SOLAR-B Instrument

EIS Baseline Thermal Design Document


Document No. BU/SLB-EIS/TN/005.01




Compiled by C V Goodall

University of Birmingham
Astrophysics and Space Research
04/07/00









Contents









• Baseline Thermal Model














APPENDIX
EIS Baseline Thermal Design


Introduction

This document describes the baseline thermal design for EIS. It is the result of the thermal modelling work carried out by Dr I G Butler. It is essentially drawn from the results for EIS4 authored by him and circulated as Document No. BU/SLB-EIS/TN/002.02. The opportunity has been taken to make some editorial corrections to that document.


The Thermal Model

The thermal model consists of 108 Nodes, of which 5 are boundaries and 45 are arithmetic nodes. The basic design of EIS is shown below with the component names used in the following text.


Mid-box
Shutter

Grating housing

Primary
mirror
Mirror tube

CCD camera

Grating








Baffle

Inner
Clamshell
ROE

Outer
Clamshell

HCU



Figure 1. Components on the EIS instrument and their names used in the thermal model.


This model has the CCD radiator on the +Y side and the E-box radiator on the -Z-side. A small sunshield is added in front of radiator to protect the radiator from direct sunlight. Both steady-state and transient simulations have been performed.






+Y


EIS4 Radiator Position, and coldfinger.
+Z



ROE Radiator
+X







The EIS structure is assumed to be aluminium honeycomb apart from the baffle, which is formed out of 2mm thick CFRP. The whole instrument is wrapped in MLI, and a small radiator is supplied to maintain the temperature of the electronics inside the EIS instrument. The CCDs are cooled by a second radiator situated on the +Y surface of the structure above the CCD.





Thermal cases

The EIS instrument is expected to operate in the following conditions:
Hot-case
Cold-case
Survival-case
Altitude of orbit
Attitude
600km
+Z Pointing towards sun, +Y pointing to North-pole
β-angle of orbit
90o
58.6o
Mid-summer 2004
1289
0.35
216
BOL
Date used in model
13/10/2004
Solar Constant W/m2
1421
Albedo
0.25
Infrared from Earth W/m2
258
Thermal optical property
EOL
Operational Condition
Max. heat dump
During observation
Min. heat dump during observation
Min. heat dump during no observation



Interfaces

The EIS instrument is supported off the Solar-B spacecraft via a number of GRP struts, which attach in three places on the EIS structure. The conductive coupling to the spacecraft have been defined and are expected to be less than:

From
To
Conductive Link W/K
From
To
Conductive Link W/K
302
9
0.032
302
10
0.045
302
24
0.02
302
25
0.02

These maximum values have been used in all of the EIS thermal models.



Boundary Temperatures

In the three thermal cases shown above the expected spacecraft temperatures have been calculated, these are shown below:
Hot-case



Node
Description
Temperature oC
Node No.
Description
Temperature oC
300
Solar-B S/C Bus
+50
302
S/C I/F points
+50
303
OPA Door
+60
304
PAS
+100
999
Space
-269



Cold-case/Survival-case



Node
Description
Temperature oC
Node No.
Description
Temperature oC
300
Solar-B S/C Bus
-40
302
S/C I/F points
-20
303
OPA Door
-10
304
PAS
-90
999
Space
-269



These temperatures have been used a boundary conditions for the EIS thermal model, though the +Y bus MLI has been modelled as an arithmetic node for completeness.



Temperature Requirements

Internal to the EIS instrument various components have specified operating temperatures. The most critical of these are the electronics boxes and the optics.

The operational temperature requirements for these components are set out below:

Component
Maximum Temperature oC
Minimum Temperature oC
HCU
+40
0
ROE
+40
0
Optics
+10
+30



During the survival-case it is expected that the temperature variations will increase, thus the non-operating temperature requirements for the various components are shown below:

Component
Maximum Temperature oC
Minimum Temperature oC
HCU
+65
-30
ROE
+65
-30
Optics
0 oC
+40 oC

These temperature requirements have been used as goals for the thermal model, though it would be preferable that the electronics operate in the range +25-+45 oC.




