Operating System and Equipment - Part 1
Section II: Facilities
B. Operating System and Equipment - Details
Telescope - Observatory
A main telescope is basic for all astronomical research. The observatory includes the housing, rotatable dome, astronomical mount, and a state of the art reflecting telescope system.
Major components of the system include:
The telescope, its mirror control, display, computer, output and software,
General conferencing facilities,
These facilities support the following programs:
general interest programs.
Telescope System Construction
by Ed Ritchie, revised February 2007 by Malcolm Saunders
1. The Mirror Grinding Machine
Once we were assured we would get the two Boeing mirrors, Ed decided to build the grinding and polishing machine which he had already designed. This was necessary as hard grinding, polishing and finishing large, heavy mirrors to wide field tolerances would have required tens of man-years of effort.
Russ Trask furnished all of the steel for the machine. Butch Bretsen did all of the welding. It has a high speed diamond spherical grinding unit which has reciprocating arms and ball drive for both ceramic and pitch laps adjustable for stroke length and position of lap on the mirror. The table under the mirror rotates in either direction. The entire mirror platen is tiltable on giant bearings to make possible Foucault and Ronchi testing. Positioning of the upper head up and down is accomplished by a 4" diameter Acme threaded main column with a small two-way gear motor. The unit is large enough to do the 40.5" mirror. As a preliminary practice exercise Ed spherically ground and polished his own 22.5" Pyrex mirror with very good results. The system performed its job superbly for BPAA's 27.5" mirror, shortening the mirror preparation cycle to one man-year from between 15 man-years to infinity.
Once the 27'' mirror and telescope were completed it was decided that the building and operation of a 40'' telescope and observatory were beyond the means of BPAA and the 40'' mirror was traded to the University of Arizona for a completed 24'' mirror. The grinding machine has recently been relocated to the workshop of BPAA member Nels Johansen who has begun learning to grind mirrors.
2. The 27.5" Mirror
Ed decided to use the 27.5" zerodur mirror rather than the 40.5" mirror in the Battle Point Observatory in order to limit the size of the dome to conform with the building height restrictions. This mirror was designed for sensor calibrations and could not be used, as was, for astronomical observation.
The grinding and polishing took approximately one year. First, about 0.5" in depth was spherically diamond ground from its surface to eliminate existing ball depressions. Then ceramic laps were used in four stages of grit to smooth the spherical surface. An 18" spherometer was used to extremely accurately monitor both sphericity and focal length. After sphericalization with 8 micron garnet, pre-pitch laps were made using the mirror as a molding template and final spherical polishing was begun on the mirror.
After almost perfect spherical polishing was completed, parabolization or figuring was begun by deepening the center of the mirror 0.00045". This was done totally with a smaller pitch lap. Both Ronchi and Foucault testing were used to monitor the figure. The final tests were completed by Foucault technique using zonal masks with Bob Mathews' help in the reading and analyses.
A 4" outer diameter tubular hole was ground leaving a 3.5" diameter plug. This plug was left in, surrounded by plaster during the entire grinding and polishing operation. After completion of the mirror, this plug was removed by grinding a tiny amount of holding glass out from its backside with diamond cutters furnished by Molly Griest.
The mirror was then carefully crated and taken to California by the Gardiners to be vapor deposit alumized and "enhanced". The mirror was installed in the telescope and the telescope was moved to the dome in December of 1997
3. The Telescope Structure
The telescope base and the drum and fork were built during this same period. Quarter inch steel plate donated by Russ Trask was used in its construction and it was flame cut by Johnnie Magnuson. Most of the extensive welding was done by Butch Bretsen. All of the columns, including the central fork column are very heavy steel. Precision bearing surfaces were machined into the columns before welding. Huge Timkin tapered bearings were used on the main fork column with a take-up nut at the bottom of the column. An internal conduit was placed inside the structure and pre-wired for control wiring. The three major base units, which include the base, the drum and the fork, weigh more than 1000 pounds. The base has mounting feet which match the bolts in the concrete pad at the Battle Point Park Observatory.
