October 31, 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 from August 1 to September 30, 1997.
Since ACIS was delivered to MSFC on April 14, standard Monthly Status Reviews have ceased. However, MSFC requested an informal status review to cover open hardware issues (mainly the capacitor issue in the PSMC) and the closure of Action Items and Comments from the ACIS Acceptance Review of June 26. This status review was conducted on August 4 at LMA. MSFC attended with Max Rosenthal, Tony Lavoie, and Trent Griffin. MIT personnel in attendance were Bill Mayer, Bob Goeke, and Brian Klatt. In addition, we had arranged for a capacitor expert (Mike Sampson) from GSFC Code 300 to attend.
ACIS participated in the weekly AXAF telecons on August 12, 19, and 26, and Sept 2, 9, 16, 23, and 30. ACIS could not participate in the telecon on August 5 since the entire ACIS management team was returning from the status review held at LMA the previous day.
The FPSI telecons that were conducted on alternate Wednesday mornings have ceased, since both the HRC and the ACIS have been delivered to MSFC.
The following is a brief summary of the status of the main ACIS elements:
The CCD status at MIT has improved. All remaining flight quality CCDs (for the spare flight focal plane) are at MIT awaiting calibration. Two of the calibration chambers have been disassembled, cleaned, and reassembled. Calibration is underway. We estimate completion by the end of December.
During this reporting period, the external calibration source for ACIS was assembled at MIT and successfully tested by the ACIS Science team. It was then sent to Lincoln Lab for 8 cycles of thermal vacuum testing from Sept. 2 to 5. A 3-axis vibration test was then conducted at Draper Lab on Sept. 9. At this point, we had planned to send the unit to MSFC for 1238 certification. However, MSFC determined that its license was not adequate to handle the quantity of Fe55 radioactive isotope contained in the assembly. So we returned to Lincoln Lab and performed the 1238 certification in the same chamber that was used to certify the flight focal plane. This certification was completed on Sept. 19. The unit was then shipped to BASD and was received on Sept. 24.
As reported last period, we had detected evidence for a vacuum leak in the ACIS Detector Assembly earlier in the program. This leak was repaired at LMA and the unit was sealed on August 1. About two weeks later, the pressure was measured and found to be unchanged (within the accuracy of the VGSE). This problem has been fixed.
The testing of the DEA/DPA with the flight RCTU and flight cables was begun at BASD on July 22. A successful bit error rate test 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. An anomaly was found on the command synch clock from the RCTU. This anomaly was then investigated by TRW and MIT throughout the next two months. It appears the discrepancy is real (in the sense that the RCTU does not meet its specification for a monotonic falling edge for the clock pulse), but it is not clear that this anomaly actually affects any of the RCTU users. MIT was requested to assemble the DPA engineering unit for a test of the signal with a RCTUE and a CTUE. This test will be conducted in mid- October.
A CCD frost test at LL was conducted in August. A total of eight units were exposed to five cycles of severe frosting, and tested for any ESD damage. Although most of the units showed no effect from the frosting, two units, which already had some ESD damage, deteriorated further. The net result is that MIT relaxed the dewpoint restrictions on the CCD operation, but did not remove the restrictions entirely. For LEO operation in the shuttle, we suggest that the small vent valve be opened, but that's all. The large (hot wax) vent valve will be kept closed through LEO and IUS burn for transfer orbit and not opened until final orbit is achieved.
During this reporting period, both MIT and LMA continued working on the two remaining issues with the flight instrument. They are:
Shades. A test on the engineering unit shades was conducted at LMA in early August. The first test was a failure due to softening of the adhesive and boiling of trapped H2O. A pattern of cuts was made in the cover layer of gold-coated kapton and the test was repeated -- this time it was successful. A structural test was performed on the shades in September to assure that they retained sufficient strength for a shuttle return -- again successful. However, various options were still considered in order to lower the shade temperature and avoid the problem altogether. The thermal group appears to be homing in on a VDA coating of the gold kapton. This will be tried on the engineering unit shades and then retested.
