Space systems -- Design guidelines for multi-geo spacecraft collocation

This document addresses the design process of a collocation and the basic contents of collocation design process which include considerations, initial collocation strategy design, simulation evaluation of collocation strategy, optimal collocation strategy selection and collocation agreement. This document gives guidelines for multi-geo spacecraft collocation, and it applies in particular to multi-geo constellation.

Systèmes spatiaux -- Lignes directrices de conception pour la colocalisation de plusieurs engins spatiaux géostationnaires

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Status
Published
Publication Date
06-Jul-2021
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
07-Jun-2021
Completion Date
07-Jun-2021
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TECHNICAL ISO/TR
REPORT 22639
First edition
2021-07
Space systems — Design guidelines for
multi-geo spacecraft collocation
Reference number
ISO/TR 22639:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO/TR 22639:2021(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/TR 22639:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

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

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

3 Terms, definitions and abbreviated terms ................................................................................................................................ 1

3.1 Terms and definitions ....................................................................................................................................................................... 1

3.2 Abbreviated terms ............................................................................................................................................................................... 4

4 Collocation design process ......................................................................................................................................................................... 4

5 Basic contents of collocation design process .......................................................................................................................... 6

5.1 Considerations ........................................................................................................................................................................................ 6

5.2 Initial collocation strategy design .......................................................................................................................................... 6

5.2.1 Fundamental principle of separation strategy ....................................................................................... 6

5.2.2 The available separation strategy ..................................................................................................................... 6

5.2.3 Selection of collocation strategy......................................................................................................................... 7

5.2.4 Simulation Evaluation of Collocation Strategy ....................................................................................... 7

5.3 Final collocation strategy ............................................................................................................................................................... 7

5.4 Collocation agreement...................................................................................................................................................................... 7

Annex A (informative) Fundamental principle of available separation strategy ................................................10

Annex B (informative) Characteristics of separation strategy ...............................................................................................15

Annex C (informative) Fundamental principle of separation strategy ..........................................................................17

Annex D (informative) Sample of collocation evaluation strategy .....................................................................................19

Annex E (informative) Common collocation cases and strategies ......................................................................................20

Bibliography .............................................................................................................................................................................................................................21

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/TR 22639:2021(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. This document was drafted in accordance with the

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

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

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

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

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

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

constitute an endorsement.

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

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

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

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

Subcommittee SC 14, Space systems and operations.

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 © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/TR 22639:2021(E)
Introduction

With the wide application of geostationary orbit in spacecraft navigation, spacecraft communication

and remote sensing, there comes a dramatic increase in the number of geostationary spacecraft while

the orbit position of geostationary spacecraft is limited. In order to solve this problem, it is often

necessary for spacecraft operators to collocate their spacecraft with spacecraft operated by other

agencies in order to deliver their services.
© ISO 2021 – All rights reserved v
---------------------- Page: 5 ----------------------
TECHNICAL REPORT ISO/TR 22639:2021(E)
Space systems — Design guidelines for multi-geo
spacecraft collocation
1 Scope

This document addresses the design process of a collocation and the basic contents of collocation

design process which include considerations, initial collocation strategy design, simulation evaluation

of collocation strategy, optimal collocation strategy selection and collocation agreement.

This document gives guidelines for multi-geo spacecraft collocation, and it applies in particular to

multi-geo constellation.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

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

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1.1
orbit maintenance

orbit control for maintaining the spacecraft’s orbit in certain prediction error around the nominal orbit

3.1.2
inclination vector

vector which points to the ascending node and which is measured from the vernal equinox

Note 1 to entry: The x and y components of the vector can be expressed as Formulae (1) and (2).

ii=sincos()Ω (1)
ii=sinsin()Ω (2)
where
i
is the magnitude of the inclination vector;
Ω
is the raan in J2000 geocentric equatorial coordinate system (3.1.5);
i is the x component of the inclination vector coordinate;
i
is the y component of the inclination vector coordinate.
Note 2 to entry: Figure 1 shows the definition of the inclination vector.
© ISO 2021 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO/TR 22639:2021(E)
Key
i inclination vector which points to the ascending node
X direction of vernal equinox
Figure 1 — Inclination vector
3.1.3
eccentricity vector

vector which points to the orbit perigee and which is measured from the vernal equinox

Note 1 to entry: The x and y components of the vector can be expressed as Formulae (3) and (4).

