Well... let's not just brush it off as one single management failure with no precedence.

Note that even the HST was hugely over budget, over time, and was mismanaged as well... so it's not like it's a one-time thing. Instead, it's more common than not.

From its original total cost estimate of about US$400 million, the hubble space telescope cost about US$4.7 billion by the time of its launch. Hubble's cumulative costs were estimated to be about US$10 billion in 2010. It was launched years behind shedule. It had a flawed main mirror. Etc.

So...sure, it provided nice pictures, and was/is a great asset, but let's not sugarcoat the truth: it was over-budget, over-time, and mismanaged as well. You could have built about 3 OWL's with that. And those would have provided better pictures, certainly in the visible spectrum.

That's why the "Just because in e.g. 20 years we can do something much cheaper we should not stop building scientific instruments today." argument doesn't hold up, imho, because it will ALWAYS be cheaper to build them on Earth. It's a given. One knows this in front. It's not about 'not' building scientific instruments; one can build new ones for Earth-based telescopes as well. It's balancing the advantages and deciding where the most bang for the buck is.

And as said, I think in many instances, unless for specific reasons or goals, space-based telescopes will always come out lower in that regard.

Now, I do understand what you're trying to say, and it's one of the reasons why - even though I personally would have liked to see 'normal' pictures - I do think it made the most scientific sense to use JWST for infra-red observations. At least, that's something that can not, or only with great difficulty, be done on Earth. But still, it's hard to argue that it was worth more than 10 billion dollars. And it's also hard to argue that's an exception, in large space projects.

with the money of the HST, one could have build a couple of EEVLT instead. With the money of the JWST, one could have build a couple of OWL's. And if one ever would send up a new teslecope, double as grand as JWST and double as costly, it's a given for the same money one would, once again, be able to build a far more powerful telescope on Earth. Yes, maybe not in the infra-red... but is getting infra-red really worth 20 billion dollars?

As for exposure-times... you could build an OWL on each side of the planet. Also: while exposure time is important for deep field viewing, *aperture* (and thus lightgathering power) is even more important. Meaning: with a much bigger mirror, you can see much more much faster. So one day with a two meter diameter telescope would demand LESS than half a day with a 8 meter telescope, if we're only talking about exposure time.

And sure, space has its advantages, but the point I'm trying to make, they're not all THAT overwhelmingly large anymore, on a lot of fronts. Not to warrant a cost/time loss of billions/years - and certainly not if it's not strictly necessary to do it that way.

Now... true, costs may come down - hopefully that will pan out for SpaceX - but if we're speculating on future technology, one may do it both ways, and what if, in the future, they find a way to capture infra-red waves in sufficient amount on Earth, for instance? Future technology works both ways, after all - adaptive optics, unimaginable only 40 years ago, is the proof of that.

So, while potentially complementary, I think a very stringent look is necessary as for what projects, exactly, a space-telesope is worth the extra effort and money, and to what degree.

For some tings, it's pretty obvious; for instance, if one wants to test out interferometry on a scale larger than the diameter of Earth. For others, it's less obvious or necessary.

Also, they had to remove a scientific instrument to make room for the corrective optics.

There is no doubt it was a kludge, and an expensive one at that. And a completely avoidable one. For the PRIMARY mirror - the main piece of the space-telescope - to be flawed in such an endeavor... you'd either need to be willfully turn a blind eye or be incompetent beyond belief.

Even NASA doesn't go without blame, here. They should have checked it independently, before shipping.

If one doesn't want to fall in the trap of meaningless semantics, one can just say it as it is: it WAS a flawed instrument, indeed. One which they corrected later, but not without paying a penalty, both in cost as in time/science wasted.

That said, they had to remove a scientific instrument to make room for the corrective optics.

The original estimate was officially 1 to 1,2 billion euro's (in 2006 currency). The *original* estimate that is. But we all know how that goes, with large projects. ;-)

That said, let's say it would have been double that amount in reality. It still would mean 4-5 OWL's. Even one OWL would produce better pictures than JWST would ever be able to, let alone 5 with interferometry...

It would have outclassed JWST without any doubt.

(If, I repeat, JWST would have been in the visible wavelength as well, which it isn't, and which makes the comparison now difficult. But overall, the 5 OWLs surely would have delivered vastly more scientific output in total.)

But, well, no crying over spilled milk. I'm sure the JWST will provide us with nice and scientific interesting things too. It's just that, in this thread/debate, if you compare space-telescopes with earth-based telescopes (including cost), it becomes clear the former only make sense in some specific circumstances or for particular goals.

Fair enough. :-)

Are you using ublock? Otherwise I recommend that. It's pretty good, and I have had very few problems with it (false positives included) on any site, thusfar.

"Space telescopes not only have advantage in some wavelengths, but they are critical, since parts of the spectrum are blocked by the atmosphere."

