I said "USian-centric", not "USian-exclusive": no need to throw a hissy fit.
As someone who works in this field (and your qualifications are exactly, AC?), I'm quite well aware of who the partners are in all of these projects, including, for your information, Canada as participants in the TMT. I'm also pretty well aware, as much as one can be when drowning under a blizzard of PowerPoint engineering, of where the various projects are in their technical readiness.
My post was in response to the rather dismissive "ESO hasn't put its money where its mouth is" aspect of Agent Orange's note, most of the rest of which was just fine. Seems to me that 57 Meuro of committed spend for a Phase A/B study for the E-ELT refutes his lazy statement.
And as for me being Eurotrash? Oh, quite possibly, but having lived and worked in the US for five years and having to suffer the indignities of the TSA, the Department of Homeland Security, the INS, and having to leave my habeas corpus rights at the door on an all too regular basis, I'm entirely comfortable with the epithet. I voted with my feet long ago.
And the only two current, viable telescope proposals for telescopes larger than 10m are the Thirty
Metre Telescope (TMT) and the Giant Magellan Telescope (GMT). OWL is not a concept that is being
taken very seriously...ESO certainly hasn't put its money where its mouth is.
And I call Usian-centric bullshit back in your direction. While the OWL 100m diameter concept proved too difficult, ESO and other European institutions are now working very hard (to the tune of 57 million Euros [$77M] investment in the Phase A/B at present) on the design of a ~40m diameter optical/infrared telescope, now going under the moniker of the E-ELT, or European Extremely Large Telescope. Speaking as someone on the Science Working Group for the E-ELT, it's very much game on...
On one hand, I'm angered to see/. so blatantly hijacked by fringe nuts with an axe to grind: the bitter tenor of the post ("this kind of crippling ignorance among professional astrophysicists is astonishing") should have set off alarm bells from here to kingdom come.
On the other, I'm gratified to see the response: even if/.ers come in varying flavours of wisdom and knowledge, there's usually someone that's able to point us in the right direction. They also generally exhibit decent bullshit detection systems, as clearly demonstrated in the response to this particular piece of bovine excrement.
But credibility is easy to lose and if stories like this start appearing on/. as a regular thing, there's only one way down.
BTW, IAAPA (I am a professional astrophysicist). We're not perfect (the Universe is a big place and full of surprises, thank goodness), but we're hardly stupid.
Kepler, TPF, and SIM are all in the business of exoplanets, yes, that much is right, but they go about it in very different ways. Kepler will stare for long periods (hundreds of days) at patches of the sky, measuring the brightness of about 100,000 fairly bright stars simultaneously, and searching for small, regular dips in their lightcurves, indicating a planet transiting across the stellar surface. No light is detected directly from the planet itself, so Kepler's main goal is measure the statistical occurence of terrestrial-mass planets (and bigger).
TPF is an imaging mission, looking at one star at a time, where there are good reasons to suspect the presence of planets. Using long baseline interferometry to null out the light from the star, TPF will then hope to pick up the (relatively) very faint light from any planets in orbit around the star. TPF will also aim to carry out spectroscopy of this planetary light, to ascertain the presence of tell-tale atmospheric tracers.
Finally, SIM, behind Kepler in the mission queue, but ahead of TPF, also uses interferometric techniques to make very precise astrometric positional measurements. Thus SIM will not image planets either, but will infer their presence as they cause stars to wobble very slightly as the two orbit around each other. For example, Jupiter causes the Sun to wobble, but the mutual centre of mass lies inside the Sun, so the wobble is very small indeed.
As someone who is closely involved in the James Webb Space Telescope (JWST), I find the way that Easterbrook chooses to pitch it against Terrestrial Planet Finder (TPF) quite peculiar. He thinks that looking for the first galaxies that formed in the Universe with JWST is esoteric, which in some senses it may well be, but searching for planets around other stars with TPF is, for all practical purposes, equally so. Both goals are, nevertheless, very exciting and inspiring.
