ACS Current Status

M.Sirianni

TIPS Feb 15, 2007

Agenda:

• ACS Side-2 failure

• SBC reactivation

• ACS programs conversion

Timeline:January 27, 2007

12:29:12 – ACS began WFC observation, shutter was closed because of a GSACQ failure

12:34:17 – Initial spike in HST structure current12:34:21 – Begin a 7-second ramp-up of HST structure and load bus current12:34:28 – ACS PDU-2 fuse blows, ACS telemetry goes to zeros12:34:33 – ACS suspended because of invalid mode12:34:37 – NCS pressure sensor detects a pressure burst, initiating HV

protection and NCS safing12:34:38 – ACS safed because of invalid mode12:34:42 – HST enters Inertial Hold

January 29 – ACS Hybrid LEI team given “go” to prepare for Side-1 switch pending ARB recommendation and HST Project approval

January 31 – ACS Side-2 ARB Kickoff Meeting. Goal: “Assess the risks of recovering SBC Operations on ACS Side-1”

February 5 – ARB Status Briefing #1 to HST ProjectFebruary 9 - ACS heater zone B switched to Side-1February 13 – ARB Status Briefing #2 to HST ProjectFebruary 15 - Flight Readiness Review

• HST was recovered from Inertial Hold Safemode DOY 028– Health and Safety SMS intercept at 028/07:00– HGA communications restored at 028:07:55

• Safing System is in its Nominal Operational Configuration– Neon Leak Safemode Test was re-enabled 028/17:45 UT

• Battery performance is nominal– Battery temperatures are below 0degC since event and converged– System SOC increased 3-5 A-H

• TPS reporting nominal pressures • FHSTs and FGSs powered back on

– Temperature and performance are as usual

• NCC was returned to its operate configuration on DOY 030/01:09 UT• NICMOS was recovered to SAA Operate on 032/15:48 UT

– Subsequent filter wheel checkout was nominal – Resumed science observations - NGC 4639

• WFPC2 resumed nominal science operations– Calibration image of Omega Cen, a globular cluster

• Structure current elevated in two events separated by ~3.5s– First event persisted for ~1.5s and peaked at ~6A– Second event persisted for ~7s, increased gradually, was very noisy,

peaked at ~18.6A, and ended abruptly

• Main Bus current elevated during both events– First event approximately tracked structure current– Increase during second event peaked at ~37A

• PDU-2 current elevated only during second event, increase peaked at ~13.6A

• ACS input current monitor saturated at 12A during peak of second event and returned to zero when event ended

• ACS input voltage sagged by ~1.5V during peak of second event and dropped to zero when next sampled after drop in currents

What was observed:

• NCS/ESM Total Pressure Sensor measured peak pressure of 1.0E-4 torr– Pre-anomaly reading was 1.6E-7

• After the overcurrent event finished, the gas pressure decreased exponentially

Possible origin of fault:

1. MEB1- LVPS2 (Side-2) 2. Auxiliary Power Box (APB)3. Harnesses between LVPS2 and APB

Most likely cause of the fault:

Exploding/burning tantalium capacitor

The ARB is still investigating ways to rule out origin of the fault.

So far the primary goal of the ARB has been the assessment whether

SBC can be safely operated under side-1.

Hold CircuitsSide-1

TEC

Calibration Lamp Controller

Hold Power 2

Heater Power 2

28V Spacecraft

Input Power (PDU)

TEC Power 2

CEB Power 2

Operate Power 2

Mechanism Power 2

Calibration Power 2

CEB

MEBSide-2

MechanismsSide-2

Hold CircuitsSide-2

Zone A2

SBC

Anneal Power

Hold Power 1

Heater Power 1

28V Spacecraft

Input Power (PDU)

