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"Perfect" Mirrors Cast For LSST

kdawson posted about 6 years ago | from the billion-pixels-of-goodness dept.

Science 114

eldavojohn writes "The Large Synoptic Survey Telescope (which was partially funded by Gates & Co.) announced a world record casting for its single-piece primary and tertiary mirror blanks, cast at the University of Arizona. From the announcement: 'The Mirror Lab team opened the furnace for a close-up look at the cooled 51,900-pound mirror blank, which consists of an outer 27.5-foot diameter (8.4-meter) primary mirror and an inner 16.5-foot (5-meter) third mirror cast in one mold. It is the first time a combined primary and tertiary mirror has been produced on such a large scale.'"

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asdf (-1, Offtopic)

Anonymous Coward | about 6 years ago | (#24852891)

asdf [youtube.com]

Gravity? (0)

Anonymous Coward | about 6 years ago | (#24852963)

Here's hoping that when they grind it, they account for gravity in the calculations.

grind it
don't mind it
figure it
Right value does it good

Apparently... (4, Funny)

Kagura (843695) | about 6 years ago | (#24852977)

Apparently it was so awesome, they just skipped the secondary mirror and went straight to tertiary. :)

Re:Apparently... (5, Informative)

Anonymous Coward | about 6 years ago | (#24853165)

Apparently it was so awesome, they just skipped the secondary mirror and went straight to tertiary. :)

The optical design is somewhat unusual as it has
three mirrors, but this is required to get a very
large field of view (with diameter equal to 7 full Moons).
The secondary mirror will be made separately.
If you are interested in more details
about LSST, please take a look at our website,
http://www.lsst.org,
and a review paper
http://lanl.arxiv.org/abs/0805.2366

      Cheers,
      Zeljko

Re:Apparently... (1)

WarJolt (990309) | about 6 years ago | (#24853331)

The secondary mirror wasn't big enough to mention. It's smaller than the primary and tertiary.

Re:Apparently... (0)

Anonymous Coward | about 6 years ago | (#24853333)

Thanks for your hard work and dedication. Hopefully the output of this telescope will amaze and inspire the coming generation.

- UW Neighbor

Re:Apparently... (4, Funny)

sokoban (142301) | about 6 years ago | (#24853335)

Your post is written
Almost like some poetry
Refrigerator

Re:Apparently... (3, Funny)

Bloodoflethe (1058166) | about 6 years ago | (#24853455)

Best haiku evar
Mad props are due all to you
Cooled food device too

Re:Apparently... (0)

Anonymous Coward | about 6 years ago | (#24854555)

What is a haiku?
When this line has 8 syllables,
and the others have 5...

Re:Apparently... (1)

jebrew (1101907) | about 6 years ago | (#24858473)

It's like a haiduken, only slightly less violent and marginally easier to catch your opponent off guard.

Re:Apparently... (3, Funny)

antic (29198) | about 6 years ago | (#24854345)

Looked to me like it was written in the Idle.Slashdot comment box.

Re:Apparently... (1)

BiggerBadderBen (947100) | about 6 years ago | (#24855189)

I just peed my pants Your poetry is to blame I hope you're happy

Re:Apparently... (1)

BiggerBadderBen (947100) | about 6 years ago | (#24855203)

Preview is for chumps

I wish that I had used it

My post looks like shit

Re:Apparently... (1)

jebrew (1101907) | about 6 years ago | (#24858461)

They let you edit

for fifteen minutes on some

websites not slashdot

...hrmmm...I'll have to work at this .

Re:Apparently... (4, Informative)

againjj (1132651) | about 6 years ago | (#24853579)

Mod parent up (despite limited details).

The design is called Paul-Baker/Mersenne-Schmidt.

