Coudé Flat Control

Implementing some of the pulpit controls has required rewriting some of the existing control functions. That's somewhat annoying, although I tried to improve them while I was at it.

The Coudé Flat controls are a good (bad?) example. The crane rotates down and places the flat on the central support column. Then it releases the flat and rotates back up again. The base of the flat is one model: it can rotate back and forth 90 degrees, between the default South-looking orientation, which reflects light toward the Coudé room, and an East-looking orientation, which reflects light toward a spectrograph in the telescope's East arm. The Coudé Flat mirror assembly is a separate model: it can either be at a fixed 45 degree tilt, for reflecting into the East arm, or it be manually or automatically tilted so it continuously reflects light toward the Coudé room as the telescope changes its Declination angle.

Previously the crane was a single model, separate from the models comprising the Coudé flat. None of the parts of the crane model moved, so in V2 its clamping mechanism passes (inappropriately) through the models of the flat when the crane rotates up after placing the flat on the central support.

However, the Pulpit includes a control for the crane's clamping mechanism. V3 now has two crane models. One of them includes a complete model of the flat, with the crane's clamping mechanism holding it securely. The other crane model has the clamping mechanism in the released position, so it'll clear the mirror's models as the crane rotates up and away. In other words, selecting the Pulpit's "place mirror" switch swaps the two crane models and changes the visibility of the parts of the mirror models that are on the support column.

I very briefly considered animating the clamp release. However, the crane has too many articulated pieces; some of them rotate, some translate and some do both. Each of them would require separate ScriptedOrbit and ScriptedRotation functions, carefully adjusted to match their motions with those of the other pieces. Maybe someday Celestia will implement animated bones (models which are constrained to stay in proximity in specified ways). Then I'll consider redoing this.

As a side-effect, I also had to redo how the Coudé flat model was controlled. That isn't entirely finished: I haven't done the code for the switch that moves control from the Pulpit to the Desk. Currently both are active simultaneously.

Here's a picture of the crane when it has just released the Coudé flat on the central support. Note the state of the Pulpit controls.

Seconday mirror covers & pulpit in use

This morning's progress: I added the covers of the secondary mirrors and animated them. When commanded from the pulpit, the appropriate secondary mirror is lowered into position while its covers open. This picture shows this happening for the first Coudé secondary, the one used for the 3 mirror Coudé light path. The mirror is in the process of going down and its covers are opening.

I originally designated this the 2nd mirror for the 5 mirror light path. After an afternoon nap I realized how wrong this was. Both Coudé mirrors have the same focal ratio of f:30. Although not obvious from this angle, the mirror that's halfway down in the picture below is raised a foot or so above the others. As a result, the length of the light path that it reflects is about 9 feet shorter than the length reflected by the lower Coudé mirror. The 3 mirror Coudé light path is shorter than the 5 mirror path, so the upper Coudé secondary has to be the one used for the 3 mirror path. It took me about 20 minutes to interchange their rotation parameters and switches.

Pulpit

No, people don't give sermons here :)

Here's my start at implementing the Hale Telescope's control pulpit, which is located at the south end of the telescope. It is still missing the counterweight balancing meters and some associated labels and switches.



Oh, and its door isn't shown either, only its hinge.

Controlling the telescope

The major features of the next version will be its control desk and the separate control pulpit. Here's the control desk. Its layout is pretty much finalized, although its functionality hasn't been fully implemented. Maybe one more display dial will be added if I can decipher the blurry picture. All the switches go up and down or 'round about, but I need to finalize the details of what some of them cause to happen. Switch action is simulated by clicking on labels -- they're implemented as if they were radio buttons.

Opposite ends of the telescope

Here are some more closeups of the primary mirror and its mirror cell. The mirror's pyrex glass and its waffle pattern were major innovations at the time it was designed, as were its counterweighted supports.









At the other end of the telescope are the focal point of the primary mirror and the secondary mirrors which magnify the image and reflect it to the f:16 Cassegrain and f:30 Coudé focal points. The prime focus cage includes adjustable supports which move the secondary mirrors and the prime focus instruments up and down +/- 1.5 inches.

Comparing versions

Here are some comparisons of a typical feature: the telescope's mirror cell and cassegrain cage as implemented in v1, v2 and v3 of the Addon. (Unfortunately, Celestia still has problems depth sorting transparent objects, so the cassegrain cage's grillework isn't shown properly.)

Hale Telescope for Celestia

Since I'm not an experienced blogger, I've gotta decide what to write. I've decided it might be of interest to some people if I wrote about the developments in the most recent Addon that I've been working on for Celestia: a model of the 200" Hale Telescope on Mount Palomar.

Information about previous versions of this Addon is available at
http://www.lepp.cornell.edu/~seb/celestia/hale_telescope.html

More information about the Hale Telescope and Mount Palomar Observatory can be found at http://www.astro.caltech.edu/palomar/hale.html and at http://palomarskies.blogspot.com/

Celestia is a 3D astronomical visualization program which has become significantly more sophisticated in recent months. Information about Celestia is available at http://www.shatters.net/celestia/

The initial version of the Addon includes a relatively low resolution model of the telescope which always pointed toward a fixed target. If you wanted to change it, the target had to be changed by editing an SSC file (the type of file which is used by Celestia to define objects.) I don't recall how long it took to create that version, several months, I think. It was published just after Christmas in 2006.

V2 of the Addon includes a more detailed model and makes it possible for its user to type commands to point toward various targets and to manipulate some of the model's components -- opening and closing the cover for the mirror, for example. (Details are at the Web site mentioned above.) Most of these updates happened over a period of about 3 months in the fall, and it was published just before Christmas in 2007.

Both versions are available at http://www.lepp.cornell.edu/~seb/celestia/hale_telescope.html

V3 of the Hale Addon is what I'm working on now. The models of the telescope and of the observatory dome are both getting more details. The telescope model is getting more holes cut into it. Less is more! The real telescope has many access holes not shown in the existing models. The support structure for the primary mirror, for example, has more than 40 of them.

The other major enhancement is the addition of two control desks. They emulate the controls which have been used for the real telescope. Instead of having to type textual commands to control the model, one can click on buttons and switches to make the telescope operate. These days, the Hale Telescope is primarily controlled from a computer, but I think that simulating its old fashioned controls is more fun.

More to follow -- maybe even a picture or two!