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August 20, 1997
NAS8-37716
DR SMA03
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ACIS-DD-144
August 20, 1997 NAS8-37716 DR SMA03 |
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![[ACIS]](/icons/acis.gif){kind=icon}
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Advanced X-ray Astrophysics Facility |
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AXAF-I 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 from June 1 to July 31, 1997.
Since ACIS was delivered to MSFC on April 14, standard Monthly Status Reviews have ceased. The last review was conducted via telecon on March 19. MSFC has requested an informal status review to cover open hardware issues and the closure of Action Items and Comments from the ACIS Acceptance Review of June 26. This status review is scheduled for August 4 at LMA.
ACIS participated in the weekly AXAF telecons on June 3, 10, 17, and 24, and July 1, 15, and 22. The telecon normally scheduled for July 8 was cancelled and ACIS could not participate in the telecon on July 29 due to a visit to ASC/ACIS/HETG by Wes Huntress from NASA Headquarters.
The FPSI telecons that have been conducted on alternate Wednesday mornings have also ceased, since both the HRC and ACIS have been delivered to MSFC.
The following is a brief summary of the status of the main ACIS elements:
The CCD status is unchanged from the last report. Basically, the CCDs are ready for calibration at MIT, but the calibration chambers are still in the process of being reworked and cleaned to avoid the contamination problem encountered at the end of the flight testing.
The only hardware item yet to be assembled, verified, and delivered is the external calibration source assembly. The fluorescent Fe55 sources for the external calibration source were completed at Isotope Products and received at MIT on May 12, and the science testing of these units was completed by the end of June. A verification program was scheduled, but when the assembly was completed, a final series of tests by the science team concluded that there were two problems: too many lines, and the lines were too weak. As a result of this testing, one of the sources (Cu) has been removed from the assembly and the collimation of the remaining sources in the assembly was redesigned. New drawings were prepared and two new parts are being fabricated by an outside shop as of July 29. Receipt of these parts and the assembly of the external calibration source is expected by the end of August.
The flight-like mechanical mockup of the SS/DEA/DPA, fabricated for the purpose of engineering vibration testing to evaluate the loads on the translation table, was delivered to MSFC on June 6. A qualification-level vibration test at MSFC, with the test unit instrumented with strain gauges and accelerometers, was completed by June 13. The results were as expected.
Once the testing of the vibration test unit was completed, the flight DEA/DPA/ SS was substituted on the shake fixture and an acceptance-level test performed at MSFC. Again, no anomalies were uncovered.
An acceptance-level random vibration test of the Detector Assembly and Vent Valve Assembly was also conducted at MSFC in mid-June. No problems were found.
As reported last period, we had detected evidence for a vacuum leak in the ACIS Detector Assembly. This was investigated at MSFC in June and then again at LMA in July. O-rings were changed on both the absolute and the differential pressure transducer gauges and finally a leak at one of the CCD connectors in the DA backplate was repaired. The final helium leak test data taken on July 31 indicates that all leaks have been found and corrected. The unit was sealed on August 1 and a 10-day leak rate test was begun.
Testing of ACIS with the flight RCTU began on May 27 and continued through June 6. Unfortunately, several problems were found with the RCTU/CTUE. An error in the ACTEL in the CTUE resulted in erroneous commands being sent to ACIS (high-level pulse vs the serial digital requested). In addition, a bit error rate test of the RCTU had to be aborted due to an error in the CTUE, which resulted in command distortion between the MIT EGSE and the CTUE.
The ACIS Acceptance Data Package was submitted on June 9 and the Acceptance Review was conducted at MSFC on June 26. All ACIS verification test reports (both MIT and LMA) were completed by June 26. The review was quite successful and MIT was instructed to deliver ACIS to BASD.
The ACIS instrument was shipped from MSFC on July 2 and delivered to BASD the next day. An incoming functional test was successfully performed the week of July 7.
As soon as permission was received from the State of Colorado to use the MIT radiation source license at LMA, the Detector Assembly (with its internal radioactive source) was transported from BASD to LMA for investigation of the Detector Assembly leak (see item f above).
