Transcript (Kellner_status.ppt)

NGAO Trade Study 3.1.2.2.9:
LOWFS type and architecture
Status report
Stephan Kellner, Ralf Flicker
NGAO Team meeting #4, WMKO Kamuela HI, 1/22/2007
LOWFS architecture and type TS
• Original WBS 3.1.2.2.9:
– Consider the cost/benefit and technical maturity of MEMS-based
correction within the LOWFS, using MOAO control techniques. Include
consideration of additional metrology systems required, if any.
Compare with cost/benefit of MCAO system to provide tip/tilt star
sharpening. Complete when LOWFS requirements and sky coverage
estimates have been documented.
• Re-scoping:
– Include WFS type (SH vs PYR) in performance/cost TS (moved from
WBS 3.1.2.2.10)
– Will not calculate sky coverage initially in this TS. WFS architectures are
compared on a 1-on-1 basis, under the assumption that whichever
performs the better at a given NGS magnitude will provide the greater
sky coverage.
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Current status
• Work on system modeling started in Jan 07
– Stephan Kellner working remotely on computers at WMKO in Waimea
– 1/19/07: model almost complete
• We decided that a fairly sophisticated numerical simulation was the
way to go (no simple analytical formulas to account for everything)
• Using the IDL based AO simulation package “CAOS”
– Yes, yet another simulation code! (number 5, I think…)
– Authors: M. Carbillet et al. (Arcetri) http://lbtwww.arcetri.astro.it/CAOS
– Good:
• modular application builder, no coding required
• Comes with a pyramid sensor (PYR) module
– Bad:
• inefficient, memory expensive = not so good for very large (e.g. NGAO)
simulations, but ok for this particular TS
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Analysis approach
• Build high-order conventional NGS AO system model
– Not feasible to model high-order multi-LGS tomography in CAOS
– use off-axis position of NGS to adjust level of partial high-order
correction, emulating varying levels of tomography (anisoplanatism)
error on the LOWFS
• Build two LOWFS sub-systems (SH & PYR) running in parallel
– compare low-order correction performance side-by-side as a function of
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Level of partial high-order correction & internal MOAO correction (on/off)
NGS magnitude
Number of modes sensed/corrected (2 or 5)
Wavelength band (visible - IR)
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CAOS system model
LO loop
On-axis GS
HO loop
Off-axis GS
Wave front adder: Offaxis residual
wavefront error plus TT etc
LOWFS unit (open loop)
Still needs some work…
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System & observing parameters
no!
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LOWFS type TS - current plan
• S. Kellner to proceed with modeling remotely (from Germany)
– Originally 160 hr allocated to 3.1.2.2.9
– SK well within this limit (assuming he is getting paid)
• Continuous support from R. Flicker (@WMKO)
– On vacation 23-31 January 2007 (but will be in communication)
• Finish modeling this week (1/26/07)
• First trade study results early February 2007
• Final results reported at NGAO meeting #5 (or sooner)
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