DRM1 design description SDT 5/17/12 1. WFIRST DRM candidate design summary At SDT6 2/2-3/2012...

Wide-Field Infrared Survey Telescope

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DRM1 design description

SDT 5/17/12


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WFIRST DRM candidate design summary• At SDT6 2/2-3/2012 consensus for full-up mission, aka “DRM1” was:

• 1.3m aperture, unobscured three mirror anastigmat telescope• Single channel instrument

• Imaging with filter wheel• Prisms with 1-2 prism assemblies for single or counter-dispersed galaxy redshift survey

respectively plus SN 1a spectroscopy prism assembly• Extend to 2.4um cutoff

• No requirement to fit on Falcon9 launch vehicle• ±36 degree pitch range [relative to 90 degrees from sun to center of FOV]

• Two options for this design are given some initial documentation here:• [baseline] DRM1 is based on a 9x4 H2RG layout focal plane array• DRM1a [requires H4RG(-10) at TRL6] is based on a 6x3 H4RG(-10) layout FPA


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WFIRST DRM1 design summary • DRM1 is based on a 9x4 H2RG

layout focal plane array– 0.18”/pixel, ie same focal length and f/#

as ImC on IDRM1– Same detector and pixel count as

IDRM1– 0.356 sq deg active pixels, 20% gaps– Auxiliary fine guider for guiding during

spectroscopy modes– Outrigger fine guider for guiding during

imaging modes– 0.387 IDRM ImC AΩ < this AΩ < 0.690

IDRM SpC AΩ [m2deg2]


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WFIRST DRM1a candidate design summary• DRM1a is based on a 6x3 H4RG(-

10) layout focal plane array• 0.17”/pixel, f/9.33, 12.13m focal length• Fewer detector arrays, larger pixel count as

compared to IDRM1• 0.671 sq deg active pixels, 300 Mpix

• May be descoped for cost when cost guidance is received

• 20% gaps• Auxiliary fine guider will be added for guiding

during spectroscopy modes• Outrigger fine guider will be added for guiding

during imaging modes• 0.387 IDRM ImC AΩ < 0.690 IDRM SpC AΩ [m2deg2]

< this AΩ


WFIRST’s Central Line of Sight (LOS) Field of Regard (FOR)

+126˚+54˚

Keep-Out Zone

Observing Zone

Keep-Out Zone

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SNe Inertially Fixed Fields must be within 20° of one of the Ecliptic Poles, and can be rotated every ~45 days

GB

SNe Fields

SNe Fields

ExP can observe Inertially Fixed Fields in the Galactic Bulge (GB) for 72 days twice a year

WL/ BAO-RSD/ GI/ GP Surveys can be optimized within the full Observing Zone

Observing Zone: 54°-126° Pitch off Sun Line360° Yaw about Sun Line±10° roll about LOS(off max power roll*)

* Larger roll allowed for SNe


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DRM1 ray trace

PM

SM

TM

F1

F2FPA

Warm side

cold side

Prism assembly

Cold stop & Filter


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DRM1a ray trace

PM

SM

TM

F1

F2FPA

Warm side

cold side

Prism assembly

Cold stop & Filter


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DRM1 CAD views

Grid is 1m

Solar array/sunshade

Telescope barrel

F2

SM

TM

F1

PM

prismsfilter {not shown}

spacecraft

FPA

Radiator (1 of 2)


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Front view showing shadowing of SAS• Payload is shadowed over entire

Field of regard• Mass summary:


JWST, Kepler, WFIRST DRM1 to same scale• All shown on

orbit, with field of view up and sun to left

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Backup charts – performance for DRM1, DRM1a

• Ray trace• ImC mode design residual map• SpC mode design residual box plot• Spot diagrams• Distortion plot• SpC prism Dθ(λ) curves {preliminary}• Prism complexity table• Throughput estimate


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DRM1 ImC error residual map, 1um


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DRM1 SpC residual error distribution

1300.00 1600.00 1800.00 2000.00 2400.000

50

100

150

200

250Design residual wavefront error distribution across field and wavelength

Min Outlier Max Outlier average Total SpC budget

Spectrometer wavefront error distribution at wavelength (nm) shown

wa

vefr

on

t e

rro

r, n

m

Much slower SpC (f/13.7) than previous, improved residuals


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DRM1 ImC spot diagram


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DRM1 SpC mode matrix spot diagram


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DRM1 Grid distortion• L ImC, R SpC


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DRM1 Dθ – preliminary dispersion

• Bandpass (TBR) is 1.3-2.4um [z range 1-2.6]

