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CRaTER Thermal Analysis
Bob Goeke for Huade Tan
Cosmic RAy Telescope for the Effects of Radiation
Contents
• System Overview
– Design & Requirements
• Inputs and Assumptions
– Power Dissipations
– Environment and Orbit
– Current Model
• Results
– Instrument temperatures
– Orbital temperature ranges
• Conclusions
– Uncertainties and Improvements
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 2
Design Approach & Requirements
• Design Approach
– Radiatively isolated with multi-layer thermal blanket over entire
surface.
– Single layer blanket covering 10cm2 telescope apertures nadir and
zenith
– Tight conductive coupling to spacecraft optical bench
• Interface Requirements at Instrument Mounting Surface
Survival -40 C
Thermal ICD para 6.1
Operational 25 C -30 C
Rate-of-Change n/a Thermal ICD para 6.2
Gradient n/a Thermal ICD para 6.3
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 3
Model Requirements
• The CRaTER thermal model is required to represent, with as much detail as
possible, the behavior of critical reference points in the CRaTER instrument
in a computer simulated mission orbit environment in order to anticipate and
correct for any possible hardware degradation or failure under similar
circumstances.
• In order to ensure the survival of the CRaTER instrument, the thermal
model should account for the worst case scenarios in both hot and cold
temperature limits.
• The model must adhere to all RGMM and RTMM requirements given in the
TICD.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 4
Instrument Power Consumption
• Power dissipations in the instrument are modeled as heat loads. The relevant
values of such heat loads are given in the following table. Hot case numbers are
taken to be 120% of nominal and cold case numbers are assumed to be 80 % of
the nominal power consumption of each electrical component.
Hot Case (W) Nominal (W) Cold Case (W)
digital board 3.19 2.66 2.12
analog board 2.52 2.10 1.68
5V power supply 1.33 1.11 0.89
dual 5 V power supply 1.94 1.62 1.29
telescope 0.10 0.08 0.06
total power 9.08 7.57 6.04
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 5
MLI and Optical Bench
• Surface finish properties:
Cold Case Hot Case
Absorptance Emittance Absorptance Emittance
Coating Location ?S ?H ?S ?H
Kapton 3mil 0.45 0.80 0.51 0.76
Black Kapton 3 mil 0.91 0.81 0.93 0.78
Germanium Black Kapton 0.49 0.81 0.51 0.78
Silver Teflon (5 mil) 3,4 MLI Blanket 0.08 0.78 0.11 0.73
Silver Teflon (10 mil) 4 MLI Blanket 0.09 0.87 0.13 0.83
• Effective emittance:
e* for MLI assumed to be .005 or .03 for best and worst cases.
• Modeled optical bench temperatures are +25 C hot case, –30 C cold case
and –40 C cold survival case.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 6
Environmental Parameters
• Orbital Heat Rate Factors:
Hot Case Cold Case Survival Case
Solar Constant 1450 W/m2 1280 W/m2 1280 W/m2
Albedo Factor 0.13 0.06 0.06
Planetshine/Infrared Emission --- 5.2 W/m2 5.2 W/m2
• Lunar surface IR constants modeled after the characteristic Lambertian surface
having a subsolar temperature of 1420 w/m2 hot case and 1280 w/ m2 cold case to a
shadow IR emission of 5 w/m2 for both cases..
• Surface IR emissions across the bright side are described in the General Thermal
Subsystem specification 431-SPEC-000091.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 7
Orbit
• The current instrument model is
assumed to be in a basic polar orbit at
a hot case altitude of 30 km.
• At a Beta angle of zero, the model
simulates the hot operational worst
case scenario where the instrument
cycles from one temperature extreme
to the other.
• The total heat absorbed (solar, albedo
& IR) by the instrument through each
orbit is computed using the Radcad
Monte Carlo ray trace method.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 8
Orbit
• This latest spacecraft geometric
model received from GSFS (as
seen to the left) corresponds to
the hot case solar array
orientation.
