish much just speculating about it. I remember Kepler was in trouble at one point for similar reasons (poor management) and NASA forced them to reorganize, but I don't remember the details. Does anyone know any details?


Posted by: nprev Jul 9 2011, 12:19 AM

Also recall that Dawn WAS effectively cancelled for many of the same reasons, but of course did fly. It's way, way too early to begin mourning for JWST, people.

Posted by: Mongo Sep 15 2011, 09:03 PM

The news has just come in: the United States Senate has decided to fully fund the James Webb Space Telescope, and it should be set to launch in 2018, which is the earliest it can possibly go ahead at this point.

Posted by: djellison Sep 15 2011, 09:59 PM

How many times do I have to clean up this thread because of rule 1.2?

Posted by: Steve G Feb 20 2015, 01:27 PM

Is the JWST going to be used for any Solar System observations? Such as asteroid imaging, monitoring weather on outer planets, moons of outer planets (such as IO), moons of Uranus and so forth. If so, what would be the resolution?

Posted by: mcaplinger Feb 20 2015, 03:57 PM

QUOTE (Steve G @ Feb 20 2015, 06:27 AM) *
Is the JWST going to be used for any Solar System observations?

Google yields

Posted by: Jaro_in_Montreal Feb 24 2015, 10:55 PM

I looked through the FAQs and even posted a question on their fb page, but never got a reply regarding whether there was any chance of coupling JWST with the StarShade project.....

Posted by: djellison Feb 24 2015, 11:33 PM

I believe you have to specifically design the instrumentation on the 'scope end to match the StarShade - and the JWST instrument manifest has been solidly defined and in development/test/build for many years.

Posted by: abalone Feb 12 2016, 11:09 AM

Time-lapse: The Assembly of the James Webb Space Telescope Primary Mirror

Posted by: B Bernatchez May 4 2016, 07:56 PM

Looks like the optics have been mated to the ISIM. Group photos are being taken as I type.

Posted by: Steve G Nov 3 2016, 03:44 PM

With the launch 2 years away, I've tried to find out what the Solar System observation resolution will be on Webb, and I need it broken down to very basic layman's terms.

ON LINE: How good is the angular resolution?

CONVOLUTED ANSWER: The specification is that the telescope is diffraction limited at 2 μm, which means a Strehl ratio of 0.8 and a wavefront error of 150 nm rms. With a 6.5 m telescope, 1.22 λ/D = 0.077 arcsec at 2 μm. The smallest pixels (NIRCam 0.6-2.5 μm) are just 0.034 arcsec. But a lot of the wavefront error is due to imperfect alignment of the parts, and it's possible to do better for a small part of the field of view

For a space enthusiast, not an astronomer, this is like converting kilo-Newtons in to pounds of thrust (and who decided to switch from a very simple and easy to understand Lbs of thrust to a kilo-Newton as if anyone is expected to know what a kilo-Newton is) . So what kind of resolution can we expect for Mars, or objects in the asteroid belt such as Pallas, or Io, or Triton, for example? How many pixels across or resolution per pixel pair? Something that is in plain English would be awesome.


Posted by: elakdawalla Nov 3 2016, 03:56 PM

One issue I hadn't appreciated until recently is how the design of JWST isn't exactly optimized for solar system observations. It has to keep the sun shield between it and the sun, but the telescope points at right angles to the sun shield. So it can't point at things when they are at opposition, only at geometries roughly tangent to JWST's orbit. Doesn't matter as much for resolution on distant targets but makes a big difference for Mars and asteroids, and limits when things can be observed.

Posted by: JRehling Nov 3 2016, 05:40 PM

QUOTE (Steve G @ Nov 3 2016, 08:44 AM) *
The smallest pixels (NIRCam 0.6-2.5 μm) are just 0.034 arcsec.
For a space enthusiast, not an astronomer, this is like converting kilo-Newtons in to pounds of thrust (and who decided to switch from a very simple and easy to understand Lbs of thrust to a kilo-Newton as if anyone is expected to know what a kilo-Newton is) . So what kind of resolution can we expect for Mars, or objects in the asteroid belt such as Pallas, or Io, or Triton, for example? How many pixels across or resolution per pixel pair?

I honestly never thought much about angular sizes until I started doing astrophotography, and then it becomes absolutely essential and I can't imagine anything more fundamental. If you give someone the resolution for Mars, then they're stuck with just that, and have to convert it to any other object they care about… and, JWST is not primarily for solar system objects, and many cosmic objects are of unknown distance, so for those cases, we can't compute resolution in absolute distances and angular diameter is all we have.

