Transcript Sample Introductory Slide - Daniel K. Inouye Solar Telescope

M2 Assembly
and Feed Optics
Ron Price
August 25, 2003
M2 Assembly Functional
Requirements
• 60 cm diameter concave reflective optical surface.
• M2 surface figure quality 32 nm rms after active optics
correction
• Six degree of freedom positioning of M2
• Fast tip-tilt motion of M2
• Operating Conditions:
– Gravity Orientations - zenith angle of 0° to 80°
– Thermal Conditions – solar load and diurnal temp
– Wind Loading – wind speeds up to 10 m/sec
• Interfaces:
–
–
–
–
Optical Support Structure (OSS) of the telescope
Secondary Mirror Lifter
Telescope Control System
Utility Service
M2 Assembly Critical Areas
• Several areas were identified early as exhibiting
somewhat higher risk. Consequently, more time
and effort has been directed into these areas to
resolve the issues as much as possible.
– Surface figure change and thermal control of M2 due
to solar loading and diurnal temperature changes
– Print-thru of substrate structure due to solar loading
– Manufacturability of SiC substrate
M2 Assembly
Major Components
Hexapod Support
Tip-Tilt Mechanism
Area for
thermal control
Flexure Mounts
M2
M2 Blank
• Configuration:
– Diameter: 62 cm
nominal
– Thickness:
• Central area: 75 mm
• Edges: taper to 30 mm
– Lightweighted structure
– triangular pockets
with 5mm face sheet
and rib thickness
M2 Environment Drives Blank
Requirements
• Thermal Environment
– Print-thru of the ribbed structured onto the optical
surface due to solar load
– Surface figure change due to solar load, diurnal
temperature change and thermal control
– Desire to have optical surface of M2 track ambient
temperature
• Mechanical Environment
– Surface figure change due to changing gravity vector
– Surface figure change due to fast tip-tilt motion
Comparison of M2 Candidate
Materials
ULE
Zerodur
Beryllium
SiC
ρ
gm/cm³
E
10¹º
N/m²
k
W/m/K
c
J/kg/K
ν
-
α
ppm/K
Ek/α
k/ρ/c
E/ρ
2.21
2.53
1.85
3.10
6.76
9.06
30.40
46.60
1.31
1.65
220.00
200
767
812
1820
700
.170
.120
.025
.280
.03
.05
11.20
2.40
295.6
124.5
597.1
3883.3
.79
.80
65.00
89.00
30.6
35.8
164.3
150.3
Ek/α is a measure of resistance to bending due to thermal transients
k/ρ/c is called thermal diffusivity
E/ρ is referred to as specific stiffness
ρ – density
E - Elastic modulus
k - thermal conductivity
c – specific heat
ν – Poisson’s ratio
α – thermal expansion coefficient
M2 Thermal & Mechanical
Analysis
• Thermal analysis of M2 is being performed to:
– Quantify the level of rib structure print-thru on optical
surface due to thermal gradients caused by solar
loading
– Evaluate the baseline cooling methods for their ability
to control M2 surface temperature under solar loading
and track diurnal temperature changes
– Evaluate global surface figure changes
• Baseline cooling uses ambient temp air jets into
pockets on back of M2
M2 Analysis – Finite Element
Model
M2 Thermal & Mechanical
Analysis - Preliminary Results
• Print-thru – less than 10 nm with SiC or Zerodur
• Tracking of ambient air temperature – within 0.9 to 1.3
deg C for SiC depending on cooling flow rates
24
22
Temperature (C)
20
18
16
Mirror Bulk Average Temperature
Ambient Temperature
14
12
10
0
2
4
6
Time (Hours)
8
10
12
SiC M2 Thermal Profile-no air
jet under flexure
M2 temperature profile for SiC substrate during peak
solar load - 0.14 C range; 0.9 C above ambient
SiC M2 Surface Profile –no air
jet under flexure
Global figure change for SiC substrate during
peak solar load - 680 nm P-V
SiC M2 Surface Profile –
uniform air jet cooling
Global figure change for SiC substrate during
peak solar load - 40 nm P-V
M2 Substrate Material
• Although other materials have excellent
performance in specific areas, silicon carbide
appears to have the best overall performance in
all of the required areas
• Further analysis will be performed, including
dynamic performance under tip-tilt conditions, to
confirm silicon carbide as the best substrate
material
• Demonstrated capability by several vendors in
silicon carbide at the 65 cm scale
SiC Fabrication Methods
• CVD (Chemical Vapor Deposition) - Gaseous chemicals react on a
heated surface (usually graphite mandrel) to form solid SiC.
