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**RECOMMENDATION FOR SPACE**

**DATA SYSTEM STANDARDS**

+-----------------------------------------------------------------------+
| **FINAL DRAFT**                                                       |
|                                                                       |
| **NAVIGATION DATA**                                                   |
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**CCSDS 501.0-WB-1**

**DRAFT -- WHITE BOOK**

May 2000

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AUTHORITY

  ----------------- -----------------------------------------------------
                    

  Issue:            DRAFT -- White Book, Issue 1.3

  Date:             May 2000

  Location:         Annapolis, Maryland, USA

                    
  ----------------- -----------------------------------------------------

This document has to be approved for publication by the Management
Council of the Consultative Committee for Space Data Systems (CCSDS) and
reflects the consensus of technical panel experts from CCSDS Member
Agencies. The procedure for review and authorization of CCSDS Reports is
detailed in reference \[1\].

This document is published and maintained by:

> CCSDS Secretariat
>
> Program Integration Division (Code MG)
>
> National Aeronautics and Space Administration
>
> Washington, DC 20546, USA

DOCUMENT CONTROL

This document is a CCSDS Report that contains technical material to
supplement the CCSDS Recommendations for the standardization of data
utilized for spacecraft navigation generated by space data systems of
the Agencies of the Consultative Committee for Space Data Systems
(CCSDS).

The topic areas covered herein include radio metric data content,
spacecraft ephemeris, planetary ephemeris, tracking station locations,
co-ordinate systems, and attitude data. This recommendation deals
explicitly with the technical definitions and conventions associated
with inter-Agency cross-support situations involving the transfer of
ephemeris, tracking, and attitude data.

Through the process of normal evolution, it is expected that expansion,
deletion or modification to this Report may occur. This Report is
therefore subject to CCSDS document management and change control
procedures. Current versions of CCSDS documents are maintained at the
CCSDS Web site:

http://www.ccsds.org/ccsds/

Questions relative to the contents or status of this document should be
addressed to the CCSDS Secretariat.

At time of publication, the active Member and Observer Agencies of the
CCSDS were

[Member Agencies]{.underline}

> -- Agenzia Spaziale Italiana (ASI)/Italy.
>
> -- British National Space Centre (BNSC)/United Kingdom.
>
> -- Canadian Space Agency (CSA)/Canada.
>
> -- Centre National d'Etudes Spatiales (CNES)/France.
>
> -- Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)/Germany.
>
> -- European Space Agency (ESA)/Europe.
>
> -- Instituto Nacional de Pesquisas Espaciais (INPE)/Brazil.
>
> -- National Aeronautics and Space Administration (NASA)/USA.
>
> -- National Space Development Agency of Japan (NASDA)/Japan.
>
> -- Russian Space Agency (RSA)/Russian Federation.

[Observer Agencies]{.underline}

> -- Austrian Space Agency (ASA)/Austria.
>
> -- Central Research Institute of Machine Building (TsNIIMash)/Russian
> Federation.
>
> -- Centro Tecnico Aeroespacial (CTA)/Brazil.
>
> -- Chinese Academy of Space Technology (CAST)/China.
>
> -- Commonwealth Scientific and Industrial Research Organization
> (CSIRO)/Australia.
>
> -- Communications Research Laboratory (CRL)/Japan.
>
> -- Danish Space Research Institute (DSRI)/Denmark.
>
> -- European Organization for the Exploitation of Meteorological
> Satellites (EUMETSAT)/Europe.
>
> -- European Telecommunications Satellite Organization
> (EUTELSAT)/Europe.
>
> -- Federal Service of Scientific, Technical & Cultural Affairs
> (FSST&CA)/Belgium.
>
> -- Hellenic National Space Committee (HNSC)/Greece.
>
> -- Indian Space Research Organization (ISRO)/India.
>
> -- Communications Research Centre (CRC)/Canada.
>
> -- Institute of Space and Astronautical Science (ISAS)/Japan.
>
> -- Institute of Space Research (IKI)/Russian Federation.
>
> -- KFKI Research Institute for Particle & Nuclear Physics
> (KFKI)/Hungary.
>
> -- MIKOMTEK: CSIR (CSIR)/Republic of South Africa.
>
> -- Korea Aerospace Research Institute (KARI)/Korea.
>
> -- Ministry of Communications (MOC)/Israel.
>
> -- National Oceanic & Atmospheric Administration (NOAA)/USA.
>
> -- National Space Program Office (NSPO)/Taipei.
>
> -- Swedish Space Corporation (SSC)/Sweden.
>
> -- United States Geological Survey (USGS)/USA.

DOCUMENT CONTROL

  -------------- ---------------------------- ------------ --------------------
  **Document**   **Title**                    **Date**     **Status/Remarks**

  CCSDS          Recommendation for Space     January 1987 Original Issue
  501.0-B-1      Data System Standards: Radio              
                 Metric and Orbit Data, Issue              
                 1                                         

  CCSDS - TBD    Recommendation for           May 1999     Revised issue for
                 Navigation Data, Issue 1                  panel P1J

  CCSDS - TBD    Recommendation for           December     Revised issue for
                 Navigation Data, Issue 1.1   1999         panel P1J (Winter
                                                           99)

  CCSDS - TBD    Recommendation for           March 2000   Revised issue for
                 Navigation Data, Issue 1.2                panel P1J (Feb 2000)

  CCSDS - TBD    Recommendation for           May 2000     Revised issue for
                 Navigation Data, Issue 1.3                panel P1J (May 2000)
  -------------- ---------------------------- ------------ --------------------

> TABLE OF CONTENTS

[Section]{.underline} [Page]{.underline}

1\. Introduction
................................................................................................1-[1](#introduction)

1.1 Purpose and Scope
.............................................................................[1](#purpose-and-scope)-2

1.2 Applicability
....................................................................................[1](#applicability)-3

1.3 References
.......................................................................................[1](#applicability)-4

2\. SCOPE OF NAVIGATION
......................................................................................2-[1](#scope-of-navigation)

2.1 DEFINITION OF NAVIGATION
.......................................................................2-2

2.2 NAVIGATION PROCESS
..............................................................................
2-3

> 2.3 NAVIGATION DATA
> TYPES...........................................................................2-4

3\. NAVIGATION MESSAGE EXCHANGE FRAMEWORK
...................................................3-1

3.1 Definitions of Navigation Message Exchange Elements
...............................3-2

3.2 Navigation Data Exchange Participants
..................................\....................3-3

3.3 NAVIGATION EXCHANGE DATA
TYPES...........................................................3-4

3.4 Navigation DATA Exchange Scenarios
.......................................................3-5

4\. ANCILLARY DATA
...............................................................................................4-[1](#ancillary-data)

4.1 Rationale
...........................................................................................
4-2

4.2
UNITS...................................................................................................\......4-3

4.3 QUALITY
................................................................................................\...
4-4

4.4 COORDINATE FRAME IDENTIFICATION
........................................................ 4-5

4.5 TIME
........................................................................................................4-6

4.6 ASTRODYNAMIC CONSTANTS..............................
.......................................4-7

4.7 ENVIRONMENTAL MODELS ..................................
......................................4-8

5\. PROPERTIES
.......................................................................................................5-[1](#refheading___toc469806315)

5.1 Rationale
..........................................................................................
5-2

5.2 Position and Orbit Data
...........................................................................5-3

5.3 Tracking STATION COORDINATES
...............................................................5-4

5.4 SPACECRAFT Attitude
data.......................................................................5-5

5.5 SPECIAL CONSIDERATIONS
..........................................................................5-6

5.6 Data Transmission Delays
.........................................................................
5-7

6\. MEASUREMENTS 6-[1](#properties)

6.1 Rationale
..................................................................................................6-2

6.2 Measurement Data Types
.......................................................................
6-3 6.3 Earth
Tracking........................................................................................
6-4

6.4 GPS ..........
...............................................................................................
6-5

6.5 Recommendations
.............................................................................
6-6

TABLE OF CONTENTS (continued)

[Section]{.underline} [Page]{.underline}

7\. SATELLITE-BASED GLOBAL NAVIGATION SYSTEMS
................................................7-[1](#satellite-based-global-navigation-systems)

7.1 Rationale
..........................................................................................
7-[1](#rationale-4)

7.2 Recommendations
..........................................................................
7-2

8\. NAVIGATION MESSAGE FORMAT RECOMMENDATION
.............................................8-[4](#__RefHeading___Toc469806330)

