Inexpensive mount for a large millimeter-wavelength telescope

S. Padin

doi:10.1364/AO.53.004431

Inexpensive mount for a large millimeter-wavelength telescope

S. Padin

Applied Optics
Vol. 53,
Issue 20,
pp. 4431-4439
(2014)
•https://doi.org/10.1364/AO.53.004431

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S. Padin, "Inexpensive mount for a large millimeter-wavelength telescope," Appl. Opt. 53, 4431-4439 (2014)

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Related Topics
Table of Contents Category
- Imaging Systems
Optics & Photonics Topics
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The topics in this list come from the OSA Optics and Photonics Topics applied to this article.
Previously assigned OCIS codes
- Telescopes (110.6770)
- Optomechanics (220.4880)
- Astronomical optics (350.1260)

About this Article
History
- Original Manuscript: April 3, 2014
- Revised Manuscript: May 27, 2014
- Manuscript Accepted: May 30, 2014
- Published: July 4, 2014

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Abstract

A telescope mount with a single-point force support at the center of gravity of the primary mirror is proposed in order to eliminate much of the structure and cost of a large, millimeter-wavelength telescope. The single-point support gives repeatable thermal and gravitational deformation, so the surface of the primary can be controlled based on lookup tables for elevation and temperature. The new design is most appropriate for a survey telescope because locating the support above the vertex of the primary limits the range of motion of the mount to about 1 rad. A 30 m diameter, $λ = 850 μm$ telescope with the proposed mount is a factor of 4 lighter than a design with a conventional elevation-over-azimuth mount, and roughly half the cost.

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Parameter	Value	Units
Primary diameter	30	m
Primary focal ratio	0.4
Primary conic constant	$- 1.071172$
Primary to secondary separation	10.56	m
Secondary radius of curvature	4.235	m
Secondary conic constant	$- 5.608707$
Secondary diameter	4.893	m
Secondary to image separation	4.5	m
Image focal ratio	1.25
Image radius of curvature	1.6	m

Component	Description	Material
Panel	30 kg point mass at each truss surface node ( $1 m^{2}$ panel at $10 {kgm}^{- 2}$ + $3 \times 1.5 kg$ actuators + 10 kg actuator frame + 5 kg hardware)
Truss top layer	25 mm OD × 2 mm wall, 1 kg point mass at each node	Steel
Truss 2nd layer	100 mm OD × 10 mm wall, 20 kg point mass at each node	Steel
Truss 3rd layer	300 mm OD × 25 mm wall, 160 kg point mass at each node	Steel
Secondary	1/3 t point mass at three top-end nodes, 1 t total ( $25 m^{2}$ tiles at $10 {kgm}^{- 2}$ + 400 kg subframe + 300 kg hexapod + 50 kg hardware)
Secondary support	150 mm OD × 7.5 mm wall	CFRP
Instrument	3 t point mass 1.5 m above force support
Jack	300 mm OD × 100 mm ID	Steel
Universal joint	1 t point mass at each end of jack
Force support	1028 kN vertical at primary COG
Fixed support	Ground end of universal joint at bottom of jack
$10 {ms}^{- 1}$ wind	50 N at each truss surface node + 500 N at each of three top-end nodes

Property	Units	Steel	CFRP
Density	$kg m^{- 3}$	7850	1550
Young’s modulus	GPa	210	290
CTE	$ppm K^{- 1}$	12	$- 1$
Poisson’s ratio		0.3	0.3

Component	Mass (t)
Panels and actuators	25
Truss	76
Secondary	1
Instrument	3
Jacks	15
Universal joints	12
Jack counterweights	63
Total	195

Subsystem	Cost $M	Component	Cost $M	Basis
Primary	11.1
		Panels	7.0	$700 m^{2}$ machined aluminum at $ $10 k / m^{2}$
		Actuators	1.1	2100 (3 per panel) at $500 each
		Truss	1.5	76 t steel at $20/kg
		Secondary support	0.5	1 t CFRP at $200/kg + $300 k for hexapod
		Secondary mirror	1.0	Machined aluminum panels on CFRP subframe
EL-over-AZ mount	17.4
		Steel structure	14	700 t steel at $20/kg
		Drives and bearings	2.5	3 bearings at $500 k each + 2 drives at $500 k each
		Pier	0.9	$300 m^{3}$ concrete at $ $3 k / m^{3}$
New mount	4.1
		Jacks and drives	0.6	6 at $100 k each
		Jack counterweights	1.3	63 t steel at $20/kg
		Universal joints	1.2	12 at $100 k each
		Spherical rotary joint	0.5	$250 k joint + 3 hydraulic cylinders at $50 k each
		Pier	0.5	$150 m^{3}$ concrete at $ $3 k / m^{3}$
Design	2.0			10 person-years, same for new and EL-over-AZ mounts

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