1
Instrument Science Report OSG-FGS-97-06
SMOV-2 CLOSURE REVIEW
Observatory Verication Procedures
O. Lupie, E. Nelan, and L. Nagel - Oct. 1997
Abstract: This memo addresses 1)the status of the requirements (SMO-1000) which fall under the
headings of F.2.5.7: Optical Telescope Assembly/Fine Guidance Sensor Verication and F.2.5.8:
Pointing Control Sub-System Verication, 2) lessons learned from the SMOV-2 FGS activities, and
3) the suggestions and actions from the SMOV-2 Closure Review Meeting at GSFC, 10/30/97.
Acknowledgements: The FGS SMOV program was smoothly and successfully implemented because
of the eorts of many people: the HDOS FGS team, S. Holfeltz, V. Balzano, J. Hershey, R. Doxsey,
M. Reinhart, G. Chapman, DC. Taylor, C. Cox, M. Lallo (STScI). and E. Kimmer, M. Wenz, C.
Connor, T. Cruz, G. Welter, L. Hallock (GSFC), and the STAT team. With many thanks.
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Index
List of SMOV Requirements.............................3
SMOV-2 Lessons Learned..................................4
F.2.5.7 OTA/FGS Verication...........................5
F.2.5.7.2 FGS Restoration Activities..................5
F.2.5.7.3 FGS Calibration................................16
F.2.5.8. Pointing Control System Verication....23
Actions from SMOV-2 Closure Review.............27
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SMOV-2 CLOSURE REVIEW
Observatory Verication Procedures
O. Lupie, E. Nelan, and L. Nagel - Oct. 1997
Abstract: This memo addresses 1)the status of the requirements (SMO-1000) which fall under the
headings of F.2.5.7: Optical Telescope Assembly/Fine Guidance Sensor Verication and F.2.5.8:
Pointing Control Sub-System Verication, 2) lessons learned from the SMOV-2 FGS activities, and
3) the suggestions and actions from the SMOV-2 Closure Review Meeting at GSFC, 10/30/97.
Acknowledgements: The FGS SMOV program was smoothly and successfully implemented because
of the eorts of many people: the HDOS FGS team, S. Holfeltz, V. Balzano, J. Hershey, R. Doxsey,
M. Reinhart, G. Chapman, DC. Taylor, C. Cox, M. Lallo (STScI). and E. Kimmer, M. Wenz, C.
Connor, T. Cruz, G. Welter, L. Hallock (GSFC), and the STAT team. With many thanks.
F.2.5.7.2 FGS Restoration Activities:
{ F.2.5.7.2.1 Optimization of the FGS1R FF3
{ F.2.5.7.2.2 Trend Analysis and Desorption Monitoring of FGS1R
{ F.2.5.7.2.3 Alignment and Obscuration Denition for FGS1R
F.2.5.7.3 FGS Calibration:
{ F.2.5.7.3.1 Optical Field Angle Distortion Calibration (all 3 FGSs)
{ F.2.5.7.3.2 FGS/FGS Alignment
{ F.2.5.7.3.3 FGS1R Alignment Stability
{ F.2.5.7.3.4 Operational PMT Calibration for FGS1R
{ F.2.5.7.3.5 Dark Count Verication for FGS1R
F.2.5.8.1 Determination of initial HST attitude
F.2.5.8.2 Calibration of the gyro drift bias
F.2.5.8.3 FHST to FGS Alignment
F.2.5.8.4 Gyro/FHST Alignment
F.2.5.8.5 Verication that all FGSs can acquire Guide Stars in Fine Lock
F.2.5.8.6 Measurement of the vehicle jitter during FGS Fine Lock
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SMOV-2 Lessons Learned
The following lessons were learned from the experiences during the FGS SMOV activities:
In order to preclude a situation where a decision must be made over a short time scale which
is governed by an impending SMS creation, we recommend, at the expense of a few extra
orbits, a more robust SMOV proposal in the following areas:
{ The Mini-OFAD for the replacement FGS should include POS mode observations in both
F583W and Pupil. The 5 extra orbits are justied on two grounds: (1) the data will be
extremely useful for cross calibration of the two lters and (2) any decision about which
lter to use for standard guiding can be made after the completion of the Mini-OFAD
rather than prior to it.
{ The FF3 Optimization test should include an additional optional mirror move and always
include S-Curves in both lters at all positions.
Require the OTA and all relevant subsystems remain unchanged during the course of an
extended test such as the FF3 optimization test. Although a small OTA secondary mirror
move (which occurred between visits of Proposal 7026) was predicted to have no impact on
the FGS1R S-Curves, it did introduce confusion and an additional variable into the analysis
of a small glitch seen in the 7026 data during the same period.
An heptathlon test should be run as part of SMOV. It should immediately follow the uplink of
the FGS/FGS alignment and OFAD calibration parameters (if a replacement FGS is inserted
into the HST).
For each replacement FGS test, the relevant K parameters and thresholds should be listed in
the proposal and the values of these parameters should be made available to scheduling and
commanding prior to SMS generation stage for that proposal.
During the SMOV Implementation stages, the proposals should be pre-processed for guide
star pairs in advance of the SMS generation stage, to insure that specic guide star pairs
are available. In most FGS-related tests, the guide stars are hand-selected from astrometric
catalogues.
We recommend some re-wording and additions to the The SMO-1000 FGS requirements to
better describe the calibration activities.
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F.2.5.7 OTA/FGS Verication
F.2.5.7.2 FGS S-Curve Resoration
INSTRUMENT OR SUBSYSTEM: FGS
REQUIREMENT: F.2.5.7.2.1 The pupil centering with respect to the face of the Koester's
prism shall be accomplished by articulating FGS fold at 3 (FF3). The modulation of the X and
Y S-curves shall be optimized at a particular eld location that is chosen to produce an acceptable
set of S-curves over the entire FGS FOV. Performance at the selected eld location shall be deemed
adequate if the S-curve modulation in each axis is within 10% of the maximum value expected.
