Space data and information transfer systems -- Attitude data messages

This document specifies two standard message formats for use in transferring spacecraft attitude information between space agencies: the Attitude Parameter Message (APM) and the Attitude Ephemeris Message (AEM). Such exchanges are used for: - preflight planning for tracking or attitude estimation support; - scheduling attitude and data processing support; - carrying out attitude operations; - performing attitude comparisons; - carrying out attitude propagations and/or sensor predictions; - testing to initialize sub-system simulators (communications, power, etc.). This document includes sets of requirements and criteria that the message formats have been designed to meet. For exchanges where these requirements do not capture the needs of the participating agencies, another mechanism may be selected.

Systèmes de transfert des informations et données spatiales -- Messages de données d'attitude

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Status
Published
Publication Date
29-Jun-2021
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
28-May-2021
Completion Date
28-May-2021
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INTERNATIONAL ISO
STANDARD 13541
Second edition
2021-06
Space data and information transfer
systems — Attitude data messages
Systèmes de transfert des informations et données spatiales —
Messages de données d'attitude
Reference number
ISO 13541:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 13541:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 13541:2021(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 (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 the Consultative Committee for Space Data Systems (CCSDS) (as

CCSDS 504.0-B-1 Cor.1, July 2015) and was adopted (without modifications) by Technical Committee

ISO/TC 20, Space vehicles, Subcommittee SC 13, Space data and information transfer systems.

This second edition cancels and replaces the first edition (ISO 13541:2010), which has been

technically revised.
The main changes compared to the previous edition are as follows:
— adds clarifying text to 1.3, Conventions and Definitions.

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
© ISO 2021 – All rights reserved iii
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
CONTENTS
Section Page

1  INTRODUCTION .......................................................................................................... 1-1

1.1  PURPOSE ............................................................................................................... 1-1

1.2  SCOPE AND APPLICABILITY ............................................................................ 1-1

1.3  CONVENTIONS AND DEFINITIONS................................................................. 1-2

1.4  STRUCTURE OF THIS DOCUMENT.................................................................. 1-2

1.5  REFERENCES ....................................................................................................... 1-3

2  OVERVIEW ................................................................................................................... 2-1

2.1  ATTITUDE DATA MESSAGE TYPES ................................................................ 2-1

2.2  ATTITUDE PARAMETER MESSAGE (APM) ................................................... 2-1

2.3  ATTITUDE EPHEMERIS MESSAGE (AEM) ..................................................... 2-2

2.4  EXCHANGE OF MULTIPLE MESSAGES .......................................................... 2-2

2.5  DEFINITIONS ........................................................................................................ 2-2

3  ATTITUDE PARAMETER MESSAGE (APM) ......................................................... 3-1

3.1  OVERVIEW ........................................................................................................... 3-1

3.2  APM CONTENT .................................................................................................... 3-1

3.3  APM EXAMPLES ................................................................................................ 3-10

4  ATTITUDE EPHEMERIS MESSAGE (AEM) .......................................................... 4-1

4.1  OVERVIEW ........................................................................................................... 4-1

4.2  AEM CONTENT .................................................................................................... 4-1

4.3  AEM EXAMPLE .................................................................................................. 4-12

5  ADM SYNTAX ............................................................................................................... 5-1

5.1  INTRODUCTION .................................................................................................. 5-1

5.2  LINES ..................................................................................................................... 5-1

5.3  KEYWORDS .......................................................................................................... 5-1

5.4  VALUES ................................................................................................................. 5-2

5.5  UNITS ..................................................................................................................... 5-4

5.6  COMMENTS .......................................................................................................... 5-4

6  SECURITY ..................................................................................................................... 6-1

6.1  INTRODUCTION .................................................................................................. 6-1

CCSDS 504.0-B-1 Page vi May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
CONTENTS (continued)
Section Page
6.2  SECURITY CONCERNS WITH RESPECT TO THIS RECOMMENDED

STANDARD ........................................................................................................... 6-1

6.3  POTENTIAL THREATS AND ATTACK SCENARIOS ..................................... 6-2

6.4  CONSEQUENCES OF NOT APPLYING STATED SECURITY TO THE

TECHNOLOGY ..................................................................................................... 6-2

6.5  DATA SECURITY IMPLEMENTATION SPECIFICS ........................................ 6-2

ANNEX A VALUES FOR SELECTED KEYWORDS (NORMATIVE) ................... A-1
ANNEX B RATIONALE FOR ATTITUDE DATA MESSAGES

(INFORMATIVE) ..........................................................................................B-1

ANNEX C ITEMS FOR AN INTERFACE CONTROL DOCUMENT

(INFORMATIVE) ......................................................................................... C-1

ANNEX D ABBREVIATIONS AND ACRONYMS (INFORMATIVE) .................... D-1
ANNEX E INFORMATIVE REFERENCES (INFORMATIVE) ...............................E-1
Figure Page

3-1  APM File Example Using Comments to Denote Updates .......................................... 3-10

3-2  APM File Example Using Frame of Another Spacecraft ........................................... 3-11

3-3  APM File Example Describing Sensor Frame to Body Frame Transform ................. 3-11

3-4  APM File Example Describing Orientation of Instrument ......................................... 3-12

3-5  APM File Example with Euler Angle Rates ............................................................... 3-12

3-6  APM File Example with Euler Angle Rates (Repeated Axis) .................................... 3-13

3-7  APM File Example with Mission Elapsed Time ........................................................ 3-14

3-8  APM File Example with Optional Euler Elements and One Maneuver ..................... 3-15