• For the Beta 0 case, the solar
array articulates during the orbit.
• Given the latest results of the
model, minor changes in heat
loads should not generate
significant changes in
temperature.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 9
Orbit
• The current instrument model is
assumed to be in a basic polar orbit at
a cold case altitude of 70 km.
• At a Beta angle of 90 degrees, the
model simulates the cold operational
worst case scenario where the
instrument never crosses the subsolar
point.
• The total heat absorbed (solar, albedo
& IR) by the instrument through each
orbit is computed using the Radcad
Monte Carlo ray trace method.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 10
Orbit
• This latest spacecraft geometric
model received from GSFS (as
seen to the left) corresponds to
the Beta 90 cold case solar array
orientation.
• The solar array is stationary in
this case and faces the sun at all
points in the orbit.
• Given the latest results of the
model, minor changes in heat
loads should not generate
significant changes in
temperature.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 11
Orbit
• This latest spacecraft geometric
model received from GSFS (as
seen to the left) corresponds to
the Beta 90 cold survival case
solar array orientation.
• The solar array is stationary in
this case and faces the sun at all
points in the orbit.
• LRO is flying in a solar inertial
mode with the –Y pointing at the
sun at all times.
• During this case, the instrument
will never be in direct sunlight
due to the placement of the solar
array.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 12
Current Instrument Model
•The coordinate system used in the
CRaTER model corresponds with
the reference coordinate system of
the spacecraft as outlined in the
TICD.
•The current instrument model
consists of 60 nodes and 52
surfaces.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 13
Current Instrument Schematic
Analog • The CRaTER instrument is
Housing divided into three distinct
radiatively coupled regions.
• Each housing consists of an
Telescope isolated PCB or group of
Digital Housing PCBs and a specific power
Housing dissipation as described in
the model inputs.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 14
Mounting Footprint
• CRaTER’s current design mounts to
the spacecraft at six points located at
the base of the electronics box.
• Each modeled mounting plate is
scaled to adjust for the true contact
surface area.
• The model assumes a contact
conductance between the mounting
feet and the optical bench of 1.3 W/C
per mounting foot.
• The surface finish of the instrument
panel directly facing the LRO is
assumed to be anodized aluminum
with an emissivity of 0.6.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 15
Results: Instrument
Cosmic RAy Telescope for the Effects of Radiation
Beta 00 Hot Temps
30
29
28