In fact, JWST is a general purpose observatory in much the same way Hubble is, and will enable a very broad base of astronomy, from cosmology at high redshift in the early Universe, all the way back to the formation of planetary systems in our own Galaxy, and to the study of objects in the Kuiper Belt of our own solar system. Again, practically speaking, these are all esoteric and yet you only have to look at the public's fascination with the enormous number of astonishing discoveries that Hubble and other astronomical telescopes have made to realise that such things play a vital role in our philosophical understanding of our part in this vast Universe.
With regards the idea that JWST is somehow NASA's spolied child, keep in mind that the US astronomy community identified it as its number one priority in the most recent Decadal Review of the National Academy of Sciences, along with the European and Canadian communities: NASA is following through on this outside recommendation. Of course, there are grave problems in the NASA space science budget and no-one likes to see missions cut or delayed, and yes, there have been cost overruns on JWST (albeit largely due to non-technical issues outside the JWST project's control), but it's simply wrong to believe that NASA has somehow made its difficult decisions in a vacuum.
Most astonishing though is Easterbrook's naive assertion about gravy train aerospace contractors building the JWST: just who, exactly, does he think is going to build TPF? A couple of University of Podunk astronomers and a dog? TPF is, if anything, even more technologically challenging than JWST and can only be built by many of the very same aerospace contractors: it's bonkers to think otherwise.
Finally, on naming the former Next Generation Space Telescope after James Webb, while, I remember very clearly the moment that was announced by NASA and yes, it was a bit of a shock. All the same, it's important to remember that Webb put in place much of NASA's space science program at the same time as running Apollo, so his credentials are respectable at the very least. In any case, get over it: let's get the JWST done and launched, and answer some of those fascinating esoteric questions.
The reason we've previously "missed" this comet is that it's normally extraordinarily faint, when far from the Sun where it spends most (if not almost all: I don't know if this is a periodic comet) of its life. Most comets originate either in the Kuiper Belt out beyond Neptune, or in the Oort Cloud, way, way out beyond Neptune: these are generally the most distant objects in the Solar System, but occasionally fall inwards.
Thus, new comets are generally only discovered when they fall in close to the Sun: they get heated up and eject material, which makes them brighter, plus, since we're pretty close to the Sun ourselves, they just appear brighter from here too.
Not that I'd turn my nose up at new money for large telescopes, mind you: as we start to build the next generation of 20-50 metre diameter telescopes, we'll be looking for a few billion $/Euro, one way or the other.
Sounds a bit picky, but a more proper way to refer to it is "Comet Pojmanski", rather than "the Pojmanski Comet". Nevertheless, it's very good to see my old friend Grzegorz having visible success with his automated all-sky monitoring cameras (ASAS) down in Chile.
Amateurs work hard to learn the sky in sufficient detail so as to be able to recognise new interlopers such as comets as they search each night, whereas Grzegorz's system is fully automated both in terms of taking the CCD images and in searching through the data for new objects and monitoring variability in known objects: the hard work lies in writing the software. The discovery of two comets is good, but almost a sideshow compared to the vast amount of useful data on transients, novae, variable stars, and so on which the ASAS project has accumulated over the years.
Returning to Comet Pojmanski finally, it's moving into the northern sky now, so even though it's not predicted to get any brighter, it should be available for more of us to see with binoculars in the early morning sky.
The problem with the whole Moon idea is that you will have to build the telescope here on Earth first, then launch it into space in order to get to the Moon. Since space itself is actually preferable to the Moon (i.e. no gravity, no dust, no retro-rockets needed to land, etc.), why not just leave it in space?
It's true that the Moon would act as a shield for radio wavelengths,m but it wouldn't achieve much for optical-IR telescopes really: the ultimate limit to sensitivity is the zodiacal light in the solar system, which you'd see just as much of from the Moon as from near-Earth space. Get the telescope out beyond Jupiter and things get way better.
As for the 1km aperture, well, interferometry is one way to go, since you can hope to get the resolving power of the very long baseline, if not the collecting area. Ground- and space-based optical/IR interferometers are improving / under development and may eventually reach 1km baselines, while 30-50m filled aperture ground-based telescopes will likely be with us within a decade or so.
Finally, all large professional telescopes use mirrors, not lenses: mirrors can be supported against gravity from behind, whereas lenses sag.
