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Louise and I became interested in amateur astonomy in 2000, and by the spring of 2001, we'd built an 8' x 12' roll-off roof observatory. In case you're wondering about the high walls and gable ends, our viewing site is surrounded by trees, so the gables don't interfere at all. We made-do with this site until . . . .
We built a house about 20 miles west, and cleared land for a new observatory with a 30° horizon, so the telescope and equipment are packed up for a year or two.
The observatory sits on concrete "deck blocks" which rest on the ground; there is no permanent foundation. The steps to the door use pre-cut stringers and treads from Lowe's. The roof is made from a tar-impregnated woven material named Ondura.
Inside there's an 8-foot square observation area, with a 12" concrete pier approximately in the center. The pier is isolated from the floor to minimize vibration transmitted to the telescope. A four-foot computer nook occupies the north one-third of the building. We ran a 3" plastic pipe under the floor from the computer nook to the pier to provide a conduit for power and computer cables.
Here we see the TMB 130-SS 130mm f/7 refractor pointing high in the southern sky, with the imaging equipment hanging off the back. A separate guider scope and camera sit off to the side; their purpose is to keep the telescope accurately pointed at an object while the main camera takes an exposure from 5 to 30 minutes long.The Astro-Physics 1200 mount was installed in October 2008. Click here for more photos showing how we attached it to the concrete pier and managed the camera cables.
This is a close-up of the imaging equipment attached to the telescope. The observatory is designed for unattended operation, and all the equipment is connected to the observatory computer.
A motorized Starlight Instruments Feather Touch focuser precisely focuses the image. The Optec Pyxis instrument rotator positions the camera for the desired target framing. The CFW-10 filter wheel places one of eight color or narrowband filters in the light path. The ST-8 CCD camera is cooled to reduce noise in the image, and has a homemade weight to counterbalance the CFW-10. To the right can be seen the rear of the ST-402 guide camera.
Here is a closeup of the CFW-10 counterweight. The wooden frame is bolted to the camera using the factory-provided ¼"-20 holes in the sides. The white plastic tray holds about 9 ounces of weight consisting of birdshot pellets and nails.
Note how the camera cables are routed to exit on the same side as the counterweight, adding their mass to the balancing act. After passing through a clip, the cables are secured with cable ties to the unused water-cooling ports.Without this routing, at some camera angles the cables hang on the same side as the CFW-10, making the total load too great for the Pyxis rotator.
The guide scope is an inexpensive 60 mm f/5 (300 mm F.L.) refractor, and the guide camera is an SBIG ST-402. The guider equipment is installed on one end of a Casady Triad Bar with six pounds of dumbbells on the other end, as a counterweight. For an external guider, rigidity is key – any flexure results in smeared stars in the image. The guide scope and ST-402 camera are securely clamped to the dovetail rail – the camera is not supported by the focuser drawtube – in fact the drawtube serves only as a shield to keep dew away from the camera chip. Focusing is accomplished by loosening the camera clamp bolt, then sliding the camera along the rail, and tightening the bolt. I've been able to achieve FWHM values of about two pixels using this method. Once focused and clamped, no further adjustment is needed from one night to the next.
In addition to being bolted to the dovetail, the guide camera is supported by an aluminum "backrest" to prevent it from flexing when pointing high in the sky. The single ¼"-20 threaded socket in the bottom of the camera is not rigid enough. Two holes were drilled in the camera's rear cover, and the backrest was screwed to it.
Here is another view of the guide scope and camera on one end of the Triad Bar, with the guide scope counterweights (dumbbells) on the far end.
A kitchen counter across the west wall of the nook holds the computer equipment for CCD photography. Originally installed at a height of 30", the counter is now at 41" to allow comfortable operation while standing. Many times I found myself alternating between the telescope and computer, bending down to view the monitor. It's much nicer to just walk up and have everything at a comfortable height. A $10 metal bar stool is available for longer sessions at the computer. Update: This is no longer a major factor, since we usually operate remotely from inside the house or even let the equipment acquire images completely unattended.
We remotely control the telescope and imaging equipment from inside the house using the Remote Desktop feature built into Windows XP Professional on the observatory computer. (Before installing this computer, we used UltraVNC, a free program with similar capabilities.) Once the equipment is powered-up and the observatory roof rolled-back, everything can be done remotely. Category 5 Ethernet cable in a buried conduit provides access to the home network. We tried wireless networking, but were disappointed with slow speeds due to degraded signals (from only 50 feet away!).
