ACP Dome Control

ACP provides automatic dome azimuth slaving with the geometric calculations needed to assure slit alignment with simple/fork equatorial, flipping German equatorial, non-flipping extended German equatorial, and alt-azimuth mounts. It also provides for manual, scripted, and automatic opening and closing of any enclosure such as a roll-off roof or clamshell as long as an ASCOM Dome driver is available for the control system. ACP adapts to varying enclosure capabilities and needs automatically.

DC-3 Dreams offers programming services for developing Dome drivers. If your dome, clamshell, or roof control has a serial or scriptable/ActiveX interface with which it can be controlled, DC-3 Dreams can develop the ASCOM Dome driver that will allow ACP to manage the dome.

A roll-off roof is treated by ACP as a dome that has shutter control, but no rotation. In order to use a roll-off roof controller with ACP, it needs to have a "dome" driver which reports that it is incapable of rotation. Simple.

General Information

When ACP dome control is enabled, ACP connects the dome automatically when the telescope is connected. Depending on the options set, ACP can automatically home and/or open the dome when the telescope is connected and/or close when the telescope is parked. After optional auto operations are completed, ACP slaves the dome to the telescope position, keeping it slaved until the telescope is disconnected or parked. Clients such as planetariums and MaxIm DL can control the telescope via ACP's hub, and when doing so, ACP provides dome slaving (as well as pointing correction, of course).

When the telescope is disconnected, ACP can optionally home and close the dome after the telescope is parked. Thus, for a roll-off roof or clamshell, ACP will do its very best to assure that the telescope is parked before closing. Some telescopes stop responding to computer commands immediately after being given a park command. In this case ACP will wait 60 seconds and assume the scope is parked.

Do not depend on ACP or any other computer program to assure that your telescope is parked if closing your roll off roof or clamshell would strike the telescope in an unparked condition! Consider this fair warning. You really need to install a limit switch or equivalent that provides basic safety without computer involvement!

One-time Setup

1. Click this button to display the ACP Dome setup panel.
2. If the Select Dome button is grayed out, disconnect the telescope in ACP.
3. Click "Select Dome" to display the ASCOM Dome Chooser. Select your dome's driver in the drop down list.
4. If the OK button is not enabled, click Properties... to open the driver's setup window. Make the settings needed for your dome (these are dome-specific). Close this window. Now the Chooser's OK button should be enabled.
5. Click OK in the ASCOM Dome Chooser.
6. Turn on "Enable ACP dome control".
7. If your dome requires homing when first powered up, turn on "Automatically home dome on first connection".
8. If you want ACP to open the dome when the telescope is first connected, turn on "Automatically open shutter on first connection". You may also open the dome manually using the ACP Dome menu.
9. If you have a real dome or a roll-off that clears the scope in any position, turn on "Safe to slew scope anywhere with shutter closed". This is important, as it will allow a faster response to weather alerts. ACP will not wait for the scope to park before starting to close the shutter.
10. If you want ACP to automatically home and close the dome whenever the telescope is parked (e.g. when one of the plan #SHUTDOWN directives is used), turn on "Close and Park/Home when (or AFTER) scope is parked by script ". Again, read the Important notice above!
11. Enter a value for the Slaving Azimuth Tolerance. Note that the smaller this value is, the more often the dome will move as your telescope tracks sidereal motion. Try to use as large a value as possible. This value is the allowable error between the perfect slit azimuth and the current slit azimuth in degrees.
12. In the Geometry section, fill in the items as appropriate for your mount: its horizontal position with respect to the center of the dome, its distance above/below the dome's equator, and the optical axis offset (for German mounts). The distances are in millimeters. See the next section Geometry Settings for details.
13. Now click Advanced...
    • If your dome shakes the telescope (even a little) when it moves, enable Inhibit slaving while imaging. NOTE: this will prevent the dome from tracking your scope's motion on long exposures. If you take long exposures, the scope may track out of the dome opening. This is a tradeoff!
    • If you have a "real" dome (as opposed to a roll-off roof), enable Safe to slew scope anywhere with shutter closed. This will relax some checks for parked scope when closing the shutter.
    • The last two checkboxes should only be used in an extreme situation, where your dome controller is broken such that it reports shutter error conditions when no problems exist. If you enable either of these, be forewarned that you are exposing yourself to electromechanical damage!
14. Click OK twice to close the Preferences window.