The PSMC capacitor issue is real. Mike Sampson assured everyone at the August 4 meeting that the 1400 operating hours on the flight PSMC do not eliminate the possibility of a subsequent failure. In addition, the vendor initially selected by LMA for the alternate buy of capacitors (UTC) was a poor choice. LMA was asked to try to find replacement capacitors from AVX. The real issue is still how to find time in the AXAF schedule to perform the remove and replace operation (and the necessary environmental tests). Weekly telecons on this topic have been conducted between LMA, MIT, and MSFC since early September.
Both of these issues are discussed further in the LMA portion of this report.
There have been many activities at BASD over the last two months (training, certification, procedure review, etc.). With both ACIS and HRC at BASD in early September, it became obvious that both instruments had to be installed in a vertical fashion, but neither could pass by the other if it was already mounted on the SIM. Since the HRC bipod actually mounts under the ACIS Support Structure, it has to go on first (and ACIS has to come off if the HRC is to come off). The part of the HRC that interfered with the ACIS installation was a threaded rod used for assembly only. Gerry Austin modified the HRC to eliminate this interference before HRC was mounted to the SIM. Finally, ACIS was installed on the ISIM over the period of Sept. 18-22.
Due to the continued positive status of the ACIS instrument and schedule, additional layoffs have been made:
|Dorothy Gordon||Electrical Engineer||Jan. 1, 1998|
|Gordon Gong||Electrical Engineer||Jan. 1, 1998|
Following final cleaning and recertification of one of the large quantum efficiency chambers (see below), we resumed calibration of ccds for the backup focal plane. Before resumption of the recalibration effort, we had on hand 2 devices (w198c1 and w461c4) which had been fully calibrated. An additional 11 devices (see list below) had been screened and will be calibrated for the backup focal plane.
13 candidate devices for ACIS backup focal plane.
All devices are front-illuminated.
|w200c1||yes||qe calibration done;
noisy; poor cc mode
|w215c1||yes||qe calibration done|
|w216c3||yes||qe calibration in
|w163c3r||yes||tbd; used for ionizing
Quantum efficiency calibration is being completed at the rate of approximately one device per week. It is expected that calibration of the backup focal plane will be completed by the end of calendar 1997.
We participated in the AXAF calibration analysis team's data analysis workshop at MSFC in late August and, together with the PSU ACIS team, submitted a comprehensive (250-page), though preliminary, calibration report to MSFC. The report is available from the MIT or PSU ACIS Web pages, or from AXAF project science. It summarizes results of CCD and optical blocking filter subassembly calibration measurements, and provides a preliminary analysis of data obtained at XRCF. We will revise and supplement this report over the coming months, and will submit a final report in mid-1998.
After extensive cleaning and bakeout efforts, one of the large quantum efficiency vacuum chambers (beavis) was certified and returned to service. No single source of contamination was identified. The certification process involved TQCM measurements and "fogging tests" of optical witness samples. Even though extremely low TQCM rates were achieved (less than 0.05 Hz/hr), we still found it necessary to accelerate the CCD warmup in order to avoid the witness sample fogging which prompted the chamber cleaning.
Testing and cleaning of the HIREFS chamber is now underway. This chamber must be in service by early November 1997 if backup detector calibration is to be completed by the the end of this year.
Two devices, w157c1(FI) w147c3(BI), were flown on STS-85 (Space shuttle Discovery) in August. The purpose of the flight was to check for unexpected radiation effects. Both devices functioned after the flight. Results are rather surprising. Preliminary comparisons of dark current maps at temperature of -120°C showed some increase in the number of hot pixels, in spite of very significant shielding provided by the detector container, and the modest proton exposure experienced in the short, very low-altitude Discovery orbit. Moreover, one large blemish present in the front-illuminated device BEFORE the shuttle flight seems to have disappeared. More detailed analysis of these data is in progress.
After collimator modification, the external calibration source was re-tested and found to have adequate flux: expected flux with the source installed in the SIM is about 150 ct/s/CCD as of September 1997. 52% of the flux is in the Mn K line; 17% of the flux appears in each of the Ti-K and Al-K lines; and 0.2% of the flux appears in the Mn-L line. Final calibration of the source, as installed in the SIM, will take place during the ISIM thermal balance test.
