Abstract

A configuration applicable to large astronomical telescopes has been developed specifically for lightweight monolithic mirrors in which the primary mirror is located on the same side of the declination axis as the secondary, placing the cassegrain focus very close to the declination axis. This configuration permits both a large instrument space and a single south polar tyne, resulting in a doubly asymmetric system. It is also shown that a passive closed-system air flotation support system can be used for both lateral and back support of the primary mirror, as contrasted to more complex active systems currently in widespread use.

© 1971 Optical Society of America

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Figures (6)

Fig. 1
Fig. 1

General diagram of a 1.8-m telescope utilizing a lightweight mirror. Note that the declination, right ascension, and optical axes do not coincide but are offset to maximize convenience of use by the astronomer.

Fig. 2
Fig. 2

Diagram of a typical lateral support point. Bags are collapsed during insertion into mirror cavities, inflated to +2 atm to seat bags and to adjust for alignment errors, then reduced to atmospheric pressure by slow bleeding prior to sealing the system.

Fig. 3
Fig. 3

Schematic diagram showing interconnection of equalizing air capillaries for mirror edge loads in the +Y and −Y directions. A similar pair of independent systems is required in the +X and −X directions.

Fig. 4
Fig. 4

Layout of back support and edge support pad locations for a 10-cm cell spacing ULE silica mirror, single row support. Pad numbers refer to interconnected back support pads.

Fig. 5
Fig. 5

Layout of double-row back support and edge support pad locations for a 10-cm cell spacing ULE silica mirror. Pad numbers refer to interconnected back support pads.

Fig. 6
Fig. 6

Diagram of a typical cell showing deformations due to lateral support pressure. Front plate slope deformation is 0.047 sec of arc; AB = 20 cm, BC = 10 cm, ribs = 0.65 cm, and plate 2.5 cm.

Tables (1)

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Table I Weight Distributions for Comparative 1.8-m Telescopes.a

Equations (6)

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Δ f = - W d cos z A M 2 1.013 kg / cm 2 + ( W cos z / A ) Δ f = - M 2 d ( 1.013 A / W cos z ) + 1 ,
Δ s = d ( 1.013 A / W sin z ) + 1 ,
Δ f = M 2 d ( Δ T / T ) .
Δ f = 6.2 μ m to 31 μ m ,
Δ f = M 2 S ( δ s - δ m ) Δ T , Δ f = 586 μ m ,
Δ f = ± W cos z N ( Δ r Δ R ) = ± 1.6 kg .

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