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Hubble Space Telescope STUC Meeting –5 November 2015

John W. MacKenty

Current Hubble Status

•  All science instruments are performing well and HST observa:ons con:nue at high efficiency

•  STScI 5-‐year HST opera:ons proposal -‐ Helmut Jenkner •  COS wavelength calibra:on – Cris:na Oliveira •  Cycle 23 and Plans for Cycle 24-‐ Claus Leitherer

STUC – November 2015

Cycle 24 Schedule (2016) CP Released – Jan 13 Mid-‐Cycle #2 – Jan 31 Proposals Due – Apr 8 TAC / Panels – Jun 5-‐10 Phase 2 / Budgets – Jul 21/8 Observa:ons Start – Oct 1

2

•  Cycle 23 Long Range Plan released in early August, 2015. •  Observing started Oct 1, 2015.

•  Early progress: 86 orbits/week through six weeks. •  Consistent with previous post-SM4 cycles:

•  Cycle 17: 84.0 orbits/week •  Cycle 18: 83.4 orbits/week •  Cycle 19: 83.2 orbits/week •  Cycle 20: 85.5 orbits/week •  Cycle 21: 84.0 orbits/week •  Cycle 22: 84.0 orbits/week

•  Previous Cycle Completeness: •  Cycle 21: completed in October 2015. •  Cycle 20: 1 orbit remains, planned for late Dec 2015.

•  Cycle 23 Frontier Fields: •  The first epoch (70 orbits) of Abell S1063 is scheduled to be completed

by mid-November.


LRP: Highlights

3


Current state of the opera:onal LRP •  complete through calendar ending 11/15/15.

Instrument Orbits

WFC3 1703

COS 886

ACS 622

STIS 574

FGS 3

Total 3788(3)

Cycle Orbits

20 1(1)

21 0

22 303(2)

23 3465

Total 3769

(1)  1 orbit planned Dec 2015. (2)  Plan Windows into January 2016.

C22 snaps 529

C23 snaps 1105

Total snaps 1634

Visits not in current plan orbits

unschedulable 45

no plan windows 0

C22 misc 113

C23 misc 306

Total not in plan 464

(3) Some programs have more than one prime SI.

4


Fron:er Field programs •  First four fields complete •  First epoch of first cycle 23 field has been observed/scheduled.

Frontier Field Cycle Total alloc

Exec/sched by 11/15/15

Planned before 9/30/16

Abell 2744 21 140 140 0

MACSJ0416.1-2403 21 140 140 0

MACSJ0717.5+3745 22 140 140 0

MACSJ1149.5+2223 22 140 140 0

Abell S1063 23 140 70 70

Abell 370 23 140 0 140

5


Cycle 22 Large/Treasury programs

Program Total alloc



Planned after 10/1/16

comment

Benneke 124 73 34 4 13 not in LRP

France 125 125 0 0 completed

Freedman 132 120 12 0 done 12/15

Malhotra 160 144 16 0 done 12/15

Oesch 132 128 4 0 done 11/15

Perlmutter(ToO) 86 86 0 0 completed

Robberto 52 52 0 0 completed

Skillman 81 81 0 0 completed

Spencer 194 194 0 0 completed

Tripp 99 99 0 0 completed

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Cycle 23 Large/Treasury programs

Program Total alloc



Planned after 10/1/16

comment

Apai 112 18 22 0 72 not in LRP

Bedin 66 22 44 0

Borthakur 100 0 74 26

Coe (ToO) 190 5 78 82 25 not in LRP

Deming 111 0 74 37

Kirshner (ToO) 100 6 1 1 92 not in plan

Lehner 93 24 22 47

Papovich 130 6 106 18

Peterson 74 0 74 0

Siana 48 0 48 0

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ACS Calibra:ons Update (N. Grogin and the ACS Team)

•  The ACS/WFC and ACS/SBC con:nue to perform well: –  Over 6.5 years with the revived WFC; no ACS anomalies in >2.5 years –  Strong Cyc23 usage: WFC = 700o. prime + 505o. parallel; SBC = 105o.