4-1  AEM Example ............................................................................................................ 4-12

4-2  AEM Spinner Example ............................................................................................... 4-13

Table

3-1  APM Header ................................................................................................................. 3-2

3-2  APM Metadata .............................................................................................................. 3-3

3-3  APM Data ..................................................................................................................... 3-4

4-1  AEM File Layout Specifications .................................................................................. 4-2

4-2  AEM Header ................................................................................................................. 4-3

4-3  AEM Metadata .............................................................................................................. 4-4

4-4  Types of Attitude Ephemeris Data Lines ...................................................................... 4-8

B-1  Primary Requirements ..................................................................................................B-2

B-2  Heritage Requirements .................................................................................................B-3

CCSDS 504.0-B-1 Page vii May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
CONTENTS (continued)
Table Page

B-3  Desirable Characteristics ..............................................................................................B-3

B-4  Applicability of the Criteria to Attitude Data Messages ..............................................B-4

B-5  Services Available with Attitude Data Messages .........................................................B-4

C-1  Items Recommended for an ICD ..................................................................................C-1

CCSDS 504.0-B-1 Page viii May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
1 INTRODUCTION
1.1 PURPOSE

1.1.1 This Attitude Data Message (ADM) Recommended Standard specifies two standard

message formats for use in transferring spacecraft attitude information between space

agencies: the Attitude Parameter Message (APM) and the Attitude Ephemeris Message

(AEM). Such exchanges are used for:
– preflight planning for tracking or attitude estimation support;
– scheduling attitude and data processing support;
– carrying out attitude operations;
– performing attitude comparisons;
– carrying out attitude propagations and/or sensor predictions;
– testing to initialize sub-system simulators (communications, power, etc.).

1.1.2 This Recommended Standard includes sets of requirements and criteria that the

message formats have been designed to meet. For exchanges where these requirements do

not capture the needs of the participating agencies, another mechanism may be selected.

1.2 SCOPE AND APPLICABILITY

1.2.1 This document contains two attitude data messages designed for applications

involving data interchange in space data systems. The rationale behind the design of each

message is described in annex B and may help the application engineer to select a suitable

message. Definition of the attitude accuracy underlying a particular attitude message is

outside of the scope of this Recommended Standard and should be specified via Interface

Control Document (ICD) between data exchange participants. Applicability information

specific to each Attitude Data Message format appears in sections 3 and 4, as well as in

annex subsection B3.

1.2.2 This Recommended Standard is applicable only to the message format and content,

but not to its transmission. The transmission of the message between agencies is outside the

scope of this document and should be specified in an ICD or by following a CCSDS standard

on transmission.

1.2.3 Description of the message formats based on the use of the eXtensible Markup

Language (XML) will be available. An XML schema is defined by the CCSDS Recommended

Standard titled ‘XML Specification for Navigation Data Messages’ (reference [5]). Agencies

should specify, via ICD, the ASCII file format to be exchanged (Keyword Value Notation

[KVN] or XML).
CCSDS 504.0-B-1 Page 1-1 May 2008
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Cor. 1
ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
1.3 CONVENTIONS AND DEFINITIONS
The following conventions apply throughout this Recommended Standard:
a) the words ‘shall’ and ‘must’ imply a binding and verifiable specification;
b) the word ‘should’ implies an optional, but desirable, specification;
c) the word ‘may’ implies an optional specification; and
d) the words ‘is’, ‘are’, and ‘will’ imply statements of fact.

As in some attitude dynamics references, in this document the term ‘nutation’ is used to

mean the motion of the spin axis of a body about an inertial axis. In many other references

this motion is called ‘precession’.
1.4 STRUCTURE OF THIS DOCUMENT
1.4.1 Section 2 provides a brief overview of the CCSDS-recommended Attitude Data

Message types, the Attitude Parameter Message (APM) and Attitude Ephemeris Message

(AEM).
1.4.2 Section 3 provides details about the structure and content of the APM.
1.4.3 Section 4 provides details about the structure and content of the AEM.
1.4.4 Section 5 provides details regarding syntax of the APM and AEM messages.

1.4.5 Section 6 provides information regarding security concerns related to the access and

transmission of the Attitude Data Messages.

1.4.6 Annex B provides a list of approved values for selected keywords in the ADM

Metadata sections.

1.4.7 Annex B lists a set of requirements that were taken into consideration in the design of

the APM and AEM, along with tables and discussion regarding the applicability of the two

message types to various attitude estimation tasks and functions.

1.4.8 Annex C lists a number of items that should be covered in ICDs prior to exchanging

ADMs on a regular basis. There are several statements throughout the document that refer to

the desirability or necessity of such a document; this annex lists all the suggested ICD items

in a single place in the document.
1.4.9 Annex D is a list of abbreviations and acronyms applicable to the ADM.
1.4.10 Annex E is a list of informative references.
CCSDS 504.0-B-1 CCSDS 504.0-B-1 Cor. 1 Page 1-2 MayJuly 2008 2015
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
1.5 REFERENCES

The following documents contain provisions which, through reference in this text, constitute

provisions of this Recommended Standard. At the time of publication, the editions indicated

were valid. All documents are subject to revision, and users of this Recommended Standard

are encouraged to investigate the possibility of applying the most recent editions of the

documents indicated below. The CCSDS Secretariat maintains a register of currently valid

CCSDS Recommended Standards.

[1] Information Technology—8-Bit Single-Byte Coded Graphic Character Sets—Part 1:

Latin Alphabet No. 1. International Standard, ISO/IEC 8859-1:1998. Geneva: ISO,

1998.
[2] Spacewarn Bulletin. Greenbelt, MD, USA: WDC-SI.

