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Roger Brissenden gave the ASC status report. He noted that work on the star catalog and star-selection algorithms was underway and that the next Users' Committee meeting would occur in June.
Bert Brinkman reported on the LETG. The grating-support structure has been redesigned to be lighter. The group has developed a ray-trace program, which includes the gratings, in order to study more systematically detailed effects.
Steve Murray described the status of the HRC, which is currently in its PDR. He discussed the design of the anti-coincidence shield and presented data showing that the ROSAT HRI (CsI) was very stable over 3 years. In response to a question, he noted that HRC will have on-board calibration sources (Cm244 fluorescing C, Al, and Ti).
Claude Canizares discussed the HETG progress, noting that the PDR would be in May. He described the redesign of the grating support structure and progress made using a high-contrast photo-resist (with Si2, Ta2O5, or HfO2 interlayer on a AU or Pt plating base). The group is confident that the high-energy gratings will approach 1 micron in height, despite the last year's setback, resulting from the unavailability of the appropriate X-ray source. His description of the `acid suckers' (used in the manufacturing process) elicited many chuckles!
Steve Holt reported the current status of the XRS and ASTRO-E. He summarized recent deliberations of the HEAMOWG; Alan Bunner assured the SWG that ASTRO-E presents no programmatic risk to AXAF-I. Steve Holt related that Japan is currently in a study phase which will last until 1995 January. Jeff Linsky asked whether AXAF investigations that planned to use the XRS would now be assigned to ASTRO-E. Claude Canizares expanded upon this, asking if ASTRO-E is part of the AXAF Program. According to Alan Bunner, the answer is `No'.
Alan Bunner concentrated on the issue of observing time, relating that the current climate in Washington has led to questioning the amount - indeed, the very existence - of GTO time. It was noted that the ASC Users' Committee appeared to have no problem with the concept of GTO time as a just reward, but was concerned over target monopolization. Alan presented his plan for the allocation and reallocation of observing time which included the approach to dealing with the removal of XRS - Steve Holt will retain his membership on the SWG and receive the equivalent of an IDS share. Observing time received more discussion during the Executive Session summarized below.
Jeff Linsky initiated the series of reports from the IDSs. His observing plan exploits the spectroscopic capabilities of AXAF-I, where both throughput and resolving power exceed those of other missions. Although he bemoaned the loss of the XRS, he presented an observing program that would accomplish his objectives, using the AXAF-I instrumentation.
Richard Mushotzky noted that much of his original proposed research - mass and mass profiles of galaxies and clusters - has been accomplished now by ASCA. Recognizing that some adjustment is now required, he described some new directions in his plans to use AXAF-I.
Richard Burg (representing Riccardo Giacconi) discussed the planned deep surveys. Both the current allotment of observing time and the restructured AXAF mission are compatible with the originally proposed research.
Andy Fabian communicated his plans to study cooling flows in clusters of galaxies. His principal target was, and remains, the Perseus Cluster.
Tony Armstrong (SAIC) summarized his updated calculations on shielding, which he performed at the behest of the AXAF Project. He emphasized that recent data indicate power-law proton spectra. He also outlined the resolution of the previous discrepancy between XMM and AXAF calculations.
Dan Schwartz provided a progress report on a possible requirement for a blue (pass) filter for the aspect camera, to minimize the influence of red `interlopers' on the aspect solution.
During the Executive Session, discussion concentrated on observing-time issues. How does the SWG propose to deal with the `reserved target' issue, highlighted by the ASC Users' Committee? Although the IDS presentations did not indicate target monopolization, the IPIs - with the bulk of the observing time - had not reported on their observing programs. Therefore, the Chair will ask the IPIs to describe their observing programs at the next SWG. Numerous other `policy issues' were discussed during this session (and on the next day). The Chair will compose a matrix of issues/questions for the next meeting, in order for the SWG to come to grips with all the issues.
John Harlow reported that all major milestones are being met and that we will complete the last mirror at HDOS by 1995 June. He noted that we are considering a structural test of the HRMA/OB at MSFC (currently not planned). Project is watching closely the weight budget, because increased loads may reduce the 1000-lb weight margin by 350 lbs. Upper Stage selection (currently in progress) may influence this.
