ISO 16694:2024

International
Standard
ISO 16694
Second edition
Space systems — Measured
2024-09
parameters at firing bench and
flight tests of liquid rocket engines
Systèmes spatiaux — Paramètres mesurés au banc d'allumage et
essais de vol des moteurs à propergol liquide
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 1
5 General . 2
6 List of parameters, measured during LRE tests . 3
6.1 General .3
6.2 List of parameters, measured during LRE firing bench test .3
6.3 List of parameters, measured during LRE flight test .11
6.4 List of parameters, measured during LTLRE test . 15
Bibliography . 19

iii
Foreword
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bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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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).
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patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
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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 16694:2015), which has been technically
revised.
The main changes are as follows:
— Clauses 4 and 5 are amended;
— the list of measured parameters is expanded;
— in Tables 1 and 3, the parameter “…pressure pulsation…” is split into two parameters: “…vibration
amplitude…” and “…vibration frequency…”; the parameter “vibro-overloads.” is split into “vibration
acceleration amplitude…” and “vibration acceleration frequency…”;
— certain parameters are moved from the category “mandatory parameters” to the category “optional”;
— superscripts and subscripts of parameter "Letter symbols" are corrected.
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.

iv
Introduction
The document provides users, designers, and manufacturers of liquid rocket engines with requirements and
guidance for parameters, measured during firing bench and flight tests. Parameters to be measured are
used for reliability analysis and quality control of liquid rocket engines.
The parameters listed in the document characterize performance of liquid rocket engines and they are used
to evaluate the technical condition of engines (operable, inoperable), their conformity with the specified
requirements and whether engines are available to be delivered to a user and put into operation. ISO 15865
is used to assess conformity of liquid rocket engines to the specified requirements.
Uniform requirements for the parameters, measured during firing bench and flight tests of liquid rocket
engines, ensure the following:
— quality and reliability of developed and operated liquid rocket engines;
— comparison of liquid rocket engine test results;
— end product safety and environmental protection.
The engine developer may identify an additional list of measured parameters for specific items, taking into
account their design features.
This document makes it possible to develop uniform criteria for performance evaluation and comparison of
liquid rocket engines, created by different countries, based on firing bench and flight tests results.

v
International Standard ISO 16694:2024(en)
Space systems — Measured parameters at firing bench and
flight tests of liquid rocket engines
1 Scope
This document specifies requirements for the list of parameters, measured during firing bench and flight
tests. The requirements of the document apply to all the types of expendable liquid rocket engines supplied
to the user:
a) operating on all types of propellant (including cryogenic);
b) with afterburning (with gradual burning) and without afterburning (without gradual burning);
c) low-thrust engines: one component (monopropellant) and two-component (bipropellant);
d) with a single firing or multiple firings.
The document doesn’t specify firing bench test preparation and testing procedure, methods of test results
processing and analysis, or requirements to measurement accuracy.
The document specifies mandatory and optional parameters.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 15864, Space systems — General test methods for spacecraft, subsystems and units
ISO 24917, Space systems — General test requirements for launch vehicles
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Abbreviated terms
AVR apparent velocity regulator
BTP booster turbo pump
CFC component-flow controller
CPT certification periodic test
DD design documentation
EV electric valve
FCR controller of the propellants ratio in a combustion chamber
IpCT in-process control test
LV launch vehicle
LRE liquid rocket engine
LTE low thrust engine
PA pressure alarm
QT qualification test
R&D research and development
SC spacecraft
SPT special periodic test
TDS tank depletion system
TP turbopump
5 General
5.1 The main purpose of LRE and LTLRE parameters measurement while performing ground and flight
tests is to obtain information for assessment of parameter conformity to DD requirements, reliability and
quality analysis of supplied engines.
5.2 Parameters, which should be measured during fire bench and flight tests of LRE, and to which
requirements of this document are applied, fall into the following groups:
a) parameters, characterizing test environment (5.3, 5.4);
b) main parameters (5.5);
c) key performance parameters (5.6);
d) parameters, characterizing the engine ability to operate without any degradation (5.7).
5.3 Parameters, characterizing test environment, include:
a) parameters of natural and artificial environmental impacts;
b) propellants status before and during tests.
5.4 Parameters, characterizing test environment, are used to evaluate conformity of physical environment
and propellants status before and during tests to the requirements of the test specification, and ensure that
the corrected characteristics of an engine (thrust, specific impulse) are identified.
5.5 Main parameters define how the engine performs the specified functions; and they are set by technical
documentation requirements of the engine developer.
5.6 Key performance parameters characterize the engine performance and define whether a test is
passed or not. Key performance parameters may be obtained either directly from measurements or from
calculations. The parameters shall comply with DD requirements of the engine developer.

