CRaTER Thermal Analysis
Huade Tan
6/27/05
Cosmic RAy Telescope for the Effects of Radiation
Contents
•
System Overview
– Requirements
•
Inputs and Assumptions
– Power Dissipations
– Lunar Orbit
– Current Model
•
Results
– Exterior instrument temperatures
– Orbital temperature ranges
•
•
Performance Predictions
Conclusions
Cosmic RAy Telescope for the Effects of Radiation
System Overview
•
Current Thermal System Requirements
Hard (Survival)
Operational
Qualification
Flight Design
CBE (Based on bench margins)
•
-40 C
-30 C
-40 C
-37 C
-32 C
Temperature Margin Philosophy
–
–
–
–
•
50 C
35 C
45 C
50 C
45 C
Hard/Survival limits define the range in which the instrument will not receive damage or permanent
performance degredation
Qualification Limits are defined as the range of temperatures 10 degrees C wider than the flight predict
limits
Flight Design limits define the range given by the current best estimates including margins of
uncertainty in the given analysis. These limits must be within 10 degrees C of the hard limits.
Current Best Estimate ranges are determined by current state of testing and analysis
Requirement Exceedances
–
Current design does not exceed the given thermal requirements.
Cosmic RAy Telescope for the Effects of Radiation
Inputs
•
Power Dissipations in the E-box
– 200 mW distributed evenly throughout analog PCB
– 2.1 W distributed evenly throughout digital PCB
– Two power supplies, 1.2W and 0.9W mounted on digital PCB with a conductive resistance
of Copper in a vacuum at 30 C
•
Power Dissipations in the telescope
– 300 mW distributed evenly through three PCB’s, evenly stacked
– Conduction characteristics modeled as wedge clamps along the sides of each board to the
telescope housing.
Cosmic RAy Telescope for the Effects of Radiation
Current Instrument Schematic
Cosmic RAy Telescope for the Effects of Radiation
MLI and Optical Bench
•
MLI outer layer optical properties:
Cold Case
Coating
Kapton 3mil
Black Kapton 3 mil
Germanium Black Kapton
Silver Teflon (5 mil)3,4
Silver Teflon (10 mil)4
Hot Case
Location
Absorptance
S
Emittance
H
Absorptance
S
Emittance
H
MLI Blanket
MLI Blanket
0.45
0.91
0.49
0.08
0.09
0.80
0.81
0.81
0.78
0.87
0.51
0.93
0.51
0.11
0.13
0.76
0.78
0.78
0.73
0.83
•
Effective emittance:
e* for MLI assumed to be .005 and .03 between best and worst cases.
•
CBE optical bench temperature margins between 16 and –19 C.
•
Modeled optical bench temperature margins between 35 and –30 C hot and cold.
Cosmic RAy Telescope for the Effects of Radiation
Orbit
•
•
•
•
•
•
The current model is generated based on a basic Beta zero orbit at an altitude
of 122.1 km.
This orbit was chosen in order to generate an
orbital period of 7200 seconds.
Reducing the orbit to 50 km will shorten the
orbital period and reduce the amplitude
of resultant temperature fluctuations.
At a Beta angle of zero, the model simulates
the worst case scenario where the instrument
cycles from one temperature extreme to the
other twice every period.
The total heat absorbed by the instrument
through the given orbit is computed by
the Radcad Monte Carlo method.
The model assumes a contact resistance
of the mounting feet to LRO to be .5 W/cm2C.
Radiation to the LRO is assumed to be through
15 layer MLI
Cosmic RAy Telescope for the Effects of Radiation
Environmental Parameters
•
Orbital Heat Rate Factors:
Hot Case
Solar Constant
Albedo Factor
Infrared Emission
---
Cold Case
1420 W/m2
1280 W/m2
0.13
0.06
---
•
Infrared Lunar Emissions are modeled after the temperature of the lunar surface.
Lunar surface temperatures are modeled after the characteristic Lambertian surface having a
subsolar temperature of 400 K and a shadow temperature of 100 K.
•
Surface temperatures across the bright side varies as a function of Tsubsolarcos1/4θ where θ is the
angle measured from the orbital position to local noon.
Brightness Temperatures of the Lunar Surface: The Clementine Long-Wave Infrared Global Data Set. Lawson SL and Jakosky BM.