8.1
RATIONALE................................................................................................8-2

8.2 SPKE Description
.................................................................................
8-3

8.3 SPKE Recommendations
.................................................................. 8-4

8.4 SPKE FOR SPACE
APPLICATIONS.................................................................
8-5

AnnEX A Navigation data message
EXAMPLE......................................................\...A-[1](#__RefHeading___Toc469806345)

Annex b Glossary B-1

index C-1

LIST OF FIGURES

\[To be revised\]

Figure 2‑1: Real-time or near real-time navigation process
...........................................................2-1

Figure 3‑1: Navigation data message exchange
.........................................................................3-1

Figure 3‑2: Navigation message in a CCSDS frame
....................................................................3-2

Figure 4‑1: Differences between time relevant
scales.....................\..............................................[4](#__RefHeading___Toc469806377)-1

Figure 5‑1: Data transmission delays
..............................................................................\.......5-1

Figure A-1: Example of a NORAD TLE file
...........................................................................A-[1](#__RefHeading___Toc469806384)

Figure A‑2: Graphical representation of the NORAD TLE file format
.............................................A-2

LIST OF TABLES

\[To be revised\]

Table 2‑1: Navigation data types
..........................................................................................2-1

Table 3‑1: Measurement data types 3-1

Table 3‑2: Property data types 3-2

Table 3-3: Ancillary data types
............................................................................................3-3

Table 4‑1: Coordinate frames 4-1

Table 4‑2: Coordinate frames ??? 4-2

Table 4‑3: Environmental models 4-3

Table 5‑1: Classical Keplerian elements 5-1

Table A‑1: Structure of first row of the NORAD TLE file
......................................................\......A-1

Table A‑2: Structure of the second row of the NORAD TLE file
....................................................A-[2](#__RefHeading___Toc469806542)

# This page intentionally blank

# 1. Introduction

## Purpose and Scope

The purpose of this document is to establish common recommendations for
adequately exchanging data involved in spacecraft navigation. This
exchange of navigation data occurs in situations in which cross-support
among space missions and facilities of member Agencies of the CCSDS is
required. In addition, the Recom­mendation provides focusing for the
development of multi-mission support capabilities within the respective
Agencies to eliminate the need for arbitrary, unique capabilities for
each mission. This Recommendation can also be used within any Agency,
for a specific project in which exchange of navigation data is required.

The document defines the navigation data and the format in which they
are transferred. The data to be covered include (among others):

-   Properties and measurements of spacecraft dynamics

-   Ground station information

-   Environmental models

-   radiometric data

## Applicability

This document applies to navigation data exchange for the classical
cases flight-to-ground, ground-to-flight, and ground-to-ground but it
also comprises the case flight-to-flight (formation flying, and
rendezvous and docking situations).

In particular, this document contemplates the exchange of processed
radio metric and orbital parameters between CCSDS Agencies in
cross-support situations. In addition, it serves as a guideline for the
development of compatible internal Agency standards in this field. This
Recommendation is not retroactive, nor does it commit any Agency to
implement the recommended radio metric and orbit data concepts at any
future time. Nevertheless, all CCSDS Agencies accept the principle those
all-future implementations of radio metric and orbit data exchange,
which are used in cross-support situations will be based on this
Recommendation.

Where preferred options or mandatory capabilities be clearly indicated
herein, the indicated sections of the specification must be implemented
when this Recommendation is used as a basis for cross-support. Where
optional subsets or capabilities are allowed or implied in this
specification, implementation of these options or subsets is subject to
specific bilateral cross-support agreements between the Agencies
involved.

The recommendations in this document are to be invoked through the
normal standards programs of each member Agency, and are applicable to
those missions for which cross-support, based on capabilities described
in these recommendations, is anticipated.

**1.3 REFERENCES**

\[Note: References are subject to change.\] \[A.I. 1 workshop #6\]

\[1\] Procedures Manual for the Consultative Committee for Space Data
Systems, Issue 1, Consultative Committee for Space Data Systems, August
1985 or later issue.

\[2\] Introduction of the Improved IAU System of Astronomical Constants,
Time Scales, and Reference Frames into the Astronomical Almanac,
Supplement to the Astronomical Almanac 1984, U.S. Government Printing
Office, Washington, D.C., 1983.

\[3\] Time Code Formats, Recommendation CCSDS 301.0-B-1, Issue 1, Blue
Book, Consul­tative Committee for Space Data Systems, January 1987 or
later issue.

\[4\] CCSDS Strategic Plan, Volume 1: Vision, Mission, Strategic Goals,
Preliminary Draft, Revision 1, October 1998.

\[5\] CCSDS Strategic Plan, Volume 2: Operation Plan for Standards
Development, Prelimi­nary Draft, Revision 1, October 1998.

\[6\] Celestial Mechanics and Dynamical Astronomy, J. Heward and M.
Morris, 1995-96, Vol. 63 No. 2.

\[7\] McCarthy D.D, 1996, \"IERS Conventions\", IERS Technical Notes 13
and 21, Observatoire de Paris, Paris.

\[8\] Reference for COSPAR Standards.

\[9\] Global Positioning Systems: Theory and Applications (Volumes I and
II). Progress in Astronautics and Aeronautics, B. W. Parkinson, J.J.
Spilker Jr., P. Axelrad, P. enge, and Paul Zarchan, volume 163, 1996.

\[10\] Understanding GPS Principles and Applications, E. D. Kaplan,
Artech House Publish­ers, 1996.

\[11\] GPS Interface Control Document, ICD-GPS-200, IRN-200B-PR-OOJ,
Rev. B-PR, anon­ymous, U.S. Air Force, July 1, 1992.

\[12\] Marine Navigation: Piloting and Celestial and Electronic
Navigation, R.R. Hobbs, Naval Institute Press Annapolis, Maryland, 1990.

\[13\] Bauersima, I. (1983): \"Navstar/Global Positioning System (II)\*.
Mitteilungen der Satelltenbeobachtungsstation Zimmirwald, Nr. 10.

\[14\] Summary of the Workshop on GPS Exchange Formats, Evans, A.
(1989), Proceedings of the Fifth International Geodetic Symposium on
Satellite Systems, pp. 917ff, Las Cruces

\[15\] A Common Exchange Format for GPS Data, Gurtner, W., G. Mader, D.
MacArthur (1989), Proceedings of the Fifth International Geodetic
Symposium on Satellite Systems,pp. 917ff, Las Cruces.

\[16\] A Proposed Standardized Exchange Format for Navstar GPS Geodetic
Data, Scott, V.D., J. Clynch (1986), Proceedings of the Fourth
International Geodetic Symposium on Satel­lite Systems, pp. 513ff,
Austin, Texas.

\[17\] Remondi, B. W. 1985: Distribution of Global Positioning System
Ephemerides by the National Geodetic Survey, Presented at the First
Conference on Civil Applications of GPS - Institute of Navigation,
September 12, 1985, 8 pp.

\[18\] Remondi, B. W. 1989: Extending the National Geodetic Survey
Geodetic Orbit Formats, NOAA Technical Report 133 NGS 46, 85 pp.

\[19\] Remondi, B. W., 1991: NGS Second Generation ASCII and Binary
Orbit Formats and Associated Interpolated Studies, Proceedings of the
Twentieth General Assembly, International Union of Geodesy and
Geophysics, Vienna, Austria, August 11-24, 1991, 28 pp.

\[20\] Gurtner, W., G. Mader (1990): \"Receiver Independent Exchange
Format Version 2.\" CSTG GPS Bulletin Vol.3 No.3, Sept/Oct 1990,
National Geodetic Survey, Rockville.

\[21\] Remondi, B. W. 1985: Distribution of Global Positioning System
Ephemerides by the National Geodetic Survey, Presented at the First
Conference on Civil Applications of GPS - Institute of Navigation,
September 12, 1985, 8 pp.

\[22\] Bauer et al., 1997. Bauer, F., Bristow, J., Folta, D., Hartman,
K., and Quinn, D. (1997). Satellite formation flying using an innovative
autonomous control system (AUTOCON) environment. In American Institute
of Aeronautics and Astronautics.

\[23\] Corazzini et al., 1997. Corazzini, T., Robertson, A., Adams, J.,
Hassibi, A., and How, J. (1997). GPS sensing for spacecraft formation
flying. In Proceedings of the Institute of Navigation GPS-97, Kansas
City, Missouri, USA.

