MESSENGER Science Data Archive
                           Radio Science Subsystem
            Description of the MESSENGER Maneuver Performance Data File
              09 October 2015 (revised for PDS4 on 18 September 2020)
                          Johns Hopkins University
                         Applied Physics Laboratory


The Maneuver Performance Data (MPD) file is used in the maneuver design
process to specify the flow rates, moment arms, and thrust magnitudes for
each spacecraft thruster. This file contains header information and seven
named data blocks.

There are two coordinate systems used by the MESSENGER team, the spacecraft
(s/c) body coordinates used by the G&C engineers (also referred to as the
"G&C" coordinates) and the adaptor-ring (AR) coordinates used by the
development engineers. The two systems differ only in the location of the
origin.  Subtract 0.89662 meters from the Z coordinate to convert the s/c body
coordinates to the adaptor-ring coordinates. The s/c body coordinate system
origin is located at (0,0,-0.89662) in the adapter ring system.

The variables in an MPD file are given in s/c body coordinates, except for
CMSC_AR, which uses the adaptor ring coordinates. The RS instrument (IK)
SPICE kernel uses the adapter ring coordinate system.

The MPD file provides the fields and named data blocks as described below.

MANEUVER_INITIAL_EPOCH - the initial time of the thrusting event in UTC.

THRDIR - a matrix of thruster unit vector directions in s/c body coordinates
(17 x 3), where the rows represent the MESSENGER thrusters ordered as
follows: A1, A2, A3, A4, B1, B2, B3, B4, S1, S2, P1, P2, C1, C2, C3, C4, LVA

THRLOCS - the thruster nozzle throat position (force/torque application
point) in s/c body coordinates (meters). The order of the thrusters is the
same as above.

MSC - spacecraft mass just prior to the first thruster firing (kg). This
corresponds to the mass at the MANEUVER_INITIAL_EPOCH.

CMSC - spacecraft center of mass just prior to the first thruster firing (m)
in spacecraft body (G&C) coordinates. This corresponds to the center of mass
at the MANEUVER_INITIAL_EPOCH. The X and Y coordinates are referenced to the
spacecraft centerline, and the Z coordinate is referenced to the solar array
axis of rotation.

CMSC_AR - spacecraft center of mass just prior to the first thruster firing
(m) in the adaptor-ring coordinate system. This corresponds to the center of
mass at the MANEUVER_INITIAL_EPOCH. This is the same center of mass as the
CMSC but it is given in the adaptor-ring system. It differs from the CMSC
only in that the Z component is offset 0.89662 m.

IISC - spacecraft inertia matrix, which contains the moments of inertia
(diagonal terms) and products of inertia (off-diagonal terms) in s/c body
coordinates for the period just prior to the first thruster firing (kg*m**2).
This corresponds to the inertia at the MANEUVER_INITIAL_EPOCH.

FMAG - the magnitude of each thruster force (N). Ordered as above.

MDOT - the mass flow rate (kg/s) for each thruster. Ordered as above.


NOTE on Data from Orbital Correction Maneuvers (OCM) 11 and Later:
OCM-12 and OCM-15 used a mix of hydrazine and helium gas for propellant.
OCM-15A, OCM-16, OCM-17, OCM-18 used primarily helium gas for propellant.

OCM Name   Special Case   Propellant Type        First Thruster Firing (UTC)
OCM11       No            Hydrazine              2014-297T18:58:11.7359
OCM12       Yes           Hydrazine/Helium Gas   2015-021T18:27:24.27
OCM13       No            Hydrazine              2015-077T14:59:39.4
OCM14       No            Hydrazine              2015-092T20:29:43.758
OCM15       Yes           Hydrazine/Helium Gas   2015-096T16:14:06.9064
OCM15A      Yes           Helium Gas             2015-098T16:55:17.79
OCM16       Yes           Helium Gas             2015-104T15:15:59.9610
OCM17       Yes           Helium Gas             2015-114T17:22:47.0539
OCM18       Yes           Helium Gas             2015-118T21:19:57.3417

The MPD products associated with these OCMs are below:
MESS_RS_2014297_2014297_MPD
MESS_RS_2015021_2015021_MPD
MESS_RS_2015077_2015077_MPD
MESS_RS_2015092_2015092_MPD
MESS_RS_2015096_2015096_MPD
MESS_RS_2015098_2015098_MPD
MESS_RS_2015104_2015104_MPD
MESS_RS_2015114_2015114_MPD
MESS_RS_2015118_2015118_MPD