The testing of the DEA/DPA with the flight RCTU and flight cables was resumed at BASD on July 22. The command anomaly had been resolved by Gulton and the CTUE was modified. The bit error rate test was successfully conducted on July 24 and 25. This was followed by an interface verification test of each wire of the interface (via breakout boxes provided by TRW). This testing was completed by August 1. The only anomaly reported was a `ringing' on the command synch clock from the RCTU. This anomaly was being investigated by TRW at the beginning of August - it might simply be a reflection due to the nature of the breakout box.
A CCD frost test was begun at Lincoln Lab during July. The purpose of the test is to determine whether or not the ACIS CCDs are sensitive to the presence of dew or frost. Due to the possibility of such a sensitivity, MIT had put constraints on the operation of the focal plane during ground thermal vacuum testing at BASD and TRW, and constraints on the allowable temperature/pressure profiles for the first several days after launch. These constraints had become quite onerous and were driving BASD and TRW T-V test planning as well as Shuttle and IUS planning for orbital insertion. MSFC had requested that MIT investigate the validity of these constraints and Lincoln agreed to perform a test program. The first results were received on August 1 and indicate that the CCDs are not sensitive to frost. The test program will be completed by mid-August.
At the end of the reporting period, there were still two potential problems which may affect the ACIS hardware. They are:
Due to a change in the Shuttle orientation while in LEO, the ACIS sun and observatory shades will see the sun in an unexpected fashion. Both will now get appreciably hotter than initially predicted. A test on the engineering unit shades will be conducted at LMA in early August.
An internal LMA alert indicated that there may be a problem with some of the capacitors used in the flight PSMC. Tests on the residual pieces from four flight lots have been underway since early June. Problems have been encountered on at least one lot. Replacement parts were ordered in early June and were received at LMA by the end of July. The real problem is finding the necessary time in the AXAF schedule to perform the swap-out.
Both of these issues are discussed further in the LMA portion of this report.
By August 1, ACIS had been delivered to BASD (or LMA), all tests and rework performed, and the instrument is ready for installation on the SIM. Installation is due to start on or about August 29. Due to limited space at BASD, the Detector Assembly is being held in the class 100 cleanroom at LMA until needed at BASD for integration.
Due to the positive status of the ACIS instrument and schedule, layoffs and reassignments have been made:
| Mary Briggs | R&QA tech | Reassigned to HETG to replace Jeanne Porter (who resigned) |
| Bob Blozie | S/W Verif Eng | June 5 |
| Isobe Takashi | Science Team | July 30 |
| Steve Jones | Science Team | Will leave about Sept 1 to enter Medical School |
| Fred Kasparian | Mech Eng | Part-time on Astro-E on June 15 |
| Matt Smith | Contam Eng | Reassigned to LIGO on June 1 |
| Myron MacInnis | Mech Tech | Part-time on LIGO on August 4 |
Following discussions with team members at Penn State and ASC, we agreed on a preliminary division of responsibility for XRCF data analysis. The MIT team will begin with analysis of the XRCF Phase I (flat-field) measurements, and will compare results obtained there to sub-assembly measurements made at MIT. Penn State will begin with analysis of ACIS-2C and ACIS measurements of the HRMA point response function. We will then proceed jointly to analysis of HRMA/ACIS effective area measurements.
We have outlined the MIT contribution to the preliminary calibration report due in September. The outline is available on the ACIS web page. We will link preliminary results to this outline as they become available.
To date we have established that the high-speed tap data obtained at XRCF are consistent with the telemetry data, after accounting for differences in bias correction. We have developed nearly-automated pipeline processing to reduce the XRCF flat-field telemetry data. We will report results on the energy scale, spectral resolution, and relative (i.e., chip-to-chip) detector quantum efficiency at the MSFC calibration workshop in August.
We have begun analysis of the wavelength-shifter data obtained at the PTB/BESSY synchrotron beamline last December. This beamline provides useful flux to energies as high as 10 keV. We have found that proper pile-up correction of these data is important (without proper pile-up correction, one tends to overestimate the high-energy efficiency of the detector). Preliminary analysis suggests that the detector depletion depth exceeds 75 microns; MIT subassembly calibration data suggest that the depletion depth of the same detector is about 70 microns.
