March 25, 1997
CCD Imaging Spectrometer
|Submitted to:||Submitted by:|
|George C. Marshall Space Flight Center
National Aeronautics and Space Administration
Marshall Space Flight Center, AL 35812
|Center for Space Research
Massachusetts Institute of Technology
Cambridge, MA 02139
This report covers the period February 1997.
A monthly status review for ACIS was conducted on February 3 and 4. Gordon Garmire from PSU attended, as well as Harvey Tannenbaum from SAO, Al Pillsbury from Lincoln Lab, Lloyd Oldham and Larry Campbell from LMA, and Max Rosenthal, Buddy Randolph, Tony Lavoie, and Nes Cumings from MSFC. The main topics were the ACIS hardware and verification schedules. Several major decisions were made: the T-V test of the Flt Detector Assembly would be done at XRCF; the flight OBFs must be acoustic tested; and the thermal vacuum test limits were defined. On the following day, a short TIM was conducted between MIT and LMA.
ACIS participated in the weekly AXAF telecons on February 11, 18, and 25. MIT did not participate in the review on February 4th due to the monthly review in process on that date (see above). ACIS participated in the FPSI telecons on February 12 and 26.
At Lincoln Lab, progress continued on the CCD front. In early February, the set of 10 flight CCDs was selected and sent to LL for installation on the flight focal plane. Upon arrival, an inspection was performed and found that three of the four CCDs assigned to the Imager were contaminated as evidenced by droplets on the OWSs that accompany each CCD. The rest of the month, and early March, were consumed with trying to determine the nature and cause of the contamination, and of course the best method of cleaning the affected CCDs. Ultimately, a vacuum bakeout for several days at 30°C was selected. The four imagers were cleaned in early March and the spectrometers by the middle of March. This contamination issue caused a loss of about six weeks in the completion of the flight focal plane.
The following is a brief summary of the status of the other ACIS elements:
The LN2 leak in the ACIS-2C unit was repaired at MSFC in late January. Unfortunately, the leak testing damaged one quadrant of the FI device. However, it was installed in the XRCF system during the mid-February re-pressurization cycle of the XRCF chamber. The BI CCD is working well.
Four sets of flight OBFs had been calibrated at the Wisconsin Synchrotron and successfully completed 1238 certification at LMA in January. However, the "best" set was delivered late by Luxel. It was calibrated at Wisconsin and selected as the primary flight candidate. As a result of the February 4 review, it has been returned to LMA for acoustic testing (as was done for all other flight sets).
The Flight DEA/DPA/SS was assembled and successfully tested at the C. S. Draper Lab from January 30 to February 3. The natural frequencies measured were less than expected until high-strength fasteners (and higher torque values) were installed. Functional testing after vibration showed no anomalies. However, the "q" values recorded during the vibration tests were higher than assumed in the structural modelling. This has raised serious concern at MSFC and TRW as to whether the translation table inserts are capable of handling the ACIS loads. Further testing of the ACIS flight unit, or a flight-like mockup, will be conducted in the near future.
After the vibration tests, the ACIS instrument (consisting of Flt DEA, DPA, SS, and PSMC, but with the engineering unit detector assembly and vent valve assembly) was installed in the thermal vacuum chamber at Lincoln Lab. The T-V test was begun on February 14 and completed by February 25. No anomalies developed during the eight cycles of T-V testing. This was immediately followed by a 1238 bakeout and certification in the same chamber. ACIS passed the 1238 certification on March 2.
Notwithstanding the above, ACIS has been subject to excessive noise throughout the verification activities. Rather than take the ACIS experiment to MSFC for XRCF, it was decided to remain in the T-V chamber at Lincoln to investigate the noise problem. This trouble-shooting began on March 2.
The overall ACIS schedule has suffered in two areas.
The contamination problem with the flight CCDs set back this effort appreciably and it now appears that the Flight Detector Assembly will not be delivered until about May 12.
The noise problem with the DEA/DPA/PSMC has stalled the expected delivery of this unit to XRCF. Work in early March has pinpointed the problem to a grounding issue and the DEA and DPA are being modified with ground wires to connect chasis and signal grounds. Delivery is now anticipated in mid-April.
The subcontract to PSI which provides the services of Peter Tappan, the Detector Assembly mechanical engineer, has been extended through the end of May.
Due to the positive status of the ACIS instrument and schedule, `end of project' layoffs were issued at the end of February to a test technician, an R&QA inspector, and the software R&QA engineer. Additional layoffs are planned for the next few months.
