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 March 1996.
The March monthly status review for ACIS was conducted at LMA on March 12 in conjunction with a monthly TIM and contract negotiations for Change Orders #25, 28 and 43. MSFC had requested this review to be at LMA since the critical path for ACIS delivery is now gated by the delivery of the flight PSMC and/or the LMA-provided Detector Housing.
As mentioned above, the monthly TIM between MIT and LMA was held at LMA on March 13 and 14. The main topics at this TIM were several analyses recently completed by LMA (venting, light shade, and PSMC reliability) and an alignment workshop to try to come up with a faster approach to the issue of the Detector Assembly alignment measurements and verification.
MIT hosted a visit by the new AXAF Program Manager at NASA, Bill Huddleston, on March 20. He met with the ACIS project in the morning, the HETG project in the early afternoon, and CSR management during the late afternoon.
MIT participated in the AXAF project level telecons on March 5, 19, and 26. MIT (and Max Rosenthal) missed the AXAF telecon on March 12 due to the monthly review at LMA on that date.
MIT participated in the ACIS bi-weekly status review on March 6. The ACIS telecon normally scheduled for March 20 was canceled due to the monthly review the previous week and the fact that Bill Huddleston was visiting MIT on that date.
During the month of March, the ACIS schedule actually improved somewhat. During the TIM on March 13 and 14, an alignment plan was generated which uses the tight mechanical tolerances of the various piece parts of the Detector Assembly and measurements on the Focal Plane Paddle made by Lincoln Lab This allows the shims for mounting the Detector Assembly to the SIM to be predetermined and fabricated while the actual flight hardware is being assembled at MIT. Upon arrival at LMA, the alignment will only need to be verified. The effect of this re-planning is that the Detector Housing will be delivered to MIT a week later than previously scheduled, but the alignment flow at LMA after delivery by MIT has been reduced from 33 days to 17 days. We picked up a few days of slack in the overall schedule, but bought an additional one week of slack for the Focal Plane, DEA, DPA and PSMC. As a result of this re-programming, the Detector Housing is now the critical path by 8-10 days. The Detector Housing is late due to several factors: the drilling of the mounting holes for the MIT Proton Shield, the extra alignment measurements to be made prior to delivery, and problems with the LMA precision cleaning facility (several shut-downs).
The following is a brief summary of the other main ACIS activities:
(a) The CCD calibration is proceeding quite smoothly. Four units (all FI) have been completed and returned to Lincoln for installation onto the flight Focal Plane. The current estimated completion date has about 13 days of slack with respect to the critical path.
(b) The DEA Analog Board is well off the critical path. In fact, the flight analog boards were shipped on April 1. However, the "11th" board in the DEA is still a problem. Layout of this board did begin on March 7, as planned, and the layout was delivered on April 4 and is under review. This board is holding at 8 days removed from the critical path.
(c) The DPA design has now been completed. However, the layout of the FEP board has suffered. The flight layout of this board was started on January 18, but after MIT rejected the layout three times in February- March, the task at ElectroArt, Inc., was terminated and given to Winter Design in mid-March. The BEP design was completed on March 28, and the layout of this board began on March 29. The BEP is now 8 days removed from the critical path.
On the positive side, after six months of searching, MIT appears to have found a PCB vendor (Speedy Circuits, Inc.) for CIC boards who seems to be able to make the high quality boards in a reasonable time. The first boards (DEA analog) were delivered in 20 days, and due to the large number, the vendor actually completed two lots in this time period, and MIT was able to inspect the first lot before work began on the second.
As discussed above, the ACIS project is still holding to a delivery date to BASD on December 15 (with a positive slack of 20 days). All of the mechanical designs of the DEA and DPA have been reviewed and released for flight fabrication. The DEA Backplanes (engineering and flight) have been fabricated and accepted. The DPA Backplanes (engineering and flight) are in fabrication. About four sets of Optical Blocking Filters have been received and passed calibration at the Wisconsin synchrotron. The radioactive source for the engineering unit internal source has been received and is under test by the MIT science team. The detailed machine shop drawings for the Proton Shield (8 separate parts) have been reviewed and released for flight. Material is on order. All the Beryllium for the flight PCB frames has been received by the local machine shop (Phoenix Precision) and fabrication of the flight frames is in process.