A comprehensive analysis of pile-up data obtained in MIT sub-assembly measurements is underway, and will be reported at the MSFC calibration workshop in August. This work estimates the effect of pile-up on measured flux as a function energy for quasi-monochromatic radiation, and should be useful for estimating pile-up corrections for XRCF effective area measurements.
Intensive efforts to identify contaminants in the large vacuum chambers are still underway. The (small) screening chamber has been successfully cleaned, and screening of backup focal plane devices has begun.
A series of measurements aimed at estimating systematic errors in the relative quantum efficiency measurements has been undertaken.
The individual radioactive source components were each characterized for flux and spectral content. The flux available from the sources with titanium and aluminum targets was found to be adequate, but the copper-target source produced very low output at the Cu-L line (930 eV); the output of this source is in fact dominated by backscattered Mn-K X-rays from the exciting Fe55 source.
The integrated source/collimator assembly was tested; measured outputs were much lower than expected. Review of the collimator design showed that too little of the source area of fluorescent sources was being exposed by the collimator. Collimator design changes were reviewed with the engineering team. The final source design will contain only 3 radioactive elements: a direct-illumination Fe55 source, and the aluminum and titanium target fluorescent sources.
The following software ECO have been prepared:
These relate to Release 1.4 of the Flight Software, which was burned into the flight instrument during the second period of Thermal Vacuum testing at Lincoln Lab. They were included in the ACIS Acceptance Data Package submission.
No changes have been made.
Release 1.4 of the Flight Software was 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 1.4 includes the correct default video set points for the flight focal plane.
Release 1.5 of the Flight Software was burned into the flight and engineering units, and is accompanied by release notes and building instructions. This release reduces bias drift during the first few minutes of CCDs clocking. It also prevents FEP bias maps from being copied to the telemetry stream while events are being detected, thereby circumventing a FEP firmware problem.
Unit testing of BEP and FEP flight software modules is now complete. No remaining anomalies have been noted.
High-level testing of flight software in FEP and BEP hardware continues, accompanied by tests using the software simulators. The following ECOs related to verification testing were reviewed during the month:
6 new software problem reports have been filed:
SPR-107 (M97050701) Primary exposure of zero does not skew properly with multiple FEPS.
SPR-108 (M97051301) In Raw Mode, Science data is not received from all FEPS after a single FEPs memory has been corrupted.
SPR-109 (M97051501) Not able to write to last word of BEP I-Cache.
SPR-110 (M97051502) SysConfig command should not accept a -1 for "bakeEnable".
SPR-111 (M97052101) Upper limits on SYSSET_DAC_RD, _DR0, _DR1, DR2, DR3 need to specified.
SPR-112 (M97052301) Incorrect Raw Histogram Mode data when CCDs clocked in AC or BD mode.
The current status may be accessed via the ACIS web server: "http://acisweb.mit.edu/axaf/spr/" .
The flight software performed satisfactorily during the HRMA and Flat Field tests at the XRCF facility. A patch was developed to circumvent the corruption of FEP ring-buffer data that was noticed when ACIS was sent two consecutive StopScience commands while the buffers were full.
HRMA testing lasted from 04/17/97 through 04/27/97 and comprised 106 ACIS science runs. Flat Field testing lasted from 05/06/97 through 05/19/97 with 156 science runs. Merging the data streams recorded by the ACIS test team with data supplied by the ASC team from the CBD, the full ACIS telemetry timeline was recovered and processed through EGSE software (programs getPackets and psci). The results were analyzed by the ACIS flight software team and passed to the ACIS instrument team and the ASC Science Operations Team.
Two serious hardware anomalies were noted during XRCF testing: the mean bias values of eight of the ten flight CCDs appeared to drift relative to their mean overclock values for several minutes after start of clocking. A software patch has been developed to alleviate this problem by temporarily altering some DEA voltages at the start of each science run. The patch was tested during the Flat Field period and performed satisfactorily.
