SIST-TP CEN/CLC/TR 17603-31-12:2021

Space Engineering - Thermal design handbook - Part 12: Louvers

Thermal louvers are thermal control surfaces whose radiation characteristics can be varied in order to
maintain the correct operating temperature of a component subject to cyclical changes in the amount
of heat that it absorbs or generates.
The design and construction of louvers for space systems are described in this Part 12 and a clause is
also dedicated to providing details on existing systems.
The Thermal design handbook is published in 16 Parts
TR 17603-31-01 Part 1 Thermal design handbook – Part 1: View factors
TR 17603-31-01 Part 2 Thermal design handbook – Part 2: Holes, Grooves and Cavities
TR 17603-31-01 Part 3 Thermal design handbook – Part 3: Spacecraft Surface Temperature
TR 17603-31-01 Part 4 Thermal design handbook – Part 4: Conductive Heat Transfer
TR 17603-31-01 Part 5 Thermal design handbook – Part 5: Structural Materials: Metallic and
Composite
TR 17603-31-01 Part 6 Thermal design handbook – Part 6: Thermal Control Surfaces
TR 17603-31-01 Part 7 Thermal design handbook – Part 7: Insulations
TR 17603-31-01 Part 8 Thermal design handbook – Part 8: Heat Pipes
TR 17603-31-01 Part 9 Thermal design handbook – Part 9: Radiators
TR 17603-31-01 Part 10 Thermal design handbook – Part 10: Phase – Change Capacitors
TR 17603-31-01 Part 11 Thermal design handbook – Part 11: Electrical Heating
TR 17603-31-01 Part 12 Thermal design handbook – Part 12: Louvers
TR 17603-31-01 Part 13 Thermal design handbook – Part 13: Fluid Loops
TR 17603-31-01 Part 14 Thermal design handbook – Part 14: Cryogenic Cooling
TR 17603-31-01 Part 15 Thermal design handbook – Part 15: Existing Satellites
TR 17603-31-01 Part 16 Thermal design handbook – Part 16: Thermal Protection System

Raumfahrttechnik - Handbuch für thermisches Design - Teil 12: Luftschlitze

Ingénierie spatiale - Manuel de conception thermique - Partie 12: Persiennes

Vesoljska tehnika - Priročnik o toplotni zasnovi - 12. del: Žaluzije

General Information

• Status: Published
• Public Enquiry End Date: 26-May-2021
• Publication Date: 23-Aug-2021
• ICS: 49.140 - Space systems and operations
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 19-Aug-2021
• Due Date: 24-Oct-2021
• Completion Date: 24-Aug-2021
• Mandate: M/496 - Mandate addressed to CEN, CENELEC and ETSI to develop standardisation regarding space industry (Phase 3 of the process)
• Ref Project: CEN/CLC/TR 17603-31-12:2021 - Space Engineering - Thermal design handbook - Part 12: Louvers

SIST-TP CEN/CLC/TR 17603-31-12:2021 - Overview

Space Engineering - Thermal design handbook - Part 12: Louvers is a CEN/CENELEC technical report published by SIST that defines the design, construction and performance considerations for thermal louvers used on spacecraft. Thermal louvers are thermal control surfaces whose radiation characteristics can be varied to maintain correct operating temperatures for components exposed to cyclical heating (e.g., orbital sunlight/eclipse). This Part 12 sits within a 16‑part Thermal Design Handbook covering view factors, radiators, heat pipes, thermal control surfaces and other spacecraft thermal topics.

Key topics and technical content

This Technical Report provides practical and theoretical guidance on louver systems, including:

• Components of a louver

  • Blade geometry and material characteristics (tabled blade types)
  • Actuators: bimetals, bellows, Bourdon tubes and their performance characteristics
  • Sensors: recommended sensor location and coupling options
  • Structural elements: actuator housings and frames

• Performance and thermal theory

  • Sunlight operation: heat rejection capability and effective absorptance vs. blade angle and sun angle (figures and analytical results)
  • Shadow operation: radiosity, blade temperature fields and net heat transfer through louver arrays
  • Definitions and symbols, and quantitative plots for effective emittance, effective absorptance, and heat rejection capability as functions of geometry and temperature

• Materials and fabrication

  • Materials used for blades, bellows and other elements (tables list typical alloys and manufacturing notes)
  • Considerations for thermal expansion and mechanical sensitivity (figures and cited references)

• Existing flight systems and test data

  • Summaries and case studies of historical louver systems (e.g., ATS, NIMBUS, SNIAS), including analytical calculations and test/flight performance data

Practical applications and who uses this standard

This Part 12 is intended for professionals involved in spacecraft thermal control and space systems engineering:

• Spacecraft thermal engineers designing passive thermal control systems
• Systems and payload engineers integrating louvers with instruments and structure
• Mechanical designers and materials engineers selecting blade and actuator materials
• Test engineers defining environmental and functional tests for louver assemblies
• Program managers and procurement specifying louver requirements in contracts Use cases include radiator control, component temperature stabilization, payload thermal protection, and heritage-system comparisons during early design and trade studies.