Most of the high level technical problems internal to ACIS seem to be under control. A few nagging interface issues remain: the details of the mounting of the Support Structure to the SIM Translation Table (full contact area or bosses, and the rotational stiffness of the mounting interface), exactly where to mount the survival heater connector bracket on the Support Structure, the need (and who provides it) for a connector bracket at the base of the PSMC due to the long cable run to the first cable clamp on the SIM, the details of the `extra' shielding for the relatively soft DAC 8800s of the DEA, and finally the on-going saga of the interference on the DPA between the LMA-provided J1 & J2 connectors and the TRW-provided connectors J6 & J7.
During March, no personnel changes were made to the ACIS staff at MIT. Several personnel problem s did occur: Ellen Sen's mother died after a long illness, and the mother of Bill Ward's replacement had a stroke and she had to fly to Germany on March 29. A replacement (for the replacement) was immediately provided by the contractor agency, but he has a lot to learn.
Four front illuminated devices were calibrated and returned to Lincoln Labs. Devices w185c3 and w163c1 (calibration completed 12 March) are excellent devices (see ACIS memo PS-106 for preliminary calibration results) and are destined for Focal Plane locations I0 and I2. Calibration of devices w190c1 and w168c4 was completed on 26 March. All planned calibration measurements (priorities 1-3) were completed on these devices on schedule.
Two flight candidates (w140c4 and w79c3) and one non-flight back- illuminated CCD were delivered in March on schedule. Both of the flight candidates exhibit relatively poor parallel charge transfer efficiency; spectral resolution at 525 eV is approximately 130-140 eV, fwhm, which is considerably worse than the best (<100 eV, fwhm) achieved on back- illuminated devices. Device w140c4, the better of the two flight candidates delivered this month (ranked by spectral resolution) may be acceptable as a TGS detector, since its spectral resolution is apparently adequate to separate first and second orders even at the low energy limit (0.4 keV) of the MEG. More detailed characterization of this device is underway.
Calibration of the best back-illuminated device received to date (w147c3) began at the end of the month.
Support to MIT CSR provided by colleagues from AXAF Science Center (Plucinsky, Woo, Glotfelty, Schultz, McNamara ) and Penn State (Grant, Nishikida) has been vital to the smooth progress of the calibration to date.
Work continued on development of SRAM and PRAM for the calibration Detector Electronics (DEA). Refinements in SRAM were required to obtain acceptable temporal stability and spatial uniformity of the bias in certain "off-nominal" readout modes.
Low-level (~0.5 photon/pix/sec) optical scintillation was discovered in the output of the tritium-excited fluorescent Li-Fl source used to produce the 677 eV line. This problem was resolved with addition of an aluminized blocking filter. Stronger tritium sources were installed to speed the quantum efficiency measurements at low-energy lines.
A software filter was developed to remove low-level synchronous noise spikes which afflict the low-energy spectral (HIREFS) test chamber.
The ACIS Contamination Monitor (Door Source) engineering unit has been assembled, including the radioactive source. It was then disassembled so that the source could be tested by itself.
The External Calibration Sources are on order. The drawing package is ready for final sign off. Quotes and materials have been received.
The flight Back Plate Assemblies are at the vendor for rework. The EU Plate is acceptable and has been assembled to the EU Detector Housing.
The details of the Proton Shield are completing the review process. Quotes for machining have been received and materials are on order.
The EU Support Structure has been assembled. Drawings for the flight unit are nearly complete. The interface of the Flexures to the SIM continues to be in question. Most effort has been spent in developing the routing and supports for the cables from the DA to the DEA.
This assembly has been modified to eliminate the RTDs that were no longer used. The EU has been assembled into the EU Detector Housing.
Flight filters are at LMA.
The EU vacuum GSE has been successfully operated at MIT.
The following boards have been through engineering review and are presently at outside vendors for layout and routing: Front End Processor, Back End Processor and DPA Backplane. All three boards have had components placed and MIT is evaluating check plots of the Backplane. The DEA Backplane has been sent to the fabrication house. Checkplots of the Heater Control and Front End Processor are expected shortly.
Detail mechanical drawings for the Detector Electronic and Digital Processing Assemblies are well underway. The DEA and flight Beryllium frame drawings have been through engineering review and will be released to the fabricators shortly. The DPA details are in engineering review.
