System Architecture 5
Cascaded relay

RGD, CB, AMM, PW, LM

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Description
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1. K mirror
2. 120arsec relay with 100mm pupil size, DM has 20 actuators across, ground conj
3. 589nm dichroic to LGS WFS unit
4. Beamsplitter to D-Niri that uses facility LOWFS
5. LOWFS package at intermediate focal plane
6. Narrow field relay with 30 arcsec unvignetted (some discussion as to why this is, no specific science justification as yet). 64 actuator DM, 1 inch pupil, conj to 0km
7. Narrow field instrument output, stacked in LEGO unit (fold mirror chooses instrument, all instruments mounted to same structure).
8. There are some solutions for acquisition, but needs further thought (a comment for all architectures)
9. PSF calibration possible but further thought re. required field for science instruments (again a comment for other architectures). TOP LEVEL QUESTION-what is the required field for PSF calibration?
10. HOWFS has no MEMS, since it sees low spatial frequency in closed loop

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Tech pros/cons
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Pros:
1. D-NIRI is away from bearing
2. D-NIRI, LGS and LOWFS have global low order corrector
3. Instruments are non-rotating
4. D-NIRI reasonably unconstrained in packaging, easier to add later
5. Smaller than large relay architecture, easier to cool, maintain etc
6. In event of MEMS mirror failure (lifetime) there is a fallback
7. K-mirror is smaller if away from focus
8. 5mm DM is (maybe) a stock item
9. Anna likes this layout
10. Can potentially feed interferometer more easily than other architectures
11. Can be extended to MCAO with third stage (after 30arcsec relay)
12. May have space to add another wide field instrument at D-NIRI location

Cons:
1. Lower transmission for LGS and other instruments
2. LOWFS away from science instruments, though all are not rotating
3. Extra complication of Woofer-tweeter control required
4. Potentially more scintillation, static aberrations etc due to large number of surfaces- needs to be controlled
5. Packaging may be constrained if this feeds interferometer?

Risk:
1. Need to look further into packaging

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Performance
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Cost
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