RELEVANT SMOV PROPOSALS:
1. Title: FF3 In-bay Functional Test
PI: L. Abramowicz-Reed and K. Chisolm (Hughes Danbury Optical Systems).
Test Date: 1997.047
Relevance: Proved that the folding at 3 moves on command and its position can be determined.
2. Title: Prop 7026 - Fold Flat 3 (FF3) Position Optimization for FGS1R
PI: J. Esper (GSFC), L. Abramowicz-Reed (HDOS), O. Lupie (STScI).
Test Date: 1997.062 - 1997.083.
Relevance: The test obtained the S-Curve data as a function of FF3 position.
DESCRIPTION OF METHODS:
In-bay Functional Test: The goal of the test was to demonstrate the successful operation of the
FF3 articulating mirror and its electronics. The test included a synchronization sequence, a move
of the FF3 that resulted in a clearly detectable change to the decenter of the pupil and return to
the original position. The change in the ITS location was used to verify the FF3 motion. The
details of the Functional are described in HDOS TE A16-018.
FF3 Optimization Proposal 7026: The amplitude and morphology of the Interference Transfer
Function, the S-curve, were used to monitor the decenter of the pupil falling on the Koester's prism
as a function of the position of the Articulating Folding Flat (FF3). The S-Curves were obtained
using the DF224 ight software 52 command. The FF3 optimization test required a unique visit
to the same target, a 9.8 magnitude single star, for each set of mirror moves. The visits were
scheduled such that time was allocated for data processing and analyses and for updating relevant
calibration parameters prior to the next mirror move. The analysis performed by HDOS consisted
of cross correlating the on-orbit S-Curves with a database of S-curves obtained on the ground over
a ne grid of mirror positions.
A single reference star was observed in TRANS mode using lters F583W and 2/3 aperture (Pupil).
Proposal 7026 and its requirements, dependencies, and contingencies are described in ISR-FGS-34.
Prior to several visits, the FF3 was commanded, via real-time PSTOL procedures, to a position
6
derived from the results of the previous visit. The initial visits placed the target near the SSTS
(ground-based test position near the center of the pickle) position and subsequent visits placed the
target at multiple locations throughout the pickle to sample the eld dependence of the S-Curve.
The dates and modes are listed in Table 7026 1. The objectives of the test were three-fold:
1. to optimize the S-Curve at one location in the pickle so that both X and Y signals are within
10% of the pre-launch modulation,
2. to optimize the S-Curve across the eld of view,
3. to determine the operational K factors for FGS1R so that commissioning of the FGS as a
guider could be achieved as soon as possible.
DESCRIPTION OF RESULTS:
In-Bay FF3 Functional Test Results: The commands issued to the FF3 were successful and
the mirror moved as predicted. A +0.2mm pupil motion in X required a forward 32 pulses on motors 1 and 2. The change in the ITS position was similar to but not exactly the same as the results
from the pre-launch VEST tests in 1996. The small discrepancy, 0.1 arcsec, was attributed to
mechanism repeatability but is well within the expected tolerances.
FF3 Optimization Test Results: The peak-to-peak amplitudes of the S-Curves after each mirror
move and the visit information are given in the Table 7026 1.
1. The rst in-orbit S-Curves obtained on day 062 were signicantly degraded with respect
to the ground measurements proving that launch trauma and gravity release does alter the
alignment of the pupil on the Koester's prism and most clearly demonstrates the usefulness
of an articulating folding at adjustment. The day 1997.062 modulation in X and Y were 1.1
and 0.43 respectively compared to the day 1996.313 ground results, 1.25 and 1.30 in X and Y
respectively. The Y axis pupil therefore moved about -1.0mm and the X pupil about -0.1mm.
2. The X and Y S-Curves were optimized at the center of the pickle to yield a symmetric S-Curve
in both axes in the clear lter F583W with peak-to-peak amplitudes of 1.21 and 1.22 in X
and Y respectively. The sum of all mirror moves yielded a net motion of 0 mm in X and 1.3
mm in Y (note some crosstalk exists betweeen the two axes). The modulation results met
the goal of 10% of the pre-launch ground-based optimized modulations in X and Y (ground
measurements on day 1996.313 were 1.25 and 1.30 in X and Y respectively). The S-Curves
at pickle center obtained on day 083 are shown in the center panels of Figure 1.
3. The S-Curve morphology and amplitude in the F583W lter were discovered to be eld
dependent, a result of small misalignments between the Koester's prism and the star selector
optics. The X-axis displays a decenter which changes sign from one side of the pickle to the
other, making it necessary to nd a compromise position for the FF3. The X-axis decenter
varies from -0.45 mm to +0.35mm across the FOV. The Y axis eld dependence is much
less pronounced. The spatial dependence of the S-Curves in lter F583W is displayed in
Figure 1 where each panel represents a dierent location in the pickle.
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4. The morphology of the S-Curves obtained the 2/3 aperture (Pupil) is nearly perfect across
the entire Field of View (FOV).
5. The selected setting of the FF3 provides an optimized S-Curve at pickle center and also
maximizes the quality of the the S-Curve in the clear F583W lter across the entire pickle.
Monte Carlo simulations of the Fine Guidance Electronics and Fine Lock walkdown were
performed by HDOS (L. Abramowicz-Reed) in order to obtain optimum K factor calibrations.