Gears were made - one of 28" diameter with 360 teeth and one of 14" diameter with 180 teeth for the polar and declination axes. The two main gear blanks, from Alaska Copper and Bronze, were accurately jet-cut by Micro Jet of Monroe. Indexing plates were first made on the milling machine using a precision rotary table, one with 360 holes, one with 180 holes, to control the spacing of the gear teeth. I then machined these, including the worms, using #4 pitch teeth.
The telescope tube, the final unit in our telescope, was made by rolling 1/8" aluminum plate into a cylinder about 30" in diameter and 36" long. Both side yoke bearings were fit and bolted into this unit. A 5/8" back plate was welded to the back of this unit with 16 threaded mounting holes. This unit is precision-matched to the cell which holds the mirror. This cell consists of two discs of 5/8" aluminum. One is bonded to the mirror with nylon spacers and silicone. The other one is mounted to the telescope tube, and the two of them are interlocked with four special mirror adjustment units. This cell weighs about 100 pounds and the mirror weighs about 200 pounds. In addition, there are 18" diameter 1/2" thick steel counterbalance discs which bolt to the back of the cell. The front of the optical tube assembly is composed of an aluminum truss tube structure. The end of the truss tubes are bolted to a ¼'' thick aluminum ring which in turn supports two more similar rings which can rotate as a unit about the optical axis. These last rings contain the spider, the diagonal flat and the focuser. A CCD or other camera may be installed in the focuser in place of an eyepiece.
4. The Drive System
Both right ascension and declination axes were originally driven with #34 series stepping motors with worm gear reduction. These stepping motors were controlled by 'Sky Probe 1000' software and a 486 computer. The stepper motor control system was plagued with problems and eventually replaced with a servo motor control system during the winter of 2004-2005. The servo motor system uses software developed by Mel Bartels and motor controllers and a wireless hand pad developed by Dan Gray. The control system is described in detail at their web sites: http://www.siderealtechnology.com/
and http://www.bbastrodesigns.com/BBAstroDesigns.html Servo motors offer a wider range of speeds and smoother motion. They also do not suffer from stalling due to low torque at higher speeds. The trade-off is that they require more sophisticated control software. That software is now available to the amateur astronomy community in a way that it was not available when the Ritchie telescope was first built. The servo system is controlled by a desktop PC computer running planetarium software. We most often use the program Cartes du Ciel but there are several alternatives available that can easily be installed and used to control the telescope. These programs allow 'point and click' control of the telescope and give a graphical feedback of the telescopes pointing coordinates to the user.
The telescope has not yet reached the level of precision tracking and go-to pointing that the control system is capable of achieving but the performance is already very good and improving as we make upgrades to the telescope.
5. The Completed Telescope
The telescope was completed and installed in the dome in December of 1997. However “completed” is a misleading word when used for a telescope. As with a wooden boat, a telescope always needs maintenance. In addition, as technology changes, dramatic improvements become possible. For these reasons, we can expect that there will always be work to do in maintaining and upgrading the telescope.
Ed Ritchie passed away shortly before the telescope was installed in the dome. He left behind very little documentation of the telescope design and construction. One on-going project is the retroactive documentation of the design in a detailed computer model of the telescope. That information is useful to have not only as a tribute to the work of Ed Ritchie but also because it makes it easier to carry out upgrade and maintenance work.
6. Telescope-related instruments
We have two electronic instruments to use with the telescopes. These are an SBIG ST8 CCD camera and a StellaCam II camera. These two instruments serve complementary purposes. The SBIG is well suited to preparing precision long exposure still images. The images are saved to a computer for later processing using software such as Adobe Photoshop to bring out faint details. The StellaCam II allows for real-time and near real-time viewing on a television monitor. Both instruments are far more sensitive than the human eye or photographic film. This means that both will allow the viewing of celestial objects too dim to be seen with the eye, even through a large telescope.
In principal, the telescope can be operated from a heated control room inside the building or even remotely. Such operation presents additional problems and this step will be some time in the future.
Eyepieces and filters
We have three high quality eyepieces used most often on the Ritchie telescope yielding approximately 80X, 200X and 270X magnification respectively. These are
Televue 35 mm Panoptic 2''
Pentax 14 mm 1 ¼ ''
Televue 10 mm Nagler type 6 1 ¼''
We also have the following filters:
2'' Lumicon O III
2'' Astronomik UHC
These filters are specialized to enhance contrast by passing only the wavelengths of light that are emitted by certain nebulae and galaxies. We will also be purchasing neutral density lunar filters.