Steve Jones supervised installation of ACIS2C in the XRCF instrument chamber. He discovered that one of the ACIS2C detectors had been partially damaged (almost certainly as a result of improper venting during a pre-installation leak- check conducted before he arrived at XRCF).
Four front-illuminated CCDs were selected for the imaging array: these are w203c4r (to be installed in focal plane loaction I0), w193c2(I1), w158c4r(I2) and w215c2r(I3).
Lincoln Laboratory (Al Pillsbury) discovered that the optical witness samples on about half of the flight candidate FI CCDs showed evidence of contamination. The contamination is visible as fluid droplets when the sample is viewed under a microscope at 50-600X. The contamination is not directly visible on the (relatively rough) surfaces of front-illuminated CCDs. The contamination almost certainly occurred during the X-ray calibration process. A number of diagnostic tests, including mass spectroscopy, infrared spectroscopy, and Auger electron spectroscopy, have failed to identify the source or composition of the contaminant more specifically, but the following information is available at present:
The contamination usually appears in droplets on the witness samples of size 1-10 microns, with thickness of 1 micron or less. The fraction of surface coverd by the droplets is typically 1-2%. For one witness sample, MSFC (Bill Naerin) has estimated the mean surface thickness of contamination to be 30 A.
The contamination is mainly composed of hydrocarbons, with dominant mass numbers at ~44 and ~170 atomic mass units.;
The IR (500-5000 cm-1) spectrum of the contaminant does not match that of the one pump lubricant sample currently available.
There are at most very low concentrations of sodium and potassium in the contaminant.
The contaminant can be removed from the witness sample, without visible residue, by an ethanol wash.
The vapor pressure of the contaminant is above 10-7 torr at 20°C; in fact, visible evidence of the contamination disappears completely if the sample remains at 10-7 torr at 20°C for 24 hours. At 25-30°C, visible evidence evaporates in less than 1 hour at this pressure.
The available X-ray data show no evidence for response variability during the calibration greater than 2% at 525 eV. This upper limit is believed to be at the limit of systematic errors inherent in analyses performed to data. There is no pattern in the presence of the contamination that implicates one calibration chamber over the other. It is thus possible that the contamination occurs in every chamber.
The bulk of the visible contamination occurs as the detector and witness sample are warmed from -120°C to room temperature following X-ray data taking. Some fraction (possibly 100%) of the contamination then evaporates after the detector reaches room temperature. However, some fraction of contaminant may remain on the detector and be present during subequent stages of the calibraton. Contamination is only visible on the witness sample if the chamber is vented before the witness sample has spent more than a few hours at room temperature.
We have elected to subject all flight detectors to a "vacuum clean" at 30°C in a chamber with pressure at 10-7 torr for 48 hours before installation in the flight focal plane. Meanwhile, efforts will continue to quantify the effect of this contamination on the reliability of the calibration, and to identify and eliminate the contamination from the calibration chambers. At present, it appears that the magnitude of the (as yet undetected) effect of the contamination on CCD response calibration will be less than 2% at 525 eV.
We obtained a great deal of information about flight instrument performance during the thermal vacuum test at Lincoln Laboratory. A summary of results is available on the ACIS Web Page. Highlights:
We characterized the noise power spectrum observed in various operating configurations and temperatures. At low temperatures, or with more than one front- end processor operating, significant excess noise is observed.
We measured the sensitivity of FEP video offsets to electronics temperature and found it to be approximately 8ADU/°C. This information is required to choose the flight video offsets.
We tested alternative CCD clocking modes (continuous clocking, 2x2 summation, and subarray readout) modes. A bug was found in the video board program for continuous clocking mode; this will be repaired in the next revision of flight software.
A light-leak was found at the interface between the imager and spectrometer optical blocking filters. An improved light seal is now being considered for the flight detector assembly.
We measured the DEA temperature dependence of the analog signal chain gain. Preliminary analysis suggests a coefficient of roughly 0.25 parts per thousand per °C., but some non-linearity is observed.
We performed many tests of bias algorithms, and found that long (5-10 minute) settling times must be allowed after CCD turn-on before accurate bias calculation can begin.
The vendor of the radioactive sources, planned to be used in the External Calibration Source, is unable to supply the original design. A new design has been made and drawings of the Source and Source Holder are ready for review.
Two of the Flight BPAs are available for flight assembly.
The parts of the Proton Shield are available for flight assembly.
