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Wide-Field Infrared Survey Telescope
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DRM1 design description
SDT 5/17/12
Wide-Field Infrared Survey Telescope
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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
Wide-Field Infrared Survey Telescope
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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]
Wide-Field Infrared Survey Telescope
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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
Wide-Field Infrared Survey Telescope
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
Wide-Field Infrared Survey Telescope
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DRM1 ray trace
PM
SM
TM
F1
F2FPA
Warm side
cold side
Prism assembly
Cold stop & Filter
Wide-Field Infrared Survey Telescope
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DRM1a ray trace
PM
SM
TM
F1
F2FPA
Warm side
cold side
Prism assembly
Cold stop & Filter
Wide-Field Infrared Survey Telescope
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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)
Wide-Field Infrared Survey Telescope
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Front view showing shadowing of SAS• Payload is shadowed over entire
Field of regard• Mass summary:
Wide-Field Infrared Survey Telescope
JWST, Kepler, WFIRST DRM1 to same scale• All shown on
orbit, with field of view up and sun to left
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Wide-Field Infrared Survey Telescope
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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
Wide-Field Infrared Survey Telescope
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DRM1 ImC error residual map, 1um
Wide-Field Infrared Survey Telescope
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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
Wide-Field Infrared Survey Telescope
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DRM1 ImC spot diagram
Wide-Field Infrared Survey Telescope
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DRM1 SpC mode matrix spot diagram
Wide-Field Infrared Survey Telescope
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DRM1 Grid distortion• L ImC, R SpC
Wide-Field Infrared Survey Telescope
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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
Wide-Field Infrared Survey Telescope
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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
Wide-Field Infrared Survey Telescope
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DRM1a ImC error residual map, 1um
Wide-Field Infrared Survey Telescope
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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
Wide-Field Infrared Survey Telescope
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DRM1a ImC spot diagram
Wide-Field Infrared Survey Telescope
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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
Wide-Field Infrared Survey Telescope
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DRM1a Grid distortion• L ImC, R SpC
Wide-Field Infrared Survey Telescope
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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
Wide-Field Infrared Survey Telescope
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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
Wide-Field Infrared Survey Telescope
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ImC throughput – note, applies for DRM1 & DRM1a
Wide-Field Infrared Survey Telescope
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SpC Throughput – note, applies for DRM1 & DRM1a
Wide-Field Infrared Survey Telescope
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SN spectroscopy throughput – note, applies for DRM1 & DRM1a