AttitudeObserverAnomaly
(AOA)on-orbittest10701
PreliminaryResults,16June2005
June2005TIPS,
M.Lallo&TelescopesBranch
TheAnomaly-Description
Since 2002 we’ve detected anomalously high gyro biases
- occur during terminator crossings
- magnitude of the bias has increased steadily
- 4 arcsec/hr after SM3B to a current -40 arcsec/hr
- predominantly seen in V3 translation
- event typically ~5-10 arcsec, beginning abruptly at day/night - night/day transition
This anomalous motion is usually only virtual, being inferred
by integrating the gyro data; once in Fine Lock, the field is
held fixed by the FGSs
However the worsening gyro bias has caused acq/reacq
failures in the past, and despite successful mitigation efforts, it
can eventually again impact the FGSs ability to acquire or reacquire guidestars.
AOA Working Group (GSFC, STScI, Goodrich) formed late
2004 to pursue this. http://edocs1.hst.nasa.gov/ota/Observer/Observer.htm
TheAnomaly-SomePossibilities
The RSUs are accurately recording a local motion (i.e.
equipment shelf movement with respect to the OTA and rest
of vehicle)
There is no motion local to the RSU and they are recording a
vehicle motion. Since there is no drift in science data this
would mean the OTA FOV is shifting and the FGSs are
driving the vehicle to hold the guidestars at fixed FGS XY
There is some problem in the control law involving both RSU
and FGS data
The RSU data is not correct for other reasons
TheTestObjectives
The test was to represent no risk to the vehicle (e.g. no cycling
RSUs)
Test was designed to determine the involvement of the OTA
structure in the AOA. It should answer the question of the
amount of anomalous motion attributable to the OTA
- obtained science data and measured off-axis PSF aberrations
- aberrations will be expressed in terms of Secondary Mirror
tilts & decenters
- magnitude and direction of image shifts resulting from the
calculated SM motions will be compared to the observed
motion, also directly quantified by the test.
TheTestDesign
Orbit 1 - Baseline and to establish known gyro bias
- FGS fine lock on previously used guidestars
- 100 TRANS mode scans with FGS1 on target star known to be single to FGS
(aberration info)
- 50 ACS/HRC custom sub-array exposures in parallel every 90 seconds. Target
known to be single to HRC (aberration and position info)
- 68 NICMOS/NIC1 multi-accum exposures in parallel every 30 seconds for
maximum time coverage (aberration and position info)
- 2 WFPC2/WF3 exposures at the end to better establish roll baseline
Orbit 2 - Measure position drift to directly observe AOA
- Drop to Gyro Track
- FGS POS mode astrometry (position info)
- 48 ACS/HRC exposures every 90 seconds (aberration and position info)
- 5 WFPC2/WF3 exposures to monitor relative roll changes
3
8
2
8.7
12.3
12.3
12.7
10.5
11.2
11.6
12.6
11.4
10.7
11.5
11.8
TheField
12.4
12.5
10.3
10.3
12.3
12.1
12.4
12.5
12.6
12.6
12.4
7.1
7.3
12.5
13.0
11.3
11.1
11.5
12.3
12.6
9.6
12.9
12.4
12.8
12.4
12.3
11.6
12.2
12.9
12.5
12.4
11.1
11.7
12.111.7
12.9
11.8
11.0
13.2
11.4
11.5
12.4
12.6
8.0
11.9
10.8
11.2
12.3 11.1
12.4
10.8
11.4
12.1
13.2
13.4
12.8
9.9
12.2
12.6
11.0
12.5
10.1
9.7
12.5
10.8
11.
14.1
13
11.9
11.9
12.3
12.8
12.8
12.69.3 13.3
14.2 13.4
12.4
13.0
10.8
11.1
8.1
8.9
11.2
13.0
1
12.5
13.4
11.7
11.5
13.9
11.9
12.0
12.6
12.2
12.5
12.1
11.5
12.7
11.9
11.9
12.6
11.5
11.2
12.5
8.8
11.2
19
14.0 7.0
12.4
13.2
13.6
12.7 12.1 11.9
12.4 10.7
12.6
14.0
13.9 12.4
11.9
12.3
12.7
13.