We don't tend to call JWST "the successor to HST" so much anymore, but of course, the moniker has stuck. That said, there is a fair amount of overlap between the two: HST gets out to 2.5 microns with NICMOS, while JWST will reach down to 0.6 microns with NIRCam and NIRSpec. Of course, with STIS dead on the HST now, it's UV capabilities are reduced.
In the end, it's a question of scientific drivers: the US Decadal Report placed JWST first on its priority list because astronomers argued more strongly for the high-redshift/star&planet formation science that it can do than argued for a new UV-optical telescope. Sure, it'd be great to have full coverage at all wavelengths, but money is finite and hard choices have to be made.
Besides, one of the key reasons JWST doesn't press too hard on the short wavelength end is because of the whole new generation of ground-based ELTs which will compete very handsomely with JWST at below 2 microns. Ok, that's not the UV, but...
On the budget overrun, well, as a European, I can't speak for NASA really, but most of the cost inflation so far has been there. The key elements which raised the budget by 1G$ this year were:
(A) Revised cost request from the contractors, Northrup Grumman Space Technologies (NGST, ironically), based on increased specifications. NASA generally lets contracts which allow cost growth like this, as true fixed-cost contracts would be completely unaffordable at the get go.
(B) A huge delay incurred by the former NASA administrator (O'Keefe) not signing off on the use of a European Ariane 5 launcher, at ESA expense. There was serious wrangling at the congressional and lobbyist level to dump this in favour of a US launcher (e.g. Delta Heavy), which led to long delays (and thus cost overruns) in interfacing NGST (the company) with Arianespace. One of the first things Mike Griffin did when he came in was to sign off on this, breaking the logjam. However, as Paul Geithner at NASA said in the parent article, this has yet to pass the highest levels of US government, so could yet bite our ass again. But it's hardly fair to lay this one on the JWST per se: it's way beyond our pay grade.
(C) The transition to full cost accounting at NASA Goddard, the prime centre for JWST. In this case, this was money that was always going to be spent at Goddard on roads, buildings, etc., but had not been posted directly on JWST's budget. Again, hardly JWST's fault per se, but makes us look bad again.
In the end, as you've worked on NGST/JWST, you'll know it's a really challenging mission. 4.5$G is a lot of money, but the project (at all levels) is working very, very hard to make this thing work and make it great scientific value for that money, whatever that really means in this game.
Thanks for that. I'm also working on ground-based Extremely Large Telescopes, of which the TMT is one of a number currently under development and planning. Indeed, I spent last week in Cape Town at a symposium of the International Astronomical Union on the science drivers for such monsters: there's a lot of very encouraging work going on, but a mountain of technical, financial, and political challenges to be tackled before we can really hope to see one built. JWST's launch date of 2013 should be compared with projected ELT first light dates of 2015-2020, for example.
In the end though, we need JWST and ELTs: there's a huge amount of complementary work to be done. Oh, and ALMA and the SKA too, please:`)
Thanks - I sometime struggle to find signs of intelligent life on \. but lurking isn't really much of a response, hence my post. It's always good to see JWST come up here (since it signals interest), but you're right that much of what's said is less than serious, let alone informed.
That's metres, not feet, i.e. the JWST primary mirror is now 6.5 metres across. It was actually very originally (in the mid-1990s) to be 4 metres in diameter, but Dan Goldin suggested NASA wasn't being ambitious enough and said that 8 metres should be do-able. Given that he had worked in the defence arena before becoming NASA administrator, it makes you wonder what he knew:`)
The drop back to 6.5 metres was part cost-driven, part schedule-driven (it takes many years to fabricate all those beryllium segments), and part risk-driven. While the mirror diameter shrank, the overall mass of the primary mirror didn't change much: it can now be stiff enough to ensure we can test it on the ground properly, hopefully avoiding a Hubble-type optical manufacturing / testing fiasco.
As for the "originally 800M$", well, it's a long story, but JWST was never really that cheap, when full lifetime costs were accounted for. Still, there has been a cost overrun as we've developed the mission, but you can believe that those of us closely involved with the project do feel a strong responsibility to ensure that the end result delivers some great science to help justify the expense.