Cosmic RAy Telescope for the Effects of Radiation
Current Instrument Model
• The reference coordinate system
shown here is used to describe the
exterior surfaces in the following
slides
•Where:
Xmax = left
Xmin = right
Ymax = front
Ymin = rear
Zmax = top
Zmin = bottom
Cosmic RAy Telescope for the Effects of Radiation
Results: Instrument
Cosmic RAy Telescope for the Effects of Radiation
Instrument Exterior Temperatures (hot case)
Cosmic RAy Telescope for the Effects of Radiation
Mean Orbital Temperatures (hot case)
330
325
320
315
interface
W
scope zmin
mean pcb
310
max pcb
mean zmax
zmax
305
300
295
290
0
1000
2000
3000
4000
5000
6000
time (s)
Cosmic RAy Telescope for the Effects of Radiation
7000
8000
Instrument Exterior Temperatures (cold case)
Cosmic RAy Telescope for the Effects of Radiation
Mean Orbital Temperatures (cold case)
275
270
265
Temperature (K)
260
interface
scope zmin
mean pcb
255
max pcb
mean zmax
zmax
250
245
240
235
0
1000
2000
3000
4000
5000
6000
time (s)
Cosmic RAy Telescope for the Effects of Radiation
7000
8000
Transient Results Summary
•
Current best estimates for CRaTER is primarily dependant upon the temperature
margins given for the optical bench.
instrument interface
pcb's
nadir
scope
Hot Case Max Operating
Cold Case Min Operating
Temperature [optical bench Temperature [optical bench
at 35C]
at -30 C]
42
-33
44.5
-32
51
-35
44.5
-36
•
Instrument Interface temperatures vary +7 to –3 degrees C from the optical bench
temperature between extremes of hot and cold.
•
Nine degrees C maximum temperature difference in instrument from mounting interface
at the top cover (hot case). May consider an MLI outer layer with a lower absorbptivity.
Cosmic RAy Telescope for the Effects of Radiation
Summary and Conclusions
•
Current Best Estimate:
– Instrument interface temperature: 35 C  1 C Hot & -30C 
– Maximum instrument temperature exceeds no more that 2.6 degrees C from the interface
temperature during orbit.
•
Uncertainties and Modeling Improvements:
– Temperature dependence of material properties: Given a temperature fluctuation of a few
degrees C through a beta 0 orbit, the temperature dependence of thermal properties can
safely be neglected.
– Incorporating TEPs into the thermal model
– Finalizing mounting interface resistance to and relative view factors (to space) from the
LRO
– Incorporating actual circuitry details on the PCBs
– Fine tuning MLI optical characteristics
Cosmic RAy Telescope for the Effects of Radiation
Backup Slides
Cosmic RAy Telescope for the Effects of Radiation
Inputs
•
Thermal and Physical properties:
Material
Aluminum 6061
PCB
3mil Black Kapton Film
MLI
•
k (W/m/K)
Cp (J/kg/K) rho (kg/m^3) e*
180
869
2700
59.8
1003
2819
0
0
0
0
0
0
Optical Properties:
Material
Aluminum 6061
PCB
3mil Black Kapton Film
a
e
0.1
--
0.025
--
0.91
0.81
Cosmic RAy Telescope for the Effects of Radiation
0.8
0.7
0.81
0.05
Assumptions
•
Material properties:
– Thermophysical properties of Al-6061 obtained from Matweb databases
– Optical properties of Aluminum obtained from Cooling Techniques for Electronic
Equipment: Second Edition
•
MLI assumptions:
– Currently modeled using bulk properties
•
PCB assumptions:
– 2 ground and power layers (80% fill), 4 signal layers (20% fill), 1 mm thick
– Properties determined at www.frigprim.com/online/cond_pcb.html
•
TEP assumptions:
– Currently not modeled
Cosmic RAy Telescope for the Effects of Radiation
Assumptions
•
Conductive Resistances:
– Between PCB and Aluminum assumed to be characteristic of copper in vacuum at 30 C
referred to in Heat Transfer. Holman, J.P
– Within the Ebox assumed to be characteristic conduction of Al-6061 (assuming that the ebox
is constructed out of a single block of aluminum)
•
Internal Radiation:
– View factors of internal surfaces determined by Radcad using radk ray trace method
– Emissivity factors calculated assuming either infinite parallel planes or general case for two
surfaces from dissipating surfaces to interior walls.
•
Heat Flow to the Space Craft:
– Assuming interface properties at 20 degrees C
– Contact resistance of mounting feet to LRO assumed to be 20 W/cm2C
– Radiation conduction to the LRO through 15 layer MLI
Cosmic RAy Telescope for the Effects of Radiation
Heat Rates Absorbed Over One Orbit
Cosmic RAy Telescope for the Effects of Radiation
Instrument Heat Losses (hot case)
80
60
40
to space
20
to space
W
interface
to space
nadir
0
0
1000
2000
3000
4000
5000
6000
-20
-40
-60
time (s)
Cosmic RAy Telescope for the Effects of Radiation
7000
8000
zenith
Instrument Heat Losses (cold case)
40
20
0
0
1000
2000
3000
4000
5000
6000
-20
7000
8000
to space
W
to space
interface
-40
to space
nadir
-60
zenith
-80
-100
-120
Time (s)
Cosmic RAy Telescope for the Effects of Radiation
Cold Case Orbit (bright to dark)
Cosmic RAy Telescope for the Effects of Radiation
Current Telescope Model
Note: the circular apertures on the top and bottom sides of the scope are insulated with a single layer of 3 mil black kapton
Cosmic RAy Telescope for the Effects of Radiation