The Support Structure along with the DEA and DPA has successfully completed vibration testing at Draper Lab. A concern about possible slippage at the interface and lower natural frequencies and higher amplification affecting the SIM Translation Table may require a rerun of the sine sweeps on the lateral axes. The unit is in Thermal Vacuum testing at Lincoln Lab.
The LED Assembly is available for flight assembly.
The EU DA has been assembled with the XRCF Focal Plane. It is in Thermal Vacuum testing at Lincoln Lab.
The ACIS Thermal Vacuum Test was conducted from February 14 through March 1. The Flight DEA, DPA, and PSMC were cycled 8 times to their hot and cold protoflight temperatures. One four-hour cold survival soak was acomplished. The EU Detector Housing and XRCF Focal Plane were operated in the TV chamber. The instrument was operated in the bakeout mode twice, once with DEA, DPA and PSMC at cold protoflight condition, and once with DEA, DPA, and PSMC at hot protoflight condition.
The Support Structure heaters were powered by a 28V power supply for one cold soak with the instrument in cold standby mode (all FEPs off, all CCDs off).
At the end of the TV Test, the ACIS was operated at its 1238 certification temperatures with the TV chamber shroud above room temperature for 24 hours. The TQCM contamination monitor within the chamber was changing frequency at a rate of 0-2 Hertz per hour, indicating that the ACIS was likely to pass the 1238 certification.
For this reporting period, the Detector Electronics Assembly is undergoing thermal vacuum testing to verify compliance with MIL-STD 449. The entire assembly is being tested at MIT Lincoln Laboratories and shall be completed soon.
The flight DPA is undergoing thermal vacuum testing at Lincoln Lab, along with the flight PSMC and DEA.
The engineering DPA is currently integrated with the engineering DEA and PSMC. This engineering assembly is being used to investigate noise artifacts which were observed at the thermal vac test setup.
Supported ACIS engineering unit integration with the XRCF RCTU and cable system. Supported ACIS Thermal Vacuum Tests at Lincoln Laboratory.
Supported Thermal VacuumTesting at Lincoln Lab. Installed the EGSE and high-speed-tap workstations and provided limited assistance in the installation of two science workstations. Modified or developed software to allow EGSE command and telemetry tools to interface with the hardware and software used for these functions at Lincoln Labs.
The following software ECOs were reviewed this month:
They relate to Release 1.1 of the Flight Software, which was burned into the flight instrument immediately prior to its being shipped to Lincoln Lab for Thermal/Vacuum testing. In addition, the following ECO was prepared to describe the changes to be implemented in Release 1.2:
Version 1.26 of the IP&CL structures table (36-53204.0204, Rev. I) has been released. It describes Release 1.1 of the Flight Software. This release fixes a number of small bugs uncovered during verification testing and also adds a new "medmean" bias mode (ECO 36-822) and a 5x5 pixel event reporting mode (ECO 36-855).
Jim Francis and Peter Ford met with several ASC representatives to discuss ASC's documentation of ACIS parameter blocks and operating procedures.
Release 1.1 of the Flight Software has been burned into the flight and engineering units, and is accompanied by release notes and building instructions. Default command blocks, bad pixel lists, etc., were supplied by the ACIS calibration team. Release 1.2, which contains the analog set points corresponding to the focal plane to be used at XRCF, is being prepared.
All BEP and FEP flight software modules continue to be subjected to unit and coverage tests.
High-level testing of Flight Software in FEP and BEP hardware continues, accompanied by tests using the software simulators. Jim Francis continues to assist on developing the Short and Long Form functional test procedures. The following ECOs related to verification testing were reviewed during the month:
Eight new software problem reports have been filed, of which three have been closed out, including all those relating to the Flight Software. A total of eleven problem reports are outstanding, two of which refer to the Flight Software; both will be closed out in Release 1.2. The status may be inspected at "http://acis.mit.edu/axaf/spr/" .
ACIS Flight Software performed well during the Thermal/Vacuum tests at Lincoln Laboratory Two anomalies were noted: (a) some CCD pixels were incorrectly clocked in continuous mode (SPR 102) due to incorrect use of SRAM library primitives, and (b) an indexing problem caused the wrong FEP to be disabled when a video board ceased to function (SPR 101). Both problems were swiftly diagnosed and will be fixed in Release 1.2 of the Flight Software.
Twelve (12) Alerts from NASA/MSFC were received over the report period. These items are listed below. Each Alert was compared with the available MIT parts lists.