Related standards and handbook parts

Part 12 is one element of the Thermal Design Handbook series (Parts 1–16), notably complementing:

• Part 6: Thermal Control Surfaces
• Part 9: Radiators
• Part 11: Electrical Heating
• Part 15: Existing Satellites (for heritage data) Refer to CEN/CLC/TR 17603-31‑01 series for linked guidance across spacecraft thermal design topics.

Keywords: thermal louvers, space engineering, thermal control surfaces, louver design, effective emittance, heat rejection capability, bimetal actuators, Bourdon tube, spacecraft thermal handbook.

Standards Content (Sample)

SLOVENSKI STANDARD
01-oktober-2021
Vesoljska tehnika - Priročnik o toplotni zasnovi - 12. del: Žaluzije
Space Engineering - Thermal design handbook - Part 12: Louvers
Raumfahrttechnik - Handbuch für thermisches Design - Teil 12: Luftschlitze
Ingénierie spatiale - Manuel de conception thermique - Partie 12: Persiennes
Ta slovenski standard je istoveten z: CEN/CLC/TR 17603-31-12:2021
ICS:
49.140 Vesoljski sistemi in operacije Space systems and
operations
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/CLC/TR 17603-31-
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
August 2021
ICS 49.140
English version
Space Engineering - Thermal design handbook - Part 12:
Louvers
Ingénierie spatiale - Manuel de conception thermique - Raumfahrttechnik - Handbuch für thermisches Design -
Partie 12 : Persiennes Teil 12: Blenden

This Technical Report was approved by CEN on 28 June 2021. It has been drawn up by the Technical Committee CEN/CLC/JTC 5.

CEN and CENELEC members are the national standards bodies and national electrotechnical committees of Austria, Belgium,
Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia,
Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.

CEN-CENELEC Management Centre:
Rue de la Science 23, B-1040 Brussels
© 2021 CEN/CENELEC All rights of exploitation in any form and by any means Ref. No. CEN/CLC/TR 17603-31-12:2021 E
reserved worldwide for CEN national Members and for
CENELEC Members.
Table of contents
European Foreword . 7
1 Scope . 8
2 References . 9
3 Terms, definitions and symbols . 10
3.1 Terms and definitions . 10
3.2 Symbols . 10
4 General introduction . 15
5 Components of a louver . 16
5.1 Blades . 16
5.2 Actuators . 18
5.2.1 Bimetals . 18
5.2.2 Bellows . 24
5.2.3 Bourdons . 35
5.3 Sensors . 37
5.3.1 Sensor location . 37
5.3.2 Coupling options . 38
5.4 Structural elements . 38
5.4.1 Actuator housing . 38
5.4.2 Frames . 38
6 Ideal louvers . 40
6.1 Sun-light operation. 40
6.1.1 Introduction . 40
6.1.2 Heat rejection capability . 40
6.1.3 Effective absorptance . 43
6.1.4 Effective emittance . 46
6.2 Shadow operation . 52
6.2.1 Introduction . 52

6.2.2 Radiosity and temperature field of the blades. 53
6.2.3 Heat transfer through the louver . 55
7 Existing systems . 66
7.1 Summary table . 66
7.2 Ats louvers . 76
7.2.1 Introduction . 76
7.2.2 Analytical calculations . 76
7.2.3 Tests . 80
7.3 Nimbus louvers . 83
7.3.1 Introduction . 83
7.3.2 Louvers of the sensory subsystem . 83
7.3.3 Louver of the control subsystem . 84
7.3.4 Flight performance . 86
7.4 Snias louvers . 87
7.4.1 Introduction . 87
7.4.2 Analytical calculations . 88
7.4.3 Tests . 95
7.4.4 The Bourdon tube used as an actuator in the SNIAS Louver system . 98
Bibliography . 104

