HST
September 30, 2002
MOSES
SM3B SMOV CLOSURE REVIEW
PCS REQUIREMENTS
LMTO/Dan Smith
September 30, 2002
1
HST
MOSES
Pointing Control Subsystem
M. Gakenheimer
September 30, 2002
REQUIREMENT:
J.10.4.8.1 “THE INITIAL ATTITUDE SHALL BE DETERMINED TO AN ACCURACY WITHIN 0.2 DEGREES USING
FIXED HEAD STAR TRACKER (FHST) DATA.”
Intent is to correct vehicle attitude to within 0.2 degrees of desired attitude for HGA communication and return to
nominal operations.
RELEVANT SMOV PROPOSAL:
CP Sequence # 173 - FHST FOV CHECK
DESCRIPTION OF METHODS:
After HST was commanded to Normal Mode, a real-time FHST map was performed and used for attitude
determination and generation of an ARU/PRT to correct vehicle attitude.
DESCRIPTION OF RESULTS:
FHST map accuracy < 20 arcsecond, which meets the requirement of 720 arcseconds.
REQUIREMENT STATUS:
SATISFIED
SUPPORTING DOCUMENTATION:
NONE
2
HST
MOSES
Pointing Control Subsystem
M. Gakenheimer
September 30, 2002
REQUIREMENT:
J.10.4.8.2 “The gyro drift rate bias shall be calibrated to within 0.05 arcseconds per second (180
arcseconds/hour) prior to the first guide star acquisition.”
RELEVANT SMOV PROPOSAL:
CP Sequence # 177 - ATTITUDE DETERMINATION FOR FIRST HLGBU
DESCRIPTION OF METHODS:
Performed by commanding two real-time maps roughly an orbit apart and using a long-baseline
technique to measure the attitude change between the two computed attitudes to determine the
gyro drift rate bias.
DESCRIPTION OF RESULTS:
The drift rate bias correction terms were all less than 20 arcseconds/hour.
REQUIREMENT STATUS:
SUPPORTING DOCUMENTATION:
SATISFIED
None
3
HST
MOSES
Pointing Control Subsystem
M. Gakenheimer
September 30, 2002
REQUIREMENT:
J.10.4.8.3 “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 refined during
normal operations to achieve accuracy comparable to the pre-Servicing Mission level.”
RELEVANT SMOV PROPOSAL:
N/A - PERFORMED ON A SERENDIPITOUS BASIS DURING THE H&S SMS
DESCRIPTION OF METHODS:
During the H&S SMS, real-time maps are performed to maintain the pointing accuracy of HST. These maps also
provide the data to perform the FHST/FHST alignment.
DESCRIPTION OF RESULTS:
Results of the FHST/FHST alignment showed a change in pitch with respect to FHST 1 of 2.1 arcseconds and a
change in yaw with respect to FHST1 of 2.54 arcseconds which is within the uncertainty of 3.01 arcseconds.
Thus there is no evidence of a change during SM3B.
REQUIREMENT STATUS:
SATISFIED
SUPPORTING DOCUMENTATION:
NONE
4
HST
MOSES
Pointing Control Subsystem
M. Gakenheimer
September 30, 2002
REQUIREMENT:
J.10.4.8.4 “The gyro-to-FHST alignment matrices shall be maintained to an accuracy that reduces the attitude
error following a vehicle maneuver to less than one arcsecond per degree of slew. If any gyros are changed out,
a full RGA calibration will be performed.”
RELEVANT SMOV PROPOSAL:
Not performed since none of the RSUs were changed out.
DESCRIPTION OF METHODS:
Performed based on scheduling large slews in the first science SMS and calibrated using procedure SAC-98,
“RGA Alignment - Scale Factor Calibration.”
DESCRIPTION OF RESULTS:
N/A.
REQUIREMENT STATUS:
N/A.