ee=+cos(Ωω) (3)
ee=+sin(Ωω) (4)
where
e
is the magnitude of the eccentricity vector;
e
is the x component of the eccentricity vector coordinate;
e
is the y component of the eccentricity vector coordinate;
ω
is the argument of perigee.
Note 2 to entry: Figure 2 shows the definition of the eccentricity vector.
2 © ISO 2021 – All rights reserved
---------------------- Page: 7 ----------------------
ISO/TR 22639:2021(E)
Key
e eccentricity vector which points to the orbit perigee
X direction of the vernal equinox
Figure 2 — Eccentricity vector
3.1.4
mean longitude

sum of the right ascension of the ascending node, the augment of perigee and the mean anomaly

Note 1 to entry: It can further be interpreted as the approximate right ascension of the near-circular orbits with

small inclination.
3.1.5
J2000 geocentric equatorial coordinate system
coordinate system with origin at the Earth’s centre

Note 1 to entry: The positive x-axis points in the direction of the mean vernal equinox of Earth at J2000 epoch.

The positive z-axis points in the direction of the normal direction of the mean equator at J2000 epoch. The y-axis

is orthogonal to both the x-axis and the z-axis and completes a right-handed frame.

Note 2 to entry: J2000 epoch: JD=2451545,0, which is 1 Jan 2000 12:00:00 TDB.
Note 3 to entry: Figure 3 shows this coordinate system.
Key
E earth equator plane
Figure 3 — J2000 geocentric equatorial coordinate system
© ISO 2021 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO/TR 22639:2021(E)
3.1.6
spacecraft coordinate system of geo spacecraft
RTN

coordinate system with origin at the centre of the geo spacecraft’s positioned point

Note 1 to entry: The R axis is outward along radial. The N axis points in the direction of the normal direction of

J2000 mean equator. The T axis is constructed as N×R.
Note 2 to entry: Figure 4 shows this coordinate system.
Figure 4 — Spacecraft coordinate system of geo spacecraft (RTN)
3.2 Abbreviated terms
E/W east/west
geo geostationary earth orbit

raan right ascension of the ascending node (the angle between the vernal equinox and the orbit

ascending node)
OD orbit determination
4 Collocation design process

Design process of a collocation includes considerations, initial collocation strategy design, simulation

evaluation of collocation strategy, initial selection of collocation strategy, optimal collocation strategy

selection and collocation agreement.

The collocation design process is basically carried out according to the following steps, which are

represented in the collocation working flow (see Figure 5).

a) Delegations of different spacecraft operators with diversity needs hold an orbit safety consultation

meeting. Commonly, the operator of spacecraft that has to collocate with other spacecraft that is

already located at the position brings forward the consultation meeting, negotiates and organizes

the meeting.

b) In the consultation meeting, each operator presents the operation status, operational issue and

then brings forward and confirms the considerations of collocation design.

c) The initial collocation strategy is designed according to the considerations. Each collocation

spacecraft operator selects and proposes the preferred collocation strategy. The collocation

4 © ISO 2021 – All rights reserved
---------------------- Page: 9 ----------------------
ISO/TR 22639:2021(E)

strategy includes the strategy during mission period and the initial phase strategy to move a

spacecraft into position of collocation configuration and the deorbit strategy.

d) Simulation is carried out to evaluate whether the collocation strategies meet the demanded

requirements of all parties.

e) If the selected initial collocation strategy can’t meet the specified requirements, the collocation

strategies are reviewed in order to identify what can be improved. If improvements are identified,

the collocation strategies are revised and the simulation evaluation step d) is carried out again.

Else, the initial design of collocation strategy step c) is carried out again.

f) If the chosen strategy meets all the specified requirements then the strategy can be confirmed as

the decided solution.

g) Once the optimal strategy is selected then the collocation agreement formalized and signed in

accordance with Clause 5.
Figure 5 — Collocation working flow
© ISO 2021 – All rights reserved 5
---------------------- Page: 10 ----------------------
ISO/TR 22639:2021(E)
5 Basic contents of collocation design process
5.1 Considerations

In the orbit safety consultation meeting, each operator presents operation status and operational issue

and then brings forward and confirms the considerations of collocation design.
The following considerations are at least involved in the process:

a) ITU regulations about frequency allocation and assigned orbital slots of the geo spacecraft;

b) number of collocated spacecraft;
c) safety separation distance between collocated spacecraft;
d) orbit maintenance requirements of collocated spacecraft;
e) precision of orbit determination of collocated spacecraft;

f) flight dynamics characteristics, e.g. Earth gravity, solar radiation pressure;

g) fuel consumption of collocated spacecraft;
h) number and ability of central management of collocated spacecraft;
i) other special restrictions of collocated spacecraft.
5.2 Initial collocation strategy design
5.2.1 Fundamental principle of separation strategy

Assuming d is the relative distance between any two collocated spacecraft, d is the required

min

minimum safe separation distance, then the collocation strategy is to make the relative distance d

qualify the demanded condition which is d ≥ d . Generally, the value of d is 10 km based on the

min min
successful experience of international collocation cases.