Which was why I said they still had advantages in those area's. ;-)

There needs to be a compelling reason to send a telescope in space that costs 10 times more for 10 times less aperture. Difficulties to get close to the diffraction limit used to be one of those, up until the late 20th century, but this reason has been starkly reduced with the advent of adaptive optics. Specific wavelengths which are difficult to observe (not impossible, however, if you use high altitude airplanes or balloons) would be a clear advantage. Longer uninterupted viewing in *some* directions, another.

The question is, whether it's worth it, and at what price (as a cost-comparison).

I'll repeat once more, that for the cost of the JWST one could have build 10 OWL terrestrial telescopes. And there is no doubt that, however good the JWST may turn out, ten OWLs would have overclassed and blown away almost everything JWST could show us. The scientific output would be an order of magnitude more.

So I don't think, in a reality where budgets are restrained, that there is always a sufficient cost-benefit analysis being done for the 'complementary' aspects you speak of. I would therefor hold my position space-based telescopes are only useful (in a cost-benefit context) in specific circumstances and special fields of endeavor, in certain scientific niches, or with with particular goals in mind - all of which are not, or only with great difficulty, possible with more feasible, cheaper Earth-based telescopes.

Not to take sides, but it was pretty clearly shown at the right of the summary, which is still 'the article', and it even says "Neptune from the VLT and Hubble". A cursory look would have been enough to find it. As I did.

While true it could have been put nicer, you're exaggerating with 'ESP' as well. And in your rebuttal you weren't very nice neither. In the end, he did give you the link for your request, so maybe you should have stayed a bit more polite as well, if you're going to complain about it in the first place.

"The diffraction limit is not due to atmospheric effects. It is a fundamental limit imposed by the aperture of your telescope, which is more or less the size of the primary mirror. + /but with the bigger ones it's hard to achieve the diffraction limit because of atmospheric effects"

Indeed. The larger the aperture, the more the disturbances are visible and noticeable as well. At a certain point, you gain nothing in resolution (though you still gather more light), even with bigger mirrors.

"The very best adaptive optics only get you to Hubble territory. JWST is bigger than Hubble."

Which is about current technology. sjb was arguing that better space-telescopes than hubble can be made (similar to your argument here), but better Earth telescopes can be made than VLT too.

There is little doubt that EELT with new adaptive optics would, once again, best the JWST (if they were going for visible light). Let alone OWL, with a span of 100 meters, if they had gone with that idea - and for only one tenth of the price.

"Interferometry, particularly image-forming interferometry, is probably easier in space."

True. And in addition, you can do it near limitless (in distance), contrary to something on earth, and with far less potential noise. My point of the interferometry was the hypothetical case, of a bang-for-the-bucks comparison between JWST and something like OWL. For the same cost, one would have had 10 OWL's. Each OWL would have already provided better images (in visible light) as what WST would be cable of, and while the latter is on segmented mirror, the OWL's could use interferometry, which would completely overwhelm anything the JWST could muster.

I would agree with the theoretical advantages of space-telescopes - of course, viewed on a aperture-vs-aperture basis (and without calculating costs) - there is little doubt space-telescopes are always going to be better. The point here rather is, that at how things are in reality, Earth-based telescopes have become so good, that the huge extra cost of space-based telescopes is just not warranted, unless in very specific circumstances.

In fact, you see that already with the JWST: there was a reason they used beryllium mirror and went for the infra-red, after all. Scientifically spoken, it was the most sensible to do.

To be clear: I'm not against space-telescopes on themselves. I think they have potential. but unless the cost is starkly reduced to build and put them up there, there is little doubt Earth telescopes are the better choice, *unless* in specific circumstances are with a specific goal in mind. For instance, if one wanted to try out optical interferometry with a a larger diameter than that of the Earth, it would stand to reason that the only way to go would be space. Even at an added cost. Same goes for infra-red and ultra-violet observations, depending on the wavelengths.

For the foreseeable future, though, if you take aperture and cost in consideration, it's clear Earth-based telescopes will continue to trump space-based telescopes in the visible spectrum.

I can follow you, up until your last sentence.

Pseudo-anonymous accounts are perfectly viable, certainly on slashdot. Have been using them for years, and never got any spam or harrassement. I mean, not outside of the commentary/thread itself.

I've never quite understood the 'online harassment' claim, frankly. Certainly not when one is posting with nicknames that don't (cor)relate with your real person. You can always just decide to not read trollish posts or put spam in the bin or auto-filter it. Straightforwardly said: you can easily ignore that crap. There is no issue there.

So I don't think an AC is really necessary for those reasons. If anything, it dilutes the incentive for posting something worthwhile as an AC, as the VAST majority of AC-post prove. I rather applaud people giving there opinion when posting under their actual nickname: at least one shows one is confident enough to put one's online reputation at stake - small comfort as that may be, it's still something. With AC's, you don't even know IF you're talking to the same AC anyumore, the next comment.