[3] JPL Solar System Dynamics. Pasadena, CA, USA: JPL.

[4] Time Code Formats. Recommendation for Space Data System Standards, CCSDS
301.0-B-3. Blue Book. Issue 3. Washington, D.C.: CCSDS, January 2002.

[5] XML Specification for Navigation Data Messages. Draft Recommendation for Space

Data System Standards, CCSDS 505.0-R-1. Red Book. Issue 1. Washington, D.C.:
CCSDS, November 2005.

[6] IEEE Standard for Binary Floating-Point Arithmetic. IEEE Std 754-1985. New York:

IEEE, 1985.
[7] Orbit Data Messages. Recommendation for Space Data System Standards, CCSDS
502.0-B-1. Blue Book. Issue 1. Washington, D.C.: CCSDS, September 2004.
NOTE – A list of informative references can be found in annex E.
CCSDS 504.0-B-1 Page 1-3 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
2 OVERVIEW
2.1 ATTITUDE DATA MESSAGE TYPES
2.1.1 Two CCSDS-recommended Attitude Data Messages (ADMs) are described in this

Recommended Standard: the Attitude Parameter Message (APM) and the Attitude Ephemeris

Message (AEM).

2.1.2 The recommended attitude data messages are ASCII text format. While binary-based

attitude data message formats are computer efficient and minimize overhead on

uplinked/downlinked data streams, there are ground-segment applications for which an

ASCII character-based message is more appropriate. For example, when files or data objects

are created using text editors or word processors, ASCII character-based attitude data format

representations are necessary. They are also useful in transferring text files between

heterogeneous computing systems, because the ASCII character set is nearly universally used

and is interpretable by all popular systems. In addition, direct human-readable downloads of

text files or objects to displays or printers are possible without preprocessing. The penalty

for this convenience is inefficiency.

2.1.3 As currently specified, an APM or AEM file is to represent attitude data for a single

vehicle. It is possible that the architecture may support multiple vehicles per file; this could

be considered in the future.
2.2 ATTITUDE PARAMETER MESSAGE (APM)

2.2.1 An APM specifies the attitude state of a single object at a specified epoch. This

message is suited to inter-agency exchanges that (1) involve automated interaction and/or

human interaction, and (2) do not require high-fidelity dynamic modeling (for high-fidelity

dynamic modeling, see 2.3, Attitude Ephemeris Message).

2.2.2 The APM requires the use of a propagation technique to determine the attitude state

at times different from the specified epoch, leading to a higher level of effort for software

implementation than for the AEM. When inertial frames are specified, the APM is fully self-

contained and no additional information is required to specify the attitude; if local orbital

frames are specified, then an APM must be used in conjunction with an Orbit Parameter

Message (reference [7]).
2.2.3 The APM allows for modeling of any number of finite maneuvers and simple

modeling of solar radiation pressure and atmospheric torque. Note that an Orbit Parameter

Message (OPM) is needed for proper solar radiation pressure modeling. The attributes of the

APM also make it suitable for applications such as exchanges by FAX or voice, or
applications where the message is to be frequently interpreted by humans.
CCSDS 504.0-B-1 Page 2-1 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
2.3 ATTITUDE EPHEMERIS MESSAGE (AEM)

2.3.1 An AEM specifies the attitude state of a single object at multiple epochs, contained

within a specified time range. The AEM is suited to inter-agency exchanges that (1) involve

automated interaction (e.g., computer-to-computer communication where frequent, fast,

automated time interpretation and processing are required), and (2) require higher fidelity or

higher precision dynamic modeling than is possible with the APM (e.g., flexible structures,

more complex attitude movement, etc.).

2.3.2 The AEM allows for dynamic modeling of any number of torques (solar pressure,

atmospheric torques, magnetics, etc.). The AEM requires the use of an interpolation

technique to interpret the attitude state at times different from the tabular epochs.

2.3.3 The AEM is fully self-contained; no additional information is required when inertial

reference frames are specified. If local orbital reference frames are specified, then an AEM

must be used in conjunction with an Orbit Ephemeris Message (reference [7]).
2.4 EXCHANGE OF MULTIPLE MESSAGES

For a given object, multiple APM or AEM messages may be provided in a message exchange

session to achieve attitude fidelity requirements. If attitude information for multiple objects

is to be exchanged, then multiple APM or AEM files must be used.
2.5 DEFINITIONS

Definitions of time systems, reference frames, attitude estimation and prediction methods and

models are provided in reference [E4].
CCSDS 504.0-B-1 Page 2-2 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
3 ATTITUDE PARAMETER MESSAGE (APM)
3.1 OVERVIEW

3.1.1 Attitude information may be exchanged between two participants by sending the

attitude state (see reference [E4]) for a specified epoch using an Attitude Parameter Message

(APM). The message recipient must have an attitude propagator available that is able to

propagate the APM state to compute the estimated attitude at other desired epochs. For this

propagation, additional ancillary information (spacecraft properties such as inertia matrix,

torque vectors, and maneuver planning data, if applicable) shall be included with the

message.
3.1.2 The use of the APM shall be applicable under the following conditions:
– an attitude propagator shall be available at the receiver’s location;

– the receiver’s modeling of satellite attitude dynamics, atmospheric torque, other

internal and external torques (e.g., magnetic, gravitational, etc.), thrust maneuvers,

and attitude control (see reference [E4]) must fulfill accuracy requirements
established via an ICD between the agencies.