The second hardware problem appeared during Flat Field tests when the X-ray count rate exceeded about 2000 threshold crossings per CCD while the BEP was copying FEP bias maps to the telemetry stream. In this situation, the FEP gate array was likely to stall and would not restart until its power was recycled. The failure was reproduced in the engineering unit at MIT and traced to a problem in the gate array itself. A software patch was prepared that prevented the BEP from starting a science run until after the bias maps had been copied to the telemetry stream.
Flight software release 1.5 was burned into the EEPROMs at Ball Aerospace in mid-July. It was subjected to long- and short-form functional tests.
This task has been taken over by the flight software team. A total of 40 procedures have been identified, of which 24 have passed the review process. 19 test suites have been completed and a further 5 are partially complete. An additional 6 procedures are under review at MIT and 4 are under review at MSFC. The daily situation is displayed at this Web site: "http://acisweb.mit.edu/axaf/testsched.html".
Thirty-two (32) Alerts from NASA/MSFC, were received over the report period. These items are listed on Alert Problem Summary Reports dated May 15, 1997, July 2, 1997, and July 14, 1997. Each Alert was compared with the MIT ACIS parts lists.
Thirty (30) of the Alerts do not impact ACIS flight hardware. The two Alerts which do impact the ACIS are:
| MSFC # | ALERT # | PART MFR | PART # |
|---|---|---|---|
| 7056 | W-P-97-04 | JDI CAPACITORS | 87106-XXX |
| 7057 | IN3-P-97-01 | UTC CAPACITORS | 87106-XXX |
MSFC was notified of this problem in MIT letter from B. Klatt to E. Trentham dated 5/23/97.
Listed below are the open MIT waivers at this time. All other waivers have been approved or withdrawn.
| Waiver # | Description | USER | Submittal | Approval |
|---|---|---|---|---|
| 36-007 | OBF VISIBLE LIGHT EFFICIENCY | MIT | 8/6/96 | OPEN |
| 36-012 | FOCAL PLANE SURVIVAL @ -136°C | MIT | 8/6/97 | OPEN |
| 36-013 | HUMIDITY CONTROL DURING TRANSPORTATION | MIT | 8/6/97 | OPEN |
| 36-014 | EMI/RE02 NONCONFORMANCE | LMA | 6/24/97 | OPEN |
| 36-015 | EMI TRANSIENT VOLTAGE NONCONFORMANCE | LMA | 6/24/97 | OPEN |
| 36-016 | USE OF OVERSTRESSED WIRE | MIT/LMA | 3/28/97 | OPEN |
| 36-017 | SINGLE POINT FAILURES | MIT/LMA | 6/5/97 | OPEN |
| 36-018 | WELD FILLER MATERIAL | LMA | 6/6/97 | OPEN |
| 36-019 | RADIATOR STANDOFFS | LMA | 6/24/97 | OPEN |
Witnessed EMI testing on the Detector Electronics Assembly (DEA)and Digital Processing Assembly (DPA ) at MSFC.
Monitored vibration testing on the DEA/DPA/Support Structure and Detector Assembly/Vent Valve Assembly at MSFC.
Monitored preparation for transportation. Escorted the flight ACIS during transport from MSFC to BASD.
Witnessed the loading and testing of version 1.5 of flight software into ACIS at BASD.
Monitored preparation for transportation. Escorted the flight Detector Assembly/ Vent Valve Assembly during transport from BASD to LMA.
Witnessed fault isolation of vacuum leaks in the ACIS flight Detector Assembly. Leaks that were repaired were the o-ring on the differential pressure transducer and a weld leak at connector S03 in the back plate.
All forty-six (46) ACIS Nonstandard Parts Approval Requests (NSPARs), data requirement SPA 03, have been submitted to and approved by MSFC.
All thirty-nine (39) ACIS Material Usage Agreements (MUAs), data requirement SHF04, have been submitted to and approved by MSFC.
MSFC comments have been incorporated into the FMEA. The final version of the FMEA and CIL will be submitted to MSFC before the end of August.
No Activity this month.
See Software Quality Assurance under paragraph 1.1.3 above.
There has been no activity on the Performance Assurance and Safety (PAS) Plan. The PAS Plan in effect is revision B.
