ISO 16378:2022

Space systems — Measurements of thermo-optical properties of thermal control materials

This document specifies the multiple measurement methods, instruments, equipment, and samples used to calculate the thermo-optical properties of thermal control materials. This document compares their features, indicates their limitations and biases, and guides the applications. This document also defines requirements for calibration and reference materials to ensure data quality. This document specifies the following test methods, including the configuration of samples and calculations. a) Solar absorptance using a spectrophotometer (αs) — Annex A. b) Solar absorptance using the comparative test method (αp) — Annex B. c) Hemispherical infrared emittance using the thermal test method (εh-t) — Annex C. d) Normal infrared emittance using an IR spectrometer (εn-s) — Annex D. e) Normal infrared emittance using ellipsoid collector optics (εn-e) — Annex E. f) Normal infrared emittance using two rotating cavities (εn-c) — Annex F.

Systèmes spatiaux — Mesures des propriétés thermo-optiques des matériaux de thermorégulation

General Information

• Status: Published
• Publication Date: 20-Sep-2022
• ICS: 49.140 - Space systems and operations
• Technical Committee: ISO/TC 20/SC 14 - Space systems and operations
• Drafting Committee: ISO/TC 20/SC 14/WG 6 - Materials and processes
• Current Stage: 6060 - International Standard published
• Start Date: 21-Sep-2022
• Due Date: 11-Oct-2022
• Completion Date: 21-Sep-2022

Relations

• Revises: ISO 16378:2013 - Space systems — Measurements of thermo-optical properties of thermal control materials
• Effective Date: 23-Apr-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 16378
Second edition
2022-09
Space systems — Measurements of
thermo-optical properties of thermal
control materials
Systèmes spatiaux — Mesures des propriétés thermo-optiques des
matériaux de thermorégulation
Reference number
ISO 16378:2022(E)
© ISO 2022
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ISO 16378:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
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ISO 16378:2022(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction .............................................................................................................................................................................................................................. vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Abbreviated terms ............................................................................................................................................................................................. 5

5 Preparatory conditions ................................................................................................................................................................................5

5.1 Hazards, health, and safety precautions ......................................................................................................................... 5

5.2 Preparation of samples ................................................................................................................................................................... 5

5.2.1 Sample property ................................................................................................................................................................. 5

5.2.2 Configuration ........................................................................................................................................................................ 5

5.2.3 Cleaning ...................................................................................................................................................................................... 6

5.2.4 Handling and storage ..................................................................................................................................................... 6

5.2.5 Identification ......................................................................................................................................................................... 6

5.3 Facilities ........................................................................................................................................................................................................ 6

5.3.1 Cleanliness ............................................................................................................................................................................... 6

5.3.2 Environmental conditions ......................................................................................................................................... 6

5.3.3 Equipment ................................................................................................................................................................................ 6

5.4 Standard materials ............................................................................................................................................................................. 6

5.4.1 General ........................................................................................................................................................................................ 6

5.4.2 Reference standard material ................................................................................................................................... 7

5.4.3 Working standard material ...................................................................................................................................... 7

5.4.4 Solar absorptance .............................................................................................................................................................. 7

5.4.5 Infrared emittance ........................................................................................................................................................... 7

6 Solar absorptance (α ) test methods .............................................................................................................................................. 7

7 Hemispherical infrared emittance (ε ) test method ..................................................................................................... 8

8 Normal infrared emittance (ε ) test methods ...................................................................................................................... 8

9 Test report .................................................................................................................................................................................................................. 9

9.1 Standard tests ......................................................................................................................................................................................... 9

9.1.1 Complete identification of the material tested ........................................................................................ 9

9.1.2 Complete identification of the measurement condition .................................................................. 9

9.1.3 Measurement results ................................................................................................................................................... 10

9.2 Non-standard tests .......................................................................................................................................................................... 10

10 Quality assurance ............................................................................................................................................................................................10

10.1 Precision ......... .................................................................................................................................. ......................................................... 10

10.2 Non-conformance ........................................................................................................................................... ................................... 11

10.3 Calibration ............................................................................................................................................................................................... 11

10.4 Traceability ............................................................................................................................................................................................. 11

10.5 Uncertainty ............................................................................................................................................................................................. 11

11 Audit of measurement equipment ..................................................................................................................................................11

11.1 General ........................................................................................................................................................................................................ 11

11.2 Initial audit of the system (acceptance) ........................................................................................................................ 11

11.3 Annual regular review (maintenance) of the system........................................................................................ 11

11.4 Special review ...................................................................................................................................................................................... 12

Annex A (normative) Solar absorptance using a spectrophotometer (α ) ...............................................................13

Annex B (normative) Solar absorptance using the comparative test method (α ) .........................................18

Annex C (normative) Hemispherical infrared emittance using the thermal test method (ε ) .......20

h-t

Annex D (normative) Normal infrared emittance using an IR spectrometer (ε ) .......................................24

n-s
iii
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ISO 16378:2022(E)

Annex E (normative) Normal infrared emittance using ellipsoid collector optics (ε ) .........................27

n-e

Annex F (normative) Normal infrared emittance using two rotating cavities (ε ) ....................................32

n-c

Annex G (informative) Key parameters for measurement........................................................................................................35

Annex H (informative) Theoretical directional emissivity ......................................................................................................36

Bibliography .............................................................................................................................................................................................................................37

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ISO 16378:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,

Subcommittee SC 14, Space systems and operations.