3.1.3 The APM shall be a text file consisting of attitude data for a single object. It shall be

easily readable by both humans and computers.

3.1.4 The APM file naming scheme shall be agreed to on a case-by-case basis between the

participating agencies, and should be documented in an Interface Control Document (ICD).

The method of exchanging APMs shall be decided on a case-by-case basis by the
participating agencies and documented in an ICD.
3.2 APM CONTENT
3.2.1 GENERAL
The APM shall be represented as a combination of the following:
a) a header;
b) metadata (data about the data);
c) optional comments (explanatory information); and
d) data.
CCSDS 504.0-B-1 Page 3-1 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
3.2.2 APM HEADER
3.2.2.1 Table 3-1 specifies for each header item:
a) the keyword to be used;
b) a short description of the item;
c) examples of allowed values; and
d) whether the item is obligatory or optional.
3.2.2.2 Only those keywords shown in table 3-1 shall be used in an APM header.
Table 3-1: APM Header
Keyword Description Examples of Values Obligatory
CCSDS_APM_VERS 1.0
Format version in the form of ‘x.y’, where ‘y’ is Yes
incremented for corrections and minor changes, and ‘x’
is incremented for major changes.
COMMENT This is a comment
Comments (allowed at the beginning of the APM No
Header after the APM version number). Each comment
line shall begin with this keyword.
CREATION_DATE 2001-11-06T11:17:33
File creation date/time in one of the following formats: Yes
2002-204T15:56:23
YYYY-MM-DDThh:mm:ss[.d→d] or
1996-12-18T14:28:15.1172
YYYY-DDDThh:mm:ss[.d→d]
where ‘YYYY’ is the year, ‘MM’ is the two-digit
month, ‘DD’ is the two-digit day, ‘DDD’ is the three-
digit day of year, ‘T’ is constant, ‘hh:mm:ss[.d→d]’ is
the UTC time in hours, minutes, seconds, and optional
fractional seconds. As many ‘d’ characters to the right
of the period as required may be used to obtain the
required precision. All fields require leading zeros.

ORIGINATOR Creating agency (value should be specified in an ICD). CNES, ESOC, GSFC, GSOC, Yes

JPL, JAXA, etc.
3.2.3 APM METADATA
3.2.3.1 Table 3-2 specifies for each metadata item:
a) the keyword to be used;
b) a short description of the item;
c) examples of allowed values; and
d) whether the item is obligatory or optional.
CCSDS 504.0-B-1 Page 3-2 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES

3.2.3.2 Only those keywords shown in table 3-2 shall be used in APM metadata. For some

keywords (OBJECT_NAME, OBJECT_ID, CENTER_NAME) there are no definitive lists of

authorized values maintained by a control authority; the references listed in 1.5 and annex E

are the best known sources for authorized values to date.
Table 3-2: APM Metadata
Keyword Description Normative Values / Examples Obligatory
COMMENT COMMENT This is a comment
Comments (allowed only at the beginning of the APM No
Metadata before OBJECT_NAME). Each comment
line shall begin with this keyword.
OBJECT_NAME EUTELSAT W1
Spacecraft name of the object corresponding to the Yes
MARS PATHFINDER
attitude data to be given. There is no CCSDS-based
STS106
restriction on the value for this keyword, but it is
NEAR
recommended to use names from the SPACEWARN
Bulletin (reference [2]), which include the Object
name and international designator of the participant.
OBJECT_ID 2000-052A
Spacecraft identifier of the object corresponding to Yes
1996-068A
the attitude data to be given. While there is no
2000-053A
CCSDS-based restriction on the value for this
1996-008A
keyword, the names could be drawn from the
SPACEWARN Bulletin (reference [2]). If this is
chosen, it is recommended that values have the format
YYYY-NNNP{PP}, where:
– YYYY = year of launch;
– NNN = three-digit serial number of launch in
year YYYY (with leading zeros);
– P{PP} = at least one capital letter for the
identification of the part brought into
space by the launch.
In cases where the asset is not listed in the bulletin,
the value should be provided in an ICD.
CENTER_NAME EARTH
Origin of reference frame, which may be a natural No
EARTH BARYCENTER
solar system body (planets, asteroids, comets, and
MOON
natural satellites), including any planet barycenter or
SOLAR SYSTEM BARYCENTER
the solar system barycenter, or another spacecraft (in
SUN
this the value for ‘CENTER_NAME’ is subject to the
JUPITER BARYCENTER
same rules as for ‘OBJECT_NAME’). There is no
STS 106
CCSDS-based restriction on the value for this
EROS
keyword, but for natural bodies it is recommended to
use names from the NASA/JPL Solar System
Dynamics Group (reference [3]).
TIME_SYSTEM UTC, TAI, TT, GPS, TDB, TCB
Time system used for attitude and maneuver data Yes
(also see table 3-3). The full set of allowed values is
enumerated in annex A, with an excerpt provided in
the ‘Normative Values/Examples’ column.
Explanations of these time systems can be found in
Navigation Definitions and Conventions
(reference [E4]).
CCSDS 504.0-B-1 Page 3-3 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
3.2.4 APM DATA

3.2.4.1 Table 3-3 provides an overview of the five logical blocks in the APM Data section

(attitude Quaternion, attitude Euler angles (three-axis), spin axis types, Spacecraft

Parameters, Maneuver Parameters), and specifies for each data item:
a) the keyword to be used;
b) a short description of the item;
c) the units to be used;
d) whether the item is obligatory or optional.
3.2.4.2 Only those keywords shown in table 3-3 shall be used in APM data. Some

important remarks concerning the keywords in table 3-3 appear immediately after the table.