The interconnection diagrams for the ACIS, DEA and DPA are in the engineering review process for changes in electrical and cabling design from the mock up and engineering units.
The thermal coatings on the DEA +Y and -X panels were changed from irradiate to black paint to cool the DPA and DEA hot-case temperatures by 4 deg C.
Performed thermal analysis of components on the DEA T/C board.
Requested and received updated boundary temperatures from TRW/ Ball for the hot, cold, cold survival and cold standby conditions. Revised the ACIS thermal models to reflect these changes. The hot case conditions are improved over the previous set, yielding approximately 7 deg C relief for the DPA hot case. The cold standby conditions indicate that the 3 baseline 33 watt heaters on the Support Structure are adequate to keep DEA and DPA temperatures within their operating limits. The backup 38 watt heaters are not required. This ACIS decision helps resolve the Spacecraft peak survival heater power problem.
Visited Lincoln Lab on March 26 to discuss the requirements for the ACIS lifting fixture.
Participated in Thermal TOP Telecon on March 28.
Reviewed LMA Thermal Balance Test Procedure for the CAMSIM DH and FU TCS, making several changes in boundary temperatures and adding a TQCM (contamination monitor) to the test setup.
The design of the DEA control card is complete. Detail layout design is underway. The design of the ACTEL FPGA controller has commenced.
The design of the passive DEA Backplane has been completed. Detail layout design and fabrication has commenced.
All engineering DEA subsystems have been debugged and are now fully operational. All cameras have seen first light and statistical noise evaluations have been completed and accepted. An attempt to integrate four of these systems onto a passive Backplane will be underway.
The video flight board design is completed and layout design has commenced.
The FEP engineering board layout is finally near completion.
The BEP Rev.A schematics have been released, and the PCB board layout is also near completion. The BEP Actel design is complete and is undergoing top-level functional simulation.
The DPA Backplane PCB layout has been approved; boards are being fabricated.
We have received high speed serial port extensions for the DPA Test/Development stations. These are currently being interfaced to the Littlefield RCTU simulator, which will allow for faster data transfer to/from the UNIX host. We have also been using the Gulton RCTU/CTUE box and hope to interface it to the engineering BEP.
The ACIS thermal vacuum test facility and equipment configuration plan is still in progress. The wiring list to modify the LMA supplied harness is complete and will be checked shortly. The wiring lists for MIT provided cables is nearly complete at this time.
Design of the fiducial light test unit and heater panel control box is complete.
Developed and tested utility software for reading the telemetry generated by the locally-developed RCTU emulator (LRCTU). These utilities describe the structure of the telemetry packets, read packets into a buffer, and write a formatted hexadecimal dump of a packet. These have been used to create programs that convert LRCTU telemetry to AXAF minor frame format and that display packet contents. Developed a directory hierarchy for arranging EGSE and testing software and began developing makefiles for software development that reflect this arrangement.
Submitted an ECO to use the ACIS 100 kHz pixel clock for internal timestamping, rather than the 1024 kHz Spacecraft clock. This change will also be implemented in the ongoing BEP redesign.
Reviewed the last module, the SRAM library classes, deciding to retain the current design through the Alpha release. This may be changed later after evaluating further the performance of the Analog Boards.
The BEP redesign effort continues. We continue to test the BEP serial telemetry interface with the original BEP. Changes to IP&CL structures have been reviewed and are being submitted to TRW. In the meantime, they are visible at "http://acis.mit.edu/ipcl".
The Alpha release of the flight software is undergoing internal review. Test data sets have been delivered to PSU and ASC. They simulate timed exposure science runs, using data from BI CCDs exposed to Fe55 with Co60 contamination. Preliminary responses from PSU and ASC are favorable.
All BEP and FEP flight software modules continue to be subjected to unit and coverage tests.
The BEP/FEP software simulator has run simultaneously on multiple DecStations. Jonathan Woo of the ASC has collaborated with us to compare simulated science runs with analysis of the same input data using tools developed by the ACIS calibration group.
Nine (9) Alerts from NASA/MSFC were received over the report period. These items are listed below. They were compared with the available MIT parts lists, none of the Alerts impact the MIT ACIS design at this time.
|ALERT #||MSFC #||Part Number and
|AAN-U-95-63A||6819A||1 1/4" NUT
A & G ENGINEERING
|96-CR01-0016||6914||RNC65 & RLR32
Generated 15 partial DEA kits, waiting for remaining parts.