Figures
Figure 5-1: Relative linear thermal expansion vs. temperature in the case of Invar. T =
273 K. From THE MOND NICKEL CO [35]. . 19
Figure 5-2: Relative linear thermal expansion vs. temperature in the case of brasses. T
= 273 K. After Baldwin (1961) [3]. . 20
Figure 5-3: Relative linear thermal expansion vs. temperature in the case of austenitic
steels. T = 273 K. After Zapffe (1961) [39]. . 20
Figure 5-4: Relative linear thermal expansion vs. temperature in the case of Nimonic
alloys. T = 273 K. After WIGGIN & Co. (1967) [38]. 21
Figure 5-5: Relative linear thermal expansion vs. temperature for different alloys. T =
273 K. After Baldwin (1961) [3], Zapffe (1961) [39], WIGGIN Co. (1967)
[38]. . 21
Figure 5-6: Difference of temperature, ∆T, vs. angle of rotation of the free end, θ, for
several values of the sensitivity, X. After Martin & Yarworth (1961) [21],
KAMMERER (1971) [16]. . 22
Figure 5-7: Sensitivity vs. ratio L/t, for different values of K . After Martin & Yarworth
c
(1961) [21], KAMMERER (1971) [16]. . 23
Figure 5-8: Dimensionless ratio M/K F ∆TL vs. L/t, for several values of w/t. After
c c
Martin & Yarworth (1961) [21], KAMMERER (1971) [16]. . 24
Figure 5-9: Values of α and β vs. ratio a/b for different cross sections of the Bourdon
tube. After Trylinski (1971) [37]. . 36
Figure 5-10: Ratio F/F vs. Bourdon initial coiling angle, ψ . Calculated by the compiler. . 37
0 0
Figure 6-1: Geometry of the blade-baseplate system . 40
Figure 6-2: Heat rejection capability, q, vs. blade angle, θ, for several values of the sun
angle, φ. From FAIRCHILD HILLER (1972) [10]. . 42
Figure 6-3: Heat rejection capability, q, vs. blade angle, θ, for several values of the sun
angle, φ. From Parmer & Stipandic (1968) [27]. . 43
Figure 6-4: Effective absorptance, α , vs. blade angle, θ, for several values of the sun
eff
angle, φ. After FAIRCHILD HILLER (1972) [10]. . 45
Figure 6-5: Effective absorptance, α , vs. blade angle, θ, for several values of the sun
eff
angle, φ. After Parmer & Stipandic (1968) [27]. . 46
Figure 6-6: Effective emittance, ε , vs. blade angle, θ. After FAIRCHILD HILLER
eff
(1972) [10]. . 48
Figure 6-7: Effective emittance, ε , vs. blade angle, θ. After Parmer & Stipandic (1968)
eff
[27]. . 49
Figure 6-8: Effective emittance, ε , vs. blade angle, θ, for several values of the
eff
baseplate emittance, ε . ε has been numerically calculated by using the
BP eff
ε
BP
ε = (1−B *)dβ
following expression. . 50
eff
∫
1− ε
BP
Figure 6-9: Effective emittance, ε , vs. blade angle, θ, for several values of the blades
eff
emittance, ε . ε has been numerically calculated by using the following
B eff
ε
BP
expression. ε = (1−B *)dβ . 51
eff
∫
1− ε
BP
Figure 6-10: Effective emittance, ε , vs. blade angle, θ, for several b/L values. ε has
eff eff
been numerically calculated by using the following expression.
ε
BP
ε = (1−B *)dβ . 52
eff
∫
1− ε
BP 0
Figure 6-11: Schematic diagram of a louver for shadow operation. . 53
Figure 6-12: Schematic diagram of the louver array showing the coordinates and the
significant geometrical characteristics. . 54
Figure 6-13: Dimensionless radiosity, B*, of the blades for several values of the blade
angle, θ. From Plamondon (1964) [28]. . 55
Figure 6-14: Dimensionless temperature, T*, of the blades for several values of the
blade angle, θ. From Plamondon (1964) [28]. . 55
Figure 6-15: Function f(θ) vs. blade angle θ. After Parmer & Buskirk (1967)a [25]. . 57
Figure 6-16: Net heat transfer through the louver, q, vs. baseplate temperature, T , for
BP
several values of the blade angle, θ. ε = 0,05, ε = ε = 0.87. Calculated
B BP I
by the compiler. . 58
Figure 6-17: Net heat transfer through the louver, q, vs. baseplate temperature, T , for
BP
several values of the blade angle, θ. ε = 0,05, ε = ε = 0,87. Calculated
B BP I
by the compiler. . 59
Figure 6-18: Net heat transfer through the louver, q, vs. baseplate temperature, T , for
BP
several values of the blade angle, θ. ε = 0,05, ε = ε = 0,87. Calculated
B BP I
by the compiler. . 60
Figure 6-19: Net heat transfer through the louver, q, vs. baseplate temperature, T , for
BP
several values of the blade angle, θ. ε = 0,05, ε = ε = 0,87. Calculated
B BP I
by the compiler. . 61
Figure 6-20: Net heat transfer through the louver, q, vs. baseplate temperature, T , for
BP
several values of the blade angle, θ. ε = 0,05, ε = ε = 0,87. Calculated
B BP I
by the compiler. . 62
Figure 6-21: Net heat transfer through the louver, q, vs. baseplate temperature, T , for
BP
several values of the blade angle, θ. ε = 0,05, ε = ε = 0,87. Calculated
B BP I
by the compiler. . 63
Figure 6-22: Net heat transfer through the louver, q, vs. baseplate temperature, T , for
BP
several values of the blade angle, θ. εB = 0,05, εBP = εI = 0,87. Calculated
by the compiler. . 64
Figure 6-23: Net heat transfer through the louver, q, vs. baseplate temperature, T , for
BP
several values of the blade angle, θ. ε = 0,05, ε = ε = 0,87. Calculated
B BP I
by the compiler. . 65
Figure 7-1: Effective emittance, ε , based on area of the large unit, vs. blade angle, θ,
eff
for ATS spacecraft. From Michalek, Stipandic & Coyle (1972) [24]. 78
Figure 7-2: Effective absorptance, α , vs. blade angle, θ, for several values of the sun
eff
angle, φ, for ATS spacecraft. From Michalek, Stipandic & Coyle (1972) [24]. . 79
θ, for several values of the sun
Figure 7-3: Heat rejection capability, q, vs. blade angle,
angle, φ, for ATS spacecraft. From Michalek, Stipandic & Coyle (1972) [24]. . 80
Figure 7-4: Effective absorptance, α , vs. sun angle, φ, for several values of the blade
eff
angle, θ, for ATS spacecraft. From Michalek, Stipandic & Coyle (1972) [24]. . 81
Figure 7-5: Heat rejection capability, q, vs. sun angle, φ, for ATS spacecraft. From
Michalek, Stipandic & Coyle (1972) [24]. . 82
Figure 7-6: Effective emittance vs. blade angle, θ, and baseplate temperature, TBP, for
sensory subsystem of NIMBUS spacecraft. From London (1967) [20]. . 84
Figure 7-7: Schematic blade geometry for diffuse body radiation analysis. Louvers of
the control subsystem. NIMBUS spacecraft. From London (1967) [20]. . 85
Figure 7-8: Effective emittance, ε , vs. blade angle, θ, for the control subsystem of
eff
NIMBUS spacecraft. From London (1967) [20]. . 85
Figure 7-9: Effective emittance, ε , vs. baseplate temperature, T , for the control
eff BP
subsystem of NIMBUS spacecraft. From London (1967) [20]. . 86
Figure 7-10: Comparison of NIMBUS 1 and 2 control subsystem panel temperatures,
T , vs. orbital position. From London (1967) [20]. . 86
p
Figure 7-11: Overall dimensions of SNIAS louver. Not to scale. . 87
Figure 7-12: Effective emittance, ε , vs. blade angle, θ, for the SNIAS louver system.
eff
From Redor (1972) [29]. . 89
Figure 7-13: Effective absorptance, α , vs. blade angle, θ, for several values of the sun
eff
angle, φ. SNIAS louver system. From Redor (1972) [29]. . 91
Figure 7-14: Heat rejection capability, q, vs. blade angle, θ, for several values of the
sun angle, φ. SNIAS louver system. From Redor (1972) [29]. 93
Figure 7-15: Maximum blade temperature, T , vs. blade angle, θ, for several values of
B
the sun angle, φ. SNIAS louver system. From Redor (1972) [29]. . 95
Figure 7-16: Effective emittance, εeff, vs. blade angle, θ, for the louver system of
SNIAS. Solid line: From Redor (1972) [29]. Dashed line: From Croiset &
Leroy (1973) [8]. . 96
Figure 7-17: Heat rejection capability, q, vs. blade angle, θ, for several values of the
sun angle, φ. SNIAS louver system. Solid line: From Redor (1972) [29].
Dashed line: From Croiset & Leroy (1973) [8]. 97
Figure 7-18: Temperature-pressure characteristic of the Bourdon spiral. From Reusser
et al. (1973) [30]. . 100
Figure 7-19: Performance of a Bourdon actuating a single blade. After Reusser et al.
(1973) [30]. . 101
Figure 7-20: Ratios (TBP−T)/(TBP−TOL) and Q/Q0 vs. time, τ. After Reusser et al. (1973)
[30]. . 103