For the F583W lter and a star of V=14.5, a 99% probablity for acquisition was found for
all tested locations (5 points) in the pickle with the exception of the X axis at the end of the
pickle (X=-400 arcsec) where a 96% probability was found. For the 2/3 aperture (Pupil), the
probablitiy of successful acquisition of a 14.5 magnitude star is 99% across the pickle.
6. As a result of 1) the eld dependence (particularly at the X=-400 asec position in the pickle),
2) a concern about desorption impacting the performance, and 3) a desire to begin using
the FGS1R as a guider, the decision was made to begin standard operations using the 2/3
aperture (Pupil) where the eld dependence of the S-Curves is negligible and the morphology
is nearly perfect. We note that the operational calibration parameters (the K Factors) used
for guiding are not expressed as eld dependent variables in the ight software.
7. The data from the 2 visits, where the FF3 was not moved, conrmed stability and repeatability
of the S-Curve and the ITS measurement conrmed that the FF3 remained stationary.
8. HDOS derived the calibration parameters (K factors) needed to optimize the Fine Lock
Acquisition and Tracking in the FGS1R Pupil aperture. The relevant K factors K1, K3 (both
a function of star brightness) , KZ, KB, and KD were are specied in HDOS TE A16-0183.
The FGS1R was commissioned in May 1997 and is performing as predicted. Renements to
the K factors have been delivered by STScI and HDOS and will be operational in late fall
1997.
8
Table 7026 1 Prop 7026 Visit Schedule
Day FF3 (mm) Mode
X Pk Y Pk
062
0,0
Comments
Trans: Pupil, F583W 1.0
0.4
establish baseline
star near SSTS
069 0,0
Trans: Pupil, F583W 1.0
0.4
stability, repeatability
star near SSTS
070 +0.1, +1.0 Trans: F583W
1.1
1.0
verify improvement,
5-pts across FGS
spatial dependence in X
076 -0.1, +0.2 Trans: F583W
1.2
1.0
optimize X at ends
5-pts across FGS
079 0.0, +0.1
Trans: F583W
1.1
1.2
optimize Y at center
5-pts across FGS
083 0.0, +0.1
Trans: Pupil, F583W 1.1
1.2
radial modulation,
9-pts across FGS
and K factor computation
An ITS measurement was obtained during each visit to track the overall FGS alignment as a function of
FF3 position.
The results and data analyses techniques are described in detail in the HDOS Document TE A160183: "Results of Initial On-Orbit Testing of FGS1R", July 1997, L. Abramowicz-Reed.
Problems/Anomalies: A 0.04 mm change in pupil decenter was noted in the X-axis S-curve
when no FF3 mirror motion was commanded. The ITS did not move which veried that the articulating mirror assesmbly itself was stable. Although a small commanded motion of the OTA
secondary mirror occurred during this time, its aect was ruled out as the cause of the anomaly.
The small change was probably a result of a desorption-related motion.
REQUIREMENT STATUS: SATISFIED
SUPPORTING DOCUMENTATION:
1. HDOS Document TE A16-0183: "Results of Initial On-Orbit Testing of FGS1R", July 1997,
L. Abramowicz-Reed.
2. HDOS Document A16-ST-1192: "AMA Mirror Moves", March 1997, U. Ravoory.
3. STScI ISR-FGS-034, "FGS SMOV Tests and Implementation Plans", December, 1996, O.
Lupie, S. Holfeltz, and L. Nagel.
4. STScI 1997 HST Calibration Workshop, "FGS1RL Potentially HST's Atsrometry Science
Workhorse," September 1997, O. Lupie, E. Nelan, and L. Nagel.
5. STScI ISR-OSG-FGS-97-04 SMOV-2 FGS1R Optimization Summary E. Nelan, O. Lupie, L.
Nagel, S. Holfeltz (STScI), L. Reed and K. Chisolm (HDOS), in preparation.
9
INSTRUMENT OR SUBSYSTEM: FGS
REQUIREMENT: F.2.5.7.2.2 A test to determine whether the optimal orientation of FF3 is
aected by desorption shall be performed two to six months after the baseline alignment of FF3 is
completed. It will consist of obtaining an S-curve near the FGS FOV location used for the baseline alignment. No reorientation of FF3 shall be attempted unless S-curve modulation in the Xor Y-axis has declined to a value that is less than 10value expected (See F.2.5.7.2.1 and F.2.5.7.3.3).
RELEVANT SMOV PROPOSALS:
Title: Prop 7027 - Near Term Stability Monitor for FGS1R
PI: O. Lupie (STScI), J. Esper (GSFC), E. Nelan (STScI).
Test Date: Visits 3,4 1997.122, Visits 1,2 1997.136
Relevance: Baseline measurements of the S-Curve and ITS position were obtained several weeks
after the 7026 test to study desorption eects. In addition, repeated measurements of the S-Curve
over the course of an orbit and from orbit to orbit were made to study short-term stability.
DESCRIPTION OF METHODS:
The test included 4 kinds of observations:
POS and TRANS mode data (Visits 3,4) on a eld in the astrometric cluster M35 repeated
over an orbit (established a baseline LTSTAB for POS mode as well as sampling changes
during an orbital cycle),
S-Curve data in F583W and Pupil lters on the 7026 (FF3 optimization test) target to study
changes due to desorption,
S-Curve data (Visit 2) on the standard star Upgren (to establish a baseline since it will be
used for monitoring throughout the cycle), and
a ne lock ITS acquisition to trend its position.