Important note: The conduit does not include cable for AC house current. It is not allowed to run signal cable in the same conduit as electrical cable, so a second conduit would have been required for that. Instead, we power the observatory with a heavy-duty extension cord run across the ground to an outdoor receptacle on the house.
Originally, equipment power was switched using an
The left photo shows the Ethernet power controller installed on the telescope pier. The second one is located near the computer. Each controller has eight switched outlets plus two always-on outlets, and a built-in Web server. Pointing a browser to its address opens a page showing the state of each outlet. Clicking on an outlet's link turns it on or off.
For example, pressing the Computer ON button turns on the computer, monitor, speakers, and two USB hubs.
Pressing Computer OFF causes MisterHouse to first "ping" the computer. Only if the computer doesn't respond (it has been shut down), does MisterHouse turn off power to it and the associated equipment. If the computer responds because it's still running, MisterHouse does not turn off the power.
Pressing Imaging Equipment ON sequentially turns on the focuser, camera rotator, imaging camera, and guide camera. The two cameras pose a special challenge: The imaging camera must be turned on and its Windows drivers loaded before the guide camera is turned on. If not, Maxim becomes confused and swaps the cameras in its configuration. To ensure proper driver loading, MisterHouse is scripted to turn on the imaging camera, wait 10 seconds, and only then turn on the guide camera.
One X-10 control box is located in my office and a second one is in the observatory to locally control the equipment power.
In 2008 we took the first step toward upgrading the observatory to operate totally unattended. This is different than remote control. Unattended operation means the telescope follows a predefined plan to acquire a target and take images of it without any human intervention. Remote control, on the other hand, means controlling each and every operation while sitting at a computer inside the house.
ACP Observatory Control software is the key to unattended operation. Prior to an imaging session, I use ACP Planner to select a target and specify the type and number of images desired. Then the observatory computer and imaging equipment are powered-up and ACP is directed to execute the imaging plan. This startup may occur hours before the appointed imaging time, so it's possible to go out with the family for the evening while ACP operates the equipment. The images will be waiting on a shared network drive the next morning.
Click here to read about a program I wrote to analyze ACP plans and calculate their timing.
Here is a screen shot taken on my home computer showing the observatory computer with ACP and the imaging software running. I use the webcam view in the lower-left to verify that the telescope is behaving before starting an ACP imaging plan. Then I turn off the white light, and shut down the webcam monitor.
Currently, I must be in the observatory to roll the roof open and uncap the telescope. This isn't a big deal, as the observatory is only 50 feet from the house. However when we build a new house and observatory 20 miles away in 2010, the observatory will be 300 feet from the house, so walking to it will become a non-trivial hike, especially on cold winter nights. The ultimate goal is to motorize the roof and telescope lens cap so they too can be controlled remotely (or automatically by ACP), thus eliminating the need to walk to the observatory for normal operations.
I've received queries about how to make a PC turn on automatically when power is applied, so the Ethernet power controller can turn it on without someone present to press the power switch. Most PCs have a Setup option to do this.
To activate this option, turn on the PC and enter Setup by pressing the key displayed on the screen, typically Delete or F2. Find and select an item labeled something like "Power management" then find an item labeled "State after power failure," or similar. Look at the choices, such as "on" and "off." Select "on," which means that the computer will turn on when power is restored. The photo below shows a typical Setup with these items in red. Notice the explanation on the right.Save the settings and exit Setup, then let the computer start up. Shut down normally, then unplug the power cord from the wall socket. Wait 15-30 seconds, then plug it in again, and the computer should start. That's all there is to it.
Tip: Do you know how to shut down Windows remotely? Start -> Turn Off Computer isn't available. Right-click on the task bar, then click Task Manager. On the menu there, click Shut Down, then click Turn Off.
I have to walk out to the observatory to open the roof, but once I return to the house to control the equipment remotely, I want to double-check visually before moving the telescope around. Nothing ruins an evening faster than crashing the telescope into the roof. So I installed a WebCam on a wall, aimed at the telescope.
Its field of view is wide enough to see some of the roof structure, so I added three signs to provide a positive indication of the position, as shown here. With the roof closed, the "CLOSED" written on a roof truss can be seen. If the roof is open, but not completely, the "CAUTION" warning is in view. When the roof is fully open, "CAUTION" is hidden, and only the "OPEN" sign remains visible.