We supported the engineering team during the instrument cross-talk test at Ball Aerospace in Boulder. A cabling problem prevented us from using the high-speed tap for this test. Nevertheless, on the basis of a limited amount of raw- mode (full-frame) data telemetered during the test, ACIS noise performance is the same with HRC operating as with HRC not operating.
At the request of ASC and AXAF project science, we reviewed some of the ACIS-related materials that ASC has prepared for publication with the forthcoming announcement of opportunity to observe with AXAF.
The following software ECO has been prepared:
|ECO 36-960||-- Interrupt Control Classes
-- FEP Devices
No changes have been made. The following deliverable is under review:
|ECO 36-957||-- ACIS Software Users' Guide|
Release 1.5 of the Flight Software (ECO 36-940) was burned into the flight and engineering units immediately prior to SIM integration at Ball Aerospace. It is accompanied by release notes and building instructions. Default command blocks, bad pixel lists, etc., are unchanged from release 1.4. Release 1.5 includes patches to circumvent all software problems extant after analysis of ACIS tests at the X-ray Calibration Facility.
Unit testing of BEP and FEP flight software modules is now complete. No remaining anomalies have been noted. The FEP histogram code was successfully retested with the patch that eliminates the problem reported in SPR-115 (see below).
High-level testing of flight software in FEP and BEP hardware continues, accompanied by tests at MIT and MSFC using the software simulators. The following ECOs related to verification testing were reviewed during this interval:
|ECO 36-935||-- Histogram Mode
-- Science Run Report, Exposures Sent and Produced, and Ignore Initial Frames
-- TE Recompute & Trickle Bias
-- CC Recompute & Trickle Bias
|ECO 36-938||-- BEP and FEP Timestamp
-- Generate DEA Housekeeping Reports
-- Manage DEA Housekeeping Parameters
-- DEA Control Board Heaters
-- Verify by Inspection
|ECO 36-956||-- Window 1D
-- Window Count
-- Histogram Mode (Rev B)
-- Science Run Report, Exposures Sent and Produced, and Ignore Initial Frames (Rev B)
-- Timed Exposure Recompute & Trickle Bias (Rev B)
-- Continuous Clocking Recompute and Trickle Bias (Rev B)
|ECO 36-961||-- Continuous Clocking CCD Options
-- Continuous Clocking Event Rate
|ECO 36-965||-- Bias Mode Verification Procedure|
The current status of ACIS software verification is detailed on the Web page.
All prior software problem reports have been closed. Four new problem reports have been filed:
SPR-113 (M97071101) Incorrect PBlock Selection when Desired Block is Corrupted.
SPR-114 (M97071102) In RawMode, Science data is not received from all FEPS after a single FEPs memory has been corrupted.
SPR-115 (M97080401) Bad varianceOverclockLow values in Raw Histogram Mode exposure packets.
SPR-116 (M97101301) Incorrect reporting of corrupted bias pixels.
As a result of discussions between the ACIS team and Project managers, it has been decided not to fix these problems by replacing the current contents of the flight unit's EEPROMs. Instead, small software patches have been developed for SPR-113, SPR-114, and SPR-116, and nothing has been done about SPR-115 since it is generally accepted that the anomalous behavior is superior to that described in the Software Requirements Specification. The current status of software problem reports may be accessed via the ACIS Web server
Flight software release 1.5 was burned into ACIS EEPROMs immediately prior to the start of SIM integration, and a subset of the formal software verification test suite was run. The choice was restricted to those tests that did not require either a focal plane or an image loader.
The following tests have been prepared. The first three verify the changes to flight software that are new to release 1.5. The remainder test the instrument more thoroughly than at XRCF.
|ECO 36-962||-- Jitter DAC Test Procedure
-- AC/BD Histogram test Procedure
-- FEP Ring Buffer Reset Test Procedure
-- FEP Hardware Stress Test Procedure
-- Clocking Mode Survey Test Procedure
Bob Blozie and Alan Braver left the project at the end of September. Their remaining software verification duties have been assumed by Peter Ford and Jim Francis with assistance from Royce Buehler (ASC) and Fred Baganoff (ACIS).
