1. Feasibilty/Concept Study Mid Term Status Review
M2 & M3
T.A. Sebring
13,14 July 2005
Feasibilty/Concept Study Mid Term Status Review

2. M2 and M3 Are Too Large To Make Monolithic
Make in Segments
Dimensions Approximate PM Segments
Can Use Same Panel & Process
Bond Together?
SiC Brazed by Boostec (FR) for Herschel
Epoxy Bonding for CFRP
Expensive…Risky?
Metrology?
Mount as Segments?
Require Stable Back Structure
Increased Mass & Complexity
Active or Passive?
1.6m
2.26m
3.2m
1.3m
1.9m
2.6m

3. Feasibilty/Concept Study Mid Term Status Review
M2 is 3.2 meters in diameter
Formed from 4 10kg/m2
Panels Maintain Figure over Full Gravity Range Mounted on 3 Points
Manufacturing Process Identical to Primary Mirror Panels
13,14 July 2005
Feasibilty/Concept Study Mid Term Status Review

4. Notional Panel Mounting Locations
Anticipate Bipod Flexures at Each Point
Panels Will Have Mounting Features

5. First Layer of Support Truss
CFRP with Bonded Invar or CFRP Joints

6. Upper Support Truss Interface to M2 Positioning Hexapod
Superimposed on First Truss Layer

7. Notional Illustration of Truss Top View

8. Side View Shows Truss Top Layer, Bottom Layer, Notional Struts
Red Boxes are Voicecoil Actuators with Internal Position Sensors

9. Mirror Mounts to Nutator Assembly
M2 Support
Nutator Assembly
Mirror Mounts to Nutator Assembly
Rigid Body Positioning of M2/Nutator Assembly Via Hexapod
Entire Assembly Weighs ~ 270 kg
80 kg Mirror, 40 kg Truss, 100 kg Nutator, 50 kg Hexapod

10. M2/M3 Mechanisms M2 Nutator M2 Hexapod
S. Radford Designed Nutator for ALMA
Probably Scaleable to Some Performance Level
Increases Mass at M2
M2 Hexapod
ALMA Hexapod
Custom Designed/Built by Polytec PI
Polytec PI Will Provide Concept Design and Cost for CCAT

11. M3 Fabrication May Be Possible to Manufacture as Monolith
Plano Figure Implies That Any Flat > 2.6 m in Diameter Could Serve as Mandrel
GrEp Mirror Formed on Mandrel Seems Acceptable
Flexure Mounting to Rotation Turret
Had Considered Fast Tip/Tilt Mount for M3
If Mount Has Unacceptable Residual Jitter
Use High Bandwidth Guider for Input
Large Aperture Should Average Atmospheric Effects in IR
Inertial Sensors Possible but Expensive to Sufficient Resolution
Resolution: Don’t Do It Unless Necessary

12. M3 Rotator & Tip/Tilt? SOAR M3 Turret Tip/Tilt
0.18 arc sec repeatability
DC Torque Motor
Large Instrument Bearings
Inductosyn Encoder
Should Be Scaleable
Requires Attention to Detail
Tip/Tilt
Not Currently Part of Baseline
Will Be Expensive and Difficult
Need to Characterize Requirements
Complex and Challenging System

13. Remaining Work for This Phase
Find Possible Vendors
Develop Baseline Cost Estimate
Assess Maturity of Constituent Technologies
Investigate Approach to Calibration Alignment of M2/M3 Segments
CMM Setup
Use of Telescope Calibration WFS
Identify Critical Risk Elements and Associated Approaches to Mitigation