Baseline Thermal Model


Nodes


Description of nodes in viewed from the sun-side of EIS.
Structural Nodes

Node No.
Description
Node No.
Description
1
Mid-box rear wall L/H
2
Mid-box rear R/H
3
Mid-Box L/H wall rear
4
Mid-Box L/H wall front
5
Mid-Box R/H wall rear
6
Mid-Box R/H wall front
7
Mid-box front wall L/H
8
Mid-box front wall R/H
9
Mid-box base rear R/H
10
Mid-box base rear L/H
11
Mid-box base front R/H
12
Mid-box base front L/H
13
Mid-box top rear R/H
14
Mid-box top front R/H
15
Mid-box top rear L/H
16
Mid-box top front L/H
17
Filter
18
HCU
19
ROE
20
Grating housing L/H wall rear
21
Grating housing L/H wall front
22
Grating housing R/H wall rear
23
Grating housing R/H wall front
24
Grating housing base rear
25
Grating housing base front
26
Grating housing top rear
27
Grating housing top front
28
Grating housing end
29
Grating
30
Baffle R/H wall rear
31
Baffle R/H wall front
32
Baffle base rear
33
Baffle base front
34
Baffle top rear
35
Baffle top front
36
Baffle end
40
Mirror tube top rear
41
Mirror tube top middle
42
Mirror tube top front
43
Mirror tube base rear
44
Mirror tube base middle
45
Mirror tube base front
46
Mirror tube L/H wall rear
47
Mirror tube L/H wall middle
48
Mirror tube L/H wall front
49
Mirror tube R/H wall rear
50
Mirror tube R/H wall middle
51
Mirror tube R/H wall front
52
Mirror support/mirror tube end
53
Primary mirror
54
Inner Clamshell
55
Outer Clamshell
56
Camera
57
Shutter
59
CCD
60
E-box radiator
61
CCD Radiator
70
Baffle





Arithmetic Nodes

Node No.
Description
Node No.
Description
101
Mid-box rear wall L/H MLI
102
Mid-box rear R/H MLI
103
Mid-Box L/H wall rear MLI
104
Mid-Box L/H wall front
105
Mid-Box R/H wall rear MLI
106
Mid-Box R/H wall front
107
Mid-box front wall L/H MLI
108
Mid-box front wall R/H
109
Mid-box base rear R/H MLI
110
Mid-box base rear L/H
111
Mid-box base front R/H MLI
112
Mid-box base front L/H
113
Mid-box top rear R/H MLI
114
Mid-box top front R/H
115
Mid-box top rear L/H MLI
116
Mid-box top front L/H
120
Grating housing L/H wall rear MLI
121
Grating housing L/H wall front MLI
124
Grating housing base rear MLI
125
Grating housing base front MLI
126
Grating housing top rear MLI
127
Grating housing top front MLI
128
Grating housing end MLI
130
Baffle R/H wall rear MLI
131
Baffle R/H wall front MLI
132
Baffle base rear MLI
133
Baffle base front MLI
134
Baffle top rear MLI
135
Baffle top front MLI
136
Baffle end MLI
140
Mirror tube top rear MLI
141
Mirror tube top middle MLI
142
Mirror tube top front MLI
143
Mirror tube base rear MLI
144
Mirror tube base middle MLI
145
Mirror tube base front MLI
146
Mirror tube L/H wall rear MLI
147
Mirror tube L/H wall middle MLI
148
Mirror tube L/H wall front MLI
149
Mirror tube R/H wall rear MLI
150
Mirror tube R/H wall middle MLI
151
Mirror tube R/H wall front MLI
152
Mirror support/mirror tube end MLI
62
CCD Radiator MLI
63
Sunshield Front MLI
64
Sunshield Rear MLI
301
S/C +Y MLI






Boundary Nodes

Node No.
Description
Node No.
Description
300
Solar-B S/C Bus
302
S/C I/F points
303
OPA Door
304
PAS
999
Space





Thermal Properties

Conductors

Aluminium Honeycomb

The aluminium honeycomb structure is modelled as 10mm thick honeycomb plus two sheets of CFRP each 1mm thick. The thermal conductivity of the CFRP is assumed to be 20W/m/K, which may be conservative, but this value is an unknown until measurements are made on an in-house manufactured sheet of CFRP.

Conductivity of honeycomb in direction of the tapes is given by



where
L is the length in the direction of the tapes
W is the length of the sheet perpendicular to the tapes
T is the thickness of the honeycomb

The conductivity of the honeycomb perpendicular direction of the tapes is given by



Bolted joints have not been included in the model as the conductivity of the honeycomb is sufficiently low as to dominate the heat flow. This may be introduced in a more detailed model.

