ISO/TR 6832:2023

Space systems - Development technology of a thermal vacuum chamber

This document describes the technology for simulating space environments such as vacuum, cold black, and heat flux, as well as the compositions and functions of a thermal vacuum chamber (TVC). This kind of facility defined in this document is suitable for thermal vacuum tests (TVT) and thermal balance tests (TBT) on spacecraft-system level as well as on large-spacecraft-component level.

Systèmes spatiaux — Technologie de développement d'une chambre thermique sous vide

General Information

• Status: Published
• Publication Date: 02-Oct-2023
• 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 - Space systems and operations
• Current Stage: 6060 - International Standard published
• Start Date: 03-Oct-2023
• Due Date: 30-Sep-2023
• Completion Date: 03-Oct-2023

Overview

ISO/TR 6832:2023 - "Space systems - Development technology of a thermal vacuum chamber" is a Technical Report that documents technologies, compositions and functions of a thermal vacuum chamber (TVC) used to simulate space environments. Published in 2023 by ISO (TC 20/SC 14), this guidance covers methods to reproduce vacuum, cold‑black background, and space heat flux (solar and infrared) for performing thermal vacuum tests (TVT) and thermal balance tests (TBT) at spacecraft-system and large-component levels.

Key technical topics and requirements

ISO/TR 6832:2023 organizes practical design and operational considerations across the full TVC lifecycle. Major topics include:

• Vacuum and thermal environment simulation - principles for simulating space vacuum, cold‑black conditions and heat flux (incident and absorbed).
• TVC configuration and general design - overall chamber architecture and integration.
• Vacuum vessel - composition, vessel shape, material selection, structural design, calculations and manufacturing.
• Shroud design - shroud materials, structure, area zoning, decontamination panels, surface treatments and leak testing.
• Nitrogen systems - liquid and gaseous nitrogen subsystem concepts, equipment layouts and piping.
• Vacuum system - pumping process schemes, system design calculations and equipment configuration.
• Heat flux simulation systems - solar simulators, infrared lamp arrays, infrared cages and thermally‑controlled panels.
• Specimen support and motion simulators - support mechanisms, horizontal adjustment and motion simulation for spacecraft testing.
• Measurement and control systems - hardware/software platform architecture, measurement strategies and control functions.
• Logistics and maintenance - operational support considerations for TVC facilities.

Note: ISO/TR 6832 is a technical report that documents technologies and recommended practices rather than prescribing mandatory numeric limits.

Practical applications

ISO/TR 6832:2023 is intended to support:

• Design and construction of large TVCs for space hardware qualification.
• Development of test procedures for spacecraft thermal vacuum and thermal balance testing.
• Procurement specifications for TVC equipment (vacuum pumps, shrouds, solar simulators, LN2 systems).
• Facility upgrades and retrofits to meet modern spacecraft testing needs.
• Validation of thermal models and verification of on‑orbit thermal performance.

Who should use this standard

• Spacecraft thermal engineers and test engineers
• Test facility designers and integrators
• Systems engineers, project managers and procurement teams
• Laboratory operators and maintenance staff
• Standards bodies and certification authorities involved in space systems testing

Related standards

While ISO/TR 6832 focuses on TVC development technology, users commonly reference other ISO and industry standards on spacecraft testing and thermal control (including standards from ISO/TC 20 and ECSS) to form a complete compliance and test strategy.

Keywords: ISO/TR 6832:2023, thermal vacuum chamber, TVC, thermal vacuum test, thermal balance test, vacuum simulation, cold black, heat flux, solar simulator, infrared simulator, space systems.