5.7 Parameters, characterizing the engine ability to operate without any degradation, are used to control
the engine health by estimating values of loads, which act on the engine’s assemblies.
This group comprises parameters, whose values cannot be determined directly by measurements, taken
during assembly manufacturing process. Among these parameters are particularly ones, characterizing
vibration strength and heat-resistance of the combustion chamber and the gas generator and stability of the
assemblies operating process. In case of emergency, these parameters (together with the main parameters
and parameters, characterizing test conditions) are used to analyse causes of emergency.
5.8 It is recommended to use sensors of the same type to measure similar parameters during static fire
and flight tests.
6 List of parameters, measured during LRE tests
6.1 General
Parameters, measured during firing bench and flight tests of the engine, are summarized in the
corresponding tables.
Static fire tests of launch vehicles shall be conducted in accordance with the general requirements in
ISO 24917.
Goals and objectives of flight tests shall be as specified in ISO 15864.
Depending on their importance, parameters, measured during an engine test, fall into the following groups:
a) mandatory;
b) optional;
c) interchangeable.
The term “optional parameter” means (in cases, when a corresponding assembly or a unit is a part of
the engine) that, according to the approved decision of a liquid engine developer, its measurement is not
mandatory, as opposed to a mandatory parameter, which shall be measured and recorded.
Additions may be made to the set of parameters, which are measured during LRE QT, in accordance to the
QT program, agreed upon with the engine developer.
The “Comment” column provides required clarifications and additions to certain parameters.
6.2 List of parameters, measured during LRE firing bench test
The list of optional and mandatory parameters to be measured during in-process control test, certification
periodic test and special periodic test (IpCT, CPT and SPT) of LRE is provided in Table 1.

Table 1 — Parameters, measured during IpCT, CPT, SPT
LRE type Comment
Letter symbol Measurement unit Without afterburning With afterburning
For LV For SC For LV For SC
1 Parameters, characterizing test environment
1.1 Ambient pressure kPa О О О О
P
amb
1.2 Ambient temperature К О О О О
T
amb
(°C)
1.3 Ambient humidity Н % Δ Δ Δ Δ
amb
1.4 Air flows direction and speed W m/s Δ Δ Δ Δ
1.5 Propellants temperature at К О О О О
p
t
flow sensor locations and at the
inlet
(°C)
engine inlet
ρ
1.6 Propellants density (except kg/m О О О О
cryogenic)
1.7 Dissolved gases content in gas % О О О О
v
p
propellants when performing
tests with forced gas saturation
1.8 Propellants pressure at the mPa Х Х Х Х Sensors are used,
ox
4.10 4.10 4.10 4.10
P
inlet
engine inlet 2 which make it
(kgf/cm )
fuel
possible to measure
P
inlet
pressure during
transient processes:
at start and during
the change of the
engine operating
mode
2 Main parameters
2.1 LRE thrust R N О О О О
(kgf)
2.2 Mass outflow of oxidizer kg/s О О О О