MSFC Alert 6996 on MIL-W-22759 and MIL-W-27500 wire was revised. MIT responded to this Alert in the November 1996 report and MIT Letter from B. Klatt to E. Trentham dated January 16, 1996.
MSFC Alert 7016 (AH6-P-97-01) is on the Comlinear CLC505A8D. MIT uses this part as an Altered Item and it is controlled by MIT Specification 36-02304. The design has been reviewed for circuit performance with regard to Table I parameters at 1.0 mA and 9.0 mA. The CLC505A8D is used at 1.0 mA in the MIT applications. This review determined that there is no performance degradation due to offset voltage errors resulting from operation at 1.0 mA. Offset error is canceled out, by design, through software command.
None of the remaining ten (10) Alerts impact the MIT ACIS flight hardware.
|Alert #||MSFC #||Part Number and Manufacturer||Part or Material Name|
Tohnichi America Corp
|Torque Screw Driver|
|Preliminary||7006||Ellanef Manufacturing Corp.||Manual Actuator|
Potter & Brumfield Inc.
|Cadmium Plating &
Black Oxide Process>
Ace Rubber Products Inc.
Morton Electronic Materials
DEB Manufacturing Inc.
|Indicator, Multichip. LED|
Coast Metalcraft Inc.
Special tests have been performed on the seven (7) fastener types used in the Support Structure Assembly. These fasteners were tested for chemical and physical properties at Altran Materials Engineering Inc. A verbal report from Altran indicates that all fasteners passed. The formal report to MIT is expected in the near future.
MIT document 36-02030 is being prepared as a process specification to cover packaging, packing, handling, marking, storage and transportation of the ACIS.
Waivers 36-001 through 36-004, 36-006, 36-009 and 36-011 have been approved by MSFC. Waiver 36-005 is not used. Listed below is the status of the remaining MIT waivers at this time.
|36-007||3% Reflectance loss on OWS for MSFC-SPEC-1238 testing||MIT||2/8/96||OPEN|
|36-008||AWG26 nickel wire from DA to DEA||MIT||2/7/96||WITHDRAWN|
|36-010||Continuity, IR, and DWV test after harness/cable installation||MIT||7/16/96||IN PROCESS|
Waiver 36-007 is being revisited by MSFC in light of the decision not to bake-out the optical bench.
MIT NSPARs 36-001 through 36-029 have been approved by MSFC. MIT NSPAR 36-024 has been canceled/withdrawn. Lockheed Martin Astronautics (LMA) NSPARs MMA/ACIS-012b through MMA/ACIS-047 have been approved by MSFC. Detailed below is the one (1) NSPAR still in process. In addition, LMA is incorporating comments on NSPARs otherwise approved.
|36-030||Transistor, Silicon, NPN,
Low Power (JANTX2N930)
The Failure Mode and Effects Analysis (FMEA), DR SPA 04, and the Critical Items List, DR SPA 05, were submitted to Ed Trentham for approval.
Specification 36-02352 has been prepared for external radioactive sources. These are targeted sources with the radioactive element Fe55. Isotope Products Inc. of Burbank, CA has promised delivery on 4/21/97.
Materials: MIT received approvals of the last 2 MUAs from MSFC.
No Activity this month.
Test Procedures: A total of 10 have been released. Four test procedures were released this month (MemPatch, IgnoreBadPixel, GradedEvent, Load Command). Two tests are in the review process (RunFromSlot, Threshold). Developed a Verification Run Procedure (36-02407) to be followed by all Test Conductors. It defines responsibilities for handling of the Test Reports from generation to filing.
Test Scripts: A total of five scripts have been completed. One script (IgnoreBadPixel) has been completed and run on the Flight 1.0 version of the ACIS software.
CEI Requirements: Upon review of the CEI requirements, 3 requirements have been identified that will not be met by ACIS. These requirements are referenced to the specific paragraphs of the CEI Specification.
184.108.40.206a-21: We cannot telemeter 750 events/sec because of limited telemetry bandwidth.
220.127.116.11a-3: The ACIS software does not provide scheduler functions.
18.104.22.168b-2: ACIS Flight Software does not provide for telemetry control functions because ACIS has no control of telemetry.
There have been 8 new problem reports identified this reporting period.
There now are 96 problem reports identified. Of those:
There has been no activity on the Performance Assurance and Safety (PAS) Plan. The PAS Plan in effect is Revision B.
