ISO 16781:2013
(Main)Space systems — Simulation requirements for control system
Space systems — Simulation requirements for control system
ISO 16781:2013 provides guidance to control system engineers on what to simulate and how to use simulation to support their system engineering tasks. ISO 16781:2013 provides simulation requirements of control system for different phases in the process of designing a control system. Control system engineers can carry out various types of simulation experiments during various phases, according to ISO 16781:2013. ISO 16781:2013 establishes a minimum set of requirements for simulation of control system. The requirements are generic in nature because of their broad applicability to all types of simulations.
Systèmes spatiaux — Exigences de simulation pour le système de contrôle
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 16781
First edition
2013-11-15
Space systems — Simulation
requirements for control system
Systèmes spatiaux — Exigences de simulation pour le système de
contrôle
Reference number
ISO 16781:2013(E)
©
ISO 2013
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ISO 16781:2013(E)
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ISO 16781:2013(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Terms and definitions . 1
3 Abbreviated terms . 3
4 Control system simulation . 3
4.1 Structure of control system . 3
4.2 Objectives of control system simulation . 4
4.3 Mathematical simulation and HITL simulation . 5
4.4 Simulation in different phases . 5
4.5 Simulation process . 8
5 General requirements . 9
5.1 General . 9
5.2 Project level requirements . 9
5.3 Simulation model requirements .10
5.4 Simulation facility requirements .11
5.5 Simulation operation requirements .12
5.6 Simulation result analysis requirements.12
5.7 Other document requirements .12
6 Requirements of conceptual design phase simulation .14
6.1 General .14
6.2 Objective .15
6.3 Input .15
6.4 Output .15
6.5 Simulation model requirements .15
6.6 Simulation facility requirements .16
6.7 Simulation operation requirements .16
7 Requirements of detailed design phase simulation .16
7.1 General .16
7.2 Objective .17
7.3 Input .17
7.4 Output .17
7.5 Simulation model requirements .17
7.6 Simulation facility requirements .17
7.7 Simulation operation requirements .18
8 Requirements of prototype phase simulation .18
8.1 General .18
8.2 Objective .18
8.3 Input .19
8.4 Output .19
8.5 Simulation model requirements .19
8.6 Simulation facility requirements .19
8.7 Simulation operation requirements .20
9 Requirements of integrated system phase simulation .20
9.1 General .20
9.2 Objective .21
9.3 Input .21
9.4 Output .21
9.5 Simulation model requirements .21
9.6 Simulation facility requirements .21
9.7 Simulation operation requirements .22
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ISO 16781:2013(E)
Annex A (normative) Phase comparison between ISO 14300 and ISO 16781 .23
Annex B (normative) Relationship between simulation phases and tables .24
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ISO 16781:2013(E)
Foreword
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The committee responsible for this document is ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 14, SC14 Space Systems and Operations.
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ISO 16781:2013(E)
Introduction
This International Standard provides space system control system engineers, simulation engineers and
customers with guidance of use simulation to support their system engineering tasks. This International
Standard is intended to help reduce the develop time and cost of space system control system design
and also enhance its quality and reliability. This International Standard focuses on requirements and
recommendations for what should be done during simulation. It does not prescribe how the requirements
are to be met.
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INTERNATIONAL STANDARD ISO 16781:2013(E)
Space systems — Simulation requirements for control system
1 Scope
This International Standard provides guidance to control system engineers on what to simulate and
how to use simulation to support their system engineering tasks. Ground testing limitations typically
preclude a comprehensive “test as you fly” approach to most space system control systems. Likewise,
flight tests are prohibitively expensive. Therefore, high-fidelity simulation models of the control system
components must be validated. Wherever, possible ground test results should be compared to simulation
model outputs. Validated models are then used in various simulation environments to predict flight
performance. As an important means of design, analysis and validation, simulation of the control system
is widely used in each phase of the control system development, including conceptual design, detailed
design, prototype validation, and integrated system verification. This International Standard provides
simulation requirements of control system for different phases in the process of designing a control
system. Control system engineers can carry out various types of simulation experiments during various
phases, according to this International Standard. This International Standard establishes a minimum
set of requirements for simulation of control system. The requirements are generic in nature because of
their broad applicability to all types of simulations. Implementation details of the requirements should
be addressed in project-specific standards, requirements, handbooks, etc.
In general, standards can focus on engineering/technical requirements, processes, procedures, practices,
or methods. This International Standard focuses on requirements and recommendations. Hence, this
International Standard specifies what must be done; it does not prescribe how the requirements are to
be met, nor does it specify who the responsible team is for complying with the requirements. Conflicts
between this International Standard and other requirements documents shall be resolved by the
responsible technical designer.
