The Monterey Institute for Research in Astronomy (MIRA) is an independent, non-affiliated, professional observatory dedicated to astronomical research and education. The Institute operates the Oliver Observing Station atop 5000 foot Chews Ridge near Monterey, CA. It is an honor to replicate the information generously provided by Dr. Bruce Weaver, Observatory Director. He provides an interesting history of the telescope, original worm gear drive mechanisms and control system as well as circumstances surrounding its humble beginnings.
Reproduced with permission from:
Dr. Bruce Weaver, Observatory Director
Monterey Institute for Research in Astronomy (MIRA)
MIRA Newsletter: Fall 2018 Volume 41, NO.3
© 2018 All rights reserved. All images © MIRA 2018
Installing the New MIRA Telescope Control System
A lot of moving parts, both figuratively and literally, go into making a modern observation at the telescope. The classical image of an astronomer peering through an eyepiece is not even a distant memory of older astronomers; even amateur astronomers are now using highly sensitive modern electronic cameras. But modern telescope and instruments, and their associated computers, bring with them the added complexity and inflexibility associated with modern electronics: all the parts must perform their intended function or no observation is possible.
Mark Kelley, Jeff Larson, Ian Huss, & Bruce Weaver work on installing the new MIRA telescope control system.
A Telescope's Simple Task
A telescope’s task is a simple one: point the optics at the correct location in the sky and smoothly compensate for the Earth’s rotation as exactly as possible. A tracking error of more than half a part in a million is too much. Until the MIRA telescope, telescopes of our size all had a large worm gear, larger than the mirror, whose tooth-to-tooth error had to be less than one part in a million. They were often more expensive than the mirror.
When we built our telescope we couldn’t afford a gear that expensive so our engineer, Frank Melsheimer, decided to use a smooth disk instead of a gear. It rests on two rollers, one of which drives the telescope in the direction to compensate for the Earth’s rotation. For several years now, we had to deal with a long-period tracking error and we traced the cause down to a 0.002 inch error in the roundness of the drive roller. That tiny eccentricity was enough to move a star image 30 times its diameter over about two hours.
So we decided to jack up a few thousand pounds of telescope, disassemble the drive mechanism, and replace the roller and its bearings (which were also in pretty bad shape) while we were installing the telescope control system. It took a couple of tries but we now have a round roller and smooth tracking.
The first step in making scientific observations of the heavens is a working telescope.
After the optical and mechanical parts are working, (see sidebar "A Telescope's Simple Task") the next critical part of the system is the telescope control system (TCS).
The Monterey Institute for Research in Astronomy (MIRA) 36-inch telescope pre-dates the advent of the personal computer and, of course, we were too poor to afford a massive custom-designed control panel made of thousands of individual parts.
The first control system, used during the initial testing of the telescope, was based on a single-board hobby computer, painstakingly programmed in machine language, to provide simple tracking and setting motions. The higher speed slew motions were strictly manual control of quarter-horsepower motors.
By the time the telescope was moved to its permanent home on Chews Ridge, the commercial hobby computer was replaced by MIRA-designed and built computers.
Since they were used as controllers for the telescope, we named them 'Trolls'.
By this time we had included the ability to display the telescope coordinates.
Finally, in 1999, personal computers had come to the world of telescope control and we were able to afford a complete TCS from DFM Engineering - MIRA’s telescope, actually predating DFM Engineering, was the first telescope designed and built by Dr. Frank Melsheimer (The DFM).
Now the astronomers had complete control of all the telescope motions and could even have the telescope move to a star by name. That permitted the astronomers to move from the open telescope floor to the warm control room. I miss the beauty of Milky Way smoothly passing overhead throughout the night, but I miss very little of the sharp winter winds and 12 hours observing in sub-freezing temperatures.
Replacing the 36" telescope drive roller requires jacking up tons of telescope, a custom tool to pull the roller and its bearings out of its casing, and at least four hands. The old drive roller was .002 inches out of round, causing a slight change of tracking rate over an hour. This error had limited unguided exposures to 90 seconds or less so that science exposures typically serveral minutes to an hour required guiding.
By 2016, our TCS had become less and less reliable. Parts for repair became harder and harder to procure and the TCS computer was based on standards that were no longer supported. Chews Ridge rodents found the TCS chassis an irresistible home. We were spending a lot of time fixing the system and less time successfully observing. We started to save money for an upgrade to a modern system.
By late 2017, the TCS was quite unreliable, and with the help of the Friends of MIRA, some foundation support, and a bequest, we were able to order the latest DFM TCS. Even though we were able to use the motors and cabling from the previous TCS, installation took two DFM engineers nearly two weeks.
Since then, we’ve been testing the system and DFM is providing minor tweaks to the software. Each telescope is unique so it is not surprising that we are still working out the last few bugs in the system. We hope the new system is good for another 20 years.
MIRA summer intern Mariah Trinity and Dr. Arthur Babcock examine the culprit at the Oliver Observing Station: the original 36 inch telescope drive roller. New drive roller bearings with improved weather seals were also installed.
Master machinist, Ian Huss of DFM Engineering, is at work on the MIRA telescope control system installation.
While inside the control room, TCS software guru Mark Kelley of DFM Engineering works to install the computer, motor driver chassis, and custom telescope control software.
For additional information about the DFM TCSGalil, please see the following links:
Telescope Control Systems (TCSGalil)
TCSGalil Standard Features
TCSGalil 20-50" Standard Features
Also for additional information about DFM Telescopes and recommendations, please see the following links:
How to Buy a Telescope
Internet Telescope Performance Requirements
Comparing Telescope Drive Technologies