# Presentation: 116776

## Section 19

***Attitude Control System***

*** ******. . . Paul Sanneman***
*EO-1 ACS Lead Systems Engineer, Swales Aerospace, Inc.*

## Contents

***Contents***

***Attitude Control Subsystem Block Diagram ***
***Changes since March 2000 Red Team Review***
***Thermal/Vacuum II Evaluation***
***Open Problem Reports***
***Special Topics***
***IRU Removal and Reinstallation***
***On-orbit Testing of Safe Hold Mode***
***Autonomous Star Tracker Issues (including IMAGE AST issue)***

## ACS Architecture Block Diagram

***ACS Architecture Block Diagram***

## “As Run” Verification Matrix

## Projected Power On Time

## Changes Since Red Team Review

***Changes Since Red Team Review***

***ACS Components***
***AST & ACDS DC/DC Converter lid stiffeners (see Special Topic)***
***Removed IRU to prevent helium exposure (see Special Topic)***
***ACE Software***
***ACE RSN S/W update to Version 3.11 on 8-JUN-00***
*PTR0927: Generic Code modified to have IRAM2 checksum protection on [had been missed since ACE is the only RSN with the extended RAM capability]*
*PTR0939: Prevent ACE 25 Hz Event Messages and use telemetry error counters instead*
***Code changes tested on 8-JUN-00; 416+ failure free hours ***
***M5 ACS Software***
***Minor parameter changes via M5 Table loads to RAM***
***Related to improving operation issues - no S/C safety issues  ***

## Summary of Open Items fromMarch Red Team Review (1 of 2)

***Verification Matrix, no update necessary (page 18-14)***
***Updated operating hours included on Slide 7-5 (page 18-15)***
***PR 674-20-41 AST number of stars issue (page 18-19)***
***Confirmed this is a star field simulator issue (see Slide 19-9)***
***GPS tensor warm start ground procedures (page 18-20)***
***Fully tested and available in MOC ASIST***
***No updates to SHM from final CPT (page 18-34)***
***Updates to remaining work***
***AST/IRU alignment...detailed in Slide 19-10***
***Conclusion of AST DC/DC Converter concern (18-40)***
***See Special Topic on AST DC/DC Converter***

## Summary of Open Items fromMarch Red Team Review (2 of 2)

***Updated summary of IRU PDV history (page 18-49)***
***Details in Special Topic.  No outstanding performance issues.***
***SIRU return to spacecraft (page 18-57)***
***Details in Special Topic. Reintegration successful. Degradation reversed.***
***Open actions from ACS Phasing Review (page 18-63)***
***CPT phasing tests following final MV S/W load -completed***
***CSS phasing following final solar array attachment -completed***
***Final magnetic phasing completed on 28-JUL-00 - no issues***

## Thermal Vacuum II Test Results

***Thermal Vacuum II Test Results***

***Attitude Control Subsystem performance validated as part of CPT segments and via other special tests***
***All CPT associated tests run at hot and cold plateaus***
***RWA Overspeed protection verified at hot and cold plateaus***
***AST Thermal Electric Cooler operation modes verified***
***AST TEC default state and Effective Focal Length changed/restored during T/V II as demonstration of planned on-orbit maintenance procedures***
***IRU internal heater control of gyro platform validated***

## Reaction Wheel Assemblies

***Reaction Wheel Assemblies***

***RWA performance has been verified in both air and vacuum***
***Control torques issued by override and closed-loop software***
***Overall run-up and coast down trends have been verified with vendor and are summarized on next page***
***T/V II testing of overspeed protection provided below with wheel speeds in RPM ***

## RWA Run-up / Coast Down Trend Table

***Trending data is consistent over time.***
***Estimated drag torque very consistent and near 50% of spec level  ***

## Critical PR Status 

***Critical PR Status ***

***PR-468-20-4 IRU Parametric Drive Voltage***
***See Special Topic ***
***PR-674-20-41  AST Number of Stars = 18***
***Issue and problem report have been closed***
***Similar operation noted on the MAP ASTs during Thermal/Vac testing at the component level***
***Investigation of MAP occurrence with AST-GSE confirmed this is a Star Field Stimulator GSE issue ***
***Contamination on lens of GSE can cause double reflection that causes a ‘match’ with a very dim star in the AST internal star catalog***