Thirteen (13) Alerts from NASA/MSFC, were received over the report period. These items are listed on MSFC Alert Problem Summary Reports dated September 4, 1997 and September 24, 1997. An Alert response was sent to MSFC for each summary on October 2, 1997 and October 8, 1997, respectively. Each Alert was compared with the MIT ACIS parts lists. Twelve of the Alerts in the previously mentioned summaries do not impact ACIS. Alert W-P-97-04A, MSFC tracking number 7056A, does impact the PSMC on ACIS. MSFC was notified of this problem in MIT letter from B. Klatt to E. Trentham dated 5/23/97.
MIT Waiver Request 36-005, Multiple Point Secondary Power Return, and 36-020, Crimp Connector Testing, were submitted to MSFC for approval. In addition, supporting information was submitted on MIT Waiver 36-018 regarding weld filler material. Listed below are the open MIT waivers at this time. All other waivers have been approved or withdrawn.
|36-005||MULTIPLE POINT SECONDARY POWER RETURN||MIT||8/29/97||OPEN|
|36-007||OBF VISIBLE LIGHT EFFICIENCY||MIT||8/6/96||OPEN|
|36-016||USE OF OVERSTRESSED WIRE||MIT/LMA||3/28/97||REJECTED|
|36-018||WELD FILLER MATERIAL||LMA||6/6/97||OPEN|
|36-020||CRIMP CONNECTOR TESTING||MIT||10/1/97||OPEN|
Escorted the flight Detector Assembly/Vent Valve Assembly during transportation from Lockheed Martin Astronautics to Ball Aerospace.
Witnessed the integration of the ACIS into the SIM at Ball Aerospace.
Prepared MIT Non-conforming Material Report #372 as an MRB action for the alteration of the Proton Shield on the Support Structure. This was attached to Ball Aerospace Material Deficiency Report (MDR) C07859. The Proton Shield was modified to avoid an interference caused by two (2) thermistors which Ball Aerospace installed within the ACIS envelope.
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 and CIL. The final version of the FMEA and CIL were submitted to MSFC.
Provided input for an update of JSC Form 44 and KSC Form 16 on the External Calibration Source Assembly.
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.
In support of the retrofit of Johanson Capacitors on the flight PSMC, PSMC- EU2 has been upgraded, vacuum baked, and certified per MSFC-SPEC-1238. PSMC-EU2 was delivered to Ball Aerospace on October 23. It is available for temporary use during Thermal Balance and Thermal Vacuum testing, while the capacitors on the flight PSMC are retrofit at Lockheed Martin Aerospace Corp.
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 test was developed in which water was injected into a vacuum system after test devices were mounted and cooled to a low temperature. A layer of frost, which was several mils in thickness, was allowed to form. Devices were held in this state for several hours, then the temperature was raised, allowing the frost to evaporate in the vacuum. Test devices were generally chosen from ones unsuitable for flight, and were characterized for shorts and opens both before and after the frost cycling test.
Frost cycling on the first batch of five devices was completed with four devices not changing but one device (W193C1) developing new problems. This device had already been weakened by ESD so it is impossible to say that the frost caused the problem. The original condition of the test was only one cycle. All of the devices passed the one-cycle test. W193C1 failed after the second cycle.
Frost cycling was then done on the second batch of three devices. Instead of testing after each cycle (as in batch #1), the devices were cycled 5 times and then tested. One device (W469C3) developed new failures, but this device had also been weakened by ESD prior to frost cycling. The other two devices showed no change.
In summary, two of the eight tested devices developed new problems. Both devices were previously damaged by ESD. There is no evidence that the frost test causes damage to healthy devices, and we cannot determine if it enhances the deterioration of devices that have already been damaged by ESD. We know from past experience that devices damaged by ESD are prone to future problems. We conclude that the frost stress probably will not affect healthy devices which have not been subject to ESD damage, as is the case for all the flight devices. It should also be mentioned that devices are often subject to frost exposure during cold wafer probing, and that this generally has not been found to cause a problem either.