m
ox
and fuel through the engine per

m
f
second
2.3 Mass outflow of oxidizer and kg/s О О О О

m
ox.n
fuel through the engine chamber

m .n
nozzle per second f
2.4 Fuel pressure upstream of the mPa О О О О Sensors are used,
P
fA.
chamber injectors 2 which make it
(kgf/cm )
possible to measure
pressure for parame-
ters 2.4 to 2.7 during
transient processes:
at start and during
the change of the
engine operating
mode
2.5 Oxidizer pressure upstream mPa О О О О For LRE without
P
ox.A
of the chamber injectors 2 afterburning
(kgf/cm )
Key
О — mandatory parameter
• — parameter measurement is not regulated by the document
Δ — optional parameter
Х — interchangeable parameter subject to mandatory measurement, where m is the numerical order of a parameter in the corresponding table, which can be used
m
instead of the parameter, specified in parameter m in this table
Parameters, which characterize test environment, shall be measured before the engine is fired.
NOTE 1 Certain parameters, specified in the parameter table, can be controlled by measuring other parameters, specified in DD, if the customer is satisfied with
control accuracy.
NOTE 2 Such parameters as pressure upstream(downstream) of PA, FCR, CFC, TDS are to be measured if the specified parameters are necessary to determine the
estimated values of the main (specified) LRE characteristics.
NOTE 3 When performing test of cryogenic engines, in addition parameters are measured, which characterize the aggregate state of propellants (temperature,
pressure).
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
LRE type Comment
Letter symbol Measurement unit Without afterburning With afterburning
For LV For SC For LV For SC
2.6 Gas medium pressure up- mPa О О О О For LRE with after-
P
gm
stream of the chamber injectors 2 burning
(kgf/cm )
c.inj
2.7 Combustion chamber pres- mPa О О О О
P
cc.
sure 2
(kgf/cm )
2.8 Run-up time of heat exchang- Τ . s О О О О
p.g.
ers, which are used to heat tank
pressurization gases
2.9 Pressurizing gases pressure P . mPa О О О О If the tank pressuri-
p.g
2 zation elements, heat
(kgf/cm )
exchanger elements
are available
2.10 Pressurizing gases flow rate kgf О О О О If the tank pressuri-
m
pg.
zation elements, heat
exchanger elements
are available
2.11 Pressurizing gases temper- T . К О О О О If pressurization ele-
p.g
ature ments are available
(°C)
2.12 Positions of flow regulators radian О О О О If the flow regulators
φ
rd.
drives, operating mode drives are available
2.13 Position of mixture ratio radian О О О О If the throttle drives
φ
td.
throttle drives are available
3 Key performance parameters
3.1 Nominal engine thrust run-up Τ s О О О О % of nominal thrust
run-up.nom.
is specified by the
engine developer
3.2 Engine specific impulse: I m/s О О О О
spec.vac
I
spec.gr
—  in vacuum;
—  on the ground
3.3 Adjustment accuracy for pro- δC % О О О О
f
pellants mass flow rate ratio
3.4 Adjustment accuracy for δР % О О О О
c
chamber pressure
3.5 Starting gradient of engine V N/s О О О О The LV developer
start
thrust change decides, whether
maximum or average
gradient is applied
3.6 Cutoff gradient of engine V N/s О О О О The LV developer
cutoff
thrust change decides, whether
maximum or average
gradient is applied
Key
О — mandatory parameter
• — parameter measurement is not regulated by the document
Δ — optional parameter
Х — interchangeable parameter subject to mandatory measurement, where m is the numerical order of a parameter in the corresponding table, which can be used
m
instead of the parameter, specified in parameter m in this table
Parameters, which characterize test environment, shall be measured before the engine is fired.
NOTE 1 Certain parameters, specified in the parameter table, can be controlled by measuring other parameters, specified in DD, if the customer is satisfied with
control accuracy.
NOTE 2 Such parameters as pressure upstream(downstream) of PA, FCR, CFC, TDS are to be measured if the specified parameters are necessary to determine the
estimated values of the main (specified) LRE characteristics.
NOTE 3 When performing test of cryogenic engines, in addition parameters are measured, which characterize the aggregate state of propellants (temperature,
pressure).
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
LRE type Comment
Letter symbol Measurement unit Without afterburning With afterburning
For LV For SC For LV For SC
3.7 Time difference between s Δ Δ Δ Δ The LV developer
td
τ
en
engines run-ups decides, whether this
parameter needs to
be applied
3.8 Temperature of the oxidizer К О О О О
gas
T
tank pressurizing gas ot.p
(°C)
3.9 Temperature of the fuel tank К О О О О
gas
T
pressurizing gas
ft.p
(°C)
4 Parameters, characterizing the engine ability to operate without any degradation
4.1 Oxidizer pressure at the pump ox mPa О О О О
P
po.ut
outlet 2
(kgf/cm )
4.2 Fuel pressure at the pump f mPa X X Х Х
4.7 4.7 4.7 4.7
P
po. ut
outlet
(kgf/cm )
4.3 Oxidizer pressure at the ox mPa Δ Δ Δ Δ
P
bp.out
booster pump outlet 2
(kgf/cm )
4.4 Fuel pressure at the booster mPa Δ Δ Δ Δ
f
P
bp.out
pump outlet 2
(kgf/cm )
4.5 Gas pressure in the gas mPa О О О О Parameter 4.5 is to
P
gg
generator 2 be measured, when
(kgf/cm )
performing CPT of
engines without
afterburning,