## ACS Flight Readiness

***ACS Flight Readiness***

***ACS components and hardware are ready***
***ACS and ACE software are ready***
***ACE Safehold Mode is ready***
***Ops preparations/training are ready***
***Remaining Work***
***No outstanding problems or issues***
***AST/IRU alignment measurements at launch site***
***Red Book Item: IRU sensitivity to helium exposure***
***Under control via upgraded purge system on S/C and at launch site***

***Attitude Control Subsystem is READY***

## Special Topic:

***Star Tracker Issues***

* ****. . . Wayne Roher***
*Litton Advanced Systems*

## AST Interpoint DC/DC Converters Failure Mode

***AST Interpoint DC/DC Converters****** Failure Mode***

***MAP experienced  failure with ± 15V DC/DC converter***
***MAP2 - Open failure during ATP at ambient after Thermal/Vacuum***
*DPA indicate inadequate stress relief on internal bond wire, insufficient solder, and solid adhesive attachment to lid caused bond wire to pull away from pad in vacuum.*
***EO-1 AST X-ray investigation***
*The two DC/DC converters on the EO-1 AST were X-rayed and found to have met the criteria determined by Code 562 as having sufficient relief distance from the transformer.*
*Code 562 speculated that an additional failure mode exists*
*  “**Oil canning” of converter package could cause adhesive on bottom of transformer to release.  Transformer would move upward with package lid, causing transformer bond wire to pull away even if adequate stress relief existed for normal operation in a vacuum.*

## AST Interpoint DC/DC ConvertersRework

***AST Interpoint DC/DC Converters******Rework***

***Lockheed Martin Palo Alto and Lockheed Martin Mission Success agreed that this failure mode potential justified corrective action.***
***Stiffening the lid to prevent “oil canning” was determined to be the best solution to address all concerns of stress, unattached adhesives, and vibration.***
***Lid stiffener of 20 mil Kovar and minimum 5 mil bond line of epoxy was added to both D/CDC converters.  (See Converter Lid Stiffening Special Topic)***
***Both converters tested to deflect less that 1 mil in vacuum***

## AST Interpoint DC/DC ConverterRework Conclusion

***Retest***
***AST workmanship vibration***
***AST Functional on Spacecraft***
***AST CPT on Spacecraft***
***Spacecraft level T/V***
***272 hours on time since lid stiffener was added***
***Conclusion***
***EO-1 AST has successfully completed all testing post lid stiffening***
***EO-1 AST is ready for flight***

## Other Subsystem DC/DC Converter Rework and Re-Qualification

***All MTRxxD type Interpoint DC/DC Converters were considered as potentially defective due to the failure mode detected on the MAP AST2***
***Two other Subsystems contained Converters that required rework***
***GPS PCU (1)***
***ACDS box (2); C&DH LVPC and ACE I/O cards***

## GPS PCU DC/DC Converter

***GPS PCU DC/DC Converter***

***Rework and Re -Qualification process of GPS PCU***
***Removed from Spacecraft***
***Added stiffener lids, 40 mil Kovar, 10 mil minimum bond line***
***Vacuum test, deflection less than I mil***
***One Axis workmanship vibration***
***Functional on Spacecraft***
***CPT on Spacecraft***
***Spacecraft level Thermal Vacuum***
***Conclusion***
***No anomalies recorded***
***GPS PCU is ready for flight***

## ACDS DC/DC Converters

***ACDS DC/DC Converters***

***Rework and Re -Qualification process of ACDS***
***Box removed from Spacecraft, C&DH LVPC and ACE I/O boards removed***
***Added stiffener lids, 40 mil Kovar, 10 mil minimum bond line***
***Vacuum test, deflection less than I mil***
***Board level functional tests***
***Boards reassembled in ACDS chassis***
***Pre-vibe box level Functional Test run***
***One Axis workmanship vibration***
***Post-vibe box level Functional Test run***
***Spacecraft Integration tests***
***CPT on Spacecraft***
***Spacecraft level Thermal Vacuum***
***Conclusion***
***No unexplained anomalies recorded***
***ACDS is ready for flight***