MLI

The MLI is treated as a temperature-variable conductor, data provided by MMS. The appropriate temperature is obtained by taking the mean of the MLI temperature and that of its corresponding wall node. This is then used to obtain an interpolated value of the conductance from a look-up table of conductances at set temperature points (see Appendix). This value is then used iteratively in deriving steady state temperature values within the thermal programme,

All MLI around the EIS instrument is assumed to be 15-20 layers thick, apart from the radiator MLI which is taken to be a medium MLI 10-15 layers due to the large number of cut-outs. The baffle is wrapped in a thin MLI, 5 layers (to prevent over-heating in the hot-case). There is thick MLI on mirror tube and sun facing sides, medium on remaining side of mid-box and thin MLI on remaining sides of the grating housing.


Baffle

The baffle is thermally de-coupled from the rest of EIS by conductive links of 0.026W/K to the grating housing and 3.8x10-3W/K to the mid-box assembly. This should minimise the impact of sunlight scattered from the filter, though this does seem to be a design driver even taking these precautions.


E-boxes

With the extended operating temperature ranges defined March 2000 the HCU is hard mounted to the mid-box structure. This will maintain the structure temperature in the cold-case without the need for extra operational heaters. The higher dissipation of the ROE electronics box means that it must be decoupled from the mid-box structure via insulating supports, and connected to a small radiator (area 0.049 m2) on the -Z side of the mid-box via a copper strap with conductivity 0.4 W/K.


CCD Camera

The CCDs are mounted off an aluminium structure via GRP struts, providing a conductive link of 0.0026W/K. The heat coupled into the CCD via the electrical connections is minimized by using flexible circuits. This should keep the conductive link to the electronics box to 1x10-3 W/K.

The CCDs are cooled to their operating temperature by a large radiator (area
0.11 m2) on the +Y side of the mid-box structure. A coldfinger with thermal conductivity 0.25W/K links the CCDs to this radiator. To mount the radiator the rear half of the mid-box top cover is permanently attached whilst the front half is detachable to allow access to the shutter mechanism. The radiator is mounted off 10 GRP struts each 10mm diameter and 30mm long, providing a conductive link to the top of the mid-box structure of 4x10-3W/K.




Surface Properties


Interior

All interior surfaces are assumed to be covered with a high emissivity Kapton tape, ε=0.78/α=0.94 BOL and EOL except for the right-hand wall of the grating housing facing the baffle, and the right-hand front wall of the mid-box facing the baffle, which are covered in a low emissivity tape, ε=0.05/α=0.1 BOL and EOL.

Other components inside the EIS instrument have the following properties:


Node
Description
α
ε
Node
Description
α
ε


BOL
EOL
BOL
EOL

BOL
EOL
BOL
EOL
17
Filter
0.08
0.1
0.08
0.1
18
HCU
0.9
0.9
0.9
0.9
19
ROE
0.08
0.1
0.05
0.05
29
Grating
0.2
0.2
0.2
0.2
53
Primary mirror
0.2/0.02
0.2/0.02
0.2/0.02
0.2/0.02
54
Inner Clamshell
0.2
0.2
0.2
0.2
55
Outer Clamshell
0.2
0.2
0.2
0.2
56
Camera
0.08
0.1
0.05
0.05
57
Shutter
0.2
0.2
0.2
0.2
59
CCD
0.5
0.5
0.5
0.5



The electronics boxes are covered in a low emissivity tape to minimise radiation to the surrounding experiment. This is required in order to prevent the EIS instrument becoming too hot in the hot-case. Clamshells, shutter, mirror and grating are mounted off bare aluminium structures at the moment. More detailed modelling of these components will be required in the future.



Exterior

All exterior MLI has a surface property of ε=0.34/α=0.7 BOL and EOL, apart from the mirror tube which has low emissivity surface layer, ε=0.05/α=0.1 BOL and EOL, to reduce the heat leakage.