The progress for this month was focused on installing the PSMC and ACIS into the Thermal Vacuum chamber at Lincoln Laboratory. The ACIS was installed onto the SIM Sim at MIT, then a final cleaning was performed. The instrument was double-bagged, placed inside its shipping container, and delivered to Lincoln Labs. The lifting crane and fixtures were sent there as well. The lifting fixtures were cleaned and the crane was bagged for acceptance into the cleanroom. The SIM Sim was then installed onto the tipper cart. With the help of many people, the ACIS and PSMC were installed into the thermal vacuum chamber. Two optical witness samples were installed onto a holder to attempt to certify the hardware to MSFC-SPEC 1238 after the eight thermal vacuum cycles are completed. The events that took place from February 14 to March 1 dealt with monitoring the temperatures of the ACIS to ensure contamination-critical surfaces were at minimal risk to contamination during these tests. The use of a TQCM was a vital tool used to determine deposition rates at various temperatures.
After the thermal vacuum cycles were completed, we started the 1238 certification process, which eventually has passed its acceptance criteria. The ACIS was left in the chamber to continue testing.
Assembly of the flight detector assembly started 6 February 1997. During the pre-installation inspection of the detectors and optical witness samples (OWS), it was observed that there were droplets on some of the optical witness samples and flexprints. Assembly was put on hold until the source and impact of this contamination could be determined. While the exact source of the contamination has not yet been identified, it is clear that it appears during the calibration of the detectors at CSR.
Al Pillsbury discovered that the oil can be removed by desorption at room temperature in vacuums of 10-7 Torr for about a day or, alternatively, with an ethanol wash. Jim Gregory found that acetone, isopropanol, and trichloroethylene are also effective solvents, suggesting it is a fairly light oil. Scrubbing with water can also remove most of the oil, but some residue is left behind Both the desorption and the ethanol cleaning procedures have been used on devices which have previously been calibrated. These devices have been sent to CSR to determine the impact of the contamination and subsequent clean on detector performance and calibration.
The desorption procedure is less risky to use in cleaning the affected devices (it is assumed now that all of the recent devices calibrated at CSR have probably been contaminated, even though the contamination is not visible). However, there is concern that if the contaminant contains a mobile ion like Na or K, the CCD device thresholds, and therefore operational conditions, may be permanently affected. Even though SIMS and Auger analysis indicated the presence of Na on some sites on some of the samples, it was concluded that the Na most likely came from handling of the analytical samples because traces of K were also present. A test was carried out on a non-flight device to see whether permanent threshold shifts could be induced by residue of the contamination. First the device was contaminated, then cleaned by the desorption process. It was then vacuum-baked to simulate the processes which the device would see during assembly; this vacuum bake might have the effect of driving mobile-ion contaminants into sensitive gate oxides. The device was measured for the electrical operational conditions of the sensitive output amplifier before the cleaning cycle then after cleaning and being electrically stressed; no significant changes were seen which could be attributed to mobile-ion contaminant residue. This result, in combination with the general lack of Na present during chemical analysis, led to the decision to use the desorption bake to clean all flight devices before assembly onto the flight paddle.
The predominant elements identified by the Auger and SIMS analysis were C and O (H cannot be seen by Auger and the SIMS samples were not scanned for light peaks). Other contaminants such as Fe were also identified. Examination of the FTIR traces of the contaminant on the optical wafer sensors suggested an ester of the form R-O-R where the organic radicals had 10 to 20 C atoms each. This is consistent with the description of the lubricant provided by Leybold Heraeus, the manufacturer of the vacuum pumps in the CSR calibration systems, and probably too light for mechanical pump oil. These findings suggest careful examination of the procedures for pumpdown and backfill. Due to concerns about the cleanliness of the ACIS test chambers, only one part was re-flexed and sent to CSR during the month.
Thermal cycling of the lot 4 flexprints from Speedy Circuits has been successfully completed. No failures were found after 200 cycles from +60 to -150°C.
Qualification testing continued in February of the Speedy Circuits Lot 6 flexprints which were delivered on January 28. Thirteen of the 55 flexprints have been used for cross-sectioning and thermal cycling. They have completed 100 cycles successfully as of the end of February. One additional panel was rejected as a result of cross-section results from a real flexprint. No serious problems were found on these boards during the Hi-Rel Laboratory evaluation of coupons and real flexprints. Assembly and cleaning of these flexprints for flight use have begun. This lot will yield 24 flexprints suitable for flight use. Graphics Research has experienced problems with their nickel/gold plating process, and the shipment schedueled for January 24 was therefore delayed. The problem was resolved and on February 28 the flexprints were in final inspection at the manufacturer.
