Module: forceTorqueThrForceMapping
Executive Summary
This module maps commanded forces and torques defined in the body frame of the spacecraft to a set of thrusters. It is capable of handling Center of Mass (CoM) offsets and non-controllable axis. In contrast to Module: thrForceMapping, this module only handles on-pulsing, but not off-pulsing. Further, it provides a single force/torque projection onto the thrusters and thus lacks some of the robustness features of Module: thrForceMapping.
The commanded force and torque input messages are optional, and the associated vectors are zeroed if no input message is connected. This provides a general capability to map control torques, forces or torques and forces onto a set of thrusters.
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. Both the cmdTorqueInMsg and cmdForceInMsg are optional.
Msg Variable Name |
Msg Type |
Description |
---|---|---|
cmdTorqueInMsg |
(optional) The name of the vehicle control torque (Lr) input message |
|
cmdForceInMsg |
(optional) The name of the vehicle control force input message |
|
thrConfigInMsg |
The name of the thruster cluster input message |
|
vehConfigInMsg |
The name of the vehicle config input message |
|
thrForceCmdOutMsg |
The name of the output thruster force message |
Detailed Module Description
Force and Torque Mapping
The desired force and torque are given as
The
The torque produced by each thruster about the body-fixed CoM is:
The total force and torque on the spacecraft may be represented as:
The force required by each thruster can computed by the following equation. Any rows within the
To ensure no commanded thrust is less than zero, the minimum thrust is subtracted from the thrust vector
These thrust commands are then written to the output message.
User’s Guide
To set up this module users must create the config data and module wrap:
module = forceTorqueThrForceMapping.forceTorqueThrForceMapping()
module.ModelTag = "forceTorqueThrForceMappingTag"
unitTestSim.AddModelToTask(unitTaskName, module)
The cmdForceInMsg
and cmdTorqueInMsg
are optional. However, the thrConfigInMsg
and vehConfigInMsg
are not. These
can both be set up as follows, where rcsLocationData
is a list of the thruster positions and rcsDirectionData
is a
list of thruster directions. CoM_B
is the center of mass of the spacecraft in the body frame.:
fswSetupThrusters.clearSetup()
for i in range(numThrusters):
fswSetupThrusters.create(rcsLocationData[i], rcsDirectionData[i], maxThrust)
thrConfigInMsg = fswSetupThrusters.writeConfigMessage()
vehConfigInMsgData = messaging.VehicleConfigMsgPayload()
vehConfigInMsgData.CoM_B = CoM_B
vehConfigInMsg = messaging.VehicleConfigMsg().write(vehConfigInMsgData)
Then, the relevant messages must be subscribed to by the module:
module.cmdTorqueInMsg.subscribeTo(cmdTorqueInMsg)
module.cmdForceInMsg.subscribeTo(cmdForceInMsg)
module.thrConfigInMsg.subscribeTo(thrConfigInMsg)
module.vehConfigInMsg.subscribeTo(vehConfigInMsg)
For more information on how to set up and use this module, see the unit test.
Functions
-
void SelfInit_forceTorqueThrForceMapping(forceTorqueThrForceMappingConfig *configData, int64_t moduleID)
This method initializes the output messages for this module.
- Parameters:
configData – The configuration data associated with this module
moduleID – The module identifier
- Returns:
void
-
void Update_forceTorqueThrForceMapping(forceTorqueThrForceMappingConfig *configData, uint64_t callTime, int64_t moduleID)
Add a description of what this main Update() routine does for this module
- 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_forceTorqueThrForceMapping(forceTorqueThrForceMappingConfig *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. Check if required input messages are connected.
- Parameters:
configData – The configuration data associated with the module
callTime – [ns] time the method is called
moduleID – The module identifier
- Returns:
void
-
struct forceTorqueThrForceMappingConfig
- #include <forceTorqueThrForceMapping.h>
This module maps thruster forces for arbitrary forces and torques.
Public Members
-
double rThruster_B[MAX_EFF_CNT][3]
[m] local copy of the thruster locations
-
double gtThruster_B[MAX_EFF_CNT][3]
[] local copy of the thruster force unit direction vectors
-
uint32_t numThrusters
[] The number of thrusters available on vehicle
-
double CoM_B[3]
[m] CoM of the s/c
-
CmdTorqueBodyMsg_C cmdTorqueInMsg
(optional) vehicle control (Lr) input message
-
CmdForceBodyMsg_C cmdForceInMsg
(optional) vehicle control force input message
-
THRArrayConfigMsg_C thrConfigInMsg
thruster cluster configuration input message
-
VehicleConfigMsg_C vehConfigInMsg
vehicle config input message
-
THRArrayCmdForceMsg_C thrForceCmdOutMsg
thruster force command output message
-
BSKLogger *bskLogger
BSK Logging.
-
double rThruster_B[MAX_EFF_CNT][3]