•  The recently approved Cyc23 ACS Cal plan newly includes: –  Refined photometric & astrometric calibra:on of WFC polarizers –  Measurement of the SBC extended PSF (out to ~5” radius)

•  Long-‐term monitoring of WFC low-‐voltage power supply (LVPS): –  CY15 : “Jump” in daily average of 8-‐bit-‐downsampled LVPS current –  High-‐frequency sampling@ full 16-‐bits suggests steady +1 mA/yr trend –  Voltages unchanging; all

exps. remain nominal


CCD rest-‐state begins crossing next 8-‐bit threshold

CCD rest-‐state ~always above threshold

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•  Subarray Redesign –  Calibra:on headaches for post-‐SM4 ACS/WFC subarrays:

•  De-‐biasing post-‐SM4 subarray images •  Readout-‐:ming Δ makes pixel-‐based CTE correc:on inapplicable to non-‐2K subarrays

•  Readout overheads longer than full-‐frame; <2K columns prevents bias-‐ship correc:on

–  Solu:on: Re-‐define WFC subarray readouts to match full-‐frame :ming •  Twelve new subarray modes, all with 2K columns: (512,1K,2K) rows on all quadrants (A,B,C,D) •  Subarray biases no longer needed (excerpt from full-‐frame); iden:cal CALACS steps as full-‐

frame

•  “Spare the Pixels” –  Elimina:ng “bad-‐column” DQ flagging

from WFC superbiases –  Stable hotpix à stable “bad cols.” –  Reducing warm-‐ & hot-‐pixel DQ flagging from “stable” dark current –  Only DQ-‐flag the “unstable” pixels (variance significantly g.t. Poisson)

ACS/WFC Subarrays Re-‐design and “Spare the Pixels” Ini:a:ve

Actual superbias (includes gradient)

Simulated readout dark (no gradient)

STUC – November 2015 9

HST Focus Maintenance

HST experiences temperature-‐induced focus varia:ons due to varying poin:ng avtude and LEO geometries. On top of this there is a long-‐term shrinkage of the HST metering truss which brings the SM closer to the PM. We periodically correct for this by backing the SM away from the PM to maintain focus. This shrinkage, and the compensa:ng SM adjustments are clear in the plot. Our three SM moves since January 2013 have reacted to recent shrinkage rates and have brought and kept us close to best focus over the past two years. In May 2014 we re-‐fit focus data to regenerate our temperature-‐based focus model, which contains a func:on describing “nominal” secular focus change (from shrinkage) along with temperature terms expressing temperature driven excursions about nominal. We made this updated model available to the community.

See hxp://www.stsci.edu/hst/observatory/focus for related informa:on and access to the model data. We con:nued inves:ga:ons this year into tracking focus using the complete library of WFC3 observed science PSFs. This holds the promise of producing a poten:ally viable focus indicator that could supplement or possibly even supplant the dedicated focus monitor program.

Plot shows the mean loca:on of the HST Secondary Mirror (SM) since SMOV4, expressed in microns of axial displacement wrt WFC3 best focus (WFC3 focus is within 0.5 microns of ACS focus and similarly confocal to STIS & COS) We obtain this secondary mirror displacement from the observed focus aberra:on as determined by our rou:ne phase retrieval code from star images taken in ACS/WF and WFC3/UVIS. 1 micron of Secondary Mirror axial displacement produces 6 nanometers rms wavefront error (via focus aberra:on), or lambda/100 at 600 nm.


HST Focal Plane Evolu:on

50% within 0.23 arcsec (monthly means)

50% within 0.26 arcsec (all points)

A B C

E

Observed minus Predicted Guidestar Separations

D

To provide insight into the evolu:on of the FGS Fields of View on the HST focal plane, we produced a plot of the observed vs. expected guidestar pair separa:ons, serving as a coarse indicator of FGS misalignments. Approx. 200,000 guidestar pair measurements spanning 10 years were obtained and ploxed. The result corroborates our understanding that focal plane calibra:ons in the form of FGS alignment updates (when performed) result in very low errors of a few tens of milliarcseconds, but that evolu:on of the FGS FOVs con:nues to steadily build posi:on errors that can grow to a few tenths of an arcsecond. Currently we are working on an update to address the accumula:ng error (mainly from FGS2).

