Minutes of the 4th AASTOWG meeting ---------------------------------- 10am Saturday 23 March 1996 at Mt Stromlo Observatory in Canberra. Attendees: Ashley (UNSW), Boccas (UNSW), Burton (UNSW), Dopita (MSSSO), Harper (CARA), Hart (MSSSO), Hovey (MSSSO), Hu (MSSSO), Smith (ADFA), Storey (UNSW), Sutherland (MSSSO), Van Harmalen (MSSSO) + mystery engineer from MSSSO... Lockheed report --------------- A report was tabled from Jack Doolittle regarding progress on the AASTO power system and computers. As of 20 March Teledyne had just begun work on the thermoelectric generator (TEG), and Lockheed was starting to order the other components for the power module. The subcontract for the Data Acquisition Unit has been initiated with the University of Maryland. Lockheed are evaluating the replacement for the Maxtor WORM drives for the Data Control Unit. ROM-DOS looks like the operating system of choice for the DCU. The low-power version of the Lockheed all-sky camera has not been started, due to no funding being available. CARA's recent activities ------------------------ Harper reviewed CARA's recent activities and plans. This year there will be a number of experiments that will yield site-testing data for South Pole: - SPIREX (a 24-inch near-infrared telescope) will be making more seeing measurements in the visible and near-IR. - There are two all-sky cameras at South Pole this year: - Jack Doolittle's camera that is optimised for auroral detection, and - Bob Loewenstein's camera with a variety of filters: UBVRI, oxygen and OH auroral. This camera is now working (last year it had problems which prevented operation). - SPIRAC (a 19-inch mid-infrared telescope, built at Goddard Space Flight Center by Harvey Moseley and Sean Casey). SPIRAC has a silicon BIB spectrometer/imaging camera sensitive to between 20 and 40 microns. The goal for this year is to obtain sky dips and possibly some astronomical observations. Currently, there are problems with the elevation drive, and the detector is warm. It is likely that South Pole will run out of liquid helium this year, and SPIRAC may only be run a couple of times. - There are a number of improvements being made to the optical DIMM measurements. Local heating will be kept to the absolute minimum. Measurements will be obtained with a C11 and the 24-inch. Double stars will be used in an attempt to measure the high-level turbulence, and find out where it is coming from. The moon can be defocused and used as a convenient light-source to probe the altitude at which turbulence is predominant. Harper then described the seeing results from 1995. - The results from SPIREX were inadvertently contaminated by having two heaters on. Also, the heat required to keep GRIM functioning may have some effects. Last year only 3 days of observations were obtained with the heaters off, but there were still tube-eddies present. At 500nm, with 5Hz sampling, the average seeing was 1.7 arcsecs last year. 25% of the time the seeing was better than 1.2 arcsecs, and the best observed was 0.7 arcsecs. - Now that the raw image frames have been obtained from SPIREX, it is planned to re-reduce them to different time resolutions. This should allow the effects of tube-seeing to be quantified. Burton discussed the preliminary analysis of the microthermal balloon data from Vernin and Marks. 15 flights were made, 8 of which were simultaneous with the HDIMM measurements. The average value obtained was 1.45 arcsecs (from 30 metres to infinity), with a dispersion of 0.7 arcsecs. The inversion layer was found to be 200 +/- 85 metres in height, and the integrated seeing above it was 0.36 +/- 0.1 arcsecs. It was mentioned that a cumulative plot showing integrated seeing versus altitude would be very helpful. Generic Tower ------------- Dopita then gave a description of the MSSSO design for a generic tower. The tower was designed with component parts that could be handled by one person. This gave a reasonable maximum height of 6m if made from steel. The design employs a serurier truss system, whereby a triangular base is fixed to a triangle platform with 6 struts joining the vertices. If the platform is exactly half the area of the base, then any deflection in the tower will produce a translation at the top that keeps the platform parallel to the base. The structure is also known as a hexapod. Dopita expressed some concern about communication with Yerkes with respect to progress on the tower design, and underlined the urgency of having the tower built this year. Hovey mentioned that he had inadvertantly failed to read a message from Yerkes, which partly explained the apparent communication difficulties. Harper described the SPIREX tower. While not suitable for the AASTO, it has some interesting features. This year the tower has seismic accelerometers attached to it, to help understand its performance. Harper explained that Pernic is progressing well on a tower design made from carbon fibre. Yerkes has a need to understand manufacturing with carbon fibre, and the tower would be a good test-bed for this program. Hovey asked if anyone had experience with ``water-crete'' (using ice as a substitute for concrete). No one had. The meeting resolved that Yerkes should proceed with their 40-foot carbon fibre design, and that close liaison be maintained with MSSSO so that the GMOUNT could be tested on the tower at the earliest possible opportunity. [Aside: it was noted that the circular platform at the NE corner of room where we were meeting was about 20 feet off the ground - which