Temp (C)
27
26
25
24
0 5000 10000 15000 20000 25000
Time (s)
CR_EBOX.T101 CR_EBOX.T102 CR_EBOX.T103 CR_EBOX.T104 CR_EBOX.T105 CR_EBOX.T106 CR_EBOX.T201
CR_EBOX.T202 CR_EBOX.T301 CR_EBOX.T302 CR_EBOX.T303 CR_EBOX.T401 CR_EBOX.T402 CR_EBOX.T403
CR_EBOX.T501 CR_EBOX.T502 CR_EBOX.T601 CR_EBOX.T602 CR_EBOX.T603 CR_EBOX.T701 CR_EBOX.T702
CR_EBOX.T703 CR_EBOX.T704 CR_EBOX.T705 CR_EBOX.T706 CR_EBOX.T707 CR_EBOX.T708 CR_EBOX.T801
CR_EBOX.T802 CR_EBOX.T802 CR_EBOX.T803 CR_EBOX.T804 CR_EBOX.T805 CR_EBOX.T806 CR_EBOX.T807
CR_EBOX.T808 CR_EBOX.T809 CR_EBOX.T810 CR_EBOX.T811 CR_EBOX.T812 CR_SCOPE.T1 CR_SCOPE.T2
CR_SCOPE.T101 CR_SCOPE.T301 CR_SCOPE.T302 CR_SCOPE.T401 CR_SCOPE.T501 CR_SCOPE.T502 CR_SCOPE.T503
CR_SCOPE.T601 CR_SCOPE.T602 CR_SCOPE.T603 CR_SCOPE.T801 CR_SCOPE.T802 CR_IF.T401 CR_IF.T402
CR_IF.T403 CR_IF.T404 CR_IF.T405 CR_IF.T406
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 17
Beta 90 Cold Case Temps
-25
0 5000 10000 15000 20000 25000
-26
-27
Temp (C)
-28
-29
-30
-31
Time (s)
CR_EBOX.T101 CR_EBOX.T102 CR_EBOX.T103 CR_EBOX.T104 CR_EBOX.T105 CR_EBOX.T106 CR_EBOX.T201
CR_EBOX.T202 CR_EBOX.T301 CR_EBOX.T302 CR_EBOX.T303 CR_EBOX.T401 CR_EBOX.T402 CR_EBOX.T403
CR_EBOX.T501 CR_EBOX.T502 CR_EBOX.T601 CR_EBOX.T602 CR_EBOX.T603 CR_EBOX.T701 CR_EBOX.T702
CR_EBOX.T703 CR_EBOX.T704 CR_EBOX.T705 CR_EBOX.T706 CR_EBOX.T707 CR_EBOX.T708 CR_EBOX.T801
CR_EBOX.T802 CR_EBOX.T802 CR_EBOX.T803 CR_EBOX.T804 CR_EBOX.T805 CR_EBOX.T806 CR_EBOX.T807
CR_EBOX.T808 CR_EBOX.T809 CR_EBOX.T810 CR_EBOX.T811 CR_EBOX.T812 CR_SCOPE.T1 CR_SCOPE.T2
CR_SCOPE.T101 CR_SCOPE.T301 CR_SCOPE.T302 CR_SCOPE.T401 CR_SCOPE.T501 CR_SCOPE.T502 CR_SCOPE.T503
CR_SCOPE.T601 CR_SCOPE.T602 CR_SCOPE.T603 CR_SCOPE.T801 CR_SCOPE.T802 CR_IF.T401 CR_IF.T402
CR_IF.T403 CR_IF.T404 CR_IF.T405 CR_IF.T406
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 18
Beta 90 Cold Survival Case Temps
-35.5
0 5000 10000 15000 20000 25000
-36
-36.5
-37
-37.5
Temp (C)
-38
-38.5
-39
-39.5
-40
-40.5
Time (s)
CR_EBOX.T101 CR_EBOX.T102 CR_EBOX.T103 CR_EBOX.T104 CR_EBOX.T105 CR_EBOX.T106 CR_EBOX.T201
CR_EBOX.T202 CR_EBOX.T301 CR_EBOX.T302 CR_EBOX.T303 CR_EBOX.T401 CR_EBOX.T402 CR_EBOX.T403
CR_EBOX.T501 CR_EBOX.T502 CR_EBOX.T601 CR_EBOX.T602 CR_EBOX.T603 CR_EBOX.T701 CR_EBOX.T702
CR_EBOX.T703 CR_EBOX.T704 CR_EBOX.T705 CR_EBOX.T706 CR_EBOX.T707 CR_EBOX.T708 CR_EBOX.T801
CR_EBOX.T802 CR_EBOX.T802 CR_EBOX.T803 CR_EBOX.T804 CR_EBOX.T805 CR_EBOX.T806 CR_EBOX.T807
CR_EBOX.T808 CR_EBOX.T809 CR_EBOX.T810 CR_EBOX.T811 CR_EBOX.T812 CR_SCOPE.T1 CR_SCOPE.T2
CR_SCOPE.T101 CR_SCOPE.T301 CR_SCOPE.T302 CR_SCOPE.T401 CR_SCOPE.T501 CR_SCOPE.T502 CR_SCOPE.T503
CR_SCOPE.T601 CR_SCOPE.T602 CR_SCOPE.T603 CR_SCOPE.T801 CR_SCOPE.T802 CR_IF.T401 CR_IF.T402
CR_IF.T403 CR_IF.T404 CR_IF.T405 CR_IF.T406
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 19
Results Summary
• CRaTER is driven by the temperature of the optical bench.