DESCRIPTION OF RESULTS:
1. Modulation and morphology changes were seen in the S-Curves in lter F583W between day
083 (7026 test) and day 122. The Y axis S-Curve showed a change of approximately -0.18 mm
in decenter which is consistent (i.e., same direction) with ground-to-orbit decenter deltas and
with those seen during thermal vac testing. The peak-to-peak amplitude in Y varied from 1.22
(day 083) to 1.09 (day 122). The X-axis S-Curve was less aected. The S-Curve evolution
is displayed in Figure 2 where the change in modulation is shown in the upper panel and
corresponding decenter in the lower panel. This trend is consistent with the interpretation
that the internal alignment of the pupil with respect to the Koester's prism bond line is
changing as a result of desorption.
2. The S-Curves obtained over the course of an orbit and from one orbit to the next showed no
changes in the morphology or modulation of either S-Curve to the accuracy of the photon
noise.
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Figure 1: The day 083 optimized X and Y S-Curves (upper and lower panels) as a function of
position across the FGS1R pickle. This gure demonstrates the S-Curve eld dependence.
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Figure 2: The upper panel contains measurements of the peak-to-peak amplitude of the S-Curves
as a function of day number. The lower panel is the corresponding decenter of the beam on the
face of the Koesters prism, modelled by HDOS. The Decenter can be modelled to 0.01 mm. The
data was provided by L. Reed and K. Chisolm, HDOS).
3. The POS mode data on M35 will be compared to a repeated measurement of the same eld
next spring to study POS mode stability and repeatability. This data set serves as a baseline.
4. The S-Curves obtained with the Pupil aperture experienced negligible modulation and morphology changes.
Further Note:
Monitoring of the FGS1R S-Curves using Upgren69 has continued via a cycle 7 program (Prop
7597 - Cycle 7 Long Term Stability of Transfer Scan Mode in FGS1R, PI: O. Lupie, E. Nelan, L.
Nagel). The visits are repeated at least 7 times from July 1997 through Jan 1999. The S-Curves
have shown a continuous trend since the 7026 test through day 1997.262. However, the changes
appear to be slowing down since day 1997.205.
The FGS1R S-Curves from day 1997.083 through day 1997.262 are shown in Figures 3 and 4. For
comparison with a relatively stable instrument, the FGS3 S-Curves obtained on 3 dierent dates
are shown in Figure 5. Once the FGS1R has stabilized, the FF3 mirror can be positioned to reoptimize the S-Curves.
12
Figure 3: The X and Y FGS1R S-Curves from days 1997 083, 136, and 205. Large changes in the
morphology of the S-Curve are evident.
REQUIREMENT STATUS: SATISFIED
SUPPORTING DOCUMENTATION:
1. HDOS Document TE A16-0183: "Results of Initial On-Orbit Testing of FGS1R", July 1997,
L. Abramowicz-Reed.
2. STScI ISR-FGS-034, "FGS SMOV Tests and Implementation Plans", December, 1996, O.
Lupie, S. Holfeltz, and L. Nagel.
3. STScI 1997 HST Calibration Workshop, "FGS1R Potentially HST's Astrometry Science
Workhorse," September 1997, O. Lupie, E. Nelan, and L. Nagel.
4. STScI ISR-OSG-FGS-97-04 SMOV-2 FGS1R Optimization Summary E. Nelan, O. Lupie, L.
Nagel, S. Holfeltz (STScI), L. Reed and K. Chisolm (HDOS), in preparation.
5. Instrument Science Report: OSG-FGS-97-03 SMOV-2 FGS1R Near Term Stability Results,
E. Nelan, O. Lupie, L. Nagel (STScI), L. Reed and K. Chisolm (HDOS).
13
Figure 4: The X and Y FGS1R S-Curves from days 1997 205,222, and 262. The S-Curves appear
to be stabilizing.
Figure 5: For comparison, the X and Y FGS3 S-Curves from days 1997 205, 217, and 262 are shown
to demonstrate stability.
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INSTRUMENT OR SUBSYSTEM: FGS
REQUIREMENT: F.2.5.7.2.3 After the orientation of FF3 has been optimized the position of
the Internal Test Source (ITS) shall be measured. This result together with a prediction of the
Optical Control Subsystem (OCS) obscuration zone shall be used to update PDB cone 5, which
describes the FOV avoidance zone about the OCS center where guide stars can neither be acquired
nor moved.
RELEVANT SMOV PROPOSALS:
1. Title: Prop 7025 FGS/FGS Alignment POST-SM2 Calibration
PI: B. Chapman, E. Kimmer, G. Welter (GSFC), O. Lupie (STScI).
Test Date: 1997.112.
Relevance: The test acquired data to calculate the FGS/FGS alignment matrices and to
derive the FOV reference position and pickle boundaries used by the guide star selection
system and stored in the PDB SCHF.DAT and SIAF.DAT les.
2. Title: Prop 7027 - Near Term Stability Monitor for FGS1R PI: O. Lupie (STScI), J. Esper
(GSFC), E. Nelan (STScI).
Test Date: Visit 4 1997.122 for ITS measurement.
Relevance: An ITS measurement was obtained about one month after the end of the FF3
optimization test (7026) to verify the stability of the alignment.
DESCRIPTION OF METHODS:
Prop 7025 FGS/FGS Alignment Test: Data were obtained on an astrometric eld NGC5617,
using FGSs 2 and 3 in guidance mode and FGS1R as the astrometer. For each sweep across the
FGS1R pickle a dierent pair of astrometric guide stars were used in the guiding FGSs. From
these data, a relative alignment was calculated for the 3 FGSs and the obscuration zones and pickle
boundaries were dened.
Prop 7027 Near Term Stability Test: One of the several test goals was the acquisition of the
ITS in ne lock to verify the alignment stability since the nal FF3 adjustment.
DESCRIPTION OF RESULTS:
The ITS measurement from test 7027 showed no positional shifts implying that the FF3 was stable
and that desorption shifts aected the alignment between internal optics and the Koesters prism.
