SPACE
TELESCOPE
SCIENCE
INSTITUTE
Operated for NASA by AURA
The Aug 3rd STIS Failure and Upcoming Tests
Paul Goudfrooij
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Disclaimer: Only ‘Public Domain’ info shown here
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FRB presentation to HSTP will occur 1:30 – 3:30 today
–
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STScI Members of FRB: Ron Pitts, Tom Wheeler;
Tony Keyes ex officio
Final info from FRB studies to be shown in later TIPS.
FRB Charter
1.
2.
3.
4.
5.
6.
Review Data: Review telemetry of the failure, and the record of events in the
STIS microprocessor memory log, construct a detailed timeline/ reconfirm
and/or update what has been learned since the August 3rd event;
Identify Most Likely Cause: Develop a complete fault tree identifying potential
causes of the August 3rd anomalies; if possible identify the root cause;
Propose Test Plan/Establish if STIS can be returned to use: Develop a plan
for diagnostic tests that will further characterize the problem and/or establish
conclusively whether STIS can be returned to use or is unrecoverable; identify
the risks presented by each test;
Consider risk of identical failure in additional HST assets: Consider, and, if
needed recommend a set of actions for assessing the susceptibility of other
HST Science Instruments (SIs) to a similar root failure mechanism;
Review thoroughness of SI safing routines: Review the self-checks and safing
architectures of the other SIs for adequacy, and, if needed, recommend
changes having high merit;
Report findings and Recommendations: Document and report the Review
Board’s conclusions.
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
2
“Home” Mechanism Configuration
(situation prior to suspend event)
Mechanism
External Shutter
Corrector Mechanism (Not initialized)
Focus
U Tip/Tilt
V Tip/Tilt
Slit wheel *
Mode Select Mechanism
Mode Isolation Shutter
Echelle Blocker
Calibration Insertion Mechanism
CCD Shutter *
Mnemonic
OXSHP
Position
Closed
OKMFOCP
0.1837134 mm
OKUTILTP
-900.0 a-s
OKVTILTP
-900.0 a-s
OSWABSP
3824311 – 3824372#
(MIRVIS, CCD imaging)
OSMPOSX
Closed
OSEPOSX
Block2
OCMMPOSX
Insert
OSCSHUTX
Closed
* All motors are stepper motors with magnetic detents except the slit wheel and CCD shutter. The latter two are brushless
DC torque motors.
# The slit wheel does not normally move unless commanded to do so. The loss of the +5V mech converter voltage
affected the servo loop permitting drift. 3824311 was the value when the mech 5 V went to zero. 3824372 was the
value at the suspend at 2004.216:16:38:58.
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
3
Observables during Anomaly
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No STIS stored commanding during anomalous events.
– OMBMC5V (STIS +5V Mechanism voltage) drops to 0V
ÿ No suspend reaction, since no lower bound in FSW limit check !
– Increase in Current & Total Power ~43 minutes after
OMBMC5V dropped to 0V
– MCE1 and MCE2 serial communication with MEB halts
resulting in execution of STIS suspend sequence
•
No evidence of outgassing or temp increase during event
– No temp sensor on LVPS2, but MEB temp sensors did not
show change between loss of +5V and suspend sequence
– No rise in pressure measured by ESM pressure sensor
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
4
STIS Current around Anomaly
NSSC-I
Safing
Limit set to
9.67 Amps
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
5
Overlay
Current
signatures taken
24 hours apart
TIPS Presentation
“normal”
Sep 16, 2004
Paul Goudfrooij
6
Main Bus
Current
During
Fault
Main Bus Current during fault
MAMAs, CEB, Mech and
Cal OFF within 500ms
77
No large current spike captured
at 100ms sample rate
76
MCE drops out
CLDBUSCP
75
16:38:22.841
1 Amp +/- 0.6 Amp
drop in current prior
to Suspend Sequence
Execution
74
73
16:38:21.341
72
SUSPEND sequence
Starts 16:38:22.000
71
16:38:23.041
70
08/03/2004
16:38:12.480
TIPS Presentation
08/03/2004
16:38:15.072
08/03/2004
16:38:17.664
08/03/2004
16:38:20.256
Sep 16, 2004
08/03/2004
16:38:22.848
08/03/2004
16:38:25.440
Paul Goudfrooij
08/03/2004
16:38:28.032
7
Cause & Effect Theory
1. Interpoint +5V converter (MFL2805S) internally fails (at bus voltage
< 28V) causing +5V output to fall to 0V
– No observed change in current at time of failure (< 100 mA)
2. At bus voltage >28V, MFL2805S current input becomes increasingly
exponential
3. Current in excess of 72 Amps in less than 40ms occurs, causing
STIS bus voltage to drop to or beyond point required to reset MAMA
electronics prior to fault clearing
4. Both MAMA electronics proceed through power on reset phase,
halting communications with MEB in process
5. MEB requests Suspend activity; meanwhile, exponential current rise
fault has already cleared in MFL2805S converter; likely component
failure within MFL2805S
6. STIS Suspend is executed; MFL2805S is inhibited
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
8
Proposed On-Orbit Tests
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Test #1: STIS Checkout
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Test #2: Attempt to Enable +5V Mechanism Converter
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Purpose: Determine if failure still exists
Test #3: Attempt to reactivate Side-1 (“Hail Mary”)
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Purpose: Verify health & viability of STIS and its detectors
Purpose: Determine whether short still exists
Estimated development time needed before tests #1
and/or #2 can be executed:
–
7-9 weeks after getting go-ahead
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
9
Test #1 (STIS Checkout)
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Test #1 - STIS Checkout (verify health and viability)
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–
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Transition from Safe mode to hybrid Operate Mode (no
mechanism initialized)
Enable each detector separately and take series of DARKs (+
BIASes for CCD) to assess detector performance.