\[24\] Crippen and Hauck, 1983. Crippen, R. L. and Hauck, F. H. (1983).
Orbiter operations in close proximity to free-flying satellites or
formation flying in space. In Proceedings of the Twenty-seventh
Symposium of the Society of Experimental Test Pilots, Beverly Hills, CA,
USA, pages 314--334.

\[25\] Fromm and Lucas, 1998. Fromm, H. H. and Lucas, R. (1998). The
European contribution to GNSS-2: A status report on the technical
preparations. In International Conference on the European GNSS-2 System.
European Space Agency.

\[26\] Hart et al., 1996. Hart, R., Gramling, C., Deutschmann, J., Long,
A., Oza, D., and Steger, W. (1996). Autonomous navigation initiatives at
the NASA GSFC flight dynamics division. In ISTS Gifu, number 20 in Paper
96-c-23.

\[27\] Scolese et al., 1991. Scolese, C., Folta, D., and Bordi, F.
(1991). Field of view location and formation flying for polar orbiting
missions. In Proceedings of the 1st AAS/AIAA Annual Spaceflight
Mechanics Meeting, Houston, TX, Feb. 11-13, 1991, pages 949--966.

\[28\] Ulybyshev, 1998. Ulybyshev, Y. (1998). Long-term formation
keeping of satellite constellation using linear-quadratic controller.
Journal of Guidance, Control, and Dynamics, 21(1):109--115.

\[29\] Zimmerman and Cannon, 1994. Zimmerman, K. and Cannon, R. (1994).
Differential carrier phase GPS techniques for space vehicle rendezvous.
In Proceedings of the Institute of Navigation, Salt Lake City, Utah,
USA.

\[30\] Zimmerman and Cannon, 1995. Zimmerman, K. and Cannon, R. (1995).
Experimental demonstration of GPS for rendezvous between two prototype
space vehicles. In Proceedings of the Institute of Navigation, Palm
Springs, California, USA.

\[31\] Clohessy, W. and Wiltshire, R. (1960). Terminal guidance system
for satellite rendezvous. Aerospace Sciences, 27, pages 653-658, 674.\
\
\[32\] McCarthy D.D (ed.), 1992, \"IERS Standards\", IERS Technical Note
13, Observatoire de Paris, Paris.

\[33\] Fricke W. et al., 1988, \"Fifth Fundamental Catalogue, Part I\",
Veröff. Astron. Rechen Inst., Heidelberg.

\[34\] Arias et al. 1995.

\[35\] Lieske et al. 1977.

\[36\] Seidelmann 1982.

\[37\] Aoki et al. 1982.

\[38\] Long et al., 1989 'GTDS mathematical theory, Rev. 1', Computer
Science Corp., FDD/552-89/001.

::: Definition-Term
The latest issues of CCSDS documents may be obtained from the CCSDS
Secretariat at the address indicated on page i.
:::

# 2. scope of navigation

**2.1 DEFINITION OF NAVIGATION**

The word **{navigate}** is derived from the Latin words {navis} meaning
ship, and {agere}, meaning to move or direct.

The common definition of navigation establishes that it is the science
of getting a craft or person from one place to the other. In order to
establish a solid recommendation for the exchange of navigation data
among space agencies, it is of crucial importance to clearly set the
definition of terms like navigation, navigation data, navigation
message, etc.

In the following, several definitions are given together with some
explanations about the nature of the navigation tasks and the formation
of the navigation messages.

::: Definition-Term
***[Navigation]{.underline} is the process to find the present and
imminent future position and orbit of a space­craft using a series of
measurements.***
:::

::: Definition-Term
***[Guidance]{.underline} is the process to define a path to move a
spacecraft from one point to another.***
:::

::: Definition-Term
***[Control]{.underline} is the process to maintain a spacecraft within
the prescribed path and attitude.***
:::

The process of navigation includes the exchange of orientation
information.

The responsibilities for guidance and control will not be covered in
these recommendations.

**2.2 NAVIGATION
PROCESS**![](media/image3.wmf){width="5.988888888888889in"
height="1.8493055555555555in"}

Figure 2‑1: Real-time or near real-time navigation process

The first part of the navigation process starts with the acquisition of
a set of measurements. This set is properly stored to allow the
calculation of the orbit in the second step. The third step accounts for
the prediction of the future state based on the measurements taken and
the calculation of the orbit.

In a real-time or near real-time scenario the previous definition
implies a three steps task as depicted in Figure 2-1. In a non-real time
scenario any kind of data may be transferred (past, current or predicted
data).

**2.3 NAVIGATION DATA TYPES**

To accomplish the navigation process information is required. The type
of data may comprise orbit, attitude, radiometric, global navigation
systems (GNS) and corresponding quality data, etc. Table 2-1 shows the
different types of navigation data that can be transmitted. The
following sections describe with detail the different navigation data
types, together with their type of data.

Table 2‑1: Navigation data types

  -------------------------------------- --------------------------------
  **Navigation data types**              **Type of navigation data
                                         involved**

  ***Orbit data***                       Position, velocity, time.

  ***Attitude data***                    Angle orientations and its
                                         derivatives

  ***Radio-metric data***                Doppler, range.

  ***Data from global navigation         GNS navigation messages
  systems***                             

  ***Ground stations data***             Co-ordinates, status

  ***Co-ordinate systems data***         Description, conventions, units

  ***Astrodynamic values***              Constants, planetary data.

  ***Auxiliary data***                   Central body potential etc.

  ***Qualifiers***                       Quality of the data, accuracy of
                                         the data.
  -------------------------------------- --------------------------------

**\
**

# 3. NAVIGATION MESSAGE EXCHANGE FRAMEWORK

## 3.1 Navigation Data Exchange Scenarios {#navigation-data-exchange-scenarios .unnumbered}

This section contains different scenarios for the applicability of
exchange of navigation data.

## (aL, add Drawing with explanations) {#al-add-drawing-with-explanations .unnumbered}

An Interface Control Document (ICD) should be jointly produced by both
Agencies participating in a cross-support involving tracking data
orbital elements. The ICD should precisely define the data to be
transferred, the formats, calibrations for tracking data, a description
of any ancillary data, and the complete description of the station
location, including the earth-centered coordinates with their defining
system, and the relative geometry of the tracking point and cross-axis
of the antenna mount.

## 3.2 Definitions of Navigation Message Exchange Elements {#definitions-of-navigation-message-exchange-elements .unnumbered}

This document describes the interaction of two or more participants in
the interchange of navigation data.

::: Definition
[Participant]{.underline} is an entity which has the ability to acquire
or broadcast navigation messages.
:::

Examples of participants can be a spacecraft, a ground station, a
control center, etc. All kinds of combinations are possible as the
exchange of navigation data is allowed between all kinds of
participants.

![](media/image4.wmf){width="2.5909722222222222in"
height="2.311111111111111in"}

Figure 3‑2: Navigation data message exchange

::: Definition
[Object]{.underline} is an entity of the environment.
:::

::: Definition
[Property]{.underline} of a participant is a data type, which allows
describing the state of an object.
:::

::: Definition
[Measurement]{.underline} is the output of a sensor or equipment.
:::

::: Definition
[Ancillary Information]{.underline} is any data type used for the
correct interpretation of measurements and properties.
:::

::: Definition
[Navigation Data]{.underline} is a set of measurements and properties
exchanged between participants during a navigation session.
:::

The navigation data are packed into a navigation message, as shown in
Figure 3-2. ![](media/image5.wmf){width="5.98125in"
height="0.47430555555555554in"}

Figure 3‑3: Navigation message in a CCSDS frame

::: Definition
[Navigation Message]{.underline} is a particular arrangement of the
navigation data whose structure and content are the subjects of this
recommendation.
:::

The contents and the format of the navigation message are the scope of
this Recommendation. The way and the means by which the navigation
message are broadcasted or acquired are not the subject of this document
and will not be discussed here.

The navigation message must fit inside a standard CCSDS data
transmission message. Therefore, this recommendation shall be compliant
with the rest of the CCSDS standards.

::: Definition
[Navigation Session]{.underline} is the process of the interchange of
data between participants for navigation purposes.
:::

## 3.3 Navigation Exchange Data Types \[a.i. 3\] {#navigation-exchange-data-types-a.i.-3 .unnumbered}

The following Tables contain a list of the most typical measurement,
property, and ancillary information data types, which may be transferred
during a navigation session within a navigation message.

