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Highland Road Park Observatory

Specifications for the Observatory Telescope & Mount


  • Ritchey-Chretien 20" f/8.1 Telescope using hyperbolic figured 20" primary and 7.25" secondary lightweight conical shaped low expansion ceramic mirrors.
  • The mirrors will be aluminized and covered with a protective coating that meets or exceeds milspec MIL-M-13508C for resistance to abrasion and corrosion.
  • The reflectance (for a single reflection) will be as flat as possible in the wavelength range from 400 nm to 750 nm, with a maximum value of at least 95% and a minimum of no less than 90%. From 750 nm to 1000 nm the reflectance should be no less than 80%.
  • The optical system will be diffraction limited, having a final wave front error of 1/4 PV and 1/30 RMS.
  • A Zygo interferogram with fringe analysis will be provided to certify the optical quality of the telescope.
  • The mirrors will be mounted in a closed painted 6061T-6 aluminum tube with anodized aluminum components and stainless steel fasteners to resist corrosion and minimize infrared scatter.
  • A sealing mirror cover will be provided.
  • Both mirrors will be held rigidly while allowing for differential coefficients of expansion between the mirror and mount.
  • Optical collimation adjustment screws are widely spaced, providing fine adjustment and secure locking.
  • A electronic, stepper motor controlled secondary focuser will be provided and designed so that the focus is stable during a change in instrument attitude.
  • Boresight stability will be ± 20 arcseconds regardless of telescope orientation.
  • The telescope assembly will be equipped with slewing handles.
  • Threaded holes, will be provided on the back plate,for instrumentation attachment.
  • Full length counter-weights on both sides will facilitate symmetrical, fine balancing of the telescope.
  • Included with the scope will be a 11 X 80 illuminated finder telescope with a Polaris reticule, a tube attachment fixture, clamping rings, a 2" star diagonal and a 55mm Tele Vue eyepiece.

OGS140 Equatorial Fork Mount:

  • Equatorial fork mount for telescope to be constructed of precision machined aluminum and stainless steel alloys with axles of 6" O.D..
  • The axes of the mount will be orthogonal to better than one arc minute.
  • The mount will have an equipment capacity of at least 290 pounds.
  • The clearance between the telescope backplate and the fork top surface will accommodate a swing-through of at least 18 inches.
  • Both axle drives will include Byers gears with a 18" gear on the Right Ascension axis, slip clutches, negligible backlash between the worm and worm wheel, ABEC7 pre-loaded ball bearings to support the worm shaft, and a beam coupling to connect the drive motor to the worm drive providing anti-backlash, constant velocity power transmission and vibration damping.
  • The telescope optical axes will be aligned with the mount axes to within 1 arcminute and the combined system will be capable of tracking objects with an accuracy of less than 3 arc second periodic error without the need for computer correction.
  • The mount will be set for a latitude of 30 degrees, 23 minutes and include fine adjustment for azimuth and elevation.

Computer Control System:

  • The computer controlled telescope system consists of software capable of providing telescope focusing, slewing, tracking, and dome control as well as the electronic interface to the telescope, mount and observatory dome.
  • A Pentium computer with monitor, keyboard and mouse, compatible with the software and electronics, will be supplied to provide the direct user interface as well as the interface to a remote control system.
  • All motors, sensors, cabling and interfaces will be provided and the system will be compatible with an existing Ash Dome (model 22.5' MEBH).
  • The slewing motor speed will be adjustable so that the telescope can be quickly positioned and then accurately centered on an object.
  • The tracking motor speed will be adjustable and provide sidereal, lunar, solar, cometary, asteroidal and user definable tracking rates.
  • A control paddle will control the speed (guide, drift, slew) on the drives and direction (all cardinal directions) of the telescope motion independent of the computer keyboard.
  • The system will be capable of compensating for an object's proper motions, the effects of precession, nutation, annual aberration, atmospheric refraction and parallax as well as for mechanical/optical/polar misalignment and periodic error.
  • This compensation enables the telescope to be positioned on any object in the full sky to within ± 30 arcseconds RMS and to track the object over 20 minutes of time to less than 1 arcsecond of error.
  • Dome control includes dome rotation and shutter open / close operations along with manual overrides.
  • A "rain sensor" signal will be supplied by LSU and will be used in the software to veto the shutter open operation and to automatically close the shutter during remote operations.
  • Finally, all control functions, readouts and displays, with the exception of configuration and calibration operations, should be accessible over a T1 internet link and should be capable of using software such as TheSky as the user interface.

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Last updated by Frederick J. Barnett on Thursday, January 20, 2005 11:48:09 AM

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