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18-20 reduxCan the focal plane accommodate both

RSC and RVS as viable NIR venders

C. Bebek

28 April 2005

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“How to maintain agility in the face of 18 m and 20 m MCT,” C. Bebek, 25 October 2002.

Essentially, this was ignored because we didn’t take Raytheon seriously.Not the case any longer!In this round of focal plane design, we should revisit a non-vender-specific

solution.Impacts• Optics• CCD• Science data• Mounts and focal plane

Glossary• RSC = Rockwell• RVS = Raytheon• MCT = HgCdTe

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2002

MCT issue

• Rockwell (RSC) and Raytheon (RVS) offer 2k x 2k format devices.

• But the pixel size is different: 18 m (RSC) and 20 m (RVS).

• The readout differences between the two are minor – home built electronics could accommodate both.

• Rockwell’s custom readout ASIC gives them an advantage but it probably can work with the RVS devices, if we can buy it separately.

• The primary challenge is how to accommodate the mechanical differences between the two.

• A secondary consideration is do we want to maintain the arcsec/pixel for the two solutions, ie, carry multiple optics designs:

— 0.100/0.171 for 10.5/18 m

— 0.100/0.190 for 10.5/20 m

— 0.115/0.171 for 12.0/18 m

— 0.115/0.190 for 12.0/20 m

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2002

Observations

• Using a grid to accommodate the RVS size is the most general, although it does exceed TMA63 focal plane area a bit.

• If we want a CCD to match the area of RVS, we should go to 12 mmpixels – maintains plates scale and controls pixel count growth to maintain reasonable readout time.

• We are building SNAP CCDs that match the RSC devices.

• We have two options— One

• Adopt the large MCT/CCD solution

• Modify TMA63 optics to accommodate the larger focal plane

• Continue “small” CCD development

• Decide later which MCT and CCD size to use

— Two

• Continue with RSC format as the default

• Continue “small” CCD development

• In two years, rework the design concept if RVS MCT is preferred.

• RSC, in my opinion, is the leading solution.

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MCT vender package data

Rockwell

Raytheon

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MCT packages

44.520

1.560 0.960

40.960

43.480

40.96043.480

0.663

1.8571.040

40.460

38.990

36.860

36.860

42.160

1.700

0.760

1.786

1.065 1.065

Some rations:Pixel size: 20/18 = 1.111Longest package dimension: 44.520/42.160 = 1.060Grid size: 45.520/43.160 = 1.055

Raytheon Rockwell

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Area-matched CCD packages

40.950

40.950

1.785

44.520

43.480

43.515

42.917

1.2651.2820.983

3900 x 3900

pad edge

pad edge

pad edge

pad edge

39.399

38.84236.897

36.834

1.283

0.973

3514 x 3508

Raytheon RockwellSNAP V2

Keep 10.5 µm pixels in both cases

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Some numerology

• Focal plane inner and outer radii (mm)— Rin = 3*(Lmax + Lgap)

— Rout = 3*S5*(Lmax+ Lgap)

— Lgap = 1 mm

Lmax Rin Rout

RSC 43.160 129.48 289.53

RVS 45.520 136.56 305.36

136.56

305.36

129.50

289.50

RSCRVS

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RSC MCT and CCD

129.9 289.9

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RSC MCT and RVS CCD

129.9 289.9

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RVS MCT and CCD

136.56 305.36

Reasonable

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RSC MCT and RVS CCD

136.56 305.36

Reasonable

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Optics impact

• What plate scale (arcsec/pixel) do we want?• Are Mike Lampton’s flexible TMAs flexible?• How long can we delay nailing it down?

• Note, this is an opportunity to reduce CCD plate a bit.

FL = 21.66 m FL = 24.07 mRSC RVS RSC RVS

CCD 0.100 0.100 0.090 0.090

MCT 0.171 0.190 0.154 0.171

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CCD impact

• Do we want to carry two CCD formats for a while?

—Make one and only one CCD format, the one that matches Raytheon?

—If we go with Rockwell, we still have more visible sq. degs. for weak lensing.

• Option—The blue shaded region is overall

size of the CCD using SNAP V2 edge overheads. Could grow to the orange region, matching Raytheon physical package dimension.

—Can move wire bond pads further from active pixel region making wire-bond package a more viable backup.

—SNAP V2 HV improvements can deal with this larger overhead region.

40.950

40.950

1.785

44.520

43.480

43.515

42.917

1.2651.2820.983

3900 x 3900

pad edge

pad edge

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Science data

• With a 3900 x 3900 CCD there is more data; 548 vs 444 Mpixel.• To acquire data, read CCDs at 128 kpixel/s or extend shutter closed time

to 38 s.• A corresponding amount more of memory is required.• And a corresponding higher telemetry rate or telemetry time is requied.

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Mounts?

• What do we do to allow both MCT types to mount to the focal plane.• Associated with this is the size of the penetrations in the focal plane for

connecter and e-box cross section.• E.g., mount RVS, RSC and CCD on structures with the same foot print at

the focal plane interface.

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Summary

• I am sure you can develop a single design to accommodate both Rockwell and Raytheon devices.

• To support this, the CCD group needs to either support two CCD sizes and their associated packages or one CCD size matching Raytheon pixel area.

• The are data rate/volume costs at the 20% level.• Optical prescription has to remain flexible up to the time of vender

selection.• A universal mount is possible, but can you force 3 interested parties into

a common footprint.

• A design accommodating the two MCT venders is good industrial politics. Public display of this sends/reinforces the message that the venders are in competition.