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 6832
First edition
2023-10
Space systems — Development
technology of a thermal vacuum
chamber
Systèmes spatiaux — Technologie de développement d'une chambre
thermique sous vide
Reference number
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.2
5 Vacuum and thermal environment simulation . 2
5.1 General . 2
5.2 Vacuum environment simulation technology . 3
5.3 Cold black environment simulation technology . 3
5.4 Space heat flux simulation technology . 3
5.4.1 General . 3
5.4.2 Incident heat flux simulation technology . 3
5.4.3 Absorbed heat flux simulation technology . 4
6 Design of TVC . 4
6.1 Configuration of TVC . 4
6.2 General design . 5
7 Vacuum vessel . 6
7.1 Composition and function . 6
7.2 Vessel design . 6
7.2.1 Structure shape . 6
7.2.2 Material. 8
7.2.3 Structure design . 9
7.2.4 Design calculation .12
7.2.5 Manufacturing .12
8 Shroud .12
8.1 Composition and function . 12
8.2 Shroud design . 13
8.2.1 Material of shroud . 13
8.2.2 Structure of shroud .13
8.2.3 Shroud area division and thermal design . 14
8.2.4 Decontamination panel design . 14
8.2.5 Temperature measurement . 15
8.2.6 Inner surface painting .15
8.2.7 Leak testing. 15
9 Nitrogen system .15
9.1 Composition and function .15
9.2 Design of LN subsystem .15
9.2.1 Technical scheme .15
9.2.2 Equipment configuration . 18
9.2.3 Piping design . 18
9.3 Design of GN subsystem . . 19
9.3.1 Technical scheme . 19
9.3.2 Equipment configuration . 20
10 Vacuum system .21
10.1 Composition and function . 21
10.2 Design of vacuum system. 21
10.2.1 General . 21
10.2.2 Scheme of the vacuum pumping process . 21
10.2.3 System design calculations . 22
iii
10.2.4 Equipment configuration . 23
11 Heat flux simulation system .25
11.1 Solar simulator . 25
11.1.1 Composition and function . 25
11.1.2 Solar simulator design . 26
11.2 Infrared heat flux simulator . 31
11.2.1 Composition and function . 31
11.2.2 Infrared lamp array . 31
11.2.3 Infrared cage . .33
11.2.4 Thermal controlled panel .34
12 Specimen support mechanism .34
12.1 General .34
12.2 Motion simulator . 35
12.2.1 Composition and function . 35
12.2.2 Motion simulator design . 35
12.3 Horizontal adjustment mechanism . 37
12.3.1 Composition and function . 37
12.3.2 Design of horizontal adjustment mechanism . 37
12.4 Test specimen support . .38
12.4.1 Composition and function .38
12.4.2 Design of test specimen support .38
13 Measurement and control system .39
13.1 Composition and function .39
13.2 Measurement and control system design . 39
13.2.1 General .39
13.2.2 Structure of measurement and control system .39
13.2.3 Measurement and control system hardware and software platform .40
13.2.4 Function implementation of measurement and control system . 41
14 Logistic support system .42
Bibliography .43
iv
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
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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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
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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.
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.
v
Introduction
Since the first artificial satellite was launched into space successfully in 1957, space activities have been
developed over the decades. The large amount of experience collected during that period demonstrates
that a significant number of failures or defects appearing during spacecraft in-orbit operation were
induced by space environment factors. These factors include space vacuum, cold black background,
solar radiation, and also albedo and eigenradiation of the Earth. Therefore, thermal balance tests and
thermal vacuum tests for spacecraft are performed in a simulated environment generated by ground
simulation facilities in order to evaluate spacecraft performance, to verify thermal analysis models,
and to discover early failures and defects in the spacecraft design and manufacturing process.
Countries engaged in spacecraft development have established several thermal test facilities, known as
thermal vacuum chambers. They also have standardized requirements for thermal vacuum tests and
thermal balance tests. These efforts greatly improved spacecraft reliability and played an important
role in space activities.
A thermal vacuum chamber is designed to simulate vacuum, cold black and heat flux environment that
a spacecraft experiences during its mission in space. It is composed of vacuum vessel, shroud, nitrogen