Page on the telescope design: http://www.lssto.org/Science/lsst_baseline.shtml [lssto.org]
Wikipedia article on telescope: http://en.wikipedia.org/wiki/Large_Synoptic_Survey_Telescope [wikipedia.org]
Wikipedia article section on the Mersenne-Schmidt design: http://en.wikipedia.org/wiki/Schmidt_camera#Mersenne-Schmidt [wikipedia.org]
Paper on the Mersenne-Schmidt design: http://adsabs.harvard.edu/abs/1984MNRAS.210..597W [harvard.edu]

Re:Apparently... (2, Insightful)

ffoiii (226358) | about 6 years ago | (#24853905)

If only we knew who invented it... Sometimes I just wish things had names that described what they were or how they worked rather than who invented it. Credit where credit is due but isn't the value of a thing in it's use rather than it's discoverer?

Re:Apparently... (1)

catmistake (814204) | about 6 years ago | (#24853445)

They didn't skip it. The secondary mirror is actually the reflection of the tertiary mirror in the primary mirror.

You know the rule (4, Funny)

Weaselmancer (533834) | about 6 years ago | (#24853725)

Microsoft products aren't worth buying until they get to the third release. So they just skipped straight to #3 this time.

Re:You know the rule (2, Interesting)

JasterBobaMereel (1102861) | about 6 years ago | (#24856825)

Charles Simonyi gave twice as much as his billness ...he was head of MS Office and has actually been into space ...

Re:Apparently... (0)

Anonymous Coward | about 6 years ago | (#24854717)

Scientist 1: I thought we were looking for black holes?
Scientist 2: Well since Microsoft is footing the bill, we are hoping for no Blue Screens!

Re:Apparently... (1)

Harold Halloway (1047486) | about 6 years ago | (#24856335)

Chuck Norris did the casting.

Re:Apparently... (0)

Anonymous Coward | about 6 years ago | (#24856627)

Huh, the seconday mirror is going to face the primary mirror. Parto of the primary mirror doesn't need to be here as the field of view is going to be obstructed by the secondary mirror (unavoidable).
Then in most designs (ecxept newton) you put the tertiary mirror or the detector
(if no tertiary mirror) behind the first mirror (which has a hole in it so light can pass). They just decided to make the primary mirror and tertiary mirror in one block of glass. It would not make sense to make the secondary and primary mirror in one block of glass: they're too far away from each other for it to be practical.

Gates & Co. (-1, Troll)

Anonymous Coward | about 6 years ago | (#24852985)

Man microsoft is trying to monopolize science. Fuck micro$oft and their evil ways. I hope Bill and Melinda Gates get brutally murdered tonight!

That is the casting done. (2, Funny)

Finallyjoined!!! (1158431) | about 6 years ago | (#24852995)

Let's hope the grinding is more accurate than the Hubble mirror.

http://www.newscientist.com/article/mg12717301.000-the-testing-error-that-led-to-hubble-mirror-fiasco-.html [newscientist.com]

Re:That is the casting done. (3, Funny)

rhyder128k (1051042) | about 6 years ago | (#24853267)

"You're *sure* about this? The calculations have to be absolutely perfect. Even the slightes..."

"Look, take it easy. Of course we're sure. We even got hold of latest chip from Intel. Look, Pen-tee-um. It's apparently the latest thing." [fx: combined lightning/thunder clap]

Re:That is the casting done. (1)

NixieBunny (859050) | about 6 years ago | (#24853339)

The LSST is a ground-based telescope, so the mount can be adjusted if it's not in the right place. Besides, the engineers are, shall we say, "sensitized" to this particular error for some reason.

Re:That is the casting done. (1)

ILuvRamen (1026668) | about 6 years ago | (#24853775)

maybe they pulled a "stargate" and the company that made it was just like, "What? This is for something in space?" Btw I feel the need to mention that if you want a really, really sweet mirror of your own, crack open a buster hard drive. Those platters are smooth to what like 10nm or something? Yeah, I look totally HD in them :D

Re:That is the casting done. (3, Informative)

budgenator (254554) | about 6 years ago | (#24856885)

the Hubble mirror is extremely accurate, unfortunately the testing mechanism, the null corrector wasn't, so the Hubble mirror was ground and figured almost perfectly wrong.