This second edition cancels and replaces the first edition (ISO 16378:2013), which has been technically

revised.
The main changes are as follows:
— updated terms and definitions according to the referenced document revision;
— revised description of sample thickness precision requirements;
— deleted solar absorptance measurement with central sample mounting sphere.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 16378:2022(E)
Introduction

Solar absorptance and infrared emittance are the key parameters of materials for both active and

passive thermal design of space systems.

This document describes the methodology, instruments, equipment, and samples used to calculate the

key parameters of thermal-control materials, i.e. solar absorptance (α or α ) and the infrared emittance

s p

(ε or ε ). The measurements defined in this document are performed at ground test facilities with the

h n

purpose of obtaining material properties. The measured properties are used for material selection,

thermal design of spacecraft, process control, quality control, etc. Also, on-orbit temperature data in

the beginning of life can be assessed using the data obtained by ground measurement.

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INTERNATIONAL STANDARD ISO 16378:2022(E)
Space systems — Measurements of thermo-optical
properties of thermal control materials
1 Scope

This document specifies the multiple measurement methods, instruments, equipment, and samples

used to calculate the thermo-optical properties of thermal control materials. This document compares

their features, indicates their limitations and biases, and guides the applications. This document also

defines requirements for calibration and reference materials to ensure data quality.

This document specifies the following test methods, including the configuration of samples and

calculations.
a) Solar absorptance using a spectrophotometer (α ) — Annex A.
b) Solar absorptance using the comparative test method (α ) — Annex B.

c) Hemispherical infrared emittance using the thermal test method (ε ) — Annex C.

h-t
d) Normal infrared emittance using an IR spectrometer (ε ) — Annex D.
n-s
e) Normal infrared emittance using ellipsoid collector optics (ε ) — Annex E.
n-e
f) Normal infrared emittance using two rotating cavities (ε ) — Annex F.
n-c
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
absorptance
quotient of absorbed radiant flux (3.8) and incident radiant flux, expressed by
α = Φ /Φ
a m
where Φ is absorbed radiant flux and Φ is incident radiant flux
a m
[SOURCE: ISO 80000-7:2019, 7-31.1]
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ISO 16378:2022(E)
3.2
emittance

quotient of the radiant exitance of a radiator and the radiant exitance of a Planckian radiator at the

same temperature, expressed by
ε = M/M

where M is the radiant exitance of a thermal radiator and M is the radiant exitance of a Planckian

radiator at the same temperature
EXAMPLE Total hemispherical emittance.

Note 1 to entry: Total hemispherical exitance M of the considered surface divided by the total hemispherical

exitance M of the blackbody at the same temperature (see ISO 9288).

Note 2 to entry: The following adjectives should be added to define the conditions.

— Total: If they are related to the entire spectrum of thermal radiation (this designation can be considered as

implicit) (see ISO 9288).

— Spectral or monochromatic: If they are related to a spectral interval centred on the wavelength λ (see

ISO 9288).

— Hemispherical: If they are related to all directions along which a surface element can emit or receive radiation

(see ISO 9288).

— Directional: If they are related to the directions of propagation defined by a solid angle around the defined

direction (see ISO 9288).

— Normal: If they are related to the normal direction of propagation or incidence to the surface.

Note 3 to entry: When there is a certain need to distinguish a property of a material from a property of a real

object, the word “emissivity” can be used. Emissivity is a property of a material defined in terms of the emittance

of an ideal material that is semi-infinite medium limited by optically smooth surface. Annex H provides further

information about theoretical emissivity and practical emittance.

Emissivity depends on the temperature at which it is determined and wavelength range.

Emittance is a property of a particular object. It is determined by material emissivity, surface roughness,

oxidation, the sample’s thermal and mechanical history, surface finish, and measured wavelength range.