system, vacuum system, heat flux simulation system, specimen support mechanism, measurement and
control system, etc. Based on the state-of-the-art simulation technology, the relevant test standards and
experiences accumulated from facilities development, this document provides development technology
of a thermal vacuum chamber.
vi
TECHNICAL REPORT ISO/TR 6832:2023(E)
Space systems — Development technology of a thermal
vacuum chamber
1 Scope
This document describes the technology for simulating space environments such as vacuum, cold black,
and heat flux, as well as the compositions and functions of a thermal vacuum chamber (TVC). This kind
of facility defined in this document is suitable for thermal vacuum tests (TVT) and thermal balance
tests (TBT) on spacecraft-system level as well as on large-spacecraft-component level.
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
thermal vacuum chamber
TVC
space environment simulator
facility to simulate the space vacuum, cold black, and heat flux environment on the ground
Note 1 to entry: It is used for thermal vacuum tests (TVT) (3.4) and thermal balance tests (TBT) (3.5) of spacecraft.
3.2
shroud
subsystem of a thermal vacuum chamber (TVC) (3.1) to simulate the cold black environment (3.3) in space
Note 1 to entry: It is cooled by liquid nitrogen or gaseous nitrogen to simulate the cold black environment in
space. It is also called heat sink.
3.3
cold black environment
space environment without considering the solar and Earth radiation and the Earth's atmospheric
albedo
Note 1 to entry: The radiated energy from spacecraft under cold black environment will be completely absorbed.
3.4
thermal vacuum test
TVT
test which is conducted to demonstrate the capability of the test item and to operate according to
requirements in vacuum at predefined temperature conditions
Note 1 to entry: A spacecraft is validated by a thermal balance test (TBT) (3.5) and a thermal vacuum test (TVT)
in a similar environment provided by a thermal vacuum chamber (TVC) (3.1) prior to launch.
3.5
thermal balance test
TBT
test which is conducted to verify the adequacy of the thermal model and the adequacy of the thermal
design
Note 1 to entry: A spacecraft is validated by a thermal balance test (TBT) and a thermal vacuum test (TVT) (3.4)
in a similar environment provided by a thermal vacuum chamber (TVC) (3.1) prior to launch.
3.6
simulation chamber
main body of a thermal vacuum chamber (TVC) (3.1)
Note 1 to entry: It includes vacuum vessel and shroud (3.2) and provides test space for spacecrafts.
4 Symbols and abbreviated terms
B/S browser/server
C/S client/server
DCS distributed control system
FCS field bus control system
GN gas nitrogen
HMI human-machine interface
LAN local area network
LN liquid nitrogen
NPSH net positive suction head
PLC programmable logic controller
SCADA supervisory control and data acquisition
SS stainless steel
TVC thermal vacuum chamber
TBT thermal balance test
TCU thermal conditioning unit
TVT thermal vacuum test
5 Vacuum and thermal environment simulation
5.1 General
Spacecrafts in-orbit are exposed to high vacuum, cold black and heat flux radiation environment.
Therefore, a spacecraft is validated by TBT and TVT in a similar environment provided by a TVC prior
to launch. This allows to evaluate the thermal control system's performance, to verify the thermal
analysis model, to discover early failures and defects in spacecraft design and manufacturing process,
and to check the performance of spacecraft in extreme high and low temperatures. With decades of
technical development and the establishment of testing standards, the simulation methodology for the
three environmental factors (vacuum, cold black and heat flux) tends to be mature.
5.2 Vacuum environment simulation technology
The pressure in space varies with the orbital altitude of the spacecraft. The higher the orbital altitude
is, the lower the pressure would be. The pressure at the Earth's sea level is about 1,013×10 Pa, and the
-2 -12
pressure in the flight orbit of Earth spacecrafts is between 10 Pa and 10 Pa. According to the heat
-2
exchange theory, under the condition that the pressure is lower than 10 Pa, heat exchange between
spacecrafts and space environment is mainly radiation, and conduction and convective heat transfer
is negligible. According to the purpose and standards of TVT and TBT of spacecraft, the vacuum
environment simulation is satisfied when the test specimen is under test condition with not higher than
-2
1,33×10 Pa. According to the development of vacuum acquisition technology, Roots pump-dry pump