2 Terms and definitions
2.1
accuracy
measure of how close a value is to the “true” value
[SOURCE: ISO 14952-1:2003]
2.2
control system
closed-loop configuration of sensors, processors/algorithms, and actuators designed to manage the
dynamic behavior of space systems
2.3
emulator
prototype of the flight equipment, which has the identical input/output interfaces as the flight equipment
and has similar operating behaviour
2.4
fidelity
degree to which a model or simulation reproduces the state and behaviour of a real world object
or the perception of a real world object, feature, condition, or chosen standard in a measurable or
perceivable manner
2.5
hardware in the loop simulation
kind of simulation, in which some simulation models of control system are implemented by real equipment
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ISO 16781:2013(E)
2.6
mathematical simulation
kind of simulation, in which all the simulation models of control system are implemented by software
2.7
real-time simulation
kind of simulation, in which the time scale of dynamic process in simulation model strictly equals to that
of the real system
2.8
reliability
ability of an item to perform a required function under given conditions for a given time interval
[SOURCE: ISO 10795:2011]
2.9
simulation
use of a similar or equivalent system to imitate a real system, so that it behaves like or appears to be
the real system
2.10
simulation of control system
complex progress of building simulation system based on the mathematical model of control system,
testing the model, solving the system dynamic equations, imitating dynamic behaviors of control system,
and taking qualitative and quantitative analysis and research about scheme, structure, parameters, and
performance of control system
2.11
simulation model
equivalent model in the simulation system, which is transformed from mathematical model of control
system by means of simulation software or hardware
2.12
simulation plan
document in which the content, operate steps, and implement method of all simulation items are specified
2.13
stability
ability of a system submitted to bound external disturbances to remain indefinitely in a bounded domain
around an equilibrium position or around an equilibrium trajectory
2.14
validation
confirmation, through the provision of objective evidence, that the requirements for a specific intended
use or application have been fulfilled
Note 1 to entry: The term “validated” is used to designate the corresponding status.
Note 2 to entry: The use conditions for validation can be real or simulated.
Note 3 to entry: Validation can be determined by a combination of test, analysis, demonstration, and inspection.
[SOURCE: ISO 10795:2011]
2.15
verification
confirmation through the provision of objective evidence that specified requirements have been fulfilled
Note 1 to entry: The term “verified” is used to designate the corresponding status.
Note 2 to entry: Confirmation can comprise activities such as
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ISO 16781:2013(E)
—performing alternative calculations,
—comparing a new design specification with a similar proven design specification,
—undertaking tests and demonstrations, and
—reviewing documents prior to issue.
Note 3 to entry: Verification can be determined by a combination of test, analysis, demonstration, and inspection.
[SOURCE: ISO 10795:2011]
3 Abbreviated terms
Table 1 — Abbreviated terms
A/D Analog/ Digital Transform
CM Configuration Management
D/A Digital/Analog Transform
DI/DO Digital Input/Digital Output
HITL Hardware-in-the-Loop
M&S Modelling and Simulation
V&V Verification and Validation
4 Control system simulation
4.1 Structure of control system
Control system is one of the most important systems of launch vehicle, satellite, spaceship, etc.
Generally, the architecture of control system is illustrated in Figure 1.
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ISO 16781:2013(E)
Figure 1 — Control System Architecture
a) Flight environment includes atmosphere or space environment in which the spacecraft exists. In
terms of different kinds of spacecraft, control system shall consider mechanical, thermodynamic,
optical, and electromagnetic environment, etc.
b) Sensors are fixed on the spacecraft to measure the states, which are provided to flight control
computer for control algorithm calculation.
c) Flight control computer receives and deals with measured information from sensors, and then
control signals are gained by control algorithm and sent to servos as commands.
d) Servos receive commands from flight control computer and drive actuators, which produce forces
and moments and affect the flight states of spacecraft, so that a closed-loop is formed and the
objective of control is achieved.
e) Command input indicates control command and binding parameter.
f) Vehicle dynamics indicates the dynamic behaviour of a plant.
g) Logger records telemetry data and flight status.
4.2 Objectives of control system simulation
Control system design is an iterative process from design, test, and validation to modification, retest, and
revalidation. Analytical method is not enough for research and design of control system, so simulation
experiment is demanded.
The primary objectives of control system simulation are as follows:
a) verify and optimize the control system scheme;
b) verify and optimize the control system parameters;
c) analyse the stability and robustness of the control system;
d) emulate control system faults that can occur in flight;
e) predict the performance of control system;
f) comprehensively verify functions of control system components;
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g) minimize the scheme design iteration;
h) shorten the development time;
i) minimize the development budget.
4.3 Mathematical simulation and HITL simulation
Compared to mathematical simulation, the structure of HITL simulation system is more complex. It can
reflect the hardware/software characteristics of control system, and verify the functions/ performances
of control system (e.g. interface matching properties). Generally, HITL simulation should be done after
mathematical simulation.
The corresponding relationship between simulation types and practical control system is listed in Table 2.
