MESSENGER Science Data Archive
                           Radio Science Subsystem
                 Description of the Momentum Dump Maneuver file
             November 7, 2013  (revised for PDS4 10 September 2018)
                          Johns Hopkins University
                         Applied Physics Laboratory


The Momentum Dump Maneuver (MDM) file contains information on each momentum
dump maneuver. All of these events were commanded angular-momentum dumps;
MESSENGER did not perform any autonomous momentum dumps. The primary
purpose of the MDM file was to supply information to the Navigation and Radio
Science teams for use in their trajectory-reconstruction analyses. A new
version of the MDM file was created after each maneuver; only the final
file is included in the PDS4 archive. 

There is one row for each angular momentum dump. There are 23 fields,
including an unused field in each row. The fields are described as follows:

CMD_ID - A unique number for each momentum dump, numbered sequentially
starting with the first momentum dump after entering orbit about Mercury.

IBFM_X - The X component of the initial body-frame angular momentum.
IBFM_Y - The Y component of the initial body-frame angular momentum.
IBFM_Z - The Z component of the initial body-frame angular momentum.

FBFM_X - The X component of the final body-frame angular momentum.
FBFM_Y - The Y component of the final body-frame angular momentum.
FBFM_Z - The Z component of the final body-frame angular momentum.

MOMENTUM_CHG - The total change in system angular momentum during the
            maneuver.

FIRST_THRUS - The time, in UTC, of the first use of a thruster for this
              maneuver.

LAST_THRUS - The time, in UTC, of the last use of a thruster for this
             maneuver.

THRUSTER_ON - The total duration, in seconds, that thrusters fired.

RESIDUAL_DELTA_V_X - The X component, in EME2000 coordinates, of the change
                     in spacecraft velocity, in millimeters per second, due
                     to this momentum dumping maneuver.
RESIDUAL_DELTA_V_Y - The Y component, in EME2000 coordinates, of the change
                     in spacecraft velocity, in millimeters per second, due
                     to this momentum dumping maneuver.
RESIDUAL_DELTA_V_Z - The Z component, in EME2000 coordinates, of the change
                     in spacecraft velocity, in millimeters per second, due
                     to this momentum dumping maneuver.

MASS_CONSUM        - The mass in grams of propellant used during the maneuver.

UNUSED             - A constant, zero.

POST_CMD_SC_MASS   - Total spacecraft mass in kilograms after the maneuver.

GC_POST_MANEUVER_SC_BODY_CM_X - The x-component of the post-maneuver center
                     of mass in the GC coordinate system.
GC_POST_MANEUVER_SC_BODY_CM_Y - The y-component of the post-maneuver center
                     of mass in the GC coordinate system.
GC_POST_MANEUVER_SC_BODY_CM_Z - The z-component of the post-maneuver center
                     of mass in the GC coordinate system.

AR_POST_MANEUVER_SC_BODY_CM_X - The x-component of the post-maneuver center
                     of mass in the adapter-ring-coordinate system.
AR_POST_MANEUVER_SC_BODY_CM_Y - The y-component of the post-maneuver center
                     of mass in the adapter-ring coordinate system.
AR_POST_MANEUVER_SC_BODY_CM_Z - The z-component of the post-maneuver center
                     of mass in the adapter-ring coordinate system.
                  

Note on the Post Maneuver Spacecraft Body Center of Mass Fields: The final 
six fields in each row give the post maneuver spacecraft body center of 
mass. These are provided in two coordinate systems (with x,y,z components 
in meters) identified as Guidance & Control (GC) and adaptor-ring (AR). 
The adaptor-ring coordinate system is also called the "development" 
coordinate system. The two systems differ only in the location of the origin;
both systems use the same orientation of the axes, as defined in the spacecraft
frames kernel (FK) file archived at the PDS/NAIF site. The GC system places
the origin so that the solar-array rotation axes goes through the origin; 
this location is closer to the physical center of the spacecraft. The 
development (AR) system places the origin at the center of the adaptor ring,
which is at one end of the spacecraft, near the location of the planet-viewing
instruments. The two coordinate systems are separated by 0.89662 m along the 
Z axis. The GC origin is located at (0,0,-0.89662) in the development system.
The RS IK file (archive at the PDS/NAIF site) uses the development system.

For PDS/NAIF archives go to
https://naif.jpl.nasa.gov/pub/naif/pds/data/mess-e_v_h-spice-6-v1.0/messsp_1000/