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Comment by dstyrb | Hacker News Reader

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.

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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.

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