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Redstone
post Aug 23 2005, 02:01 PM
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The manufacture of the JWST mirror blanks has now been completed.

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

The JWST home page can be found here.

The Space Telescope Science Institute, which runs Hubble, also has a site here. As does ESA.
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helvick
post Jun 19 2007, 07:22 PM
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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 - http://ircamera.as.arizona.edu/nircam/

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 http://ircamera.as.arizona.edu/nircam/features.html ) and attempted to compare them to Hubble's NICMOS ( from http://www.nasa.gov/pdf/160431main_fact_sheet_NICMOS.pdf ) 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.
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- Redstone   James Webb Space Telescope   Aug 23 2005, 02:01 PM
- - djellison   Just how does it end up costing $4.5B ( which...   Aug 23 2005, 02:10 PM
- - Redstone   Well, a 6.5m telescope is pretty big even on the g...   Aug 23 2005, 02:42 PM
|- - Bob Shaw   The JWST has always struck me as being a prime exa...   Aug 23 2005, 03:03 PM
|- - dilo   4.5 billion is a lot. If I'm not wrong, this i...   Aug 23 2005, 09:22 PM
|- - GravityWaves   QUOTE (dilo @ Aug 23 2005, 06:22 PM) 4.5 ...   Apr 1 2006, 07:27 PM
- - Redstone   It seems JWST is safe from outright cancellation f...   Aug 26 2005, 09:50 PM
|- - antoniseb   QUOTE (Redstone @ Aug 26 2005, 04:50 PM)JWST ...   Aug 26 2005, 10:31 PM
|- - Bob Shaw   IMHO, JWST should be put on hold, and then back ou...   Aug 26 2005, 10:39 PM
- - Redstone   First JWST mirror segment delivered for polishing....   Oct 9 2005, 04:16 PM
- - BruceMoomaw   "Really, it's nuts to NOT make JWST man-t...   Oct 9 2005, 10:07 PM
- - SigurRosFan   "The James Webb Space Telescope is a large, i...   Oct 9 2005, 10:24 PM
- - Redstone   Some more detail on the JWST delay to 2013. The ar...   Nov 21 2005, 01:53 PM
- - AlexBlackwell   I moved this from a thread I started to this one. ...   Mar 8 2006, 08:56 PM
- - BruceMoomaw   My attempt to attach this article failed; it overl...   Mar 14 2006, 03:07 AM
- - BruceMoomaw   Particularly interesting quotes from the article: ...   Mar 14 2006, 03:47 AM
- - AlexBlackwell   To keep things tidy and prevent sprawling, disconn...   Mar 14 2006, 05:02 PM
- - ljk4-1   James Webb Telescope Sunshield Membrane Passes Tes...   May 16 2006, 02:44 PM
- - ljk4-1   ATK To Provide More Components For James Webb Spac...   May 31 2006, 05:53 PM
- - ljk4-1   Astrophysics, abstract astro-ph/0606175 From: Jon...   Jun 9 2006, 07:28 PM
- - Decepticon   I'm looking forward to seeing alpha centauri i...   Jun 16 2006, 10:29 PM
- - DonPMitchell   QUOTE JWST is a partnership between ESA, NASA, and...   Jun 16 2006, 10:35 PM
|- - GravityWaves   QUOTE (DonPMitchell @ Jun 16 2006, 07:35 ...   Jul 5 2006, 01:09 AM
- - Littlebit   http://www.irconnect.com/noc/press/pages/n....mhtm...   Jan 22 2007, 03:27 PM
- - SigurRosFan   - Telescope mirror nears completion QUOTE Enginee...   Feb 9 2007, 05:36 PM
- - GravityWaves   "6.6m (22ft) in diameter", that's fa...   Feb 19 2007, 02:12 PM
- - ollopa   NASA, ESA and the CSA are holding a technical rev...   May 21 2007, 01:09 PM
- - helvick   Great stuff - finally something to go to that is c...   May 21 2007, 06:24 PM
- - djellison   This thread will be useless without pics. You hav...   May 21 2007, 08:18 PM