Yes, but (0)

Anonymous Coward | about 6 years ago | (#24853063)

Since the University of Arizona was made in China, I don't think USians can take credit for this one.

Re:Yes, but (0)

Anonymous Coward | about 6 years ago | (#24855283)

That's why Americans are taking the credit.

Kong (1)

KaeloDest (220375) | about 6 years ago | (#24853099)

Kongratulations

That is da hoojest. I remember when the 200 inch Hale was the largest optical.

Holeey Frijkin haooY00j !!!

Kongratulations!

No such thing as "perfect"... (3, Insightful)

QuietLagoon (813062) | about 6 years ago | (#24853105)

... perfection is only a limitation of the measurement process used to find flaws.

Re:No such thing as "perfect"... (0)

Anonymous Coward | about 6 years ago | (#24853161)

Unless you are talking about math.

Re:No such thing as "perfect"... (1)

kmac06 (608921) | about 6 years ago | (#24853183)

That's not true. In this case, you can have perfect to the atomic level. And you can even measure the surface to the atomic level. Of course, this mirror is not actually perfect.

Re:No such thing as "perfect"... (1)

WarJolt (990309) | about 6 years ago | (#24853285)

Then in this case perfect is the limitation of the manufacturing equipment to correct flaws.

Re:No such thing as "perfect"... (3, Insightful)

QuietLagoon (813062) | about 6 years ago | (#24853415)

But then the question becomes: is measurement at the atom level really good enough? Or is it accepted as good enough only because we can do no better?

I can haz atomsnes? (3, Funny)

Nefarious Wheel (628136) | about 6 years ago | (#24854759)

"perfect" is a malleable term for "flawless within the constraints and granularity of one's ability to measure". It may be perfect on the molecular level, and on the atomic, but ... some of thoze particalzorz haz a deviant spin!!

Re:No such thing as "perfect"... (1)

kmac06 (608921) | about 6 years ago | (#24858075)

This isn't insightful, it is ignorant. YES, measurement at the atomic level is good enough. It can essentially measure the exact quantum state of the mirror. You cannot do any better than that.

Re:No such thing as "perfect"... (3, Informative)

budgenator (254554) | about 6 years ago | (#24856905)

At this point, perfection is measured by the glass being approximately the correct shape and without air bubbles or strains being too close together or the surface. If you watch the video, someone was actually walking on the mirror, something that couldn't be done after the blank was ground and figured to an accuracy of a few millionths of an inch.

Re:No such thing as "perfect"... (5, Informative)

hey! (33014) | about 6 years ago | (#24853275)

In optics, you get to the point where further "perfection" doesn't give you any pratical benefit. That is being "diffraction limited". Diffraction limited optics are for practical purposes as "perfect" as you can get.

For a telescope operating through the Earth's atmosphere, you run out of marginal advantage before you reach diffraction limitation. Therefore for such a system, unless special techniques such as adaptive optics are used, practical "perfection" is considerably lower.

I don't know much about the LSST, except that it is a fast (short focal length relative to aperture) optical system. Such systems are much more difficult to get right. Long focal lengths are much more forgiving. Therefore to reach practical perfection in such an aggressive design is quite an achievement. Of course, we aren't there yet. There's three absolutely huge surfaces to grind to very price specifications. But simply casting a blank this size is a huge technical challenge. The amount of heat energy in twenty six tons of molten glass is mind-boggling. Getting it cast into a shape that can be ground and polished into an optical mirror is an engineering tour de force in itself.

Re:No such thing as "perfect"... (1)

QuietLagoon (813062) | about 6 years ago | (#24853435)

In optics, you get to the point where further "perfection" doesn't give you any pratical benefit.
.

Practical benefit is not perfection, it is good enough. You are confirming my point. :)

Yes... (1, Funny)

msauve (701917) | about 6 years ago | (#24853549)

but the summary did say that Microsoft money (via a level of indirection) was involved, so "good enough" is in its genes.