unit, molecular pump and cryopump are generally combined for obtaining an ultimate pressure about
-5 -2
10 Pa under non-load condition, so as to ensure that the pressure is not higher than 1,33×10 Pa with
load and meet the test for spacecrafts.
5.3 Cold black environment simulation technology
Without considering the solar radiation and earth (or other planet) albedo and eigenradiation, deep
space is similar to an infinite dissipation black body. Under such conditions a passive body experiences
a balance temperature between −270,15 °C (3 K) and −269,15 °C (4 K), and the black body energy
-6 2
density is about 5×10 W/m . This concept, known as cold black environment, implies that the heat
emitted by a spacecraft will be absorbed completely. The device on the ground which simulates this
environment is called shroud. However, to generate the exact space environment on the ground is
economically unviable and proved to be unnecessary. Based on the error analysis, generating an
environment of below 100 K, shroud absorptivity of about 0,95, and shroud emissivity of no less than
0,9 can reduce the temperature error on the spacecraft to less than 1 % under vacuum environment.
Therefore, the state-of-the-art simulation requirement for cold black environment requires a balance of
performance, cost and schedule that can be achieved in the design and production of thermal systems.
Typically shroud consists of SS or aluminium. Its surfaces facing towards the test volume are coated
with black paint to obtain high absorptivity (α) and high emissivity (ε). The volume inside of the shroud
is part of a cooling circuit with fluids that are capable of cooling down the shroud to a temperature of
approximately −173,15 °C (100 K). Nitrogen with a boiling point at 77 K is widely used for that purpose
since it is relatively cheap compared to hydrogen, oxygen or helium.
5.4 Space heat flux simulation technology
5.4.1 General
The external heat flux experienced by spacecrafts in Earth orbit comes from solar radiation, albedo and
eigenradiation of the earth. The space heat flux is simulated in two different ways, the incident heat flux
simulation and the absorbed heat flux simulation.
5.4.2 Incident heat flux simulation technology
The incident heat flux method is used to simulate the effect of solar radiation only. For the incident heat
flux method, the heat flux is generated by a solar simulator.
A predefined volume of the thermal vacuum chamber is exposed to solar type energetic illumination
which complies in each respect with the basic parameters of the sun: irradiance, spectrum, divergence,
illumination stability, and spatial uniformity. This is typically achieved by collect light from xenon
lamps through an arrangement of lenses and mirrors. The light beam is focused and superimposed to
the predefined volume. Typically, a solar simulator provides the range of irradiance from 0,5 to 1,3 solar
constant and collimation angle of no more than ±2°. A solar simulator provides an accurate simulation
of the actual solar spectrum. A solar simulator is restricted in application due to high-cost, complicated
system and fixed illumination surface. In addition, when using a solar simulator, the satellite can be
installed on the motion simulator which guides the spacecraft with respect to artificial solar beam.
5.4.3 Absorbed heat flux simulation technology
For the absorbed heat flux simulation technology, the heat flux is generated by heat sources within
the test volume. State-of-the-art, there are three ways to generate absorbed heat flux. The first way is
using infrared heat flux simulator, such as infrared lamps, infrared cage, or thermal controlled panel, to
generate infrared radiation to simulate the absorbed heat flux. The second way is using resistive film
heater attached to the specimen surface with the absorbed heat flux controlled by electrical power. The
third way is using a temperature-adjustable shroud to simulate the absorbed heat flux. It requires a set
of GN thermal conditioning unit (TCU).
The first two ways are widely used due to the characteristics of low-cost, flexible combination and
simple system configuration. However, the equipment used for these two ways will partially block the
radiation of the shroud to the specimen during the test, which brings difficulties to the realization of
low-temperature conditions for the specimen. In addition, due to poor versatility, infrared heat flux
simulators and resistive film heaters must be designed and manufactured according to the structural