provided that the
engine design allows
for installation of
respective sensors
4.6 Combustion starter chamber mPa Δ Δ Δ Δ For engines, which
P
ch.cs
pressure 2 are started, using a
(kgf/cm )
pyrotechnic device
4.7 Steering actuators inlet mPa X X Х Х Steering actuator is
P 4.2 4.2 4.2 4.2
sa.
pressure 2 a device, designed
(kgf/cm )
to provide engine
chambers gimbaling
and thrust vector
control
4.8 Gas pressure at the turbine mPa Δ Δ Δ Δ
P
to. ut
outlet
(kgf/cm )
4.9 Gas pressure in tank pressuri- mPa Х Х Х Х Parameter 4.9 is
P
1.8 1.8 1.8 1.8
tp.
zation system 2 applicable to the
(kgf/cm )
gas-generating
tank pressurization
systems
4.10 Pressure drop at the propel- mPa Δ Δ Δ Δ
ΔP
fl.rc
lants flow rate controller
(kgf/cm )
Key
О — mandatory parameter
• — parameter measurement is not regulated by the document
Δ — optional parameter
Х — interchangeable parameter subject to mandatory measurement, where m is the numerical order of a parameter in the corresponding table, which can be used
m
instead of the parameter, specified in parameter m in this table
Parameters, which characterize test environment, shall be measured before the engine is fired.
NOTE 1 Certain parameters, specified in the parameter table, can be controlled by measuring other parameters, specified in DD, if the customer is satisfied with
control accuracy.
NOTE 2 Such parameters as pressure upstream(downstream) of PA, FCR, CFC, TDS are to be measured if the specified parameters are necessary to determine the
estimated values of the main (specified) LRE characteristics.
NOTE 3 When performing test of cryogenic engines, in addition parameters are measured, which characterize the aggregate state of propellants (temperature,
pressure).
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
LRE type Comment
Letter symbol Measurement unit Without afterburning With afterburning
For LV For SC For LV For SC
4.11 Driving pressure in control mPa О О О О
P
contr
assemblies 2
(kgf/cm )
4.12 Pressure vibration ampli- mPa Δ Δ Δ Δ Parameters 4.12,
fuel
A
injc.
tude upstream of 2 4.13 under CPT of
(kgf/cm )
The chamber fuel injectors engines without
afterburning are to
4.13 Pressure vibration frequen- fuel Hz Δ Δ Δ Δ
be measured, if the
f
injc.
cy upstream of the chamber fuel
engine design allows
injectors
for installation of
respective sensors
4.14 Pressure vibration ampli- ox mPa Δ Δ Δ Δ Parameters 4.14
A
injc.
tude upstream of the chamber and 4.15 under CPT
(kgf/cm )
oxidizer injectors of engines without
afterburning are to
4.15 Pressure vibration frequen- Hz Δ Δ Δ Δ
ox
be measured, if the
f
injc.
cy upstream of the chamber
engine design allows
oxidizer injectors
for installation of
respective sensors
4.16 Pressure vibration ampli- mPa Δ Δ Δ Δ
f
A
injg. g
tude upstream of the gas-gener- 2
(kgf/cm )
ating fuel injectors
4.17 Pressure vibration frequen- f Hz Δ Δ Δ Δ
f
injg. g
cy upstream of the gas-generat-
ing fuel injectors
4.18 Pressure vibration ampli- mPa Δ Δ Δ Δ
fox
A
injg. g
tude upstream of the gas-gener- 2
(kgf/cm )
ating oxidizer injectors
4.19 Pressure vibration frequen- ox Hz Δ Δ Δ Δ
f
injg. g
cy upstream of the gas-generat-
ing oxidizer injectors
4.20 Pressure vibration ampli- Δ Δ Δ Δ
A
cc
tude in the combustion chamber 2
(kgf/cm )
A
gg
and in the gas generator
4.21 Pressure vibration frequen- Hz Δ Δ Δ Δ
F
cc
cy in the combustion chamber
F
gg
and in the gas generator
4.22 Propellants pressure vibra- mPa Δ Δ Δ Δ
p
A
tion amplitude at the engine inlet 2
en.inlet
(kgf/cm )
4.23 Propellants pressure fre- Hz Δ Δ Δ Δ
p
f
quency amplitude at the engine
en.inlet
inlet
Key
О — mandatory parameter
• — parameter measurement is not regulated by the document
Δ — optional parameter
Х — interchangeable parameter subject to mandatory measurement, where m is the numerical order of a parameter in the corresponding table, which can be used
m
instead of the parameter, specified in parameter m in this table
Parameters, which characterize test environment, shall be measured before the engine is fired.
NOTE 1 Certain parameters, specified in the parameter table, can be controlled by measuring other parameters, specified in DD, if the customer is satisfied with
control accuracy.
NOTE 2 Such parameters as pressure upstream(downstream) of PA, FCR, CFC, TDS are to be measured if the specified parameters are necessary to determine the
estimated values of the main (specified) LRE characteristics.
NOTE 3 When performing test of cryogenic engines, in addition parameters are measured, which characterize the aggregate state of propellants (temperature,
pressure).
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
LRE type Comment
Letter symbol Measurement unit Without afterburning With afterburning
For LV For SC For LV For SC
4.24 Engine chamber vibration m/s Х Х Х Х For newly developed
ec.
4.26 4.26 4.26 4.26
A
par.
acceleration amplitude in the LRE, decision on
(g)
plane, parallel to the assembly whether measure-
main axis ment of parame-
ters 4.24-4.35 is
4.25 Engine chamber vibration ec. Hz Х Х Х Х
4.27 4.27 4.27 4.27
mandatory, is based
f
par
acceleration frequency in the
on R&D results
plane, parallel to the assembly
main axis
4.26 Engine chamber vibration m/c Х Х Х Х
ec.
4.24 4.24 4.24 4.24
A
norm
acceleration
...