Table 3-3: APM Data
Normative
Keyword Description Obligatory
Units/Values

Comments (Shall appear only at the beginning of the logical blocks, but not between components of the logical blocks.)

COMMENT
...

INTERNATIONAL ISO
STANDARD 13541
Second edition
Space data and information transfer
systems — Attitude data messages
Systèmes de transfert des informations et données spatiales —
Messages de données d'attitude
PROOF/ÉPREUVE
Reference number
ISO 13541:2021(E)
ISO 2021
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ISO 13541:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO 2021 – All rights reserved
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ISO 13541:2021(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 (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 the Consultative Committee for Space Data Systems (CCSDS) (as

CCSDS 504.0-B-1 Cor.1, July 2015) and was adopted (without modifications) by Technical Committee

ISO/TC 20, Space vehicles, Subcommittee SC 13, Space data and information transfer systems.

This second edition cancels and replaces the first edition (ISO 13541:2010), which has been

technically revised.
The main changes compared to the previous edition are as follows:
— adds clarifying text to 1.3, Conventions and Definitions.

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
© ISO 2021 – All rights reserved PROOF/ÉPREUVE iii
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
CONTENTS
Section Page

1  INTRODUCTION .......................................................................................................... 1-1

1.1  PURPOSE ............................................................................................................... 1-1

1.2  SCOPE AND APPLICABILITY ............................................................................ 1-1

1.3  CONVENTIONS AND DEFINITIONS................................................................. 1-2

1.4  STRUCTURE OF THIS DOCUMENT.................................................................. 1-2

1.5  REFERENCES ....................................................................................................... 1-3

2  OVERVIEW ................................................................................................................... 2-1

2.1  ATTITUDE DATA MESSAGE TYPES ................................................................ 2-1

2.2  ATTITUDE PARAMETER MESSAGE (APM) ................................................... 2-1

2.3  ATTITUDE EPHEMERIS MESSAGE (AEM) ..................................................... 2-2

2.4  EXCHANGE OF MULTIPLE MESSAGES .......................................................... 2-2

2.5  DEFINITIONS ........................................................................................................ 2-2

3  ATTITUDE PARAMETER MESSAGE (APM) ......................................................... 3-1

3.1  OVERVIEW ........................................................................................................... 3-1

3.2  APM CONTENT .................................................................................................... 3-1

3.3  APM EXAMPLES ................................................................................................ 3-10

4  ATTITUDE EPHEMERIS MESSAGE (AEM) .......................................................... 4-1

4.1  OVERVIEW ........................................................................................................... 4-1

4.2  AEM CONTENT .................................................................................................... 4-1

4.3  AEM EXAMPLE .................................................................................................. 4-12

5  ADM SYNTAX ............................................................................................................... 5-1

5.1  INTRODUCTION .................................................................................................. 5-1

5.2  LINES ..................................................................................................................... 5-1

5.3  KEYWORDS .......................................................................................................... 5-1

5.4  VALUES ................................................................................................................. 5-2

5.5  UNITS ..................................................................................................................... 5-4

5.6  COMMENTS .......................................................................................................... 5-4

6  SECURITY ..................................................................................................................... 6-1

6.1  INTRODUCTION .................................................................................................. 6-1

CCSDS 504.0-B-1 Page vi May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
CONTENTS (continued)
Section Page
6.2  SECURITY CONCERNS WITH RESPECT TO THIS RECOMMENDED

STANDARD ........................................................................................................... 6-1

6.3  POTENTIAL THREATS AND ATTACK SCENARIOS ..................................... 6-2

6.4  CONSEQUENCES OF NOT APPLYING STATED SECURITY TO THE

TECHNOLOGY ..................................................................................................... 6-2

6.5  DATA SECURITY IMPLEMENTATION SPECIFICS ........................................ 6-2

ANNEX A VALUES FOR SELECTED KEYWORDS (NORMATIVE) ................... A-1
ANNEX B RATIONALE FOR ATTITUDE DATA MESSAGES

(INFORMATIVE) ..........................................................................................B-1

ANNEX C ITEMS FOR AN INTERFACE CONTROL DOCUMENT

(INFORMATIVE) ......................................................................................... C-1

ANNEX D ABBREVIATIONS AND ACRONYMS (INFORMATIVE) .................... D-1
ANNEX E INFORMATIVE REFERENCES (INFORMATIVE) ...............................E-1
Figure Page

3-1  APM File Example Using Comments to Denote Updates .......................................... 3-10

3-2  APM File Example Using Frame of Another Spacecraft ........................................... 3-11

3-3  APM File Example Describing Sensor Frame to Body Frame Transform ................. 3-11

3-4  APM File Example Describing Orientation of Instrument ......................................... 3-12

3-5  APM File Example with Euler Angle Rates ............................................................... 3-12

3-6  APM File Example with Euler Angle Rates (Repeated Axis) .................................... 3-13

3-7  APM File Example with Mission Elapsed Time ........................................................ 3-14

3-8  APM File Example with Optional Euler Elements and One Maneuver ..................... 3-15

4-1  AEM Example ............................................................................................................ 4-12

4-2  AEM Spinner Example ............................................................................................... 4-13

Table

3-1  APM Header ................................................................................................................. 3-2

3-2  APM Metadata .............................................................................................................. 3-3

3-3  APM Data ..................................................................................................................... 3-4

4-1  AEM File Layout Specifications .................................................................................. 4-2

4-2  AEM Header ................................................................................................................. 4-3