Five (5) component lots were sent to Associated Testing Laboratories (ATL), Inc., Burlington, MA for multi-stage part testing (PIND, X-ray, DPA). Eleven (11) lots were received back from ATL.
Back plates, 36-10107, have been rejected for failure to meet the hermeticity requirements. Pacific Coast Technologies has verified the leaks and are reworking the back plates.
Twenty-three (23) PCB coupons were sent to HiRel Labs for cross section analysis per NHB 5300.4(3I).
Final source inspection was performed at Harris Semiconductor, Melbourne, FL on 35 pieces of HS1-26C32RH-Q.
Received results from MSFC on 1443 testing on eight (8) samples. Results have been extremely slow coming back on submittals.
Prepared SCD 36-02314 for Nickel Wire.
NSPAR 36-026 for Electrical Connectors and NSPAR 36-027 for Nickel Wire were submitted. In addition, NSPAR 36-028 was submitted for Polypropylene Capacitors. Nine (9) NSPARs were submitted for Lockheed Martin Astronautics.
|36-002||A to D Converter
|36-003||CA Memory Module
|36-004||FB Memory Module
|36-005||Programmable Supply current
Op Amp 36-02304
Only Memory 36-02306
|36-008||Electrical Connectors, PCB
Mount SND Type
|36-009||Electrical Connectors, PCB
Mount KA Type
|36-012||Junction Field Effect Transistor
|36-013||Dual Surface Mount Diode
|36-014||Dual Operational Amplifier
|36-015||8000 Gate Anti-fuse Field
Programmable Gate Array
|36-017A||Charge Coupled Device
|36-018||Microcircuit, Octal Buffer
|36-019||Microcircuit, Octal Bus
Transceiver (Harris HCS245)
Flip-Flop (Harris HCS374)
Line Driver (Harris HS26C31)
Differential Line Receiver
Q-Tech part type
WIMA P/N FKP2 (36-02312)
|36-025||Wire, Electrical, Nickel
Wirecraft P/N E267U9N
|36-027||Wire, Electrical, Nickel
Specialty Cable AWG26
WIMA P/N FKP2 per
CECC 31 800
|Microcircuit, Rad Hard
|Relay, Latching, DPDT, 5A||4/4/96||OPEN|
|Microcircuit, Logic, HC||4/4/96||OPEN|
|Diode, Rectifier, Schottky||4/4/96||OPEN|
|Transistor, Power Switching||4/4/96||OPEN|
|Resistor, Precision, Low TC||4/4/96||OPEN|
Lockheed Martin Astronautics (LMA) has three (3) more NSPARs in process.
Radiation testing has been completed at Space Electronics, Inc. (SEI) on sixteen (16) device types. Results of these tests are listed below.
|Manufacturer||Part Number||Radiation Test
|Analog Devices||DAC8800BR/883||<2K Rads|
|Com Linear||CLC505A8D||>100K Rads|
|Harris (Chip Supply)||36-02305 (CA 3080)||<100K Rads|
|Analog Devices||OP220AJ/883 (TO-5 can)
|Texas Instruments||TL082/883B||>100K Rads|
|Analog Devices||REF43BZ/883||>200 K Rads|
Devices which have not passed 100K Rads of Cobalt 60 testing will be shielded or design work-arounds will be implemented. Six (6) more device types are planned for radiation testing. These are listed above without results.
Four (4) lots of components are in the process of being shielded for total dose radiation.
Working on radiation input for TRW safety review.
Re-wrote Beryllium handling procedure. It is in the ECO review cycle.
There has been no activity on the Performance Assurance and Safety (PAS) Plan. The PAS Plan in effect is revision B.
Two sets of flight CCDs were packaged and delivered to Lincoln Laboratory.
Visited the synchrotron in Wisconsin and certified the clean tent and instructed the PSU scientist on the contamination procedures for installing the Optical Blocking Filters onto the platens.
Visited LMA to review their contamination analysis procedures.
Cleaning and vacuum conditioning of flight parts has begun. Lincoln Laboratory is providing continued support in this effort.
