Millennium Telescope

Meeting 2

Requirements and Design Goals

Requirements...

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.

Mirror

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

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.

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.

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.

Open Structure

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

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?

Stiffness

Minimise flexure with rigid structures.

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.

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.

Optical System

Mechanical assembly must be repeatable such that telescope is approximately pre-aligned.

Telescope must be capable of easy remote-site fine-alignment.

Baffling

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

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.

Economy of Materials

Minimise costs by keeping material weight down.

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 AS14” F/4.5 Dobsonian

Jim Brace, Wadhurst AS18” F/5 Dobsonian

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

Wadhurst AS, Norfolk

Other Designs…Alternative materials

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

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

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

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

Jaques Civetta, France465mm Dobsonian, fibreglass construction

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

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