Transcript Solar orbiter – EUS instrument mechanical design

Solar orbiter – EUS instrument mechanical design
Tim Froud and Doug Griffin
Talk outline
• Mechanical-thermal-optical considerations for the Primary Mirror
• Silicon Carbide Testbed Study
• Structural layout
Primary mirror WFE under Solar IR Loads
•
The Solar radiation load will introduce thermal gradients in the Primary Mirror
– Thermal stresses
• Internal mirror temperature gradients
• Possibly also from CTE mismatches
•
The thermal load will vary by roughly an order of magnitude during each orbit
•
Goal is to meet the optical performance during the encounter and during down
link phases of the orbit
•
Mirror distortions will introduce distortions in the surface of the mirror which will
reduce the spectral and spatial resolution of the instrument
Primary Mirror WFE Tolerance Estimates
RMS Irregularity
l/X @ 633nm
(in waves at test
wavelength)
0.5
0.2
0.1
0.05
0.0333
0.025
•
•
RMS
Irregularity
Approx PTV
Irreg
Change in RMS
Spot Size
(with mirror
irregularity)
Total spot
size
448 nm
179 nm
90 nm
45 nm
30 nm
22 nm
67.0 um
23.0 um
8.9 um
3.2 um
1.7 um
1.1 um
74.6 um
30.6 um
16.5 um
10.8 um
9.3 um
8.7 um
(in nm)
X= 2
X= 5
X = 10
X = 20
X = 30
X = 40
317 nm
127 nm
63 nm
32 nm
21 nm
16 nm
Calculation based on encircled energy and are to be considered provisional
Given the Spectral and Spatial resolution requirements:
– Derived requirement on PSF ~ 10um:
• Mirror rms WFE: ~l/30 i.e. 21nm rms
NI Primary Mirror Distortion Estimates
Model Geometry
Uniform heat load B/C
35kW/m2
5mm
Fixed
Temperature
B/C
10mm
25mm
40mm
5mm
5mm
Axis of symmetry
NI Primary Mirror Distortion Estimates
Material Assumptions
•
•
Assume that the mirror is made from homogeneous Silicon Carbide
– E=249GPa
– Poission ratio: 0.16
– CTE: 2.7x10-6 m/m
– Thermal conductivity: 127 W/m/K
– Mirror is absorbing in the IR
Thermal interfaces have identical mechanical properties as Mirror
– No interface stresses
NI Primary Mirror Distortion Estimates
Temperature Distribution
Temperature
T (K)
NI Primary Mirror Distortion Estimates
Thermal distortions
Axial displacement
0
0
5
10
15
20
25
-100
Displacement (nm)
-200
-300
-400
-500
-600
-700
-800
Distance from C/L (mm)
30
35
40
45
NI Primary Mirror Distortion Estimates
Conclusions
•
•
The analysis has to be considered as a preliminary estimate
– Optical
– Thermal
– Mechanical
– Layout
Nonetheless: The conclusion is that the thermal control of the Primary
Mirror will have to be considered in tandem with the overall instrument
optical performance
– It could be one of the largest challenges for the instrument design
– Rastering of the instrument via the Primary mirror could be very difficult
with the complexity of the thermal control
Primary Structure Material Selection
Test Bed Study
A study was carried out on a SiC based
Optical Bench
– Looked at the practical details of
designing structural components in SiC
– Very useful in terms of understanding:
• Detailed manufacturing processes
• Achievable tolerances
• Mounting and interface designs
• Lightweighting
• Non-destructive Testing
– Procurement of test-bed did not
proceed due to cost
– Promising outcome for Flight-build
Primary Structure Material Selection
Test Bed Study
Components of system
Components of system
Optical bench
Primary mirror
Slit mechanism
Grating
Detectors and electronics
Enclosure and baffling