The LMA received Change Order 72 from MIT and submitted a proposal back to MIT during this reporting period (August and September 1997). The CO72 proposal was based on discrete estimates for the three primary tasks including: (1) delay to SIM integration, (2) "Hot Shade" issues and support activities, and (3) Johanson DESC SPEC-87106 capacitor issues and support activities.
LMA personnel continued post-ACIS Acceptance Review support activity. LMA maintained a level of Systems Verification personnel through 9/1/97, as a means of response to any MSFC raised issues or Action Items generated regarding formal ACIS verification.
All previously DD250'd LMA build flight hardware was shipped to Ball for SIM integration. These hardware elements consisted of the remaining Thermal Control Structure (shades, posts, and flight MLI), and the flight W1/W2 cable harness. This hardware was be held in clean storage at LMA until needed for ISIM integration.
The flight Detector Assembly and Venting Subsystem, previously received at LMA and placed in the Class 100 clean room, had their previously identified vacuum leaks in the transducer o-ring and backplate connector successfully repaired in situ.
An ACIS/MSFC TIM was held this reporting period, addressing a wide variety of "Hot Shade" issues and risk mitigation plans. 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 month. 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 PSMC DESC SPEC 87106 stacked capacitor investigation was completed in this period. Testing of capacitor lot/date codes contained in the flight PSMC yielded a conclusion that the flight PSMC contains suspect parts that represent an increased reliability risk. Direction was received from MIT, per MSFC concern, that replacement parts continue to be procured and plan for installation in the flight unit PSMC. The replacement capacitors, procured from multiple sources are long lead items with some AVX parts awaiting receipt. Replacement part upscreening is expected to complete during October 1997.
The program continued to place priority and emphasis on completion of the ACIS flight and ground support hardware assembly, integration, and test at BASD. All planned hardware activities have been completed, except for final assembly and testing of VGSE #1. Retrofit modifications to the ACIS lifting fixture and residual spare PSMC board testing were completed.
Major LMA technical accomplishments for August and September are summarized in the following sections.
Testing of the Johanson Dielectric Inc. (JDI) ceramic chip capacitors, bought to DESC SPEC 87106, have proved them to be a reliability risk for the flight PSMC. Given the excessive 87106-071 failures (5 failures of 38 pieces) and 87106-069 (4 failures of 31 pieces), the need to replace these two lots, and possibly all four JDI lots within the PSMC, has become almost unavoidable.
Two items are required in order to remove and replace these capacitors, the replacement piece parts and a process that is 100% safe for the flight hardware.
The remove and replace process development was a primary focus during this reporting period. Two processes were considered, hot plate used in combination with a custom-machined fixture (similar to how the parts were initially installed), and a second method involving the use of a solder fountain. Preliminary trials demonstrated the solder fountain to be very promising and hence, a more detailed process development was initiated.
The solder fountain process development involved three distinct activities to assure a reliable remove and replace (R&R) process. First, 87106-type capacitors were electrically screened to assure that known good parts were being used. EU#1 PWBs were conformally coated to make them "flight-like", allowing all flight assembly conditions to be adequately simulated during the remove and replace process development. These known good parts were then installed into EU#1 PWBs and promptly removed using the solder fountain. The capacitors were then electrically tested to confirm the R&R process did not alter or damage the parts in any way. This was repeated several times to instill process repeatability confidence.
A second activity was performed which tested solder joint reliability. Capacitors were installed at the solder fountain into an engineering unit PWB and the assembly was temperature-cycled eighteen times, concluding with a solder joint inspection. Finally, the durability of the PWB itself was investigated to establish an upper limit on the number of R&R cycles that can safely be performed on a given assembly.
Combination of the above activities provided the information and confidence to acknowledge this process as the preferred remove and replace method of 87106 capacitors on populated PWB assemblies. The final step was the formal program process documentation writeup, the MPP. This process will be used on the spare board assemblies as a final validation prior to use on the actual flight hardware.