That said, Mars covered about 18.5 arcsec during this opposition, so for the instrument quoted above, Mars would be about 540 pixels across, so a JWST pixel on Mars would be about 12.5 km wide. Ganymede would be about 50 pixels wide, with pixels roughly 100 km wide.

More relevant, that translates into pixels about 6.3 million km = 0.04 AU wide at Proxima Centauri and Alpha Centauri. That is coincidentally almost exactly the orbital radius of Proxima b, which tells you that direct observation of planets in the "habitable zone" of red dwarfs is going to be very difficult with telescopes, even in that best-case scenario. Planets in the habitable zone of sunlike stars 100 light years away would have the same angular separation from their primary as Proxima b, but there are a lot of stars closer than that, so JWST is going to give us an all-new capability for direct visual observation of exoplanets… but what can be learned from such observations is still an open question.

The ground-based E-ELT, however, will have much better (more than ten times better) resolution than JWST, so it will be the ace instrument for fine resolution when it comes online.

JWST is not going to be the ultimate telescope for high resolution and, while I'm sure it will make some great solar system observations, it's not designed for any such purposes. Its distinguishing characteristics will be its abilities to observe through cosmic dust, heavily red-shifted objects, and exoplanets. The first two of those address major blindspots we have – about 20% of the deep sky is hidden by the Milky Way, and lots of the "back" sides of deep sky objects are hidden by their own front sides. And cosmic structures whose light left them in the first ~500 million years after the Big Bang are going to be seen much better by JWST than anything else. For solar system objects, JWST will not be a great upgrade in sheer resolution from existing telescopes, and its resolution will within a decade be utterly blown away by new, massive telescopes on Earth.

Posted by: SteveM Nov 12 2016, 02:19 PM

QUOTE (elakdawalla @ Nov 3 2016, 10:56 AM) *
One issue I hadn't appreciated until recently is how the design of JWST isn't exactly optimized for solar system observations. It has to keep the sun shield between it and the sun, but the telescope points at right angles to the sun shield. So it can't point at things when they are at opposition, only at geometries roughly tangent to JWST's orbit. Doesn't matter as much for resolution on distant targets but makes a big difference for Mars and asteroids, and limits when things can be observed.
Thanks for pointing that out. A positive aspect of that geometry is that JWST can only observe stars six months apart when the line of sight is tangent to the Earth's orbit. That's the ideal geometry for stellar parallax measurements. With appropriate analyses of the stars' point spread functions, JWST might get up to the level of Gaia's parallax measurements.

Posted by: Holder of the Two Leashes Dec 22 2016, 02:31 PM


Posted by: B Bernatchez Dec 22 2016, 08:20 PM

I don't imagine that they crank up the shaker table to 11 until later in the test sequence. I would hope that this was discovered early on at a low vibration setting. Hopefully nothing more than an incorrect test setup.

Posted by: JRehling Dec 28 2016, 11:37 PM

It sounds like the anomalous vibration at least did no harm:

Switching subtopics mid-post, I've read some more encouraging things about JWST's expected ability to observe exoplanets, including Proxima B. If all is well on the engineering side, those results may be only ~3 years away.

Posted by: Holder of the Two Leashes Jan 26 2017, 02:15 PM

Good news. The problem has been resolved ...

Posted by: Holder of the Two Leashes Oct 6 2017, 06:46 PM

One more (hopefully final) launch delay. No one thing in particular, just a lot of little things adding up. They claim there will be no cost penalties as a result.

Posted by: JRehling Apr 2 2018, 03:12 PM

And that last delay was not final. Now we're hoping for an early 2020 launch.

Damage suffered during testing is at least some of the cause.

This article lays out the facts and adds some insightful commentary on how this delay might affect future planning.

From the standpoint of exoplanet observations, I will add that the ability of the JWST to observe exoplanets, and if so, to what extent, inevitably will be known in detail only after it attempts such observations. It also closes the gap between when JWST was going to make such observations and when new ground based telescopes will be able to demonstrate their capabilities for similar, but not identical observations. Of course, the dates when those telescopes will become operational aren't guaranteed yet, either.

Posted by: JRehling Mar 23 2020, 07:34 PM

This is not a great surprise, but work on the JWST has been put on pause.

Unlike many other missions, JWST has no dependencies on any particular launch window. Of course, any changes to a program are a potential source of trouble.

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