IAAA (I am an astronomer) and I work on the JWST project from the European Space Agency side (JWST is a joint NASA, ESA, and Canadian Space Agency project).
While it's true that ground-based telescopes with adaptive optics can compete (or beat) the spatial resolution that JWST will deliver, JWST's image quality should be extremely stable across a fairly large field of view, which will deliver more precise measurements. Just as importantly though, at L2, JWST will be very cold (roughly 50 Kelvin or -223C) and thus will detect almost no background emission from the telescope. On the ground, the warm telescope and atmosphere lead to a very bright infrared background against which it's really difficult to see very faint sources.
As a result, JWST will be able to detect and analyse the first galaxies as they formed in the Universe at high redshift and very low-mass stars and planets being born in the Milky Way. At key wavelengths between 2.5 and 20 micrometres, the JWST will be more sensitive than even 30-50 metre diameter ground-based telescopes for imaging.
In the end, JWST and the next generation of extremely large telescopes (ELTs) on the ground will be highly complementary, much as Hubble and the Keck were: JWST will find the very faintest sources in surveys and determine their statistical properties, while the ELTs will take follow-up high-resolution spectroscopy for detailed characterisation of individual sources.
As for L2, there's at least one astronomical satellite (WMAP) there already, with more (e.g. ESA's Herschel) to come before JWST. But don't worry: it's a big place. As for us spending the money on other pet astro projects, err, nope, we're not. JWST involves some very challenging technology and that stuff is just very expensive. Finally, on the issue of flight hardware, we do actually have some of it done: the 18 hexagonal segments of the primary mirror (made out of beryllium) have been fabricated and are now being machined and polished.
Just who do these bozos think they are? My 30Gb iPod is stuffed to the gills with music, but not one track was downloaded from anywhere: every single one was ripped from CDs which I have bought over the past twenty years. These parasites have had my money once (and twice in many cases, since I bought many things on CD that I already had on LP) and I'll be buggered if they're going to get it again if and when I buy another iPod. It's enough to make me think thrice about buying anything else from them.
The iPod phenomenon is not synonymous with downloaded music: it's the Walkman of the 21st century, dammit, and how the music gets on there is entirely secondary. Did the music cartel get money from Sony for every Walkman sold?
Slashdot Mirror
As someone who works in this field (and your qualifications are exactly, AC?), I'm quite well aware of who the partners are in all of these projects, including, for your information, Canada as participants in the TMT. I'm also pretty well aware, as much as one can be when drowning under a blizzard of PowerPoint engineering, of where the various projects are in their technical readiness.
My post was in response to the rather dismissive "ESO hasn't put its money where its mouth is" aspect of Agent Orange's note, most of the rest of which was just fine. Seems to me that 57 Meuro of committed spend for a Phase A/B study for the E-ELT refutes his lazy statement.
And as for me being Eurotrash? Oh, quite possibly, but having lived and worked in the US for five years and having to suffer the indignities of the TSA, the Department of Homeland Security, the INS, and having to leave my habeas corpus rights at the door on an all too regular basis, I'm entirely comfortable with the epithet. I voted with my feet long ago.
And I call Usian-centric bullshit back in your direction. While the OWL 100m diameter concept proved too difficult, ESO and other European institutions are now working very hard (to the tune of 57 million Euros [$77M] investment in the Phase A/B at present) on the design of a ~40m diameter optical/infrared telescope, now going under the moniker of the E-ELT, or European Extremely Large Telescope. Speaking as someone on the Science Working Group for the E-ELT, it's very much game on ...
See http://www.eso.org/projects/e-elt/ for more information.
On one hand, I'm angered to see /. so blatantly hijacked by fringe nuts with an axe to grind: the bitter tenor of the post ("this kind of crippling ignorance among professional astrophysicists is astonishing") should have set off alarm bells from here to kingdom come.
/.ers come in varying flavours of wisdom and knowledge, there's usually someone that's able to point us in the right direction. They also generally exhibit decent bullshit detection systems, as clearly demonstrated in the response to this particular piece of bovine excrement.
/. as a regular thing, there's only one way down.