A.) HST’s opera:onal guidestar catalog is changed over from GSC1 to GSC2. Note the scaxer of the individual (grey) points decreases at this :me. B.) Freshly characterized FGS alignments were updated in HST opera:ons. Note the improvement in the mean error to < 0.1 arcsec for the next year. C.) During SM4 Observatory Verifica:on, the newly installed FGS2 was characterized. (Disregard servicing-‐mission-‐related points in first half of 2009.) D.) Freshly characterized FGS alignments were updated in HST opera:ons. Improvement is clear, though FGS2’s dynamics are primarily responsible for con:nued trending. E.) Freshly characterized FGS alignments and distor:on mappings produce ~<0.05 arcsecond mean errors for a number of months before con:nued FGS trending causes error to steadily accumulate.


COS + STIS – Generic Updates (C. Oliveira and the COS/STIS Team)

•  Flux and flat-‐field reference files to calibrate COS LP3 data were released in July 2015

•  New version of the COS Data Handbook published in Oct 19 2015 (v3) –  Contains many updates from v2, including a descrip:on of the new TWOZONE extrac:on

algorithm for FUV data taken at Life:me Posi:on 3

•  New CalCOS pipeline to be installed by mid-‐November –  Contains code and a new reference file to exclude events affected by hotspot from final co-‐

added products and minor tweaks related to TWOZONE extrac:on

•  Monitoring of gain sag on COS/FUV detector –  High voltage in FUVB will need to be increased in mid-‐Dec 2015 to maintain modal gain

above PHA of 3 in the whole detector

•  Have started high level planning for COS/FUV Life:me Posi:on 4 –  At current usage rate will need to move to LP4 in ~Summer 2017 –  LP4 will likely be below LP3, impact on resolu:on will be evaluated using LSF models and

data

•  Pixel-‐based stand-‐alone automated script to correct STIS CCD CTI was released to the community in Sep 2015


COS – FUV TDS Trending (C. Oliveira and the COS/STIS Team)


LP1 LP2 LP3

Data up to Sep 2015 included

Breakpoints in slope HV Increase

•  TDS slopes in 2014 steeper than 2013, up to ~8% per year, stable up to now

•  Updated TDS ref. file delivered Fall 2014 •  Overall decrease since COS installation varies

~ 10 – 35%

•  Rate of decline of COS FUV Time Dependent Sensitivity (TDS) varies with time, detector, and λ

•  Steeper TDS slopes in periods of increased solar activity – likely due to atomic O at HST’s orbit reacting with CsI photocatode of open-faced COS FUV detector

•  Increase in sensitivity with HV and TDS dependence on cenwave are under study

TDS slope vs. wavelength t > 2013.8

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COS+STIS Cy 23 Calibra:on Plans (C. Oliveira and the COS/STIS Team)

•  COS calibra:on program –  Nine programs monitor the performance of the FUV and NUV detectors (dark rate, sensi:vity, TA, gain, and

wavelength scale) as well as a special program to obtain Lyα airglow spectra

•  STIS calibra:on program –  Twenty programs monitor the performance of the CCD and FUV + NUV MAMAs (dark rate, read noise, flat field,

sensi:vity, etc.) as well 3 special programs •  Measure the gain of Amps A, C, and D •  Monitor STIS focus in rela:on to WFC3, ACS •  Push the limits of coronographic BAR5 (see discussion below)


•  STIS has the sole coronograph still operating in space –  Current STIS performance is 10-4 contrast at 0.25”

•  NIR ground-based extreme-AO has ~10-6 contrast at 0.18” •  WFIRST/AFTA CGI will have ~10-9 at 0.18”

–  Goal of special BAR5 program (9 orbits) is to demonstrate contrast levels of 10-7 at 0.15” •  Will enable new discovery science with increase in

contrast by 1-3 more orders of magnitude compared to current capability

•  Processed data and new capability will be advertised to users before Cycle 24 proposal deadline

•  Data obtained recently from first 3 visits (3 orbits) indicates a contrast of 10-6 at 0.5” (~10 pix)

Pushing the Limit of BAR5 (cont.)!

•  Current STIS performance: ~10-4 contrast at 0.25”!

•  NIR ground-based extreme-AO: ~10-6 @ 0.18”!

• WFIRST/AFTA CGI: 10-9 @ 0.18”!

=> Push STIS performance to 10-7 contrast at 0.15”!

F1V! K6V!

Classical PSF Subtraction!

24!