SUPPORTING DOCUMENTATION:
NONE
5
HST
MOSES
Pointing Control Subsystem
A. Bradley
September 30, 2002
REQUIREMENT:
J.10.4.8.5
“The PCS shall acquire guide stars in fine lock.”
RELEVANT SMOV PROPOSAL: 8994
DESCRIPTION OF METHODS:
Demonstrate the ability of each of the three FGSs to acquire a primary guide star while another FGS acquires a
secondary guide star. After acquiring a guide star pair, HST will track these stars in fine lock for approximately
10 minutes.
DESCRIPTION OF RESULTS
Proposal was executed on 2002:071 from 01:30 to 03:44, the South BEA guide star targets were selected. Three
acquisitions were executed, which allowed each FGS a turn at being Primary and Dominant.
The first acquisition occurred at 71:01:30 and was successful.
Primary = FGS 1, Secondary = FGS 2, Dominant = FGS 1
6
HST
Pointing Control Subsystem
September 30, 2002
MOSES
The second acquisition occurred at 71:02:21 and was successful.
Primary = FGS 3, Secondary = FGS 1, Dominant = FGS 3
The third acquisition occurred at 71:02:48 and was successful.
Primary = FGS 2, Secondary = FGS 1, Dominant = FGS 2
REQUIREMENT STATUS:
SATISFIED
SUPPORTING DOCUMENTATION:
NONE
7
HST
MOSES
Pointing Control Subsystem
A. Bradley
September 30, 2002
REQUIREMENT:
J.10.4.8.6
“The vehicle jitter during periods of fine lock shall be measured. “
RELEVANT SMOV PROPOSAL: 8999
DESCRIPTION OF METHODS:
With HST in fine lock control using FGSs 2R and 3, FGS 1R will acquire a target star in fine lock. Since FGS1R is
not in the control loop, it is an independent observer of jitter.
DESCRIPTION OF RESULTS
Although proposal 8999 was executed 4 times, only the results from the last test at 127:19:24 to 127:20:30 was
used. At this time the NICMOS cooler was at the cooling temperature and the control law rate gain was adjusted
to the as-launched value. The Sun angle was 53.9 degrees and the controlling gyros were #3,4,2. With respect to
Enter Orbit Night (EON) and Enter Orbit Day (EOD), the observation times are listed in the following table.
8
HST
A. Bradley
September 30, 2002
Pointing Control Subsystem
MOSES
Test
4
4
4
4
POS mode observations start and stop times.
Segment
Start time
End time
1
EON + 24m21s EOD + 11m59s
2
EOD + 12m37s EOD + 31m09s
3
EOD + 31m47s EOD + 50m15s
4
EOD + 50m54s EON + 04m45s
The target star information is shown in the following Table.
The target stars’ for the POS and TRANS mode observation’s.
Test
4
Star
HD#
225146
mv
BT
VT
B-V
V-I
8.59
9.0±.013
8.69±.014
.360±.014
.42±.01
9
Spectra
l type
BOIbp
FGS 1 magnitude
Obs. Obs. Obs. Obs.
1
2
3
4
9.412 9.414 9.415 9.414
HST
MOSES
Pointing Control Subsystem
A. Bradley
September 30, 2002
The following jitter measurements were obtained from the four segments of each test for the Astrometer
(AST) and the Dominant (DOM) FGS, the data from each segment was processed in whole.
POS mode jitter measurements from Astrometer and Dominant FGS’s.
AST de-trended (mas) DOM de-trended (mas)
Test Segment V3
V2
rss
V3
V2
rss
4
1
3.5
3.8
5.2
3.6
3.3
4.9
4
2
3.8
3.7
5.3
3.5
3.5
4.9
4
3
4.1
4.0
5.7
3.8
3.8
5.4
4
4
3.4
4.8
5.9
4.7
3.2
5.7
avg
5.5
5.2
The Astrometer RSS jitter measurements are in the 5.0 to 6.0 mas range and are under the 0.007 mas
specification.