Node
Description
α
ε
Node
Description
α
ε


BOL
EOL
BOL
EOL

BOL
EOL
BOL
EOL
60
E-Box Radiator
0.09
0.15
0.9
0.9
61
CCD Radiator
0.09
0.15
0.9
0.9
61
CCD Radiator MLI
0.34
0.34
0.7
0.7
300
S/C Bus
0.32
0.4
0.57
0.57
301
S/C +Y MLI
0.32
0.4
0.57
0.57
+303
OPA Door +Z
0.15
0.2
0.05
0.05
-303
OPA Door -Z
0.15
0.2
0.9
0.9
+304
PAS +Z
0.65
0.78
0.8
0.8
-304
PAS -Z
0.9
0.9
0.76
0.76
300
+Y Radiator
0.08
0.16
0.78
0.78




Masses and heat capacitance

To compute the transient temperature variations around the orbit the mass and heat capacity of all nodes need to be included. The values used are shown below:


Node
Description
Mass
Cp
Node
Description
Mass
Cp


kg
J/kg/K

kg
J/kg/K
1
Mid-box rear wall L/H
0.254
850
2
Mid-box rear R/H
0.137
850
3
Mid-Box L/H wall rear
0.37
850
4
Mid-Box L/H wall front
0.37
850
5
Mid-Box R/H wall rear
0.37
850
6
Mid-Box R/H wall front
0.37
850
7
Mid-box front wall L/H
0.254
850
8
Mid-box front wall R/H
0.637
874
9
Mid-box base rear L/H
0.418
850
10
Mid-box base rear R/H
0.418
850
11
Mid-box base front L/H
0.418
850
12
Mid-box base front R/H
0.418
850
13
Mid-box top rear R/H
0.418
850
14
Mid-box top front R/H
0.418
850
15
Mid-box top rear L/H
0.418
850
16
Mid-box top front L/H
0.418
850
17
Filter
8.9x10-6
880
18
HCU
2.5
880
19
ROE
6.0
880
20
Grating L/H wall rear
0.35
850
21
Grating L/H wall front
0.35
850
22
Grating R/H wall rear
0.35
850
23
Grating R/H wall front
0.35
850
24
Grating base rear
0.35
850
25
Grating base front
0.35
850
26
Grating top rear
0.35
850
27
Grating top front
0.35
850
28
Grating end
0.141
850
29
Grating
1.95
850
30
Baffle R/H wall rear
0.35
850
31
Baffle R/H wall front
0.35
850
32
Baffle base rear
0.35
850
33
Baffle base front
0.35
850
34
Baffle top rear
0.35
850
35
Baffle top front
0.35
850
36
Baffle end
0.089
850
40
Mirror top rear
0.38
850
41
Mirror top middle
0.38
850
42
Mirror top front
0.38
850
43
Mirror base rear
0.38
850
44
Mirror base middle
0.38
850
45
Mirror base front
0.38
850
46
Mirror L/H wall rear
0.35
850
47
Mirror L/H wall middle
0.35
850
48
Mirror L/H wall front
0.35
850
49
Mirror R/H wall rear
0.35
850
50
Mirror R/H wall middle
0.35
850
51
Mirror R/H wall front
0.35
850
52
Mirror end
0.164
850
53
Primary mirror
5.61
880
54
Inner Clamshell
1.0
880
55
Outer Clamshell
1.0
880
56
Camera
3.0
880
57
Shutter
1.2
880
59
CCD
0.5
880
60
E-box radiator
0.73
880
61
CCD Radiator
0.73
880
70
Baffle
0.141
850




Power Dissipations

The main dissipations within the EIS structure are from the camera electronics (ROE) and the heater control unit (HCU). The power dissipations used in the thermal model are shown below:

Node
Description
Power/W
Node
Description
Power/W
18
HCU
5
19
ROE
7.1
59
CCD
1.0










Preliminary Results for Baseline Model EIS4


The temperatures shown in this section are the average orbital temperatures, using the average heat fluxes calculated by the Thermica analysis package.

Hot-case Temperatures




27.7oC
29.7oC






HCU 33.2oC
ROE 23.4oC
Grating 27.3oC

27.3oC




Filter 101.9oC

18.6oC
Mirror 20.7oC
21.6oC

Shutter 31.5oC




29.3oC
26.5oC

1W




Other Components
CCD Radiator -63.3 oC
CCD -54.7oC
E-Box Radiator 5.0 oC
Inner Clam Shell 30.0oC
Outer Clam Shell 26.5 oC
S/C i/f +50 oC.

Cold-case Temperatures



EIS temperature control 4.5W (Baseline design 15W)
(NB. No CCD control power)


1W

11.8oC
12.2oC






HCU 20.6oC
ROE 3.4oC
Grating 11.7oC

14.8oC




Filter 75.6oC

-23.3oC
Mirror 13.6oC
16.2oC

Shutter 11.6oC




10.9oC
11.1oC

2.5W

1W







Other Components
CCD Radiator. -91.7 oC
CCD -86.4 oC
E-Box Radiator -15.8oC
Inner Clam Shell 11.8 oC
Outer Clam Shell 0.2 oC
S/C i/f -20.0 oC


Survival Temperatures


It is assumed that during the survival mode the spacecraft maintains its attitude with respect to the sun. Therefore the filter and front of the instrument will remain warm.