BAR5 contrast curves from !commissioning data (P12923)!

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Smart archives organized by target and science use: all relevant co-

added data in one click!

Full database starting with COS FUV (10000 datasets) available in

time for Cy24 Proposals

Preview release to be shown at AAS in Kissimmee in January -

come to the STScI booth to see a demo and provide feedback!

Contact for more information: Jason Tumlinson (tumlinson)

Molly Peeples (molly) Andrew Fox (afox)

² WFC3 is operaHng nominally

²  New features available to the observers: ²  IR SPARS5 Sample Sequence – First GO observa:ons successfully

acquired on September 29, 2015 ²  2 new full array UVIS aperture defini:ons (place the target near the C

amplifier) ²  New version of CALWF3 delivered to TEST – will be sent to OPS (and release

to the community) in December 2015 – all WFC3 data (sta:c archive) will have to be reprocessed.

²  Ongoing ac:vi:es: ²  IR background model for GRISMs and and imaging ²  Extend astrometric solu:on to all the UVIS filters ²  GRISM tools ²  CMS monitoring + CMS movement/week <30

Wide Field Camera 3


UVIS Channel Performance

²  UVIS read noise over a period of 6 years (from installa:on to May 2015) increased by 1.4-‐1.9%, due likely to CTE losses, the ever-‐growing hot pixel popula:on, and the general aging of the instrument.

²  Over 6 years of observa:ons the varia:on in exposure :me across the detector due to shuxer shading remain less than 0.1%.

²  There is no no:ceable difference in the present performance of the shuxer mechanism compared to its performance during SMOV

²  Aper 6 years UVIS gain measurements remain within 1-‐2% of the values derived in TV3 and SMOV.


UVIS Charge Transfer Efficiency (CTE)

Radia:on damage effects in low-‐earth orbit CCDs are responsible for degrading CTE

Flux loss due to CTE degrada:on is a func:on of the source’s distance from the amplifier, the source signal level, the background within the image, and the epoch of the observa:ons. In the worst cases in early 2015 losses for faint sources can be as high as 50%. Small amount of pos}lash reduces the losses for faint sources to 15% Pos}lash + pixel-‐based CTE correc:on reduce losses to 3%

CTE close to the Amp CTE far from he Amp

CTE as a func:on of background STUC – November 2015 18

IR Channel Performance

²  Aper 6 years of opera:ons IR gain measurements remain within 2% from the values derived during SMOV

²  Since Cycle 18 we observed a decrease of 0.3% yr-‐1 in the count rate of the tungsten lamp (aging)

²  Par:culate maxer on the CMS mirror is imprin:ng small roughly circular regions of moderate axenua:on on IR images (a.k.a. blobs). ²  Blob-‐corrected flats are improving stellar photometry ²  Blob-‐corrected flats are now available to GOs. ²  Very few new blobs in recent years


Improved Model for Persistence in IR

²  Faint aperglows of earlier exposures are some:mes seen in WFC3 IR data ²  Persistence is due to traps in the pixels of an IR detector

²  The amount of persistence is a func:on of exposure history of a pixel in the detector

²  We improved our model by including the exposure :me of the earlier exposure as an addi:onal factor in the persistence predic:on

²  Persistence clearly varies across the WFC3 IR detector

²  Varia:ons appear to primarily on large spa:al scales, with pixel to pixel varia:ons being small.

²  A correc:on “flat” has been incorporated into the persistence predic:on sopware used to es:mate persistence in HST images.

Persistence decay as a func:on of exposure :me


GRISM tools

In progress advanced GRISM data reduc:on algorithms/sopware

o  Tool to handle observa:ons at mul:ple roll angles

o  Forward Modeling methods to extract fainter sources and understand errors

o  Contamina:on predic:on code: use a direct image of field to predict the contamina:on for each target of interest

Recalibrated 1st order using 250/350 G102/G141 datasets, 800+ uniformly distributed posi:ons on the field, bexer field coverage and solu:on.

IR wavelength solu:on using the Zero order image as reference point.


