Comment by dstyrb | Hacker News Reader

Comment by dstyrb | Hacker News Reader

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I don't understand. They haven't been denied a permit, they had the permit. Construction had begun. They were given the go ahead, handshook on a deal with the state of Hawaii-- giving way more than any telescope before. And now, they've been cut off in the middle of full scale production.

It's a bit of a sucker punch because, for eight years, survey planning, software programming, building design, etc. have been underway with this specific site in mind. There are hundreds of people working on this. Tens to hundreds of thousands of man hours are wasted if this decision stands. PhD work on "site predictions for TMT" "Error estimations for TMT" "Optic Performance for TMT" etc. etc. are worthless.

This isn't a back-yard telescope you just prop up anywhere. This is a precision instrument that was designed for this exact spot. The optics designed Mauna Kea atmospheric seeing; the dome designed for Mauna Kea atmospheric temperature, air pressure and turbulence; the survey strategy planned for Mauna Kea weather patterns and sky visibility.

Yes they had the permit but it was issued in violation of apparent rules. Appeals to lost investment and appeals to how great science is don't automatically trump this or do you want to live in a world where one government bureaucrat's wrong decision is set in stone?

I don't disagree with your overall sentiment here; this is disappointing. But if all this is true, then there's been real failures of risk analysis and over-specialization to a particular site. They should have a backup plan, considering how contentious this issue has been all the while. In particular there should be some adaptations that can be made to the main designs that, though not optimal, could make it feasible to relocate, or to replace one of the (many!) existing telescopes on the mountain.

For a start the telescope isn't actually that specialised, while the facility structure will have been designed for MKs typical wind patterns little else is site specific and it could be changed. Metal hasn't been cut yet. No survey strategy exists, it's too early for that.

The problem is not that the telescope wouldn't work anywhere else but that it's really too late in the day to be making such changes. A change in site will set the telescope back about 5 or more years, they will have to start site selection again because their other location choice is now taken by another telescope. All the other sites surveyed were in Hawaii. There is nowhere else in the US of this quality. A new site will also likely cost much more as few are developed. So the telescope will lose at least 5 years on it's competitors and all the cost of starting again and keeping everyone employed 5 more years. It may well miss out on key work in that time, it will probably loose the ability to do joint observations with the James Webb Space Telescope.

So even if it moved it will come much later than the larger European telescope and may have to be scaled back in performance after all the cash it will waste in the site swap. It may loose out on some early science or some science cases altogether if downsized. The real problem is it may not survive the change. Some countries currently signed up will decide to withdraw and back other projects which can be delivered on time. It may be that the cost of the change is large and too many people leave to continue the project. That is not some hypothetical, projects like this which lose momentum often fail. More money could be found but that's unlikely.

If it cannot be built here the whole project is seriously at risk and it will sacrifice science considerably even if it does survive.

You're right. I misspoke a bit; I mean all this type of work is Mauna Kea specific:

http://www.tmt.org/documents

Preliminary work on pipelines relating to the optics, PSFs, band throughputs, etc are simulated with Mauna Kea in mind.

Then that affects the possible science cases. And "survey strategy" at this point would mean allocation of time to contributors which is based on how much money they want to give for their projects by taking those prior simulations into account.

Perhaps the instrument isn't that specialized, but the project kind of is. TMT on Mauna Kea is essentially a completely different telescope from TMT at Apache Point.

They are simulated with MK in mind but that's just using the site parameters. It doesn't affect the design of the telescope only the simulated performance. You don't change your telescope because the site is poorer, it's just not as good.

TMT at APO would never be built because it's not that good a site. TMT at Armazones would be no different other than the enclosure would be modified for the conditions. Yes it effects the performance and science case slightly but you don't redesign a telescope because of that.

Money is committed on the basis of guaranteed time not on the basis of performance. The money was even committed before the design was finalised. There is no agreement for example over which bodies will receiver dark time and good seeing, those scheduling decisions are far more important in performance.

The telescope is not that specialised.

It would fundamentally change the science case, not just slightly. You have E-ELT and GMT in the southern hemisphere. A major part of the TMT science case is its survey footprint in the north to augment these other 30-meter class projects.

Money is committed on the basis of time -- with the expectation that the telescope will be able to deliver the type of science that your institute wants to do -- so an institute doing astroseismology is probably not going to put in money to a spectroscopy project like 4most or weave.

Money is absolutely committed on the basis of expected performance. And part of TMT performance is its location.

I agree physically the telescope is not that specialized. But TMT the project _is_ that specialized.

It's not fundamental to the science case. Nine of the major topics in the science case, if you read it, are hemisphere specific. It is not emphasised that a northern telescope is a big deal, few astronomers will have access to both.

This a national level project, institutions aren't making funding decisions. They do not consult the funding countries every time WFOS is redesigned with different performance. They did not consult them when the AO IFS MOS was replaced with MOSfire. With a big project like this the performance isn't well known at the point when you commit funding.

None

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