4-3  AEM Metadata .............................................................................................................. 4-4

4-4  Types of Attitude Ephemeris Data Lines ...................................................................... 4-8

B-1  Primary Requirements ..................................................................................................B-2

B-2  Heritage Requirements .................................................................................................B-3

CCSDS 504.0-B-1 Page vii May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
CONTENTS (continued)
Table Page

B-3  Desirable Characteristics ..............................................................................................B-3

B-4  Applicability of the Criteria to Attitude Data Messages ..............................................B-4

B-5  Services Available with Attitude Data Messages .........................................................B-4

C-1  Items Recommended for an ICD ..................................................................................C-1

CCSDS 504.0-B-1 Page viii May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
1 INTRODUCTION
1.1 PURPOSE

1.1.1 This Attitude Data Message (ADM) Recommended Standard specifies two standard

message formats for use in transferring spacecraft attitude information between space

agencies: the Attitude Parameter Message (APM) and the Attitude Ephemeris Message

(AEM). Such exchanges are used for:
– preflight planning for tracking or attitude estimation support;
– scheduling attitude and data processing support;
– carrying out attitude operations;
– performing attitude comparisons;
– carrying out attitude propagations and/or sensor predictions;
– testing to initialize sub-system simulators (communications, power, etc.).

1.1.2 This Recommended Standard includes sets of requirements and criteria that the

message formats have been designed to meet. For exchanges where these requirements do

not capture the needs of the participating agencies, another mechanism may be selected.

1.2 SCOPE AND APPLICABILITY

1.2.1 This document contains two attitude data messages designed for applications

involving data interchange in space data systems. The rationale behind the design of each

message is described in annex B and may help the application engineer to select a suitable

message. Definition of the attitude accuracy underlying a particular attitude message is

outside of the scope of this Recommended Standard and should be specified via Interface

Control Document (ICD) between data exchange participants. Applicability information

specific to each Attitude Data Message format appears in sections 3 and 4, as well as in

annex subsection B3.

1.2.2 This Recommended Standard is applicable only to the message format and content,

but not to its transmission. The transmission of the message between agencies is outside the

scope of this document and should be specified in an ICD or by following a CCSDS standard

on transmission.

1.2.3 Description of the message formats based on the use of the eXtensible Markup

Language (XML) will be available. An XML schema is defined by the CCSDS Recommended

Standard titled ‘XML Specification for Navigation Data Messages’ (reference [5]). Agencies

should specify, via ICD, the ASCII file format to be exchanged (Keyword Value Notation

[KVN] or XML).
CCSDS 504.0-B-1 Page 1-1 May 2008
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Cor. 1
ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
1.3 CONVENTIONS AND DEFINITIONS
The following conventions apply throughout this Recommended Standard:
a) the words ‘shall’ and ‘must’ imply a binding and verifiable specification;
b) the word ‘should’ implies an optional, but desirable, specification;
c) the word ‘may’ implies an optional specification; and
d) the words ‘is’, ‘are’, and ‘will’ imply statements of fact.

As in some attitude dynamics references, in this document the term ‘nutation’ is used to

mean the motion of the spin axis of a body about an inertial axis. In many other references

this motion is called ‘precession’.
1.4 STRUCTURE OF THIS DOCUMENT
1.4.1 Section 2 provides a brief overview of the CCSDS-recommended Attitude Data

Message types, the Attitude Parameter Message (APM) and Attitude Ephemeris Message

(AEM).
1.4.2 Section 3 provides details about the structure and content of the APM.
1.4.3 Section 4 provides details about the structure and content of the AEM.
1.4.4 Section 5 provides details regarding syntax of the APM and AEM messages.

1.4.5 Section 6 provides information regarding security concerns related to the access and

transmission of the Attitude Data Messages.

1.4.6 Annex B provides a list of approved values for selected keywords in the ADM

Metadata sections.

1.4.7 Annex B lists a set of requirements that were taken into consideration in the design of

the APM and AEM, along with tables and discussion regarding the applicability of the two

message types to various attitude estimation tasks and functions.

1.4.8 Annex C lists a number of items that should be covered in ICDs prior to exchanging

ADMs on a regular basis. There are several statements throughout the document that refer to

the desirability or necessity of such a document; this annex lists all the suggested ICD items

in a single place in the document.
1.4.9 Annex D is a list of abbreviations and acronyms applicable to the ADM.
1.4.10 Annex E is a list of informative references.
CCSDS 504.0-B-1 CCSDS 504.0-B-1 Cor. 1 Page 1-2 MayJuly 2008 2015
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
1.5 REFERENCES

The following documents contain provisions which, through reference in this text, constitute

provisions of this Recommended Standard. At the time of publication, the editions indicated

were valid. All documents are subject to revision, and users of this Recommended Standard

are encouraged to investigate the possibility of applying the most recent editions of the

documents indicated below. The CCSDS Secretariat maintains a register of currently valid

CCSDS Recommended Standards.

[1] Information Technology—8-Bit Single-Byte Coded Graphic Character Sets—Part 1:

Latin Alphabet No. 1. International Standard, ISO/IEC 8859-1:1998. Geneva: ISO,

1998.
[2] Spacewarn Bulletin. Greenbelt, MD, USA: WDC-SI.

[3] JPL Solar System Dynamics. Pasadena, CA, USA: JPL.

[4] Time Code Formats. Recommendation for Space Data System Standards, CCSDS
301.0-B-3. Blue Book. Issue 3. Washington, D.C.: CCSDS, January 2002.