Re:Yes... (0, Flamebait)

QuietLagoon (813062) | about 6 years ago | (#24853843)

the summary did say that Microsoft money (via a level of indirection) was involved, so "good enough" is in its genes.
.

If Microsoft is involved, non-responsiveness to users, bloat, and crashing are in its genes. And don't forget DRM.

~~~Do you have the license to look at those stars?~~~

~~~You may only make one copy of those star images.~~~

Re:Yes... (1)

QuietLagoon (813062) | about 6 years ago | (#24856839)

Flamebait?!? I thought it was funny. :)

Re:No such thing as "perfect"... (3, Informative)

Trogre (513942) | about 6 years ago | (#24853873)

I'm not sure "good enough" is the right term. The point is that the mirror produces results utterly indistinguishable from a mathematically perfect surface.

Nothing to do with settling for "good enough" which usually implies a compromise has been made somewhere.

You could say it was practically perfect in every way. I'll go stand outside now.

Re:No such thing as "perfect"... (1)

QuietLagoon (813062) | about 6 years ago | (#24853929)

I'll go stand outside now.
.

No need to stand outside. You drilled right into the crux of the matter.

Think about it. "utterly indistinguishable" What does that really mean?

Perhaps it means that the limits of our measurement capabilities have been reached.....

Re:No such thing as "perfect"... (3, Informative)

Muad'Dave (255648) | about 6 years ago | (#24857489)

It's not that the surface is perfect to the limit of our ability to measure, it's that the performance of the telescope _system_ is constrained by something other than the shape of the mirror (diffraction-limited). The mirror is "utterly indistinguishable" from perfect because any more perfection out of the mirror will not increase the _system's_ performance. In other words, the telescope's performance would not be enhanced at all if the mirror were replaced with a mathematically perfect one.

Re:No such thing as "perfect"... (0)

Anonymous Coward | about 6 years ago | (#24856329)

Not "mathematically perfection", so much as engineering "good enough". Just make sure the optics aren't the limiting factor in the error budget and you win. Perfect or not.

Re:No such thing as "perfect"... (1)

kmac06 (608921) | about 6 years ago | (#24858163)

I'm sure it's not that good. Imperfections could certainly be distinguished with an atomic force microscope or electron microscope. The point is that they could not be distinguished by the intended use of this thing.

Re:No such thing as "perfect"... (0)

Anonymous Coward | about 6 years ago | (#24856947)

even sometimes you don't want to go up in the "perfection" of the surface, because you want to scatter the smaller wavelengths you don't plan to observe (like far UV in optical telescopes, or IR and visible in case of mm and sub-mm telescopes), so you minimize the noise coming form those bands.

Perfect? (0)

Anonymous Coward | about 6 years ago | (#24853143)

The last time I heard that we were talking about the mirrors for the Hubble.

#irc.trolltalK.com (-1, Offtopic)

Anonymous Coward | about 6 years ago | (#24853179)

community at FUCKING USELEES 3 simPle steps! Fly They looked

everything made by man fails (-1, Flamebait)

Anonymous Coward | about 6 years ago | (#24853197)

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Re:everything made by man fails (0)

Anonymous Coward | about 6 years ago | (#24853343)

Which brings me to my next point, children.

Don't smoke crack.

Re:everything made by man fails (4, Funny)

bluefoxlucid (723572) | about 6 years ago | (#24853367)

I don't understand, what is this post about? It looks like random mindless babbling, not really a structured conspiracy theory or criticism or anything.

Re:everything made by man fails (1)

jannesha (441851) | about 6 years ago | (#24854317)

I don't understand, what is this post about? It looks like random mindless babbling, not really a structured conspiracy theory or criticism or anything.

Did you miss the part where it's "partially funded by Gates & Co."? Sheesh, you must be new here.

Re:everything made by man fails (2, Funny)

Anonymous Coward | about 6 years ago | (#24855113)

It's easy to understand once you realize there are four simultaneous days in each rotation of the earth!