To date, all four lots of 87106 capacitors have been ordered from Union Technologies Corp. (UTC) and have been received. A second lot of each part number was also ordered from AVX-Olean. One of the four AVX has been received and two more are expected in early October with the fourth expected in early November. AVX is performing Group A and Group B testing, meaning the parts will be ready for use upon receipt. The UTC parts, on the other hand, have been subjected to lot qualification and 100% screening at LMA and are complete. Two lots of UTC parts have passed and are ready to use. One lot is acceptable, but not desirable for use (87106-091) and is being held pending receipt of the AVX parts. The fourth lot of UTC, 87106-069, were rejected and are not acceptable for use. The AVX 87106-069 are expected in early October.
EU#2 is in the process of being prepared so that it can temporarily replace the Flight PSMC 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 capacitor replacement would have on the flight critical path. It is currently being vacuum- baked with the expectation it can be 1238-certified.
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 and test of the flight spare PSMC boards has been completed. The spare assemblies are currently being prepared for JDI 87106 capacitor remove and replace activities.
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 LMA in the RDL Cleanroom since unacceptable leak rates were measured after XRCF testing. Two leaks were observed, with a leak at one of the GSE pressure transducers and the other leak at one of the spectrometer backplate electrical feed-throughs. Both leaks were fixed and subsequent leak rates were well within the specified requirements. While the detector and venting subsystem were at LMA, the housing and focal plane were heated to approximately 50°C for 48 hours to help bakeout any residual solvents or water. Subsequent measurements after several weeks did not show any measurable leakage.
The Flight Detector Housing and Venting Subsystem were delivered and installed onto the ISIM in September along with the rest of the ACIS components. There were no significant problems and installation was successful. Electrical testing showed that the entire ACIS was fully functional after installation.
The damaged S/N 005 actuator has completed final acceptance testing. This flight spare actuator has been returned to MIT.
All TCS components have been integrated onto the ISIM. Thermal Vacuum Testing of the ISIM will start next month. There are some "Hot Shade" issues which remain open after the completion of the EU shade thermal tests. Cross-cut vents were tested and qualified on the EU shades for the current goldized kapton surface. Post-thermal vacuum proof testing showed that the shade is structurally sound after exposure to 170-193°C temperatures. However, MIT has requested LMA to pursue an alternate design which lowers the temperatures on the shades while in the orbiter and during roll maneuvers while on-orbit. Cross-cut vents were not installed on the flight shades prior to installation on the ISIM. Therefore, whatever the final fix, the shades will need be removed after thermal vacuum testing to complete the modifications.
Two alternate designs which minimize impact to the flight-qualified hardware are being investigated: 1) Direct Vapor Deposition of Aluminum (VDA) over the gold surfaces with an SiO2 protective overcoat and 2) Design and build MLI blankets which cover the gold surfaces of the shades. Both have their advantages but schedule constraints may best be accommodated by the direct vapor deposition of Aluminum and SiO2 onto the gold surfaces which get exposed to direct sunlight. Test coupons will be sent to Thin Film Technologies which has previously metalized other components on the TCS. Both bare VDA and SiO2 overcoated coupons will be evaluated. Optical measurements will be made at both LMA and MSFC to help evaluate the design approach for the flight shades. In addition, the EU sunshade will also be retested at MSFC with surface heating to qualify the VDA method and also the 3" center cross-cut approach. This testing will occur in October, allowing the final design fix decision to be made prior to the next shade removal opportunity at Ball.
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, with in-bay hot case thermal loading also analyzed. The updated stress analysis indicated positive margin for both conditions. Proof testing was successfully completed on the EU sun shade after thermal vacuum testing at 170-193°C. Post-test NDE evaluations did not reveal any new anomalies.
Significant analysis has been performed in support of the Hot Shade issues. Detailed analyses of both the sun shade and the telescope shade has not significantly reduced the maximum predicted temperatures while in the orbiter or during transfer orbit. Design solutions have been analyzed, including the addition of MLI over the gold surfaces and a direct VDA coating. Both methods will work for cooling the shades; however, the latter reduces focal plane margins several degrees when on-orbit. In either case, the -120°C goal can be achieved. Analysis support will continue as more information becomes available regarding optical properties of VDA and VDA with SiO2 overcoat.