Gyro 4 Bias Drips


Gyros – Take away message

•  Highly likely that HST Gyro’s will support science opera:ons un:l (and probably beyond) end of the decade

•  Hubble has a very complex poin:ng control system with considerable resilience to failures of its various components –  6 (now 5) Gyros, 3 FGS, 3 FHST (plus addi:on elements to support safe modes)

•  Most likely impacts are to scheduling efficiency and field of regard


Rate Gyro Assemblies (RGA)"Consists of Electronics Control Unit (ECU) and Rate Sensor Unit (RSU) (manufactured by L-3 Communications (then Bendix))"

–  Each RSU contains 2 Rate Integrating Gyros; HST has a total of 6 Gyros"

–  3 Gyros are routinely in control loop"


HST Poin:ng & Avtude Control System

•  HST uses two types of sensors to maintain vehicle avtude –  Rate Gyro Assemblies (RGAs) –  Fine Guidance Sensors (FGSs)

•  RGAs are used to provide the rate input to the 40 Hz vehicle control law (VCL) during all science mission phases

•  FGSs provide posi:on and rate correc:on in vehicle frame to the VCL through the 1 Hz Avtude Observer during fine guiding intervals

•  During FGS guiding intervals, the feedback from the FGSs is used to provide real :me measure and compensa:on of the gyro rate bias error produced by all of the gyros in the control loop


Impacts to Opera:ons

•  Gyros are needed to acquire guide stars (i.e. knowledge of vehicle avtude during slew and occulta:on periods) –  Poorly performing gyros lead to guide star acquisi:on failures –  One or two gyro modes developed

•  Lower observing efficiency •  Dependent upon FHST avtude updates

•  Avtude error accumulates due to the varying bias signal between FGS guiding intervals (AOA = Avtude Observer Anomaly)

•  There are two types of GS Acquisi:ons –  Primary Acquisi:ons (Acqs)

•  Occur aper large vehicle slews & are preceded by an FHST OBAD avtude correc:on which corrects any avtude errors from AOA bias errors

•  These also typically have search radii of 55 arcsec or bexer –  Reacquisi:ons (Reacqs)

•  Occur aper primary acquisi:ons and other Reacqs with no FHST OBAD avtude correc:ons

•  These always have search radii of 30 arcsec


Impacts to Opera:ons

•  During the FGS guide star acquisi:on process the FGSs measure the residual avtude error aper gross avtude correc:ons (>0.3 arcsec) have been completed

•  The observer convergence period is then executed to drive the residual error to zero within 40 seconds

–  This convergence is affected by any residual or uncompensated rate error –  If the error is not within the Loss of Lock threshold, the acquisi:on will be re-‐axempted up to

3 :mes –  Generally uncompensated bias errors (due to the AOA) will cause all 4 axempts to fail and

the acquisi:on will fail –  It can also delay the sevng of the science ini:aliza:on flag and impact science opera:ons to

varying degrees •  Two complementary approaches have been iden:fied to reduce the vehicle errors

induced by the AOA –  A historical observer that will supplement the exis:ng gyro bias compensa:on, providing

varying levels of gyro rate bias compensa:on depending on the vehicles orbital posi:on rela:ve to EOD.

–  An ini:aliza:on of the exis:ng avtude observer to rates observed by the Dominant FGS, that will allow the observer to more rapidly reduce rate error residuals and posi:on error during the acquisi:on sequence.

•  Cascading failures are more likely to occur in automated opera:ons


HST Gyro Run Times through 2015/Sep-30"

Key"" = Failed Gyro""SFL = Standard Flex Lead "EFL = Enhanced Flex Lead (silver plated)""RR = Rotor Restriction "AOA = Attitude Observer " Anomaly"

1 Flight Times are powered-on times and do not account for increased degradation when off due to thermal effects from a companion gyro that is powered on"

Launch Gyros 1 – 108 – 1005 SFL Failure 3.9343 0.4573 4.3916 38470

(4/1990) 2 – 113 – 1005 healthy 4.1884 0.4219 4.6103 403863 – 110 – 1002 healthy 3.6142 1.1620 4.7762 418404 – 138 - 1002 healthy 2.4964 1.0763 3.5727 31297

5 – 104 – 1003 healthy 3.6142 1.2574 4.8716 426756 – 127 - 1003 SFL Failure 2.4570 1.5185 3.9755 34825