Measurement data will be exchanged in SI units. However, there are cases
where it is not possible to convert raw measurements from hardware
specific units to SI units, without risking some degradation of
measurement quality. For example, for Doppler and range measurements
collected during periods when the transmitter frequency is time varying,
a conversion to SI units is only possible with accurate trajectory
information. In this case, the recommendation is for the participating
agencies to agree upon a hardware-specific unit.

Table 3‑2: Measurement data types

  --------------------- --------------- ---------------------------------
  Type                  Units           Comments

  Range                 km              It is the distance between two
                                        participants

  Range rate            km/s            It is the derivative of the
                                        distance between two participants

  Variable Transmitter  Range Units     Ref. DSN doc
  Range                                 

  Antenna angles        deg             

  Doppler (coherent)    MHz             

  Doppler               MHz             
  (non-coherent)                        

  Variable Transmitter                  
  Doppler                               

  Alan variance                         

  Integrated Doppler    \-              
  count                                 

  Quality of                            depending on quantity
  measurements                          

  IMU output            deg/s^2^        
  --------------------- --------------- ---------------------------------

Table 3‑3: Property data types

  --------------------- --------------- ---------------------------------
  Type                  Units           Comments

  Position              km              

  Angular Velocity      deg/s           

  Linear Velocity       km/s            

  Angular acceleration  deg/ s^2^       

  Acceleration          km/s^2^         

  Epoch                 Sec             Gregorian Format, UTC, sec+J2000

  Attitude              deg             

  Attitude rate         deg/s           

  Length                M               Lateral dimension of a
                                        participant

  Moment of Inertia     kgm^2^          

  Force                 kgm/ s^2^       

  Torque                kgm^2^/ s^2^    Moment of force

  Mass                  kg              

  Energy, work, or heat kgm^2^/ s^2^    Same dimension as torque

  Power                 kgm/s³          

  Pressure              kgm/ s^2^       For per unit area

  Temperature           K               

  Transmitter delay     ms              

  Receiver delay        ms              

  Surface               m^2^            

  Antenna angles        deg             

  Oscillator frequency  MHz             

  Oscillator stability  ns              

  Ballistic coefficient m^2^/kg         C~d~ A / m, solar pressure,
                                        albedo

  Aerodynamic                           Depends on the spacecraft
  coefficient                           

  Reflectivity                          
  --------------------- --------------- ---------------------------------

Table 3‑3: Ancillary information data types

  --------------------- --------------- ---------------------------------
  Type                  Units           Comments

  Physical constants                    Ref. IERS

  Transmitter ID                        Ref. IERS

  Receiver ID                           Ref. IERS

  Co-ordinate system    \-              
  description                           

  Time system           \-              
  description                           

  Quality of property                   Depending on quantity
  --------------------- --------------- ---------------------------------

**3.4 NAVIGATION DATA EXCHANGE SCENARIOS**

**3.4.1 SPACECRAFT RENDEZVOUS AND DOCKING OPERATIONS**

Spacecraft rendezvous and docking is defined as the set of tasks which
allow the approach, the mating, and the separation in a controlled
manner of two or more spacecraft.

A typical rendezvous and docking scenario is the mating of a servicing
spacecraft with a space station. Servicing to a space station comprises
the tasks of assembly, re-supply, repair and maintenance of manufactured
space parts in-orbit.

With space programs like the U.S. Space Shuttle, the Russian MIR
station, and the International Space Station (ISS), rendezvous and
docking operations are starting to become frequent. In the near future,
a big system like the International Space Station will require dozens of
flights a year to accomplish in-orbit servicing. In such a scenario,
inter-spacecraft communications, formation flying and rendezvous and
docking task will be a routine.

For the typical case of the servicing to a space station, the in-orbit
servicing requires the assembly of small chasers in comparison with the
big target (space station). Usually, the chaser is the active element,
and has a guidance, navigation, and control (GNC) system which allows
active servicing. The GNC system has sensors to measure the
spacecraft\'s position and orientation in space. It determines the
present state of the vehicle, and computes the control actions required
to maintain or achieve a desired position and orientation. The target is
the passive element during these operations. It has also sensors to
measure the distance and orientation with respect to the chaser.
However, in most of the time, it does not perform any maneuvers.

The rendezvous is completed in several phases: homing, closing, final
approach, docking and structural latching .

Attitude determination and control plays a relevant role during the last
part of the approach and the beginning of the departure. Typical
distances between chaser and target start in the order of hundreds of
meters. A set of sensors for very close measurement, allows the fine
alignment between vehicles.

The relative translational motion of two spacecraft orbiting around the
Earth can be mathematically described using the Clohessy-Wiltshire-Hill
(C-W-H) equations (Ref. 31). This is a set of non-linear differential
equations with constant coefficients, describing the movement of two
small masses in a near-circular orbit around a third big mass. These
equations have as input the chaser\'s initial position and velocity. The
output is the chaser\'s position and velocity after a time interval.

The translation and rotation of the servicing vehicle (chaser) may be
realized by means of thrust impulses. In general, during the docking
maneuvers the space station is maintained passive.

**3.4.2 SPACECRAFT CONSTELLATION AND FORMATION FLYING**

In most of the technical literature, the terms spacecraft constellation
and spacecraft formation flying are used to describe grouping of
satellites. In what follows, the term formation flying will be reserved
for satellite sets with inter-spacecraft communication.

The reasons for using satellites flying in formation are:

-   Reduce the cost and/or the risk of a mission by splitting the
    payload on smaller platforms. Each satellite can be developed by
    different entities (Agencies, companies, etc).

-   Enhance the result of two already self-consistent missions by
    bringing some added value through the synergy of the measurements or
    add a new type of measurements to a more advanced mission scenario.

In addition, collateral benefits of formation flying missions are:

-   The implicit reduction of the risk of delay on an important program
    due to only one instrument by setting the instrument on a small
    companion.

-   The possibility of the replacement of a failed key instrument on a
    large platform by adding a companion flying in formation with a
    spare instrument.

Therefore, the most important requirement of a formation-flying mission
is to ensure that the desired synergy of observations is obtained. This
requirement can be translated in a set of requisites in terms of spatial
co-registration and on simultaneity of measurements.

The mission requirements are often expressed in terms of formation
requirement in having the same ground track for all the satellites of
the formations. The literature established three different types of
formations: Close, Ideal and Dynamic Formations. In the Close Formation,
the satellites are on the same orbit only separated by a small bias in
argument of latitude resulting in an along-track direction ranging from
a few tens of meters to less than a kilometer. In the Ideal Formation,
the satellites are separated by a larger constant bias in argument of
latitude resulting in an along-track separation of greater than a
kilometer to hundreds of kilometers. The Dynamic Formation is in fact a
derivation of the Ideal formation, where the along-track separation will
not be kept constant, for example, under the action of different
ballistic coefficients between each formation maintenance maneuver.

**3.4.3 APPLICABILITY OF FORMATION FLYING SCENARIOS**

The applications of formation flying in the space environment can be
catalogued depending on the type of the mission considered (science,
telecommunications, Earth observation). However, the mathematical and
physical principles behind are identical. This strength allows
repeatability across platforms facilitating substantial reductions in
cost.

The applications in **Astronomy and Astrophysics** allow the deployment
of a constellation of satellites, which can carry all together a
distributed payload. The virtual payload is in fact distributed among
several quasi-identical satellite payloads. Scientist can benefit of the
fantastic aperture for observations granted by instruments, which could
resemble a huge telescope in space, etc.

The applications for **Earth observation** are focused in the
possibility to have dual observations of a single common Earth
phenomenon. A satellite (SAT~1~) carrying certain payload is in charge
of measuring phenomenon A. Another similar satellite (SAT~2~ ) is in
charge of measuring another phenomenon B. For reasons of launch cost and
operations, at a given point in time payload users of SAT~2~ want also
to measure phenomenon A but at a rigorous time intervals between
observations of both satellites. This scenario is more and more common
as the demand for frequent and high quality observations is increasing
every. In that case, both satellites have to keep a strict formation in
their relative positions making periodic observations, etc.

The applications for **In Orbit Infrastructure (IOI)** covered by
rendezvous and docking. The problem of the space rendezvous is about the
mating of two spacecraft in orbit. An active chaser spacecraft
(servicing vehicle) will dock with a passive target (normally a space
station.