1-corner god is a fraud! Are you afraid to know?

Re:everything made by man fails (1)

kubitus (927806) | about 6 years ago | (#24855769)

the wise man was asked : What are you doing?

He answered: I am very busy - I am preparing my next error!

why not an array? (1)

SuperBanana (662181) | about 6 years ago | (#24853407)

I'm confused- I thought mirror arrays were far superior at least in part because they don't have sagging problems and can correct on the fly for atmospheric disturbances by actuating the segments of the mirror. It certainly is a hell of a lot cheaper; U Texas did it for one third the cost [utexas.edu] of this thing, and theirs is almost a meter larger in "effective" diameter.

In fact, there are 7 or 8 telescopes larger than this [wikipedia.org] , and eleven if you widen it to "larger or equal to".

Obviously, they wouldn't have done something like this if it was inferior, unless this was just for PR/bragging rights. So, why? Is the image quality inferior?

Re:why not an array? (1)

NixieBunny (859050) | about 6 years ago | (#24853485)

Roger Angel likes to make mirrors this way. If they wanted to use a segmented mirror, then it wouldn't be cast in Tucson.

Re:why not an array? (1)

mr_mischief (456295) | about 6 years ago | (#24853563)

Just wait until there are four or five of these things spread across a continent and ganged together by a computer. Bigger mirrors and more mirrors both gives the advantages of both. There has to be a first one of this size, though.

Re:why not an array? (0, Redundant)

freeasinrealale (928218) | about 6 years ago | (#24853635)

I'm trying to imagine a Beowolf cluster of these mirrors...

Re:why not an array? (1)

lordofwhee (1187719) | about 6 years ago | (#24853767)

All running Linux, I trust?

Re:why not an array? (1)

morgan_greywolf (835522) | about 6 years ago | (#24854173)

No, that's sooo last year. The new question is: But does it run Vista? Especially since for many things, the answer seems to be no.

Re:why not an array? (1)

againjj (1132651) | about 6 years ago | (#24853741)

From Wikipedia [wikipedia.org] :

Optical interferometers are mostly seen by astronomers as very specialized instruments, capable of a very limited range of observations. It is often said that an interferometer achieves the effect of a telescope the size of the distance between the apertures; this is only true in the limited sense of angular resolution. The combined effects of limited aperture area and atmospheric turbulence generally limit interferometers to observations of comparatively bright stars and active galactic nuclei. However, they have proven useful for making very high precision measurements of simple stellar parameters such as size and position (astrometry), for imaging the nearest giant stars and probing the cores of nearby active galaxies.

Re:why not an array? (4, Informative)

Nyeerrmm (940927) | about 6 years ago | (#24854893)

There's a difference between a segmented or even sparse primary mirror and an interferometer.

A telescope with a segmented mirror works almost exactly the same way as a normal telescope, except its easier to manufacture mirrors. Of course, this is with the cost of making it harder to keep aligned, and introduce unnecessary complexity for a small mirror, but as the sizes grow it becomes more and more cost effective to segment.

A sparse mirror with a well designed layout (say a Golay array) will be very effective also as a traditional telescope. The array is designed to gather all the spatial frequencies (think of a telescope as an analog Fourier transform) with as few elements as possible. Thus, though gathering less light, it will create an image of the same resolution. Of course less light leads to lower SNRs which can be tricky and is why you don't see too many sparse systems right now.

An interferometer, while conceptually similar to a sparse aperture system, only measures a single frequency component at a time, by taking the light from two distant telescopes and interfering them to determine the "fringes" (Young's experiment) which measure how similar the light beams are. It is thus very precise, but also very limited. Given enough time and patience you could move the relative positions of the telescopes to fill out the Fourier transform, but this is usually not very practical given that alignments need to be maintened within 10s of nanometers.