Tables
Table 5-1: Blade Characteristics of Existing Louver Assemblies R: Rectangular, T:
Trapezoidal . 16
Table 5-2: Materials Used . 19
Table 5-3: Typical Alloy Used in Bellows D: Deposited, F: Formed, W: Welded . 25
Table 5-4: Typical Nonmetallic Materials Used in Bellows . 27
Table 5-5: Typical Fluids Used in Bellows . 28
Table 5-6: Bellows Convolutions and Relevant Characteristics . 28
Table 5-7: Spring Rate for Several Bellows . 30
Table 5-8: Frequency of Bellows Vibration . 31
Table 5-9: Characteristics of Convoluted Bellows . 32
Table 7-1: Assumed Values of the Optical Properties of the Surfaces for the First
Computer program . 77
Table 7-2: Assumed Values of the Optical Properties of the Surfaces for the Second
Computer program . 77
Table 7-3: Ideal Optical Properties of the NIMBUS Louvers Surfaces . 83
Table 7-4: Optical Characteristics of the Surfaces of SNIAS Louver. . 87
Table 7-5: Effective Absorptance α , for Several Values of Sun Angle, φ, and Blade
eff
Angle, θ. . 90
Table 7-6: Heat Rejection Capability, q, for Several Values of Sun Angle, φ, and Blade
Angle, θ. . 92
Table 7-7: Maximum Blade Temperature, T , for Several Values of Sun Angle, φ, and
B
Blade Angle, θ. . 94
Table 7-8: Several Characteristics of the Bourdon Spiral . 98
Table 7-9: Several Parameters of the Bourdon Spiral . 99

European Foreword
This document (CEN/CLC/TR 17603-31-12:2021) has been prepared by Technical Committee
CEN/CLC/JTC 5 “Space”, the secretariat of which is held by DIN.
It is highlighted that this technical report does not contain any requirement but only collection of data
or descriptions and guidelines about how to organize and perform the work in support of EN 16603-
31.
This Technical report (TR 17603-31-12:2021) originates from ECSS-E-HB-31-01 Part 12A.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such
patent rights.
This document has been prepared under a mandate given to CEN by the European Commission and
the European Free Trade Association.
This document has been developed to cover specifically space systems and has therefore precedence
over any TR covering the same scope but with a wider domain of applicability (e.g.: aerospace).
Scope
Thermal louvers are thermal control surfaces whose radiation characteristics can be varied in order to
maintain the correct operating temperature of a component subject to cyclical changes in the amount
of heat that it absorbs or generates.
The design and construction of louvers for space systems are described in this Part 12 and a clause is
also dedicated to providing details on existing systems.