• ADEPT requirement on Dθ == λ/{dλ/da} where a is sky angle was range 200-240 over 1.3-2.0um

• ISWG requirement was Dθ >100 λ

• New materials being investigated


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Prism complexity• Conic is axisymmetric surface

with conic constant1• Zernike15 is a general freeform

asphere described by up to 15 Zernike terms

• Biconic is surface with differing x, y radii and conic constants

• Cylinder has either x or y curvature but other axis is flat

• All prism sets have P2 made from S-TIH1 and rest at CaF2


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DRM1a ImC error residual map, 1um


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DRM1a SpC residual error distribution

A bit slower SpC (f/13.7) than previous, but larger field; mixed result

1300.00 1600.00 1800.00 2000.00 2400.000

50

100

150

200

250Design residual wavefront error distribution across field and

wavelength

Min Outlier Max Outlier average

Total SpC budget

Spectrometer wavefront error distribution at wavelength (nm) shown

wa

vefr

on

t e

rro

r, n

m


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DRM1a ImC spot diagram


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DRM1a SpC mode matrix spot diagram

S u r f a c e I M A : F P A

0 . 0 0 0 0 , 0 . 0 0 0 0 ( d e g )

1 . 3 0 0 0 0 0W a v e l e n g t h - >F i e l d :

30.00

1 . 3 2 0 0 0 0 1 . 4 0 0 0 0 0 1 . 5 0 0 0 0 0 1 . 6 0 0 0 0 0 1 . 7 0 0 0 0 0 1 . 8 0 0 0 0 0 1 . 9 0 0 0 0 0 2 . 0 0 0 0 0 0 2 . 2 0 0 0 0 0 2 . 3 8 0 0 0 0 2 . 4 0 0 0 0 0

0 . 0 0 0 0 , 0 . 3 2 8 0 ( d e g )

0 . 0 0 0 0 , - 0 . 3 2 8 0 ( d e g )

0 . 2 8 0 0 , 0 . 0 0 0 0 ( d e g )

0 . 2 8 0 0 , 0 . 3 2 8 0 ( d e g )

- 0 . 2 8 0 0 , - 0 . 3 2 8 0 ( d e g )

0 . 6 7 7 0 , 0 . 0 0 0 0 ( d e g )

0 . 6 7 7 0 , 0 . 3 2 8 0 ( d e g )

0 . 6 7 7 0 , - 0 . 3 2 8 0 ( d e g )

- 0 . 6 7 7 0 , 0 . 0 0 0 0 ( d e g )

- 0 . 6 7 7 0 , 0 . 3 2 8 0 ( d e g )

- 0 . 6 7 7 0 , - 0 . 3 2 8 0 ( d e g )

D . C o n t e n t / N A S A G S F C

H 4 E 2 _ 1 2 0 2 1 1 d v . z m xC o n f i g u r a t i o n 3 o f 3

M a t r i x S p o t D i a g r a mT M A T e l e s c o p e2 / 1 3 / 2 0 1 2 U n i t s a r e µ m . A i r y R a d i u s : 1 5 . 3 µ m

S c a l e b a r : 3 0 R e f e r e n c e : C e n t r o i d


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DRM1a Grid distortion• L ImC, R SpC


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DRM1a Dθ -- preliminary

• Bandpass (TBR) is 1.3-2.4um [z range 1-2.6]

• ADEPT requirement on Dθ == λ/{dλ/da} where a is sky angle was range 200-240 asec over 1.3-2.0um

• ISWG requirement was Dθ >100 λ

• New materials being investigated

1.2 1.4 1.6 1.8 2 2.2 2.4120

160

200

240

280

320

Dθ, arcsec

Dθ, arcsec


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Throughput comments• QE estimated updated, again

– Now includes “internal trap inefficiency” model which degrades short wavelength response somewhat

– Net result is less effective area below ~1.5um• Similar average (81%) 0.6-2.0 to IDRM1 baseline and prior results

• Retained gold mirror coatings• SpC mode improves, 4 instead of 3 prisms but 4 focal reducer

lenses are not used• ImC mode optical throughput nearly unchanged; 1 fewer fold

mirror

Throughput summary table


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ImC throughput – note, applies for DRM1 & DRM1a


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SpC Throughput – note, applies for DRM1 & DRM1a


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SN spectroscopy throughput – note, applies for DRM1 & DRM1a

DRM1 design description SDT 5/17/12 1. WFIRST DRM candidate design summary At SDT6 2/2-3/2012...

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Transcript of DRM1 design description SDT 5/17/12 1. WFIRST DRM candidate design summary At SDT6 2/2-3/2012...