Re:why not an array? (5, Informative)

edremy (36408) | about 6 years ago | (#24855357)

LSST isn't interesting because of the mirror diameter, it's interesting because of its incredibly wide field of view and amazingly fast optics. This thing has a field of view of almost 10 square degrees and can image down to ~24th magnitude every 15 seconds. Nothing else built or planned even comes close. PAN-STARRS4 will be the nearest thing to LSST and it has an etendue* that's something like 1/6th of LSST, although the PAN-STARRS people like to point out it's also something like a 5th of the cost of the LSST. (* a measure of mirror diameter*field of view. Bigger is better for survey telescopes)

The UT system isn't even the same idea- the main mirror can't even be moved in elevation and doesn't cover the entire sky- it only sees 70% of it. Hobby-Eberly is a spectroscope, designed to look at specific targets for a long time to get the spectrum of the target. LSST is a survey telescope- it's going to scan the visible sky every 3 days in multiple wavelengths, so you have to have an entirely different grade of mount, support structure and drive system. As any amateur astronomer will tell you, cheaping out on the mount will save you quite a few bucks. :^) (Although looking over the Hobby-Eberly, they did some really neat stuff with the mount to get it to track.)

Entirely different missions, different optics, different mounts, etc etc.

Re:why not an array? (2, Informative)

budgenator (254554) | about 6 years ago | (#24856959)

this is a fast wide-field telescope, it's designed to be wide-angled and low magnification, most other scopes are narrow-field and high magnification. This one will take pictures of the whole observable sky over and over so changes over time can be easily seen, hell they could even make time-lapse movies!

Re:why not an array? (1)

Perf (14203) | about 6 years ago | (#24858207)

Google Earth, meet Google Sky.

mod 04 (-1, Offtopic)

Anonymous Coward | about 6 years ago | (#24853433)

how it was supposed in any way related lay down paper TRYING TO DISSECT

Re:mod 04 (1)

aurispector (530273) | about 6 years ago | (#24857305)

looks like someone is testing a new spam machine.

Oh come on! (0)

Anonymous Coward | about 6 years ago | (#24853529)

Science is metric you banana heads! What the hell is 51900 pounds in real money?

Re:Oh come on! (0)

Anonymous Coward | about 6 years ago | (#24856919)

Science is metric you banana heads! What the hell is 51900 pounds in real money?

I think it's the mass of a couple of Americans.

finally... (1)

Brain Damaged Bogan (1006835) | about 6 years ago | (#24853537)

A mirror big enough for RMS, now if only we could get him to look into it each morning...

Re:finally... (1)

eclectro (227083) | about 6 years ago | (#24854163)

A mirror big enough for RMS, now if only we could get him to look into it each morning...

The problem may not so much be getting him to look in it in the morning, the problem may be the sun rising over his shoulder...

Re:finally... (1)

gardyloo (512791) | about 6 years ago | (#24854607)

Every time I see "RMS" I think "Root Mean Square -- that can't be right!" Then I remember who we're talking about, parse the words a little differently, and think, "Actually, it's entirely apropos."

Re:finally... (1)

aproposofwhat (1019098) | about 6 years ago | (#24856287)

of what?

Re:finally... (1)

chromeshadow (1211190) | about 6 years ago | (#24857141)

Could be worse - that acronym makes Porsche drivers wake up sweating at night.

/.ed (0)

Anonymous Coward | about 6 years ago | (#24853703)

so what happens when the site gets /.ed?

For the love of Ballmer...... (1)

gemada (974357) | about 6 years ago | (#24853797)

i am sure Billy G was glad it wasn't a giant, perfect window!

What about Expansion? (1)

missileman (1101691) | about 6 years ago | (#24853925)

I wonder how much that mirror will expand and contract with temperature changes. They would surely have to factor it in. Oh well, I guess they can always cut an expansion joint across the middle if it looks like cracking. :)

Forget the mirror! 3.2Gigapixel camera! (2, Interesting)

jriskin (132491) | about 6 years ago | (#24854609)

The digital camera in this thing generates 15TB of data a day from its 3200megapixel camera. I'm assuming it has an array of sensors, but thats still a ridiculous amazing pixel count.

