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                               CONSULTATIVE
                               COMMITTEE FOR
                            SPACE DATA SYSTEMS

                         RECOMMENDATION FOR SPACE
                           DATA SYSTEM STANDARDS

                    +-----------------------------------+
                    |                                  |
                    |           RADIO METRIC           |
                    |               AND                |
                    |            ORBIT DATA            |
                    |                                  |
                    |                                  |
                    +-----------------------------------+

                              CCSDS 501.0-B-1

                                 BLUE BOOK

                               JANUARY 1987

                                 AUTHORITY

                *******************************************
                *   Issue:     Blue Book, Issue 1         *
                *   Date:      January 1987               *
                *   Location:  CCSDS Plenary Meeting      *
                *              November 1986              *
                *              Frascati, Italy            *
                *******************************************

This Recommendation reflects the consensus technical agreement of the
following member Agencies of the Consultative Committee for Space Data
Systems (CCSDS):

o  Centre National D'Etudes Spatiales (CNES)/France.
o  Deutsche Forschungs-u. Versuchsanstalt fuer Luft und Raumfahrt e.V
   (DFVLR)/West Germany.
o  European Space Agency (ESA)/Europe.
o  Indian Space Research Organization (ISRO)/India.
o  Instituto de Pesquisas Espaciais (INPE)/Brazil.
o  National Aeronautics and Space Administration (NASA)/USA.
o  National Space Development Agency of Japan (NASDA)/Japan.

The following observer Agencies also concur with this Recommendation:

o  British National Space Centre (BNSC)/United Kingdom.
o  Chinese Academy of Space Technology (CAST)/People's Republic of China.
o  Department of Communications, Communications Research Centre (DOC-
   CRC)/Canada.

This Recommendation is published and maintained by:

   CCSDS Secretariat
   Communications and Data Systems Division  (Code-TS)
   National Aeronautics and Space Administration
   Washington, DC 20546, USA

                            STATEMENT OF INTENT

The Consultative Committee for Space Data Systems (CCSDS) is an
organization officially established by the management of member space
Agencies.  The Committee meets periodically to address data systems
problems that are common to all participants, and to formulate sound
technical solutions to these problems.  Inasmuch as participation in the
CCSDS is completely voluntary, the results of Committee actions are
termed RECOMMENDATIONS and are not considered binding on any Agency.

This RECOMMENDATION  is issued by, and represents the consensus of, the
CCSDS Plenary body.  Agency endorsement of this RECOMMENDATION is
entirely voluntary.  Endorsement, however, indicates the following
understandings:

o  Whenever an Agency establishes a CCSDS-related STANDARD, this
   STANDARD will be in accord with the relevant RECOMMENDATION.
   Establishing such a STANDARD does not preclude other provisions
   which an Agency may develop.

o  Whenever an Agency establishes a CCSDS-related STANDARD, the Agency
   will provide other CCSDS member Agencies with the following
   information:

   --  The STANDARD itself.

   --  The anticipated date of initial operational capability.

   --  The anticipated duration of operational service.

o  Specific service arrangements shall be made via memoranda of
   agreement.  Neither this RECOMMENDATION nor any ensuing STANDARD is
   a substitute for a memorandum of agreement.

No later than five years from its date of issuance, this Recommendation
will be reviewed by the CCSDS to determine whether it should: (1) remain
in effect without change;  (2) be changed to reflect the impact of new
technologies, new requirements, or new directions;  or (3) be retired or
cancelled.

                                 FOREWORD

This document is a technical Recommendation for standardization of radio
metric and orbit data generated by space data systems of Agencies of the
Consultative Committee for Space Data Systems (CCSDS).

The topic areas covered herein include radio metric data, spacecraft
orbital elements, solar system ephemeris, tracking station locations,
astrometric data, reference systems, astrodynamic constants and
spacecraft dynamics parameters. This Recommendation deals explicitly
with the technical definitions and conventions associated with inter-
Agency cross-support situations involving the transfer of orbital
elements and ground-based conventional radio metric data, i.e., doppler
and range.

Through the process of normal evolution, it is expected that expansion,
deletion or modification of this document will occur. This
Recommendation is therefore subject to CCSDS document and change control
procedures which are defined in Reference [1].