made a 40 foot platform sound like a scary proposition...] Report from Bob Pernic ---------------------- A report was tabled from Pernic addressing many of the issues on the meeting's agenda. Yerkes is proceeding with a generic tower design using CFRP (carbon fibre) to maximise the stiffness and minimise the weight. The goal is a 40 foot tower with a carrying capacity of 400 pounds. The current schedule is for construction to start in June, testing in August and shipping in September. Total tower weight is envisaged to be 150 pounds, and when broken down into two 20 foot lengths it should not be a problem for a Hercules. GMOUNT and ADIMM ---------------- Dopita and Hovey described the progress being made on the GMOUNT and ADIMM. The design of the GMOUNT was progressing satisfactorily, with construction due to start in mid-April. This is some months behind schedule due to over-run on the tip-tilt project for the 2.3 metre telescope. The goal is to deploy the GMOUNT on a tower at South Pole this comming summer. The ADIMM, however, can not now be made ready this season. The working group expressed concern at the delay with the ADIMM, particularly since it is an instrument that needs testing at South Pole before being deployed to a remote location on the plateau. The delay with the ADIMM could therefore lead to a one-year delay in the AASTO project. Ashley was particularly concerned at the optics icing problem, for which no solution has yet been found, and for which no experiments are currently underway to resolve at South Pole. At the very least we must have some optics-icing experiments at South Pole next year, with the hope that they may be sufficiently informative to allow the ADIMM to have a high probability of success when first deployed. Hovey reported on the status of the parts delivery for the GMOUNT. Two torque motors rated for -85C are in hand, with the inductosyns being delivered within a month. The PC-104 computer has arrived and is being tested with the QNX operating system. Work has started on the design of the electronics. Ashley asked about the possibility of using the MSSSO-designed PC-104 readout card for the UV/Vis experiment, but the feeling was that this card would be so specific to the 221 CCD being used, that it was unlikely to be easy to modify it to drive a different CCD. Nevertheless, the engineers were asked to keep such usage in mind when designing the card. Harper mentioned that a CCD using the MPP (multi-pinned phases) technique (which basically requires a simple change to the high-low clock levels, and a CCD optimised for these changes) gives much lower dark-currents at a given temperature, and would obviate the need for a peltier-cooled CCD. Dopita described the optical design of the ADIMM, and Sutherland showed results of testing of the micro-lens array idea using the ADIMM C-14 piggy-backed on the 74-inch telescope. Sutherland described the software he had developed to process the ADIMM data in real-time - it can sustain a 1Hz rate using a 20 Mhz 68030 processor (substantially less powerful than the one being considered for the ADIMM). The data are stored as the (x,y) coordinates of the image centroids, and a 1-byte intensity per star image. The software has to be able to cope with focussing the telescope, as well as correcting the telescope pointing and recognising when icing has occurred. The ADIMM should be sensitive to seeing in the range from 0.4 to 3 arcsecs. The UV/Vis instrument --------------------- Storey led a discussion of the UV/Vis instrument. While construction has not yet started, the conceptual design is nearly complete, and the major components will be ordered within a month. The telescope is envisaged as having a 30cm aperture, and using 100 micron fibres with a numerical aperture of 0.22. At an f/# of 2.27 this system has a 30 arcsec field of view per fibre. The telescope will sit on one side of the GMOUNT, at the top of the GTOWER, and will feed a 40 metre fibre bundle into a Jobin-Yvon CP200 spectrometer (f/2.9, fixed grating, blazed at 400 nm). The detector will be an Oriel PC-based CCD system, with 256x1200 pixels, giving a resolution of 2.3 nm FWHM (4 pixels FWHM), a coverage of 190 to 820 nm (although this could be shifted to 300 to 940 nm if this was more scientifically useful). The following table summarises the instrumental efficiencies as a function of wavelength: Lambda Fibre loss Transmission Grating efficiency [nm] [dB/m] for a 40m fibre ------------------------------------------------------ 300 0.15 25% 30% 330 0.10 40% 35% 650 0.01 >90% 30% 750 0.08 50% 25% The instrument will measure the following: Column densities in the atmosphere of ozone, NO3, ClO2, NO2, and H20; the UV tranmission; auroral lines; airglow; and possibly some astronomical science (e.g., long term monitoring of a bright star). With the 256 pixel slit-width of the spectrometer we can fit about 20 fibres. The possibility exists of having two seperate fibre-bundles: one optimised for UV and the other not. The telescope could be driven between the two sets. When working longwards of 500-600 nm we will need to block 2nd order radiation using a filter wheel or a separate set of OH fibres (not UV optimised). The Oriel CCD will need cooling, possibly by a thermo-siphon using glycol, with a radiator on the roof of the AASTO. The UV/vis telescope is invisaged as being either a prime-focus parabolic mirror with a flat window (to reduce the icing problem to one surface), or a cassegrain system. Exposure times are expected to