Change Order activity this month was limited to LMA preparation of a draft Statement of Work (SOW), draft Basis of Estimate, and an engineering estimate for additional technical tasks and a change in the ACIS Acceptance Review date. This new effort was defined and coordinated at the February Technical Interchange Meeting (TIM) held at MIT. A change order directing this work is anticipated in early March. Change Order 58 and Change Order 64 are currently the only change orders not yet definitized.
LMA supported the ACIS NASA/MIT Monthly Status Review and MIT/LMA Technical Interchange meeting conducted at MIT/CSR this month. The MIT/LMA Technical Interchange meeting placed specific emphasis on the upcoming ACIS System Thermal Vacuum Test to be performed at MIT/Lincoln Labs, final CDRL update requirements, and preparation of the ACIS Acceptance Data Package (ADP). LMA also supported an ACIS Verification Plan coordination working meeting with MIT and NASA/MSFC at MIT one day before the ACIS NASA/MIT Monthly Status Review. This coordination will be continued via telecon since insufficient time was available to complete the objectives of the meeting. Technical coordination was also conducted throughout the month by program telecons and LMA technical personnel supporting hardware assembly, test, and checkout at MIT.
Major LMA accomplishments for February included delivery of the Flight Thermal Control System (TCS) Radiator and Thermal Straps to MIT, and providing flight-quality MLI Thermal Blankets for use in the MIT/Lincoln Labs (LL) Thermal Vacuum (T-Vac) and XRCF Tests. LMA also supported the MIT assembly and integration of the ACIS XRCF Test Unit at MIT by performing the assembly of the LMA-built hardware elements and providing test hardware and components to support assembly and test activities. Other accomplishments this month were the completion of final upgrades, and acceptance and performance tests to enable delivery of the Flight Detector Assembly. Similar activities were performed for the Venting Subsystem (VSS) and VGSE #2 which are planned for delivery in March. Activities remaining for the VSS and VGSE are 1238 re-certification of the flight hardware, final flow restrictor size verification in the venting subsystem, and completion of final verification testing.
The program continued to review internal company Mission Success Bulletins and GIDEP ALERTS received during the month. None of these ALERTS were judged to be applicable to any of the parts or components being used by LMA on the ACIS program. There have been no items defined during the month that warranted generating a Contractor-Initiated ALERT.
The program continued to place priority and primary emphasis on completion of the LMA-fabricated ground support and flight hardware assembly, integration and test prior to delivery to MIT; and support of the test and integration of the ACIS hardware at MIT/CSR and MIT/LL. Also, significant effort was directed toward definition and initiation of the final deliverable CDRL documentation and verification reports coordination and preparation.
Problems encountered during the month were associated with correcting an increase in the background contamination of the LMA 1238 Certified vacuum chamber. Empty chamber bake-out to correct this situation caused a delay in the planned ship date of the Flight Detector Assembly. However, schedule-critical MIT need dates were met so there was no critical path schedule erosion.
The Flight Unit PSMC and EU2 PSMC were jointly used at CSR in support of ACIS Flight Instrument integration testing. The Flight PSMC was integrated into the system thermal vacuum test at Lincoln Labs. At the close of this reporting period, the system T-Vac test was proceeding through the planned 8 thermal cycles without incident. Some noisy telemetry was observed and attributed to test and chamber configuration effects. Overall system noise performance was under evaluation as of the end of this reporting period.
At the end of this reporting period, RCTU interface questions still remained regarding the EU2 PSMC. Command interfaces seem acceptable, with some open items involving telemetry interfaces. After the conclusion of ACIS thermal vacuum testing, and when a "known good" RCTU is available at CSR, LMA personnel will travel to MIT to resolve these open telemetry interface issues.
Efforts on the Flight PSMC build and test documentation data package continued, with top assembly drawing redline incorporation nearly complete. The documentation package is scheduled into reproduction early in the next reporting period, with package delivery to MIT planned for approximately March 10, 1997.
Assembly of the flight spare PSMC boards continued on a non-interference basis. The thermal control board is nearly complete, with final QA inspections and MPP sign off planned prior to beginning the board-level test. Work on the IO/EMI Cavity resumed, after technician support of the Flight Detector Housing and Venting Subsystem testing was completed. The IO/EMI Cavity should complete during March. Vent Valve & Mechanism Control board assembly is underway. EEE piece part kitting was initiated for the remaining spare board builds.