dimensions and heat flux requirements of spacecrafts. When the third way is adopted, there is no need
to develop extra heat flux simulator for thermal test, which saves preparation time and cost. However,
it has low simulation accuracy and slow heat reflection.
6 Design of TVC
6.1 Configuration of TVC
A thermal vacuum chamber is designed to simulate vacuum, cold black and heat flux environment that
a spacecraft experiences during its mission in space. It is composed of vacuum vessel, shroud, nitrogen
system, vacuum system, heat flux simulation system, specimen support mechanism, measurement and
control system, etc. The heat flux simulation system can consist of any combination of the different
heat flux simulation technology: solar simulator, infrared flux simulator and temperature-adjustable
shroud. The system composition of TVC is shown in Figure 1.
Key
1 vacuum vessel
2 shroud
3 test specimen
4 specimen support mechanism
5 heat flux simulator
6 cooling circulating water, equipment electricity, compressed air, liquid nitrogen
7 logistic support system
8 measurement and control system
9 vacuum system
10 nitrogen system
11 LN tank
Figure 1 — Schematic diagram of a typical TVC
The simulation chamber composed of vacuum vessel and shroud is the main body of TVC, in which the
specimen and its support mechanism are fixed during the test. The nitrogen system provides liquid
nitrogen or gas nitrogen for the shroud to simulate cold black environment. The vacuum system
provides the required vacuum environment for the simulation chamber. The heat flux simulation
system provides the heat flux environment for the specimen. The measurement and control system
realizes the operation control of the whole system and data acquisition.
6.2 General design
Firstly, the test requirements are analysed, including the maximum weight, the maximum structural
dimensions, the attitude regulation, and the method of heat flux simulation of the test specimen, etc.
Secondly, the design standards are selected from the relevant international, national, industrial and
enterprise standards.
Thirdly, the overall scheme is determined, including equipment configuration, the structural type of the
simulation chamber, the way the specimen access to the simulation chamber, and the overall equipment
layout, etc.
Then, technical specifications are determined, including the size of the simulation chamber, the
maximum weight and the attitude regulation of the specimen, the vacuum degree with load and the
pumping time, ways of heat flux simulation, the shroud temperature, the cleanliness requirement
of simulation chamber, the measurement and control requirements, the reliability, safety and
maintainability requirements. In order to diminish the simulation error brought by the limited volume
of simulation chamber to be acceptable, the space between the specimen and the shroud is at least 1/3
of a characteristic dimension of the test specimen.
Finally, the executive plan of TVC is determined, including the development period, transportation,
assembly, commissioning, and cost.
7 Vacuum vessel
7.1 Composition and function
The vacuum vessel is the main body of the TVC and provides a benchmark for other subsystem
equipment installation. It houses the test specimen and the shroud. The vacuum vessel provides
interfaces for nitrogen system, vacuum system, heat flux simulation system, specimen support
mechanism, measurement and control system. The vacuum vessel is composed of cylinder, door, flanges,
and support as shown in Figure 2.
Figure 2 — Block diagram of vacuum vessel
7.2 Vessel design
7.2.1 Structure shape
The size of the vacuum vessel is determined together by the size of the test specimen, the room size and
the other test requirements.
There are several structural shapes available for vacuum vessel, e.g. cylinder, sphere, and box. The most
common shape of TVC is a cylinder vessel. Although its stress state is not as good as that of a spherical
vessel, it has the advantages of simple structure and convenient manufacturing. Compared with the
box-shaped vessel, its rigidity is much better. Table 1 shows structural shapes of vacuum vessel.
Table 1 — Structural shapes of vacuum vessel
Name Diagram Notes
This type vessel occupies small
floor area and has high height.
Vertical type
The sealing ring is compressed by
the weight of the door itself, so no
preload mechanism is required.
This type vessel is easy and safe
access to the vessel for specimen.
Horizontal
Cylinder
type
The self-weight of the vessel pro-
duces a bending moment.
This type vessel combines the
features of vertical and hori-
