mrpProportionalDerivative#

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.

Class MrpProportionalDerivative#

class MrpProportionalDerivative : public SysModel#

MRP PD control class.

Public Functions

MrpProportionalDerivative() = default#: Constructor.

~MrpProportionalDerivative() = default#: Destructor.

void reset(uint64_t currentSimNanos) override#

Reset member function.

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.

Parameters:: callTime – [ns] Time the method is called
Returns:: void

void updateState(uint64_t currentSimNanos) override#

Update member function.

This method takes the attitude and rate errors relative to the reference frame, as well as the reference frame angular rates and acceleration, and computes the required control torque Lr.

Parameters:: callTime – [ns] Time the method is called
Returns:: void

double getDerivativeGainP()#

Getter method for derivative gain P.

Getter method for the derivative gain P.

Returns:: const double

const Eigen::Vector3d &getKnownTorquePntB_B() const#

Getter method for the known external torque about point B.

Getter method for the known torque about point B.

Returns:: const Eigen::Vector3d

double getProportionalGainK()#

Getter method for proportional gain K.

Getter method for the proportional gain K.

Returns:: const double

void setDerivativeGainP(double P)#

Setter method for derivative gain P.

Setter method for the derivative gain P.

Parameters:: P – [N*m*s] Rate error feedback gain applied
Returns:: void

void setKnownTorquePntB_B(Eigen::Vector3d &knownTorquePntB_B)#

Getter method for the known external torque about point B.

Setter method for the known external torque about point B.

Parameters:: knownTorquePntB_B – [N*m] Known external torque expressed in body frame components
Returns:: void

void setProportionalGainK(double K)#