The following FGS1R calibration parameters were extracted from the 7025 FGS/FGS alignment
data: TVS Matrix (PDB SCHF.DAT), reference position and eld of view descriptors (SCIOPSDB
SIAF.DAT), OCS (obscuration) zones (SCIOPSDB SIAF.DAT) and pickle boundaries for use by
the Guide Star Selection System. The change in the alignment of FGS3 is 900 mas from the
current operational calibration.
REQUIREMENT STATUS: SATISFIED.
15
SUPPORTING DOCUMENTATION:
1. SMOV-2 Requirements Closure Review, Oct 30. 1997 at GSFC, presentation by E. Kimmer
on FGS Alignment.
2. SMOV-2 FGS Calibrations Memo by E. Kimmer, C. Luu, and G. Welter, April 24, 1997 and
presentation April 29, 1997.
3. STScI ISR-FGS-034, "FGS SMOV Tests and Implementation Plans", December, 1996, O.
Lupie, S. Holfeltz, and L. Nagel.
4. Instrument Science Report: OSG-FGS-97-05 SMOV-2 PCS Calibration Results: FGS/FGS
Alignment and Mini-Ofads O. Lupie, E. Nelan, L. Nagel (STScI), E. Kimmer and G. Welter
(GSFC), in preparation.
5. Instrument Science Report: OSG-FGS-97-03 SMOV-2 FGS1R Near Term Stability Results,
E. Nelan, O. Lupie, L. Nagel (STScI), L. Reed and K. Chisolm (HDOS), in preparation.
16
F.2.5.7.3 FGS Calibration
INSTRUMENT OR SUBSYSTEM: FGS
REQUIREMENT: F.2.5.7.3.1 Mini-OFAD/Plate Scale calibrations shall be exe-cuted in all
three FGSs. Database updates incorporating the new calibrations shall be made.
RELEVANT SMOV PROPOSALS:
1. Title: Prop 7001 FGS1 Delta Mini OFAD Post-SM2 Calibration
PI: A. Bradley, E. Kimmer, G. Welter (GSFC), E. Nelan, O. Lupie (STScI)
Test Date: 1997.111
Relevance: The test was designed to determine the the operational calibration of the optical
eld angle distortions in FGS1R.
2. Title: Prop 7023 FGS2 Delta Mini OFAD Post-SM2 Calibration
PI: Same as above.
Test Date: Same as above.
Relevance: Same as above but for FGS2.
3. Title: Prop 7024 FGS3 Delta Mini OFAD Post-SM2 Calibration
PI: Same as above.
Test Date: Same as above.
Relevance: Same as above but for FGS3.
See the presentation of Requirement F.2.5.7.3.1 by the Principle Investigator E. Kimmer (GSFC), SMOV-2 Closure Review Oct 30., 1997.
The Table (PASS LOADS) on the following page lists the output products from this proposal.
17
INSTRUMENT OR SUBSYSTEM: FGS
REQUIREMENT: F.2.5.7.3.2 FGS-to-FGS alignment calibration shall be performed and result-
ing alignment matrices computed. The PDB shall be up-dated with the new calibration parameters.
RELEVANT SMOV PROPOSALS:
1. Title: Prop 7025 FGS/FGS Alignment POST-SM2 Calibration
PI: B. Chapman, E. Kimmer, G. Welter (GSFC), O. Lupie (STScI).
Date: 1997.112.
Relevance: acquired data to calculate the FGS/FGS alignment matrices and to derive the
FOV reference position and pickle boundaries used by the guide star selection system and
stored in the PDB SCHF.DAT and SIAF.DAT les.
See SMOV-2 Closure Review Documentation - presentation of Requirement F.2.5.7.3.2
by the Principle Investigator E. Kimmer (GSFC).
The following Table (PASS LOADS) lists the output products from this proposal.
PASS TABLE LOADS for FGS1R
Name
Description
FMTVT
FGS/Vehicle Transformation for each FGS
FPVXTP
FGS Frame Quaternion Transformation
FOCD01-11
Optical Distortion Coecients
FSSSDA,FSSSDB Deection Angle A and B
FVTABO
Star Selector A and B Servo Osets
FVGOPT
Nominal Optical Gain Table
FSIGPT
Optical Gain Tables
FSGOM1
Function of Optical Gain Table
FVUQU1,2,3,4,5 Deection Angle Tables
FAARG,FABRG Deection Angle/Optical Gain
DATER1-8
Deection Angle Function
18
INSTRUMENT OR SUBSYSTEM: FGS
REQUIREMENT: F.2.5.7.3.3 If an FGS is replaced, one check on the stability of the Mini-
OFAD and FGS-to-FGS Alignment parameters, and on the stability of the S-curve restoration,
shall be made two to six months after the calibrations. In the replaced FGS two orbits shall be
used to acquire the following: 1. Position information on the stars at one Mini OFAD orientation
using dierent guide star pairs for each of the two orbits. 2. One S-curve on a star that is near the
FGS FOV location used for optimizing the FF3 orientation (Ref. 2.5.7.2.2). 3. One set of position
information for the Internal Test Source. If the data in step 3 cannot be acquired in the same orbit,
it should be obtained as close in time as possible to steps 1 and 2.
RELEVANT SMOV PROPOSALS:
1. Title: Prop 7027 - Near Term Stability Monitor for FGS1R PI: O. Lupie (STScI), J. Esper
(GSFC), E. Nelan (STScI).
Test Date: Visits 3,4 1997.122, Visits 1,2 1997.136
Relevance: the test obtains baseline measurements of the S-Curve and ITS position a few
months after the 7026 test and also acquires S-Curve data over the course of an orbit to
study orbital stability.