On the other, I'm gratified to see the response: even if
But credibility is easy to lose and if stories like this start appearing on
BTW, IAAPA (I am a professional astrophysicist). We're not perfect (the Universe is a big place and full of surprises, thank goodness), but we're hardly stupid.
Kepler, TPF, and SIM are all in the business of exoplanets, yes, that much is right, but they go about it in very different ways. Kepler will stare for long periods (hundreds of days) at patches of the sky, measuring the brightness of about 100,000 fairly bright stars simultaneously, and searching for small, regular dips in their lightcurves, indicating a planet transiting across the stellar surface. No light is detected directly from the planet itself, so Kepler's main goal is measure the statistical occurence of terrestrial-mass planets (and bigger).
TPF is an imaging mission, looking at one star at a time, where there are good reasons to suspect the presence of planets. Using long baseline interferometry to null out the light from the star, TPF will then hope to pick up the (relatively) very faint light from any planets in orbit around the star. TPF will also aim to carry out spectroscopy of this planetary light, to ascertain the presence of tell-tale atmospheric tracers.
Finally, SIM, behind Kepler in the mission queue, but ahead of TPF, also uses interferometric techniques to make very precise astrometric positional measurements. Thus SIM will not image planets either, but will infer their presence as they cause stars to wobble very slightly as the two orbit around each other. For example, Jupiter causes the Sun to wobble, but the mutual centre of mass lies inside the Sun, so the wobble is very small indeed.
Hope this clarifies things.
As someone who is closely involved in the James Webb Space Telescope (JWST), I find the way that Easterbrook chooses to pitch it against Terrestrial Planet Finder (TPF) quite peculiar. He thinks that looking for the first galaxies that formed in the Universe with JWST is esoteric, which in some senses it may well be, but searching for planets around other stars with TPF is, for all practical purposes, equally so. Both goals are, nevertheless, very exciting and inspiring.
In fact, JWST is a general purpose observatory in much the same way Hubble is, and will enable a very broad base of astronomy, from cosmology at high redshift in the early Universe, all the way back to the formation of planetary systems in our own Galaxy, and to the study of objects in the Kuiper Belt of our own solar system. Again, practically speaking, these are all esoteric and yet you only have to look at the public's fascination with the enormous number of astonishing discoveries that Hubble and other astronomical telescopes have made to realise that such things play a vital role in our philosophical understanding of our part in this vast Universe.
With regards the idea that JWST is somehow NASA's spolied child, keep in mind that the US astronomy community identified it as its number one priority in the most recent Decadal Review of the National Academy of Sciences, along with the European and Canadian communities: NASA is following through on this outside recommendation. Of course, there are grave problems in the NASA space science budget and no-one likes to see missions cut or delayed, and yes, there have been cost overruns on JWST (albeit largely due to non-technical issues outside the JWST project's control), but it's simply wrong to believe that NASA has somehow made its difficult decisions in a vacuum.
Most astonishing though is Easterbrook's naive assertion about gravy train aerospace contractors building the JWST: just who, exactly, does he think is going to build TPF? A couple of University of Podunk astronomers and a dog? TPF is, if anything, even more technologically challenging than JWST and can only be built by many of the very same aerospace contractors: it's bonkers to think otherwise.
Finally, on naming the former Next Generation Space Telescope after James Webb, while, I remember very clearly the moment that was announced by NASA and yes, it was a bit of a shock. All the same, it's important to remember that Webb put in place much of NASA's space science program at the same time as running Apollo, so his credentials are respectable at the very least. In any case, get over it: let's get the JWST done and launched, and answer some of those fascinating esoteric questions.
The reason we've previously "missed" this comet is that it's normally extraordinarily faint, when far from the Sun where it spends most (if not almost all: I don't know if this is a periodic comet) of its life. Most comets originate either in the Kuiper Belt out beyond Neptune, or in the Oort Cloud, way, way out beyond Neptune: these are generally the most distant objects in the Solar System, but occasionally fall inwards.
Thus, new comets are generally only discovered when they fall in close to the Sun: they get heated up and eject material, which makes them brighter, plus, since we're pretty close to the Sun ourselves, they just appear brighter from here too.
Not that I'd turn my nose up at new money for large telescopes, mind you: as we start to build the next generation of 20-50 metre diameter telescopes, we'll be looking for a few billion $/Euro, one way or the other.