- - helvick   I'm on it boss.   May 21 2007, 08:32 PM
- - jaredGalen   Some one has posted some pics (2) of the Full scal...   May 23 2007, 10:23 AM
- - djellison   That's two of you. STEREO OBSERVATIONS. Do i...   May 23 2007, 10:35 AM
- - AlexBlackwell   NASA Adds Docking Capability For Next Space Observ...   May 23 2007, 07:29 PM
- - jaredGalen   Anyone have new info on events associated with nex...   Jun 6 2007, 11:11 AM
- - helvick   I stopped by the Royal Hospital today at lunchtime...   Jun 8 2007, 02:27 PM
- - ollopa   Members of this forum are especially welcome to th...   Jun 9 2007, 01:17 AM
- - ollopa   Currently - and remember these things can change -...   Jun 9 2007, 01:53 AM
|- - helvick   I just re-arranged my Monday schedule so I'll ...   Jun 9 2007, 01:31 PM
- - helvick   I went back to check on the model's progress a...   Jun 9 2007, 05:19 PM
- - climber   Thanks helvick. I'll come to Ireland by mid au...   Jun 9 2007, 06:01 PM
- - helvick   My understanding is that it is going to remain for...   Jun 9 2007, 09:43 PM
|- - ollopa   QUOTE (helvick @ Jun 9 2007, 10:43 PM) It...   Jun 10 2007, 12:53 AM
- - nprev   Helvick, do you know the rest of its schedule? Hop...   Jun 10 2007, 12:22 AM
- - ollopa   Direct from its Washington premier just last month...   Jun 10 2007, 11:25 PM
- - nprev   This is gonna sound trite, but damn that thing is ...   Jun 11 2007, 01:25 AM
- - dilo   What an impressive shot, allopa! I'm fasci...   Jun 11 2007, 06:00 AM
- - helvick   As promised by Ollopa UMSF folks were allowed to a...   Jun 11 2007, 09:39 PM
|- - Analyst   QUOTE (helvick @ Jun 11 2007, 09:39 PM) N...   Jun 19 2007, 12:46 PM
- - helvick   Oh and I forgot to thank Ollapa for the inivtation...   Jun 11 2007, 09:44 PM
- - djellison   Good job - your forum title has been appropriately...   Jun 11 2007, 10:12 PM
- - ollopa   It seems to be one of the worst-kept secrets in As...   Jun 16 2007, 02:54 PM
- - helvick   JWST Partner's Workshop - Dublin 11 June 2007 ...   Jun 19 2007, 07:22 PM
- - helvick   JWST Partner's Workshop - Dublin 11 June 2007 ...   Jun 19 2007, 08:55 PM
- - PhilCo126   Just superb: http://sci.esa.int/science-e/www/obj...   Apr 22 2008, 04:00 PM
- - climber   Air & Cosmos oct 17th issue says that a mockup...   Oct 18 2008, 03:55 PM
|- - Oersted   I think this is the best deployment animation: ht...   Dec 3 2008, 11:54 PM
- - bkellysky   A full-sized mockup of the James Webb Space Telesc...   Jun 4 2010, 08:02 PM
- - Ron Hobbs   Xinhua has some really great pictures of the mock-...   Jun 4 2010, 09:12 PM
- - bkellysky   Photo of the mock-up from the world science festiv...   Jun 5 2010, 01:04 PM
- - Ron Hobbs   bob, That is a great picture! Thanks.   Jun 5 2010, 03:44 PM
- - Big_Gazza   Oh dear, the spectre of cancellation of the JWST i...   Jul 7 2011, 10:42 AM
- - Syrinx   I became ill when I read about this yesterday. I ...   Jul 7 2011, 09:38 PM
- - nprev   Let's all take a deep breath, calm down, and h...   Jul 7 2011, 11:08 PM
- - Explorer1   Surely the components already made won't be tr...   Jul 8 2011, 12:58 AM
- - Hungry4info   If it goes like SIM(-lite), the hardware will prob...   Jul 8 2011, 03:12 AM
- - Greg Hullender   If no one has any new facts to bring to the discus...   Jul 8 2011, 02:56 PM
- - nprev   Also recall that Dawn WAS effectively cancelled fo...   Jul 9 2011, 12:19 AM
- - Mongo   News Flash: James Webb Space Telescope SAVED! ...   Sep 15 2011, 09:03 PM
- - djellison   How many times do I have to clean up this thread b...   Sep 15 2011, 09:59 PM


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