2. Title: Prop 7800 - Cycle 7 FGS/FGS Alignment Check PI: O. Lupie (STScI), E. Kimmer
(GSFC)
Test Date: 1997.259
Relevance: the test was a shorter version of the SMOV FGS/FGS alignment test, and was
designed specically to verify the stability of the FGS1R (and FGS2 and 3) alignments derived
during the SMOV test 7025.
3. Title: Prop 7678 - Cycle 7 Monitor the Long Term Stability of FGS1R in POS Mode
PI: E. Nelan, L. Nagel (STScI)
Test Date: 6 visits from Sept 1997 through Nov 1998.
Relevance: the test uses one of the SMOV Mini-OFAD orbits to monitor the POS mode
stability of FGS1R.
4. Title: Prop 7597 - Cycle 7 Long Term Stability of Transfer Scan Mode in FGS1R.
PI: O. Lupie, E. Nelan, L. Nagel (STScI)
Test Date: 7 visits from July 1997 through Jan 1999.
Relevance: the test monitors the desorption impact on the FGS1R S-Curves.
DESCRIPTION OF METHODS:
Prop 7027 - Near Term Stability Monitor for FGS1R: This proposal included 4 types of
observations:
1. POS and TRANS mode data (Visits 3,4) on a eld in the astrometric cluster M35 repeated
over an orbit (established a baseline LTSTAB for POS mode as well as sampling changes
during an orbital cycle)
19
2. S-Curve data in F583W and Pupil lters on the 7026 (FF3 optimization test) target to study
changes due to desorption,
3. S-Curve data (Visit 2) on the standard star Upgren (to establish a baseline since it will be
used for monitoring throughout the cycle), and
4. 4) a ne lock ITS acquisition to trend its position.
Prop 7800 - Cycle 7 FGS/FGS Alignment Check: This test obtained data on an astrometric
eld NGC5617, using FGSs 2 and 3 in guidance mode and FGS1R as the astrometer. For each of 3
sweeps across the FGS1R pickle a dierent pair of astrometric guide stars were used in the guiding
FGSs.
Prop 7678 - Cycle 7 Monitor the Long Term Stability of FGS1R in POS Mode:
FGS1R POS mode data in lter F583W are obtained on M35 star eld observed during the rst
orbit of the SMOV-2 Mini OFAD to track the stability of the POS mode.
Prop 7597 - Cycle 7 Long Term Stability of Transfer Scan Mode in FGS1R: A series of
S-Curves (target Upgren69) at a central position in the FGS1R pickle are obtained in both F583W
and Pupil lters over the course of cycle 7 to monitor desorption changes.
DESCRIPTION OF RESULTS:
1. Modulation and morphology changes were seen in the S-Curves from day 083 to day 122 (7027
Near Term Stability Test) which were consistent with decenter shifts due to desorption.
2. The POS mode data on M35 (Prop 7678) will be compared to a repeated measurement of
the same eld next spring to study POS mode stability and repeatability.
3. From prop 7800 FGS Alignment Verication, the changes in the boresight location (from the
SMOV April alignment) are about 300 mas for FGS1R. FGS3 alignment since April remained
constant. (E. Kimmer, Oct. 22 1997 memo to Chris Connor).
4. The morphology of the Pupil S-Curves have not exhibited large variations. Therefore, guidance is unaected by desorption.
REQUIREMENT STATUS: SATISFIED
SUPPORTING DOCUMENTATION:
1. FGS/FGS Alignment Check Memo, October 1997, E. Kimmer.
2. Instrument Science Report: OSG-FGS-97-03 SMOV-2 FGS1R Near Term Stability Results,
E. Nelan, O. Lupie, L. Nagel (STScI), L. Reed and K. Chisolm (HDOS), in preparation.
3. STScI FGS Cycle 7 Calibration Plan.
20
INSTRUMENT OR SUBSYSTEM: FGS
REQUIREMENT: F.2.5.7.3.4 A PMT calibration for a replacement FGS shall be derived from
brightness measurements of stars acquired while conducting other FGS and non-FGS SMOV activities.
RELEVANT SMOV PROPOSALS:
1. Title: Prop 7001 FGS1 Delta Mini OFAD Post-SM2 Calibration
PI: A. Bradley, E. Kimmer, G. Welter (GSFC), E. Nelan, O. Lupie (STScI).
Test Date: 1997.111.
Relevance: The observations of the stars in M35 for the Mini-OFAD were used to derive a
PMT calibration for the operational use of FGS1R.
2. Title: Prop 7025 FGS/FGS Alignment POST-SM2 Calibration
PI: B. Chapman, E. Kimmer, G. Welter (GSFC), O. Lupie (STScI)
Date: 1997.112.
Relevance: The observations of the stars in NGC5617 for the FGS Alignment test were used
to verify the PMT calibration for the operational use of FGS1R.
DESCRIPTION OF METHODS: The PMT counts from the stars in both tests were used
to derive the PMT calibration accessed by the magnitude dependent K factors K1X and Y (Fine
Error Signal gain) and K3 X and Y. The Van Altena catalog provides the M35 photometry with
accuracies of < 0.1 magnitudes, suciently adequate for Guide Star acquisitions. Note: A PMT
calibration with astrometric/scientic accuracies is in work along with trends on the PMT sensitivity.
DESCRIPTION OF RESULTS: The magnitude dependent operational parameters for FGS1R
were delivered in April 1997 by HDOS. The high accuracy PMT calibration and sensitivy verication for future scientic uses are in work by members of the STScI FGS team.
