Slashdot Mirror
Mirrors Finished For James Webb Space Telescope
eldavojohn writes "On August 15th, sendoff ceremonies were held at Ball Aerospace (subcontractor to Northrop Grumman) for the 18 gold-coated, ultrasmooth, 4.2-foot (1.3 meters) hexagonal beryllium primary mirror segments that will comprise the 21.3-foot (6.5 m) primary mirror of the James Webb Space Telescope (JWST). Over 90% of the back material was taken out of these mirrors to make them light enough so that 18 could be launched into space where they must operate at minus 400 degrees Fahrenheit (minus 240 degrees Celsius). The mirrors will be adjusted by computer controlled actuators that are vital to JWST producing high-quality sharp images. The tennis court sized JWST will reside at L2 and is hyped to allow us to see 'back to the beginning of time.' NASA has provided a video of the computer animated metamorphosis with many more videos at the JWST site."
Guys, really? Fahrenheit? In a science article? On an international website?
I don't even advocate the usage of Celcius in this case, so why not use 33 degrees Kelvin? This at least give us _some_ idea of how close to absolute zero we are. Otherwise, why not use 'near absolute zero' and leave out the numbers completely?
</getoffmylawn>
The Hubble mirror was the most precisely and uniformly shaped mirror ever made up to that time. They just happened to make it precisely to an incorrect shape.
Hubble = HST.Look again.
For instance:
The deepest images of the universe include the Hubble Ultra-Deep Field (UDF) in the optical (Beckwith et al., 2003), which reaches AB = 29.0 mag in the I band, HST near-IR images of the UDF, which reach AB = 28.5 in the J and H bands (Bouwens et al., 2005a), and the Spitzer Great Observatories Origins Deep Survey (Dickinson, 2004), which reaches AB = 26.6 mag at 3.6 m. Galaxies are detected in these observations at 6
Or how about this:
Hierarchical Assembly: The dark matter mass function of bound objects at very high redshifts can be uniquely measured in two ways with JWST. First, the dynamics of groups of galaxies or sub-galactic fragments can be used to determine the typical masses of halos (Zaritsky and White, 1994).
These measurements require observations of emission lines in the rest-frame optical, such as [OII] 3727, [OIII] 5007, and H. These are very difficult to measure from the ground when redshifted into the near-IR.
Second, JWST will measure halo masses through the gravitational bending of light. Using this weak-lensing method, ground-based programs have measured the mass within 200–500 kpc of galaxies at redshifts of z 0.1 (McKay et al., 2002) and z 1 (Wilson et al., 2001). Using the superior resolution of HST, these measure- ments are likely to be extended into 30–50 kpc for galaxies at z 1 (e.g., Rhodes et al., 2004; Rhodes, 2004). While there are some hints of variable halo struc- tures for galaxies of different luminosity and total halo mass, the radial penetration of these surveys, and the ability to compare galaxies of different morphologies are
518 J. P. GARDNER ET AL.
limited by statistics. We expect that HST will establish the statistical mass functions for spiral and elliptical galaxies at z 1, but not much beyond that, because of its limited sensitivity and sampling at > 1.6 m.
JWST will extend the equivalent measurements of galaxies to z 2.5 and thus determine the development of the dark matter halos during the peak growth of galaxies and star formation. JWST will require near-IR imaging with high spatial resolution and sensitivity to achieve this greater depth. Background galaxies with a size comparable to the resolution of JWST will be measured at 20 .
The same near-IR sensitivity and resolution will also make JWST superior to those of ground-based facilities and HST for the study of dark matter structures on larger scales, e.g., 1–10 arcmin or 2–20 Mpc (co-moving) at z 3. These volumes measure the clustering of dark matter on cluster or even supercluster scales, and would extend the study of the mass function into the linear regime. The goal of these observations would be to verify the growth of structure between z 1000 (the CMB large-scale structure) and z 2.5, i.e., during the period that dark matter dominated the cosmological expansion of the universe prior to the beginning of dark energy dominance at z 1.
It's not all about the redshift, the paper also describes potentially useful observations in the IR-- planet formation, star formation, etc. And,of course, optical telescopes have a hard time resolving what's behind dust clouds-- ir telescopes can see beyond them
Collimation wasn't the issue, the mirror was incorrectly shaped due to a fault in the QA process where a tool used to measure the sphericity of the mirror called a null corrector was assumed to be set up to spec.
More details here for those who are interested: http://en.wikipedia.org/wiki/Hubble_Space_Telescope#Origin_of_the_problem
Collimation refers to the arrangement, or alignment, of the optical surfaces and lenses in relation to each other.
That money is being spent in the USA, it is going to our own citizens to advance our own science.
With your reasoning, just about EVERY SINGLE project this government has EVER undertaken:
- electrification
- interstate highway system
- moon shot
- internet
- big dig
- just about everyting NASA has done
would be considered a "failure" because ALL of them overran their original budgets.
If "budgetary concerns" are your ONLY criterion for success or failure, you're CLEARLY one of those "Harvard MBA Spreadsheet" wonks who thinks that all of life and reality can be boiled down into an excel spreadsheet.
Ok, Accepting that flyingsquid's remark and mine will be moderated into Negativeland, I will feed his/her troll-ness just this once.
Budgets running "over": I agree that you have, using perfect 20/20 hindsight, identified a worrisome trend: rising NASA project costs over time. I will argue against this as a legitimate complaint on 2 fronts:
A) All government projects rise, at rates at least equal to NASAs. By the time the projects "end" they all appear wildly delayed, and hugely inflated. B1, B2, F22, F35, LCS, Stryker, M2 Bradley, M1 Abrams, F18 (which was the loser in the competition for the F16), NexRad, IRS software upgrades, the list is endless. You've chosen to reframe NASA's behavior as out-of-place, when creeping budgets and timelines are the norm. These "creeps" are in fact reviews, where congress revisits the project's justification and reconsiders continuance or abandonment.
B) Hindsight is unavoidable, but somewhat useless. All government projects are engaged in for the best reasons at the time. (Including pork: politics and perception are both, unhappily, reasons.) All of them are initially put up with gigantic dark-areas of knowledge. The proponents of the project have to name the best number they can with the available knowledge, then run with it. Each successive increase is a far harder battle than the initial start, and the fact that a project eventually flies means that the best congressional minds decided it was worth it at each of those increases.
My conclusion: You are offended by a pattern of behavior that is visible looking back, but invisible looking forward. I welcome your proposal to eliminate this problem, but to tote out the tried-and-true phrases like "accountability for failures" and "leadership is failing them" is to cloth Luddism in conservative gowns. I've attempted to make the case that while the system isn't elegant, it is your perception of it that is your problem. This inelegant system produces investments that it believes are worthy, using the best information available at the time, at each step along the way. That it follows a Drunkard's Walk is meaningless if it gets to the desired goal.
We could build one of these EVERY MONTH, for what we've been spending on the useless waste in afghanistan. and that's been going for over a decade... The money that NASA 'wastes' is a PITTANCE to what gets truly wasted by the 'defense' department and the pentagon.