Presentation to HST Project
8 Jul 09
Recommendation for achieving best SMOV & cycle 17 focus with ACS & WFC3
STScI SMOV Team
Presentation to HST Project
8 Jul 09
SMOV/Cycle 17 Focus Recommendation
1.) Offset WFC3 & COS focus during SI SMOV fine alignment by equiv. –2.5
microns to achieve confocality with ACS/WFC
• confocality of ACS/WFC and WFC3 best optimizes science in cycle 17 and
beyond
• determination of this value covered in later 2 slides
2.) Follow-up with a Secondary Mirror move of 2.5+0.5 = 3.0 microns to leave
the three SIsʼ focii ~ +0.5 micron.
• Perform by day 200: restoration of optimal focus for WFC3 must precede WFC3
PSF specification tests, Early Release Science, and Cycle 17
• WFC3 wishes to maintain focus comfortably within 2 microns
• Leaving the OTA focus at +0.5 microns should result in passing through best
focus (0) in cycle 17, and not reaching –2 microns until mid-2012
• Mirror move amount at the small end of historical moves (backup slide), but goal
is for best cycle 17 focus
• STIS slit focus should remain within typical ranges seen in the past since STIS
was originally optimized with OTA at comparable focus values.
Determining Overall Focus State
Presentation to HST Project
8 Jul 09
• Best fitting exponential:
• F = –6.16 + 201.64 e–t / 1754.4
• rms deviation 1.7 microns
• predicts -2.5 microns on August 1
SMOV STIS imageplane coarse check
SMOV ACS
• Best fitting straight line:
• rms deviation 1.8 microns
• predicts –3.4 microns on August 1
• Double exponential fitting lifetime focus data:
• rms deviation 2.7 microns
• predicts -1.5 microns on August 1
August 1
Notes: • All points from phase retrieval on ACS/HRC, ACS/WFC, WFPC2/PC, and STIS/CCD images.
•
•
•
•
•
Data has been model-corrected to reduce temperature- associated effects. (Reduces scatter from 2 to 1.7 mic 1 sigma)
Data plotted and fit from 2003. Two secondary mirror moves have been removed to present continuous curve.
Values expressed in microns at Sec. Mirror, relative to ACS/WFC best focus (Zero microns = ACS/WFC in focus)
1 micron at Secondary induces 6 nm of rms wavefront error ~1/90 wave (V-band) at focal plane.
Points are orbital means. Typical temperature-driven variations in OTA focus over orbits to days is usually ~5 microns +/–2
Presentation to HST Project
8 Jul 09
Observed Focus since last Secondary Mirror Move
All Observed Focus Data, since last OTA refocus (31 July 2006)
ACS/WF frame
Mean focus since last mirror move = –1.3 mic
(+/-1.8 microns 1 sigma)
SMOV STIS coarse
image plane check
ACS & STIS SMOV
measurements well
within range of
observed focus since
2006 mirror move.
Focus “as observed”.
No model correction
SMOV ACS
Presentation to HST Project
8 Jul 09
Long-Term Trend of the HST OTA
·Phase retrieval focus results from WF/PC,
WFPC2/PC, & ACS/HRC images since HST
launch culled together, averaged per visit and
put onto same frame (WFPC2/PC focus)
·Secondary mirror moves have been removed
to present continuous curve.
·Curve shown is a fit double exponential:
-5.04 + 56.26e–t/364.53 + 106.24e–t/2237.2
·RMS residuals 2.7 microns
·Asymptote of -5 mic
TIMELINE
175 (6/24) – ACS/WFC SMOV focus checked
180 (6/29) – STScI quantified plan for confocality & OTA focus setting
188-190 (7/7-7/9) – WFC3 UVIS & IR, & COS NUV fine alignment uplinks with focus offsets
200 (7/19) – Desired compensatory Secondary Mirror move
201 SMS – WFC3 PSF performance and specifications observations
201 SMS – Early Science enabled (50% of GO program)
215 (1st week August) – WFC3 Early Release Science
BACKUPS
Secondary Mirror Moves since SM1
Previous mirror move determination
Linear fit to all HRC visits since last refocusing:
–3.9µm ± 0.7
Linear fit to last 8 visits (all negative since mid-December ‘05):
–4.5µm ± 2.9
Averaging the last 8 visits (assumes a single OTA event):
–3.7µm ± 2.0
Mean of above methods:
–4.0µm
ACS/HRC Focus Measurements since last mirror move
8
7
6
5
STScI is requesting a sec.
mirror move of +5.3µm.