Re:Forget the mirror! 3.2Gigapixel camera! (1)

Muad'Dave (255648) | about 6 years ago | (#24857643)

The digital camera in this thing generates 15TB of data a day ...

I hope they don't have Comcast.

Re:Forget the mirror! 3.2Gigapixel camera! (1)

suggsjc (726146) | about 6 years ago | (#24858509)

First, you were wrong [lsst.org] .

The 30 terabytes of data obtained each night

Obviously, this is a great achievement deserving of the /. homepage...
However, I'm more interested in hearing about how they are going to process/archive/use that much data!

I'll be honest and say that I'd never heard (or at least remembered) anything about the LSST, so I just did a brief lookover of their site [lsst.org] and it seems like a ridiculously cool project.

LSST will rapidly scan the sky, charting objects that change or move

That means it will have to store multiple versions (history) to be able to do trend analysis. So at multiple TB's of data, how exactly are they planning on processing/analyzing it?!?

As is traditional in the US for many large ground-based telescopes, the LSST is a public-private project. Private support leverages even larger federal support. This traditionally has been true even for facilities where the data was not public immediately. LSST breaks with that tradition in that the data and data products from LSST are immediately public, without a proprietary time period. Thus, private funding for LSST supports open access.

It also mentioned that they are hoping that individuals (and groups) do interesting things with the data...but seriously, I was talking with my brother the other day about how cheap 1TB disks were now. But even if they were only $100 a piece, you'd still be dropping some major $$$ just to be able to begin to do anything (comprehensive) with it.

Mirror and Camera (5, Informative)

stewardwildcat (1009811) | about 6 years ago | (#24854659)

I am an astronomer at the UA and the mirror is a major feat of engineering. It will be the first telescope to have the tertiary and the primary mirror on the same piece of glass. They will have to grind both parts to be perfectly aligned (point to the same place) as well as make the transition area as small as possible. The secondary mirror is a doughnut shape that will be placed above the primary and will have the $100M camera behind it. The camera itself will be the size of a small car and will be as stated before a 3.2 Gigapixel ccd. It will have 200+ 4k by 4k CCD chips that will be read out in 2 seconds. This coupled with the fact it will image the night sky in 5 colors every week will lead to petabytes of data by the programs terminus. Its basically the coolest telescope that will ever be built. ESPECIALLY since the data is set to be public (for US residents) the moment it is processed each morning.

Re:Mirror and Camera (1)

chromeshadow (1211190) | about 6 years ago | (#24857155)

Why US residents only?

Re:Mirror and Camera (0)

Anonymous Coward | about 6 years ago | (#24857407)

That's really cool and all.....except I feel really bad for you being a wildcat. Signed, A Sun Devil

It was as if... (3, Funny)

dave562 (969951) | about 6 years ago | (#24854701)

...all the ants on the planet screamed out in horror at the same time, then suddenly went silent.

LSST is cool - but this isn't why. (4, Informative)

Anonymous Coward | about 6 years ago | (#24854813)

Casting 8-meter-class blanks simply isn't that uncommon any more. The Large Binocular Telescope has a pair of 8.4-meter primaries; Subaru has an 8.3-meter; VLT has four 8.2-meter, Gemini North and South each have an 8.1-meter. Oh, and the Giant Magellan Telescope [gmto.org] is planned to have seven 8.4-meter mirrors.

The LSST is unusual in that its light path is more "folded", hitting 3 mirror surfaces on the way to its primary camera, which means that relatively run-of-the-mill 8-meter-class blank has to be ground pretty uniquely. (And I wish them the best of luck with the process.)

Also, its secondary mirror is absofreakinglutely huge, at 5 meters. To put this in context, just ten years ago there was only one operational telescope in the whole world with a primary mirror larger than 5 meters.