The common method of the relative distance between any two collocated spacecraft is shown in

Annex C.
5.2.2 The available separation strategy

The fundamental separation strategies are listed as follows and the detailed principle about each

strategy is given in Annex A. The characteristics of each separation strategy are shown in Annex B (see

Table B.1).
a) the complete longitude separation strategy;
b) coordinated station keeping strategy;
c) the absolute eccentricity separation strategy;
d) the relative eccentricity vector separation strategy;
e) the eccentricity and inclination vector separation strategy.
6 © ISO 2021 – All rights reserved
---------------------- Page: 11 ----------------------
ISO/TR 22639:2021(E)
5.2.3 Selection of collocation strategy
5.2.3.1 Selection principle

The separation strategy is one of the fundamental strategies of 5.2.2, some other new strategies or the

combination of them. In any case, the separation strategy to be selected meets the following design

considerations:

a) safety assured: the design ensures that the in-flight safety of the spacecraft involved in the

collocation strategy;

b) operational mission: the design takes into account all the operational specifications;

c) experience-based: the design is based on current operational best practices and return of

experience (lessons learned); for the common collocation cases and strategies, refer to Annex E;

d) easily realized: the designed separation strategy is operationally feasible.
5.2.3.2 Selection method

During the selection process, the selection principle listed in 5.2.3.1 is always applied. Annex D (see

Table D.1) provides common collocation cases as well as commonly adopted collocation design results.

5.2.4 Simulation Evaluation of Collocation Strategy

The strategy is usually evaluated through simulation considering the orbit perturbation, orbit control,

OD error and some other error sources. The detailed evaluation items are listed as follows:

a) evaluate whether the safety separation distances between collocated spacecraft are ensured;

b) evaluate whether the orbit maintenance period qualifies the perspective requirements;

c) evaluate whether the fuel consumption of collocation spacecraft is within the budget requirement.

Based on the designed collocation strategy, some factors are considered, such as orbit perturbation,

orbit maintenance error, orbit determination error, to evaluate whether the considerations including

the safety separation distance, orbit maintenance period, fuel consumption and other factors are

sufficiently taken into account.
5.3 Final collocation strategy

Once the selected strategy meets all specifications, it is confirmed as the decided optimal collocation

strategy.
5.4 Coll
...

TECHNICAL ISO/TR
REPORT 22639
First edition
Space systems – Design guidelines for
multi-geo spacecraft collocation
PROOF/ÉPREUVE
Reference number
ISO/TR 22639:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO/TR 22639:2021(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
---------------------- Page: 2 ----------------------
ISO/TR 22639:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

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

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

3 Terms, definitions and abbreviated terms ................................................................................................................................ 1

3.1 Terms and definitions ....................................................................................................................................................................... 1

3.2 Abbreviated terms ............................................................................................................................................................................... 4

4 Collocation design process ......................................................................................................................................................................... 4

5 Basic contents of collocation design process .......................................................................................................................... 6

5.1 Considerations ........................................................................................................................................................................................ 6

5.2 Initial collocation strategy design .......................................................................................................................................... 6

5.2.1 Fundamental principle of separation strategy ....................................................................................... 6

5.2.2 The available separation strategy ..................................................................................................................... 6

5.2.3 Selection of collocation strategy......................................................................................................................... 7

5.2.4 Simulation Evaluation of Collocation Strategy ....................................................................................... 7

5.3 Final collocation strategy ............................................................................................................................................................... 7

5.4 Collocation agreement...................................................................................................................................................................... 7

Annex A (informative) Fundamental principle of available separation strategy ................................................10

Annex B (informative) Characteristics of separation strategy ...............................................................................................15

Annex C (Informative) Fundamental principle of separation strategy ..........................................................................17

Annex D (Informative) Sample of collocation evaluation strategy .....................................................................................19

Annex E (Informative) Common collocation cases and strategies ......................................................................................20

Bibliography .............................................................................................................................................................................................................................21

© ISO 2021 – All rights reserved PROOF/ÉPREUVE iii
---------------------- Page: 3 ----------------------
ISO/TR 22639:2021(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. This document was drafted in accordance with the

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

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

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

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

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

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

constitute an endorsement.

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

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

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

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

Subcommittee SC 14, Space systems and operations.