The observatory dome is constructed of ¼'' plywood formed over bent aluminum tubing. The wood is coated on the outside with a weather-resistant white paint. The dome is mounted on large rubber casters that roll on a circular track allowing the dome to rotate 360 degrees. There is a slot that opens to the sky. Both the dome and the opening slot are motorized.
Uses of the observatory
BPAA is unusual among amateur astronomy organizations in that we have facilities. We can not only hold meetings at the observatory, but we can carry out telescope building projects, offer classes, store equipment and of course, we have a home for the Ritchie telescope.
What are possible projects and research that can be carried out with the use of a telescope of these capabilities? The observatory:
directly supports basic research, permitting the serious observer to precisely quantify the location, velocity, illuminance, intensity and color spectrum of celestial objects,
allows for general viewing of celestial objects,
focuses community interest in astronomy,
increases monitoring of celestial events,
allows, enhances interface with other observers,
helps point to answers to questions of origin, extent, resolution of the universe,
contributes to related scientific, geometric, mathematical sciences,
helps predict climatic conditions on earth,
gives information about chemical, electro-magnetic composition of elements of the universe,
allows participation in asteroid and comet watches to facilitate the search for new comets and novas.
The original architectural model for the observatory included a planetarium in the meeting room. Just one little hitch: when John Rudolph designed the BPAA meeting room in 1994, in all these years there has been no suitable planetarium projector on the market. The available projectors were either: · far too expensive for a small community, · too unwieldy for portable shows in public schools · not sophisticated enough educationally. Various members toyed with various designs but none of them came to fruition.
But, to BPAA’s delight, everything changed in 2003 when Digitalis Education Systems, Inc. of Bremerton developed a reasonably priced, educationally rich and versatile, highly portable planetarium system . With the availability of this unique new system, the John H. Rudolph Planetarium became a reality.
The Digitalis Alpha Planetarium
The Digitalis Alpha Projector: This fisheye-lens, electronic projector is a state-of-the art planetarium. At 32 pounds, the projector is highly portable. The Digitalis Alpha runs a sophisticated software program called Stellarium that includes stunning Hubble photographs and allows for development of scripts for specific course and circicumlum development. Also, Digitalis includes a set of excellent pre-designed planetarium shows.
A Semi-permanet dome
The semi-permanet dome resides in the meeting room of the Edwin Ritchie Observatory. The dome was designed and constructed by BPAA members. The dome for the meeting room had to be light enough to hang from the ceiling and leave the room usable for other purposes. Since the room is 14.5 feet high, the horizon is set at seven feet so that most people could walk under it. This leaves an elliptical dome 7 feet high and 19 feet in diameter. The screen is a cloth screen similar to the type used on stage for a projection screen called a ‘Cyclorama’. There are 20 triangular panels with a single circular panel at the apex. The ribs are made of electrical coduit. The ceiling behind the dome is painted a dark blue to reduce glare.
The Portable Dome
The Portable Dome is from Digitalis. It is a16 foot dome, weighing about 35 pounds, inflated by a fan weighing under 30 pounds.
Intended Audiences for the Planetarium
- Bainbridge public school children and beyond: It is possible that an economical planetarium show would be used widely throughout Kitsap county and even farther afield on the peninsula.
- Special groups such as Scouts, 4-H, etc.: These groups visit the observatory now and would in all likelihood enjoy planetarium shows as well as the telescope tour.
- BPAA astronomers: The planetarium could be a teaching/learning tool, and a programming adventure for BPAA members.
- Astronomy Class: The planetarium could be used by Paul Middents, professor of Astronomy for Olympic College, in teaching the BPAA astronomy courses on Bainbridge Island.
- Teachers: Teachers are required to continually educate themselves, keeping current in their professions. BPAA planetarium shows could help them meet their educational requirements.
- General public attending Star Parties and Astronomy Day: Planetarium shows could run during the various public events BPAA now holds at the observatory.
- Students of Celestial Navigation: This audience was suggested to Planetarium Committee members, but we have not yet had an opportunity to investigate whether they could use the planetarium.