AO optomechanical design architectures Cost Impact

1
AO opto-mechanical design architecturesCost
Impact

• Don Gavel
• NGAO Team Meeting 5
• February 5, 2009

2
Impact of Build to Cost on the Opto-mechanical
design

• One tier (140 mm beam) vs two-tier (100 mm beam)
  designs
• Woofer DM cost impacted by the likely inability
  to reuse the current systems DM
• Cilas
• increasing DM from 100mm to 140mm could increase
  cost 15
• increasing diamter 100mm to 140mm decreases TT
  bandwidth by 30
• cost of TT stage 50-100 of DM cost.
• Xinetics
• Not much difference between 100mm and 140mm DM
  regarding cost, probably also not resonant
  frequency.
• No ROM cost response yet

3
One-tier vs Two-tier

• Support structure for the K-mirror derotator -
  90K engineering cost makes it a wash with
  eliminating the second tier.
• Switchyard choice impact (essentially none both
  switchyard options doable for both first relay
  design options

4
Tip/Tilt Stages

• DM on Tip/tilt stage
• Tip/tilt stage cost (baseline is to put woofer on
  a t/t stage, possibly a woofer tt stage)
• Cilas cost of TT stage 50-100 of DM cost - I
  believe this is what we costed at SDR 200K on
  woofer, 20K on tweeter.
• Xinetics Have done 2 designs of TT with heavy
  mirror insert 100Hz bandwidth at 0.5 mrad
  mechanical displacement, or 0.62mrad of TT to
  1.4kHz
• PI to get back to us
• Lick shops gimbaled TT stages for both woofer
  and tweeter look reasonably doable at low cost
• Bottom line there is room for reducing the 220K
  cost significantly, perhaps by as much as 100K,
  but at some risk

5
Switchyard

• Dichroic set (6 keyhole designs) and changer
  mechanism vs single focal plane and common
  pickoff design
• Dichroics
• Custom Scientific
• Tgt80 in the transmission region and Rgt90 in the
  reflection region
• Tavggt90 and Ravggt98 but that would require more
  layers in the coating and that could
  significantly degrade the lambda/10 surface
• Cost 10,000-25,000 per piece
• Barr Associates
• J trans/HK reflect will be difficult to make
• Cost ROM pending
• Cost of changer mechanisms (NGAO_SD_Cost_Estimate_
  Don_Gavel_Penult6.xls 4.2.4FSD) 30K
• Cost of dichroics 10K per, 6 post relay 1
  dichroics (KAON 550) 60K

6
Switchyard

• Pickoffs
• Cost of pickoff mechanisms note cost of
  mechanisms is same as in split to IFS/LOWFS
  design, so zero delta cost
• Single focal plane pickoff approach requires care
  in packing LOWFS and IFS packages to allow narrow
  field second relay room to be mounted.
  Preliminary layout design shows this is doable.
  There is still plenty of room for post second
  relay switchouts (to NGSWFS, IR
  Imager/Spectrograph, VisImager)
• Science impact
• Pickoffs may need to enter 30 arcsec narrow field
  if a tt star is there
• No provision to use the science object itself as
  the tt star in LGS mode observing. This effects
  only some science scenarios (asteroids,
  companions to low mass stars, AGNs, between
  v12-20)
• Should be able to use 3 TT stars in the 30-120
  arcsec annulus and still get good sky coverage
• And we have a proposed work-around to this problem

7
Refrigerator-free low surface count single relay
option?

• Memo of Jan 28 shows high leverage of cooling
  leads to no improvement or even worse emissivity
  for this option
• Gain in LGS throughput with no windows and no
  K-mirror (or K-mirror after LGS splitter). But
  new data concerning window AR coatings mitigates
  LGS throughput (see Drew Phillips chart). (1/2
  per surface vs 1 loss per surface assumed
  earler). K-mirror has 3-reflections loose 1
  each, so total double pane window plus K-mirror
  loss is 5 instead of pessimistic 7 in memo.
  273K cost of laser light compared to 383K.

8
Cost Impact of not refrigerating the LGS WFS
assembly

• Requires another double-pane window that LGS
  light must pass through. (2 loss on 75 W 1.5 W
  at 73K/W 109K)

9
Cost Impact of Reduced RTC

• 4-plus-3, with 4 on 1 arcmin field, vs 9 on 2
  arcmin field
• Reduces size of tomography engine (which scales
  with field)
• Reduces number of processors needed for wfs (7 vs
  9) but this may be negligible because these
  processors are reused in the tomography engine
  step of the algorithm, and the tomography engine
  processor need is larger
• Lower cost of the telemetry disk array (fewer raw
  camera outputs)
• We are still investigating this. Possible cost
  gains
• Less tomography hardware (but capped by 450K
  total cost of all computer and interface boards)
• Fewer WFS cameras, and camera interface boards
  (2632K savings on cameras, 5K on interface
  boards)
• Less complexity and hence lower IT costs
• We do not anticipate any decrease in programming
  costs, perhaps even a modest increase due to need
  to add point-and-shoot algorithm support.