There is no such thing as an uninterrupted view in all angles and directions, if one stays in Earth's orbit - and certainly not a low Earth orbit, as the HST does.

0ne can get longer uninterrupted exposures in some directions, especially if you move out of Earth's low orbit, but the question is, if that's relevant. Deep field imagery is depended on the lightgathering, which, indeed, is dependent on exposure-time BUT even far more so on aperture size. Meaning, you can see far more with a bigger aperture in less time. And since since Earth-telescopes can be built MUCH larger - and for far less money - than space-based telescopes, I think the clear advantage still goes to the former.

For instance, if they had built OWL, it would have overwhelmed and provided better pictures than anything that the WST will be able to do, for less than a fifth of the cost.

EXCEPT of course, for infra-red wavelengths, which is exactly the reason they shifted to that, instead of visible light as with the HST. It's a pitty we won't see 'real' pictures in visible light from the WST, but scientifically spoken, it was the right decision. If you're going to spend 10 billion on something, at least spend it at something that can't be done otherwise.

There is no denying that since the adoption of adaptive optics, one of the major advantages of space-telescopes has been starkly reduced. And if you consider the cost as well, it's clear space-telescopes only make sense anymore in very specific circumstances.

"True in both cases but irrelevant to my point."

Granted, but then you shouldn't have used it in substantiation of the point.

The original point being: "The achievement is that due to adaptive optics, an earth based telescope can deliver pictures as sharp or sharper than a space based telescope."

Which, basically, is true. As we seem both to agree, the fact that one can built better space-telescopes does not change or counter anything to the above claim, since better Earth-based telescopes can be built as well.

If one wants to qualify it, it would be that, for exactly the same aperture, and in visible light, the space-telescope only has a small advantage anymore, due to adaptive optics. For the same *cost* however, an earth-telescope provides much, much sharper images than any space-based telescope. For infra-red and ultra-violet wavelengths, the space telescope still has moderate to far better advantages (depending on which specific wavelength you're looking).

Note that the bang-for-the-bucks argument will ALWAYS be true, no matter how 'better' space-telescopes will become, provided that technology doesn't stand still for neither concepts. One can call this a generalization or speculation or assumption, but it's a reasonable and very logical assumption, bordering on being an obvious certitude. At least, up until technology moves in such direction, both the cost of sending it up into space (SpaceX?) goes drastically down, and/or the structural components can only be fulfilled by a space-environment (which isn't the case for classical mirror-segments).

Only partially true. Space-telescopes still have an advantage in some area's, especially for the deep and near-infrared wavelengths, and ultraviolet wavelengths, but the other advantages are becoming less and less obvious, especially if you consider the cost of both space-based as Earth-based telescopes.

The disturbances of the atmosphere - the major drawback (diffraction limit) up until the last decade of the 20th century - have become largely reduced thanks to adaptive optics and other technological advances.

The argument that we are now capable of constructing space-telescopes that are better than Hubble has no bearings on the comparative advances, since we can also create better earth-based telescopes than VLT, these days. As the Extremely Large Telescope will show, no doubt. There is little doubt this latter one will exceed the JWST, just as the VLT did with Hubble - IF the JWST was going for the visible light waves, which it isn't. In fact, it's the main reason Beryllium mirrors were used that excel in infra-red wavelengths, about the last advantage space-telescopes still have that warrant the vastly more expensive cost (now at more than 10 *billion* for the JWST, if I remember correctly).

Note that for that price, you could have made 10 Overwhelmingly Large Telescopes (OWL) which would completely DWARF the JWST on almost all other fronts, certainly when using interferometry.

errata:

"if implied to some high(er) moral stake" = "if applied to some high(er) moral stake "
"all hominids fall under 'people' automatically" = "all humans fall under 'people' automatically"

And probably a few others, but it's getting awfully late. I'll assume you will know what I mean, even if I made some additional minor spelling- and other mistakes.

"Yes I do, I just think you're focusing on a minor mundane detail and missing the purpose of the lawsuit."

Exactly. You fail to see the principle of the matter. If it was NOT such a rather mundane topic, but something of importance, *exactly the same reasoning* would NOT be accepted. This shows that the reasoning is flawed and applied arbitrarily.

"Yikes. I'm going to skip the loaded appeal-to-emotion example if you don't mind."

I do mind a bit. Because you're basically ignoring it, then, while the example was put there to demonstrate how arbitrarily your reasoning is, if implied to some high(er) moral stake - which is why it has to be emotionally laden, indeed. But if your *reasoning* is correct and consistent, than emotional load should not have any bearings on your argumentation. As you will note, *I* will not skip around your own example.