Sounds a bit picky, but a more proper way to refer to it is "Comet Pojmanski", rather than "the Pojmanski Comet". Nevertheless, it's very good to see my old friend Grzegorz having visible success with his automated all-sky monitoring cameras (ASAS) down in Chile.
Amateurs work hard to learn the sky in sufficient detail so as to be able to recognise new interlopers such as comets as they search each night, whereas Grzegorz's system is fully automated both in terms of taking the CCD images and in searching through the data for new objects and monitoring variability in known objects: the hard work lies in writing the software. The discovery of two comets is good, but almost a sideshow compared to the vast amount of useful data on transients, novae, variable stars, and so on which the ASAS project has accumulated over the years.
Returning to Comet Pojmanski finally, it's moving into the northern sky now, so even though it's not predicted to get any brighter, it should be available for more of us to see with binoculars in the early morning sky.
The problem with the whole Moon idea is that you will have to build the telescope here on Earth first, then launch it into space in order to get to the Moon. Since space itself is actually preferable to the Moon (i.e. no gravity, no dust, no retro-rockets needed to land, etc.), why not just leave it in space?
It's true that the Moon would act as a shield for radio wavelengths,m but it wouldn't achieve much for optical-IR telescopes really: the ultimate limit to sensitivity is the zodiacal light in the solar system, which you'd see just as much of from the Moon as from near-Earth space. Get the telescope out beyond Jupiter and things get way better.
As for the 1km aperture, well, interferometry is one way to go, since you can hope to get the resolving power of the very long baseline, if not the collecting area. Ground- and space-based optical/IR interferometers are improving / under development and may eventually reach 1km baselines, while 30-50m filled aperture ground-based telescopes will likely be with us within a decade or so.
Finally, all large professional telescopes use mirrors, not lenses: mirrors can be supported against gravity from behind, whereas lenses sag.
We don't tend to call JWST "the successor to HST" so much anymore, but of course, the moniker has stuck. That said, there is a fair amount of overlap between the two: HST gets out to 2.5 microns with NICMOS, while JWST will reach down to 0.6 microns with NIRCam and NIRSpec. Of course, with STIS dead on the HST now, it's UV capabilities are reduced.
...
In the end, it's a question of scientific drivers: the US Decadal Report placed JWST first on its priority list because astronomers argued more strongly for the high-redshift/star&planet formation science that it can do than argued for a new UV-optical telescope. Sure, it'd be great to have full coverage at all wavelengths, but money is finite and hard choices have to be made.
Besides, one of the key reasons JWST doesn't press too hard on the short wavelength end is because of the whole new generation of ground-based ELTs which will compete very handsomely with JWST at below 2 microns. Ok, that's not the UV, but
On the budget overrun, well, as a European, I can't speak for NASA really, but most of the cost inflation so far has been there. The key elements which raised the budget by 1G$ this year were:
(A) Revised cost request from the contractors, Northrup Grumman Space Technologies (NGST, ironically), based on increased specifications. NASA generally lets contracts which allow cost growth like this, as true fixed-cost contracts would be completely unaffordable at the get go.
(B) A huge delay incurred by the former NASA administrator (O'Keefe) not signing off on the use of a European Ariane 5 launcher, at ESA expense. There was serious wrangling at the congressional and lobbyist level to dump this in favour of a US launcher (e.g. Delta Heavy), which led to long delays (and thus cost overruns) in interfacing NGST (the company) with Arianespace. One of the first things Mike Griffin did when he came in was to sign off on this, breaking the logjam. However, as Paul Geithner at NASA said in the parent article, this has yet to pass the highest levels of US government, so could yet bite our ass again. But it's hardly fair to lay this one on the JWST per se: it's way beyond our pay grade.
(C) The transition to full cost accounting at NASA Goddard, the prime centre for JWST. In this case, this was money that was always going to be spent at Goddard on roads, buildings, etc., but had not been posted directly on JWST's budget. Again, hardly JWST's fault per se, but makes us look bad again.
