HSTAR 11932
2009/200
Body Rate Low Safemode Test Failure
Following Planetary Tracking on Gyros
July 22, 2009
P. 1
HSTAR 11932 on DOY 2009/200
Observables
•
02:55:32
•
02:55:43
PLCP group, TERMEXP, turns off Velocity Aberration and
Parallax (VA/P) corrections
PLCP group, PQSLWVAB for Anti-Sun WFC3 IR background
measurements under gyro control with Planetary Parallax on
− Acq Init command with Planetary Parallax on, redefines target vector for VA/P to
default vector
− 4 second wait, then T2 Vehicle slew command, turns VA/P on
− Followed by a couple orbits under gyro control with large T4 maneuvers
•
06:35:06
PLCP group, PQSLWVAB for North Pole WFC3 IR
background measurements under gyro control with Planetary
Parallax off
− Acq Init command with Planetary Parallax off, redefines target vector for VAP to
default vector (NOTE THIS IS DONE WITH VA/P STILL ENABLED)
− 4 second wait, then T2 Vehicle slew command (06:35:10)
•
06:35:12
July 22, 2009
Body Rate Low test fails – (req. 5 second persistence)
P. 2
HSTAR 11932 on DOY 2009/200
Body Rate Test Flow
enter
MagnitudeDeltaErrorSquared = 0
MagnitudeDeltaErrorSquared =
DVTHED(V1)^2 +
DVTHED(V2)^2 +
DVTHED(V3)^2
MagnitudeDeltaErrorSquared
< BodyRateLimit
Y
BodyRateCount = 0
BodyRateErrorFlag = False
exit
(2 as/sec2)
BodyRateCount = BodyRateCount + 1
BodyRateCount >=
BodyRateCount Limit
(5 seconds)
exit
July 22, 2009
Y
BodyRateErrorFlag = True
ESB [BODY_RATE_ERROR, MagnitudeDeltaErrorSquared]
Set gyros to High mode, disable autonomous mode switching
Disable Body Rate Error test, set test active flag
Record event in Safemode Fault Recorder
P. 3
)
c
e
s
/
c
e
s
c
r
a
(
r
o
r
r
E
Recreated Body Rate Test
Recreated SBRELE test (Q4DVP
30
VEH
- 2*QDPCZXC)
RSS
28
26
24
22
20
18
e
t
a
R
16
y
d
o
B
10
14
12
8
6
4
2
SBRELE threshold = 2.0 as/sec
0
0
5
10
15
20
25
30
35
40
Seconds since 06:35:00
July 22, 2009
P. 4
Velocity Aberration & Parallax Quaternion
-2.0489097e-08
3.8306698e-05
1.3672283e-05
-4.6566101e-10
9.3132269e-10
-4.6971254e-06
3.5162087e-05
-4.6566101e-10
-2.7140602e-05
-2.2793654e-05
-8.912757e-07
-4.6566101e-10
06:35:09.610
06:35:21.610
July 22, 2009
P. 5
Delta Velocity Aberration & Parallax Quaternion
0
6.3300781e-10
2.8376212e-10
0
0
3.2741782e-10
8.7311422e-11
0
-6.5483619e-11
2.9103808e-11
-3.3469405e-10
0
06:35:09.460
06:35:21.460
July 22, 2009
P. 6
RWA Torques
-0.81909943
-0.81909943
0.81800473
-0.81909943
06:35:08.810
July 22, 2009
06:35:20.810
P. 7
Gyro Counts
06:35:09.460
1826.0001
06:35:09.085
62.0
06:35:12.385
06:35:07
06:35:11.285
-1726
July 22, 2009
P. 8
Proper Motion & Parallax
06:35:10.660
July 22, 2009
P. 9
HSTAR 11932 on DOY 2009/200
12/6/2006
Body Rate Low test failure in OAT of TRT macro
Investigation documented in Vreeland memo showed cause to be
Acquisition Initialization Command sent using a default target vector for
velocity aberration (VA) while VA was enabled. This resulted in a step
change in the VA contribution that directly impacts the vehicle pointing.
New CARD item written:
3.1.9.49 Acquisition Initialization Commanding
a. The FGS acquisition initialization command (#38) must not be
executed from any source other than the Science Mission Specification
(SMS) unless the velocity aberration processing is turned off.
b. The acquisition initialization command includes changing the guide
star positions and target direction that are used for velocity aberration.
The new guide star position and target direction may not match the
vehicle attitude as defined by the SMS and can produce large step
changes in velocity aberration contributions to the vehicle control law.
c. Large step change contributions to the vehicle control law
parameters could cause body rate errors resulting in SAFEMODE.
Commanding for TRT was changed to add terminate commanding prior to on-orbit
execution.
July 22, 2009
P. 10
HSTAR 11932 on DOY 2009/200
CARD item assumed that SMS commanding always terminated VA prior
to issuing an Acquisition Initialization command. Typically an Acquisition
Initialization command defining a new target is sent while VA corrections
are off, followed by a T2 slew which smoothly slews the vehicle to the
new VA corrected target and then leaves continuous VA corrections
enabled.
The assumption was true until a change was made to PCPTERM for TGS
operations.
- PCPTERM changed to check a global such that group was not
issued if called out when the global TERMGRP was not “ON”.
- This allowed for putting Save Quaternion command in
PCPTERM which was required for re-acquisitions in TGS
Gyro only observations do not set TERMGRP global. This was not an
issue in TGS since gyro only observations were not done. With return to
3 gyro observations, we have had gyro only observations. This case due
to the planetary parallax had an even bigger change.
All Gyro only observations must be reviewed even if planetary parallax is
not being used until commanding is updated. Need to review all
scenarios to ensure proper change is made to have PCPTERM after gyro
observations without another impact.
July 22, 2009
P. 11