SM1 Gyros 3 – 112 – 1007 SFL Failure 5.3731 0.4776 5.8507 51252

(12/1993) 4 – 158 – 1007 SFL Failure 3.3434 0.2553 3.5987 315255 – 118 – 1006 healthy 6.0478 0.4943 6.5421 573096 – 151 - 1006 SFL Failure 4.8808 0.4019 5.2827 46276

SM3A Gyros 1 – 155 – 1003 healthy 6.2003 0.6997 6.9000 60444

(12/1999) 2 – 110 – 1003 SFL Failure 6.4126 0.2128 6.6254 580393 – 104 – 1002 RR, stall 3.3482 0.4369 3.7851 331574 – 138 – 1002 AOA 5.6929 0.4046 6.0975 534145 – 156 – 1008 RR, stall 1.3458 0.2361 1.5819 138576 – 159 - 1008 healthy 2.8769 0.2217 3.0986 27144

SM4 Gyros 1 – 127 – 1005 healthy 1.6583 0.7339 2.3922 20956

(5/2009) 2 – 160 – 1005 healthy 1.6583 0.7535 2.4119 21128

EFL 3 – 148 – 1004 AOA (powered off) 1.8833 0.6684 2.5517 22353

EFL 4 – 150 – 1004 RR, high motor current 6.3847 1.1981 7.5828 66425

5 – 161 – 1006 SFL Failure 4.8174 1.0613 5.8787 51497

EFL 6 – 152 - 1006 Healthy (powered off) 3.1089 0.9944 4.1033 35945

Total(Hrs)Gyro-ID/RSU Status at End Flight time 1

(Yrs)Test Time

(Yrs)Total (Yrs)

ß Gyro 4 à longest on-orbit run time"

Current On-Orbit Configuration:"G1 – G2 – G4"


Gyro 1 Gyro 2 Gyro 4

Post SM4 Gyro 4 has been exhibi:ng rela:vely significant bias ships perhaps indica:ve of flex lead degrada:on

4/30 5/28 6/25 7/23 8/20 9/17 10/15 10/29


" " "Recent Gyro 4 Trends"

-  Over the last several months, Gyro 4 has been exhibiting large bias rate shifts [see plot]"-  On September 19, Gyro 4 experienced a large ~150 arcsec/hr rate bias shift "

•  Attitude errors accumulated as a result of the large drift rate and caused the failure of several Guide Star Acquisitions over the course of ~ 4 orbits"

•  The effect was exacerbated by the unusually long delay between the FGS Guide Star Acquisition and the preceding On-Board Attitude Determination update"

-  Another large bias shift of ~80 as/hr occurred on September 23, however the onboard control system was able to compensate "

-  A third large bias shift of ~ 86 arcsec/hr occurred on October 16 and subsequent bias updates of the same general level indicated a rapidly changing bias"

•  The large bias rate accumulated error over an 8 hour period because onboard bias updates could not be be scheduled during the 8 hour science observations "

•  The rate of the changing bias slowed and returned to nominal values with no loss of science"-  The Gyro 4 bias trend has re-stabilized after the large bias shift on October 16 and it appears to be

following the trend-line established prior to May 2015, albeit noisier [now up again!]"-  Mitigations"

-  The GS Acquisition maximum search radius was increased to support larger potential attitude errors from uncompensated biases"

-  The minimum data threshold for performing an onboard gyro bias update was reduced from 20 minutes to 5 minutes (to accommodate rapidly changing bias rates)"

-  Other mitigations are being considered; the effectiveness of the mitigations have not been determined because of the quieting down of Gyro 4"

-  Other than the loss of science on October 19, no further impacts have occurred"STUC – November 2015 30

RGA Anomalies – Flex Lead Failure"

Standard Flex Lead (SFL) Failure"–  Lead Composition 85% Ag, 15% Cu"–  Corrosion along the flex lead(s) creates a hot spot"

•  Spot is sensitive to nominal temperature variation, causing mechanical motion (large Gyro bias rates)"

–  Lead eventually breaks causing loss of 1 phase of motor"•  Large bias shift in gyro frame (hundreds of arcsec/hour)"•  Motor current ~doubles "•  Increased heater duty cycle due to less current power

dissipation in the motor"–  Rate of SFL degradation increases exponentially with temperature

and continues even if gyro is off when companion gyro is on"–  Successful spin-up after powering down is not possible as both

leads are required for full phasor to be applied to solid core rotor"