[5] XML Specification for Navigation Data Messages. Draft Recommendation for Space

Data System Standards, CCSDS 505.0-R-1. Red Book. Issue 1. Washington, D.C.:
CCSDS, November 2005.

[6] IEEE Standard for Binary Floating-Point Arithmetic. IEEE Std 754-1985. New York:

IEEE, 1985.
[7] Orbit Data Messages. Recommendation for Space Data System Standards, CCSDS
502.0-B-1. Blue Book. Issue 1. Washington, D.C.: CCSDS, September 2004.
NOTE – A list of informative references can be found in annex E.
CCSDS 504.0-B-1 Page 1-3 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
2 OVERVIEW
2.1 ATTITUDE DATA MESSAGE TYPES
2.1.1 Two CCSDS-recommended Attitude Data Messages (ADMs) are described in this

Recommended Standard: the Attitude Parameter Message (APM) and the Attitude Ephemeris

Message (AEM).

2.1.2 The recommended attitude data messages are ASCII text format. While binary-based

attitude data message formats are computer efficient and minimize overhead on

uplinked/downlinked data streams, there are ground-segment applications for which an

ASCII character-based message is more appropriate. For example, when files or data objects

are created using text editors or word processors, ASCII character-based attitude data format

representations are necessary. They are also useful in transferring text files between

heterogeneous computing systems, because the ASCII character set is nearly universally used

and is interpretable by all popular systems. In addition, direct human-readable downloads of

text files or objects to displays or printers are possible without preprocessing. The penalty

for this convenience is inefficiency.

2.1.3 As currently specified, an APM or AEM file is to represent attitude data for a single

vehicle. It is possible that the architecture may support multiple vehicles per file; this could

be considered in the future.
2.2 ATTITUDE PARAMETER MESSAGE (APM)

2.2.1 An APM specifies the attitude state of a single object at a specified epoch. This

message is suited to inter-agency exchanges that (1) involve automated interaction and/or

human interaction, and (2) do not require high-fidelity dynamic modeling (for high-fidelity

dynamic modeling, see 2.3, Attitude Ephemeris Message).

2.2.2 The APM requires the use of a propagation technique to determine the attitude state

at times different from the specified epoch, leading to a higher level of effort for software

implementation than for the AEM. When inertial frames are specified, the APM is fully self-

contained and no additional information is required to specify the attitude; if local orbital

frames are specified, then an APM must be used in conjunction with an Orbit Parameter

Message (reference [7]).
2.2.3 The APM allows for modeling of any number of finite maneuvers and simple

modeling of solar radiation pressure and atmospheric torque. Note that an Orbit Parameter

Message (OPM) is needed for proper solar radiation pressure modeling. The attributes of the

APM also make it suitable for applications such as exchanges by FAX or voice, or
applications where the message is to be frequently interpreted by humans.
CCSDS 504.0-B-1 Page 2-1 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
2.3 ATTITUDE EPHEMERIS MESSAGE (AEM)

2.3.1 An AEM specifies the attitude state of a single object at multiple epochs, contained

within a specified time range. The AEM is suited to inter-agency exchanges that (1) involve

automated interaction (e.g., computer-to-computer communication where frequent, fast,

automated time interpretation and processing are required), and (2) require higher fidelity or

higher precision dynamic modeling than is possible with the APM (e.g., flexible structures,

more complex attitude movement, etc.).

2.3.2 The AEM allows for dynamic modeling of any number of torques (solar pressure,

atmospheric torques, magnetics, etc.). The AEM requires the use of an interpolation

technique to interpret the attitude state at times different from the tabular epochs.

2.3.3 The AEM is fully self-contained; no additional information is required when inertial

reference frames are specified. If local orbital reference frames are specified, then an AEM

must be used in conjunction with an Orbit Ephemeris Message (reference [7]).
2.4 EXCHANGE OF MULTIPLE MESSAGES

For a given object, multiple APM or AEM messages may be provided in a message exchange

session to achieve attitude fidelity requirements. If attitude information for multiple objects

is to be exchanged, then multiple APM or AEM files must be used.
2.5 DEFINITIONS

Definitions of time systems, reference frames, attitude estimation and prediction methods and

models are provided in reference [E4].
CCSDS 504.0-B-1 Page 2-2 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
3 ATTITUDE PARAMETER MESSAGE (APM)
3.1 OVERVIEW

3.1.1 Attitude information may be exchanged between two participants by sending the

attitude state (see reference [E4]) for a specified epoch using an Attitude Parameter Message

(APM). The message recipient must have an attitude propagator available that is able to

propagate the APM state to compute the estimated attitude at other desired epochs. For this

propagation, additional ancillary information (spacecraft properties such as inertia matrix,

torque vectors, and maneuver planning data, if applicable) shall be included with the

message.
3.1.2 The use of the APM shall be applicable under the following conditions:
– an attitude propagator shall be available at the receiver’s location;

– the receiver’s modeling of satellite attitude dynamics, atmospheric torque, other

internal and external torques (e.g., magnetic, gravitational, etc.), thrust maneuvers,

and attitude control (see reference [E4]) must fulfill accuracy requirements
established via an ICD between the agencies.

3.1.3 The APM shall be a text file consisting of attitude data for a single object. It shall be

easily readable by both humans and computers.

3.1.4 The APM file naming scheme shall be agreed to on a case-by-case basis between the

participating agencies, and should be documented in an Interface Control Document (ICD).

