F.A.Q.

Answers are the opinions of the person attributed.



So; Why is 'it' taking forever? (not really the zen telescope project)

Chassing the parabola:

Rick

The short story is this. A few years back (that long ago), we over corrected the mirror, and so brought the mirror back to spherical. None of us have ever worked on a mirror of such short focal ratio (f2.8). Sense that time, we have been slowly bringing the mirror back to parabolic. Classic (amateur) technique for "correcting" the sphere is to deepen the center of the mirror. After correcting the center 80% of the mirror, the edge has turn out to be turned up. While working on the edge, we have a tendency to "raise" the center. (chasing the parabola). i.e. fixing one part of the mirror, "screws-up" other parts of the glass, (it is like squeezing a water balloon). So having said this; We believe that we are converging on our desired parabola. Then we can work on the mirror cell and tube!

Well, the best I can say is the following: Dan

Imagine that you are the manager of a project that takes several people to execute. You know how many people you have. You know that they will be there 40 hours a week. You have a pretty good idea how much work there is to do. And, you know how to go about doing it. Now, estimate how much time it will take.

Sounds pretty easy, doesn't it? Well, those who have tried this know that its harder than it looks.

Now, imagine that you no longer manage the project. You can't really tell your people what to do. The best you can do is lead them by example. You don't know how many people you have to do the job. You don't know when they will show up. When they DO show up, it is only on Saturday. And, only one or two Saturdays a month. While you know what the final result is supposed to look like, none of you have ever done this particular project before. (Or, at least, not on this scale.) And, when the time comes, I'm sure there will be an argument about whether we're done or not. Now, estimate how long it will take to finish.

That is, more or less, explains the problem. Actually, it explains both why it is taking so long and why we can't accurately say when it will be finished.

But, I have lately been reading about the making of the 200" telescope at Mt Palomar and have found out that they had it as bad or worse than we do. At least, WE haven't been interrupted for 3 years by a war.

Well, not yet anyway.

Dan Zuras

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When will the LAT be finished?

We don't really know. We hope to finish the primary mirror in 2002. If the steel work takes about a year, and about a year is spent negotiating for a site, and the observatory building takes about a year, and we go to first light as a Newtonian, then we will be looking at stars around the year 2014. Uncertainties in the scheduling of volunteer projects might change that by a year or more either way. Problems in funding when the observatory is being built could push it out some.

Dan Zuras

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Where will we put it?

The bylaws say we must put it "within 4 hours driving time" of Cupertino. Unless you're driving REAL fast, that puts it in Northern California. While we have looked at 6 or 8 sites over the years, there are 3 that are currently viable. They are (in no particular order) :

  1. Chews Ridge. The membership has expressed a preference for a dark sky site and Chews Ridge certainly qualifies. MIRA already has a couple of smaller instruments there. On the other hand, like almost any dark sky site, it is undeveloped. That means problems with roads & power.
  2. Mount Hamilton. People at Lick and in the UC Santa Cruz optical group have expressed an interest in having us there. Advantages: good roads; power; water; sewage; a machine shop on site; and hot & cold running astronomers. Disadvantages: dealing with the Regents of UC; overlooking a large city (San Jose).
  3. Mount Wilson. (This falls into the driving real fast category.) Sallie Baliunas of the Mount Wilson Institute has expressed an interest in us. Advantages & disadvantages are the same as with Mount Hamilton but with a longer driving time and without the Regents getting involved.

Wherever we put it, we will be the 4th largest instrument in California (behind the 200" at Mount Palomar, the 120" at Mount Hamilton, and the 100" at Mount Wilson). This suggests that any observatory would want us around. We'll see, I guess.

Dan Zuras

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Glass type

Corning Pyrex(R) brand code 7740.
This type glass was used for all large mirrors in the U.S.A. in the 1930s.

Rick Powell (letter from Frank Fehlner)

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How big is this thing anyway?

About 7 ft. wide and when the telescope is pointed straight up, it is about 25 ft. tall.

Rick Powell

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Who is it for?

It's for anyone who has ever wanted to look at the sky through a REALLY good telescope but didn't have access to one.

It's for the bright high school student who wants to do a survey of Northern hemisphere Cepheids for her science fair project.

It's for the experienced amateur who wants to try to do an AUTOMATED Messier tour in a single night.

It's for the wheelchair bound kid in LA who can't make it to the top of a mountain, much less to the eyepiece of a telescope.

It's for the taxi driver in New York city who wants to discover a comet so he can name it after himself.

It's for the teenager in Denver who wants to discover an an asteroid so he can name it after his girl.