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 PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/TR 22639:2021(E)
Introduction

With the wide application of geostationary orbit in spacecraft navigation, spacecraft communication

and remote sensing, there comes a dramatic increase in the number of geostationary spacecraft while

the orbit position of geostationary spacecraft is limited. In order to solve this problem, it is often

necessary for spacecraft operators to collocate their spacecraft with spacecraft operated by other

agencies in order to deliver their services.
© ISO 2021 – All rights reserved PROOF/ÉPREUVE v
---------------------- Page: 5 ----------------------
TECHNICAL REPORT ISO/TR 22639:2021(E)
Space systems – Design guidelines for multi-geo spacecraft
collocation
1 Scope

This document addresses the design process of a collocation and the basic contents of collocation

design process which include considerations, initial collocation strategy design, simulation evaluation

of collocation strategy, optimal collocation strategy selection and collocation agreement.

This document gives guidelines for multi-geo spacecraft collocation, and it applies in particular to

multi-geo constellation.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

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

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1.1
orbit maintenance

orbit control for maintaining the spacecraft’s orbit in certain prediction error around the nominal orbit

3.1.2
inclination vector

vector which points to the ascending node and which is measured from the vernal equinox

Note 1 to entry: The x and y components of the vector can be expressed as Formulae (1) and (2).

ii=sincos()Ω (1)
ii=sinsin()Ω (2)
where
is the magnitude of the inclination vector;
is the raan in J2000 geocentric equatorial coordinate system (3.1.5);
i is the x component of the inclination vector coordinate;
is the y component of the inclination vector coordinate.
Note 2 to entry: Figure 1 shows the definition of the inclination vector.
© ISO 2021 – All rights reserved PROOF/ÉPREUVE 1
---------------------- Page: 6 ----------------------
ISO/TR 22639:2021(E)
Key
i inclination vector which points to the ascending node
X direction of vernal equinox
Figure 1 — Inclination vector
3.1.3
eccentricity vector

vector which points to the orbit perigee and which is measured from the vernal equinox

Note 1 to entry: The x and y components of the vector can be expressed as Formulae (3) and (4).

ee=+cos(Ωω) (3)
ee=+sin(Ωω) (4)
where
is the magnitude of the eccentricity vector;
is the x component of the eccentricity vector coordinate;
is the y component of the eccentricity vector coordinate;
is the argument of perigee.
Note 2 to entry: Figure 2 shows the definition of the eccentricity vector.
2 PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 7 ----------------------
ISO/TR 22639:2021(E)
Key
e eccentricity vector which points to the orbit perigee
X direction of the vernal equinox
Figure 2 — Eccentricity vector
3.1.4
mean longitude

sum of the right ascension of the ascending node, the augment of perigee and the mean anomaly

Note 1 to entry: It can further be interpreted as the approximate right ascension of the near-circular orbits with

small inclination.
3.1.5
J2000 geocentric equatorial coordinate system
coordinate system with origin at the Earth’s centre

Note 1 to entry: The positive x-axis points in the direction of the mean vernal equinox of Earth at J2000 epoch.

The positive z-axis points in the direction of the normal direction of the mean equator at J2000 epoch. The y-axis

is orthogonal to both the x-axis and the z-axis and completes a right-handed frame.

Note 2 to entry: J2000 epoch: JD=2451545,0, which is 1 Jan 2000 12:00:00 TDB.
Note 3 to entry: Figure 3 shows this coordinate system.
Key
E earth equator plane
Figure 3 — J2000 geocentric equatorial coordinate system
© ISO 2021 – All rights reserved PROOF/ÉPREUVE 3
---------------------- Page: 8 ----------------------
ISO/TR 22639:2021(E)
3.1.6
spacecraft coordinate system of geo spacecraft
RTN

coordinate system with origin at the centre of the geo spacecraft’s positioned point

Note 1 to entry: The R axis is outward along radial. The N axis points in the direction of the normal direction of

J2000 mean equator. The T axis is constructed as N×R.
Note 2 to entry: Figure 4 shows this coordinate system.
Figure 4 — Spacecraft coordinate system of geo spacecraft (RTN)
3.2 Abbreviated terms
E/W east/west
geo geostationary earth orbit

raan right ascension of the ascending node (the angle between the vernal equinox and the orbit

ascending node)
OD orbit determination
4 Collocation design process

Design process of a collocation includes considerations, initial collocation strategy design, simulation

evaluation of collocation strategy, initial selection of collocation strategy, optimal collocation strategy

selection and collocation agreement.