## Image AST Anomaly

***The IMAGE AST was unable to acquire between June 9 and August August 3***
***The AST remained in standby mode during this time; power was not recycled***
***On August 3, the AST re-acquired***
***1.4 degree angle further from the sun than on June 9***
***Dropped out twice during that day, quickly recovered***
***Has not dropped out since.***

## Image AST Anomaly Investigation

***Image AST Anomaly Investigation***

***A Failure Review Board (FRB) was held to determine potential causes of the AST acquisition failure. ***
***Stray Light is the most probable root cause ***
***Housekeeping nominal (voltages, temperatures)***
***Increased elevated background and reduction in guide star identification were observed during and leading up to the failure to acquire after a loss of track.  ***
***Periodic trending occurred nearest the sun; loss of track and re-acquisition.  Symptoms got worse as sun angle decreased. ***
***Symptoms improved and re-acquisition was attained during eclipse portion of the the orbit.***
***No increase in brightness or position error was found.  ***
***All observation are symptomatic of stray light effects. ***

## Image AST Anomaly Investigation

***Image AST Anomaly Investigation***

***Straylight analysis indicates the AST should have been able operate under the current mission attitude. ***
***The IMAGE AST uses a lightshade (or baffle) designed to keep the sun or Earth out of the boresight (within 12.5 degrees) with no redirected light within 15.1 degrees of the boresight. ***
***Image minimum bore sight axis to the sun in July at loss of track was 22 -42 degrees (AST is 10 degrees off spin axis)***
***Most likely sources of Stray light are:***
***Contamination***
***Glint from 10 Meter Boom***
***Contributions from CCD Mask***

## Differences Between Image & EO-1

***Differences Between Image & EO-1***

***Sun Angle***
***Image AST approaches within 4 degrees of the Sun***
*Lost track at 22-42 degrees*
***EO-1 AST approaches within 70 degrees of the Sun for nominal nadir pointing operations***
***Baffle differences***
***Image***
*16 inches*
*12.5 degrees of protection from sun*
***EO-1***
*12 inches*
*30 degrees of protection from sun*

## Results of Image AST Anomaly and Investigation

***Results of Image AST****** Anomaly and Investigation***

***Lockheed believes the anomaly occurred due to unknown form of contamination***
***Evidence indicates the AST did not experience a functional failure of the electronics***
***Data indicates the AST is functioning nominally and the data is good***
***Lockheeds preliminary conclusion of the anomaly event and investigation analysis is that this event is not a systemic failure of the ASTs and does not impact the expected reliability of the ASTs built for other missions.***
***Formal conclusion of the FRB is expected late August***
***Lockheed believes EO-1s AST is ready for flight.***

## What Happens If the AST Fails?

***What Happens If the AST Fails?***

***AST has been extensively tested on S/C and performance has been nominal.  All issues have been aggressively pursued.***
***Demonstrated reliability of product line is less than desirable.***
***Error prone manufacturing and test efforts***
***Similar AST on DSI failed 15 months into mission***
***Flight dynamics ground based attitude determination could achieve 1 to 5 degree pointing accuracy***
***Would allow Landsat 7 limited image comparison since we would be within its 15 degree swath width***
***Ground attitude estimate developed using TAM and gyro data***
***Current flight ACS S/W has capability to use daily uploaded attitude estimate, propagated using gyro data***
***Would require some ground software to prepare and uplink daily attitude data; would be developed if AST fails.  Sun sensor safehold used until software developed.***

## Special Topic:

***IRU Removal and Re-installation***

*** ******. . . Paul Sanneman***
*EO-1 ACS Lead Systems Engineer, Swales Aerospace, Inc.*

## SIRU Nitrogen Purge - Background

***SIRU Nitrogen Purge - Background***

***Litton Guidance & Control Space Inertial Reference Unit***
***Utilizes three Hemispherical Resonator Gyros (HRGs)***
***Quartz crystal hemisphere oscillated at specific amplitude and frequency***
***Input angular rate measured by nodal displacement on rim***
***Quartz crystal becomes permeated with Helium***
***Increases gaseous damping, requires larger drive voltage - Parametric Drive Voltage (defined as a negative voltage)***
***Not an issue prior to arrival at GSFC Building 7***
***Significant amounts of Helium released in Building 7 by environmental chamber testing processes***

