Module: thrusterPlatformState

Executive Summary

This module simulates receives the measured tip and tilt angles of the thruster platform, together with the thruster configuration information expressed in platform-frame coordinates. The purpose of this module is to output the thruster configuration information in body-frame coordinates, at any instant in time, given the measured platform states (tip-and-tilt angles).

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.

Module I/O Messages
Msg Variable Name	Msg Type	Description
thrusterConfigFInMsg	THRConfigMsgPayload	Input thruster configuration message containing the thrust direction vector and magnitude in platform frame coordinates. The entry `rThrust_B` here is the position of the thrust application point, with respect to the origin of the platform frame, in platform-frame coordinates (\({}^\mathcal{F}\boldsymbol{r}_{T/F}\)).
hingedRigidBody1InMsg	HingedRigidBodyMsgPayload	Input message containing the current tip angle and tip rate of the platform frame \(\mathcal{F}\) with respect to the mount frame \(\mathcal{M}\).
hingedRigidBody2InMsg	HingedRigidBodyMsgPayload	Input message containing the current tilt angle and tilt rate of the platform frame \(\mathcal{F}\) with respect to the mount frame \(\mathcal{M}\).
thrusterConfigBOutMsg	THRConfigMsgPayload	Output thruster configuration message containing the thrust direction vector and magnitude in body frame coordinates, as a function of tip and tilt angles. The entry `rThrust_B` here is the position of the thrust application point, with respect to the origin of the body frame, in body-frame coordinates (\({}^\mathcal{B}\boldsymbol{r}_{T/B}\)).

Detailed Module Description

This module reads the tip and tilt angles from the Module: spinningBodyTwoDOFStateEffector that simulates the platform. These angles allow to define the direction cosine matrix \([\mathcal{FM}]\) that describes the rotation between the platform frame \(\mathcal{F}\) with respect to the mount frame \(\mathcal{M}\). Accounting for the known offsets between the two frames, as well as the offset between the thruster application point and the origin of the frame \(\mathcal{F}\), this module outputs the thrust direction vector in body-frame coordinates \({}^\mathcal{B}\hat{t}\) and the position of the thrust application point with respect to the origin of the body frame \({}^\mathcal{B}r_{T/B}\).

A more detailed description of the thruster-platform assembly can be found in R. Calaon, L. Kiner, C. Allard and H. Schaub, “Momentum Management of a Spacecraft equipped with a Dual-Gimballed Electric Thruster” and in Module: thrusterPlatformReference.

User Guide

The required module configuration is:

platformState = thrusterPlatformState.thrusterPlatformState()
platformState.ModelTag = "platformState"
platformState.sigma_MB = sigma_MB
platformState.r_BM_M = r_BM_M
platformState.r_FM_F = r_FM_F
scSim.AddModelToTaskAddModelToTask(simTaskName, platformState)

The module is configurable with the following parameters:

Module Parameters
Parameter	Default	Description
`sigma_MB`	[0, 0, 0]	relative rotation between body-fixed frames \(\mathcal{M}\) and \(\mathcal{B}\)
`r_BM_M`	[0, 0, 0]	relative position of point \(B\) with respect to point \(M\), in \(\mathcal{M}\)-frame coordinates
`r_FM_F`	[0, 0, 0]	relative position of point \(F\) with respect to point \(M\), in \(\mathcal{F}\)-frame coordinates

Functions

void SelfInit_thrusterPlatformState(thrusterPlatformStateConfig *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 Reset_thrusterPlatformState(thrusterPlatformStateConfig *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.

Parameters:

configData – The configuration data associated with the module
callTime – [ns] time the method is called
moduleID – The module identifier

Returns:

void

void Update_thrusterPlatformState(thrusterPlatformStateConfig *configData, uint64_t callTime, int64_t moduleID)

This method updates the platformAngles message based on the updated information about the system center of mass

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

struct thrusterPlatformStateConfig

#include <thrusterPlatformState.h>

Top level structure for the sub-module routines.

Public Members

double sigma_MB[3]: orientation of the M frame w.r.t. the B frame

double r_BM_M[3]: position of B frame origin w.r.t. M frame origin, in M frame coordinates

double r_FM_F[3]: position of F frame origin w.r.t. M frame origin, in F frame coordinates

double K: momentum dumping time constant [1/s]

THRConfigMsg_C thrusterConfigFInMsg: input thruster configuration msg

HingedRigidBodyMsg_C hingedRigidBody1InMsg: output msg containing theta1 reference and thetaDot1 reference

HingedRigidBodyMsg_C hingedRigidBody2InMsg: output msg containing theta2 reference and thetaDot2 reference

THRConfigMsg_C thrusterConfigBOutMsg: output msg containing the thruster configuration infor in B-frame

BSKLogger *bskLogger: BSK Logging.