Although emissivity is a major component in determining emittance, the emissivity determined under laboratory

conditions seldom agrees with actual emittance of a certain sample.
ελ= LT,/ελ dLλλ,Tdλ
() () ()
where
−5 CT/λ
L (λ,T)
b is the spectral Planck distribution of blackbody radiation, C λ e −1 ;
–16 2
C is 3,741 77 × 10 W·m ;
C is 1,438 8 × 10 m·K;
T is the absolute temperature, K;
λ is the wavelength, m;
–1 4
σπ T ;
LT()λλ, d
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ISO 16378:2022(E)
–8 -2 -4
σ is the Stefan-Boltzmann constant, 5,670 400 (40) × 10 W·m ·K .

[SOURCE: ISO 80000-7:2019, 7-30.1, modified — The term has been changed to "emittance"; the

EXAMPLE and notes to entry have been added.]
3.3
diffuse

indicating that flux propagates in many directions, as opposed to direct beam, which refers to a

collimated flux

Note 1 to entry: When referring to reflectance (3.9), diffuse reflectance is the ratio of the diffusely reflected part

of the (whole) reflected flux to the incident flux.
3.4
infrared emittance
emittance (3.2) in the infrared range at least from 5 μm to 25 μm
3.5
integrating sphere

optical device, which is used to either get flux proportional to that reflected or transmitted from a

sample into a hemisphere or to provide uniform irradiation of a sample from the whole hemisphere

Note 1 to entry: It consists of a cavity with apertures for admitting and detecting flux and usually having

additional apertures over which sample and reference specimens are placed.
3.6
irradiance

density of incident radiant flux (3.8) with respect to area at a point on a real or imaginary surface,

expressed by
E = dΦ /dA
e e

where Φ is radiant flux and A is area (see ISO 80000-3) on which the radiant flux is incident

Note 1 to entry: It is expressed in W/m .
[SOURCE: ISO 80000-7:2019, 7-7.1, modified — Note 1 to entry has been added.]
3.7
near-normal-hemispherical

indicating irradiance (3.6) to be directional near-normal to the specimen surface and that the flux

leaving the surface or medium is collected over an entire hemisphere for detection

3.8
radiant flux
change in radiant energy with time, expressed by
Φ = dQ /dt
e e

where Q is the radiant energy emitted, transferred, or received and t is time(ISO 80000-3)

Note 1 to entry: It is expressed in W.

[SOURCE: ISO 80000-7:2019, 7-4.1, modified — The alternative term "radiant power" has been removed;

note 1 to entry has been added.]
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ISO 16378:2022(E)
3.9
reflectance
quotient of reflected radiant flux (3.8) and incident radiant flux, expressed by
ρ = Φ /Φ
r m
where Φ is reflected radiant flux and Φ is incident radiant flux
r m
[SOURCE: ISO 80000-7:2019, 7-31.3]
3.10
solar

indicating that the radiant flux involved has the Sun as its source or has the relative

spectral distribution of solar flux

Note 1 to entry: The adjective “solar” is used for optical field as indicating a weighted average of the spectral

property, with a standard solar spectral irradiance (3.6) distribution as the weighting function.

3.12
solar absorptance

ratio of the solar (3.10) radiant flux (3.8) absorbed by a material (or body) to the radiant flux of the

incident radiation
Note 1 to entry: Differentiation is made between two methods:

a) Method of spectral measurements using a spectrophotometer covering the range from 250 nm to 2 500 nm

for the determination of α . In this case a weighted mean value of spectral characteristics with standard

spectral distribution of solar irradiation as a weighting function is calculated.

b) Method of α measurements using the tools which measure integral reflection factor by using a comparison

method. In this case a portable equipment is used which has a source of irradiation with spectral distribution

near to solar spectral distribution or when the registration is performed by using spectral correcting

elements, which can simulate registration of solar irradiation flux.
3.13
solar irradiance

radiation of the Sun integrated over the full disk and expressed in SI units of power through a unit of

area, W·m
[SOURCE: ISO 21348:2007, 7-4.1, modified — Note 1 to entry has been removed.]
3.14
spectral

indicating that the property was evaluated at a specific wavelength, λ, within a small wavelength

interval, Δλ about λ

Note 1 to entry: The parameters of frequency, ν, wave number, κ, or photon energy can be substituted for

wavelength, λ, in this definition.

Note 2 to entry: At a specific wavelength, the wavelength at which the spectral concentration was evaluated can

be indicated by the wavelength in parentheses following the symbol, such as α (350 nm), or as a function of the

wavelength, such as α (λ).
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ISO 16378:2022(E)
3.16
specular

indicating that the flux leaves a surface or medium at an angle that is numerically equal to the angle of

incidence, lies in the same plane as the incident ray and the perpendicular, but is on the opposite side of

the perpendicular to the surface

Note 1 to entry: Reversing the order of terms in an adjective reverses the geometry of the incident and collected

flux, respectively.
3.17
transmittance

quotient of transmitted radiant flux (3.8) and incident radiant flux, expressed by

τ = Φ /Φ
t m
where Φ is transmitted radiant flux and Φ is incident radiant flux
t m
[SOURCE: ISO 80000-7:2019, 7-31.5]
4 Abbreviated terms
IR infra-red
RT room temperature
5 Preparatory conditions
5.1 Hazards, health, and safety precautions

Attention shall be given to health and safety precautions. Hazards to personnel, equipment, and

materials shall be controlled and minimized.
5.2 Preparation of samples
5.2.1 Sample property

This document is applicable to materials having both specular and diffuse optical properties.

