mrpPD_C#

Executive Summary#

This module provides a MRP based PD attitude control module. It is similar to mrpFeedback, but without the RW or the integral feedback option. The feedback control is able to asymptotically track a reference attitude if there are no unknown dynamics and the attitude control torque is implemented with a thruster set.

Message Connection Descriptions#

The following table lists all the module input and output messages. The module msg variable name 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.

../../../../../_images/moduleIOMrpPd.svg

Figure 1: mrpPD() Module I/O Illustration#

Module I/O Messages#

Msg Variable Name

Msg Type

Description

cmdTorqueOutMsg

CmdTorqueBodyMsgPayload

Commanded external torque output message

vehConfigInMsg

VehicleConfigMsgPayload

Vehicle configuration input message

guidInMsg

VehicleConfigMsgPayload

Vehicle configuration input message

Detailed Module Description#

This attitude feedback module using the MRP feedback control related to the control in section 8.4.1 in Analytical Mechanics of Space Systems:

(1)#\[{\bf L}_{r} = -K \pmb\sigma - [P] \delta\pmb\omega + [I](\dot{\pmb\omega}_{r} - [\tilde{\pmb\omega}]\pmb\omega_{r}) +[\tilde{\pmb \omega}_{r}] ] [I]\pmb\omega - \bf L\]

Note that this control solution creates an external control torque which must be produced with a cluster of thrusters. No reaction wheel information is used here. Further, the feedback control component is a simple proportional and derivative feedback formulation. As shown in Analytical Mechanics of Space Systems, this control can asymptotically track a general reference trajectory given by the reference frame \(\cal R\).

Module Assumptions and Limitations#

This control assumes the spacecraft is rigid and that the inertia tensor does not vary with time.

User Guide#

The following parameters must be set for the module:

  • K: the MRP proportional feedback gain

  • P: the \(\pmb\omega\) tracking error proportional feedback gain

  • knownTorquePntB_B: (Optional) the known external torque vector \({}^{B}{\bf L}\). The default value is a zero vector.