zontal type, but is complex and
expensive to build.
T type
This type vessel is often used
along with solar simulator and
motion simulator.
Under the same external pres-
sure condition, the sphere type
vessel has the best stress state
and the minimum wall thickness
required, which means saving the
Sphere
material.
But it is complex to manufacture
and expensive to build. It’s not
widely used due to the low effec-
tive space.
Key
1 door
2 cylinder
3 flange
4 support
TTabablele 1 1 ((ccoonnttiinnueuedd))
Name Diagram Notes
This type vessel is easy and safe
access to the vessel for specimen,
Cube
and high effective space. But it
has poor stress state.
Box
This type vessel has similar
Mailbox features to the cube vessel with
better stress state.
Key
1 door
2 cylinder
3 flange
4 support
7.2.2 Material
The vacuum vessel is placed indoor. Its external environment is ambient temperature and atmospheric
pressure, and the internal environment is vacuum and cryogenic temperature. The material of the
vacuum vessel not only bears low temperature and air corrosion, but also has low outgassing rate under
vacuum environment.
The stainless steel is often used for the cylinder, dome ends, flanges, and inner parts of the vessel.
Because it has many advantages, such as good rigidity, easy processing, easy welding, high chemical
stability, oxidation resistance, corrosion resistance, cryogenic environment resistance, good air
tightness, low outgassing rate, etc. Other components use in ambient environment, such as the support
and stiffening ring etc. These components use carbon steel to reduce the consumption of stainless steel
and reduce the manufacturing cost. The performance of the stainless steels commonly used in vacuum
vessel are shown in Table 2.
Table 2 — Performance of stainless steel
Name
No. Performance
SS 304 SS 304L SS 316 SS 316L
-3
1 Mass density/g∙cm 7,93 7,93 7,98 7,98
Yield strength/MPa
2 205 180 205 180
(20 °C)
3 Allowable stress/MPa 137 120 137 120
Modulus of elasticity/10 MPa
4 195
(20 °C)
-1 -2
Outgassing rate/ × 133,3 Pa∙L∙s ∙cm
-9 -10
5 2,1 × 10 to 1,7 × 10
(Pump 1 h to 25 h)
7.2.3 Structure design
7.2.3.1 Cylinder
The cylinder, the main body of the vacuum vessel, mainly includes the straight cylinder, the end, and the
flanges. Refer to 7.2.1 for the structure shape of the cylinder.
The end shape is categorized into spherical, spherical crown, ellipse, disc, cone, flat etc. The spherical
crown, ellipse and disc end are preferred for vacuum vessel because of their good stress state.
In order to increase the rigidity and minimize the thickness of vessel, the stiffening ring is designed
on the outer wall of the vessel. By this way, the consumption of stainless steel is reduced, saving
manufacturing cost. Common shapes of stiffening rings include T type, H type and II type as shown in
Figure 3.
Key
1 T type
2 H type
3 II type
Figure 3 — Types of stiffening ring
7.2.3.2 Door mechanism
The door provides the access way for test specimen and personnel. The type of door mechanism
depends on the vessel shape and the room layout. Table 3 shows the types of door mechanism.
Table 3 — Types of door mechanism
Name Diagram Notes
The door slides along the
radial direction on overhead
tracks.
The door slides along the
Sliding door radial direction on tracks
on the floor.
The door slides along axial
direction.
The door is hinged on one
Hinged door side to allow itself to rotate
along the doorway.
The door is lifted up and
Hanged door down by the crane. It is usu-
ally used for vertical vessel.
The door sealing ring is compressed before pumping. For vertical vessel, the sealing ring is compressed
by the weight of the door itself. For horizontal vessel, preload mechanism is used to compress the
door sealing ring. They are evenly and radially arranged on the door flange to ensure enough force for
compressing the sealing ring.
7.2.3.3 Flanges
Flanges are used to connect other subsystems to the vessel. And the flanges can provide the
feedthroughs for connecting the equipment inside and outside the vessel. In addition to meet the
requirements of strength, rigidity and sealing, the flange is also easy to be installed and removed, and
does not affect the sealing performance after repeated operation. Flanges on the vessel are mainly
classified as non-knife edge flanges, quick-release flanges, knife-edge flanges. They are designed with
[1] [2] [3]
reference to ISO 1609 , ISO 2861 and ISO 3669 .
7.2.3.4 Support
The support bears the weight of the vacuum vessel and all equipment mounted on it. The type of the