The flight PTS W1/W2 cable harness was shipped to MSFC for completion of Dielectric Withstanding Voltage (DWV) testing. LMA received a fax confirmation that the W1/W2 flight harness successfully passed DWV.
Since the 1500 volt DWV test exceeds the harness 600 volt wire rating, MSFC has agreed to provide LMA with written documentation granting an exception to the MIL-STD-975 EEE part voltage rating criteria. This should allow formal cable harness verification to complete without issue.
The harness is now "in-the-queue" for 1238 certification at MSFC. The certification temperature of +46°C was communicated to MSFC.
There are no changes to the MIT load table during this reporting period.
The Flight Detector Housing MSFC-SPEC-1238 re-certification was reinitiated since modifications were made to the Flight Detector Housing as discussed in the January progress report. However, the TQCM readings showed the chamber background was too high for a final certification to be completed. Therefore, the Detector Housing and Venting Subsystem were removed from the chamber to enable high-temperature bare-chamber bakeout. Elevated temperature bakeout was started on the bare chamber to bring the TQCM background down to an acceptable level by the end of this reporting period. The flight hardware is scheduled to go back into the chamber in early March so the re-certification can be completed. It is not expected to take more than a few days for a final certification once the chamber has been cleaned up and the Detector Housing delivery will occur shortly thereafter. Final functional and performance tests were successfully performed on the Detector Housing in parallel with the chamber bakeout in preparation for the planned early March delivery of the Detector Housing to MIT.
There has been no significant problems with the operation of the EU Venting Subsystem and Detector Housing in the Lincoln Labs Thermal Vacuum Test. The thermistor and resistor fixes have been verified during this test by normal operation of both subsystems. Telemetry showing actuator temperatures has worked well and the high-temperature shutoff was successfully verified during one of the cold temperature operations on the Door Actuator.
The flight radiators, straps, and test MLI were delivered to MIT and installed on the SIM Sim in support of the Lincoln Labs Thermal Vacuum Test. Thermal Vacuum testing has quantified the hot and cold thermal performance. The warm radiator performance is very close to the predictions for all operating modes. The PSMC was able to accurately control the Detector Housing to - 60°C for normal operation and also at 25°C for bakeout mode. Power requirements for the heaters also were close to predictions. The cold temperature system performance was not as good as predicted and, under hot case conditions, the focal plane was only at -116°C vs. the -120°C goal. The thermal data indicates that there may be a thermal short between the support structure and the cold straps. Therefore, 3D computerized mechanical modeling of the straps and +Z support panels was performed. This modeling verified that there is a potential for mechanical interference. Fitchecks with the EU hardware will be performed in early March to further evaluate the problems with flight hardware. Prior to installation in the XRCF, modifications to either the straps or the support structure may have to be made to solve this problem.
Thermal models were modified to the Lincoln Labs test configurations for both the PSMC and the flight radiators. Math model correlation showed a potential thermal short between the cold straps and the support structure. Thermal modeling also allowed for operation of the PSMC at higher than Proto-flight temperatures during bakeout and 1238 certification. Without LN2 in the shrouds, the shroud temperatures approached 40°C which was an inadequate sink to keep the PSMC less than 46°C. However, math model correlations to the test data allowed for hotter operation of the PSMC without exceeding the derated temperature limits for components inside the PSMC.
The Stress analysis was completed and submitted to MSFC during this reporting period. No new waivers will be required and there is no reason to suspect that any updates will be required after a review by MSFC. The fracture analysis is continuing and the projected completion date supports Acceptance Data Package delivery dates.
The SIM-Sim has performed as designed as evidenced by the successful installation into the Lincoln Labs chamber and its thermal performance during the test.
Two new flight filters were received from MIT for another acoustic test planned for early March. Since the filters are already 1238-certified, the CAMSIM was recleaned and verified to be 1238-compatible so that there is no risk in contaminating the filters during the test.
Since all flight hardware except the MLI blankets has been built and weighed, there is no update to the weight summary from the previous reporting period. This data is shown below:
|Assembly||Weight, lb.||Uncertainty, lb.|
|Thermal Control & Isolation||5.4||+0.1|
|Sun & Telescope Shades||16.0||+0.1|
|Power Supply & Mechanisms Controller||32.7**||+0.2|
|Cables & Connectors||9.1||+0.1|
|Total Basic Weight||102.9||+0.9 -0.0|
** Includes Survival Heaters, Thermistors, connectors, and bracket which are not part of ACIS budget. Mark Kilpatrick's (BECD) worksheet dated 12/8/95 assumed 1 pound for these components. LMA does not have an actual breakdown.
