Recently, the Telescope Scientist (Leon Van Speybroeck) and I mused over our near disbelief that AXAF is actually coming to fruition. Having each worked nearly 19 years on this project, neither can readily imagine not working on AXAF. However, we also hope that we shall be contributing to the Project for many years to come.
Over the past several months, there has been an avalanche of progress of direct scientific interest:
(1) Eastman Kodak Company (EKC) has installed and aligned 5 of the 8 mirrors into the High-Resolution Mirror Assembly (HRMA). Thus far, the alignment accuracy is about as expected and will result in superb X-ray images.
(2) The X-ray Calibration Facility (XRCF) at MSFC is nearing activation, in preparation for rehearsals with a surrogate optic (to begin in mid August) and for the actual calibration of the HRMA (to begin in 1996 December) and flight instruments (to begin in 1997 January). For more details, see the AXAF X-ray Test Conductors web page.
(3) We (MSFC Project Science) have nearly completed characterization of the X-ray Source System (XSS): The Electron-Impact Point Source (EIPS); the Double-Crystal Monochromator (DCM), with a Rotating-Anode Source (RAS) X-ray generator; the HIREFS reflection-grating monochromator, with a Rotating-Anode Source (RAS) X-ray generator; and the Penning Ionization Gas-discharge Source (PIGS). We have posted charts from the XSS Scientific Readiness Review, at the Project Science Calibration web page.
(4) SAO Mission Support Team is completing installation and testing of the X-ray Detection System (XDS): 7 Flow Proportional Counters (FPC), 2 Solid-State Detectors (SSD), and 1 microchannel-plate High-Resolution Imager (HRI). One each of these detectors is for the focal plane; the remaining serve as Beam-Normalization Detectors (BNDs), located either about 38 m from the XSS or about 527 m (near the HRMA entrance aperture). At each location, one of the FPCs is on a beam mapper. We have posted a summary chart from the HXDS Scientific Readiness Review, at the Project Science Calibration web page.
For more information, see the SAO Mission Support Team web page.
(5) The Low-Energy Transmission Grating (LETG) and High-Energy Transmission gratings (HETG) are both nearing completion. Each is on schedule for delivery to the MSFC XRCF for calibration.
(6) The SAO High-Resolution Camera (HRC) team reports similar progress. Every effort is being made to include a mirror near the HRC spectroscopy array, to serve as a high-energy suppression filter. The filter suppresses higher spectral orders, albeit at diminished throughput, and may be selected or de-selected by appropriately locating the HRC in the focal plane. Users should note that we cannot yet guarantee that this option will be available.
(7) The AXAF CCD Imaging Spectrometer (ACIS), the most complex AXAF instrument, has experienced difficulty, particularly in the ``flexprint" cabling that attaches to the CCDs. This has delayed ACIS delivery until possibly quite late into the calibration phase at the XRCF. Fortunately, the Project planned for such a contingency, hence, the Penn State - MIT team is completing the ACIS ``2-chip", a surrogate CCD focal-plane with one chip of each flavor (back- and front-illuminated), cross calibrated with respect to synchrotron-calibrated standards. During the XRCF activities, the ACIS-2C can be used initially and (if necessary) throughout for the ACIS and HETG calibrations with the flight optics.
Finally, we are reviewing the AXAF observing policy recommended by the ASC. Later this year, NASA will issue the official policy, which will very likely incorporate most of these recommendations and, in addition, address other issues (e.g., conflict resolution within the Guaranteed-Time Observer allocation). The policy will attempt to avoid ``source monopolies" by GTO observers without totally tying their hands; it will also seek to encourage long observations. The first AO should be be issued next year!
Martin C. Weisskopf