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