Enable each calibration lamp.
Place STIS back in Safe Mode, and start analyzing data &
telemetry
Estimated execution time ~24 hours, no impact to other SI
observing schedule
Note: STIS was already in similar mode (suspend) for 4 days after
failure without any noted anomalies. Hence extremely low risk of
clearing fuse.
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
10
Test #2: Enable +5V Mech
Converter
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Test #2- Enable +5 volt Mechanism Converter
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–
Transition from Safe mode to hybrid Operate Mode (no
mechanism initialized) in real-time commanding.
Enable Side-2 Mech Power (similar test to STIS Side-1 failure).
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
ÿ
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Activate HST486 ACR to monitor PDU current (shut off if current
exceed expected value plus a delta).
Start high-rate telemetry collection.
Start internal STIS high rate diagnostic on +5volt, +30volt, +15volt,
and other telemetry (TBD) of SES collected items.
Enable STIS Side-2 mechanism relay
Start series of Mechanism moves (clear optical path to enable
observations).
Disable STIS Side-2 mechanism relay.
Dump diagnostic data and place STIS back in Safe Mode.
Note: If bus A/B fuse already stressed, fault might clear fuse,
leaving STIS unpowered.
(Fuse stress rendered unlikely)
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
11
Impact of Fuse Clearing
•
•
STIS Side 1 presently powered off at HOLD relay
– Side-1 Survival Heaters can not be utilized
If STIS Side-2 testing were to interrupt 20 Amp PDU#1 fuse
– Isolation to side-2 Bus-C Fuse would be major impact to HST
ÿ
ÿ
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Following STIS items would be at high risk
ÿ
ÿ
ÿ
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Other SIs would have to switch to side-2 as well, single-fused
Bus-C only 35 Amps of fusing to PCU instead of 70 Amps
MAMAs:
Optical Bench:
Mechanisms:
Survival Limit –5C
Survival Limit –10C
Survival Limit –10C
Hence any robotic STIS servicing may not be useful anymore
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
12
Test #3: Side-1 Reactivation
•
•
Same test as during June 2001: Close Hold Relay
(Fuses were replaced during SM3B)
Why?
– No comparable spectroscopic capability in space at present
– STIS offers unique capabilities that will not be replaced by COS
– HST is thinly instrumented now (before addition of WFC3 and
COS), with minimal spectroscopic capability;
– STIS was regularly scheduled for 25-30% of HST time
– STIS performance would be better now than after SM4:
ÿ
ÿ
ÿ
ÿ
Degradation of the CCD detector with radiation exposure
Increasing throughput losses in the UV due to contamination
Increases in the dark current levels of the MAMA detectors
NOTE: these effects should not be drastic; definitely still worth
repairing STIS in the robotic mission!!
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
13
Test Results Prediction
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Test #1: STIS Side 2 except Mech power supply
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Test #2: STIS Side 2 Mech supply
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PDU fuse will remain intact
All STIS side-2 systems tested will be 100% functional
PDU fuse will remain intact
+5V Mech voltage will not be present; no mechanism
movement will be accomplished
Test #3: STIS Side 1 Test
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PDU STIS Side-1 20 Amp fuse (connected to HST A/B bus)
will blow upon closure of STIS HOLD relay
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
14
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
15
Fusing Lay-Out
TIPS Presentation
Sep 16, 2004
Paul Goudfrooij
16