The method of exchanging APMs shall be decided on a case-by-case basis by the
participating agencies and documented in an ICD.
3.2 APM CONTENT
3.2.1 GENERAL
The APM shall be represented as a combination of the following:
a) a header;
b) metadata (data about the data);
c) optional comments (explanatory information); and
d) data.
CCSDS 504.0-B-1 Page 3-1 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
3.2.2 APM HEADER
3.2.2.1 Table 3-1 specifies for each header item:
a) the keyword to be used;
b) a short description of the item;
c) examples of allowed values; and
d) whether the item is obligatory or optional.
3.2.2.2 Only those keywords shown in table 3-1 shall be used in an APM header.
Table 3-1: APM Header
Keyword Description Examples of Values Obligatory
CCSDS_APM_VERS 1.0
Format version in the form of ‘x.y’, where ‘y’ is Yes
incremented for corrections and minor changes, and ‘x’
is incremented for major changes.
COMMENT This is a comment
Comments (allowed at the beginning of the APM No
Header after the APM version number). Each comment
line shall begin with this keyword.
CREATION_DATE 2001-11-06T11:17:33
File creation date/time in one of the following formats: Yes
2002-204T15:56:23
YYYY-MM-DDThh:mm:ss[.d→d] or
1996-12-18T14:28:15.1172
YYYY-DDDThh:mm:ss[.d→d]
where ‘YYYY’ is the year, ‘MM’ is the two-digit
month, ‘DD’ is the two-digit day, ‘DDD’ is the three-
digit day of year, ‘T’ is constant, ‘hh:mm:ss[.d→d]’ is
the UTC time in hours, minutes, seconds, and optional
fractional seconds. As many ‘d’ characters to the right
of the period as required may be used to obtain the
required precision. All fields require leading zeros.

ORIGINATOR Creating agency (value should be specified in an ICD). CNES, ESOC, GSFC, GSOC, Yes

JPL, JAXA, etc.
3.2.3 APM METADATA
3.2.3.1 Table 3-2 specifies for each metadata item:
a) the keyword to be used;
b) a short description of the item;
c) examples of allowed values; and
d) whether the item is obligatory or optional.
CCSDS 504.0-B-1 Page 3-2 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES

3.2.3.2 Only those keywords shown in table 3-2 shall be used in APM metadata. For some

keywords (OBJECT_NAME, OBJECT_ID, CENTER_NAME) there are no definitive lists of

authorized values maintained by a control authority; the references listed in 1.5 and annex E

are the best known sources for authorized values to date.
Table 3-2: APM Metadata
Keyword Description Normative Values / Examples Obligatory
COMMENT COMMENT This is a comment
Comments (allowed only at the beginning of the APM No
Metadata before OBJECT_NAME). Each comment
line shall begin with this keyword.
OBJECT_NAME EUTELSAT W1
Spacecraft name of the object corresponding to the Yes
MARS PATHFINDER
attitude data to be given. There is no CCSDS-based
STS106
restriction on the value for this keyword, but it is
NEAR
recommended to use names from the SPACEWARN
Bulletin (reference [2]), which include the Object
name and international designator of the participant.
OBJECT_ID 2000-052A
Spacecraft identifier of the object corresponding to Yes
1996-068A
the attitude data to be given. While there is no
2000-053A
CCSDS-based restriction on the value for this
1996-008A
keyword, the names could be drawn from the
SPACEWARN Bulletin (reference [2]). If this is
chosen, it is recommended that values have the format
YYYY-NNNP{PP}, where:
– YYYY = year of launch;
– NNN = three-digit serial number of launch in
year YYYY (with leading zeros);
– P{PP} = at least one capital letter for the
identification of the part brought into
space by the launch.
In cases where the asset is not listed in the bulletin,
the value should be provided in an ICD.
CENTER_NAME EARTH
Origin of reference frame, which may be a natural No
EARTH BARYCENTER
solar system body (planets, asteroids, comets, and
MOON
natural satellites), including any planet barycenter or
SOLAR SYSTEM BARYCENTER
the solar system barycenter, or another spacecraft (in
SUN
this the value for ‘CENTER_NAME’ is subject to the
JUPITER BARYCENTER
same rules as for ‘OBJECT_NAME’). There is no
STS 106
CCSDS-based restriction on the value for this
EROS
keyword, but for natural bodies it is recommended to
use names from the NASA/JPL Solar System
Dynamics Group (reference [3]).
TIME_SYSTEM UTC, TAI, TT, GPS, TDB, TCB
Time system used for attitude and maneuver data Yes
(also see table 3-3). The full set of allowed values is
enumerated in annex A, with an excerpt provided in
the ‘Normative Values/Examples’ column.
Explanations of these time systems can be found in
Navigation Definitions and Conventions
(reference [E4]).
CCSDS 504.0-B-1 Page 3-3 May 2008
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ISO 13541:2021(E)
CCSDS RECOMMENDED STANDARD FOR ATTITUDE DATA MESSAGES
3.2.4 APM DATA

3.2.4.1 Table 3-3 provides an overview of the five logical blocks in the APM Data section

(attitude Quaternion, attitude Euler angles (three-axis), spin axis types, Spacecraft

Parameters, Maneuver Parameters), and specifies for each data item:
a) the keyword to be used;
b) a short description of the item;
c) the units to be used;
d) whether the item is obligatory or optional.
3.2.4.2 Only those keywords shown in table 3-3 shall be used in APM data. Some

important remarks concerning the keywords in table 3-3 appear immediately after the table.

Table 3-3: APM Data
Normative
Keyword Description Obligatory
Units/Values

Comments (Shall appear only at the beginning of the logical blocks, but not between components

...

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