REQUIREMENT STATUS: SATISFIED
SUPPORTING DOCUMENTATION:
1. HDOS Document TE A16-0183: "Results of Initial On-Orbit Testing of FGS1R", July 1997,
L. Abramowicz-Reed.
2. STScI ISR: FGS1R PMT Calibration, in-work.
21
INSTRUMENT OR SUBSYSTEM: FGS
REQUIREMENT: F.2.5.7.3.5 If an FGS is replaced, dark count data will have been obtained
in all FGSs during the replacement FGS functional checkout. If no FGS is replaced, dark counts
shall be acquired on a target of opportunity basis.
RELEVANT SMOV PROPOSALS:
Title: In-bay Functional Check-out
PI: L. Abromowicz-Reed and K. Chisolm (Hughes Danbury Optical Systems)
Date: 1997.046 and 1997.047
DESCRIPTION OF METHODS: This series of tests were performed with FGS1R in HST bay
1 and while HST was docked in the shuttle bay and consisted of the following:
1. Filter Wheel - Command the lter wheel to move between the Pupil and F583W positions to
conrm proper functioning.
2. Dark Count - Measure dark counts and verify that values were comparable to thermal vac
values.
3. Fine Lock on ITS - verify activation of the ITS, conrm that the alignment had not changed
radically since pre-launch measurements, check that the FGE can slew the IFOV to the ITS
location, verify the ne lock acquisition sequence, and verify that the PMT sensitivity is
comparable to pre-launch values.
4. LOS Scan - veries that eld stop alignments were not aected by launch trauma and the
misalignments are within acceptable limits.
DESCRIPTION OF RESULTS:
1. The lter moved as commanded.
2. The measured dark counts (per 25 milliseconds) were within a few percent of the pre-launch
ground-based measurements:
Table FGS1R Dark Count
PMT Pre-Launch Day 1997.046 Standard Deviation
Ax
Bx
Ay
By
3.71
1.55
3.35
5.43
3.78
1.18
3.88
6.05
2.09, 2.17
1.39, 1.23
1.90, 2.11
2.49, 2.57
3. The measured dark counts of FGS2 and FGS3, obtained serendipitously, were also comparable
to pre-launch values.
4. The ITS was found within 2 arcsec of its pre-launch position which is well within the anticipated value (based on changes to the original 3 FGSs as a result of orbital insertion).
22
5. The ne lock acquisition of the ITS was nominal.
6. The expected PMT counts from the ITS was 3 to 4 % lower than the thermal vacuum
test. HDOS believes that the variation arises from the output of the ITS rather than PMT
sensitivity changes because the ITS output has been seen to vary by a comparable amount.
Also, the PMT dark current measurements were nominal. Lastly, the measured count rates
from astrometric targets (observed later in SMOV) were comparable to predicted count rates.
7. The eld stop misalignments were veried from the LOS scans and were well within operational limits.
REQUIREMENT STATUS: SATISFIED
SUPPORTING DOCUMENTATION:
1. HDOS Doc TE A16-0183: Results of Initial On-Orbit Testing of FGS1R, July 1997, L.
Abramowicz-Reed.
23
F.2.5.8 Pointing Control Subsystem Verication
Contingency Proposals
The following requirements did not have to be implemented during SMOV-2. Contingency proposals were in the system and ready for implementation. A description of the test method and
implementation plan may be found in STScI-ISR-FGS-034.
REQUIREMENT: F.2.5.8.3 The FHST/FHST alignment matrices shall be computed,
using FHST observations at the initial attitude, to an accuracy of 5 arcseconds (1s). The
FHST/FHST alignment matrices shall be updated if the change in the pitch or yaw alignment
exceeds 20 arcseconds. The alignment computations will be further rened during normal
operations to achieve accuracies comparable to the pre-Servicing Mission level.
Title: Contingency Proposal 7005 - FHST to FGS Alignment Proposal
PI: A. Bradley and E. Kimmer (GSFC).
REQUIREMENT: F.2.5.8.4 If gyros are changed out, the gyro to FHST alignment matrices shall be updated to an accuracy that reduces the atti-tude error following a vehicle
maneuver to less than one arcsecond per degree of slew.
Title: Contingency Proposal 7004 - Gyro/FHST Scale-Factor and Alignment Calibration.
PI: E. Kimmer (GSFC).
24
PCS Verication
INSTRUMENT OR SUBSYSTEM: FGS
REQUIREMENT: This section describes two SMOV tests which address the following
Pointing Control Subsystem Verication Requirements (F.2.5.8):
F.2.5.8.1 The initial attitude shall be determined to an accuracy within .2 degrees using
Fixed Head Star Tracker (FHST) data. (See SMOV2 Closure Review Documentation, C.
Connor Oct. 30, 1997).
F.2.5.8.2 The gyro drift rate bias shall be calibrated to within 0.05 arcseconds per second
prior to the rst guide star acquisition. (See SMOV2 Closure Review Documentation, C.
Connor Oct. 30, 1997).
F.2.5.8.5 The PCS shall acquire guide stars in ne lock. (See SMOV2 Closure Review
Documentation, C. Connor Oct. 30, 1997).
F.2.5.8.6 The vehicle jitter during periods of FGS ne lock shall be measured. (See SMOV2
Closure Review Documentation, C. Connor Oct. 30, 1997).
RELEVANT SMOV PROPOSALS:
1. Title: Prop 7028 Guide Star Acquisition Verication for FGS2 and FGS3
PI: O. Lupie, R. Doxsey, L. Nagel, J. Hershey (STScI)
Test Date: 1997.053
Relevance: After release of the HST from the shuttle bay, the PCS performance was tested
by performing 4 guide star acquisitions in FGS2 and FGS3.