The Thermal design handbook is published in 16 Parts
TR 17603-31-01 Thermal design handbook – Part 1: View factors
TR 17603-31-02 Thermal design handbook – Part 2: Holes, Grooves and Cavities
TR 17603-31-03 Thermal design handbook – Part 3: Spacecraft Surface Temperature
TR 17603-31-04 Thermal design handbook – Part 4: Conductive Heat Transfer
TR 17603-31-05 Thermal design handbook – Part 5: Structural Materials: Metallic and
Composite
TR 17603-31-06 Thermal design handbook – Part 6: Thermal Control Surfaces
TR 17603-31-07 Thermal design handbook – Part 7: Insulations
TR 17603-31-08 Thermal design handbook – Part 8: Heat Pipes
TR 17603-31-09 Thermal design handbook – Part 9: Radiators
TR 17603-31-10 Thermal design handbook – Part 10: Phase – Change Capacitors
TR 17603-31-11 Thermal design handbook – Part 11: Electrical Heating
TR 17603-31-12 Thermal design handbook – Part 12: Louvers
TR 17603-31-13 Thermal design handbook – Part 13: Fluid Loops
TR 17603-31-14 Thermal design handbook – Part 14: Cryogenic Cooling
TR 17603-31-15 Thermal design handbook – Part 15: Existing Satellites
TR 17603-31-16 Thermal design handbook – Part 16: Thermal Protection System

References
EN Reference Reference in text Title
EN 16601-00-01 ECSS-S-ST-00-01 ECSS System - Glossary of terms

All other references made to publications in this Part are listed, alphabetically, in the Bibliography.

Terms, definitions and symbols
3.1 Terms and definitions
For the purpose of this Standard, the terms and definitions given in ECSS-S-ST-00-01 apply.
3.2 Symbols
Clause 5: bellows effective area, [m ]
A
Clause 7: contact surface (bourdon sensing element),

[m ]
−
radiosity, [W.m ]
B
dimensionless radiosity, B* = B/σT
B*
bellows innermost diameter, [m]
Di
bellows outermost diameter, [m]
Do
−2
modulus of elasticity, [N.m ]
E
−
flexibility, [m.Pa ]
F
− −
2 1
coil force constant, [N.m .Angular degrees ]
Fc
−
energy flux impinging on the unit area, [W.m ]
H
−
heat flux to the skin arriving from outside, [W.m ]
J
−
bellows spring rate, [N.m ]
K
−
coil deflection constant, [angular degrees, K ]
Kc
Clause 5: coil active length, [m]
L
Clause 5: length of all convolutions in bellows, [m]

Clause 6: louver blade spacing, [m]

length of a single convolution in bellows measured
Lc
along the surface, [m]
torsional moment of a coil, [N.m]
M
fluid pressure, [Pa]
P
proportionality limit pressure in a bourdon, [Pa]
Pt
heat transfer to the fluid within the bourdon, [J]
Q
heat transfer to the fluid within the bourdon after an
Q0
infinitely large time, [J]
equivalent thermal resistance of the louver system, it
R(θ)
is a function of the optical properties of blades, and
inner skin surface, but for a given system R depends
only on the blade angle
coiling radius of a bourdon, [m]
R0
mean radius of the bellows, [m]
Rm
−
heat flux from the space to the skin, [W.m ]
S
−
solar constant, S0 = 1353 W.m
S0
temperature, [K]
T
bourdon filling fluid temperature, [K]
TC
reference temperature, [K]
T0
temperature differential, [K], ∆T = T−T0
∆T
starting fluid temperature, [K]
T0L
skin temperature, [K]
TS
4 4
local dimensionless temperature, T* = T /T BP
T*
inside volume of bellows, [m ]
V
−
sensitivity of a bimetal, [angular degrees, K ]
X
semi-major axis of the bourdon tube cross section, [m]
a
Clause 5: semi-minor axis of the bourdon tube section,
b
[m]
Clause 6: louver blade width, [m]

Clause 5: numerical coefficient given in Table 5-7
c
under additional data
− −
1 1
Clause 7: fluid specific heat, [J.kg .K ]

defined as f(θ) = 1 - [1/R(θ)]
f(θ)
−
fundamental natural frequency, [s ]
fn=1
total thermal conductance of a bourdon (sensing
h
− −
2 1
element plus fluid, [W.m .K ]
length of a given metallic strip when the temperature
l
is T [m]
live length of the bellows, [m]

length of a given metallic strip when the temperature
l0
is T0, [m]
mass of bellows active convolutions, [kg]
ma
mass of one convolution, [kg]
mc
mass of fluid trapped in active length at rest, [kg]
mfa
2 2
mfa = ρL[0,262(Do +DoDi)-0,524Di ]
mass of liquid within the bellows, [kg]. ml = ρAl
ml
mass on bellows free end, [kg]
m1
bellows mass, [kg]
m2
−
louver heat rejection capability, [W.m ]
q
−
heat rejection capability for zero solar input, [W.m ]
qshadow
thickness of the strip of the coil, [m]
t
wall thickness for bellows or bourdon tube, [m]