support depends on the shape of vacuum vessel. Types of support commonly used in TVC are column
type, skirt type, saddle type, as shown in Table 4.
Table 4 — Types of support
Name Diagram Notes
This type is used for hori-
Column type zontal, vertical, spherical
and cube vessel.
This type is used for ver-
Skirt type
tical and spherical vessel.
This type is used for hori-
Saddle type
zontal vessel.
7.2.4 Design calculation
The design calculation of vacuum vessel includes stress and stability calculation. The calculation steps
are as following.
a) The external pressure of the vacuum vessel is ambient pressure, while the internal pressure
environment is vacuum. It means that the maximum differential pressure is 0,1 MPa. So, the design
pressure is 0,1 MPa.
b) The design temperature of the vacuum vessel is ambient temperature.
c) The following loads are commonly considered in the design:
— the maximum differential pressure between the inside and outside of the vacuum vessel;
— the weight of the vacuum vessel;
— additional load, such as pipelines, platforms, test specimen, etc.;
— reaction force of the supports;
— seismic load, referring to the local seismic grade requirements.
d) The calculation includes wall thickness of cylinder, wall thickness of end, section size of door flange,
section size of strengthening ring, and reinforcement of the openings, etc. Refer to ASME BPVC.
[4]
VIII for calculation method.
e) The finite element method is also used for the TVC stress analysis, deformation analysis, and
buckling analysis, to check the strength and stability of the vessel.
7.2.5 Manufacturing
During the processing of vacuum vessel, these factors are considered, such as industrial manufacturing
standards, flatness of door flange, the inner surface roughness, and leakage rate of the vessel.
Door flange is prone to deformation during processing to affect the sealing performance. Therefore, the
flatness of the door flange is considered during the manufacture.
The inner surface of vessel outgases in vacuum environment. If it is rough, the amount of outgassing
increases from the material. In addition, heat exchange between the vessel and the shroud is related to
the surface roughness. The inner surface of the vacuum vessel is polished to obtain minimize roughness,
to decrease the outgassing and heat radiation.
In order to ensure the high vacuum environment in the vacuum vessel, the leakage rate is detected by
helium mass spectrometry. The total leakage rate of the vessel can meet the requirements of the test.
The vacuum vessel is welded, and the removable parts are connected with flanges. So, leak detection
objects are welding lines and flanges.
8 Shroud
8.1 Composition and function
The shroud is installed inside the vessel and covers the inner surfaces of the vessel as much as possible.
It is a kind of structure made of large numbers of metal panels and pipes with good heat conductivity,
to simulate cold black environment in space. At the same time, the shroud is coated with specific paints
on the surfaces facing the test specimen, to meet the requirements of absorptivity and hemispherical
emissivity. By flooding with LN / GN , shroud temperature keeps below 100 K (LN circulating) or 93 K
2 2 2
to 423 K (GN circulating) during the test.
8.2 Shroud design
8.2.1 Material of shroud
The shroud experiences high vacuum, cryogenic environment during the test of specimen. It is generally
made of aluminium, SS or red copper, which has low outgassing rate in high vacuum environment, good
mechanical performance at low temperature and better welding performance. The performances of all
materials are shown in Table 5.
Table 5 — Performance of shroud materials
Material
No. Item
Stainless steel Red copper Aluminium
SS 304 T4 L4
193 to 241 87 to 186 31 to 39
1 Yield strength (MPa) (20 °C to -180 °C)
High Moderate Low
0 to 1,12 0,771 to 0,892 0,91 to 1,55
2 Impact toughness (MPa·m) (20 °C to -180 °C)
Good Good Excellent
-1 -1
Specific heat capacity (W·m ·K ) 490 to 251 386 to 254 902 to 376
(20 °C to −180 °C) High Higher Highest
-1 -1
Thermal conductivity coefficient (W·m ·K ) 15 to 8 395 to 609 152 to 351
(20 °C to −180 °C) Lower High High
-3
5 Density (g·cm ) 7,9 8,9 2,7
60 to 42 30 to 31 35 to 48
6 Elongation (%) (20 °C to −180 °C)
Excellent Good Good
7 Processing difficulty High Moderate Low
8 Welding difficulty Low Moderate High
8.2.2 Structure of shroud
The shroud structure is related to the materials. The aluminium shroud is generally welded by various
pipes with wings on both sides. T
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