Table 2 — Relationship between simulation types and practical control system
Parts of control sys- Mathematical
HITL simulation
tem simulation
Mathematical model and
Vehicle dynamics
motion simulator (turn table, robotic arm, air bearing)
Physical device (either flight hardware or engineering
Sensors development hardware) or
equivalent mathematical model of sensors
Mathematical mod-
Flight control com- Physical device (either flight hardware, engineering hardware,
els
puter or emulator)
Equivalent servo/actuator mathematical model or
Servos and actuators Physical device (either flight hardware or engineering
development hardware)
Flight environment Emulator or mathematical model
4.4 Simulation in different phases
Design of control system is not a simple iterative process. It can be divided into conceptual design phase,
detailed design phase, prototype phase, and integrated system phase. Simulation is demanded in each
phase in order to realize flight equivalent examples for the control system validation or equipment
verification. Relationship between each design phase and simulation can be described in Figure 2.
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ISO 16781:2013(E)
Figure 2 — Relationship between each design phase and simulation
In the conceptual design phase simulation, mathematical simulation is used for control system
architecture and conceptual design studies. This pure software simulation environment supports
the identification of optional control system architecture/top level design that meets both mission
performance requirements and stability robustness requirements. Low order/low fidelity models and
simple operational environment models are adopted for mathematical simulation. Multiple co-existing
models and simulation tools are managed by individual engineers.
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In detailed design phase simulation, mathematical simulation is used for system optimizations,
parameter sensitivity assessments, performance evaluations, stability robustness assessments, etc.
This simulation environment supports the identification of the final control system design that matches
mission performance and stability robustness requirements. High order/high fidelity, possibly nonlinear
models and detailed flight-equivalent operational environment models are adopted. Some formal
configuration management/control of models, parameter databases, and simulations are required in
this simulation environment.
HITL simulation, which combines hardware and software, is often introduced in the prototype phase
simulation. The basic components of control system are realized by prototype. In this phase, correctness
of control algorithm prototype and flight software and compatibility between various interfaces
are validated, in order to reduce the integrated risk of control system and the entire spacecraft.
This simulation environment can allow substitution of control system sensors/actuators models for
hardware engineering units as needed. Simple software plant and environment models are used to close
the control system loop. Also, some formal configuration management/control of this HITL simulation
environment is required.
Testing of control system flight software nominal functionality as well as failure mode functions is
accomplished by HITL simulation in integrated system phase simulation. The basic components of
control system are realized by real devices, at least including a flight processor hosting the control
algorithm as well as other relevant flight software elements. Consistency of all parts of control system
is certified to ensure that requirements of space system are satisfied. This M&S environment is often
maintained after space system launch to allow the following.
a) Model validation via comparing operational performance of actual in-flight control system with
pre-launch M&S results.
b) The checkout and verification of control system flight software modifications (e.g. a flight software
“patch”) prior to implementing the change to on-board space system.
c) The support of space system anomaly resolution. Very high degree of formal configuration
management/control of this simulation environment is needed.
Basic characteristic of the four phases in Figure 2 is listed in Table 3.
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ISO 16781:2013(E)
Table 3 — Basic characteristic of the four phases
Conceptual Detailed design
Prototype phase Integrated system
design phase phase
simulation phase simulation
simulation simulation
hybrid hardware/ hybrid
Simulation pure software, pure software,
software, Prototype or hardware/software,
environment non-real-time non-real-time
simulators, real-time HITL, real-time
signal/data/timing
functional
mission mission nominal flight
compatibility, inter-
performance, performance, software function-
Demonstrated items face
stability robust- stability robust- ality, failure mode
compatibility, soft-
ness requirements ness requirements functions
ware processing func-
tions
high order/high
low order/low
fidelity detailed
fidelity simple
model, nonlinear,
Model fidelity model, linear, e.g. detailed model detailed model
e.g. flexible body
rigid body
dynamics, distur-
dynamics
bances
flight-equivalent code,
Control law not necessarily in on-board flight
modular form not necessarily on-
algorithms coding modular form software
board
mathematic model mathematic model
mathematic model V&V, simulation soft- V&V, simulation
mathematic model
Simulation system V&V V&V, simulation ware V&V, software V&V, simu-
V&V
software V&V simulation hardware lation
V&V hardware V&V
Configuration very high degree
little or no formal partly formal partly formal
management/control formal
4.5 Simulation process
In each control system development phase, simulation process should include the following.
a) Requirements analysis
Identifying the input of simulation task, e.g. mathematical model of control plant, control algorithm,
control system criterion, control system specification, and corresponding documents.
Identifying the output of simulation task, e.g. simulation data, simulation result analysis, and
corresponding documents.
Identifying the simulation functions and all the resources needed (e.g. human resource, staff
responsibility, field, equipment).
b) Simulation system design
Designing simulation system, deciding to realize each part of control system by software, prototype
or real equipment, determining interface in the simulation system, compiling simulation plan and
simulation system design report.
c) Simulation software development
Coding and debugging simulation software, implementing mathematical models (e.g. vehicle dynamics,
flight environment, servo) with software.
d) Simulation hardware development
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ISO 16781:
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