Millennium Telescope Meeting 2 Requirements and Design Goals

Requirements...

Portability 4 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.

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

Height 4 Primarily fixed by mirror focal length and diameter- otherwise the lower the better, minimises the climb up a ladder. Will be approx 7 feet.

Footprint 4 The disassembled telescope should fit into a hatchback- e.g. Golf or Focus. 4 Must be easily stored at OASI e.g. in storage area at bottom of dome steps.

Weight 4 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.

Open Structure 4 Avoids fans and promotes rapid cooling of the primary. Less prone to wind vibration. Minimises weight.

Struts/Truss-Tubes 4 Short enough to fit into a hatchback; look into multi-section struts; struts cannot exceed a certain length (subject to design). 4 Can we use 6 struts rather than 8; this simplifies telescope balance and reduces weight?

Stiffness 4 Minimise flexure with rigid structures.

Rocker/Mirror Box 4 Rocker may be more elegant, simpler to make and achieve weight targets - but design is more speculative. 4 Mirror box is proven design but much heavier- and may not meet design requirements.

Secondary Cage 4 Keep as light as possible- consistent with mechanical rigidity. 4 Design should consider (optically) best available eyepieces- probably 2". 4 Secondary mirror pre-alignment should be designed-in. 4 Design needs to be safe for transportation.

Optical System 4 Mechanical assembly must be repeatable such that telescope is approximately pre- aligned. 4 Telescope must be capable of easy remote- site fine-alignment.

Baffling 4 Upper cage and primary mirror baffles need to be de-mountable and easily installed.

Drive System 4 Although initially envisioned to be manually tracking, it would be highly desirable to be capable of upgrading to automatic tracking, at a later date.

Economy of Materials 4 Minimise costs by keeping material weight down. 4 Use plywood + steel where possible and standard components if available.

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.

FAS Website Trawl...

John Cross, Bristol AS 14” F/4.5 Dobsonian

Jim Brace, Wadhurst AS 18” F/5 Dobsonian

Gary Poyner, Heart of Eng AS 18” F/4.4 Dobsonian

Wadhurst AS, Norfolk

Other Designs… Alternative materials

Gary Wolanski, USA 16” F/5 Dobsonian, 40 Pound, all-metal construction

Charlie Wicks, USA 20” F/4.5 Dobsonian - all-metal construction

Jaques Civetta, France 465mm Dobsonian, fibreglass construction

Doug Tanaka, USA 12.5” F/6 String-Truss Dobsonian

Michael Koch, Germany 8” F/4 “Folding Ruler” Airline Travel Scope