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