System Architecture 180 arcsec relay
Number 3

RGD, VV, AMM, CN

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Questions
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What is the correction obtained over a 120 arcsec field using a 2 mirror MCAO system optimized for EE?

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Tech pros/cons
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Pros:
Closed loop. Lasers, LOWFS etc all behind 1 and possibly 2 DMs.
Can adopt MCAO architecture NOW and then change to MOAO with MEMS when proven, with little issues. D-NIRI performance will be not be perfect to 120arcsec, ie 50% EE out to maybe only 60arcsec, then will fall off to some level (what?). But is this good enough??
The 180" relay has the ability to deliver a large contiguous field so that in the future one could take advantage of this using a large imager, with some correction over the field.

Cons:
Large instrument that needs cooling- though we have reduced the size of the relay, may only need 2 DAZLE size meat locker
Unsure of issues with having a large instrument on the platform- it could be annoying for observatory staff or easy because there is clear access to the bearing. Need advice from Observatory for this.
LOWFS not near instruments, but if a k-mirror is adopted this may be ok.
More on MCAO architecture: for TT field impossible to get 180 arcsec corrected, so will need MEMS in outer field maybe.

For MCAO: DMs at ground and 5km. One is 225mm (64 actuators, 3.5mm pitch 0 conj) and the other is 330mm (N=64 actuators, 5mm pitch). Cost increase.

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Revised working definition
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Relay:
No reason for 180 arcsec relay to have DM 320mm size, this reduces the size of the relay to 3.36m from focus to OAP1.
DM 64 actuators across, 3.5mm pitch

Instrument locations:
Could have all instruments located at one location- fed by flip mirror. Possibly can even get D-NIRI in there as well.

Layout:
Can place TT mirror after K mirror. Want 600Hz for TT for galactic science case (40Hz) which is most stringent case, so could have fast TT at fold mirror, for all instruments, except for NIR imager that has it's own extra TT mirror.

MCAO layout possible:
Can place another DM at 6km ish, so may avoid MEMS in DM??

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Performance
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If MCAO is adopted only- generalized anisoplanatism is 170nm over 60 arcsec diameter. RGD suspects 200nm over 90arcsec diameter maybe. Need to check performance of field outside of 90arcsec. Maybe 30% strehl rather than 50% but need to check.

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Cost
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