13.5
13.8
13.2
14.0
7.8
6.8 13.1
7.8
12.6
1
13.2
12.6
10.4
11.6
10.5
10.7
11.3
11.6
8.9
12.5
13.3
12.7
11.6
12.7
13.0
12.1
12.5
11.9
11.5
13.0
11.1
12.4
12.0
13.0
12.6
10.
11.1
9.8 11.0
6.2
10.6
12.7
11.5
12.4
12.4
8.9
12.7
10.9
12.0
11.4
9.8
9.7
11.0
10.7
12.4
9.9
9.4
12.1
11.0
7.8
7.7
8.4
8.5
11.5
10.8
10.9
11.3
12.2
11.9 10.4
12.2
10.8
12.612.4
12.8
10.9
10.1
12.5
8.0
8.8
13.9
13.3
12.5
13.5
11.9
11.412.7
11.9
12.1
11.7
13.4
7.5
6.8
7.4
12.3
8.813.3
10.8
11.4
10.4
13.9
12.1
11.6
11.0
12.3
7.9
8.210.9
9.5
9.5
12.6
9.6 10.3
11.0
11.112.8
12.9
12.3
12.7
12.0
12.6
12.9
13.0
9.3
12.5 11.4
11.1
11.5
11.4
11.2
12.3
13.0
12.9
12.1
12.3
12.6
11.3
10.0
9.6
11.3
11.3
9.2
8.8
9.2
11.1
9.5
9.4
9.8
12.6
12.8
10.4
12.7
9.3 12.8
9.4
10.6
MeasuredMotions
Observed Motion of Target in HRC during gyro-guiding Orbit 2
750
700
HRC Y pixels (0.025 arcsec/pix)
650
V3
600
-V2
550
500
450
400
350
350
400
450
500
550
600
HRC X pixels (0.028 arcsec/pix)
Movie courtesy E. Bergeron & M. Reinhart
650
700
750
MeasuredMotions
Observed Motion of Target in HRC & WFPC2/WF3 during gyro-guiding Orbit 2
5.0
arcseconds displacement
3.0
2.0
Day entry
Night entry
4.0
1.0
0.0
V2
V3
V2
V3
-1.0
from
from
from
from
HRC
HRC
WF3
WF3
-2.0
-3.0
-4.0
18.8
18.9
19.0
19.1
19.2
19.3
19.4
19.5
19.6
Day 142 hours
19.7
19.8
19.9
20.0
20.1
20.2
MeasuredZernikes-Focus
ACS/HRC ACS/HRC
AOA Test: Focus
Measurements
& Lightshield Breathing Model
AOA Test:
Focus Measurements
0.00
0.00
0.00
Focus
Focus (in
(in microns
microns @
@ Secondary
Secondary Mirror)
Mirror)
Focus (in microns @ Secondary Mirror)
-1.00
-1.50
-2.00
-2.50
-0.50
-0.50
Day entry
-0.50
ACS/HRC AOA Test: Focus Measurements & Lightshield Breathing Model
-1.00
-1.00
-1.50
-1.50
-2.00
-2.00
-2.50
-2.50
-3.00
-3.00
-3.00
-3.50
-3.50
-3.50
-4.00
-4.00
-4.00
-4.50
-4.50
-4.50 AOA
-5.00
-5.00
-5.00
0.00
AOA
Test 1)
(Orbit 1)
Test
(Orbit
AOA
Test (Orbit
1)
AOA
Test
(Orbit
2)
AOA Test (Orbit 2)
AOA Test (Orbit 2)
Breathing
Breathing
Model Model
17.00 0.10
17.25
17.25
17.00
17.50
17.75 0.30
18.00
0.20 17.75
17.50
18.00
18.25
18.50 0.50
18.75
0.40 18.50
18.25
18.75
19.00
19.25 0.7019.50
0.60 19.25
19.00
19.50
Orbital Phase
( 0(Day
= night
entry)
Hours
2005.142)
Hours (Day 2005.142)
19.75
20.00 0.9020.25
0.80 20.00
19.75
20.25
20.50
1.00
20.50
MeasuredZernikes-Aberrations
ACS/HRC AOA Test: Y-Coma v. Time
0.003
-0.001
0.002
-0.002
0.001
-0.003
0.000
-0.004
-0.001
Y-Coma
X-Coma
ACS/HRC AOA Test: X-Coma v. Time
0.000
-0.005
-0.002
-0.006
-0.003
-0.007
-0.004
-0.005
-0.008