Vacuum chambers are being disassembled, cleaned at Lincoln Laboratories, and reassembled, in anticipation of resuming calibration of CCDs.
Cleaned, bagged, and purged ACIS flight hardware for shipment from MSFC to BASD.
Cleaned, bagged, and purged ACIS flight Detector Assembly/Vent Valve Assembly for shipment from BASD to LMA.
A preliminary estimate was made for the potential for frost formation on the detector array during launch and before the spacecraft is deployed. A worst case analysis of the potential for frost formation on the detectors indicated that several mils of ice could form if the pressure in the camera is the maximum expected at launch and if all this is due to water vapor.
A planning meeting for a frost test of CCDs was held at Lincoln Lab on July 3, with both MIT and LL staff. Lincoln agreed to modify an existing vacuum chamber for the injection of water. The chamber selected is the one currently in use for the thermal cycling of flexprints.
The flexprint testing was completed by mid-July (see below) and modification of the chamber begun. The first "dry-run" test, using an optical witness sample rather than a CCD, was conducted on July 28. We were concerned that the presence of frost would be difficult to detect and the interference patterns on the OWS would be the only indication. This turned out not to be the case - the layer of frost can easily be seen (and photographed).
The first CCD test was conducted on July 29-30 with no measurable effect on the ESD status of the chip. Four additional CCDs were then added to the test program. By August 1, the first unit had successfully undergone 2 cycles, and four others had seen one cycle.
The test program will proceed with these five devices through five cycles (with an ESD test after each cycle). When this is completed, a second set of 4-5 devices will undergo a series of five frost cycles.
If successful, the unit will then be sent to MIT for an imaging characterization. It is expected that a final decision on the CCD sensitivity to frost will be forthcoming by the end of August.
Representative flexprint samples from Graphics Research Inc.(GRI) have been prepared for slow thermal cycling. These samples have now completed 200 thermal cycles without failure. This completes the acceptance testing of these spare components.
Devices from Lot 14 have shown a low packaging yield compared to the previous lots. This is due to poly to substrate shorts and poly to poly shorts. To learn more about the failures, W469C4 was sent to Hi Rel Laboratories for analysis. This part had a poly 3 to substrate short and a poly 3 to poly 1 short; Hi Rel could locate the first failure using liquid crystal display mapping, but could not locate the poly to poly short with this technique. Hi Rel then proceeded to strip the device back layer by layer to determine what caused the poly to substrate short and revealed an apparent location of an ESD event. At this time, the processing traveler for Lot 14 suggests that all operations were normal. It would be useful to submit for analysis both another device with the poly to substrate short to determine if the failure mechanism is the same and a third chip that contains only the poly to poly short.
The LMA overrun proposal was negotiated on July 29. The overrun was based on a bottoms-up program Estimate-To-Complete (ETC). Therefore, all submitted change orders have been negotiated with CO67 awaiting definitization.
The ACIS Acceptance Review was conducted at MSFC in June. LMA and MIT personnel supported this review for ACIS. ACIS deliverable hardware and software status were discussed, as well as verification status of the 6/26/97 review date. LMA agreed to maintain its current level of Systems Verification personnel through 8/1/97, should MSFC raise any additional issues or generate new Action Items regarding formal ACIS verification.
Prior to the ACIS Acceptance Review, all remaining LMA Flight Unit hardware was DD250'd, in place, to MIT. These hardware elements consist of the remaining Thermal Control Structure (shades, posts, and flight MLI), and the flight W1/W2 cable harness. This paves the way for ACIS DD250 from MIT to MSFC. This hardware will be held in clean storage at LMA until needed for ISIM integration.
The flight Detector Assembly and Venting Subsystem were received at LMA in mid-July and placed in the Class 100 clean room. The previously identified vacuum leaks in the transducer o-ring and backplate connector were successfully repaired in situ.
A MIT/LMA TIM was held in early August, addressing Ball integration coordination, EU shade testing plans, Detector Assembly/Venting Subsystem leak issues, and the new ACIS flight software load. Additional technical coordination was achieved by program telecons and LMA technical personnel supporting hardware integration, test, and checkout activities at BASD.