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

                             DOCUMENT CONTROL

 Document            Title               Date     Status/Remarks

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

                                 CONTENTS

Sections                                                 Page

   REFERENCES                                               vi

1  INTRODUCTION                                             1-1

   1.1 PURPOSE AND SCOPE                                    1-1
   1.2 APPLICABILITY                                        1-1

2  TRANSFER OF SPACECRAFT ORBITAL ELEMENTS
   FROM ONE AGENCY TO ANOTHER                               2-1

3  REFERENCE SYSTEM                                         3-1

4  TRACKING DATA                                            4-1

Annexes

A  TRANSFORMATION OF BARYCENTRIC DYNAMICAL TIME
   (TDB) TO APPROXIMATE COORDINATED UNIVERSAL
   TIME (UTC)                                               A-1

                                REFERENCES

[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 Atronomical 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.

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

1  INTRODUCTION

1.1    PURPOSE AND SCOPE

The purpose of this document is to establish common recommendations for
adequately exchanging data involved in orbit computation (extrapolation,
reconstitution,...) to provide cross-support among missions and facilities
of member Agencies of the Consultative Committee for Space Data Systems
(CCSDS).  In addition, it 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.

The topic areas to be covered include radio metric data, spacecraft orbital
elements, solar systems ephemerides, tracking station locations,
astrometric data, reference systems, astrodynamic constants, and spacecraft
dynamic parameters.  These parameters define the scope of the panel
activities, and all should deal explicitly with the technical definitions
and conventions associated with inter-agency cross-support involving the
transfer of orbital elements and ground-based conventional radio metric
data, i.e., doppler and range.

1.2    APPLICABILITY

This Recommendation applies to 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 that 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 are 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 in 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.

2  TRANSFER OF SPACECRAFT ORBITAL ELEMENTS
   FROM ONE AGENCY TO ANOTHER

It is recognized that transfers of spacecraft orbital element from one
Agency to another are useful for purposes such as:

   (1) Pre-flight planning of a mission support, covariance analysis,
       tracking station viewperiods, etc.,

   (2) In-flight inter-agency comparison of estimated spacecraft
       trajectories, software compatibility checks, solutions comparisons,
       etc.,

   (3) Tracking station predicts in support of radio metric data
       interchanges.

In all cases it is important that Agencies participating in the interchange
of orbital elements 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:

   (1) Orbital parameters interchanged between Agencies should be
       osculating rather than mean elements.

   (2) The fundamental coordinates should be cartesian state (position and
                                   .  .  .
       velocity) elements x, y, z, x, y, z at chosen time t.

   (3) A secondary set of elements should accompany the primary cartesian
       set.  These should be the Keplerian set a, e, i, <OMEGA>, <omega>,
       and <upsilon>, the true anomaly at time t.  The transformation to
       the Keplerian set should be performed at time t using a selected
       mass constant <mu>, which is also to be provided in the
       interchange.
                                                     .  .  .
   (4) Units for x, y, z and a are to be kilometers; x, y, z in
       kilometers/second.  Units of i, <OMEGA>, <omega>, and <upsilon> are
       to be in degrees and decimal fractions; <mu> in km**3/s**2.

   (5) Time 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.  For deep space trajectories, which
       are normally numerically integrated in Barycentric Dynamical Time
       (TDB), which is essentially the same as Ephemeris Time (ET), an
       approximate UTC is suggested.  This is derived from the simplified
       equations shown in Annex A.  Alternatively, time t may be specified
       as a continuous count of seconds and subseconds.  Suitable time
       code formats are given in Reference [3].

   (6) The origin of the reference system should be selected as the center
       of body of a major gravity force and should be so specified in the
       interchange.

   (7) The area/mass ratio in m**2/kg and the unitless drag coefficient
       should be provided when appropriate for drag computation.

   (8) The area/mass ratio in m**2/kg and unitless solar reflectivity
       coefficient for solar pressure computations should be provided when
       appropriate.

   (9) Other model parameters may be needed for some applications.
       Possible examples include solar flux and magnetic indicies for the
       atmospheric model, and gravitational terms.

3  REFERENCE SYSTEM

The following is a list of recommendations for reference system parameters
to be exchanged between Agencies.

   (1) Interchanged orbital elements (cartesian vector at time t) should be
       referred to one of the following four systems:

       (a) The mean equator and equinox of J2000.0.(1)
       (b) The mean equator and equinox of the date defined by t using the
           precession adopted in the J2000 system.

       (c) The true equator and equinox of the date defined by t using
           precession an nutation adopted in the IAU J2000 system.  This
           is an instantaneously-fixed system.

       (d) The Earth-fixed system, which uses the true equator as defined
           in (c), above, but is rotating with the Earth and has the x-
           axis fixed with the prime meridian.  The velocity is with
           respect to the rotating  system.

