sg3

Telescope Specifications

1.) Dobsonian

2.) Truss-type construction

3.) f/5, 17.5" main mirror, temperature controlled

4.) 3.1" secondary mirror, temperature controlled

5.) 4.5" reflector telescope as finder

6.) Crayford focuser

Design Issues

Baseball's Yogi Berra said it best- "It's deja vu all over again." The Stargate-2 is nearly done, but already it is apparent that things could be better. Design flaws, such as with the rocker became apparent when I put things together. I started out designing a mirror box that would be extremely rigid and fit into my Jeep. Oh, I got that, all right. I also got a mirror box nearly strong enough to support my Jeep (althought it is still lighter than its predecessor). After some study, I think that I can trim ten pounds off the mirror box. Plus, since the mirror box is so shallow, there seems no benefit for a full-height secondary cage. And I have also come up with better ways of doing the same thing- such as an improved controller and an idea for a no-pump mirror cooler. In short, a top-down redesign. With that, below are the original design objectives, plus new ones:

1.) Rich-field telescope

2.) Easy to transport and set up by one person

3.) Quick assembly and disassembly

4.) Light, and compact when disassembled

5.) The entire telescope- including the ground board- will be made from welded aluminum.

6.) The unassembled telescope (excluding truss tubes) will be able to fit stacked into my Jeep.

7.) The mirror box will be smaller, and the weight should not exceed 85 pounds.

8.) The mirror box design will be simpler to allow for faster assembly.

9.) The secondary cage will be smaller, allowing the reflector finderscope to be clamped on top during travel.

10.) Develop a mirror cooler without the need for water cooling.

11.) Improve the design of the controller.

12.) The light shield will be part of the mirror box design, not an afterthought.

Mirror Box

The main goal of this new mirror box is to make it lighter and more compact. It has been reduced in length and width by 1/2", and 1-1/2" in height. Plus it will be made of thinner components, where possible. Best analysis says it will be 10 pounds lighter, and should weigh in near 14.4 pounds. Also, a light shield of 0.04" aluminum sheet will be added to cover exposed areas on the front, back and sides.

While the Stargate-3 did not meet my goals as far as portability, it works well despite the flaws. For example, there is no sling for the mirror. My attempt at a rear-adjust bolt did not work, so I simply padded the mirror stoppers with rubber. Everything that I learned on this telescope is being plowed into the mini-Stargate. The painted scale worked well. Too well, in fact. I had to mount a pushbutton on the secondary cage to keep the glare from clouding the view (since there is no scope shroud). At IDSSP 2008, I tested a cloud detector that I found online while looking for a commercial product. It worked beyond my hopes. Imagine being the only person at a star party hoping for clouds (well, only a few)! I will incorporate this in the control for the mini-Stargate as part of a sky quality detector. If successful, it will be part of the controller for the Stargate-3.

In order for the Stargate-3 to fit into my Jeep Liberty, I needed to modify it. I cut 1-1/2" off of the secondary cage, and welded 1-1/2" spacers (shown above) onto the mirror box. And this worked! Before, I would have had to wrestle getting the secondary cage in through the passenger door. As an added benefit, the secondary cage is a half pound lighter (although I can't feel the difference).