Continued effort is being made to clean and vacuum condition the engineering harnesses for testing in the thermal vacuum chamber without the risk of contamination. This provides the information required for developing the process in which the flight harnesses will be fabricated.
Procedures are being updated and developed as engineering assemblies are being completed.
Three more test procedures were developed. (FEP memory access, load from ROM, load from Uplink).
Developed a program (code) to uplink and to use in memory patch verification procedures.
We are shifting emphasis. Since hardware is not available, we are using virtual software version of BEP/FEP to verify parameter tables.
Due to problems in making adequate bonds with gold wire, as detailed below, packaging of back-illuminated devices has been on hold pending resolution of the problem. The present scarce supply of Flexprints has been allocated for back-illuminated devices only, so packaging of front-illuminated devices (which use aluminum wire and therefore are not affected by the bonding problem technically) has also been on hold for this period. Two FI devices were finished up and shipped before the hold was imposed. Measures implemented in January to suppress ESD loss continue to be successful for both AXAF and CCID 18 BI parts.
The packaging problem is in the attachment of Au wire bonds to the Au plated leads on the Flexprints with wedge bonds. This appears to be worst on those Flexes where a hard Au was plated inadvertently, rather than a soft Au. After much experimentation an optimized set of parameters was found by varying bond time, ultrasonic power, and pressure as well as tool and base temperatures. Unfortunately, this set does not allow an adequate number of bonds to be above the 1.2 g pull strength (required for MIL SPEC conformance), so we are using a compound bond to hold the wires in place. This requires the wire to be attached at both ends using wedge bonds and then a separate Au ball bond is made on top of the wedge bond on the Flexprint. These bonds pass the bond pull test and CSR QC concurs that the procedure meets MIL STD 20.17. Bonding of BI part 140-4 has resumed and will be ready for test shortly. Flex Tech (the supplier of the Flex circuits) has been made aware of the problem with the gold plating and has committed to avoid its recurrence on the Flex circuits currently in fabrication. There are four more BI candidates available for packaging.
The CAMSIM Detector Assembly was returned from LMA to have the Detector positions measured. This assembly had been subjected to additional qualification level acoustic and random vibration testing as part of the Optical Blocking Filter (OBF) test program. Prior to these tests the Detector positions had been measured to establish reference positions. Measurements taken after testing show no movement within our measurement capability. For these measurements, it is estimated that the standard deviation of the measurement error is 2.3 microns for lateral directions (AXAF Y and Z) and 3.6 microns for the out of plane direction (AXAF X). For these tests, four points on each Detector where measured. When the pre- and post-test measurements are compared, the largest out-of-plane difference is 8.25 micron and the largest lateral difference is 6.5 micron. The standard deviation of the difference is 2.3 micron laterally and 3.8 micron out-of-plane. The requirement is to position Detectors to within +/- 100 microns laterally and +/- 25 microns out-of-plane.
The Detectors on the CAMSIM Assembly were retested after the OBF test program. One of the units developed a short which was not measured previously to the test. No physical evidence was found which could account for the presence of this new defect.
Assembly of the Detector Assemblies is well underway. The heaters, RTDs, and terminal strips have been bonded to the flight and back-up Beryllium structures. The wire harness has been dressed in and connectors attached. Installation of the Alignment Mirror and locating blocks is expected to be complete before the first of the flight Detectors are returned to Lincoln Laboratory.
The delayed delivery of the final group of Flexprint circuits has temporarily stopped assembly of front illuminated devices. Seven Flexprints that had been metalized with aluminum (which subsequently proved to be prone to delamination) were available for reprocessing. A procedure was developed and qualified to remove the aluminum coating to allow the flight-quality coating of titanium/gold coating to be sputtered on. Processing of these Flexprints has begun.
The second week of February the entire lot of Flex circuits, which were about to finish fabrication, were rejected by the vendor. A trip was made to the vendor facility to discuss the problem and a plan of action to recover. The problem was traced to an inadequate etch of glass fibers after the Flexprint vias are drilled. At this point, the holes must be etched back to remove any glass fibers, in preparation for plating the through-holes. The glass etch bath used in this process did not do its job. The plated through-holes did not meet MIL-P-50884 standard, and were not reliable. It was agreed that a new lot of Flexprints would be started, with the goal of reducing the 2 1/2 months it takes to run the lot to about 6 weeks. In addition, increased attention would be given to quality control during the fabrication. Finally, the vendor would keep us appraised of his work toward recovering a reliable glass etch process. Lincoln offered to try to find someone that might help to resolve the problem; an expert who had previously worked with CSR called to consult. As of Feb. 29, Flex Technology claims to have solved the glass etch problem. However, they will be two days late in sending the Flexprints out to the drill vendor, but say they can make up the time and still have the lot done on April 5th.
