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TOPIC: James Webb Space Telescope


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RE: James Webb Space Telescope

Title: How JWST can measure First Light, Reionisation and Galaxy Assembly
R.A. Windhorst, S.H. Cohen, R.A. Jansen, C. Conselice and H. Yan.

To appear in the Proceedings of the UC Irvine Workshop on "First Light and Reionisation: Theoretical Study and Experimental Detection of the First Luminous Sources"

The research team summarises the design and performance of the James Webb Space Telescope that is to be launched to an L2 orbit in 2011, and how it is designed, in particular, to study the epochs of First Light, Reionisation and Galaxy Assembly.
The James Webb Space Telescope (JWST) is currently designed as a fully
deployable 6.5 meter segmented IR telescope, optimized for imaging and spectroscopy from 0.6 m to 28 m.
After its launch, currently planned with an Ariane V.
JWST will make a several month journey to the Earth-Sun Lagrange point L2.
The Optical Telescope Element (OTE) of the 6.5 meter JWST has 18 hexagonal mirror segments , each of 1.3 m diameter , and a total edge-to-edge diameter of 6.60 m.
Its effective circular diameter is 5.85 m, and its effective collecting area is 25 m2. Instead of the original design of 36 smaller segments, the OTE design converged on 18 larger segments. This had both risk- and cost- benefits, was easier to construct, and provided better mid-spatial frequency OTE errors, resulting in better 1.0 m performance.

The WMAP polarization results suggested that the universe was first reionised at redshifts as early as z.20. This epoch of First Light is thought to have started with Population III stars of 200-300M⊙ at z.15- 25.
These Pop III star clusters and their extremely luminous supernovae should be visible to JWST at z.15-25.


Read More (PDF 587kb)

-- Edited by Blobrana at 22:23, 2005-06-14



Posts: 131433

Faced with a $1 billion cost overrun, NASA may scale back the planned $3.5 billion James Webb Space Telescope and delay its planned 2011 launch.
Boulder's Ball Aerospace & Technologies was awarded a $200 million contract in 2002 to develop the telescope's optical system.
Ball is the main subcontractor on a team headed by aerospace giant Northrop Grumman.

"I'd say it is a crisis. (NASA) headquarters just doesn't have any more money for us. Something's got to give, but we don't know what it's going to be." - John Mather, project scientist for the telescope at NASA's Goddard Space Flight Centre in Maryland.
Northrop Grumman recently informed NASA that the company and its subcontractors expect to spend $309 million more than planned. In addition, the rocket that will launch the Webb telescope could cost more than expected.
Those and various other unforeseen increases bring the total overrun to about $1 billion.
As a result, the telescope's launch is likely to be delayed at least a year.
A Ball executive said the Boulder company has experienced some overruns but is not a major contributor to the problem. He wouldn't specify the overrun amounts.

"We have not caused any upset to the JWST program. Take our $200 million contract and put it into the context of 31/2 billion. Our contract value is too small to help fix the problem." - Harold Reitsema, director for advanced programs at Ball.
A Northrop Grumman spokeswoman directed all budget questions to NASA.
"Northrop Grumman, NASA and the JWST science team are working together to develop solutions for the issues facing JWST. Right now they're tackling tough problems, and we do not want to speculate on the outcome."
To trim the Webb telescope costs, NASA managers this month suggested cutting the diameter of the telescope's main light-gathering mirror from 21.4 feet to 13.2 feet.
But astronomers on the Webb science team rejected the plan, saying the smaller reflector could not achieve the project's main science goals.
The James Webb Space Telescope, a collaboration between NASA and the European Space Agency, will be a successor to the Hubble Space Telescope. The orbiting observatory will operate at infrared wavelengths, at a temperature of 370 degrees below zero.
A prestigious National Academy of Sciences panel ranked the Webb telescope as the most important NASA astronomy project of this decade. Its main job is to observe the first generation of galaxies, assemblages of stars that started to form when the universe was a mere 200 million years old.
If the telescope's main light- gathering mirror is reduced to 13.2 feet in diameter, it could not see those primeval galaxies.

"We tried this very quick exercise of just throwing things off, and we found that that wasn't a good answer, an answer that everyone liked." - Eric Smith, program scientist for the telescope at NASA headquarters.
Other potential cost-cutting measures will be explored.
Smith is assembling a panel of astronomers who, over the next two months, will rank the Webb telescope's science priorities.

The ranked list of science goals will be used to "restructure the mission".
"You need some pretty large measures in order to get a billion dollars out of a $31/2 billion program. That's a big number to try to squeeze out of your program." - Harold Reitsema.
Ball is responsible for designing the telescope's optics and supervising their construction.
The company and ITT Industries will test the finished telescope at NASA's Johnson Space Centre in Houston.

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