MOAO vs MCAO
Trade Study
(Supplementary Material)
Donald Gavel
UCO/Lick Observatory
December 12, 2006
Merit Function
for MOAO deployable IFU
From carlberg@astro.utoronto.ca Thu Jul 22 07:45:11 2004
merit = L * W * N_IFU * sqrt(N_slitlets) * e/sqrt(1+b_ins/b_sky)
* S * (1- exp(-S/S_0)), where S_0 ~=0.4
where
L = length of accesible sky field
W = width of accesible sky field
N_IFU = number of deployable IFUs
N_slit = number of slitlets in each dIFU
e = efficiency
b_inst/b_sky = background light added by the instrument
divided by the sky background at that lambda
S= Strehl, S_0~0.3
The problem with low S is that there is "spectral confusion". The image
still has a visible peak, but the spectrum has contributions from a region
that is over the size of the seeing disk. This can completely ruin any
line measurement where a local strength or velocity is required.
The function of Strehl is derived from the brightest super star cluster in
the Antennae, redshifted to z=0.3 as shown in the attachment. This case
is about the easiest one that can be imagined. A tighter requirement would
push S_0 up to about 0.5 or 0.6, but it depends on specific science
objects.
comments welcomed of course--this is rather back of the envelope.
-Prof. R. Carlberg
Department of Astronomy and Astrophysics
60 St. George Street, Toronto, ON M5S 3H8 Canada
416-978-2198 fax: 416-946-7287 cell: 647-886-5991 (tri-band/sms)
MEMS Open-Loop Modeling for
“Go-To” Operation
• Step 1: Use the thin plate equation to solve for
the required plate force distribution
D 4 z  x   f p  x  
 f x  x 
i 1n
pi
i
• Step 2: Look up the actuator spring force at that
displacement
f p zi   f E Vi , wi   f s wi 
• Step 3: Resultant force is the electrostatic force.
Look up the voltage that provides that force at
that displacement.
Open loop control to 15 nm surface demonstrated in the lab.
We expect to get better than this with calibration refinement.