During this month negotiations were conducted at LMA for Change Orders 25 and 28 and update proposals reflecting the negotiations were submitted. Confirmation of acceptance by MIT is pending. Negotiations were also conducted for Change Order 41 and fact finding was conducted for Change Order 43. As a result Change Order 43 proposal modifications, scope changes and preliminary negotiations of labor hours were agreed to. An updated proposal to reflect the results of the fact finding will be submitted in April. One issue remains open on Change Order 41. Also, during this month, a proposal was prepared and submitted for Change Order 46.
The ACIS MIT Monthly Status Review was conducted at LMA. This enabled LMA to participate and provide detailed status of the LMA schedule status, technical progress and to present the results of the PSMC reliability prediction to MSFC. This prediction showed a PSMC reliability for a 5 year mission of 0.994740 for the baseline design; 0.922893 if the redundant DPA power supplies are operated with both `On' for mission operation, and 0.994129 with degraded operations if the redundant DPA power supplies are operated with both `On'. Degraded operation was defined as one DPA failing. This would reduce the number of CCDs operating at a given time but would preclude collecting scientific data. This showed operating both DPA power supplies simultaneously is a viable operational approach. A successful ACIS Program Technical Interchange Meeting (TIM) was also held at LMA on March 13 and 14.
The cabling form board, for fabrication of the ACIS flight cables, was fabricated based on the LMA proposed 3D model layout for the ACIS cables on the SIM. This layout and model was provided to Ball Aerospace in February. Initiation of test and flight cable fabrication was delayed pending receipt of additional final cable layout details from Ball Aerospace.
An LMA cabling engineer supported the assembly of the cabling on the ACIS mockup and the AXAF Cable Mockup Fit Check TIM held at Ball Aerospace. This TIM was helpful but did not result in obtaining the final date needed to begin flight cable fabrication.
Major accomplishments for March included providing a completion of PSMC EU #2 open-frame assembly, completion of the flight TCS shades, completion of the flight cold and warm radiators fabrication, completion of the flight Collimator Proton Shield modification and camera body matched drilling, performed additional prebake of flight OBFs, completed initial NASA-STD 1238 certification of the 3' x 5' bakeout chamber and completed the hardware fabrication and test setup for the CAMSIM Detector Assembly Thermal Balance test.
The RCTU serial digital interface, which received significant interface requirement attention during February, was validated with testing of the PSMC EU#2 at the box-level. All 32 bits (4 ea. 8 bit words) of PSMC serial digital data are sampled by the LMA built RCTU Approximator (RAPP), every major frame. Modifications were made internal to the PSMC to assure transient digital status will be latched into the serial digital shift registers and reported during the next major frame after its occurrence.
The revised MIT load table presented at the January TIM, was discussed at the March TIM. Primary focus of these discussions involved PSMC over voltage protection (OVP) and over current protection (OCP) characteristics and DEA/DPA compatibility with respect to OVP/OCP. The PSMC over voltage protection (OVP) and over current protection (OCP) transient response characteristics, as well as EU2 OVP/OCP transient response optimization continued to be aggressively worked during March. Open items exist on the DPA and DEA over voltage protection (OVP) limits that were carried over into April in search of final agreement. In addition, during simulated DPA load switching tests, an in-rush current issue was discovered. The interim conclusion is that transient current and voltage peaks are generated during DPA Front End Processor (FEP) load switching causing OVC and/or OCP nuisance trips, and voltage "droop" on the + 5VDC PSMC output during the transient recovery period. This issue will be aggressively worked with MIT during the next reporting period and the load table updated at that time.