The flow restrictor was successfully sized for a maximum 60 Torr/minute pressure rise. This allows for the VGSE to pump down the Detector Housing to a safe pressure in about 90 minutes. The parallel resistors were added to the thermistors to provide safe detection of an over-temperature condition on the wax actuators.
The lifting fixture modified part fabrication was nearly complete and will finish early next month. The lifting fixture will be shipped as-is to MIT for use in testing. Incorporation of the modifications will be made later this year prior to shipping ACIS to BASD.
A set of shipping cases that allow shipping of the Venting Subsystem and the Detector Housing were received. These containers have been specially sized to allow shipment onboard commercial jet aircraft.
VGSE #2 is complete. Performance testing has been completed. All that is left to be performed is the acceptance test with the Flight Venting Subsystem. This will begin early in March and should be completed by mid-March.
During the month, the systems engineering group continued preparation of verification assessment and test reports for the ACIS compliance verification activities, maintaining program requirements documents, and engineering specialties activities in support of flight hardware verification. Additionally, the group continued planning for preparation and delivery of the Acceptance Data Package (ADP) and CDRL update coordination for ACIS.
Updating the final CDRL/SDRL submittals in support of the Acceptance Data Package continued during this month. The ACIS Wire List will be updated during March, following receipt of PIRNs, to accommodate needed wiring changes for the RCTU-to-PSMC interfaces and collection of final wiring changes, if any, from the hardware verification activities.
The ACIS System Schematic was released. The preparation of a Special Consideration Item Drawing (SCID) has started. This book-form drawing will identify the "Remove Before Flight" red tag items, "Install Before Flight" green tag items, and those items of special consideration; such as, warnings and cautions to be included in procedures that operationally protect the instrument and specify handling requirements. This drawing is scheduled for completion in time to support the Acceptance Data Package.
System level overview, support of program scheduling, and update of ground processing flows for ACIS instrument flight hardware testing continued this month. Final update of the ACIS Verification Requirements and Specification Document SVR02 was partially reviewed prior to the NASA/MIT Monthly Status Review. Completion of the review will be conducted via telecons during the next reporting period. Following the telecon, comments will be incorporated into the VRSD, and it will be released as final. ACIS program support and MIT and NASA/MSFC liaison were maintained.
Review of program activities and scheduling of the PTS and ACIS verification events continued throughout February. This activity, along with satisfactorily completing scheduled events, will confirm that the ACIS instrument meets requirements and will be ready for delivery to NASA/MSFC. Continued support of testing being conducted at Lincoln Labs.
MSFC-SPEC-1238 bakeout activities continued throughout this reporting period. This activity is nearing completion. Instrument-level MSFC-SPEC-1238 certification is planned to be performed during the Lincoln Labs ACIS performance testing.
The initial ACIS Instrument EMI/EMC Test Report has been completed by test laboratory personnel. The report was reviewed by LMA ACIS personnel and forwarded to MIT for integration into the overall instrument report. Four Requests for Waiver were prepared which accompany the report to accommodate the exceedances encountered during testing.
System Safety continued to support and monitor the program during this reporting period. The Ground Safety Data Review presentation package is completed and ready to support the meeting at KSC early in the next reporting period.
The Failure Modes and Effects Analysis (FMEA) completed in January was reviewed in real time during the February Technical Interchange Meeting at Cambridge. Comments are expected from MSFC early in the next reporting period. Changes to the FMEA will require the Critical Items List (CIL) to be updated. This activity is expected to be completed during the next reporting period.
The Power Summary Tables that summarize the power requirements have not changed since the June 1996 Progress Report. For current Power Summary date refer to Progress Reports for June or July 1996.
Electrical power requirements (Watts) are summarized in the following table:
|Peak power distribution
in Standby Mode
|Peak power distribution
in Max. Operating Mode
|Peak power distribution
in Bakeout Mode
|Peak power distribution in
Normal Operating Mode*
Note: Normal operating mode refers to the ACIS operating with six analog chains at full power, six front-end processors at full power, one back-end processor at full power and the focal plane temperature being maintained at -120°C.