## Summary of PDV History

## Gyro A PDV Slope Estimate

## PDV Trends Since S/C Thermal/Vac

## SIRU Return To Spacecraft

***SIRU Return To Spacecraft***

***Re-integration performed 11-MAY-00 ***
***Building 7 air sampling validated low helium concentration***
***Building 7 air under constant He monitoring using leak detector***
***Continue to have close coordination with Building 7 operations personnel to further minimize exposure***
***Re-integration included new aluminum-wrapped Teflon tube inside spacecraft and stainless steel tube from S/C to tank***
***Gyro Parametric Drive Voltages indicate that both the storage at Swales and the upgraded purge system have reversed the degradation***

## Outlook

***Outlook***

***Mechanical and launch vehicle I/F engineers have focused activity for IRU protection throughout remaining S/C I&T at GSFC, during transport and launch site processing***
***The increased PDV is NOT a performance issue - just needs to stay within (-5V) capability***
***About one volt of margin required for full 10 deg/sec rate capability***
***Desire PDV values of 3.5 V (@25C) at time of SC mount on LV***
***PDV Voltages on 28-JULY-00: A=-2.66, B=-2.23, C= -2.50  @23C***
***Purge installation on Launch Vehicle (L/V) has been improved to the extent allowable by the L/V vendor/operator***
***Expect Parametric Drive Voltage to remain stable or slight improvement through launch and will slowly recover over the course of the mission - residual risk has been minimized***

## Special Topic:

***On-Orbit Testing of Safe Hold Mode***

*** ******. . . Paul Sanneman***
*EO-1 ACS Lead Systems Engineer, Swales Aerospace, Inc.*

## RFA 33.33 

***RFA 33.33 ***

***Reviewer: ******	******Ann Merwarth***
***Specific Request: ***
***Hold a technical peer review with operations experts from outside the project to identify the pros and cons of conducting the safemode test on orbit. Review the results with Center and Program management and ensure that all parties "buy into" the plan for this test. If the Project decides to do this test, we recommend that it be delayed as long as possible.***
***EO-1 Response: Peer review held on 20 APR 2000***
***Chaired by Eric Holmes, GSFC Code 571  GNC Systems Engineering***
***Board members: Alan Reth, Sam Placanica, Landis Markley***

## Summary of Peer Review

***Summary of Peer Review***

***Review Agenda:***
***Review Team Introductions and Purpose***
***Safe Hold Mode Implementation***
***Safe Hold Mode Reviews***
***Safe Hold Mode Testing during S/C I&T***
***On-orbit SHM Test Plans for Two tests***
***Benefit/Risk Summary for On-orbit SHM Test***
***Review Conclusion:***
***The review panel unanimously agreed with the plan to proceed with the planned on-orbit test of SHM with the following actions to Swales Aerospace***

## Peer Review Action Items

***Peer Review Action Items***

***Action 1 (by Sam Placanica):***
***Verify that all instruments can survive dwelling on the Sun for at least 10 minutes.***
*ACS, Thermal and Systems investigated and determined that there is enough attitude variation following SHM entry to prevent instrument thermal issues*
***Action 2 (by Sam Placanica):***
***The duration of the SHM shall be at least 1 complete orbit.***
*This is now included in the launch & early orbit mission plan.*
***Action 3 (by review panel):***
***Augment test 1 as follows: Have the solar array outside of the 5 degree "indexed" tolerance at the time SHM is initiated, so that SHM's indexing function via ECU#2 and Pot #2 are demonstrated.***
*STOL procedure ACS_SAD_10 developed and tested to perform this function prior to commanded SHM entry*
***Second SHM test removed from mission plan as there was limited benefit and timing would be obtrusive to instrument activation/checkout***

***All action items closed.  RFA 33.33 closed.  ***