The program continued to review internal company Mission Success Bulletins and GIDEP ALERTS received during the period. The LMA internal Mission Success Alert that applies to flight PSMC Johanson ceramic chip capacitors bought to DESC Spec 87106 continues to be worked. The ACIS PSMC contains Johanson 87106 caps, but earlier lot/date codes than those specified in the alert. A test plan has been established to perform non-destructive screening and testing of lot residuals used in the flight PSMC.
The LMA Thermotron chamber's vapor generation unit was repaired and 85/85 testing (85°C/ 85% humidity for 240 hours) was completed. Preliminary testing of the 4 lot/date codes of affected PSMC capacitors yielded no part failures for 3 of 4 part lots. The 87106-071 showed 1 of 4 parts failed the post-85/85 low voltage IR test. All remaining "-071" residual parts were gathered and sent back into an additional round of lot exoneration testing. These 34 parts have been split between 85/85 (19 ea.), and Hot IR testing (15 ea.) with 10 of the Hot IR parts going into accelerated life testing.
Lot exoneration testing of residual 87106 capacitors contained in the flight PSMC has yielded ambiguous results. Therefore, additional testing will be accomplished during August.
For schedule risk reduction, a "rebuy" of 87106 capacitors has been initiated from a different vendor(s) and are due at LMA during July 1997. MIT is receiving regular status updates, and concurs with our course of action.
The program continued to place priority and emphasis on completion of the ACIS flight and ground support hardware assembly, and integration and test at BASD. All planned hardware activities have been completed, except for the additional cleaning of VGSE #1, retrofit modifications to the ACIS lifting fixture, and some residual spare PSMC board test,s held up for two EEE piece part shortages.
In conjunction with the ACIS Acceptance Data Package, the final deliverable CDRL documentation and verification reports were submitted to MIT and MSFC.
The Johanson ceramic chip capacitors bought to DESC Spec 87106 remain an open issue. Two parallel paths are currently being pursued to address this concern. First, in an attempt to exonerate the lots contained within the PSMC, extensive testing, including Low-voltage IR, 85-85, and Hot IR, has been performed on the residual parts. The results yielded a single failure in one of the four lots. The failed part number lot was 87106-071. An additional thirty-four pieces of 87106-071 were available and these were subjected to the same series of tests to provide a more significant statistical sample. The testing yielded a total of five piece part failures of the thirty-eight pieces tested. This result raises concern for the JDI-071 parts contained within the PSMC. The next logical question is the quality of the other JDI parts contained within the PSMC. Even though the other JDI residual parts passed the abbreviated lot qualification process, the lots were sufficiently small to raise suspicion. Therefore, the only remaining residual parts, 87106-069 (qty 31), were provided to an outside testing lab, Bell Technologies, Inc., to receive the same suite of tests. The results are expected in mid-August and they will be considered when determining which, if any, parts within the PSMC need to be replaced.
The second path to address this concern is to replace these suspect parts. To date, all four lots of parts have been ordered from Union Technologies Inc., and have been received. A second lot of the suspect part number (87106-071) has also been ordered from Union Technologies. A duplicate order for all four lots of parts is also being pursued with AVX-Olean. A modified 87106 parts Lot Qualification and Lot Screening has been established and is being implemented on all incoming parts. A process to replace these parts has had favorable results to date and is progressing. At present, EU#1 PWBs are being conformally coated to make them "Flight-like", so that all Flight assembly conditions are adequately simulated during the remove and replace process development. During the process development, a detailed manufacturing process plan (MPP) will also be developed to provide strict control over the flight PSMC board rework. Before any rework is considered, a process MUST be in place which provides low risk to the flight circuit card assemblies.
Preliminary discussion has taken place regarding what would be necessary to make EU#2 capable of being placed in a clean thermal vacuum environment. This would allow EU#2 to take the place of the Flight PSMC temporarily and minimize the impact that the capacitor replacement would have on the flight critical path. No specific conclusions have been reached.
At the end of this reporting period, RCTU interface questions still remain regarding the EU#2 PSMC. Command interfaces seem acceptable, with some open items involving telemetry interfaces. Sometime after the ACIS XRCF testing, and when a "known good" RCTU is available at CSR, LMA personnel will travel to MIT to resolve these open telemetry interface issues. This is currently an open issue.