-0.009
-0.010
17.00
AOA Test (Orbit 1)
AOA Test (Orbit 2)
17.25
17.50
17.75
AOA Test (Orbit 1)
AOA Test (Orbit 2)
-0.006
18.00
18.25
18.50
18.75
19.00
19.25
19.50
19.75
20.00
20.25
-0.007
17.00
20.50
17.25
17.50
17.75
18.00
18.25
0.012
0.011
0.011
0.010
0.010
0.009
0.009
0.008
0.008
0.007
0.007
0.006
0.006
0.005
0.005
0.004
0.003
0.002
0.001
19.25
19.50
19.75
20.00
20.25
20.50
19.50
19.75
20.00
20.25
20.50
AOA Test (Orbit 1)
AOA Test (Orbit 2)
0.004
0.003
0.002
0.001
0.000
0.000
-0.001
-0.001
-0.002
-0.002
-0.003
AOA Test (Orbit 1)
AOA Test (Orbit 2)
-0.004
-0.005
-0.006
17.00
19.00
ACS/HRC AOA Test: Y-Astigmatism v. Time
Y-Astigmatism
X-Astigmatism
ACS/HRC AOA Test: X-Astigmatism v. Time
0.012
-0.004
18.75
Hours (Day 2005.142)
Hours (Day 2005.142)
-0.003
18.50
-0.005
17.25
17.50
17.75
18.00
18.25
18.50
18.75
19.00
Hours (Day 2005.142)
19.25
19.50
19.75
20.00
20.25
20.50
-0.006
17.00
17.25
17.50
17.75
18.00
18.25
18.50
18.75
19.00
Hours (Day 2005.142)
19.25
MeasuredZernikes-Aberrationswithphase
ACS/HRC AOA Test: Y-Coma v. Orbital Phase
Day entry
0.003
0.002
0.001
-0.001
-0.002
-0.003
-0.004
-0.005
AOA Test (Orbit 1)
AOA Test (Orbit 2)
-0.006
ACS/HRC AOA Test: 0o Astigmatism v. Orbital Phase
0.012
0.20
0.30
0.40
0.50
0.60
0.70
0.011
0.80
Orbital Phase (0 = night entry)
0.90
1.00
0.010
0.009
0.008
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0.000
-0.001
-0.002
-0.003
-0.004
-0.005
AOA Test (Orbit 1)
AOA Test (Orbit 2)
0.012
0.011
0.01
0.009
-0.006
0.00
0.008
0.007
0.10
0.20
0.30
0.40
0.50
0.60
Orbital Phase (0 = night entry)
0.70
0.80
0.90
1.00
0.006
./!+,0123,0+2
0.10
Day entry
-0.007
0.00
0o-Astigmatism (in microns)
Y-Coma (in microns)
0.000
0.005
0.004
0.003
0.002
0.001
0
-0.001
-0.002
-0.003
-0.004
-0.005
-0.006
-0.022
-0.023
-0.024
-0.025
UpcomingWork
Optical modeling will back out Secondary Mirror movements
like tilt and decenter needed to produce the observed coma
and astigmatism at the off-axis ACS/HRC (and secondarily, at
NICMOS/NIC1). From these tilts and decenters over time,
the resulting image motion will be derived and compared with
observed to tell us the OTA’s role in the anomaly
FHST maps (also taken throughout the test) are being
processed for maximum spatial resolution and can provide
additional information. They are mounted to the same local
shelf as the RSUs
More reporting to come
0.012
0.011
0.01
0.009
0.008
0.007
./!+,0123,0+2
0.006
0.005
0.004
0.003
0.002
0.001
0
-0.001
-0.002
-0.003
-0.004
-0.005
-0.006
-0.022
-0.023
-0.024
-0.025