Module: mtbMomentumManagement

Executive Summary

This module computes the appropriate wheel torques and magnetic torque bar dipoles to bias the wheels to their desired speeds. Note that there is no gurantee that the wheel speeds will converge to their bias when less than 3 orthornormal torque rods are in use. In this case it is recommended that a nullspace controller be used to drive the wheels toward their bias. Documentation for the math used in this module can be found in a paper by Eric Hogan.

Message Connection Descriptions

The following table lists all the module input and output messages. The module msg connection is set by the user from python. The msg type contains a link to the message structure definition, while the description provides information on what this message is used for.

Module I/O Messages

Msg Variable Name	Msg Type	Description
rwParamsInMsg	RWArrayConfigMsgPayload	input message for RW parameters
mtbParamsInMsg	MTBArrayConfigMsgPayload	input message for MTB layout
tamSensorBodyInMsg	TAMSensorBodyMsgPayload	input message for magnetic field sensor data
rwSpeedsInMsg	RWSpeedMsgPayload	input message for RW speeds
rwMotorTorqueInMsg	ArrayMotorTorqueMsgPayload	input message for RW motor torques
mtbCmdOutMsg	MTBCmdMsgPayload	output message for MTB dipole commands
rwMotorTorqueOutMsg	ArrayMotorTorqueMsgPayload	output message for RW motor torques

User Guide

See the example script scenarioMtbMomentumManagement for an illustration on how to use this module.

The user must set the momentum dumping gain value cGain to a postive value. The required input messages are described above. The optional module list wheelSpeedBiases can be set to desired RW spin rates in terms of rad/sec. If this is not set, the default values are zero rates.

Note that the MTB input configuration message variable GtMatrix_B must be provided in a row major format.

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Functions

void SelfInit_mtbMomentumManagement(mtbMomentumManagementConfig *configData, int64_t moduleID)

This method initializes the configData for this module. It checks to ensure that the inputs are sane and then creates the output message of type MTBCmdMsgPayload and ArrayMotorTorqueMsgPayload.

Parameters

• configData – The configuration data associated with this module

• moduleID – The module identifier

Returns

void

void Update_mtbMomentumManagement(mtbMomentumManagementConfig *configData, uint64_t callTime, int64_t moduleID)

Computes the appropriate wheel torques and magnetic torque bar dipoles to bias the wheels to their desired speeds.

Parameters

• configData – The configuration data associated with the module

• callTime – The clock time at which the function was called (nanoseconds)

• moduleID – The module identifier

Returns

void

void Reset_mtbMomentumManagement(mtbMomentumManagementConfig *configData, uint64_t callTime, int64_t moduleID)

This method performs a complete reset of the module. Local module variables that retain time varying states between function calls are reset to their default values. The local copy of the message output buffer should be cleared.

Parameters

• configData – The configuration data associated with the module

• callTime – [ns] time the method is called

• moduleID – The module identifier

Returns

void

void v3TildeM(double v[3], void *result)

struct mtbMomentumManagementConfig

#include <mtbMomentumManagement.h>

Top level structure for the sub-module routines.

Public Members

double wheelSpeedBiases[MAX_EFF_CNT]

[rad/s] reaction wheel speed biases

double cGain

[1/s] reaction wheel momentum feedback gain

RWArrayConfigMsg_C rwParamsInMsg

input message for RW parameters

MTBArrayConfigMsg_C mtbParamsInMsg

input message for MTB layout

TAMSensorBodyMsg_C tamSensorBodyInMsg

input message for magnetic field sensor data in the Body frame

RWSpeedMsg_C rwSpeedsInMsg

input message for RW speeds

ArrayMotorTorqueMsg_C rwMotorTorqueInMsg

input message for RW motor torques

MTBCmdMsg_C mtbCmdOutMsg

output message for MTB dipole commands

ArrayMotorTorqueMsg_C rwMotorTorqueOutMsg

output message for RW motor torques

BSKLogger *bskLogger

BSK Logging.

double tauDesiredMTB_B[3]

[N-m] desired torque produced by the magnetic torque bars in the Body frame

double tauDesiredRW_B[3]

[N-m] desired torque produced by the reaction wheels in the Body frame

double hDeltaWheels_W[MAX_EFF_CNT]

[N-m-s] momentum of each wheel

double hDeltaWheels_B[3]

[N-m-s] momentum of reaction wheels in the Body frame

double tauDesiredRW_W[MAX_EFF_CNT]

[N-m] Desired individual wheel torques

double tauIdealRW_W[MAX_EFF_CNT]

[N-m-s] Ideal individual wheel torques

double tauIdealRW_B[MAX_EFF_CNT]

[N-m-s] Ideal wheel torque in the body frame

double wheelSpeedError_W[MAX_EFF_CNT]

[N-m-s] difference between current wheel speeds and desired wheel speeds

RWArrayConfigMsgPayload rwConfigParams

configuration for RW’s

MTBArrayConfigMsgPayload mtbConfigParams

configuration for MTB layout