And f/1.25 is crazy fast, yes. The newest, fastest survey scopes out there right now are VISTA at f/3.25 and Pan-STARRS PS1 at f/4. SDSS is f/5, and VLT is f/5.5.

So there you have it - what's really cool about LSST, from a guy who drives a boring old f/10 2.2-meter. ;)

Re:LSST is cool - but this isn't why. (2, Informative)

Shag (3737) | about 6 years ago | (#24854831)

So there you have it - what's really cool about LSST, from a guy who drives a boring old f/10 2.2-meter. ;)

...and who absent-mindedly checked the "Post Anonymously" box for no reason. Whoops.

Re:LSST is cool - but this isn't why. (1)

Fallen Andy (795676) | about 6 years ago | (#24855843)

Thanks for that post, still waking up so haven't RTFA yet, but your post reminded me of this [wikipedia.org] scope which although smaller is f/1.

Andy

Re:LSST is cool - but this isn't why. (1)

Shag (3737) | about 6 years ago | (#24856089)

VATT's primary mirror is f/1. The entire optical system is, according to the same Wikipedia page you linked to, an "Aplanatic Gregorian f/9."

If I've read the LSST web site correctly, I believe the design calls for its entire optical system to be f/1.25.

LSST's field of view will also be much wider than VATT. As a camera user, this seems sensible to me - my short/wide lenses are "faster" than my long zooms.

"f" = F-stop? And what's a "fast" telescope? (1)

zooblethorpe (686757) | about 6 years ago | (#24855615)

Is your "f" notation here the same thing as for cameras? I'm used to SLRs, where "f" denotes the f-stop, the size of the lens aperture versus the focal length, with smaller numbers meaning a wider aperture, resulting in a greatly reduced depth of field (i.e., you have to be a lot more careful about focusing correctly), but also more light coming through and therefore shorter exposure times. Is this what you mean by "fast"? And why is this important? Does it allow for imaging of darker objects?

Curious,

Re:"f" = F-stop? And what's a "fast" telescope? (3, Informative)

bdeclerc (129522) | about 6 years ago | (#24856439)

Yes, it's the same. A shorter focal ratio ("fast") allows for a larger field of view with the same size CCD-chip. The "side-effect" of this is that a larger bit of sky falls onto the individual pixels, which means you sacrifice resolving power for sensitivity.

LSSTing for this (1)

jagdish (981925) | about 6 years ago | (#24854873)

51,900-pound mirror blank, which consists of an outer 27.5-foot diameter (8.4-meter) primary mirror and an inner 16.5-foot (5-meter) third mirror cast in one mold

I have no idea what that means, but I want one anyway.

Can someone explain... (1)

harkabeeparolyn (711320) | about 6 years ago | (#24855391)

Can someone explain why a mirror this size has to weight 25 tons? Aren't there lighter materials that could be used to support the mirrors surface?

Re:Can someone explain... (3, Informative)

bdeclerc (129522) | about 6 years ago | (#24856711)

A telescope mirror needs a number of special properties, from rigidity and weight, but also thermal stability and the ability to polish it efficiently.

For nearly 50 years the largest mirror was the 5 meter Hale telescope, but in the late '80s materials science and casting techniques had evolved to the point where we could reliably cast larger, lighter telescope mirrors, and computing power to the point where active suspension of thinner mirrors is possible.

However, this doesn't mean we can create weightless mirrors, and an 8.4m mirror with a short focal length and two different surfaces still requires quite a bit of internal strength. Glass still has a higher density than water.

An 8.4m mirror has a surface area of 220 square meters, even assuming the density of water (1000 kg/m3) 25 tons corresponds to a thickness of only about 12 cm, or less than 5 inches, which is very very thin, and as I said, glass has a density higher than water, so the actual thickness would be substantially less.

/. just isn't what it used to be (1)

elrous0 (869638) | about 6 years ago | (#24858159)

I scrolled through these comments without finding a single "Real Genius" reference of question about using the mirror for making popcorn. For shame, slashdotters, for shame!
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