Completion of designs and incorporation of Change Order #43 changes into the EU #2 and associated test is nearing completion. In parallel with these efforts, strong effort continues to complete flight schematics and PWB layouts, and place flight PWB orders. The flight temperature control PWB is expected at LMA in early April. IO/EMI filter PWB engineering is out for vendor quotes, with delivery anticipated in late April. The flight thermal control board frame purchase order will be placed early in the next reporting period. The EMI cavity mechanical detail drawings are nearing flight release, with its signature table top planned for early April.
The following additional activities were accomplished:
Parts procurement continues to get significant attention. Delivery dates on at least two Harris radiation hardened parts still extend to a point were use of already procured alternate parts will probably be necessary. Delivery of Rad Hard "9160" transistors from Harris are now projected for early August delivery. This is clearly unacceptable for the ACIS schedule. Several work arounds have been initiated, including additional procurement of commercial parts followed by full QCI upscreening as an alternative for flight use.
LMA believes the final "ripple effects" from C/O 43 redesign has been fully realized. Therefore, we do not anticipate any additional flight EEE piece part requirements will be generated.
All test plans for radiation testing of electronic parts were completed during the prior reporting period. Test completion for all twelve parts is on schedule for a May 3 completion.
Engineering for the Lincoln Lab cables was completed. The three dimensional cable form board design, drawing release, and form board fabrication was completed. Fabrication of the Lincoln Lab cable harness was initiated.
The holes which MIT requested for additional proton shielding were drilled in the titanium Collimator. In addition, holes were added in the camera body and Collimator for shear pins to aid in alignment. After dye penetrant inspection and cleaning, the parts will be available for assembly. Heaters, thermistors, and PRTs will be bonded to the camera body prior to cleaning. Fabrication of a new shaft assembly was started since the other shaft assembly was lost somewhere in the system between the machine shop operations and precision cleaning completion conducted at another facility. A replacement part will be available in early April so detector assembly can start at that time.
Fabrication of TCS components is on schedule with no major problems to date. Martin Black was applied to the warm radiator this month and is ready for the upcoming thermal balance test. The flight radiator standoffs (excluding gold coating) were proof tested and 12 of 14 passed. The other two standoffs were not tested due to visible flaws. Gold coating of the 12 standoffs which passed proof test will occur in April. Five new standoffs will be machined leaving three flight spares and the other two standoffs can be added to the radiator assembly at a later date. The shades are waiting for the proof test procedure to be approved and the test will occur next month. The final MLI blanket fabrication has started. 1238 bakeout of the blankets will occur in April. The final information on the MLI mounting approach for the +Z panel and sun shade and telescope shade were received from Ball Aerospace. In addition, the support posts which will be bonded to the sun and telescope shades were also received from Ball Aerospace.
Assembly of the fixturing and test articles was completed in preparation for the upcoming test. The test is due to begin on April 1, 1996. The flight warm and cold radiators were assembled using the engineering unit standoffs. The flight unit warm and cold straps were also attached to the CAMSIM and the radiators. All modifications were made to the engineering unit hardware which has been added to the flight design. The data from this test will be used in validating thermal models for flight.
Stress analysis progress has been made in the areas requiring immediate attention. The analysis of the radiator standoffs and sun and telescope shades was completed since the data from the analysis was required for the proof tests of the flight hardware. The rest of the time was spent tracking the flight hardware and writing test procedures for the upcoming tests. After the environmental testing is completed on the detector, PSMC EU2, and the TCS components, more time will be applied to finalizing the analysis.
Pre-thermal balance test predictions were completed for the upcoming test conditions. The predictions show that the Focal Plane will be right at -120 deg C at the hot case conditions (0.45 Watts of dissipation on Focal Plane) with the new radiators. The cold case survival temperature will be -142 deg C for the Focal Plane. Cold case operating temperatures will put the Focal Plane at -132 deg C at 0.25 Watts of power on the Focal Plane.
The Detector Housing Assembly drawing was modified to add a requirement for X-raying the actuators prior to assembly at 0 and 9. This was the recommendation made by StarSys as part of their final failure analysis report. This will confirm that the O-rings are seated properly and that the Actuators are ready for flight.
The final reports on the Door Actuator and Venting Subsystem life cycle tests will be completed as time permits.
The welded tube assemblies were started through the flight qualification inspection process this month. The first inspection, dye penetrant, was completed with all vent tubes passing without concerns. Only superficial cosmetic defects were found which have no impact on flight performance. After dye penetrant inspection, the tubes will go to X-ray and then on to leak check. Leak check is being performed last so that any processing, such as inspection etching, will not open up undetected leak paths.
