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Portable Dobsonian Telescope Design Requirements and Goals

This document outlines the critical design goals for a portable Dobsonian telescope, emphasizing portability, mirror support, height, weight, and assembly considerations. It details the requirements for the mirror, structure, drive system, and economy of materials and machining. The design aims for easy transportation, setup, and alignment while maintaining optical performance and mechanical rigidity.

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Portable Dobsonian Telescope Design Requirements and Goals

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  1. Millennium Telescope Meeting 2 Requirements and Design Goals

  2. Requirements...

  3. Portability • The telescope unlikely to be used in dome or on balcony- so must be portable. This also implies it must be de-mountable and easily assembled.

  4. Mirror • The mirror spec is fixed; the cell must be designed to support the 'thin' 19" mirror without significantly degrading optical performance.

  5. Height • Primarily fixed by mirror focal length and diameter- otherwise the lower the better, minimises the climb up a ladder. Will be approx 7 feet.

  6. Footprint • The disassembled telescope should fit into a hatchback- e.g. Golf or Focus. • Must be easily stored at OASI e.g. in storage area at bottom of dome steps.

  7. Weight • All de-mounted components should be capable of unaided lifting and manoeuvring by two (unexceptional) persons; imposes an upper limit of about 60 pounds per component.

  8. Open Structure • Avoids fans and promotes rapid cooling of the primary. Less prone to wind vibration. Minimises weight.

  9. Struts/Truss-Tubes • Short enough to fit into a hatchback; look into multi-section struts; struts cannot exceed a certain length (subject to design). • Can we use 6 struts rather than 8; this simplifies telescope balance and reduces weight?

  10. Stiffness • Minimise flexure with rigid structures.

  11. Rocker/Mirror Box • Rocker may be more elegant, simpler to make and achieve weight targets - but design is more speculative. • Mirror box is proven design but much heavier- and may not meet design requirements.

  12. Secondary Cage • Keep as light as possible- consistent with mechanical rigidity. • Design should consider (optically) best available eyepieces- probably 2". • Secondary mirror pre-alignment should be designed-in. • Design needs to be safe for transportation.

  13. Optical System • Mechanical assembly must be repeatable such that telescope is approximately pre-aligned. • Telescope must be capable of easy remote-site fine-alignment.

  14. Baffling • Upper cage and primary mirror baffles need to be de-mountable and easily installed.

  15. Drive System • Although initially envisioned to be manually tracking, it would be highly desirable to be capable of upgrading to automatic tracking, at a later date.

  16. Economy of Materials • Minimise costs by keeping material weight down. • Use plywood + steel where possible and standard components if available.

  17. Economy of Machining • Design as many non-standard components as possible that can be produced "in-house". Consider use of plywood, for rocker or mirror box, etc; and Martin's metal working expertise for other components.

  18. FAS Website Trawl...

  19. John Cross, Bristol AS14” F/4.5 Dobsonian

  20. Jim Brace, Wadhurst AS18” F/5 Dobsonian

  21. Gary Poyner, Heart of Eng AS18” F/4.4 Dobsonian

  22. Wadhurst AS, Norfolk

  23. Other Designs…Alternative materials

  24. Gary Wolanski, USA16” F/5 Dobsonian, 40 Pound, all-metal construction

  25. Gary Wolanski, USA16” F/5 Dobsonian, 40 Pound, all-metal construction

  26. Gary Wolanski, USA16” F/5 Dobsonian, 40 Pound, all-metal construction

  27. Charlie Wicks, USA20” F/4.5 Dobsonian - all-metal construction

  28. Jaques Civetta, France465mm Dobsonian, fibreglass construction

  29. Doug Tanaka, USA12.5” F/6 String-Truss Dobsonian

  30. Michael Koch, Germany8” F/4 “Folding Ruler” Airline Travel Scope

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