The deployment and maintenance of a satellite constellation inside the
same orbital window could represent some of the applications for
**telecommunications satellites**. Every year, more and more satellites
are placed in the geostationary ring. The demand for broadcasting and
telecommunications is forcing commercial and government entities to
place a high number of satellites inside the same orbital window.

# 4. ancillary data

## 4.1 Rationale {#rationale .unnumbered}

This chapter describes the ancillary data types: these are the pieces of
information needed to interpret measurements and properties of
navigation participants. In general, ancillary information makes it
possible to take properties or measurements and incorporate them in
numerical computations correctly. In some cases, very detailed modeling
information is passed along so that measurements and properties can be
used in state-of-the-art high-fidelity computations. For each ancillary
data type covered, descriptions of formats and systems supported by
member agencies are included in a unified manner, and recommendations
made where applicable.

### 4.2 units {#units .unnumbered}

The default units for any values in a navigation message are those
listed in Tables 3-1 and 3-3, unless otherwise specified in the message.

### 4.3 quality {#quality .unnumbered}

###  {#section .unnumbered}

The quality of properties or measurements can be defined as necessary.
Examples are provided in Annex A.3.

### 4.4 coordinate frame identification \[A.I. 5\] {#coordinate-frame-identification-a.i.-5 .unnumbered}

Table 4-1 Coordinate frames \[To be combined with table 4-2?\]

+--------------------+----------------+-------------------------------+
| CASE               | RECOMMENDATION | EXAMPLE                       |
+--------------------+----------------+-------------------------------+
|                    | Ascent/Descent | Body center fixed             |
+--------------------+----------------+-------------------------------+
|                    | Interplanetary |                               |
|                    | cruise orbit   |                               |
+--------------------+----------------+-------------------------------+
|                    | Rendezvous     | Spacecraft centered           |
|                    |                |                               |
|                    | Formation      |                               |
|                    | Flying         |                               |
+--------------------+----------------+-------------------------------+

Usually, docking operations are accomplished using a reference
coordinate system known as local vertical, local horizontal (LVLH). This
system has its origin in the docking port of the station, and is defined
as follows: +X (roll) in the direction of target flight, +Z (yaw) in the
direction of the center of Earth, and +Y (pitch) orthogonal to these
two. The chaser is approaching the target using the V-bar technique,
where the docking axis lies along the velocity vector of the space
station and against the radial velocity of the station.

**4.4.1. COORDINATE SYSTEM DEFINITIONS**

**4.4.1.1 INTERNATIONAL CELESTIAL REFERENCE SYSTEM (ICRS)**

Since 1991 the concept of the International Celestial Reference System
(ICRS) was established by the IAU as the fundamental inertial coordinate
system (Ref. 32). The origin of the ICRS is defined as the solar system
barycenter within a relativistic framework and its axes are fixed with
respect to distant extragalactic radio objects. The fundamental plane of
the ICRS is closely aligned with the mean Earth equator at J2000 and the
origin of right ascension is defined by an adopted right ascension of
the quasar 3C273.

The practical realization of the ICRS is designated the International
Celestial Reference Frame (ICRF) (Ref. 7).

**4.4.1.2 INTERNATIONAL TERRESTRIAL REFERENCE SYSTEM (ITRS)**

Complementary to the ICRS, the International Terrestrial Reference
System (ITRS) provides the conceptual definition of an Earth-fixed
reference system (Ref. 7). Its origin is located at the Earth\'s center
of mass (including oceans and atmosphere) and its unit of length is the
SI meter. The orientation of the IERS Reference Pole (IRP) and Meridian
(IRM) are consistent with the previously adopted BIH system at epoch
1984.0 and the former Conventional International Origin (CIO).

The time evolution of the ITRS is such that it exhibits no net rotation
with respect to the Earth\'s crust. Realizations of the ITRS are given
by the International Terrestrial Reference Frame (ITRF).

New versions of the ITRF are published annually and exhibit global
differences on the centimeter level.

The transformation of a vector between ITRF and ICRS is performed as
follows:

**r~ITRF~** = **Π(t) Θ(t) N(t) P(t) r~ICRS~**

\[HKK: velocity vector to be included\] \[A.I. 4\]

with:

**Π**: Polar Motion Transformation Matrix

**Θ**: Earth Rotation Transformation Matrix

**N**: Nutation Transformation Matrix

**P**: Precession Transformation Matrix

Details for these transformations are given in Ref. 7.

**4.4.1.3 TRUE OF DATE COORDINATE SYSTEM (TOD)**

The True of Date (TOD) coordinate system is frequently used for
astrodynamical applications.

The transformations between the International Celestial Reference System
(ICRS), the International Terrestrial Reference Frame (ITRF), and the
True of Date (TOD) coordinate system are performed as follows:

**r~TOD~** = **N(t) P(t) r~ICRS~**

**r~ITRF~** = **Π(t) Θ(t) r~TOD~**

**4.4.2 RECOMMENDATIONS**

Table 4-2

+-----------------------+-----------------------+-----------------------+
| Case                  | Recommendation        | Examples              |
+-----------------------+-----------------------+-----------------------+
| Ascent/Descent        | Bod                   | Earth (ITRF), Mars    |
| (launch               | y-centered/Body-fixed |                       |
| support/re-entry)     |                       |                       |
+-----------------------+-----------------------+-----------------------+
| Interplanetary cruise | Barycentric/Inertial  | EME2000               |
|                       |                       |                       |
| Planetary/Body        |                       | MMEdate               |
| orbiter               |                       |                       |
+-----------------------+-----------------------+-----------------------+
| Rendezvo              | ž-nadir/ ŷ-orbital    | LVLH/RTW              |
| us/Re-entry/Formation | normal                |                       |
| Flying                |                       |                       |
|                       | spacecraft centered   |                       |
+-----------------------+-----------------------+-----------------------+

5.  **TIME**

**4.5.1 Rationale**

The exact definition and understanding of time systems is essential for

-   the modeling of satellite orbits and attitude,

-   exchange of navigation data, and

-   satellite ground operations.

In this section definitions of time scales are given which are of
relevance for navigation messages. The relative differences between time
frames appear as (1) step functions (for example, when leap seconds are
added), or (2) monotonically increasing differences (when relativistic
effects are added), or (3) periodic differences (due to solar system
dynamics).

**4.5.2 Time Scales**

Figure 4-1 gives an overview about the differences between the most
relevant time scales described in the following.

![](media/image6.wmf){width="5.0625in" height="3.4125in"}

Fig. 4-1: Differences between relevant time scales between 1950 and
2020. Periodic terms in TCB and TDB have been exaggerated by a factor of
100 to make them discernible. (Adapted from Seidelmann & Fukushima 1992)

**4.5.2.1 Time Scales for Earth Orbiting Satellites**

The following time scales are of relevance for Earth orbiting
satellites:

**Terrestrial Time (TT)**

The Terrestrial Time is a conceptually uniform time scale that would be
measured by an ideal clock on the surface of the geoid and is a rename
of the previously used Terrestrial Dynamical Time TDT. TT is measured in
days of 86400 SI seconds.

**International Atomic Time (TAI)**

The TAI provides the practical realization of a uniform time scale based
on atomic clocks and agrees with TT except for a constant offset of
32.184 s and the imperfections of existing clocks.

Between TAI and TT the following relation holds:

TAI = TT - 32.184 s

**Global Positioning System (GPS) Time**

GPS time is an atomic time scale like TAI but differs in the chosen
offset and the choice of atomic clocks used in its realization.

The origin of GPS was arbitrarily chosen as

GPS = UTC on 1980 January 6.0,

i.e. GPS time differs from TAI by a constant offset of

GPS = TAI(GPS) - 19 s

**Greenwich Mean Sideral Time (GMST)**

The GMST is defined as the Greenwich hour angle of the mean vernal
equinox of date.

**Universal Time (UT1)**

UT1 is the today\'s realization of a mean solar time, which is derived
from GMST by a conventional relation.

**Coordinated Universal Time (UTC)**

UTC is tied to International Atomic Time (TAI) by an offset of integer
seconds (leap seconds) that is regularly updated to keep UTC in close
agreement with UT1 within 0.9 s. Leap seconds may be introduced on Jan 1
and Jul 1 (as well as Apr 1 and Oct 1).