• Reaction Bonded SiC - SiC slurry is poured into a mold, freeze dried,
sintered to form a porous SiC structure, then subjected to a high
temperature process that introduces silicon and results in high
density.
• Direct Sintered SiC- Very small SiC particles are Cold Isostatically
Pressed into shape, machined, then sintered at 2500 deg C.
• Hot Pressed SiC - Very small SiC particles are Hot Isostatically
Pressed (HIgh temp and Pressure) into shape.
• C/SiC - Carbon felt made of short randomly oriented carbon fibers is
machined to shape. This “green body” is heated in a vacuum and
infiltrated with liquid silicon; this results in a silicon carbide matrix.
M2 Blank Status
• Currently evaluating vendors and processes for
SiC substrates
–
–
–
–
Boostec (CoorsTek USA) - Direct Sintered SiC
ECM (GE Power System Composites USA) - C/Sic
POCO Graphite - Reaction Bonded
Xinetics - Reaction Bonded
• Obtaining material properties and ROM cost and
schedule estimates
M2 Polishing Specifications
• Surface Parameters
–
–
–
–
Surface Shape:
Conic Constant:
Radius of Curvature:
Surface Roughness:
Off-axis Ellipsoid
K= -0.53936
-2,081.259
20 A rms or better
• Preliminary specifications are being developed
that meet the error budget allocation for surface
figure yet allow large spatial frequency errors
correctible by the active optics system
M2 Support System
Functional Requirements
• Functional Requirements
– Mirror Support - Support M2 weight
and minimize surface figure changes
over operational zenith angles
– Mirror Defining - Control the position
and orientation of M2
– Provide fast tip-tilt motion
• Configuration
– Commercial hexapod to provide
basic positioning motion
– Custom Tip-Tilt mechanism will
mount on hexapod to provide fast
image motion compensation
– M2 will attach to tip-tilt mechanism
kinematically via three flexures
M2 Support System
Performance Requirements
• Performance Requirements
– Positioning
• Six degrees of freedom – 1 micron accuracy
• Range of motion: 5 to 10 mm
– Tip-Tilt
• Amplitude: 10 arc seconds
• Rate: 10 hz; goal of 25 hz
Safety Restraint System
• Requirement - the M2 Restraint System provides
protection of the primary mirror in the event of
shock and vibration due to seismic activity.
• Configuration: safety restraints between rear of
M2 structure and tip-tilt mechanism
M2 Control System
Functional Requirements:
• Control M2 positioning system
• Control M2 thermal management system
• Control M2 fast tip-tilt system
• Interface to AOCS
• Interface to TCS
Feed Optics
From M2
M4
M6
M3
M5
To coude
Feed Optics
• M3 Flat Fold
– 12 cm
– Heat Load: 27.2 watts
• M4 Concave Ellipsoid
– 34 cm
– Heat Load: 24.5 watts
• M5 - Deformable Mirror
Device
– 33 cm
– Heat Load: 22.1 watts
• M6 Flat Fold
– 26 cm
– Heat Load: 19.9 watts
M2 Thermal and
Mechanical
Analysis will be
extended to Feed
Optics to
determine
optimum
substrate and
configuration for
each optic