2. Title: Prop 7030 Guide Star Acquisition Verication for FGS1R
PI: O. Lupie, R. Doxsey, L. Nagel, J. Hershey (STScI)
Date: 1997.097
Relevance: This test veried the acquisition and tracking performance of FGS1R and served
as a prerequisite for the Mini-OFAD calibration.
DESCRIPTION OF METHODS:
Attitude Updates and Calibration: Prior to the rst guide star acquisition and also after the
slew to the rst pointing, the GSFC PCS team (C. Connor, T. Cruz, E. Kimmer GSFC) performed
a series of calibrations and attititude determinations and updates according to standard procedure.
Following these procedures, proposal 7028 was executed.
Proposal 7028 Guide Star Acquisition Verication for FGS2 and FGS3: The test was
designed to verify the following:
1. Verify the FHST Update and Gyro Drift Correction after occultations and after large slews,
2. Verify the FGS Search, Coarse Track, Walkdown and Fine Lock modes (and veries the
DF224 and FGE interfaces),
25
3. Verify the FGS/FGS and FGS/FHST Alignments, and
4. Compare S/C jitter to pre-SM2 jitter
Prop 7030 Guide Star Acquisition Verication for FGS1R: Four pairs of Guide stars were
acquired with FGS1R in various combinations with FGS2 and FGS3. Fine Lock Tracking was
held for at least several minutes in all cases. The Coarse mode angle check tolerance and primary
and secondary search radii were increased to allow for uncertainties in the FGS1R-to-FGS relative
alignments.
DESCRIPTION OF RESULTS:
1. Following the release of HST from the shuttle, HST was commanded to normal mode and a
real-time FHST map and attitude determination ensued. The FHST map showed an accuracy
of better than 20 arcsec which is well under the requirement of 0.2 degrees. (See SMOV2
Closure Review Documentation, C. Connor GSFC Oct. 30, 1997).
2. Preceeding the rst guide star acquisition (proposal 7028) the gyro bias drift rates were
determined by the GSFC PCS team per standard operational procedure and results were
nominal. (See SMOV2 Closure Review Documentation, C. Connor GSFC Oct. 30, 1997).
3. At the attitude for the rst guide star acquisition, FHST maps using all three FHSTs in
various combinations were executed each orbit to determine the FHST relative alignment.
Results were accurate to 3 arcsec. (See SMOV2 Closure Review Documentation, C. Connor
GSFC Oct. 30, 1997).
4. Proposal 7028 - FGS2 and FGS3 Guiding:
(a) The FHST residual errors after the slews and before the acquisition were consistent with
the pre-SM2 values. The following table lists the FHST residual errors for 3 of the guide
star pairs.
Table 7028 1 FHST Residual Error
GS Pair V1(asec) V2(asec) V3(asec)
Comments
50a
50b
50c
0.3
0.6
16.8
0.04
0.13
1.4
5.75
0.2
0.42
1.2
74
0.9
after update, pre-50a acq
after update, pre-50b acq
after 180 deg slew
after 2nd update, pre-50c acq
(b) The accuracy of the telescope pointing was demonstrated by the acquisition miss-distance
(the distance between the start of the FGS search and the ne lock tracking position).
Table 7028 2 lists the miss distances for the acquisitions and re-acquisitions. The mean
miss-distance for generic guide star acquisitions is 15 arcsec.
(c) The rms jitter during the 7028 ne lock tracking was measured from the 40Hz ne lock
servo data and is comparable to pre-SM2 jitter, about 3-4 mas. Large peak-to-peak
excursions (40-60 mas) are seen in some of the data and correlate with the entry of the
S/C into orbital night.
26
Table 7028 2 GS Acquisition Results
GS Pair Miss-Dist (") Meas OTA V2V3 Comments
50a
8.5
-0.008,-0.41 0.48
acq
50b
50c
2.5
8.8
5.1
3.1
4.0
-0.01,-0.27 0.39
-0.01,-0.27 0.40
-0.38,0.16 0.42
reacq
acq
reacq
acq
re-acq
5. Proposal 7030 - FGS1R Guiding Verication
(a) FGS1R successfully acquired the guide stars and held lock for the duration of the measurement.
(b) The miss-distances were within the expected tolerances, given that the FGS alignments
were not yet onboard the S/C. The initial miss distance was 30 arcsec and the subsequent miss distances did not exceed 8 arcsec.
(c) The S/C jitter was comparable to the pre-launch statistics.
REQUIREMENT STATUS: SATISFIED
SUPPORTING DOCUMENTATION:
1. SMOV2 Requirements Closure Review, Oct. 30, 1997 GSFC: PCS Requirements, C. Connor
(GSFC).
2. STScI TIR-OSG-FGS-036 SMOV2 7028 Guide Star Acquisition Verication: FGS2 and
FGS3, March 1997, O. Lupie, S. Holfeltz, L. Nagel, and E. Nelan (STScI).
3. STScI TIR-OSG-FGS-97-02 SMOV2 FGS1R Guide Star Acquisition Verication, O. Lupie,
S. Holfeltz, L. Nagel, and E. Nelan, in preparation.
27
Suggestions/Actions from SMOV-2 Closure Review
The following are suggestions and actions pertaining to the FGS that resulted from the Oct.
30, 1997 SMOV-2 Closure Review at GSFC (meeting arranged by G. Repass and C. Biagetti).
1. The magnitude and extent of the desorption displayed in FGS1R leads to the conclusion that
a conservative approach should be adopted with regard to the operational commissioning of
any new FGS: that the PUPIL aperture stop be used for operational commissioning and that
use of the F583W lter will follow some time later after desoprtion eects have ceased.
2. Action on FGS group at STScI to work with the PCS Team at GSFC to reqork the FGS
SMO-1000 requirements.
3. The Lessons Learned and suggestions stated there were acceptable to the review panel.