Gives:
+1.3µm ACS/HRC
–0.3µm ACS/WFC
Focus (in microns @ Secondary Mirror)
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
-12
Jan-05 Feb-05 Mar-05 Apr-05 May-05 Jun-05 Jul-05 Aug-05 Sep-05 Oct-05 Nov-05 Dec-05 Jan-06 Feb-06 Mar-06 Apr-06 May-06 Jun-06 Jul-06
Medium-Short-Term focus changes
Focus behavior over one week as predicted by the attitudebased model. Trends can be significantly larger than the orbital
variation (high frequency structure):
How we determine aberrations
STScI has used parametric phase retrieval (Krist 1995) to
characterize the HST PSF quite accurately (~1nm rms WFE!)
by iteratively fitting an observed PSF and expressing its
morphology in terms of a Zernike polynomial series (Mahajan
1991):
where αnZn is the normalized Zernike polynomials & c is the
solved-for coefficients representing rms wavefront error in
microns.
For n = 4 to 8, an Zn are given below:
a4Z4=
a5Z5=
a6Z6=
a7Z7=
a8Z8=
3.89(r2-0.55445)
2.31(r2cos(2θ))
2.31(r2sin(2θ))
8.33(r3-0.673796r)cosθ
8.33(r3-0.673796r)sinθ
focus
0º astigmatism
45º astigmatism
X coma
Y coma
For HST, focus c4 = 0.0061 • Sec. Mirror despace in microns
HST wavefront error budgets
rms WFE for HST OTA (excluding the half-wave spherical!) is
measured at ~15 nm, with majority (between 7 & 10 nm)
thought to be coming from the “clover” aberration (Z9 & Z10)
due to the PM supports, and most of the remainder due to the
zonal errors. That’s lambda/33 at 0.5 microns.
The rms WFE for HST+SIs is greater, measured around 26 nm
for HRC (Hartig) and between 50 & ~75 nm for WFPC2 (Krist
& Burrows).
So total combined system WFE for HST is somewhere
between lambda/20 & lambda/7 depending on the SI.
Orbital Focus Effect (“breathing”)
ACS/HRC Focus Measurements & Lightshield Breathing Model
0.0
Focus (in microns @ Secondary Mirror)
-0.5
-1.0
-1.5
-2.0
FWHM measured in HRC plotted
with breathing model (Sirianni)
-2.5
-3.0
HRC TGSMOV PSF Measurements & Breathing model
-3.5
2.5
-4.0
2.4
-4.5
-5.0
17.00
2.3
17.25
17.50
17.75
18.00
18.25
18.50
18.75
19.00
19.25
19.50
FWHM HRC pixels
Hours (Day 2005.142)
Focus from phase retrieval (blue)
and Bély “breathing” model
19.75
20.00
20.25
20.50
2.2
2.1
2.0
1.9
1.8
1.7
1.6
Breathing Model
FWHM measured
1.5
53611.6
53611.7
53611.8
MJD (29 August 2005)
53611.9
Presentation to HST Project
8 Jul 09
Focus Offset for STIS image plane (with OII filter)
STIS CCD to WFPC2 PC Focus Offset
15
STIS CCD visit mean
WFPC2 PC visit mean
Measured Focus in SM microns
10
5
0
-5
-10
-15
230
240
250
260
270
280
290
300
310
320
330
340
350
360
DOY 2000
·At PC best focus (0 microns @ Secondary):
·ACS/WFC = –1.0 to–1.7 microns.
Value to be refined prior to assessing ACS/WFC images ~10 June
·STIS OII filter+CCD = –7.2 microns +/–0.43
Determined from 5 visits using PC & STIS in parallel, top plot.
·STIS offset corroborated by straight line fit to 50 STIS visits between May 97 to Jan 04, compared to fit to PC data over
same time period (bottom plot). 7.2 micron offset best reproduced PC fit. STIS offset to PC assumed constant with time, but
slightly different slopes may indicate a trend.