Hot Case Max Operating Cold Case Min Operating Cold Case Survival Min
Temperature [optical bench Temperature [optical bench Operating Temperature
at 25C] at -30 C} [optical bench at -40 C}
instrument interface 25 to 28C -29 to -30C -38 to -40C
pcb's 27 to 30C -26 to -27C -37 to -39C
nadir 26 to 29C -28C -38C
scope 26 to 29C -28.5C -37
• Instrument Internal temperatures vary <5 C from the optical bench temperature
between extremes of hot and cold.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 20
Summary and Conclusions
• Estimate of Internal Temperatures:
– Maximum internal temperatures are no more than 5 degrees C above the interface
temperature.
• Uncertainties and Modeling Improvements:
– Temperature dependence of material properties: variations in thermal conductivity
can be neglected given an instrument temperature fluctuation of no more than a few
degrees C through the beta 0 orbit.
– Incorporating TEPs into the thermal model
– Incorporating actual circuitry details on the PCBs
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 21
Electronic Component Temperatures
• There are only 3 electrical components on the PC boards which draw more
than 100mw of power:
Part Typ. Pwr. Theta JC Rise
– 1553 Interface 1100 mw 7.6 C/W 8.4 C
– Actel FPGA 330 mw 2.0 C/W 0.7 C
– BAE SRAM 100 mw 11 C/W 1.1 C
– 2.5 Linear Regulator 170 mw 2.3 C/W 0.4 C
• The 1553 part has a surface area of 4 in2; if the only heat rejection path were
radiation from its top surface to the e-box walls, the junction temp would be
101C -- still below the required (derated) limit of 110C. Tests on the
engineering unit will guide us in adding some more margin to this component.
• The other point sources of heat are the regulated power supplies; these are
mounted directly to the enclosure mid-plate with 3 #10-32 bolts each.
• Both the 1553 Interface and the dual power supply are monitored in the
normal housekeeping stream.
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 22
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 23
Backup Slides
Cosmic RAy Telescope for the Effects of Radiation
Inputs
• Thermal and Physical properties:
Material k (W/m/K) Cp (J/kg/K) rho (kg/m^3) e*
Aluminum 6061 180 869 2700 0.8
PCB 59.8 1003 2819 0.7
3mil Black Kapton Film 0 0 0 0.81
MLI 0 0 0 0.05
• Optical Properties:
Material a e
Aluminum 6061 0.1 0.025
PCB 0.7 0.7
3mil Black Kapton Film 0.91 0.81
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 25
Assumptions
• Material properties:
– Thermophysical properties of Al-6061 were taken 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) and 4 signal layers (20% fill), 1 mm total thickness
– PCB properties determined at www.frigprim.com/online/cond_pcb.html
• TEP assumptions:
– Currently not modeled
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 26
Assumptions
• Conductive Resistances:
– Interface characteristics between PCB and Aluminum are assumed to be of copper to
aluminum in vacuum at 30 C referred to in Heat Transfer. Holman, J.P
– Surfaces of the Ebox are assumed to behave under characteristic conduction of Al-6061
(assuming that the ebox is constructed out of a single block of aluminum)
– Conductive resistances are modeled between the top and bottom covers of the ebox, and the
interface between the ebox and the telescope assembly.
• Internal Radiation:
– View factors between internal surfaces determined by Radcad using radk ray trace method
– Emissivity factors are calculated assuming either infinite parallel planes or general case for
two surfaces from PCBs to the interior walls.
• Heat Flow to the Space Craft:
– Assuming interface temperatures of –40 -30 and 25 degrees C
– Contact conductance of mounting feet to LRO assumed to be 1.3 W/C per foot
– Radiative heat transfer to the LRO through 15 layer MLI
Cosmic RAy Telescope for the Effects of Radiation
June 22, 2006 Thermal Engineering 27