   (2) Gravity parameters and the particular choice of JPL planetary
       ephemeris should not be standardized, since these are updated on a
       periodic basis and Agencies will often want to use the latest most
       modern values.  Agencies which provide gravity parameters and
       ephemerides are encouraged to:

       (a) Provide products referenced to the J2000 system.

       (b) Provide thorough and up-to-date documentation of any new
           product.
_____________________
(1) The J2000 system adopted by the International Astronomical Union (IAU)
in 1984 (Reference [2]), defines coordinate axes associated with earth's
mean dynamical equator and equinox of the Julian ephemeris date 2451545.0.
The system adopts modern values for earth precession and nutation and a
modern transformation from universal to sidereal time. It also defines an
earth fixed reference system presently maintained by the BIH (Bureau
International de l'Heure:  circulars D) and referred to the CIO
(Conventional International Origin) and a zero point in longitude.  It
should be noted that the MERIT campaign has adopted the J2000 system as its
standard for use in the intercomparing of new methods for the measurements
of the Earth Rotation.

4  TRACKING DATA

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:

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

   (2) Data should be provided in a time-ordered sequence, and tagged in
       UTC by year, month, day, hour, minutes, seconds and decimal
       fractions of seconds.

   (3) 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.

   (4) Non-destruct doppler data should be provided as a time average of
       the frequency difference between the transmitted and received
       signals.

       The doppler observable F, with units of hertz, is given by:

                         [GRAPHIC ELEMENT OMITTED]

       where the effective transmitter frequency f[sub]T is the actual
       constant transmitted frequency multiplied by any intermediate
       transponder frequency ratios, f[sub]R is the frequency of the
       signal received at the receiving station and time t is the midpoint
       of the averaging interval <DELTA>t.  The tag time (usually
       identified as the start, midpoint, or end of the averaging
       interval), the averaging interval <DELTA>t (in seconds), and the
       effective transmitter frequency f[sub]T should be provided with the
       doppler observables.  They also may be provided in the ICD, as
       appropriate.

   (5) Range data should be provided as round trip light time in seconds
       and decimal fractions (one way light time when it is the case).
       The tag time (start or end of the round trip) should be specified
       with the range observables.

   (6) Differenced observables,which may be derived when two stations are
       tracking (i.e., VLBI), should be provided in units analogous to
       doppler and range.  They are, respectively, differential phase
       count per unit  time, in hertz, and differential light time, in
       seconds.

   (7) 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.  For AZ-EL stations, it is recommended that the
       Azimuth be measured East from North.

   (8) 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.

   (9) Agencies are encouraged to calibrate for tracking station delay in
       the tracking data, and define the calibrations in the ICD.

   (10)Agencies are encouraged to provide local measurements of
       atmospheric conditions (temperature, pressure, and humidity) to aid
       users in their own media calibration.  Further, ancillary data for
       the calibration of media effects are considered non-standard but
       can be provided if so desired if defined in the ICD.

   (11)In general, all acquired data should be transferred in a cross-
       support activity, not just an edited data set, although flags can
       be set on some specific data to indicate that the generating agency
       believes those data to be sub-standard.  Data sampling to reduce
       data volume is not precluded for high volume data if a previous
       agreement is documented in an ICD.

                                  ANNEX A

                             TRANSFORMATION OF

                     BARYCENTRIC DYNAMICAL TIME (TDB)

                              TO APPROXIMATE

                     COORDINATED UNIVERSAL TIME (UTC)

              (THIS ANNEX IS NOT PART OF THE RECOMMENDATION)

                                 Purpose:

This Annex provides equations which can be used to convert Barycentric
Dynamical Time to Approximate Coordinated Universal Time.

The conversion from Barycentric Dynamical Time (TDB) to Coordinated
Universal Time (UTC) may be approximated by the equation:

                   UTC = TDB - (TDB - TAI) - (TAI - UTC)

where

TAI - UTC                   =   integer number of seconds offset, from
                                the BIH annual report (23 seconds as of
                                July 1, 1985)

TDB - TAI (seconds)         =   32.184 + 1.658 x 10**-3 sin E

ECCENTRIC ANOMALY        E  =   M + e sin M

MEAN ANOMALY (radians)   M  =   6.248291 + 1.99096871 x 10**-7 t
                                t = TDB or TAI seconds past 1950 Jan 1,
                                0h

ECCENTRICTY OF           e  =   .01672
EARTH'S ORBIT