Since all flight hardware has been built and weighed, there is no update to the weight summaries from the previous reporting period. The weight 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 the ACIS budget. Mark Kilpatrick's (BASD) worksheet dated 12/8/95 assumed 1 pound for these components. LMA does not have the actual breakdown.
Note -- Numbers in bold indicate actual measurements.
The ACIS Detector Housing and Venting Subsystem have been successfully integrated onto the ISIM. The electrical interface bracket has been delivered to BASD and was installed on the ISIM with the ACIS Venting Subsystem.
After installation, the system was connected to the VGSE and a pressure measurement was made. The VGSE showed no appreciable pressure rise in the flight detector housing and venting subsystem despite nearly three weeks without pumping.
Work on upgrading VGSE #1 is nearing completion. All components have been cleaned and reassembled. A minor leak in the RVA was repaired and pressure proof testing will commence in early October.
New EPROMs were tested and installed in VGSE #2. Added to the state-machine code were:
Close low conductance vent valve during error condition.
Cycle roughing pump once per day to keep accumulator pressure low.
Emergency high conductance valve close command if valve is half open or closed. (This command is password protected.)
These additions were made with insights and knowledge gained from about one year of operation on the VGSE. While none of these modifications affect normal operation, they do add an extra degree of safety for the flight hardware.
The EPROM for VGSE #1 will also incorporate these changes. Performance and functional testing will be performed on VGSE #1 after pressure proof testing.
The lifting fixture was sent to BASD where it was used to install the detector housing on the ISIM. No further use for the fixture is planned during the remainder of the program.
During this period of performance, the Systems Engineering Group supported post-Acceptance Data Review and next-level assembly integration activities. The group mainly concentrated on supporting the integration of ACIS onto the ISIM. The Group has downsized as verification and integration activities were completed.
Supported the review, release, and submittal of various engineering drawings revised to reflect the "as-built" configuration and the incorporation of Acceptance Data Review comments.
Revised and supported the review, release, and submittal of the Special Consideration Items Drawing (SCID), revised to reflect the incorporation of Acceptance Data Review comments.
Continued tracking comments and Action Items received from MSFC on the submitted Acceptance Test and Assessment Reports.
Support provided for the integration of ACIS onto the ISIM.
System-level support of program scheduling for ACIS instrument flight hardware testing continued this period.
Sun shade thermal issues continue to be investigated. Thermal cycling of Engineering Unit shades was performed during this period. Results were satisfactory and consistent with the LMA recommendation that flight shades could/ should be used as-is with inclusion of the cross-cut vents. However, to mitigate risk due to additional investigative testing, materials are being procured to build a new set of shades that will better tolerate high temperature conditions. Support for this effort continues and will remain so until a final resolution.
The Material Identification and Utilization List, MIUL, has been updated and submitted in this period. The revision was performed in compliance with MIT direction in response to MSFC concerns raised during the ADP.
The PSMC DESC SPEC 87106 stacked capacitor investigation was completed in this period. Testing of capacitor lot/date codes contained in the flight PSMC yielded a conclusion that the flight PSMC contains suspect parts that represent an increased reliability risk. Direction was received from MIT, per MSFC concern, that replacement parts be procured and installed in the flight unit to preclude failure. The replacement capacitors, procured from multiple sources, are long lead items with some AVX parts awaiting receipt
New processes to remove and replace the existing suspect parts were investigated and documented in this period. Significant coordination has taken place to support the receipt of the PSMC from NASA/MSFC (at BASD for ISIM integration) for the removal, replacement, and re-acceptance activities. All efforts are being made to minimize the impact to the program and AXAF launch schedule.
MSFC-SPEC-1238 bakeout activities were 100 percent completed this period with successful baking of "Red" and "Green" tags for attachment to non-flight and flight hardware requiring installation or removal prior to launch.
EMI/EMC activities were slowed during this reporting period. The final effort remains to close out open test procedures after receipt of approved waivers.
The FMEA and CIL revisions have been updated and submitted in this period. The revisions were performed in compliance with MIT direction in response to MSFC concerns raised during the ADP. As MSFC 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.