Geometry Settings

German (or non-flipping extended German) Mount Geometry

Fork Mount Pivot Point

The dome controller geometry items are:

• Mount Pivot EW Offset: The east-west distance from the center of the dome to the pivot point, in millimeters. Positive values mean the pivot point is east of the dome center.
• Mount Pivot NS Offset: The north-south distance from the center of the dome to the pivot point, in millimeters. Positive values mean the pivot point is north of the dome center.
• Mount Pivot Vert Offset: The vertical distance from the plane of the dome's equator to the pivot point, in millimeters. Positive values mean the pivot point is above the dome's equator.
• Optical Axis Offset: The distance from the centerline of the RA axis (German and non-flipping extended German mounts) or the Dec axis (fork mounts) to the centerline of the optical axis, in millimeters. See the figure above for both types of German mounts. This is normally 0 for fork mounts, and may be positive or negative for extended (non-flipping) German mounts.
  If you have an external guide scope, try to mount it on the top or bottom of the OTA. Then add half the distance between the OTA optical axis and guide scope optical axis to the Optical Axis Offset. This will optimize sky view of both the OTA and guide scope through the opening. This applies to both German and fork mounts (which will have a base offset of 0). Note that ACP's geometry calculations cannot compensate for a side-mounted guide scope.
• Dome Radius: The radius of the dome (half its diameter). To be most precise, this should be the radius of the dome for the slit opening.
• Dome Az Bias: Not strictly a geometry setting, this should be used to remove any constant pointing error that the dome controller has. If you find that the opening is always off in one direction regardless of the part of the sky, you can adjust this to correct that constant error. For most domes this will be zero.

Routine Use

After doing the above one-time setup, ACP will manage your dome automatically. Shutter control and park/home are available on the System Status display of the web interface, via the Dome menu, or via the dome control mini-panel (use the Dome Control button on the main window). The dome control mini-panel also has annunciator lights. Also, you can schedule the opening of your dome shutter or roof via the #DOMEOPEN plan directive.

Be sure to use ACP's dome controls for parking, homing and operating the shutter. Some dome states that can be changed with a dome hand-box will not be fed back to ACP, and ACP may lose track of the dome state.

If you want to do things not supported by ACP, shut ACP down and use the free POTH or ASCOM Dome Control programs that come with the ASCOM Platform. They are accessible from the Start menu under ASCOM Platform.

Taking Dome Flats

To take dome flats, make sure the Dome Control Preferences option "Slave dome when shutter is closed" is turned off, then close the shutter. At this point you will be able to slew the telescope to the flat screen without the dome following the scope. If you need to rotate the dome to a particular azimuth, you can use a scriptlet (run in ACP's console) for this. See the next section for more info on scripting the dome. Here's a sample, which will unslave the dome (if needed) and rotate to 260 azimuth:

Sub Main()
    Dome.Slew 260
End Sub 

You could integrate this with a dome-flat script that does the things your dome flat system needs (they vary all over the place, with lightboxes to turn on, etc.). You can re-enable slaving by script with this:

Sub Main()
    Dome.Slaved = True
End Sub 

Script Control

ACP (intentionally) does not expose a "hub" for the Dome. Instead, it provides a few properties and methods for use by ACP scripts during routine operation and shutdown (using the ACP-Startup, ACP-Shutdown or ACP-Weather scripts). The properties and methods supported by ACP.Dome are given in the ACP Dome Object documentation. These are accessible from within ACP console scripts and ASP pages as Dome.xxx.

If you have the "Automatically park or home and close AFTER scope is parked" option set in Dome preferences, the Telescope.CanPark Boolean will report True even if the scope cannot be parked. This is to allow you to call Telescope.Park() as the way to park/home and close the dome anyway. Just keep in mind that the dome is tied into the telescope in an intimate way.