At the beginning of the year 2000, the difference between UTC and TAI
was

UTC - TAI = -32 s

**4.5.2.2 Time Scales for Interplanetary Missions**

In addition to the above time scales the following scales are of
relevance for interplanetary missions (and Space Geodesy).

**Barycentric Dynamical Time (TDB)**

The TDB is the independent variable of current barycentric solar system
ephemerides (e.g. DE405). This time was introduced by the IAU in 1976
and defined to deviate from the Terrestrial Dynamical Time TDT (which is
now identical with TT) by periodic terms (≈2 ms), only.

**Barycentric Coordinated Time (TCB)**

The Barycentric Coordinated Time is the relativistic time coordinate of
the 4-dimensional barycentric frame. TCB and TDB exhibit a scale
difference of

L~B~ = 1.5505197487⋅10^-8^

which results in a secularly increasing difference of

TCB - TDB ≈ 46.7s/cy (year-1977.0)

**4.5.3 Recommendations**

UTC shall be used for the interagency exchange of navigation data;
except for participants beyond Earth orbit.

[]{#refheading___toc469806315 .anchor}**4.6 ASTRODYNAMIC CONSTANTS**

Speed of light, GM, and reference radius. Complete list of constants as
referenced in IERS.

## 4.6.1 Recommendations {#recommendations .unnumbered}

To follow IAU84 and IERS standards.

###  {#section-1 .unnumbered}

### 4.7 ENVIRONMENTAL MODELS {#environmental-models .unnumbered}

Listed below are various models and data that are used for spacecraft
trajectory determination. Some models have been derived to help compute
effects on measurements, while others help to compute effects on the
equations of motion.

Table 4-3 Environmental models

  ----------------------- ----------------------- -----------------------
  Models and data         Measurements            Properties

  Gravity                                         √

  Orientation of spin                             √
  axis                                            

  Rotation state                                  √

  Time history of                                 √
  precession                                      

  Solar flux                                      √

  Central body ionosphere √                       

  Central body atmosphere                         √

  Central body magnetic                           √
  flux                                            

  Central body            √                       
  troposphere                                     

  Solar plasma            √                       

  Solar radiation                                 √
  pressure                                        
  ----------------------- ----------------------- -----------------------

## 4.8 Recommendations {#recommendations-1 .unnumbered}

The following recommendations are made:

-   Use of metric units ( km, kg and seconds )

##  {#section-2 .unnumbered}

# 5. properties

## 5.1 Rationale  {#rationale-1 .unnumbered}

Transfers of navigation data, as described in Table 3-2, are required
for purposes such as:

1.  Pre-flight planning of mission support, orbit covariance analysis,
    tracking station planning and preparation, etc.

2.  In-flight inter-agency comparison of the estimated spacecraft flight
    path, or trajectory, including software compatibility checkout,
    comparisons of orbit determination solutions, etc.

3.  Tracking station preparation (often referred to as predicts) in
    support of radio metric data interchanges.

In all cases it is important that Agencies participating in the
interchange of navigation data have a common understanding of the choice
of parameters and the reference systems employed. The required
resolution of each parameter is dependent on its intended use and should
be jointly specified. The major items of the consensus proposal of the
CCSDS are provided below.

\[Add new text here, per A.I. 7\]

## 5.2 position and orbit data {#position-and-orbit-data .unnumbered}

### 5.2.1 Spacecraft State Vector (Position, Velocity and Time) {#spacecraft-state-vector-position-velocity-and-time .unnumbered}

For the transmission of a spacecraft state vector, the following
recommendations are applicable:

(1) The Cartesian state vector (position and velocity) x, y, z, x_dot,
    y_dot, z_dot shall be given at a specified epoch t (Gregorian
    format) in a specified reference frame.

(2) SI units (kilometers and kilometers/second) are to be used.

(3) The epoch t is to be specified in Coordinated Universal Time (UTC)
    and given by year, month, day of month, hour, minute, seconds and
    decimal fractions of seconds.\]

###  {#section-3 .unnumbered}

### 5.2.2 Spacecraft Classical Orbital Elements {#spacecraft-classical-orbital-elements .unnumbered}

For the transmission of spacecraft classical orbital elements, the
following recommendations are applicable:

(1) The elements shall be given as osculating Keplerian elements (Ref.
    Table 5-1) at a specified epoch t (Gregorian format) in a specified
    reference frame.

(2) SI units (kilometers and degrees) are to be used.

(3) The epoch t is to be specified in Coordinated Universal Time (UTC)
    and given by year, month, day of month, hour, minute, seconds and
    decimal fractions of seconds.

Table 5‑4: Classical Keplerian elements

  ---------------------------------------- ------------------- -----------
  **Description**                          **Mathematical      **Units**
                                           Symbol**            

  Semimajor axis                           a                   km

  Eccentricity                             e                   \-

  Inclination                              i                   deg

  Right ascension of ascending node        Ω                   deg

  Argument of perigee                      ω                   deg

  True anomaly                             Μ                   deg
  ---------------------------------------- ------------------- -----------

**5.3 TRACKING STATION COORDINATES**

## 5.3.1 Rationale {#rationale-2 .unnumbered}

Spacecraft tracking and communications is possible by a network of
stations located around the world. Whenever an orbiting spacecraft
passes across the field of coverage of a ground station, it collects
tracking data which determines the spacecraft position and velocity.

The location of the tracking station on earth should be specified by its
geocentric spherical or cylindrical coordinates referred to the mean
pole, equator, and zero degree meridian of 1903.0 (CIO). The x axis is
along the intersection of the zero degree meridian (passing through the
mean north pole of 1903.0) and the mean equator of 1903.0, the z axis is
along the mean pole of 1903.0, directed north, and the y axis completes
the right-handed rectangular coordinate system. The source of polar
motion values (e.g., BIH or Naval Observatory) and their use should be
included in the ICD.

## 5.3.2 recommendations {#recommendations-2 .unnumbered}

The tracking station geodetics will be defined based on the
International Terrestrial Reference Frame (ITRF,
http:\\\\www.ngs.noaa.gov/CORS/itrf.html).

5.3.3 TBD

**5.4 SPACECRAFT ATTITUDE DATA**

> \[Add revised text, per A.I. 9\]

## 5.4.1 Rationale {#rationale-3 .unnumbered}

Attitude of a rigid spacecraft is its orientation in a 3-dimensional
space at a given time. Attitude motion describes the attitude evolution
around its center of mass.

Spacecraft attitude is the pointing orientation at each time of an
orbiting spacecraft with respect to known references (celestial objects,
frame, etc.). Attitude determination is the process of computing a set
of parameters that describes this orientation using onboard
measurements.

The process of attitude determination also includes evaluating the
telemetry from the various onboard attitude sensors for any sign of
physical deterioration, improper configuration, or changes in
calibration or alignment. All available attitude telemetry can be
processed to compute a best-estimate time history of what the spacecraft
attitude was. This history is called definitive attitude.

Most spacecraft carry on-board-computers (OBC) with the capability of
computing their own attitude parameters. The attitude data can come via
the telemetry from on board or from ground processed attitude
determination.

Transfers of spacecraft attitude data from one Agency to another are
useful for the following

scenarios:

1\) To ensure scientific observations of specific targets.

2\) To maximize solar energy collection for onboard power usage.

3)  To ensure successful on orbit, deorbit, or rendezvous operations and
    maneuvers.

4)  To ensure and evaluate efficient ground/on-board communication links
    connected with on-board antenna pattern.

## 5.4.2 Recommendations {#recommendations-3 .unnumbered}

The following is a list of recommendations for the transfer of attitude
data between Agencies:

Depending on the attitude mode of the spacecraft

-   single axis

-   three axis

-   uncontrolled

-   gravity gradient

The attitude evolution can be modelized as kinematic or dynamic

For kinematic models the participant needs

Inertia matrix of the spacecraft

Initial conditions (quaternion) at a given time

Kinematic conditions at the same time

For dynamic models the participant needs

Inertia matrix of the spacecraft

Initial conditions (quaternion) at a given time

Kinematic conditions at the same time

Dynamic conditions at the same time

Applied torques (perturbations or maneuvers)

### 5.4.2.1 Quaternions {#quaternions .unnumbered}

The mathematical representation of rigid body rotations is based on
EULER angles convenient for attitude kinematics and can be used for
rotation or three axis configuration.