"no more revenue for you"

Since when is it the courts job to provide the government with more revenue? It's those little remarks of you that make me feel how distant your premise from mine is. How dangerous would that be, if that was truly the job of the courts, instead of, you know, meet out justice in a logical and consistent way. Also, while one can argue it was the politician/lawmakers job, he didn't do a very good job of it, and should have been required to write it better, IF he wanted to make a distinction. That would be the same for all the things you described above, if you want to make a distinction between all kinds of different things. But all this misses the point.

Let me give a simple example where your objections would be nullified: the lawmaker could have NOT made such a distinction, and said that taxes were equally due for vegetables AND fruits. There. 'Revenue for the government' ensured! (If that were to be deemed the goal for the court, which I refute). So you see, your objection to it didn't go to heart of the matter at all. If one wants to make complex laws, one can not complain afterwards about the complexity of it. Saying but what about those, those, and those things then? Indeed, what about them? Do you WANT to differentiate and exempt some from taxes and some not, and on what objective grounds? Any competent lawmaker would realize you either keep it simple and then you have less work to do to keep it consistent and concise, or you make it more complex, and then you have more work to do to keep it consistent and concise. But I've been over this before.

You gave a counterexample with the homo sapiens, but one big glaring omission is, that you did not give any clear definition of 'people' or 'human'. Scientifically, for instance, all species with 'homo' in it, are per definition 'human', since that is what the word means (as I'm sure you know, because you don't seem to be an idiot). So it reinforces my point once again: if you take a clear scientific definition, for instance; all hominids fall under 'people' automatically, this would be FAR more clear and consistent than saying something like "what is seen as human in common parlance". IF one would argue it's only valid for 'people' and you have a wishy-washy vague definition again, you would have to argue this for EVERY case of species, or even subspecies, or even ethnicity. Even worse, if we take the analogy further to its correct statement, then it would be like this: a law saying "You have humans and you have animals. You can kill animals but you can't kill humans EXCEPT for homo sapiens neanderthalis". Because THAT is the equivalent of the courtcase. And then the court arguing: "Yes, we KNOW that Neanderthals are also human, but in common parlance it's viewed differently; only the homo sapiens sapiens is seen as human. Therefor they can be killed like an animal. The lawmaker too, only knew of homo sapiens sapiens, so his intent was to safeguard us, and not other humans. So for the sake of killing, we judge they may be killed, but that doesn't mean we don't consider them humans.

This, as said, makes NO SENSE. The exact reverse of what you claimed, thus. Fruits are fruits, like humans are humans. It makes as much sense to say 'but you can tax tomatoes even though they're fruits and not vegetables' as saying 'but you can kill neanderthals even though they're humans and not animals'. You *assume* this wouldn't happen because you assume 'common parlance' would include the Neanderthals, as well as the intent of the lawmaker would. But you don't actually know that, do you? People regarded other ethnicities as less than humans, even in the 19th century - the same timeperiod, thus. Including lawmakers, who made slave-laws. So how much would they mind killing another subspecies of humans, if they didn't even care about fellow humans? Are you seeing where the problem lays with your kind of reasoning? Following your reasoning, it would be perfectly valid, in that case, that the courts decided Neanderthals may be killed like animals, even though they themselves know they're human. As long as they use the 'common parlance' of the populace - wrong as it may be, and follow the intent of the lawmaker, ignorant as he may be.

"I like how you try to frame my argument "

You seem to let your own feelings play too much in reading something into my words that isn't there. The sentence "For me, facts, reality, logic and consistency trumps considerations of 'not rocking the boat' or 'being easy on traders', or 'to cater to the intent, ignorance or wishful thinking of people or lawmakers'." speaks for itself, and if I wanted to say 'contrary to you', I would have said so, rest assured. You seem to interpret the preceding sentence as being in juxtaposition with this, but it should be clear the 'you do not concur with this' is referencing to what came before, not what comes after. If you feel that is already framing, I think you should take note of your own paragraph(s) preceding this. And no, they didn't judge a tomato a fruit in a *de facto* way. We are, indeed, in a fundamental disagreement on this, which is why I gave you the examples of the black man / animal and the flat-earth - which you basically ignored.

Of course, I can't really tell your take on facts, logic, etc., because you seem to both disregard, as well as acknowledge the importance of all those things. Though I guess you would disagree with this as well. In any case, I clearly only spoke for myself.

That said, we've been on long enough as it is. I think we both made our positions pretty clear by now, and there is little chance the claims, notions, statements, arguments and viewpoints we still don't agree with each other will change in a near future, nor that we can add something meaningful that hasn't already been said in some way or form.

As said, I guess we'll have to agree to disagree.

"Yeah, I agree."

Well, at least we both agree to something, then. And I'm glad to note it's not a of trivial importance, that which we agree on. :-)

On slashdot, one may already consider the discussion a success, then. ;-)