Assembly of the flight spare PSMC boards has been completed. DEA Power Supply and the Serial Digital Telemetry require final testing. This will be completed by the end of August.
LMA is still holding open final PTS flight cable harness verification pending receipt of the MSFC memo and/or MSFC waiver approval. MIT has submitted a waiver to MSFC regarding the issue of DWV testing at voltages that exceed flight wire ratings (waiver # 36-016).
There are no changes to the MIT load table during this reporting period.
There has been no change in power dissipation since the last reporting period.
The Flight Detector Housing and Venting Subsystem were leak-checked at BASD, resulting in an approximate leak rate of 2.5 Torr per day, consistent with what was observed at MSFC prior to delivery to BASD.
Owing to limited workspace at Ball, the flight Detector Assembly and Venting Subsystem were shipped to and received at LMA, and placed in the Class 100 cleanroom. The previously identified vacuum leaks in the transducer o-ring and backplate connector were successfully repaired in situ.
The damaged S/N 005 actuator has completed final acceptance testing. This flight spare actuator was returned to MIT on August 1.
All hardware has now been DD250'd and is in storage in the ACIS RDL lab awaiting final delivery to Ball for SI integration. There are some "Hot Shade" issues which remain open after discovery by TRW of an in-bay situation with a Beta -52°, which heats the sunshade to ~170°C. This is outside the presently quoted ICD temperature range. Additional analysis continues to be performed by LMA to verify this situation and determine appropriate fixes (if necessary). Some additional tests are currently planned to be performed with the EU shades which were hand carried from BASD to LMA.
The "Hot Shades" thermal analysis predictions were made available and the Stress Analysis was updated and submitted as an addendum to the Stress Analysis CDRL. The main concern was the case of a hot abort. The updated stress analysis indicated positive margin for the hot abort case.
Since all flight hardware has been built and weighed, there is no update to the weight summaries from the previous reporting period.
The electrical interface bracket has been completed and will be 1238-certified in August after which it will be sent to Ball Aerospace for installation onto the ISIM.
After vacuum testing at Lincoln Labs pressure inside the detector housing showed a pressure rise of about 2.5 Torr per day. It was felt that this represented a leak in the vacuum enclosure and that leak testing should be performed at MSFC after XRCF testing. The VGSE was configured for leak test operations at XRCF and connected to the venting subsystem. Leak testing revealed a leak in the absolute pressure transducer on the venting subsystem. The transducer was removed and the seal inspected. A damaged o-ring seal was found to be the leak cause. The damaged seal was replaced and subsequent leak testing found no other significant leaks.
After re-evacuation, the VGSE was removed and the internal pressure of the detector assembly was monitored for leakage. After several days the leak rate appeared to be 1 Torr per day. Since the leak test performed after the o-ring repair showed no leak large enough to account for this rate of rise, it was decided to perform vibe testing and see if the apparent leak was consistent over the span of several days. It was quite possible that the apparent leak was primarily due to residual water vapor and outgassing from the Detector Assembly non-metallic contents.
A leak test just prior to shipment from MSFC still showed signs of flight hardware leakage after the repair at XRCF. At Ball Aerospace the leak rate was tested and found to be 2.4 Torr per day. This leak was consistent with measurements made at XRCF after vibe testing. The VGSE was configured for leak checking and a leak was found at the differential pressure transducer and at one of the detector housing backplate connectors.
The working space at BASD was somewhat cramped so the flight detector housing was relocated to Lockheed Martin and placed in our Class 100 cleanroom. The transducer leak proved to be an o-ring flaw. This transducer was replaced at Lincoln labs and was not the same one that leaked at XRCF. We currently believe the alcohol used to repair the o-ring at XRCF masked the leak on this transducer.
The leak in the connector was repaired by MIT in the LMA cleanroom. Subsequent testing has shown no appreciable leak in the detector housing at any seal locations. A long-term rate of rise test has been performed and has shown no long-term leak larger than the electronic drift of the transducers and drive electronics.