width of the strip of the coil, [m]
w
coordinate along the louver baseplate, [m]
x
Coordinates along the outer and inner faces of the
y,z
blade, [m]
Φ sun angle, [angular degrees]
α absorptance
numerical coefficient which appears in the expression

of bourdon flexibility
solar absorptance
αs
α spectral absorptance
λ
−
β Clause 5: linear thermal expansion coefficient, [K ]
Clause 5: numerical coefficient which appears in that

expression of bourdon flexibility
Clause 6: Dimensionless coordinate along the louver

baseplate, β = x/L
linear thermal expansion coefficient of the high
βH
−
expansibility component of a bimetal, [K ]
linear thermal expansion coefficient of the low
βL
−
expansibility component of a bimetal, [K ]
ε hemispherical total emittance
emittance of the skin inner surface
εI
emittance of the skin outer surface
εs
dimensionless coordinates, η = y/L, ζ = z/L
η,ζ
Clause. 5: angular deflection of a coil, [angular
θ
degrees]
Clause 6: louver blade angle, [angular degrees]

poisson's ratio
ν
−
Clauses 5 and 7: fluid density, [kg.m ]
ρ
Clause 6: reflectance
ρ spectral reflectance
λ
s
specular reflectance
ρ
initial coiling angle in a bourdon, also called
ψ0
mechanical preload angle, [angular degrees]
−
Stefan-Boltzmann constant, σ = 5,6697 x 10
σ
−2 −4
W.m .K
τ time, [s]
Subscripts
concerns louver blades
B
concerns the inner face of the louver blade
BI
concerns the outer face of the louver blade
B0
concerns louver baseplate
BP
effective value
eff
General introduction
Thermal louvers are thermal control surfaces whose radiation characteristics can be varied in order to
maintain the proper temperature of a component which experiences cyclical changes in the amount of
heat that it absorbs or generates.
Louvers are constituted by five main components: baseplate, blades, actuators, sensing elements, and
structural elements.
The baseplate is a surface of low absorptance to emittance ratio which covers the critical set of
components whose temperature is being controlled.
The blades, driven by the actuators, are the elements of the louvers which give variable radiation
characteristics at the baseplate. When the blades are closed, they shield the baseplate from the
surroundings, while when they are fully open, the coupling by radiation of the baseplate to the
surroundings is the largest.
The radiation characteristics of the baseplate can be varied in the range defined by these two extreme
positions of the blades.
The actuators are the elements of the louvers which drive the blades according to the temperature
sensed by sensors placed in the baseplate. Up to now, the actuators of the louvers flown on satellites
have been bimetal spirals or bellows, although other types could be used, such as Bourdon spirals,
and electrical devices.
In a single actuation system all the blades are driven by the same actuator. In the multiple blade
actuator system several actuators are required to operate the system. Generally, bimetals are used as
multiple blade actuation system, and bellows as single blade systems.
The sensing element senses the temperature of the baseplate and activates the actuators, which drive
the blades according to this temperature. The type of sensing element depends on the kind of actuator.
When the actuator is a bimetal, the sensing element is the bimetal itself. If the actuators are bellows or
Bourdon, the sensing element can be a tank or a tube, containing a liquid or a liquid-vapor mixture,
and soldered to the baseplate.
The different components of the louver system are supported by means of a frame. When bimetallic
actuators are used, they are enclosed in a housing to shield the bimetal from the environment. This
actuator housing may be a structural part of the frame.
Louver systems can be made for shadow or sunlight operation. In the first case heat is radiated
through the louver to the outer skin of the spacecraft, while in the second the excess heat is transferred
from the emitting baseplate to the outer space.
Louvers do not consume power except those that are electrically actuated.