The collocation design process is basically carried out according to the following steps, which are

represented in the collocation working flow (see Figure 5).

a) Delegations of different spacecraft operators with diversity needs hold an orbit safety consultation

meeting. Commonly, the operator of spacecraft that has to collocate with other spacecraft that is

already located at the position brings forward the consultation meeting, negotiates and organizes

the meeting.

b) In the consultation meeting, each operator presents the operation status, operational issue and

then brings forward and confirms the considerations of collocation design.

c) The initial collocation strategy is designed according to the considerations. Each collocation

spacecraft operator selects and proposes the preferred collocation strategy. The collocation

4 PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 9 ----------------------
ISO/TR 22639:2021(E)

strategy includes the strategy during mission period and the initial phase strategy to move a

spacecraft into position of collocation configuration and the deorbit strategy.

d) Simulation is carried out to evaluate whether the collocation strategies meet the demanded

requirements of all parties.

e) If the selected initial collocation strategy can’t meet the specified requirements, the collocation

strategies are reviewed in order to identify what can be improved. If improvements are identified,

the collocation strategies are revised and the simulation evaluation step d) is carried out again.

Else, the initial design of collocation strategy step c) is carried out again.

f) If the chosen strategy meets all the specified requirements then the strategy can be confirmed as

the decided solution.

g) Once the optimal strategy is selected then the collocation agreement formalized and signed in

accordance with Clause 5.
Figure 5 — Collocation working flow
© ISO 2021 – All rights reserved PROOF/ÉPREUVE 5
---------------------- Page: 10 ----------------------
ISO/TR 22639:2021(E)
5 Basic contents of collocation design process
5.1 Considerations

In the orbit safety consultation meeting, each operator presents operation status and operational issue

and then brings forward and confirms the considerations of collocation design.
The following considerations are at least involved in the process:

a) ITU regulations about frequency allocation and assigned orbital slots of the geo spacecraft;

b) number of collocated spacecraft;
c) safety separation distance between collocated spacecraft;
d) orbit maintenance requirements of collocated spacecraft;
e) precision of orbit determination of collocated spacecraft;

f) flight dynamics characteristics, e.g. Earth gravity, solar radiation pressure;

g) fuel consumption of collocated spacecraft;
h) number and ability of central management of collocated spacecraft;
i) other special restrictions of collocated spacecraft.
5.2 Initial collocation strategy design
5.2.1 Fundamental principle of separation strategy

Assuming d is the relative distance between any two collocated spacecraft, d is the required

min

minimum safe separation distance, then the collocation strategy is to make the relative distance d

qualify the demanded condition which is d ≥ d . Generally, the value of d is 10 km based on the

min min
successful experience of international collocation cases.

The common method of the relative distance between any two collocated spacecraft is shown in

Annex C.
5.2.2 The available separation strategy

The fundamental separation strategies are listed as follows and the detailed principle about each

strategy is given in Annex A. The characteristics of each separation strategy are shown in Annex B (see

Table B.1).
a) the complete longitude separation strategy;
b) coordinated station keeping strategy;
c) the absolute eccentricity separation strategy;
d) the relative eccentricity vector separation strategy;
e) the eccentricity and inclination vector separation strategy.
6 PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 11 ----------------------
ISO/TR 22639:2021(E)
5.2.3 Selection of collocation strategy
5.2.3.1 Selection principle

The separation strategy is one of the fundamental strategies of 5.2.2, some other new strategies or the

combination of them. In any case, the separation strategy to be selected meets the following design

considerations:

a) safety assured: the design ensures that the in-flight safety of the spacecraft involved in the

collocation strategy;

b) operational mission: the design takes into account all the operational specifications;

c) experience-based: the design is based on current operational best practices and return of

experience (lessons learned); for the common collocation cases and strategies, refer to Annex E;

d) easily realized: the designed separation strategy is operationally feasible.
5.2.3.2 Selection method

During the selection process, the selection principle listed in 5.2.3.1 is always applied. Annex D (see

Table D.1) provides common collocation cases as well as commonly adopted collocation design results.

5.2.4 Simulation Evaluation of Collocation Strategy

The strategy is usually evaluated through simulation considering the orbit perturbation, orbit control,

OD error and some other error sources. The detailed evaluation items are listed as follows:

a) evaluate whether the safety separation distances between collocated spacecraft are ensured;

b) evaluate whether the orbit maintenance period qualifies the perspective requirements;

c) evaluate whether the fuel consumption of collocation spacecraft is within the budget requirement.

Based on the designed collocation strategy, some factors are considered, such as orbit perturbation,

orbit maintenance error, orbit determination error, to evaluate whether the considerations including

the safety separation distance, orbit maintenance period, fuel consumption and other factors are

sufficiently taken into account.
5.3 Final collocation strategy

Once the selected strategy meets all specifications, it is confirmed as the decided optimal collo

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