It can be defined by:

Q1=e1\*sin (Φ/2)

Q2=e2\*sin (Φ/2)

Q3=e3\*sin (Φ/2)

Q4=cos (Φ/2)

And it must verify Q1\*Q1+Q2\*Q2+Q3\*Q3+Q4\*Q4=1

Quaternions are defined in dimensionless units. Where Φ is the rotation
angle between the body frame and the reference frame and e1, e2, e3 are
the components of the rotation vector.

### 5.4.2.2 Units {#units-1 .unnumbered}

Use of :

-   degrees for angles

-   degrees/sec for angular velocity

-   m\*\*2/kg for inertia matrix

-   Tu time for initial conditions

-   Tu time for interval of validity

## 5.5 Special Considerations {#special-considerations .unnumbered}

Many specific cases.

1.  RESTITUTION FOR NON-REAL-TIME DATA.

(TBD)

## 5.5.2 Attitude Determination for Spacecraft in Closed Vicinity {#attitude-determination-for-spacecraft-in-closed-vicinity .unnumbered}

Docking missions share in common kinematics and dynamics for orbit and
attitude. For docking missions the attitude information can be absolute
or relative.

For formation flying missions the attitude can be connected with one the
other partnered spacecraft and can be given relative to a common
external reference frame, or to the reference frame of the master
satellite in the formation.

In the majority of the cases, the attitude control of the assembly of
spacecraft is three axis stabilized.

For these missions, several strategies can be followed to perform the
attitude determination tasks: centralized, de-centralized, and mixed.
When the spacecraft formation is centralized, one spacecraft (the
master) collects information of all others, and solves the problem of
the determination of the attitude for the entire constellation. In a
decentralized approach, each spacecraft solves it own attitude state and
communicates it to the rest of the constellation. The mixed approach
uses features of the other two by multiplexing in time and space the
algorithms of the centralized and de-centralized solutions.

For each of the strategies chosen, attitude determination for a
spacecraft constellation is a cyclic function which can be split in
three fundamental steps: attitude measurements acquisition, attitude
propagation, and attitude filtering update. The measurements acquisition
comprises the process of extracting the raw data out of the sensors. The
attitude propagation function computes the relative quaternions and the
relative attitude rates between the spacecraft of the formation. The
attitude filtering update prepares the sub-system for the next cycle
computations. Attitude determination tasks rely heavily on Kalman
filtering techniques and fast propagation algorithms.

### 5.6 DATA TRANSMISSION DELAYS {#data-transmission-delays .unnumbered}

Data transmission delays must be taken into account in the navigation
message broadcasting.

Figure 5-4 shows a typical scenario with data transmission delays: at
time T1 a ground station transmits data to a spacecraft. During the
transmission of the message the spacecraft has moved to the point T2.
Indeed, if this first spacecraft broadcast the same navigation message
to another one a further transmission delay can occur.

[]{#__RefHeading___Toc469806377 .anchor}Figure 5-4: Data transmission
delays![](media/image7.wmf){width="5.146527777777778in"
height="3.1479166666666667in"}

# 6. measurements

[]{#__RefHeading___Toc469806330 .anchor}**6.1 RATIONALE**

Spacecraft navigation is based on measurements of velocity, distance,
and angular direction.

Data for orbit determination is obtained from telemetry or radar
tracking signals.

**6.2 MEASUREMENT DATA TYPES**

**6.2.1 ANGLES**

Tracking stations on separate locations around the Earth track a single
spacecraft simultaneously. High-rate recordings are made of the
downlink\'s wave fronts by each station, together with precise timing
data. Antenna pointing angles are also recorded; and the antennas slew
directly to the position of any extragalactic object whose position is
known with high accuracy. Then they slew back to the spacecraft.
Correlation and analysis of the recorded data yields a very precise
triangulation from which both angular position and radial distance may
be determined.

**6.2.2 RADIO METRIC/TRACKING DATA**

Tracking of a spacecraft is a process to establish where the spacecraft
actually is in its orbital trajectory at any particular time. Tracking
data is obtained from the spacecraft in flight as it passes within the
field of signal acquisition from one participant to another.

**6.2.3 RANGE**

**Measurement of distance between the flying spacecraft and other
participant(s).**

**6.2.4 RANGE-RATE**

Measurement of relative velocity between the flying spacecraft and other
participant(s). Normally the integrated Doppler count is converted to
range-rate in a suitable way (Ref. 38).

**6.2.5 PHASE**

Phase is the relative measure of the alignment of two waveforms of
similar frequency, expressed in degrees from 0 to 360.

**6.2.6 ACCELERATION**

Measurement of body acceleration provided normally by accelerometers or
other specific devices.

**6.3 EARTH TRACKING (?)**

**6.4 GPS**

NAVSTAR and GLONASS navigation systems provide several observable
quantities to the user´ s receivers: the code, the carrier, etc. From
the phase of the code, the receiver can extract the pseudorange. From
the frequency of the carrier the receiver can extract the Integrated
Doppler Count. Apart from this observables, the receiver can get the GPS
system time. The final output is the so-called PVt (Position, Velocity
and time) solution.

\[Add text\]

##  {#section-4 .unnumbered}

## 6.5 Recommendations {#recommendations-4 .unnumbered}

The objective here is to facilitate exchanges of tracking data. Tracking
data, however, are submitted to a variety of different computational
devices. The philosophy now should be more oriented to the simplicity of
exchange and the nature of data transmitted. This would guarantee
correct usage.

The CCSDS recommends the following items relating to the exchange of
tracking data:

-   Tracking data should be available for inter-agency support with all
    parameters given in powers of 10.

-   Data should be tagged in UTC by year, month, day, hour, minutes,
    seconds and decimal fractions of seconds.

-   The exact reference time within the measurement window shall be
    defined in the ICD.

-   Differenced observables, which may be derived when two stations are
    tracking (i.e., VLBI), should be provided in units analogous to
    Doppler and range. See Table 3-2.

-   Tracking antenna angle data should be provided in degrees and
    decimal fractions in a system best suited to the antenna mount and
    defined in the ICD.

-   Agencies are encouraged to calibrate for tracking station delay in
    the tracking data. Initial estimates to be defined in the ICD.
    Subsequent measurements to be provided in ancillary messages.

-   Agencies are encouraged to provide local measurements of atmospheric
    conditions (temperature, pressure, and humidity) to aid users in
    their own media calibration.

-   For tracking data transfers in a cross-support activity flags can be
    defined to indicate data that is substandard. These flags shall be
    docu­mented in an ICD.

# 7. SATELLITE-BASED GLOBAL NAVIGATION SYSTEMS

## 7.1 Rationale {#rationale-4 .unnumbered}

There is a growing dependency in space applications on orbiting systems
such as GLONASS, NAVSTAR, and GalileoSAT. These systems will be referred
to as Global Navigation Systems (GNS).

The development of the present three satellite-based global navigation
systems (the U.S.'s NAVSTAR, the former U.S.S.R.'s GLONASS and the
European GalileoSAT) represent a huge change in the technology of
navigation and positioning. Although initially planned for military
purposes, the civil sector (non military) has quickly recognized the
potential value of these positioning systems in the areas of civil
aviation, marine and ground navigation, spacecraft navigation, and
surveying and geodesy. The development of products and services has
opened a new market with rapid growth.

The two active constellations for global positioning are the US NAVSTAR
system and the Russian GLONASS system. The European GalileoSAT will join
these two, officially, in the year 2010.

The USA GPS system NAVSTAR is managed by the U.S. Air Force (USAF) for
the Government of the United States. The NAVSTAR satellite constellation
is composed of 27 satellites deployed in near-elliptical orbits around
the Earth. The satellites are located in 4 orbital planes where each
orbital plane contains 6 active satellites.

The Russian GNS system GLONASS is similar to the American NAVSTAR. GPS
uses code division multiple access (CDMA) to broadcast its data.
Presently, GLONASS is operated by the air command of the Russian
military forces. GLONASS is formed also of 24 satellites having 3
orbital planes, with 8 satellites per plane. Unlike GPS, GLONASS uses
the Frequency Division Multiple Access (FDMA) technique to broadcast the
data. In Spring 1999, the Council of the European Space Agency has
approved the space mission GalileoSAT. At the time of this writing, the
definition of the Galileo system is planned to be completed by the end
of the year 2000. Galileo shall be fully operational by the year 2008.
It will be inter-operable with the NAVSTAR system. The GalileoSAT
constellation will consist of a medium Earth orbit satellite
constellation and a number of geostationary satellites plus some other
local complements.