Components of a louver
5.1 Blades
Louver blades are normally of rectangular plan form. Trapezoidal plan forms are preferred for
circular assemblies.
Each blade is mounted around a shaft. This provides the torsional stiffness required to transmit the
actuator torque:
Characteristics of blades used in several existing configurations are given in Table 5-1.
Table 5-1: Blade Characteristics of Existing Louver Assemblies
R: Rectangular, T: Trapezoidal
PRODUCER SPACECRAFT αs BLADE MATERIAL CONFIGURATION
ε
LAUNCH DATE DIMENSIONS
x10 [m]
−
MARINER 2 0,12 0,508x10 m thick Polished R
Aluminium
8/26/1962 0,04
COMMENTS: Louver blades are center pivoted.
−
O.G.O. 0,12 Two layers of 0,127x10 m R
thick Polished Aluminium
9/4/1964 0,04 500x45
COMMENTS: The blade is a rectangular center-rotating member constructed of two formed
aluminium sheets spot-welded together along the two edges. Plastic end fittings are provided at each
end of the blades.
−
MARINER 4 0,12 Two layers of 0,127x10 m R
thick Polished Aluminium
11/28/1964 0,04 150x30
COMMENTS: Each louver blade is a rectangular center-pivoted member consisting of an aluminium
−
tube whose square cross section has a side of 3,5x10 m.
Fairchild Hiller PEGASUS II 0,11 Polished Aluminium 5052 R
5/25/1965 0,05 200x50
COMMENTS: Each louver blade is a rectangular center-pivoted member constructed from Aluminium
Alloy 5052.
Louver for shadow operation.
−
GENERAL NIMBUS 1 & 2 0,15 32 Layers of 6,35x10 m R
PRODUCER SPACECRAFT αs BLADE MATERIAL CONFIGURATION
ε
LAUNCH DATE DIMENSIONS
x10 [m]
ELECTRIC (SENSORY thick embossed preshrunk
SUBSYSTEM) aluminized Mylar
1-8/28/1964 0,03
2-5/15/1966
−
COMMENTS: The blades are side pivoted and are covered by a layer of Mylar 2,54x10 m thick not
embossed, to maintain specular external surface.
−
GENERAL NIMBUS 1 & 2 0,20 11 Layers of 6,35x10 m R
ELECTRIC (CONTROL thick matted glass fiber
SUBSYSTEM) paper
1-8/28/1964 0,80
2-5/15/1966
COMMENTS: The blades are covered on both sides by an additional layer of glass fiber paper, and are
−
enclosed with a 5,08x10 m thick woven glass fiber fabric that is impregnated with Teflon. The blades
are diffuse.
a
Fairchild Hiller ATS 0,17 Polished Aluminium with a R
whitepaint strip (6% of area)
a
5/30/1974 0,05
COMMENTS: Blades are sandwiched with a BR-34 polyimide adhesive bond. A white paint strip (DC
92-007) was added to the top of each blade along its entire length to lower the blade temperature
during operation in a solar environment.
a
Values measured before the white strip was added.
Fairchild Hiller O.A.O. 0,12 Two stamped sheets of R
Polished Aluminium
0,06
COMMENTS: Louver for shadow operation.
−
TRW-Systems PIONNER IV 0,15- 0,076x10 m Aluminium foil T
0,20 sheets (1100-H 18)
3/3/1959 0,04 Length = 267.
Width at the large end =
76,2.
Width at the narrow end
= 25,4.
COMMENTS: To obtain the appropriate stiffness and longitudinal rigidity, sheet blades are formed
−
into 6,35x10 m thick rectangular cross section, containing a hollow-internal shaft. Circular system.
SNIAS 0,10 Polished Aluminium (A 9) R
0,04 123x38
COMMENTS:
ERNO HELIOS Uncoated Aluminium T
Sandwich
12/10/1974 Length = 220
Width at the large end =
PRODUCER SPACECRAFT αs BLADE MATERIAL CONFIGURATION
ε
LAUNCH DATE DIMENSIONS
x10 [m]
COMMENTS:
RCA  Foam with glued aluminized R
Mylar
COMMENTS: Louver made per blade, actuated by bimetal. Price: US $ 2100 per blade.
5.2 Actuators
5.2.1 Bimetals
5.2.1.1 Introduction
Bimetal is a composite material having two or more metallic layers of different thermal expansion
coefficients, that are permanently bonded together. If the bimetal temperature raises, the metal layer
with the higher thermal expansion coefficient (high expansion component) tends to expand more than
the one with the lower coefficient (low expansion component). The differences in thermal expansion
cause the bending of the bimetal. If one end of the bimetal is fixed, the displacement at the free end
can be used for operating electrical contacts or tripping a mechanism.
In order to achieve large deflections, the bimetal is frequently used in the form of helicoidal spring. If
this spring is fixed at its outer extremity, the inner end may be attached to a shaft which will then
rotate when the temperature changes. The available forces will depend both on the material
mechanical and thermal characteristics, and on the spring dimensions.
Bimetals have been used in many spatial louver systems such as: Mariner, ATS, OGO, Pegasus,
Pioneer, etc. In these systems the bimetal is thermally coupled to the nearest portion of the radiator
plate, and is, therefore, used as actuator and as sensing element.
5.2.1.2 Materials
Materials which are used in the manufacture of the bimetals for low expansion components or for
high expansion components are given in Table 5-2.
Table 5-2: Materials Used
MATERIAL ALLOYS WITH LARGEST β
ALLOYS WITH SMALLEST β
LOW EXPANSION INVAR, Also called; NILO 36, NILEX,
COMPONENT NILVAR, and INDILATANS
HIGH BRASSES CARTRIDGE BRASS
EXPANSION
RED BRASS
COMPONENT
AUSTENITIC ALLOY STEELS STAINLESS STEEL 347
STAINLESS STEEL 310
NICKEL-MANGANESE-CHROMIUM NIMONIC ALLOY PE 16
ALLOYS
NIMONIC ALLOY PK 33
Thermal Expansion Coefficient
Values of the relative linear thermal expansion of the above alloys are plotted as functions of
temperature in Figure 5-1 to Figure 5-4.

Figure 5-1: Relative linear thermal expansion vs. temperature in the case of Invar.
T0 = 273 K. From THE MOND NICKEL CO [35].
Figure 5-2: Relative linear thermal expansion vs. temperature in the case of brasses.
T0 = 273 K. After Baldwin (1961) [3].