Work on upgrading VGSE #1 continues. The components for the VCU have been cleaned and it has been reassembled. We are still waiting on the RVA components, which should be completed in August.
The firmware codes for both VGSEs have had several additional fail-safe features identified. New EPROMS will be installed into the systems after testing. This is expected to be completed in August.
The lifting fixture has been modified and will be proof loaded in early August. After cleaning, the fixture will be sent to Ball Aerospace for use in fitchecking and preparation for flight detector integration.
In June, the systems engineering group continued preparation of verification assessment and test reports in support of ACIS verification activities and continued maintenance of program requirements documents. Engineering specialties activities focused on resolution of EMI/EMC test exceedance investigations. Additionally, the group completed preparation of the ACIS Acceptance Data Package (ADP) and coordinated its submittal to MSFC.
During July, the Systems Engineering Group supported post-Acceptance Data Review activities. The group mainly concentrated on responses to Action Items and closure on comments received during the Acceptance Data Review.
At the beginning of the reporting period, we prepared and submitted the ACIS Acceptance Data Package to MSFC. Tracked all requirements for program compliance and completed the Verification Requirements Specification Document Compliance Report. The Compliance Report shows verification report submittal has been completed for all ACIS CEI Specification and Observatory to SI ICD Requirements.
At the end of the period, we began tracking comments and Action Items received from MSFC on the submitted Acceptance Test Reports.
Support provided to MSFC and BASD in understanding W1/W2 cable harness layout. Started support discussions and activities for the integration of ACIS onto the ISIM.
System-level support of program scheduling for ACIS instrument flight hardware testing continued this month. ACIS program support and MIT/MSFC liaison were maintained. Performed post-XRCF EMI/EMC testing of the instrument at MSFC.
Sun shade thermal issues continue to be investigated. Thermal cycling of Engineering Unit shades will be started in early August.
Issue identified by MSFC relative to format used for the ADP MIUL CDRL submittal. LMA has received direction from MIT to update the MIUL and MUA's to accommodate MSFC concerns raised during the ADP. A new MIUL, consistent with the negotiations between MSFC, MIT and LMA, is in process and will be completed by the end of August.
PSMC DESC SPEC 87106 stacked capacitor issue continues to be investigated. Life testing of selected capacitors from the 87106-071 flight lot is in progress.
Additional parts from the lot of concern have been subjected to low voltage internal resistance testing and environmental testing in an 85°C/85% R.H. chamber. No conclusive Johanson capacitor results to report at this time.
MSFC-SPEC-1238 bakeout activities continued this period with the baking of "Red" and "Green" tags for attachment to non-flight and flight hardware requiring installation or removal prior to launch.
Re-testing of the instrument at MSFC for compliance with CS01, CS06, RE01, and RS03 was started and completed during June. Tests results show that the instrument meets the ACIS EMC Control Plan requirements for CS01, CS06, RE01, RS03, and transient voltage emissions. The instrument did not meet the AXAF-I requirements for inrush current. This anomaly was reported by Sverdrup Technology, Inc., and incorporated as part of the LMA test report for the retests. Three of the four open Requests for Waiver that resulted from the instrument-level EMI/EMC testing performed last December were resolved by these tests and one new Request for Waiver was created for Inrush Current.
A revised Hazard Report 16 has been completed and submitted to TRW and KSC for review. This revised Hazard Report answers the single Action Item received by ACIS during the last Safety Data Review at KSC.
The FMEA and CIL revisions were in process during July. MSFC had found the Revision A FMEA to be acceptable except for the following areas which require further attention:
The DEA interface boards (A11 and A12) were not addressed in Revision A and will be addressed in Revision B, as is the case with the DEA backplane connectors.
Similarly, the DPA power interface board was not addressed in Revision A and will be covered in Revision B.
Any single failure points associated with the above will be incorporated into Revision B of the CIL.
Additionally, all valid MSFC comments previously made to the Revision A CIL will be incorporated into Revision B. As MSFC has had the opportunity to review numerous revisions to both the FMEA and CIL, ACIS considers the Revision B submittals to be the Final submittals for both documents.