SPACE TELESCOPE SCIENCE INSTITUTE
TIPS
18 April 2002
Russell Makidon
Monitoring HST Focus in Y2002
• Last Secondary Mirror Move on 2000.197 (+3.5 µm); previous secondary mirror move on 2000.009 (+4.2 µm)
• WFPC2 program 8829 (PI: Gilliland) enacted in late June 2000 to monitor
HST focus at monthly intervals, supplementing existing WFPC2 focus checks.
– 14 orbit program with STIS images obtained in OII and OIII filters in parallel with
some WFCP2 observations.
– program completed in July 2001 with no significant focus excursions noted.
• WFPC2 program 9258 (PI: Gilliland) enabled in July 2001 to continue focus
monitoring started with 8829.
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TIPS
SPACE TELESCOPE SCIENCE INSTITUTE
18 April 2002
Russell Makidon
(no breathing correction applied)
focus
in microns @@
secondary
Focus in
microns
Secondary
Focus Measurements Since Last Mirror Move (2000.197)
(no breathing correction)
SM3b
WFPC2 9258 Focus
WFPC2 8829 Focus
460
440
420
400
380
360
340
320
300
280
260
240
220
200
180
DOY 2001
160
140
120
100
80
60
40
20
0
-20
-40
-60
-80
-100
-120
-140
-160
-180
-200
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
-12
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TIPS
SPACE TELESCOPE SCIENCE INSTITUTE
18 April 2002
Russell Makidon
focus
in microns @@
secondary
Focus
in
microns
Secondary
(breathing corrected unless otherwise noted)
Focus Measurements Since Last Mirror Move (2000.197)
(breathing correction applied)
SM3b
WFPC2 9258 Focus
WFPC2 8829 Focus
460
440
420
400
380
360
340
320
300
280
260
240
220
200
180
DOY 2001
160
140
120
100
80
60
40
20
0
-20
-40
-60
-80
-100
-120
-140
-160
-180
-200
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
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-10
-11
-12
SPACE TELESCOPE SCIENCE INSTITUTE
TIPS
18 April 2002
Russell Makidon
Monitoring HST Focus in Y2002
• No apparent trending with HST focus through from 2000.197 through SM3b.
– The few excursions from ‘nominal’ focus during this period can be explained by
breathing-induced variations.
• During periods of larger than normal temperature variations in OTA, the
breathing model tends to underestimate the extent of focus excursions.
– Observations noted as part of programs 8829 and 9258 with observed focus variations within an orbit as large as 10 µm!
– Breathing-induced focus excursions might be a concern for ACS HRC
observations...
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SPACE TELESCOPE SCIENCE INSTITUTE
TIPS
18 April 2002
Russell Makidon
Monitoring HST Focus in Y2002
• Post-SM3b Observations showed variability in focus measurements not unlike
those experienced in programs 8829 and 9258
– long periods of atypical HST pointing attitudes led to large excursions of HST focus
from nominal.
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SPACE TELESCOPE SCIENCE INSTITUTE
6
TIPS
18 April 2002
Russell Makidon
Focus Measurements Since Last Mirror Move (2000.197)
(data since SM3b, no breathing correction)
8
7
6
5
4
focus in microns @ secondary
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
WFPC2 9258 Focus
WFPC2 9574 Focus
-10
-11
-12
459
458
457
456
455
454
453
452
451
450
449
448
447
DOY 2001
SPACE TELESCOPE SCIENCE INSTITUTE
7
TIPS
18 April 2002
Russell Makidon
Focus Measurements Since Last Mirror Move (2000.197)
(data since SM3b, breathing correction applied)
8
7
6
5
4
focus in microns @ secondary
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
WFPC2 9258 Focus
WFPC2 9574 Focus
-10
-11
-12
459
458
457
456
455
454
453
452
451
450
449
448
447
DOY 2001
SPACE TELESCOPE SCIENCE INSTITUTE
TIPS
18 April 2002
Russell Makidon
Monitoring HST Focus in Y2002
• Current Status: Nominal
– Little to suggest a secondary mirror move is warranted at this time
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SPACE TELESCOPE SCIENCE INSTITUTE
TIPS
18 April 2002
Russell Makidon
Monitoring HST Focus in Y2002
• ACS HRC and WFC now confocal with WFPC2 (PC1)
• Upcoming Events:
– Eleventh set of WFPC2 9258 observations scheduled for period between
29 Apr 2002 (2002.119) and 05 May 2002 (2002.125).
• To be considered...
– Field Dependence of focus over ACS WFC and HRC
– Should secondary position be biased (on ACS) to better center focus distribution
function to zero?
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SPACE TELESCOPE SCIENCE INSTITUTE
TIPS
18 April 2002
Russell Makidon
Oh, the places we’ve come...
HST focus trend over mission life
Notable focus-related events in
HST Mission Lifetime
150
1
1. First WF/PC Focus Monitoring
100
2. First SM and start of WFPC2 focus
monitoring
3. Breathing Model Enabled
2
50
4. Second Servicing Mission
3
4
5. Servicing Mission 3a
5
6
0
-1000
0
1000
Days since Jan 1, 1994
2000
3000
6. Servicing Mission 3b
Figure courtesy of Matt Lallo
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