1st focus
check in
SMOV
5/29
STIS focus check
(CCD)
STIS-11, 11386
STIS image quality acceptable
Image quality appears
degraded but STIS SMOV
activities can proceed
Image quality
too poor to
continue STIS
SMOV activities
Deferred
contingency pending
other SI results
STIS Optical
Alignment
Contingency
STIS-12
11387
Schedule Placement TBD
Decision Tree:
Details & Timeline
Assumes:
• May 12 launch
• NICMOS unavailable for external observations during SMOV
Note:
All boxes’ left sides align with approximate start time unless otherwise
noted. COS & WFC3 box lengths indicate approximate duration of
activity and analysis. All others activities are comparatively short.
5/30 (1st visit),
6/15 (2nd visit)
ACS/SBC image
quality verification
ACS-16, 11378
NGC6681, NGC604
Note: ACS CTE obs likely
to be moved forward by a
few days to immediately
follow BEA-end
(SBC PSF gives
only coarse
focus check)
6/27
ACS/HRC Image
Quality verification
ACS-17, 11379
NGC188
6/11 (1st visit)
6/27 (2nd
visit)
ACS/WFC
CTE Monitor
11510-03
6/21
ACS/WFC Image
Quality
verification
ACS-17, 11379
NGC188
ACS & STIS
image quality
acceptable
6/26
ACS/HRC&WFC
Geometric
Distortion
ACS-11, 11397
47 Tuc
ACS Image quality
unacceptable
STIS also unacceptable, and
WFC3 & COS mechanism
displacements all indicate
consistent
defocus magnitude and
N
direction?
Y
6/22
ACS CTE
Monitor
11510-04
47 Tuc
If focus as measured by STIS and ACS up
to and including this activity is acceptable
but indicating a consistent, significant
offset, then inform new SI alignments with
this delta to increase confocality
6/13 – 6/25
COS/NUV Optical Alignment
COS-09 parts 1 - 5, 11469
STIS Optical
Alignment
Contingency
STIS-12 11387
ACS Image quality
nominal but STIS’s is not.
STIS
focus
nominal?
Y
N
ACS Optical
Alignment
Contingency
ACS-13
11375
COS cannot focus within
OSM1’s desirable range
OTA Refocus
Contingency
Assessment
Schedule Placement TBD
6/14 – 6/21
WFC3/UVIS Initial Optical
Alignment
WF-11, 11424
6/15 – 6/21
WFC3/IR Initial Optical
Alignment
WF-12, 11425
6/26
COS/FUV
Optical Alignment
COS-26,11484
WFC3/UVIS cannot focus
within M1’s desirable range
6/22 – 6/29
WFC3/UVIS Fine Alignment
WF-21, 11434
WFC3/IR cannot focus within M2’s desirable range
6/28 – 7/4
WFC3/IR Fine Alignment
WF-22, 11435
CAL/OTA Cycle
17 Focus Monitor,
visit-01 initiates.
Uses ACS/HRC,
WFC3/UVIS, &
STIS/CCD
Assess
relative focii
of all SIs,
including
NICMOS,
and consider
OTA and/or
SI
adjustment
in early cycle
17 to
increase
confocality
and/or
better
position SI
mechanism(s
)
SI/OTA Focus Mechanism Settings
OTA Secondary Mirror(WFPC2/PC)
-30
-20
-4
-10
-3
0 mic
-2
10
-1
20
0 mm
30
1
2
ACS M1 +/-5.5, yellow regime ~5
-4
-3
-2
–0.4 mm
-1
0 mm
1
2
3
STIS CM1 +/-5, No yellow regime
-3
-2
-1
0 mm
1
2
3
-1
0 mm
1
2
3
-0.25
0 mm
0.25
0.5
0.75
COS OSM1 +/-7, yellow regime ~5
-3
-2
WFC3/UVIS M1 +/-10,
yellow regime ~3, red regime ~3.5 (vignetting)
-0.75
-0.5
WFC3/IR M2 +/-10,
yellow regime at 0.6, red regime 0.8 (aberrations)
1.8 mm
-1
0 mm
1
2
NICMOS/NIC1 PAM +/-9.5
-3
3
4
5
0.2 mm
-2
-1
0 mm
1
2
3
4
NICMOS/NIC2 PAM +/-9.5
-9
Note: Green range defined as approximate range over which image can be well optimized for science.
NICMOS/NIC3 PAM +/-9.5
-8