Telescope - Mechanical
Albert Lin
The Aerospace Corporation
Mechanical Engineer
(310) 336-1023
albert.y.lin@aero.org
6/27/05
Cosmic RAy Telescope for the Effects of Radiation
Problem Statement
The CRATER Telescope must:
• Hold three pairs of thin-thick detectors
• Hold two samples of TEP
• Be configured to meet geometry for science mission
• Hold interface circuit boards
Subject to:
• Positive stress margin for all environments
• Minimum first fundamental frequency
• Weight constraints of overall instrument
Cosmic RAy Telescope for the Effects of Radiation
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Telescope Requirements
From Level 2 Mission Requirements Document 32-01205
Section
Requirement
3.1.1
Pairs of thin (approximately 150 micron) and thick (1000
micron) Si detectors
3.2.1
0.030” thick aluminum wall on both ends of the telescope
3.3.1
A-150 TEP of 27 mm and 54 mm in length
3.5.1
30 degree FOV zenith, 80 degree nadir
All requirements incorporated into model
Cosmic RAy Telescope for the Effects of Radiation
Telescope Geometry
All Requirements Met
• Pairs of thin (~150 micron) and
thick (~1000 micron) Si detectors
used
• 0.030” thick Aluminum on top
and bottom apertures
• A-150 TEP of 27 mm and 54 mm
in length
• 30 degree FOV Zenith
• 80 degree FOV Nadir
Cosmic RAy Telescope for the Effects of Radiation
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Cosmic RAy Telescope for the Effects of Radiation
Mechanical Requirements
•
•
From Environments, 431-RQMT-000012
All components must have positive stress margin with an appropriate factor of safety
used for the material analyzed
Requirement
Description
Levels
3.1.2
Net cg limit loads
•Superceded by Random Vibration
12 g
3.4.2
Sinusoidal Vibration Loads
•Superceded by Random Vibration
Frequency:
Protoflight/Qual:
Acceptance:
3.5
Acoustics
•Enclosed box without exposed thin
surfaces
OASPL Protoflight/Qual: 143.0 dB
OASPL Acceptance:
140.0 dB
3.6.1
Random Vibration
See next slide
4.2.1
Minimum Fundamental Frequency
Minimum > 35 Hz
Recommended > 50 Hz
Will not provide FEM model > 75 Hz
6.0
Cosmic RAy Telescope for the Effects of Radiation
5-100 Hz
8g
6.4g
Random Vibration
Random Vibration will drive most of the analysis
For resonances in the Random Vibration Spec, Miles’ Equation shows 3 sigma loading
on the order of 100-150 g
Random Vibration Spec
Frequency (Hz)
1
10
100
1000
10000
Protoflight/ Qual
1
Freq Protoflight/
(Hz) Qual
20
50
800
2000
0.026
0.16
0.16
0.026
Acceptance
0.013
0.08
0.08
0.013
0.1
0.01
Cosmic RAy Telescope for the Effects of Radiation
Acceptance
Power Spectral Density (g^2/Hz)
•
•
Stress Margins
•
•
Load levels are superceded by random vibration spec
Factors of Safety used for corresponding material (MEV 5.1)
– Metals:
1.25 Yield, 1.4 Ultimate
– Composite: 1.5 Ultimate
•
Margin of Safety = (Allowable Stress or Load)/(Applied Stress or Load x FS) – 1
Description
MS yield
MS ultimate
Bolt Interface Loading
+2,662
+5,615
Detector Boards
brittle
+18.6
Silicon Detector*
brittle
+31.5
TEP Clamp
+0.91
+1.21
All components have positive Margin of Safety
*Assumes an ideal 3-point mount, to be discussed later
Cosmic RAy Telescope for the Effects of Radiation
First Fundamental Frequency
•
•
First Fundamental Frequency at 1,410 Hz
Much greater than 75 Hz frequency where the FEM model will not need to be supplied
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Cosmic RAy Telescope for the Effects of Radiation
Design Overview
•
Telescope is assembled using card guides for the circuit
boards and screws for the TEP holders
Cosmic RAy Telescope for the Effects of Radiation
Overall Dimensions
•
Weight = 2.7 lbs
Cosmic RAy Telescope for the Effects of Radiation
How to Mount TEP
•
•
Limited Material Properties information on A-150 TEP
Need to mount TEP to account for
– Minimal deformation of material during assembly
– Allowance for thermal contraction
– 20 lbs preload to withstand random vibration
Springy Clamp
Cross Section
TEP
Solution: Oversized mounting hole to allow for radial thermal expansion
with a thin, springy clamp to hold in TEP.
With differential thermal contraction at -40°C, spring still pushes with 7.4 lbs force
Cosmic RAy Telescope for the Effects of Radiation
Mounting Detectors
•
•
Detectors mounted using three point mounts on circuit boards to minimize stress
caused by circuit board vibration
Further investigation needed for the effectiveness of the three point mount interface
Thin Detector
Wires strain relieved
away from mount to
minimize stress from
vibration
Thick Detector on
Underside
Cosmic RAy Telescope for the Effects of Radiation
Purging and Venting
Detector Mounts suspended
above circuit board allows
for gaps that equalize
pressure
Purge Inlet
Purge and
Vent Outlet
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•
•
•
A limitation to the current design is the uncertainty of the detector mounting scheme in
minimizing the effects of circuit board vibration
An alternative design is to clamp the detectors in a stiff structure and decouple it from
the circuit board using cables
The detectors are tested at the manufacturer in a similar configuration but there are
issues with using Rigiflex cables
?