be at least several minutes. Some discussion ensued on the data storage requirements, with Ashley commenting that a substantial amount of the raw data could be stored, thereby guarding against the failure of on-board data reduction software. NISM and MISM ------------- Boccas introduced a discussion of the Near Infrared Sky Monitor (NISM) and Mid-Infrared Sky Monitor (MISM), and circulated documents describing both. Stirling cycle cooler MTBF were in the range 5000 - 8000 hours, requiring a refit each year. A typical cooler draws 7W. The availability of window materials which the cooler manufacturers can use limits the choice to zinc selenide, thereby imposing a 16 micron long-wavelength cut-off for the MISM. Diamond was suggested as a possibility, although it has some nasty absorption troughs near some areas of interest. The MISM will have an 8-12 micron CVF and fixed filters at 8.3, 10.3, and 12.5 microns. De-icing -------- There was some discussion about ice detection and de-icing. It was suggested that Bob Loewenstein be asked to forward suggestions to Chris Bero at Pole for de-icing experiments. Carnegie Mellon Skymonitor -------------------------- A progress report (see below) was received from Ethan Schartman at Carnegie Mellon University on the sub-millimeter bolometer (the Skymonitor). The colour images of the instrument construction showed impressive progress. Here is Schartman's report: ``The skymonitor is an instrument designed to measure the emissivity of the atmosphere in the far-infrared and microwave regions. The versions we are currently producing will be equiped with bandpass filters for 200um, and 350um.'' ``The essential components of the skymonitor are a scanning mirror, chopper, filter, photometer, and lock-in amplifier. The package is designed to interface directly with a remote pc via an a/d converter card, and serial lines. We are currently working on modifying the design to accomodate a low power-budget for use in the AASTO. These modifications will largely consist of cycling power to various portions of the instrument via the pc, and modifying the chassis to accomodate the AASTO guidelines. We'd like to mount the skymonitor in one of the roof mounts of the AASTO in order to take advantage of the AASTO's heat. On the roof, we would like a clear view to the horizon on at least one side (preferably both). The physical package will accomodate the design guidelines as specified in Revision B of the Automatic Geophysical Observatory Interface Specification, of 15 June, 1992, by J.H Doolittle. If these specifications have been changed, I need to recieve a copy of the changes.'' Mir-IR all-sky camera --------------------- Harper suggested that perhaps a more interesting instrument than the MISM would be a mid-IR all-sky camera that was able to record the cloud coverage. A single element pyroelectric detector could do the job. He suggested that we contact Charlie Hall for advice (he constructed the Apache Point all-sky camera, which is accessible via a Web page). Power management ---------------- Various allocation schemes were discussed for the AASTO power. The following power budget was agreed as a nominal goal. Instrument Power Duty Power (at duty cycle) [W] cycle [W] ---------------------------------------------------- GMOUNT 20 50% 10 (+10 for heaters) ADIMM 10 50% 5 UV/Vis 10 50% 5 NISM 9.5 50% 4.75 MISM 9.5 50% 4.75 Carnegie Mellon 8 50% 4 TOTAL ................................ 43.5 Software -------- Since the GMOUNT is an essential part of the ADIMM and UV/Vis experiments, it was agreed that the GMOUNT software be responsible for scheduling the operation of the ADIMM and UV/Vis. Number of people required over summer ------------------------------------- It was envisaged that of the order of 6 people would be required from UNSW/ANU in order to install the experiments in the AASTO over the 1996/97 austral summer. The names put forward were Boccas, Philips, and Storey from UNSW, and Dopita, Hovey, and Sutherland from Mt Stromlo. Electrical power and ethernet for the AASTO at Pole in 1997 ----------------------------------------------------------- Ashley argued that while it was essential to test the AASTO propane-powered TEG modules during 1997 at the Pole, it would be beneficial to have 110V/60Hz power available throughout the year so that (1) we could run instruments simultaneously for testing without concern about the total power budget, (2) if our prototype instruments could not meet the power specifications, at least we could run them at Pole while we worked on improvements in the lab, and (3) it would be convenient if a winterover needed a power tool or light. After some discussion it was agreed that this was a good idea, although care should be taken to ensure that the overall systems were given a realistic test. One way to do this would be to use the external power to charge the AASTO batteries if usage went above 50W. Ashley also argued for ethernet connectivity to the AASTO during 1997, to assist with instrument control, data retrieval, and software development. This was also agreed to. 10-base-T is probably the standard to use since it is common at Pole. AASTO location -------------- The AASTO is currently in the cargo burms near the summer-camp at South Pole. During the summer of 96/97 it is planned to relocate the AASTO ``east'' of ASTRO (i.e., between the ASTRO building and the skiway). Next meeting ------------ The next meeting of the AASTOWG was set for 2 months hence, Friday 24 May 1996 at 10am at UNSW in Sydney.