TEC Power 1

CEB Power 1

Operate Power 1

Mechanism Power 1

Calibration Power 1

MEBSide-1

MechanismsSide-1

Anneal Power 1Anneal Htrs

Side-1Anneal Htrs

Side-2

Powered Units

Unpowered Units

PreviouslyFailed Unit

Zone B2

Zone A1

Zone B1

ACS

Current Situation

Hold CircuitsSide-1

TEC

Calibration Lamp Controller

Hold Power 2

Heater Power 2

28V Spacecraft

Input Power (PDU)

TEC Power 2

CEB Power 2

Operate Power 2

Mechanism Power 2

Calibration Power 2

CEB

MEBSide-2

MechanismsSide-2

Hold CircuitsSide-2

Zone A2

SBC

Anneal Power

Hold Power 1

Heater Power 1

28V Spacecraft

Input Power (PDU)

TEC Power 1

CEB Power 1

Operate Power 1

Mechanism Power 1

Calibration Power 1

MEBSide-1

MechanismsSide-1

Anneal Power 1Anneal Htrs

Side-1Anneal Htrs

Side-2

Powered Units

Unpowered Units

PreviouslyFailed Unit

Zone B2

Zone A1

Zone B1

ACS

Side-1 powered on for SBC Operation

ACS Side-1 Checkout Programs

– Filter Wheel Check (#11094, 2 internal orbits, P.I. = C. Cox)• Commands the SBC filter wheel to each of its positions (in both

directions)• Verifies proper motion of wheel through encoder readout• Test has been used previously (e.g., Side-2 switch)

– SBC MAMA Recovery (#11048, 4 internal orbits, P.I. = C. Cox)• Initial MAMA turn-on and recovery from anomalous shutdown

– SBC was off when ACS was safed, so this is a conservative procedure

• Brings the MAMA back to operating condition while watching for possible problems

– Signal processing check– Intermediate high voltage ramp-up– Full high voltage ramp-up

• Fold analysis provides detailed performance information– Measures charge cloud size on anode and gain

• Darks and flats obtained during test• Test has been used previously (e.g., Side-2 switch)

– Three Stage Contamination Check/Monitor• Modification of Internal Flatfield Program (#11052, P.I. = R. Bohlin)

– D2 flat for all 6 filters (6 orbits)– Subset of filters (2 orbits) each week to monitor until external

(NGC6681) observation is obtained (maximum of three weeks)

• Modification of SBC Flux Calibration Program (#11056, P.I. = J. Walsh)

– Single orbit ASAP on white dwarf standard WD1657+343 (visible now)

» F122M, F165LP, PR110L PR130L– Second orbit one week later

• UV Contamination Monitor (#11050, P.I. = R. Gilliland)– Observation of NGC6681 (1 external orbit)– NGC6681 becomes visible ~ February 28– Comparison against historical data– Exposures in all 6 filters and 2 darks (in occultation period)– Repeat up to 4 times

Conversion of ACS programs

SPD and HST MO have asked INS to review existing cycle15 ACS

proposals to identify candidates for a conversion to WFPC2 or NICMOS

~ 120 programs are receiving a double technical review by INS. An internal Feasibility Review panel will asses science and time with

guidance from the technical reviews.

Most of the PIs will be notified in early March. (PI can/will appeal

Review of phase-1s is coordinated by L.Smith.

Phase-2s will be processed following the usual procedures

(with limited reviews).

Backup Slides

WFPC2: Omega Cen - f814W (after anomaly event)

MEB 1

LVPS 2

MEB 2

LVPS 1

CEBs

SBC

APB

Physical Isolation

Debris possible in LVPS2 and APB Side 2

Physical Isolation

Fuse Open

Hold Power presently active

Fuse OK

Only new powered state in vicinity of anomaly suspects is MEB1 CS/SES sections; Physical

Isolation is provided

STIS MEB

ACS, Side-2 with panels removedAPB is mounted to truss; here shown unsecured and resting in cavity

WFC Dark CurrentWFC Dark Current

WFC Hot PixelsWFC Hot Pixels

The new the temperature setpointbrought dark Current and hot pixels back to the level after only 18 monthson orbit.