5.2.2 Configuration

The material samples shall be prepared according to the relevant process specification or manufacturer’s

data and shall be representative of batch variance.

The samples shall represent the work piece as exactly as possible. Expected changes in thermo-optical

properties from the measured sample to the flight equipment shall be considered in thermal design.

For instance, the application procedure for paint can result in different thermo-optical properties

depending on the painter and the type of spray gun used; therefore, the samples should be coated or

made at the same time as the work piece.

The surface roughness strongly affects the measurement results. Bare (uncoated) samples shall be

finished to the same surface condition as the work piece.
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ISO 16378:2022(E)
5.2.3 Cleaning

The cleaning method and other treatment of the sample shall always be the same as for the flight

hardware. Further cleaning or treatment of the sample is not allowed.

In particular, solar absorptance properties are very sensitive to contamination and if the sample or the

flight hardware is contaminated (even by hand grease), the test results can be significantly in error.

5.2.4 Handling and storage

Samples shall only be handled with clean nylon or lint-free gloves and shall be stored in a cleanliness-

controlled area, with a room temperature of 15 °C to 30 °C and a relative humidity of 20 % to 65 %.

Care should be taken to prevent excessive change from storage condition to measurement condition.

a) Coated surfaces shall be shielded from contact by using soft and inert material such as polyethylene

or polypropylene bags or sheets.

b) Mechanical damage shall be avoided in the standard way by packing the wrapped samples in clean

and dust and lint-free material.

c) Limited-life materials shall be labelled with their relative shelf lives and dates of manufacture.

5.2.5 Identification

a) Samples submitted for testing shall be accompanied by a completed “Material identification card”.

b) Hazardous samples shall be accompanied by a completed “Safety data sheet”.

c) The surface of the samples which is to be measured shall be clearly indicated unless the samples

have completely even properties on both surfaces.
5.3 Facilities
5.3.1 Cleanliness
a) The work area shall be clean and free of dust.

b) Air used for ventilation should be filtered to prevent contamination of the sample.

5.3.2 Environmental conditions

The ambient conditions for the process and work areas shall be from 15 °C to 30 °C with a relative

humidity of 20 % to 65 % unless otherwise stated.
5.3.3 Equipment
The equipment is specific for each test and defined in the Annexes.
5.4 Standard materials
5.4.1 General

Both reference and working (comparison) standards are required. Highly durable materials are

preferred. Standard materials shall be handled and stored in accordance with the associated

specification. Avoid touching the optical surfaces even with gloves.
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ISO 16378:2022(E)
5.4.2 Reference standard material

Reference standards are the primary standard material for the calibration of instruments and working

standards. Reference standards shall be traceable to a national or an international authority having

jurisdiction.
5.4.3 Working standard material

Working standards are used in the daily operation of the instrument to provide comparison curves

for data reduction. A working standard shall be calibrated annually by measuring its thermo-optical

properties relative to the properties of the appropriate reference standard. If degradation is noticeable,

the working standard shall be cleaned, renewed or replaced.
5.4.4 Solar absorptance

For transmitting samples, incident radiation shall be used as the standard relative to which the

transmitted light is evaluated. For some applications, calibrated transmittance standards are available.

For diffuse high-reflectance samples, a working standard that has high reflectance and is highly

diffusing over the range of the solar spectrum is required.

NOTE 1 White diffuser is commonly used as a diffuse high-reflectance standard material. Various white

diffusers are provided by a national or an international authority such as NIST. Spectralon® is a commercially

available material that provides high-diffuse reflectance for 250 nm to 2 500 nm. BaSO and magnesium oxide

have been widely utilized but are no longer recommended for use as a standard since they are not stable for

longer periods.

For specularly reflecting samples, a working standard that is highly specular is required. Identified

suitable working standards are vacuum-deposited thin opaque films of metals. All front surface

metalized working standards shall be calibrated frequently with an absolute reflectometer or relative

to a national or an international standard reference material before being acceptable in this test

method.

NOTE 2 Aluminium-coated glass mirror is widely used because of its high reflectance and ease of deposition.

Although bare aluminium surface is highly vulnerable, protective coating can maintain the optical property.

For absorber materials, a working standard that has low reflectance over the range of the solar

spectrum is required in order to obtain an accurate zero line correction.
5.4.5 Infrared emittance
A set of high- and
...