It's for the girl in Dallas who wants to see if Mars really IS the angry red planet.

It's for the boy in Rome who wants to see if Venus really IS the goddess of love.

It's for the kid in Seattle who can't see Saturn because of the clouds but can access the LAT over the Internet because he is used to thinking of EVERYTHING as a video game.

It's for the little old man in Boca Raton who knows what's happening in M57 but has never seen it for himself.

It's for the father in San Jose who wants to hold his daughter up to the eyepiece and hear her go, "OOoohh!"

It's for you.

It's for me.

It's for your kids.

It's for their kids.

It's for your parents.

It's for their parents.

It's for the future. Because the only way to discover it is to make it.

Dan Zuras
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    The LAT; Who is it for?

    1. Public Access:

      Via the web. Similar to the

    Bradford robotic telescope. This probably will be the greatest time slot. (telescope tasking)

  2. Public Access:

    Direct viewing. Perhaps one or two nights a week; All yearround!

  3. Group 70 projects:

    Of coarse, some time will be reserved for the members; Determined by the Board of Directors. A guess, up to 25%.

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PRIMARY MIRROR

The 1.8M f2.8 LAT Mirror is estimated to weigh 2420 lbs. ***(+/- 128 lbs.)
For more mirror information see mirror mass.

Rick Powell

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Altitude/Azimuth telescope mount

The Altitude/Azimuth mount, looks very much like a naval turret gun

The "Alt-AZ" mounting has some important advantages over the equatorial mounting. Most (all) large modern telescopes use the alt-az system.

All in all, for all the seemingly short-comings. The alt-az is a practical price/performance solution. Solution to the Alt-az to equatorial motion are well known. Computers (needed for image processing, telescope control and tasking) are now relatively inexpensive.

Rick Powell

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Secondary and tertiary mirrors

For the sort of Cassegrain we are making, f3 primary to f10 at the Naismith, the secondary should ideally be 22" in diameter. This is the best compromise between field of view and vignetting of the secondary.

The blank we have is actually 24" in diameter. But, it is a honeycomb laminate made of quartz that weighs only 85 pounds and is otherwise perfect for our needs. So, unless we can get better blank, we will probably just live with a little vignetting.

When we completely finish the primary, we will use its final figure to determine the figure of the secondary.

It is planned that we will then have the secondary turned on a diamond lathe to get its rough figure and then polish to its final figure.

Testing it is another issue. We will need a Hindle sphere at least 5 feet in diameter. Or, if the tube assembly is done at the time, we could test it by pointing the telescope at Polaris on a clear night. We'll see.

Tertiary:

The tertiary will need to be an elliptical flat at least 10" by 14" (or more, depending on the desired field of view).

We haven't thought much about this yet. Any suggestions?

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(If we use the 24in. secondary, where should it be placed)

Well, we could move it in, change the shape and call it f9.

But, why not do that? Well, we could. Maybe we will. But, as I understand it, if you reduce the number of variables in the system to one (the diameter of the secondary) and you adjust its position & curvature so as to leave the position of the focal plane fixed, that this one-dimensional system has two ends. At one end, you have small mirrors of high curvature near the primary focus producing high f# images of small field of view with little blockage by the secondary. At the other end, you have big mirrors of low curvature far from the primary focus producing low f# images of large field of view with a great deal of blockage by the secondary.

Somewhere in the middle are compromises. One of the compromises is to increase the size of the secondary until the field of view just starts to be vignetted near its edges by the shadow of the secondary. As I understand it, that happens for us at 22".

So, if we design the system for a 24" secondary we will have a little larger secondary with a little lower curvature that is placed a little farther from the primary focus which would SEEM to produce a little larger field of view with a little more light blocked by the secondary.

But, because we have passed the sweet spot in that 1-D system described above, we ACTUALLY have a little SMALLER field of view due to the fact that the secondary is vignetting it near the edges.

Now, suppose we design the system for a 22" secondary but replace the 22" secondary with a 24" secondary but with the same curvature as the 22" would have had. What does that do to the system? I believe it blocks just as much light as before but the field of view is reduced slightly less due to the longer focal length.

I suppose we could look at the last two systems as two ends of a somewhat smaller 1-D system and ask the question where in this system is the ACTUAL field of view largest? The answer might be somewhere in between.

Dan Zuras

There is a secondary concern; As the sencondary get larger (and moves in on the primary) the tertiary mirror also must be larger.

Rick Powell

LAT SUPPORT

The LAT project is supported by public donations and membership in Group70 Inc. For further information, please write.

for now please use our "backup" email address for more information.
group70.telescope.project@gmail.com

This web page marked up by

Rick Powell