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Telescope Project
TELESCOPE PROJECT:
WHO I AM: My background is engineering, 60 years old. I am far to being an expert in astronomy but have been interested for years in this field of activity and rather technically oriented. In view of my retirement, I plan to Design/Build a telescope having the following characteristics: SCOPE TYPE : Classical Cassegrain, f/4.4, equipped with a SBIG CCD auto tracking Camera ST9XE 512 x 512 Pixels, 20m, operated at 40m (Bin 2 x 2), for up to some 20 Min. integration time, giving a Pixel scale of 2.5 Arc-Sec, and a field of view of 10.8 Arc-Min. PRELIMINARY DESIGN CRITERIA: PRIMARY MENICUS MIRROR: Dia 750MM (30In), 63MM Thick (2.5In), f/3.0, with or without central hole, depending on the difficulty to figure such a mirror with a hole. Coude arrangement with flat diagonal mirror to direct the beam through an hollow declination axis could be considered. Blank material to be Pyrex or BVC. SECONDARY MIRROR OBSTRUCTION: 0.20 FIELD FLATTENER: May be required as a consequence of field curvature. TYPE OF TELESCOPE MOUNT: Equatorial, Horseshoe, similar to the one built by AutoScope for Lawrence Berkely Laboratories. DRIVE SYSTEM: Open loop with stepper motor, 2 steps precision belt reduction plus friction drive, for both R.A. and Dec. axis. DRIVE SYSTEM ACCURACY: Pointing: 10 Arc-Min; Tracking: 10 Arc-Sec over a period of some 20Min. MAIN MIRROR SUPPORT: Closed mirror cell with 9 or 18 support floating points. TYPE OF OPTIC ENCLOSU Open, Secondary mirror supported by quadruped truss. (this choice is a compromise as it is believed that a closed tube system, normally necessary for the expected environmental conditions of the observatory site, would be too difficult and too costly to build, too heavy and consequently not stable enough. END USE: Astrometry, more specifically high magnitude Main Belt Asteroid search and orbit determination. I realize this system will not be at high professional level but it is important that valuable scientific data be obtained from it. SITE LOCATION: Canada, province of Quebec, Saguenay Region, in mostly unpopulated low mountain environment at approx. 70° North Latitude, at some 250M (800Ft) from the Saguenay River and 80M (260Ft) above sea, medium humidity environment, on a rock escarpment with very few small buildings around, far from any light pollution and vibration. There is a 30M (100Ft) direct access to a control room located on the 4 Th floor of my residence through a 9M long (30Ft) foot bridge at 9M (30Ft) above ground. Seeing is presumably poor to medium with rare good conditions. HOUSING: Roll-off roof remotely operated from the control room. PROJECT PLANNING: I plan to personally Grind/Polish/Figure/Test the primary mirror. A Hindle/Draper type machine is to be used for Grinding/Polishing/Figuring. I also plan to design and build the whole telescope. The first manufacturing step to begin with as soon as possible (after site seeing evaluation) is the Design/Construction of the Mirror grinding machine. An heated and air conditioned garage space on the 1 St floor (10M x 7.5M x 4.1M), is available for mirror work with an hydraulic elevator service (1.2M x 0.9M x 2.1M, 350Kg capacity) from basement to control room and observatory level. Extensive use of available software will be provided for Raytrace, mirror floating point support optimization, finite element analysis … I can have access to modern industrial manufacturing facilities (casting, machining, welding) and I currently use CAD systems (AutoCad, SolidWorks …) The computer system I am using now is Windows Me, Pentium III, 1 GHz, 512 Mo RAM, 2 Go Hard Disk. It could be upgraded whenever necessary. Timing is not a reel concern as this project will eventually be close to a full time retirement activity. I can allow an annual budget of some 20,000$ for the supply of Material/Components. PURPOSE OF THIS MESSAGE: I would like to share information in view of this project. Eventually, it would be highly interesting to also share expertise and exploit this observatory facility for astronomical projects through remote access. THE VERY FIRST STEP TO BEGIN WITH IS THE EVALUATION OF THE YEAR ROUND SEEIN POTENTIAL OF THE OBSERVATORY SITE AS THIS MAY HAVE A DIRECT IMPACT ON THE WHOLE PROJECT. DOES ANYBODY HAVE AN IDEA ON HOW TO PERFORM THIS TASK ? A 3 In REFRACTOR, FLUORITE OBJECTIVE, ZOOM EYEPIECE 20X-60X IS AVAILABLE (LEICA APO-TELEVID 77) SHOULD IT BE OF ANY VALUE. It would be highly appreciated to receive opinions and guide lines on the whole project concept in regards to the end use and the characteristics of the scope, in relationship with the probable seeing characteristics of the site. In other words: 1. what can I expect from this system to detect Main Belt Asteroids with enough positioning accuracy to allow orbit calculation ? Is magnitude 18 realistic ? 2. Is the field of view large enough to allow guide star acquisition and tracking ? 3. Is the combination aperture/focal ratio/field size/CCD detector/Paraboloid main mirror, in association with the seeing optimum for an acceptable Signal/Noise ratio, or a smaller aperture/spherical main mirror, without field flatner, with similar Pixel scale be just as good ? 4. What maximum mirror surface error can be tolerated (1/4, 1/8, 1/12, 1/20 wave ?). For the type of arrangement contemplated what is the minimum demand on the mirror support system (3, 9, 18, 27 floating points ?) 5. What should I target as maximum moment of inertia for a stable and controllable scope ? 6. What should be considered as minimum stiffness for the scope structure, and for the backlash mechanism of the drive system, pre-loading of bearings … ? Rejean |
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