REQUIREMENT STATUS:
SATISFIED
SUPPORTING DOCUMENTATION:
LMMS/P564402
10
HST
MOSES
Pointing Control Subsystem
Post-SM3B Jitter Profile, consisting of 1 minute averages.
Gyros 2,3,4 in control.
11
A. Bradley
September 30, 2002
HST
MOSES
Pointing Control Subsystem
B. Clapp
September 30, 2002
REQUIREMENT:
J.10.4.8.7 “Perform a Vehicle Disturbance Test (VDT) to characterize the disturbance environment of the HST
using a low-bandwidth attitude control law during gyro-hold with the gyros in low-mode. The VDT is a passive
test (not a forced-response test). Obtain signatures for both externally induced (e.g. SA-3) and internally induced
(e.g. NCC) disturbances for comparison with past VDT results and characterize jitter induced by the SA-3, NCS,
and the ACS Filter Wheel. The VDT shall consist of five separate tests that need not occur consecutively. The
overall duration of the VDT tests are at least 17 orbits of spacecraft time including (1) at least 1 full orbit at +V3
sunpoint prior to NCC operation while performing ACS Filter Wheel moves simulating routine flight operations,
(2) at least 5 full orbits at +V3 sunpoint prior to NCC operation, (3) at least 1 full orbit at +V3 sunpoint during NCC
startup, (4) at least 5 full orbits at +V3 sunpoint while NCC is operating at steady-state, and (5) at least 5 full
orbits at –V1 sunpoint with the NCC operating at steady-state.”
RELEVANT SMOV PROPOSAL:
#8968 Vehicle Disturbance Test
DESCRIPTION OF METHODS:
Time and frequency domain analysis of flight telemetry to identify and characterize disturbance sources acting
upon HST.
DESCRIPTION OF RESULTS:
The predominant persistent disturbance post-SM3B is due to HGA articulation exciting HST structural modes.
Other disturbances, observed less frequently, that affect HST jitter include thermal gradients on the SSM and
SA3, reaction wheel zero-speed crossings, ACS filter wheel motion, NCC compressor surging, and high-rate
HGA slews. These disturbances excite numerous HST structural modes that were identified during the VDT:
HGA gimbal and boom modes, aperture door pitch, SA3 first and second bending modes, NCS conduit and
radiator modes, OTA-SSM “scissors” modes, and the aft bulkhead drum mode. The frequencies of HST
structural modes observed in the VDT were within 11% of analytically predicted values.
REQUIREMENT STATUS:
SATISFIED
SUPPORTING DOCUMENTATION:
MOSES EM #1226, Vehicle Disturbance Test Report for SMOV-3A/B (9/2002)
12
HST
MOSES
Pointing Control Subsystem
B. Clapp
September 30, 2002
REQUIREMENT:
J.10.4.8.8 “Contingent upon analysis of PCS performance post-SM3B, perform a Transfer Function Test (TFT).
The TFT is a forced response test that measures HST system modal parameters (modal gains, modal damping
ratios and frequencies) by applying a RWA forcing function and measuring RGA gyro response. This test will be
performed if PCS analysis of post-SM3B HST flight data (such as the VDT) suggests that HST system modal
parameters significantly differ from pre-SM3B analytical models. On-orbit modal parameters that differ from preSM3B models can cause degraded performance of the HST attitude control system because of reductions in
stability margins and/or increased vehicle jitter.”
RELEVANT SMOV PROPOSAL:
#8971 Vehicle Transfer Function Test Contingency
DESCRIPTION OF METHODS:
Spectral methods used to extract structural dynamic properties of the HST from flight telemetry.
DESCRIPTION OF RESULTS:
PCS post-SM3B analysis showed that HST jitter and control law stability were within required levels, so the
Transfer Function Test Contingency was not required during SMOV-3B.
REQUIREMENT STATUS:
SATISFIED
SUPPORTING DOCUMENTATION:
http://edocs1.hst.nasa.gov/doc/publish/subsys/pcs/Smov3b/SMOV3Bmain.htm
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