Cosmic RAy Telescope for the Effects of Radiation
Telescope – Mechanical
Albert Lin
Cosmic RAy Telescope for the Effects of Radiation
Backup Slides
Cosmic RAy Telescope for the Effects of Radiation
Bolt Interface Loading
Inputs
Outputs
Normal Load
In-Plane Load X
In-Plane Load Y
In-Plane Load Offset
Tensile Yield
Tensile Ultimate
Shear Yield
0
421.88
0
1.2
617
943
370
lb
lb
lb
in
lb
lb
lb
Worst Case Bolt
Normal Load
Shear Load
Margin of Safety Yield
Margin of Safety Ult
Assuming worst-case loading at 1410 Hz
fundamental frequency
18
8.60 lb
17.58 lb
1,950
4,077
9.000
6.000
3 sigma load = 125 g
Worst
Case
Bolt
3.000
A286 CRES Bolts at Interface
Mechanical Engineering Design, by Shigley
0.000
-3.000
0.000
RP-1228 NASA Fastener Design
-3.000
Cosmic RAy Telescope for the Effects of Radiation
3.000
6.000
9.000
Detector Board Resonance
•
•
•
First Mode:
1237 Hz
Total nodes:
60546
Total elements: 33546
COSMOSWorks 2005
Cosmic RAy Telescope for the Effects of Radiation
Detector Board Stress
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•
•
•
Using Miles Equation, assume Q = 15, FS = 1.5
3σ g loading = 133g
Max Stress = 1,527 psi
MS ultimate = 45,000 psi / (1.5 * 1,527 psi) - 1 = 18.6
Cosmic RAy Telescope for the Effects of Radiation
Thin Detector Analysis
•
•
•
Assuming Detector is mounted on an ideal 3 point mount, the silicon behaves linearly,
and Q = 15
Fundamental Frequency = 1795 Hz, which yields 3 sigma load of 111g
Margin of Safety = (17,400 psi / (1.4 * 382 psi) – 1 = 31.5
Cosmic RAy Telescope for the Effects of Radiation
TEP Thermal Contraction
Analysis of Beryllium Copper clamp
Temperature (°F)
Relative Displacement (in)
Force (lbs)
Stress (ksi)
MS yield (psi)
MS ult (psi)
•
•
•
•
70
0.0114
20
67
0.91
1.21
-40
0.0042
7.4
25
4.21
5.03
TEP CTE assumed to be same as polyethylene, 77.8 μin / in-°F
During launch, temperature is ~70°; TEP clamp exerts 20 lbs to resist vibration
During cold survival mode at ~-40°, TEP clamp still exerts a preload of 7.4 lbs. The
preload is lower due to the relative thermal contraction
All stress margins are positive
Cosmic RAy Telescope for the Effects of Radiation
Sensitivity Analysis
Preceding calculations used a nominal Q of 15
This table shows how the 3 sigma g-loads vary with Fundamental Frequency and Q
(g's)
Q Factor
•
•
5
10
15
20
25
1000
85
121
148
170
191
1100
81
115
141
163
182
1200
78
110
135
156
174
Fundamental Frequency (Hz)
1300
1400
1500
1600
75
72
70
68
106
102
99
96
130
125
121
117
150
144
140
135
168
162
156
151
1700
66
93
114
131
147
Most structures have Q between 10 and 20
Cosmic RAy Telescope for the Effects of Radiation
1800
64
90
111
128
143
1900
62
88
108
124
139
2000
61
86
105
121
136
Factors of Safety Used
MEV Table 5.1
Design Factor of Safety
Type of Hardware
Yield
Ultimate
Tested Flight Structure - Metallic
1.25
1.4
Tested Flgiht Structure - Beryllium
1.4
1.6
Tested Flight Structure - Composite
N/A
1.5
Pressure Loaded Structure
1.25
1.5
Pressure Lines and Fittings
1.25
4.0
Untestest Flight Structure - Metallic Only
2.0
2.6
Cosmic RAy Telescope for the Effects of Radiation
Material Properties
1
1
1
2
3
Material
Aluminum 6061-T6
Beryllium Copper TH02
A286 AMS 5731
Single Crystal Silicon
G-10 Fiberglass
Density
(lb/in3)
0.098
0.298
0.287
0.084
0.065
Young's
Modulus
Tensile
(ksi)
Yield (ksi)
9,900
35
18,500
160
29,100
85
27,557
brittle
2,000
28
Tensile
Ultimate
(ksi)
42
185
130
17.4
45
Poisson's
Ratio
0.33
0.27
0.31
0.19
-
Where Used
Structure
TEP Spring
Fasteners
Detector
Circuit Boards
1. MIL-HDBK-5J
2. Silicon as a Mechanical Material, Proceedings of the IEEE, Vol 70, No. 5, May 1982, pp 420-457
3. Boedeker Plastics via www.matweb.com
Cosmic RAy Telescope for the Effects of Radiation