In the end, as you've worked on NGST/JWST, you'll know it's a really challenging mission. 4.5$G is a lot of money, but the project (at all levels) is working very, very hard to make this thing work and make it great scientific value for that money, whatever that really means in this game.
Thanks for that. I'm also working on ground-based Extremely Large Telescopes, of which the TMT is one of a number currently under development and planning. Indeed, I spent last week in Cape Town at a symposium of the International Astronomical Union on the science drivers for such monsters: there's a lot of very encouraging work going on, but a mountain of technical, financial, and political challenges to be tackled before we can really hope to see one built. JWST's launch date of 2013 should be compared with projected ELT first light dates of 2015-2020, for example.
:`)
In the end though, we need JWST and ELTs: there's a huge amount of complementary work to be done. Oh, and ALMA and the SKA too, please
Thanks - I sometime struggle to find signs of intelligent life on \. but lurking isn't really much of a response, hence my post. It's always good to see JWST come up here (since it signals interest), but you're right that much of what's said is less than serious, let alone informed.
That's metres, not feet, i.e. the JWST primary mirror is now 6.5 metres across. It was actually very originally (in the mid-1990s) to be 4 metres in diameter, but Dan Goldin suggested NASA wasn't being ambitious enough and said that 8 metres should be do-able. Given that he had worked in the defence arena before becoming NASA administrator, it makes you wonder what he knew :`)
The drop back to 6.5 metres was part cost-driven, part schedule-driven (it takes many years to fabricate all those beryllium segments), and part risk-driven. While the mirror diameter shrank, the overall mass of the primary mirror didn't change much: it can now be stiff enough to ensure we can test it on the ground properly, hopefully avoiding a Hubble-type optical manufacturing / testing fiasco.
As for the "originally 800M$", well, it's a long story, but JWST was never really that cheap, when full lifetime costs were accounted for. Still, there has been a cost overrun as we've developed the mission, but you can believe that those of us closely involved with the project do feel a strong responsibility to ensure that the end result delivers some great science to help justify the expense.
IAAA (I am an astronomer) and I work on the JWST project from the European Space Agency side (JWST is a joint NASA, ESA, and Canadian Space Agency project).
While it's true that ground-based telescopes with adaptive optics can compete (or beat) the spatial resolution that JWST will deliver, JWST's image quality should be extremely stable across a fairly large field of view, which will deliver more precise measurements. Just as importantly though, at L2, JWST will be very cold (roughly 50 Kelvin or -223C) and thus will detect almost no background emission from the telescope. On the ground, the warm telescope and atmosphere lead to a very bright infrared background against which it's really difficult to see very faint sources.
As a result, JWST will be able to detect and analyse the first galaxies as they formed in the Universe at high redshift and very low-mass stars and planets being born in the Milky Way. At key wavelengths between 2.5 and 20 micrometres, the JWST will be more sensitive than even 30-50 metre diameter ground-based telescopes for imaging.
In the end, JWST and the next generation of extremely large telescopes (ELTs) on the ground will be highly complementary, much as Hubble and the Keck were: JWST will find the very faintest sources in surveys and determine their statistical properties, while the ELTs will take follow-up high-resolution spectroscopy for detailed characterisation of individual sources.
As for L2, there's at least one astronomical satellite (WMAP) there already, with more (e.g. ESA's Herschel) to come before JWST. But don't worry: it's a big place. As for us spending the money on other pet astro projects, err, nope, we're not. JWST involves some very challenging technology and that stuff is just very expensive. Finally, on the issue of flight hardware, we do actually have some of it done: the 18 hexagonal segments of the primary mirror (made out of beryllium) have been fabricated and are now being machined and polished.
Just who do these bozos think they are? My 30Gb iPod is stuffed to the gills with music, but not one track was downloaded from anywhere: every single one was ripped from CDs which I have bought over the past twenty years. These parasites have had my money once (and twice in many cases, since I bought many things on CD that I already had on LP) and I'll be buggered if they're going to get it again if and when I buy another iPod. It's enough to make me think thrice about buying anything else from them.
The iPod phenomenon is not synonymous with downloaded music: it's the Walkman of the 21st century, dammit, and how the music gets on there is entirely secondary. Did the music cartel get money from Sony for every Walkman sold?