Heater Dissipations
CCD control heater 11W

EIS thermal control 9.5W + CCD control 11W. (Baseline design 15W)
2W


0.7 oC
4.0 oC






HCU 3.8
ROE -34.2 oC
Grating 11.2oC

1W
17.8oC




Filter 72.4oC

-21.3oC
Mirror 6.4oC
9.0oC

Shutter 4.0oC




2.3 oC
1.4 oC

2.5W

4W





Other Components
CCD Radiator. -36.1 oC
CCD 7.93oC
E-Box Radiator -43.8oC
Inner Clam Shell 2.9 oC
Outer Clam Shell -5.2 oC
S/C i/f -20.0 oC


Heaters

Additional heaters are required to maintain the instrument temperature during the various operating phases. Powers are derived from performing a steady-state analysis with the average heat flux from the sun and Earth and are included in the ESATAN N.TAN file. A summary of the power requirements is shown below:
Hot-case



Node
Description
Power/W
Node
Description
Power/W
52
Mirror Support
1



Total
1









Cold-case



Node
Description
Power/W
Node
Description
Power/W
52
Mirror Support
2.5
28
Grating Support
1
13
MBX Base
1



Total
4.5









Survival-case



52
Mirror Support
2.5
29
ROE
1
10
Mid-box base rear R/H
1
11
Mid-box base front L/H
1
12
Mid-box base front R/H
1
9
Mid-box base rear L/H
1
28
Grating Support
2



Sub-Total
9.5


59
CCD
11



Total
20.5






Orbital Variations

The plot (Option D) shows the orbital variation of the CCD temperature for the hot-case. The variation can be described as

steady state temperature ± 3º C


Powers Across S/C Interface

The EIS instrument is supported off the Solar-B spacecraft via a number of GRP struts which attach in three places on the EIS structure. The conductive coupling to the spacecraft has been defined and are expected to be less than:


From
To
Conductive Link W/K
From
To
Conductive Link W/K
302
9
0.032
302
10
0.045
302
24
0.02
302
25
0.02

These maximum values have been used in all of the EIS thermal models, and the calculated power flows are as follows:

Hot-case

From
To
Power Flow W
From
To
Power Flow W
302
9
0.64
302
10
0.87
302
24
0.42
302
25
0.45

Total power flow 2.38W

Cold-case

From
To
Power Flow W
From
To
Power Flow W
302
9
-1.52
302
10
-1.25
302
24
-0.77
302
25
-0.77

Total power flow from S/C 4.3W

Survival-case

From
To
Power Flow W
From
To
Power Flow W
302
9
-2.1
302
10
-1.57
302
24
-0.86
302
25
-0.78

Total power flow from S/C -5.3W



Conclusions

The temperature requirements of the EIS instrument are meet by the design EIS4. The relaxation of the E-box temperature limits has allowed the HCU to be hard mounted to the structure. This has lead to a reduction in the operational heater power budget. Also the lower survival temperature limit for the ROE has dropped the survival case power budget. The difficulty is controlling the CCD temperature. At the moment large powers are required to warm the CCD to 0oC. This could be reduced with the introduction of a thermal impedance in the coldfinger, but this would have a detrimental effect on the operational CCD temperature.



Caveats

The coldfinger plus supports has not been modelled and it is conceivable that there could be a 5oC increase in temperature at the CCDs in both of these models.

The issue of a thermal impedance in the CCD coldfinger could be of importance in this analysis, though with the careful design of an enclosure for the CCDs the radiative and conductive couplings into the CCD could be minimized, thus reducing the temperature drop across an impedance during operation.

APPENDIX


MLI Efficiency Tables


0.0299
0.061
0.105
0.154
273
0.0338
0.069
0.119
0.175
293
0.071
0.149
0.257
0.378
393
0.081
0.171
0.295
0.434
413
0.0385
0.079
0.136
0.200
313
0.0085
0.017
0.029
0.042
93
Gap
Large (L)
Medium (M)
Small (S)
Temperature (K)
0.0447
0.092
0.159
0.234
333
0.0193
0.039
0.067
0.098
213
0.0085
0.017
0.029
0.042
0
Efficiency W/m2/K