Enhanced Flex Leads (EFL)"-  Coat the flex lead with a protective barrier to stop

degradation caused by the BFTE float fluid"-  Silver plating will double the life expectancy of the gyros"

•  Copper dissolves 100x more quickly than silver"


RGA Anomalies – Rotor Restriction"

Gyro 5 Rotor Restric:on Jump in Motor Current

~50.8 mA"5 min"

–  A build-up of particles and lubricant between the shaft and the rotor results in a transient load torque and a momentary disruption in spin motor phase, causing motor to draw more current to maintain speed"

–  Gyro operates at higher current until a power cycle"

•  Jumps of 30-50 mA not uncommon"•  Moderate bias shifts in gyro frame

(Tens of arcsec/hour)"–  Successive jumps may cause gyro to stall (stall

current ~ 330 mA)"–  Power cycle may bring gyro back to pre-rotor

restriction current levels, however vendor recommends that gyros that continue to run following rotor restrictions not be power cycled due to increased risk of non-start"

–  It was determined that gyros that failed on the ground and on orbit due to rotor restriction tended to have shaft to rotor spacing on the low end of tolerance. Tolerance was modified to ensure greater spacing. Gyros already built were evaluated with new tests to ensure rotor freedom of movement about the shaft (Tumble Test)."


RGA Anomalies - Attitude Observer Anomaly (AOA)""

•  Trending showed that the day/night cycles were causing increasingly larger variations in the estimated bias in the V2 axis (in current on-orbit configuration, V2 axis bias error is driven by Gyro 4, although Gyro 4’s AOA signature continues to be small) "

–  These variations caused uncompensated rate errors sufficiently large enough to cause the subsequent GS Acquisition to declare Loss of Lock as insufficient time is allowed for bias estimate to be established"

•  The cause of the AOA signature is not completely established; a possible cause is asymmetric corrosion-induced degradation between the 7 gyro flex leads "

–  The orbit terminator heat pulse creates mechanical stresses as it travels through the asymmetrically corroded flex leads, these impose a force on the float."

-  Not all of the Gyros with AOA signatures impacted science operations"-  Mitigation:"

–  The Historical Observer (HO) algorithm developed to mitigate AOA bias and activated in November, 2012 was designed to measure/compensate the orbital variation per minute (vs. an orbital average applied previously) in the gyro rate bias "

–  Currently, only a nominal orbital variation is evident in the gyro bias compensation; Gyro bias is well monitored."

•  Additionally, the vehicle control law’s Attitude Observer, which determines real time estimates of uncompensated gyro bias from the FGS while fine guiding, was modified to initialize with a coarse estimate of the uncompensated bias from FGS data early in the acquisition sequence, allowing for rapid convergence on large bias error during allotted time during guide star acquisition (Attitude Observer Initialization (AOI))."

•  For Gyro 4, the AOI and HO compensation have been successful in minimizing the effect of the bias variations. To date, there has been relatively minor impact to science operations due to the Gyro 4 bias"

"

"


"Though Gyro 4 is an EFL gyro, there is the possibility that the recent bias signature indicates Gyro 4 may fail in the near term (hopefully not). ""-  In the event of Gyro 4 failure (or any of the current complement), the vehicle will enter Kalman Filter Sun

Point (KFSP) safemode interrupting science "

-  The failed gyro will be replaced with Gyro 6 to maintain the 3-Gyro Science Mode configuration "•  3-Gyro Mode provides maximum science performance and scheduling flexibility while HST and

Science Instruments are operating at near peak performance "

-  The KFSP Safemode recovery procedure was recently updated and tested"•  A redlined procedure is in development specifically for a Gyro 4 failure

"As the failure described above would be the second gyro failure (since SM4), an assessment would need to be made as to the gyro configuration for subsequent failures"

Note:!Though Gyro 3 has some performance problems, it can support 3-Gyro Mode (with some impacts).!Also, when down to only two viable gyros, the option of going to One Gyro Science Mode rather than Two Gyro Science mode is very advantageous for preserving the second gyro. Modeling and on-orbit testing has demonstrated that One Gyro Science is as effective (assessed over all metrics) as Two Gyro Science Mode.!

Forward Plan (to date, and regularly revisited)


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