Several factors make these global navigation systems attractive to
spacecraft navigation:

-   Its coverage: It has an almost complete coverage of the Earth for
    LEO orbits, and a reasonable coverage for HEO orbits.

-   Its accuracy: All these systems can or will provide accuracy in
    orders of magnitude better than conventional ground tracking. (Refs.
    11 and 25).

-   Its integrity: The system is guaranteed to function continuously
    without performance degradation.

-   Its price: The degraded signal of NAVSTAR is gratis, as well as the
    GLONASS signals. GalileoSAT will carry both commercial and
    non-commercial signals.

**7.2 RECOMMENDATIONS**

RINEX format is recommended for the exchange of GNS measurement in
ground to ground scenarios.

# 8. NAVIGATION MESSAGE FORMAT RECOMMENDATION

\[A.I. 11\]

**8.1 RATIONALE**

(Why SPKE)

2.  **SPKE DESCRIPTION**

3.  **SPKE RECOMMENDATION**

4.  **SPKE FOR SPACE APPLICATIONS**

# annex a 

\[A.I. 13\]

**NAVIGATION DATA MESSAGE EXAMPLE**

(THIS ANNEX **IS NOT** PART OF THE RECOMMENDATION)

**A.1 PURPOSE**

[]{#__RefHeading___Toc469806345 .anchor}

This annex contains an example of a navigation message data exchange
format for particular applications.

This example should be taken into account during the discussion for a
particular recommendation of a more generic format of navigation data
message exchange.

## A.2 NORAD Two Line Elements Format {#a.2-norad-two-line-elements-format .unnumbered}

NORAD two line element set is a file containing 3 rows of 69 characters
of data which can be used to determine the position and velocity for a
space object rotating the Earth.

[]{#__RefHeading___Toc469806384 .anchor}Figure A‑5: Example of a NORAD
TLE file

The example of the TLE format is taken from the Orbital Information
Group (OIG).

The TLE format contains three lines, namely line 0, line 1 and line 2.
Line 0 provides the catalog number and/or possibly other information
such as the common name assigned to the satellite. In the example of
Figure A-5 the line 0 describes the satellite number, its name, etc.

The structure of the NORAD TLE file format is described in , Table A-2
and Figure A-6.

Table A‑5: Structure of first row of the NORAD TLE file

  ---------- ----------- -------------- -------------------------------------
  **First    **Number    **Number of    **Description**
  Column**   last**      characters**   

  1          1           1              Line No. Identification

  3          7           5              Catalog No.

  8          8           1              Security Classification

  10         17          8              International Identification

  19         32          14             YRDOY.FODddddd

  34         34          1              Sign of first time derivative

  35         43          9              1st Time Derative

  45         45          1              Sign of 2nd Time Derivative

  46         50          5              2nd Time Derivative

  51         51          1              Sign of 2nd Time Derivative Exponent

  52         52          1              Exponent of 2nd Time Derivative

  54         54          1              Sign of Bstar/Drag Term

  55         59          5              Bstar/Drag Term

  60         60          1              Sign of Exponent of Bstar/Drag Term

  61         61          1              Exponent of Bstar/Drag Term

  63         63          1              Ephemeris Type

  65         68          4              Element Number

  69         69          1              Check Sum, Modulo 10
  ---------- ----------- -------------- -------------------------------------

[]{#__RefHeading___Toc469806542 .anchor}Table A‑2: Structure of the
second row of the NORAD TLE file

  ---------- ----------- -------------- -------------------------------------
  **First    **Number    **Number of    **Description**
  Column**   last**      characters**   

  1          1           1              Line No. Identification

  3          7           5              Catalog No.

  9          16          8              Inclination

  18         25          8              Right Ascension of Ascending Node

  27         33          7              Eccentricity with assumed leading
                                        decimal

  35         42          8              Argument of the Perigee

  44         51          8              Mean Anomaly

  53         63          11             Revolutions per Day (Mean Motion)

  64         68          5              Revolution Number at Epoch

  69         69          1              Check Sum Modulo 10
  ---------- ----------- -------------- -------------------------------------

Figure A‑6: Graphical representation of the NORAD TLE file format

**A.3 EXAMPLES OF QUALITY**

# ANNEX B 

**GLOSSARY**

(THIS ANNEX **IS NOT** PART OF THE RECOMMENDATION)

**B.1 PURPOSE**

This annex provides a glossary of navigation terminology.

Ancillary data: Data other than instrument data required to perform an
instrument\'s data processing. They include orbit data, attitude data,
time information, spacecraft engineering data, calibration data, data
quality information, and data from other instruments.

Apogee: The point in an orbit furthest away from the Earth. The point in
an orbit when the geometric distance is a maximum.

> Attitude: The direction in which a spacecraft is oriented in space.

Doppler: The apparent change in the frequency of a signal caused by the
relative motion of the transmitter and receiver.

Eccentricity: The ratio of the distance from the center of an ellipse to
its focus to the semimajor axis.

Ephemeris: A list of (accurate) positions and velocities of satellite as
a function of time.

Epoch: Epoch signifies the beginning of an era (or event) or the
reference date of a system of measurements.

::: Definition-Term
Global Positioning System (GPS): A highly accurate, global satellite
navigation system based on a constellation of 24 satellites orbiting the
earth at a very high altitude. In addition to navigation, the system
also provides very precise time.
:::

Inclination: The angle between the orbital plane of a body and its
equatorial plane.

::: Definition-Term
Orbit: The path followed by a celestial body.
:::

Orbital elements: A set of parameters describing any astronomical or
spacecraft orbit.

Phase angle: The angle between the Sun, an object, and an observer.

Perigee: The point in an orbit of closest approach to the Earth. The
point in an orbit when the geometric distance is a minimum.

Nutation: The short-period oscillations in the motion of the pole of
rotation of a freely rotating body that is undergoing torque from
external gravitational forces. Nutation of the Earth\'s pole is difined
in terms of components in obliquity and longitude.

Polar motion: Motion of the instantaneous axis of the rotation of the
Earth with respect to the solid body of the Earth. Irregular but more or
less circular motion with an amplitude of about 15m and a main period of
about 430 days (called Chandler Wobble).

Precession: The change in orientation of a spinning body\'s rotational
axis.

Range rate: The rate of change of range between the satellite and
receiver. The range to a satellite changes due to satellite and observer
motions. Range rate is determined by measuring the Doppler shift of the
satellite beacon carrier.

Right ascension of ascending node: The angular distance measured from
the vernal equinox, positive to the east, along the celestial equator to
the ascending node.

RINEX: A set of standard definitions and formats to promote the free
exchange of GPS data and facilitate the use of data from any GPS
receiver with any software package.

SPK: \"Spacecraft and Planet Kernel\". It is a file element of the SPICE
system devised and maintained by the NAIF (Navigational and Ancillary
Information Facility) team at JPL. SPK files may hold ephemerides for
any kind of spacecraft, vehicle, or solar system body.

SPICE kernel contents are summarized below:

S- Spacecraft ephemeris, or more generally, location of an observer,
given as a function of time.

P- Planet, satellite, comet, or asteroid ephemerides, or more generally,
location of a target body, given as a function of time.

The ephemeris data for spacecraft and target bodies are normally
combined in a single file called the SPICE SPK file. (But either target
ephemerides alone or a spacecraft ephemeris alone can be held in an SPK
file; it is not necessary that both types be present.)

The P kernel also logically includes certain physical, dynamical and
cartographic constants for target bodies, such as size and shape
specifications, and orientation of the spin axis and prime meridian.
These target body physical and cartographic constants are found in the
SPICE PCK file.

I- Instrument description kernel, containing descriptive and operational
data peculiar to a particular scientific instrument, such as mounting
alignment, internal timing relative to the spacecraft clock, and
field-of-view model parameters. This instrument information is contained
in the SPICE IK file.

C- Pointing kernel, containing a transformation traditionally called the
C-matrix that provides time-tagged pointing (orientation) angles for a
spacecraft structure upon which science instruments are mounted.
Attitude data are contained in the SPICE CK file.

E- Events kernel, the principal contents of which are derived from the
integrated sequence of events used to produce actual spacecraft
commands. Events data are contained in the SPICE EK file set. (There are
three components to the EK).

**INDEX**

(THIS CHAPTER **IS NOT** PART OF THE RECOMMENDATION)

Index to be added here.