John Humphreys summarized the status of Telescope Systems. HDOS schedules currently meet need dates, with 3 months to spare. PMS, CIDS1, MPROS, polishing and end-cut stations are operational; MPMI will be operational for P1 in 1994 May. At OCLI, the Critical Design Audits (CDAs) will be completed by 1994 May. (Leon Van Speybroeck was favorably impressed with OCLI.) At EKC, the Central Aperture Plate and 5 (of 8) mirror support sleeves are completed. The VETA-2 simulator will undergo vibrational testing in mid May. Finally, the SSA (Support Structure Assembly = Optical Bench) Preliminary Design Audit (PDA) is on 1994 April 20. At Ball, the SIM (Science Instrument Module) design now allows for a larger focus adjustment (+/- 0.4" ). The EPHIN (the german charged-particle monitor) has been moved from the SIM to the S/C to save weight (factor of 2).
Tom Irby reported on the status of the ground-system.
Leon Van Speybroeck focussed on the revised specifications (due to the effects of end cut) and their implications. He emphasized that HDOS's contractual position was very different from its activities: The expected performance (as opposed to the contractual performance) would be near our previous Level-II requirements. Leon also reported on HDOS activity - e.g., more slurry, less stiff laps - to achieve TMA-2 surface roughness (~ 3 Angstrom) as opposed to VETA-1 (~ 6 Angstrom). (Note that P1/H1 are being repolished because of end-cut.)
Ping Zhao gave a detailed report on refinement of the VETA-1 data analysis and modeling. He emphasized the importance of obtaining subsidiary data for AXAF-I, to avoid impediments at the XRCF. Final results from VETA-1 should be available by the next SWG.
Alan Bunner related Dan Weedman's thoughts about the allocation of GTO time and the possibility of an AO for AXAF-I key projects. Dan's proposal would restate GTO time allocation as a percentage of the total time (to encourage the GTOs to optimize the efficiency of AXAF), revise the percentages to 100% in months 1, 30% in months 3-20, and 15% for the life of the mission. The topic of key projects generated much discussion. It was noted that the ASC has already been charged to study the question of key projects and to make a recommendation to NASA. Other comments ranged from the statement that such a plan was premature, to a concern that writing proposals would distract from the current activities. By and large, the working group opposed proceeding along these lines without due deliberation. The Chair observed that this would be included in the "issue" matrix discussed in the previous day.
Steve O'Dell summarized considerations and trades in replacing the in-situ (but not flown) interior-to-the-HRMA witness samples with a ground-to-orbit flux-scale calibration transfer - i.e., radioactive sources mounted to the interior of the forward HRMA contamination cover. Figure 1 shows the effective area of AXAF-I for various thicknesses of thicknesses of hydrocarbon film over 95%-bulk-density iridium. Plot shows effective area for hydrocarbon thicknesses ranging from 0 A (thinnest line) to 50 A (thickest line), in 5-A increments. The SWG (members present or represented) unanimously agreed that (subject to on-going detailed studies) this approach is preferred, given that we could not afford to implement both.
Martin Weisskopf discussed the need to establish the maximum dither amplitude required. Both ACIS and HRC representatives agreed on +/-15 arcsec.
Gordon Garmire and Mark Bautz gave the ACIS report. There are no current CCDs available for testing, due to slip dislocations in the last batch of wafers. Lincoln Labs identified the cause (a thermal mismatch between the quartz holder and the wafer during thermal cycling), has solved this problem, and has just completed a new batch. Martin Weisskopf strongly emphasized that the time for delivery of well calibrated and characterized chips is rapidly approaching: XRCF activities begin in only two years! Consequently, ACIS must accelerate its efforts to characterize and test flight chips.
The next meeting is scheduled for 1994 September 8 9.
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Editor: Dr. Douglas Swartz System Administrator: Mr. Bob Dean Privacy Policy and Important Notices Accessibility Statement |
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