MESSENGER Science Data Archive
                           Radio Science Subsystem
                 Description of the Antenna Configuration File
               12 June 2015 (revised for PDS4 on 17 October 2020)
                          Johns Hopkins University
                         Applied Physics Laboratory


The Antenna Configuration (ANT) file contains the configuration of the
MESSENGER spacecraft RF antennas during the period when MESSENGER was in orbit
about Mercury. There are also configurations for each of the three flybys of
Mercury and for a period of a few weeks before and after each Mercury flyby.
Continuous reporting of the antenna configuration began in February 2011,
about a month before Mercury orbit insertion.

The primary purpose of the ANT file was to supply information to the
navigation and Radio Science teams for use in their trajectory-construction
analyses. A new version of the ANT file was created for each PDS release.
The ANT file was an accumulating file, with each row indicating a change in
antenna configuration. Between the rows, antenna configuration was unchanged.
Since a row was added only when the antenna configuration changed, the rows
are not separated by equal increments in time.  Only the final ANT file was
included in the PDS4 archive.

The values in the ANT file were based on the command load sent to the
spacecraft.  In rare cases, the as-flown configuration may have been different
due to a real-time command that changed the antenna configuration or due to a
spacecraft anomaly that triggered an autonomous spacecraft response that
reconfigured the RF system. For example, when the spacecraft entered a safe
mode, it may have reconfigured the RF system to use the fan beam antenna.
In some such cases, such as in the third flyby, the ANT file was modified to
reflect the as-flown configuration.

The ANT file begins with a single header row which serves as a memory aid
for the 4875 data records that follow.

In the original file for PDS3, each data row had five entries or columns,
separated by one or two spaces. The first three entries describe the time
that the change in antenna configuration occurred. The last two entries
describe the new antenna configuration. Note that each row contains two
times. The first time is the Earth-receive time (in UTC), and the second
time is spacecraft time (in MET) at which the configuration change occurred.
These times differ by the one-way light time.


First entry/column: the year of the time that the configuration changed,
    followed by a colon (:).

Second entry/column: the Earth-receive (ERT) time that the antenna
    configuration changed, in DOY:HH:MM:SS.sss, where DOY represents
    the three-digit day of year.

Third entry/column: the time on board the spacecraft that the spacecraft
    changed antenna configuration, in spacecraft mission elapsed time (MET)
    given in SPICE encoded SCLK form. A value of 000000000 indicates that
    the MET was not captured (i.e., missing data).

Fourth entry/column: downlink antenna used on the spacecraft in the new
    configuration. It is a digit from 0 to 8, with the following meanings:
    0: Front Fan beam
    1: AFT LGA
    2: Front LGA
    3: Back Fan beam
    4: FWD LGA5: Back LGA
    6: Front Phased Array
    7: Back Phased Array
    8: Hardware Error

Fifth entry/column: uplink antenna used on the spacecraft in the new
    configuration. It is a digit from 0 to 8, with the following meanings:
    0: Front Fan beam
    1: AFT LGA
    2: Front LGA
    3: Back Fan beam
    4: FWD LGA
    5: Back LGA
    6: N/A
    7: N/A
    8: Hardware Error

In the PDS4 version of the file, the data fields have been adjusted
slightly so that fields always appear in the same position in a record.
That is:

Bytes 01-04: year of the antenna configuration change
Bytes 07-09: day of year of the configuration change (ERT/UTC)
Bytes 11-12: hour of the configuration change (ERT/UTC)
Bytes 14-15: minute of the configuration change (ERT/UTC)
Bytes 17-22: second of the configuration change (ERT/UTC)
Bytes 24-34: spacecraft clock time of the configuration change (MET)
Byte  36:    downlink antenna selected at the configuration change
Byte  38:    uplink antenna selected at the configuration change
Bytes 39-40: ASCII carriage-return line-feed pair (record delimiter)