The final version of the venting analysis was completed during March. Venting analysis determines the effects to the system during the rapid depressurization of launch and the long term stability once orbit has been achieved. The analysis revealed that the fragile Optical Blocking Filters will not be in danger during any launch or ground processing. On orbit, however, a difficulty with water ice accumulation on the Focal Plane was discovered as a possibility during the early part of the mission. An approach using mini-bakes (30 deg C increase) of the Focal Plane during perigee where data cannot be taken was shown to be effective at eliminating any continuous accumulation. Further, preliminary results from TRW predictions of the partial pressure of water in the ISIM on orbit indicated that the initial analysis, performed by TRW, may have been overly pessimistic. Assuming this is conclusion is borne out by ongoing analyses, there may be little or no concern regarding the accumulation of water ice on orbit. The ACIS team is awaiting this final analysis, however, there have been ameliorating methods defined no matter what the outcome of this analysis.
An initial analysis was begun into Earthshine into the venting subsystem causing difficulty during certain parts of the orbit. A potential error was found in the original analysis that may reduce or eliminate the requirement for painting the venting subsystem elements black. This analysis will continue and be resolved in April.
The vendor fabricated case for VGSE #2 was received and has been sent to the shop for continued processing. The engineering for VGSE #2 is being updated to reflect the changes that were made to VGSE #1 during testing and verification. Manufacturing plans are being written, this process will be complete in April allowing final assembly to begin in May.
The control circuit boards wire wrap was initiated this month and will be complete by the end of April. A third circuit board has to be added to the initial design because of increased complexity of the flight vent valve drive circuitry. This addition is also scheduled for completion by the end of April.
A simulated launch test was performed using the CAMSIM engineering unit. This test measured how rapid depressurization would effect pressure differentials across the OBFs. A second set of tests was run where known amounts of gas were forced past the door seal and the pressure differentials across the OBFs was measured. The results of both of these tests were very encouraging showing safety factors of nine (9) or greater for OBF safety during launch. The results of these tests are described in the Venting Analysis, SSE03.
A further test was run to determine if the door seal vibrated when gas flowed out of the Detector Housing, a concern during high altitude ascent. The results of this test were also negative with no indication of vibration of any kind. The test was sensitive to frequencies less than 1 kHz where possible OBF damage was thought to be a possibility.
The change order #28 bakeout chamber and all supporting hardware was certified for use during this reporting period. LMA now has the capability to certify hardware to MSFC-SPEC-1238.
Preparation of the ACIS FMEA/CIL at LMA continues during this reporting period. Collection of FMEA and CIL update information for ACIS DPS hardware continues. Incorporation of the collected comments is scheduled for completion mid-April 1996.
The EMI/EMC Test Plan/Procedure for tests of the EU#2 PSMC was prepared, tabletop reviewed and released during this reporting period. These tests are scheduled to be completed during the next reporting period.
The ACIS PTS Specification, PTS to DPS ICD, and Focal Plane to Detector Housing ICD were in process of being updated to reflect impacts from Change Orders #43 and #46. Update completion is scheduled for April.
Update of the GSE CEI Specification continues during this reporting period. It is anticipated that this document will be released for on-project review in early-April.
Update of the GSE to ACIS and Facilities ICD process continued during this reporting period. A draft version of this ICD release is scheduled for late-April 1996. Following an on-project review and comments incorporation, a final version will be released on or about 5/22/96.
System design activities focused on supporting update and release of flight hardware engineering.
ACIS System Schematics development was continued during this reporting period. This activity is being closely coordinated with MIT to effectively use common software tools and produce a document useable for fault isolation as well as developing an understanding of the design.
Compatibility Analysis continued during this reporting period. However, progress was limited by placing emphasis on other higher priority activities.
The group continued support of the AXAF-I Weekly Action Item Tracking telecon scheduled on Wednesday, as well as the weekly MIT/LMA telecon on Thursday.
Update of the ground processing flows for test of the ACIS instrument hardware continued throughout March. LMA continues to maintain the ACIS component and system level test flows as a matter of normal business.
Schedule remains the most significant management problem.
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 deg C.