070711 Wednesday Notes NGAO Architecture Meeting Notes by Claire Max 180" Big Relay: Dekany, Neyman, Velur, McGrath Similar to NFIRAOS in many ways Doesn't meet the requirement for 50% enclosed energy within 0.07 arc sec Assume every instrument is 0.5m x 0.5m x 1m Is this plausible? Probably yes for the visible instruments. For NIR, might be plausible if there were fewer "modes" (e.g. 1 or 2 camera scales instead of 3, no slit spectrograph, etc) People seem quite worried about feasibility and reliability of MEMS and open-loop wavefront sensing. For example, want to implement MCAO as an insurance policy in case the MEMS open-loop stuff doesn't work. Claire argued that if you are going to implement any open-loop MEMS based systems, you need to invest up front in building and testing prototypes of the MEMS systems and pay for the engineering in advance, to be sure they work. An issue for several of these architectures: how important is it to have a (large) tip-tilt mirror in front of the tip-tilt sensors, rather than have them function entirely open-loop in tip-tilt. Rich makes the point that any of these systems that have high-order DMs will need to be able to switch to a fewer number of subapertures if the lasers are faint for some reason. This would apply to any of the really high order AO architectures. Keck 1 Upgrade: Wizinowich, Bauman, Gavel, Max Chris: consider putting electronics below the Nasmyth platform, so as to have more room for the opto-mechanical systems on the deck. Rich: Would want to use new stages and motors and electronics. Won't be able to spare the existing ones in 7 years. Claire's thought on this: even if we choose not to follow the Keck 1 upgrade path, we'd want to replace the stages and motors etc on Keck 1 sometime in the next 7 years, for reasons of reliability during single-LGS AO observations. Backgrounds: Peter says you could probably get the Keck 1 AO system to ~85% transmission through straightforward upgrades to coatings etc. And you can do thermal management better within the AO room: currently it's running at 5C above ambient, so just flushing the room with ambient air would cool it down to 0C. Important advantage of Keck 1 upgrade: supports KI. Rich has question for Liz and me: how important would it be to have a nearer- term system that gives better performance but only over e.g. 1% of the sky. Part of a phased plan could be first build a "core" system that has smaller field, lower sky coverage, and higher AO performance. Then around it, build the big relay and all the patrolling tip-tilt sensors etc for a high sky coverage system. Rich: first upgrade could be to first buy a big laser, and implement multi- guide star tomography but over a narrow field and hence with a much more constrained set of tip-tilt stars.