The onset of cold weather brings howls of protest from the rotating machinery in the observatory computer. The hard drive and fans just don't like spinning-up when it's 10°F or colder out there!
To help them along, I installed a heater inside the computer. It consists of a 75-watt lamp and a thermostat for a 120V electric heater. A metal shield protects the hard drive directly above the lamp.
The electrical box and lamp holder are standard outdoor items available at home-improvement stores. The thermostat is a Honeywell model CT410A, also available at home-improvement stores. It switches both sides of the AC line, which is a safety benefit. Do not use a regular wall thermostat intended for gas or oil furnaces, or heat pumps. These are designed for non-lethal, low-voltage circuits. Aside from ruining the thermostat, the 120V house current present on such a thermostat's unprotected electrical contacts could electrocute you.
The AC power cord runs through a 1" hole punched in the computer's rear panel. I lined the hole with plastic "grommet strip" to prevent the metal edges from cutting into the power cord, and stuffed it with foam to keep rodents and bugs out.
Before an imaging session, I turn on the heater and let things warm up for a while. The thermostat turns off the lamp when the temperature inside the computer reaches about 55°F. When the computer is powered-up later, all those rotating components sound much happier.
It's hard to see a keyboard in the dark! Here's our illuminated keyboard. Four white LEDs, with their rounded ends filed flat to diffuse the light, are glued to a styrene backboard. The LEDs are powered through current-limiting resistors by the keyboard's +5V power from the computer; a toggle switch (far right) turns the lights on and off.
The telescope mount and imaging equipment use external power supplies. I needed a way to keep these and the Ethernet power controller off the floor and to manage the cables. The solution was an equipment holder attached to the concrete pier.
I made four identical plywood brackets with circular cutouts, clamped them in pairs around the pier using 5/16" threaded rod, then attached plywood panels to hold the equipment.
The Ethernet power controller is attached with screws. Velcro patches on the opposite panel hold the focuser control box. Its "black box" power suppply rests on the lower pier bracket. The camera power supply can be seen nestled behind the Ethernet power controller. Large holes in the top and bottom brackets allow cables and connectors to pass through. The Pyramid supply for the AP1200 mount is too large for the plywood panel, so it sits on the floor. The 3" plastic conduit runs beneath the floor to the omputer area, and the red string above the Pyramid is used to pull cables through it.
The earlier photo on the right shows the long threaded rod that holds the two plywood sections together. The white strip at the top is 0.030" styrene from a hobby shop, and prevents moving cables from snagging on the brackets. Notice the two small black power supplies held with Velcro inside the right bracket.
This 3" plastic pipe carries cables from the computer area to the telescope pier. The red string is used to pull additional cables. The pipe provides a convenient location to attach a USB hub with Velcro.
Power Supply Modification
I traced occasional erratic behavior of the AP1200 mount to a questionable power cable connection. The Pyramid power supply's plastic thumbscrew terminals sometimes can't be tightened sufficiently to ensure good contact.
To remedy this, I drilled a ¼" hole in the bottom of the case and fed a cable through it. I soldered one end of the cable to the power terminals inside, and soldered a 2-pin Cinch-Jones connector on the other end. I installed a mating connector on the AP1200's power cable, and now the connection is robust and reliable.
The critter screen keeps out rodents, snakes, and other curious animals (but not bugs, which come in around the roll-off roof). The screen also catches small parts that drop while working on equipment at the pier. It is attached with construction adhesive to the pier and to the sides of the hole in the floor.
The roll-off roof is supported by six hard-rubber wheels riding on a 2x4 track. a 1/8"-thick aluminum angle on each track guides the wheels.
When closed, the roof is locked in place by a 12" J-bolt in each corner. The bolts have a right-angle hook at one end, and threads on the other. The hook fits into a hole drilled in the roof structure, and the threaded end goes through an eyebolt screwed to the observatory wall. Gentle tightening of the wing nut is all it takes to hold the roof securely in place. (For high wind, we attach the steel cable visible in the lower-left corner to the large eyebolt in the upper-right corner; the cable is attached to an anchor screwed into the earth.)
Roof End Detail
The southern end of the rolling roof extends 4" beyond the gable wall, keeping out the rain.