Figure 5-3: Relative linear thermal expansion vs. temperature in the case of
austenitic steels. T0 = 273 K. After Zapffe (1961) [39].
Figure 5-4: Relative linear thermal expansion vs. temperature in the case of
Nimonic alloys. T0 = 273 K. After WIGGIN & Co. (1967) [38].
This relative linear thermal expansion is defined as
(l−l0)/l0 = β ∆T
Figure 5-5 is a summary of the data given in the four foregoing figures.

Figure 5-5: Relative linear thermal expansion vs. temperature for different alloys.
T0 = 273 K. After Baldwin (1961) [3], Zapffe (1961) [39], WIGGIN Co. (1967) [38].
5.2.1.3 Deflection of spirals and helical coils. sensitivity
Bimetalic spirals and helical coils deflected rotationally when the temperature changes. The deflection
is given by
K ∆TL
c
θ =
[5-1]
t
where the coil deflection constant, Kc, may be written as:
3 360 270
K = (β − β ) = (β − β ) [5-2]
c H L H L
4 π π
The sensitivity, X, of spirals and helical coils is:
θ K L
c
[5-3]
X = =
∆T t
Although the above expressions are always valid, it should be pointed out that Kc depends on the
temperature and it is really constant only when the relative linear thermal expansion is a linear
function of temperature.
− − −
4 4 1
Typical values of Kc for different bimetals are from 5x10 to 25x10 Angular Degrees.K .
Figure 5-6 gives the ∆T required to achieve a given rotation θ, for different sensitivities, X, while
Figure 5-7 shows X as a function of the bimetal slenderness, L/t, for different values of the deflection
constant Kc.
Figure 5-6: Difference of temperature, ∆T, vs. angle of rotation of the free end, θ,
for several values of the sensitivity, X. After Martin & Yarworth (1961) [21],
KAMMERER (1971) [16].
Figure 5-7: Sensitivity vs. ratio L/t, for different values of Kc. After Martin &
Yarworth (1961) [21], KAMMERER (1971) [16].
References: Martin & Yarworth (1961) [21], KAMMERER (1971) [16], Trylinski (1971) [37].
5.2.1.4 Torsional moment of spirals and helical coils
The Torsional Moment of spirals and helical coils is given by
M = KcFc ∆T w t
where the so called thermal force of the spiral, KcFc, is:
( )
K F = E β − β [5-4]
c c H L
− −
5 5 2 1
Typical values of KcFc, for different bimetals are of order of 1x10 to 5x10 N.m .K .
The Figure 5-8 gives the ratio M/KcFc∆TL versus L/t, for different values of w/t.
Figure 5-8: Dimensionless ratio M/KcFc∆TL vs. L/t, for several values of w/t. After
Martin & Yarworth (1961) [21], KAMMERER (1971) [16].
5.2.2 Bellows
5.2.2.1 Introduction
Bellows are flexible, thin-walled, circumferentially corrugated cylinders with open or closed ends.
The principle of operation of the bellows is simple: an inner to outer pressure difference causes a
change in the bellow length, unless both ends are clamped. If an end is clamped while the other is free,
the bellows can behave as an actuator.
Bellows serve many different functions, either as independent units or as integral parts of more
complex components. Filled with a liquid they are used as measuring devices. Louvers of the
NIMBUS spacecraft are actuated by bellows containing a liquid-vapor mixture of Freon (Freon-11 for
the louvers of the control subsystem and Freon-114 for those of the sensory subsystem).
Bellows constituted by one or more layers of materials are called respectively one-ply or multi-ply
bellows.
5.2.2.2 Materials
Both metallic and non-metallic materials can be used to manufacture the bellows. Metallic bellows can
be either formed, welded, machined, or deposited. In the last method the metal is deposited by
electroplating or chemically onto machined aluminium mandrels which are later dissolved.
The characteristics of the metallic and non-metallic materials more used in the manufacture of bellows
are summarized in the following pages.
Table 5-3: Typical Alloy Used in Bellows
D: Deposited, F: Formed, W: Welded
MATERIAL TYPE OUTSTANDING
CHARACTERISTICS
COPPER ALLOYS BRASS, BRONZE F D HIGH PROPORTIONAL LIMIT.
GOOD TOUGHNESS.
BERYLLIUM COPPER
ZIRCONIUM COPPER
ALUMINIUM 5083 F HIGH STRENGTH-WEIGHT
ALLOYS RATIOS.
GOOD TOUGHNESS AT LOW
AND INTERMEDIATE STRESS
LEVELS AT TEMPERATURES AS
LOW AS 20 K.
NICKEL AND NICKEL 200 F D GOOD CORROSION
CUPRO-NICKEL RESISTANCE.
MONELS 400
ALLOYS
LOW MAGNETIC
PERMEABILITY.
K 500
TITANIUM ALLOYS Ti - 75 A F HIGH STRENGTH AND
STRENGTH TO WEIGHT RATIO.
Ti - 6 Al - 4 V
GOOD CREEP STRENGTH FROM
530 K TO 6
...